Nearly zero energy communities : Proceedings of the Conference for Sustainable Energy (CSE) 2017 978-3-319-63215-5, 3319632159, 978-3-319-63214-8

Table of contents :
Front Matter ....Pages i-xiii
Front Matter ....Pages 1-1
Implementing Renewable Energy Systems in Nearly Zero Energy Communities (Ion Visa, Anca Duta, Macedon Moldovan, Bogdan Burduhos)....Pages 3-24
Refurbishment Solutions for Public Buildings Towards Nearly Zero Energy Performance (Laura Aelenei, Helder Gonçalves)....Pages 25-38
Renewable Energy Management Using Embedded Smart Systems (Viorel Miron-Alexe, Iulian Bancuta, Nicolae Vasile)....Pages 39-49
The Role of Energy Management Systems in nZEB and nZEC (Bogdan Burduhos, Anca Duta, Macedon Moldovan)....Pages 50-69
EfDeN Prototype - A Sustainable and Low Energy Consumption House Presented at Solar Decathlon 2014 (Tiberiu Catalina, Mihai Baiceanu, Eduard-Daniel Raducanu, Mihai Toader Pasti, Claudiu Butacu)....Pages 70-79
Building with the Sun. Passive Solar Daylighting Systems in Architecture (Ana-Maria Dabija)....Pages 80-88
Energy Initiatives in Europe (Yoram Krozer)....Pages 89-101
Energy Consumption in Buildings. Performance Breakdown Analysis Considering the Building Services Efficiency and the Usage Pattern (Eugen Mandric, Mugurel-Florin Talpiga, Florin Iordache)....Pages 102-119
On the Problem of the Contemporary Building Energy Systems (Nicolay Mihailov, Ognyan Dinolov, Katerina Gabrovska-Evstatieva, Boris Evstatiev)....Pages 120-128
Renewable Energy Systems for a Multi-family Building Community (Macedon Moldovan, Ion Visa)....Pages 129-147
Sustainable Solutions for Extensive Retrofitting of Residential Buildings Built in the 1970s (Daniel Muntean, Viorel Ungureanu)....Pages 148-158
Materials from Renewable Sources as Thermal Insulation for Nearly Zero Energy Buildings (nZEB) (Cristian Petcu, Horia-Alexandru Petran, Vasilica Vasile, Mihai-Constantin Toderasc)....Pages 159-167
Evaluation of Material Compositions of Sloping Roofs from Environmental and Energy Perspectives (Silvia Vilcekova, Eva Kridlova Burdova, Marek Kusnir)....Pages 168-178
Solutions to Reduce Energy Consumption in Buildings. Green Roofs Made up of Succulent Plants (Ileana Nicolae, Sorina Petra)....Pages 179-197
Front Matter ....Pages 199-199
Simulation-Based Investigation of the Air Velocity in a Naturally Ventilated BIPV System (Rafaela Agathokleous, Soteris Kalogirou)....Pages 201-217
Design Aspects of Building Integrated Solar Tile Collectors (Istvan Fekete, Istvan Farkas)....Pages 218-226
Modelling and Simulation of the Solar - Biomass Base Heating System for Low Energy Buildings Developed for Rural Area (Sándor Bartha, Boglárka Vajda)....Pages 227-238
Closed Sorption Seasonal Thermal Energy Storage with Aqueous Sodium Hydroxide (Mihaela Dudita, Xavier Daguenet-Frick, Paul Gantenbein)....Pages 239-246
Comparative Analysis of the Energy Demand by Standard Method and the TRNSYS-Weather Data Method (Adrian Constantin Ilie, Ion Visa)....Pages 247-262
Development of Black and Red Absorber Coatings for Solar Thermal Collectors (Luminita Isac, Ramona Panait, Alexandru Enesca, Cristina Bogatu, Dana Perniu, Anca Duta)....Pages 263-282
A New Approach on the Protection Against Overheating of Flat Plate Solar-Thermal Collectors (Mircea Neagoe, Ion Visa, Anca Duta, Nadia Cretescu)....Pages 283-295
Numerical Assessment of a Dynamic Daily Heating Unit Using Both Solar Collector and Heat Pump Coupled in a Dynamic Working (Mugurel-Florin Talpiga, Eugen Mandric, Florin Iordache)....Pages 296-313
Front Matter ....Pages 315-315
Optimized Management for Photovoltaic Applications Based on LEDs by Fuzzy Logic Control and Maximum Power Point Tracking (Dan Craciunescu, Laurentiu Fara, Paul Sterian, Andreea Bobei, Florin Dragan)....Pages 317-336
Characterizing the Variability of High Resolution Solar Irradiance Data Series (Robert Blaga, Marius Paulescu)....Pages 337-347
Semiconductor Graphenes for Photovoltaics (Doru Buzatu, Marius Mirica, Mihai Putz)....Pages 348-363
Deployable Mobile Units Concepts for Photovoltaic and Solar Thermal Arrays (Mihai Comsit, Macedon Moldovan, Mircea Neagoe)....Pages 364-374
Recycling Silicon-PV Modules in Composites with PVC, HDPE and Rubber Wastes (Mihaela Cosnita, Cristina Cazan, Anca Duta, Ion Visa)....Pages 375-394
Sizing and Optimization of Cost-Efficient PV Generator System at Residential Buildings in the Region of Ruse, Bulgaria (Katerina Gabrovska-Evstatieva, Boris Evstatiev, Ognyan Dinolov, Nicolay Mihailov)....Pages 395-404
Modular Electrochemical Reactivity for Photovoltaics’ Machines (Mirela Iorga, Marius Mirica, Mihai Putz)....Pages 405-420
The Efficiency and the Profitability of the Photovoltaic Panels as Generator for Household Electricity in the Region of Banat/Romania (Stefan Pavel, Ioan Silviu Dobosi, Daniel Stan, Gabriel Fischer Szava)....Pages 421-433
Extracting the I-V Characteristics of the PV Modules from the Manufacture’s Datasheet (Andreea Sabadus, Marius Paulescu, Viorel Badescu)....Pages 434-442
PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application (Codruta Jaliu, Radu Saulescu, Daniela Ciobanu, Florin Panaite)....Pages 443-459
Large Conversion Ratio DC-DC Hybrid Converters for Renewable Energy Applications (Nicolae Muntean, Octavian Cornea, Dan Hulea)....Pages 460-472
Life Cycle Assessment of the Romanian Electricity Mix: Impacts, Trends and Challenges (George Barjoveanu, Carmen Teodosiu, Daniela Cailean (Gavrilescu))....Pages 473-489
Developing Modified Hydrodynamic Rotor for Flow Small Hydro (Ion Bostan, Viorel Bostan, Valeriu Dulgheru, Oleg Ciobanu, Radu Ciobanu, Vitalie Gladis)....Pages 490-499
Development of a Horizontal Axis Wind Turbine for the Production of Thermal Energy (Viorel Bostan, Ion Bostan, Ion Sobor, Valeriu Dulgheru, Vitalie Gladis)....Pages 500-510
Front Matter ....Pages 511-511
Sustainable Autonomous System for Nitrites/Nitrates and Heavy Metals Monitoring of Natural Water Sources (WaterSafe) (Mariuca Gartner, Carmen Moldovan, Marin Gheorghe, Anca Duta, Miklos Fried, Ferenc Vonderviszt)....Pages 513-520
Design and Development of TiO2 Based Dispersions for Photocatalytic Fabrics (Cristina Bogatu, Dana Perniu, Luminita Isac, Maria Covei, Anca Duta)....Pages 521-549
Sustainable Wastewater Treatment for Households in Small Communities (Alexandru Enesca, Luminita Andronic, Anca Duta, Ion Visa)....Pages 550-565
Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents (Ileana Manciulea, Lucia Dumitrescu, Cristina Bogatu, Camelia Draghici, Dora Lucaci)....Pages 566-585
A Comparative Analysis of Pollutants Adsorption and Photocatalysis on Composite Materials Synthesized from Fly Ash (Maria Visa, Nicoleta Popa, Andreea Chelaru)....Pages 586-608
Front Matter ....Pages 609-609
Extending Production Waste Life Cycle and Energy Saving by Eco-Innovation and Eco-Design: The Case of Packaging Manufacturing (Maria Gavrilescu, Teofil Campean, Dan-Alexandru Gavrilescu)....Pages 611-631
Sustainability - A Principle of Education in Architecture (and Not Only) (Ana-Maria Dabija)....Pages 632-640
Sustainable Energy in Buildings: Academy Massive Open Online Courses (Carlos Silva, Laura Aelenei)....Pages 641-650
Competences Development - Towards an Effective Implementation of nZEB in Romania (Horia-Alexandru Petran, Marian-Ciprian Niculuta, Cristian Petcu)....Pages 651-665
P.A.E.S. Project and Housing Policies for Sustainable Buildings (Renato Olivito, Mircea Neagoe, Petru Mihai, Nikolaos Karanasios, Eva Krìdlova Burdovà, Marco Della Puppa)....Pages 666-685
Maintenance of Renewable Energy Systems - A Challenge in Academic Education (Sanda Budea, Carmen-Anca Safta)....Pages 686-698
Sustainable Buildings - Technological Innovation or a Different Way of Interpreting the Traditional House (Teodora Raduca)....Pages 699-710
Multi-functional Products - A Way to Decrease the Products Environmental Impact (Anca Barsan, Lucian Barsan, Aurelian Leu, Larisa Zafiu)....Pages 711-719
Using “Serious Game” for Children and Youth Education in Sustainable Energy Field and Environment Protection (Mihaela-Ioana Baritz)....Pages 720-729
Erratum to: Energy Consumption in Buildings. Performance Breakdown Analysis Considering the Building Services Efficiency and the Usage Pattern (Eugen Mandric, Mugurel-Florin Talpiga, Florin Iordache)....Pages E1-E1
Back Matter ....Pages 731-732

Citation preview

Springer Proceedings in Energy

Ion Visa Anca Duta Editors

Nearly Zero Energy Communities Proceedings of the Conference for Sustainable Energy (CSE) 2017

Springer Proceedings in Energy

About this series The series Springer Proceedings in Energy covers a broad range of multidisciplinary subjects in those research fields closely related to present and future forms of energy as a resource for human societies. Typically based on material presented at conferences, workshops and similar scientific meetings, volumes published in this series will constitute comprehensive state-of-the-art references on energy-related science and technology studies. The subjects of these conferences will fall typically within these broad categories: - Energy Efficiency - Fossil Fuels Nuclear Energy - Policy, Economics, Management & Transport - Renewable and Green Energy - Systems, Storage and Harvesting - Materials for Energy eBooks Volumes in the Springer Proceedings in Energy will be available online in the world’s most extensive eBook collection, as part of the Springer Energy eBook Collection. Proposals for new volumes should include the following: - name, place and date of the scientific event - a link to the committees (local organization, international advisors etc.) - description of the scientific aims and scope of the meeting - list of invited/plenary speakers - an estimate of the proceedings book details (number of pages/articles, requested number of bulk copies, submission deadline). Please send your proposals to Dr Maria Bellantone, Senior Publishing Editor, Springer ([email protected]).

More information about this series at http://www.springer.com/series/13370

Ion Visa Anca Duta •

Editors

Nearly Zero Energy Communities Proceedings of the Conference for Sustainable Energy (CSE) 2017

123

Editors Ion Visa Transilvania University of Brasov Brasov Romania

ISSN 2352-2534 Springer Proceedings in Energy ISBN 978-3-319-63214-8 DOI 10.1007/978-3-319-63215-5

Anca Duta Transilvania University of Brasov Brasov Romania

ISSN 2352-2542

(electronic)

ISBN 978-3-319-63215-5

(eBook)

Library of Congress Control Number: 2017952845 © Springer International Publishing AG 2018 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Printed on acid-free paper This Springer imprint is published by Springer Nature The registered company is Springer International Publishing AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Foreword

The implementation of the sustainable development principles asks for novel knowledge and technical advancements mainly focusing on energy production to be used in various environmentally friendly processes. Thus, the general frame of R&D was changed to be able to meet the general interest for clean energy production and consumption. During the past decade, it has become obvious that to successfully implement these principles, there is a need for additional actions to increase the acceptance of the novel technologies and equipment. This is why education, social sciences and economics have completed the picture with specific topics of interest in developing the society of tomorrow, based on sustainable processes and products, and developed using environmentally friendly, cost-effective technologies. Sensing these trends, in 2005 the R&D Centre Renewable Energy Systems and Recycling, RES-REC, in the Transilvania University of Brasov, Romania, developed the first edition of the international event: Conference for Sustainable Energy, CSE. Every three years, a new edition of this event was organized on specific topics identified according to the sustainable energy prerequisites formulated, as follows: Sustainable energy (2005), Solar energy (2008), Sustainable communities (2011) and Nearly zero energy buildings (2014). As these topics show, during these past twelve years there was a significant shift of interest from the mainly theoretical topics (as was the case of the first two editions) towards the topics focusing on more concrete approaches, based on novel findings and novel trends (as was evident in the last two editions). During the past years, the legal frame was also developed supporting the quest for sustainable development, with a specific focus on sustainable energy. All the parts of our day-to-day life are expected to be subjected to changes in the future and to embedding the sustainability aspects. The pace to which this will happen depends on the already-mentioned knowledge development, implementation and the economic aspects as part of these scenarios. While there is a large common effort to meet the need for sustainable development at a government level all over the world, the concrete measures so far v

vi

Foreword

implemented are rather limited. Specific paths are so far identified for various production processes (e.g. the IT industries are frontrunners), but less extended effort and particular solutions target nowadays, e.g. the agricultural development. The built environment is currently a hot topic because of many reasons: it is used and known by each member of the community, it is one of the largest energy consumers in a given society, and its’ changing needs require significant investments largely supported by the inhabitants. These reasons lead to the societal involvement in the promotion of specific measures for mitigating the energy consumption and for increasing the share of green energy to meet the overall demand. The past decade experienced large advancements in many directions linked to the built environment, and these were mirrored in the past three editions of the CSE conference. Thus, CSE represents a framework for sharing the recent knowledge and research results and a meeting point among the research providers and the users of the research results. The research progress was quickly transferred into applications that evolved from energy efficiency in buildings to nZEB and further on to groups of nZEB. It was observed that these groups of nZEB may get more affordable when the entire community is involved, from the design steps, and with focus on using the community facilities to meet the general and specific needs. So, a new concept is emerging: Nearly Zero Energy Community (nZEC). The 5th edition of the Conference for Sustainable Energy runs in the R&D Institute of the Transilvania University of Brasov. The location of the institute was designed as a sustainable community, and various renewable energy systems are already installed and monitored, allowing to contribute with detailed data in identifying the challenges and the implementable solutions for reaching the status of Nearly Zero Energy Community. Since 2013 when the built environment of the institute was ready and functioning, there were registered significant results and findings that can contribute to the affordable development of such nZEC. Thus, this edition of CSE represents a good opportunity for sharing experience and for discussing the current and further R&D topics that are emerging at this moment. We are glad to welcome experienced researchers and young members of the research community to discuss the present and the future in our field of activity. The proceedings volume represents an additional asset, gathering the recent results from many groups all over the world. The volume edited by Springer to accompany the CSE 2014 edition reached over 28,000 downloads, and this is a concrete proof of the quality of the presentations (published in the proceedings volume) and their impact on the R&D community. We are dedicated to keep the high interest in the presentations and deliver, at the 5th CSE edition, this proceedings volume that contains the latest research results obtained in investigating the multiple facets of Nearly Zero Energy Communities. October 2017

Ion Visa Anca Duta

Organization

Scientific Committee CSE 2017 Badescu Viorel Balan Mugur Barsan Lucian Bostan Viorel Burduhos Bogdan Carstea Marcian Chemisana Daniel Comsit Mihai Dabija Ana Maria Duic Neven Duta Anca Fara Laurentiu Farkas Istvan Gavrilescu Maria Haeberle Andreas Helerea Elena Ilasi Nicolae Iordache Florin Jaliu Codruta Jinescu Valeriu Kalogirou Soteris Marinescu Corneliu Meghea Aurelia Mihailov Nikolay Moldovan Macedon Neagoe Mircea

Romanian Academy and Politehnica University of Bucharest Technical University of Cluj-Napoca, Romania Transilvania University of Brasov, Romania Technical University of Chisinau, Republic Moldova Transilvania University of Brasov, Romania Anglia Ruskin University, Cambridge, UK University of Lleida, Spain Transilvania University of Brasov, Romania “Ion Mincu” University, Bucharest, Romania University of Zagreb, Croatia Transilvania University of Brasov, Romania Politehnica University of Bucharest, Romania Szent Istvan University and Hungarian ISES President, Hungary Technical University Gheorghe Asachi, Iasi, Romania SPF Rapperswil, Switzerland Transilvania University of Brasov, Romania University of Petrosani, Romania University of Civil Engineering, Bucharest, Romania Transilvania University of Brasov, Romania Romanian Academy of Technical Sciences Cyprus University of Technology, Cyprus Transilvania University of Brasov, Romania Politehnica University of Bucharest, Romania “Angel Kanchev” University of Ruse, Bulgaria Transilvania University of Brasov, Romania Transilvania University of Brasov, Romania

vii

viii

Olariu Nicolae Paulescu Marius Perniu Dana Petran Horia Quaglia Giuseppe Romanca Mihai Simionescu Bogdan Tanasescu Teodor Teodosiu Carmen Ungureanu Viorel Visa Ion Zacharopoulos Agellos Zaharescu Maria

Organization

Valahia University Targoviste and SUN-E, Romania West University of Timisoara, Romania Transilvania University of Brasov, Romania INCD URBAN-INCERC Bucharest, Romania Polytechnic University of Torino and IFToMM, Italy Transilvania University of Brasov, Romania Romanian Academy and Petru Poni Institute, Iasi Romanian Academy of Technical Sciences Technical University “Gheorghe Asachi”, Iasi, Romania Politehnica University of Timisoara, Romania Transilvania University of Brasov, Romania University of Ulster, UK Romanian Academy and Institute for Physical Chemistry

Contents

Nearly Zero Energy Buildings and Communities Implementing Renewable Energy Systems in Nearly Zero Energy Communities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ion Visa, Anca Duta, Macedon Moldovan, and Bogdan Burduhos

3

Refurbishment Solutions for Public Buildings Towards Nearly Zero Energy Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laura Aelenei and Helder Gonçalves

25

Renewable Energy Management Using Embedded Smart Systems . . . . . Viorel Miron-Alexe, Iulian Bancuta, and Nicolae Vasile

39

The Role of Energy Management Systems in nZEB and nZEC . . . . . . . Bogdan Burduhos, Anca Duta, and Macedon Moldovan

50

EfDeN Prototype - A Sustainable and Low Energy Consumption House Presented at Solar Decathlon 2014 . . . . . . . . . . . . . . . . . . . . . . . . . Tiberiu Catalina, Mihai Baiceanu, Eduard-Daniel Raducanu, Mihai Toader Pasti, and Claudiu Butacu Building with the Sun. Passive Solar Daylighting Systems in Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ana-Maria Dabija Energy Initiatives in Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yoram Krozer

70

80 89

Energy Consumption in Buildings. Performance Breakdown Analysis Considering the Building Services Efficiency and the Usage Pattern. . . . 102 Eugen Mandric, Mugurel-Florin Talpiga, and Florin Iordache On the Problem of the Contemporary Building Energy Systems . . . . . . 120 Nicolay Mihailov, Ognyan Dinolov, Katerina Gabrovska-Evstatieva, and Boris Evstatiev

ix

x

Contents

Renewable Energy Systems for a Multi-family Building Community . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Macedon Moldovan and Ion Visa Sustainable Solutions for Extensive Retrofitting of Residential Buildings Built in the 1970s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Daniel Muntean and Viorel Ungureanu Materials from Renewable Sources as Thermal Insulation for Nearly Zero Energy Buildings (nZEB) . . . . . . . . . . . . . . . . . . . . . . . . 159 Cristian Petcu, Horia-Alexandru Petran, Vasilica Vasile, and Mihai-Constantin Toderasc Evaluation of Material Compositions of Sloping Roofs from Environmental and Energy Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Silvia Vilcekova, Eva Kridlova Burdova, and Marek Kusnir Solutions to Reduce Energy Consumption in Buildings. Green Roofs Made up of Succulent Plants . . . . . . . . . . . . . . . . . . . . . . . . 179 Ileana Nicolae and Sorina Petra Solar Heating and Cooling in Buildings and Communities Simulation-Based Investigation of the Air Velocity in a Naturally Ventilated BIPV System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 Rafaela Agathokleous and Soteris Kalogirou Design Aspects of Building Integrated Solar Tile Collectors . . . . . . . . . . 218 Istvan Fekete and Istvan Farkas Modelling and Simulation of the Solar - Biomass Base Heating System for Low Energy Buildings Developed for Rural Area . . . . . . . . . 227 Sándor Bartha and Boglárka Vajda Closed Sorption Seasonal Thermal Energy Storage with Aqueous Sodium Hydroxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Mihaela Dudita, Xavier Daguenet-Frick, and Paul Gantenbein Comparative Analysis of the Energy Demand by Standard Method and the TRNSYS-Weather Data Method . . . . . . . . . . . . . . . . . . 247 Adrian Constantin Ilie and Ion Visa Development of Black and Red Absorber Coatings for Solar Thermal Collectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Luminita Isac, Ramona Panait, Alexandru Enesca, Cristina Bogatu, Dana Perniu, and Anca Duta A New Approach on the Protection Against Overheating of Flat Plate Solar-Thermal Collectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 Mircea Neagoe, Ion Visa, Anca Duta, and Nadia Cretescu

Contents

xi

Numerical Assessment of a Dynamic Daily Heating Unit Using Both Solar Collector and Heat Pump Coupled in a Dynamic Working . . . . . . 296 Mugurel-Florin Talpiga, Eugen Mandric, and Florin Iordache Solar Power in Buildings and Communities Optimized Management for Photovoltaic Applications Based on LEDs by Fuzzy Logic Control and Maximum Power Point Tracking . . . . . . . . 317 Dan Craciunescu, Laurentiu Fara, Paul Sterian, Andreea Bobei, and Florin Dragan Characterizing the Variability of High Resolution Solar Irradiance Data Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 Robert Blaga and Marius Paulescu Semiconductor Graphenes for Photovoltaics . . . . . . . . . . . . . . . . . . . . . . . 348 Doru Buzatu, Marius Mirica, and Mihai Putz Deployable Mobile Units Concepts for Photovoltaic and Solar Thermal Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364 Mihai Comsit, Macedon Moldovan, and Mircea Neagoe Recycling Silicon-PV Modules in Composites with PVC, HDPE and Rubber Wastes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375 Mihaela Cosnita, Cristina Cazan, Anca Duta, and Ion Visa Sizing and Optimization of Cost-Efficient PV Generator System at Residential Buildings in the Region of Ruse, Bulgaria . . . . . . . . . . . . . 395 Katerina Gabrovska-Evstatieva, Boris Evstatiev, Ognyan Dinolov, and Nicolay Mihailov Modular Electrochemical Reactivity for Photovoltaics’ Machines . . . . . . 405 Mirela Iorga, Marius Mirica, and Mihai Putz The Efficiency and the Profitability of the Photovoltaic Panels as Generator for Household Electricity in the Region of Banat/Romania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 Stefan Pavel, Ioan Silviu Dobosi, Daniel Stan, and Gabriel Fischer Szava Extracting the I-V Characteristics of the PV Modules from the Manufacture’s Datasheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434 Andreea Sabadus, Marius Paulescu, and Viorel Badescu PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443 Codruta Jaliu, Radu Saulescu, Daniela Ciobanu, and Florin Panaite Large Conversion Ratio DC-DC Hybrid Converters for Renewable Energy Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460 Nicolae Muntean, Octavian Cornea, and Dan Hulea

xii

Contents

Life Cycle Assessment of the Romanian Electricity Mix: Impacts, Trends and Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 George Barjoveanu, Carmen Teodosiu, and Daniela Cailean (Gavrilescu) Developing Modified Hydrodynamic Rotor for Flow Small Hydro . . . . . 490 Ion Bostan, Viorel Bostan, Valeriu Dulgheru, Oleg Ciobanu, Radu Ciobanu, and Vitalie Gladis Development of a Horizontal Axis Wind Turbine for the Production of Thermal Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 Viorel Bostan, Ion Bostan, Ion Sobor, Valeriu Dulgheru, and Vitalie Gladis Solar Energy for Water Re-use Sustainable Autonomous System for Nitrites/Nitrates and Heavy Metals Monitoring of Natural Water Sources (WaterSafe) . . . . . . . . . . . 513 Mariuca Gartner, Carmen Moldovan, Marin Gheorghe, Anca Duta, Miklos Fried, and Ferenc Vonderviszt Design and Development of TiO2 Based Dispersions for Photocatalytic Fabrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 Cristina Bogatu, Dana Perniu, Luminita Isac, Maria Covei, and Anca Duta Sustainable Wastewater Treatment for Households in Small Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550 Alexandru Enesca, Luminita Andronic, Anca Duta, and Ion Visa Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566 Ileana Manciulea, Lucia Dumitrescu, Cristina Bogatu, Camelia Draghici, and Dora Lucaci A Comparative Analysis of Pollutants Adsorption and Photocatalysis on Composite Materials Synthesized from Fly Ash . . . . . . . . . . . . . . . . . 586 Maria Visa, Nicoleta Popa, and Andreea Chelaru Policies, Education and Training on Sustainability Extending Production Waste Life Cycle and Energy Saving by Eco-Innovation and Eco-Design: The Case of Packaging Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 Maria Gavrilescu, Teofil Campean, and Dan-Alexandru Gavrilescu Sustainability - A Principle of Education in Architecture (and Not Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 Ana-Maria Dabija

Contents

xiii

Sustainable Energy in Buildings: Academy Massive Open Online Courses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641 Carlos Silva and Laura Aelenei Competences Development - Towards an Effective Implementation of nZEB in Romania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651 Horia-Alexandru Petran, Marian-Ciprian Niculuta, and Cristian Petcu P.A.E.S. Project and Housing Policies for Sustainable Buildings. . . . . . . 666 Renato Olivito, Mircea Neagoe, Petru Mihai, Nikolaos Karanasios, Eva Krìdlova Burdovà, and Marco Della Puppa Maintenance of Renewable Energy Systems - A Challenge in Academic Education . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686 Sanda Budea and Carmen-Anca Safta Sustainable Buildings - Technological Innovation or a Different Way of Interpreting the Traditional House . . . . . . . . . . . . . . . . . . . . . . . . 699 Teodora Raduca Multi-functional Products - A Way to Decrease the Products Environmental Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 711 Anca Barsan, Lucian Barsan, Aurelian Leu, and Larisa Zafiu Using “Serious Game” for Children and Youth Education in Sustainable Energy Field and Environment Protection . . . . . . . . . . . . 720 Mihaela-Ioana Baritz Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 731

Nearly Zero Energy Buildings and Communities

Implementing Renewable Energy Systems in Nearly Zero Energy Communities Ion Visa(&), Anca Duta, Macedon Moldovan, and Bogdan Burduhos Renewable Energy Systems and Recycling Research Center, Transilvania University of Brasov, Brasov, Romania [email protected]

Abstract. The sustainability challenges involve the built environment responsible for a large share in the total energy consumption. Steps toward a sustainable path were formulated and started to be implemented all over the world and, it is important to notice that the technical focus is mainly set on the energy production and consumption. Thus starting from the already formulated concept of Nearly Zero Energy Buildings (nZEB) and from the lessons learned when implementing it, this paper presents a study on the development of a Nearly Zero Energy Community (nZEC). The Community of the R&D Institute of the Transilvania University of Brasov was built starting with 2009 till 2013 and consists of 12 low energy buildings hosting 29 R&D Centers. The energy consumed in 2015 and 2016 in this community was monitored and a seasonal variation was registered for both, electrical and thermal energy. It was observed that the variability in the thermal energy demand is much larger and has a specific trend for each year. This community has partially installed renewable energy systems and their output is registered and discussed, considering the consumption variability over the year aiming at delivering a preliminary assessment of the renewable energy systems that can insure the Nearly Zero Energy (nZEC) status to this micro-community. The results show that the electrical energy produced should give full use of the current existent transportation and distribution infrastructure, while the thermal energy should be well managed at the micro-community level, to reduce the losses. An average share of 50% renewable energy was found to be able to cover the total energy demand in the laboratory buildings and in the R&D micro-community, confirming its goal as nZEC. Keywords: Energy efficient building
Renewable electrical energy in the built environment
Thermal energy in the built environment
Solar energy conversion systems

1 Renewable Energy Systems in Sustainable Communities Implementing the sustainable development concepts with concrete actions is now-a-days part of the development strategy of many countries and is supported by appropriate instruments, tailored according to the initial state of the art and to the issues that have to be tackled to reach the final goal. These issues are mainly related to the materials and energy consumption in various sectors of economic activities (industry, © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_1

4

I. Visa et al.

agriculture, transportation) and to the social activities, as education and health. The built environment has both an economic and a social dimension and represents a distinct topic of interest in this view. The most important potential threats identified for the next decades are related to the resources depletion (including those for the conventional energy fuels) along with pollution and its direct consequence - the global warming. The resources depletion lead to a more careful product design and to processing technologies with less losses; additionally, the smart use of the end-of-life products as resources for further novel materials (mainly composites) and products is an important path in the future development scenario. Pollution has many causes mainly coming from the industrial processes and agriculture, and an extensive effort is involved in limiting these sources, by redesigning the production processes and the products. However, a large share of pollution is linked to the energy production processes; traditionally these process are relying on fossil fuels, thus the CO2 (greenhouse gas) emissions resulted in burning these fuels are directly influencing the global warming posing a significant stress on the environmental quality. Therefore, a significant share of the research during the recent decades was dedicated to avoiding the use of fossil fuels by involving novel energy sources, as the renewable ones (solar energy, wind, hydro, geothermal, biomass, etc.). The research results were further implemented in the production processes, allowing the development of renewable energy systems that were estimated to cover about 19% of the energy consumption in 2012 and 23.7% in 2014, [1, 2]. Renewables became in the past decade important energy resources because of the environmental concern and the adequately imposed restrictions but also due to security reasons as the traditional energy resources (carbon and nuclear fuels) have a well-known and rather limited dispersion all over the world. Globally, the spread and the development level of the economic activities is highly uneven, thus concrete, specific solutions towards sustainability are expected to solve the identified problems. On the other hand, the built environment, although depending on the implementation location and on the development level, is characterized by a more homogeneous list of pre-requisites, aiming at insuring the quality of life with little environmental costs. Integrating the renewable energy systems for meeting the energy demand in the built environment lead to various conceptual notions that are briefly defined as follows: – Nearly zero energy building, represents a very high energy efficient building, where the required energy mainly comes from renewable sources, as defined by the European Commission in 2010 through the Directive on the energy performance of buildings, [3]; – Net zero energy building is a building which has an annual energy consumption equal to the energy onsite produced from renewable sources. These concepts are well exploited now and specific national action plans are formulated to increase the share of renewable energy used in the built environment. Developing energy efficient buildings asks for certain investments in quality materials used in the building construction or during refurbishing, in clean and efficient energy installations, etc.; further on increasing the feasibility of the implementation

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

5

solutions askes for focusing on the sustainability concepts. One of the strongest concept is, in this view, the „sustainable energy community”. In a sustainable energy community the renewable-based energy along with the energy efficiency and conservation represent the main focus, [4]. In Europe, among the frontrunners in developing Sustainable Energy Communities is Germany where the leading roles are played by specific actors/investors that develop and implement the plans, in agreement with the community inhabitants/authorities. The result is a significant increase in the renewable share in the electricity production: from 19% in 2004 to 42.8% in 2014, [5]. For the first time, the newly published Renewable energy report 2017, [6] outlines that during the past 12 months there was a large increase in the renewable energy production (161 GW newly installed), especially on electrical energy; the leading countries in EU are Germany and Denmark. However, defining and developing a sustainable energy community asks for an interdisciplinary project matching the renewable energy resources with the commercially available systems in a feasible way, to meet the energy demand. Additionally, educating/training the community inhabitants to implement energy efficient systems and to act according to the energy saving guides asks for specific actions, along with the legislative support. This is why although many communities have set the sustainability goals in their development plans, there are not many fully sustainable communities in the world yet. The near future is likely to register significant changes in the economy structure and a 3D topic was recently formulated to describe the near future trends: digitalization, decarbonization and decentralization, [7]. The widespread implementation of these concepts asks for implementing specific tasks among which processes management and security of data. Developing a sustainable community asks for significant investments in the existing and in the new community infrastructure according to the community planning and global trends. This is why, the transition phase needs to be carefully designed for the specific implementation location, considering the geographical location and the available financial resources at the design moment and for a given period in the future, [8]. Planning the implementation of renewable energy systems in the built environment should consider the already existing knowledge and experience for increasing the efficient use of the produced energy and for minimizing the losses. The community energy users can be located in the built environment as (1) residential houses/flats and (2) dedicated (public) spaces for the community needs as schools, hospitals, administration, etc. Additionally, specific needs are linked to the economic activities as: (3) industry and (4) agricultural energy users, and to (5) transportation. The consumption profile in terms of thermal and electrical energy is quite different among these five categories. Thus, the complementary time variation of the energy consumption may support the sustainable community concept vs. the sustainable buildings (individually brought to this status), [9]. One important issue to be solved is related to the energy management of the combined traditional - renewable energy systems. The fossil fuel based production of the electrical energy systems is now-a-days centralized. This feature has to be preserved as the distribution infrastructure is well developed with well-functioning security and control system [10].

6

I. Visa et al.

2 The R&D Institute of the Transilvania University of Brasov: Towards a Micro-Research Community In 2013, the construction of the R&D Institute of the Transilvania University of Brasov was finalized. The Institute is located in the Brasov City outskirts and was built within a structural founds project which was approved based on competition in 2009. The about 20 million EUR project allowed the development of the R&D Institute: the entire built environment and part of the high-tech research infrastructure. The Institute consists of 12 buildings that hosts the research activities of 29 R&D centers in the university, with a major focus on various aspects of sustainable development. The design project of the Institute aims at satisfying the need for unity (typical for the common interest for research) in the diversity of the aspects typical to the main topic; therefore, the 12 buildings are interlinked with a spine, as a common meeting place. The buildings envelopes were designed for reaching energy efficiency in the mountain implementation location (and climate). These 12 buildings act as a professional micro-community aiming at the status of Nearly Zero Energy Community, nZEC. This paper presents an overview of the main design steps and the results obtained after two years of functioning and monitoring the energy production and consumption, outlining the adequate solutions for this specific type of built environment and location. An algorithm was previously proposed for the micro-community design, [8], based on collecting the weather data and on estimating the energy demand in the micro-community. The main steps of this algorithm supporting sustainability are: (a) Identifying the energy demand; (b) Evaluating the renewable energy potential; (c) Designing the energy mix.

3 The Energy Demand in the Built Environment of the R&D Micro-Community Each building has three floors: a basement floor, and above this two more levels, as presented in Fig. 1a. Initial monitoring data (2014) showed an average thermal energy demand of 66.69 kWh/m2/year out of which 86.7% for heating, 8.6% for cooling and 4.7% for domestic hot water (DHW). The total estimated thermal energy demand in 2014 was of 90.030 kWh/year divided as: 4244 kWh/year for domestic hot water, 78.027 kWh/year for heating and 7759 kWh/year for cooling. During the next years (2015 and 2016), the monitored data of the reference building (Laboratory L7) showed lower values, as result of implementing the rules for using the building; the overall yearly thermal energy consumption was measured as 32 kWh/m2/ year in 2015 and 41 kWh/m2/year in 2016. These values are significantly lower compared to the values published in 2014 on the average consumption in the built

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

7

Fig. 1. (a) The R&D Institute of the Transilvania University of Brasov and (b) The built environment google maps satellite positioning of the institute

environment implemented after 2000, of 120 … 230 kWh/m2/year, [8], and include this infrastructure in the nearly zero energy buildings category, if the amount of energy covered using renewables is at least 10% (according the Romanian law). The energy needs vary from one R&D Center to another, according to the type of activities and to the R&D infrastructure used. Relevant differences are registered among the buildings in the electrical energy consumption, while thermal energy has an almost identical value in all the laboratory buildings. The results presented in Figs. 2 and 3 have as input data those corresponding to the laboratory L7, the location of the R&D Center Renewable Energy Systems and Recycling. The yearly variation of the energy demand in the same building (L7), Fig. 2, can have various causes, among which important are the weather data: cloudy periods ask for higher electrical energy consumption, the outdoor temperature correlated with sunshine days have significant influence on the thermal energy demand, etc. As expected, the highest thermal energy production (and consumption) has the peak values during the winter months (Fig. 3) but this is not only due to the weather profile,

8

I. Visa et al.

Fig. 2. Electrical energy consumption of the L7 building in 2015 and 2016

Fig. 3. Monthly thermal energy supplied by the condensing gas boiler installed in L7 building in 2015 and 2016

as the available solar radiation in Fig. 4 does not fully follow a similar trend in the two discussed years. Thus the differences are the result of different operation modes of the building.

4 Solar Energy Potential in the Implementation Location For the monitoring period the available global horizontal solar irradiance (Gh) and its direct component (Eb) measured with a Solys 2 system in the implementation location are presented in Fig. 4. Based on these monitoring data, the total yearly available solar radiation in the horizontal plane was measured as 1310 kWh/m2/year (2015) and of 1246 kWh/m2/year (2016). The results in Fig. 4 outline an average yearly variation in the available solar radiation of about 4.89% with higher monthly variations (among the two testing years) of 11.42% registered in July and 11.57% in February.

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

9

Fig. 4. (a) Global horizontal solar energy and (b) Direct solar energy in the implementation location

5 Implementing the Renewable Energy Systems Close to the Institute’s location there are no water flows (for implementing small hydros) and the wind potential is average. This is why the renewable based energy mix was mainly focused on solar energy and on geothermal energy conversion systems. While the functioning of geothermal systems is less influenced by the weather data, the solar energy conversion systems to produce electrical and thermal energy are highly sensitive to the specific climatic profile and to its variations. Based on the solar energy and wind potentials and on the available implementation area on the building’s rooftops, solar energy conversion systems and small wind turbines are installed and tested on the L6 and L7 laboratories roofs, Fig. 5: The Institute is connected to the medium AC voltage grid through a 600 kW distribution substation (1) which transforms voltage and isolate faults when transferring power to each building. The entire electrical energy consumption is measured centralized in the distribution substation and also individually on each building’s main distribution panel. The renewable energy supplied to the Institute is produced by: (a) five ground installed grid-connected photovoltaic platforms, 2 kWp each, (2) in Fig. 5, which injects the DC power in individual single phase SolarEdge SE2200 inverters (i2) connected to the internal distribution system of the building L6; four

10

I. Visa et al.

Fig. 5. The electrical energy equipment installed in the R&D Institute of the Transilvania University of Brasov: 1 - distribution substation, 2 - 10 kWp ground installed photovoltaic platforms, 3 - 5 kWp photovoltaic platform installed on the L7 rooftop, 4 - 12 kWp photovoltaic string platform installed on the L11 rooftop, 5 - 0.9 kWp wind turbines system, 6 - 1.8 kWp wind turbines system, 7 - submersible well pump, 8 - water distribution system, 9 - fresh water storage tank, 10 - wastewater treatment plant

of these photovoltaic platforms have solar tracking systems and the fifth one is fixed tilted, as reference; different types of photovoltaic modules are installed on each platform: Si-mono, Si-Poly, CdTe, CIS and CIGS, Table 1. Table 1. Photovoltaic modules specifications Characteristic

M.U. Heliene

Model Type Nominal power, STC

LDK

Uni-solar

Avancis

Solibro

Calixo

250P-20

ePVL-136

PowerMax

SL2

CX3

Si-mono

Si-poly

Si-amorphous CIS

CIGS

CdTe

250

250

136

120

80

HEE215 M W

125

MPP voltage, STC

V

30.3

30.3

33.0

43.8

76.9

47

MPP current, STC

A

8.22

8.27

4.1

2.85

1.56

1.72

Open circuit voltage

V

37.4

37.7

46.2

59.1

97.6

62.8

Short circuit current

A

8.72

8.69

5.1

3.24

1.69

2.01

Length/Width/Thickness mm

1680/990/40 1642/994/40 5412/373/3

1595/686/45 1190/790/15 1200/400/21

Surface

m2

1.66

1.63

2.02

1.09

Module efficiency

%

15.03

15.32

6.74

11.9

16.7

(b) one 5 kWp grid-connected photovoltaic platform (3) installed on the rooftop of the L7 building, injecting the power, through a 5 kWp SolarEdge SE5000 single phase inverter (i3), in the internal distribution system of the building L7; fixed tilted Si-mono, Si-poly and Si-amorphous photovoltaic modules are installed as reference for four different types of solar tracking systems; (c) two PVT modules are installed on the rooftop of the L7 building. PV/T modules (Volther PowerTherm) are installed in an experimental rig to evaluate their electrical and thermal efficiencies in different outdoor experimental conditions; their specifications are presented in the Table 1;

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

11

(d) one 12 kWp grid-connected photovoltaic platform (4) installed on the rooftop of the L11 building, injecting the power, through a SMA Sunny Tripower 10000TL three phase inverter (i4), in the internal distribution system of the building L11; 24 Si-mono and 24 Si-poly PV modules are mounted in 8 strings having each a monoaxial solar tracking system driven by a single tracking mechanism with linear actuator; the specifications of the PV modules are presented in the Table 1; (e) one 0.9 kWp off-grid wind turbine system (5) installed on the L5 rooftop, composed of three Black 300 small wind turbines, which supply electrical energy to be stored in 4 Solar 12–250 rechargeable batteries and further used through a Sunny Island SI2224 invertor (i5) for the exterior lighting of the building; as back-up solution, the lighting system is switched to the building AC grid when the electrical energy supplied by the wind turbine system is scarce; (f) one 1.8 kWp of-grid wind turbine system (6) on the L6 building rooftop, composed of three Black 600 small wind turbines, which supply electrical energy to be stored in 6 Solar 12–250 accumulators and further used through a Sunny Island SI2224 invertor (i6) for the exterior lighting of the building; as back-up solution, the lighting system is switched to the building AC grid when the wind output is scarce. Besides the buildings’ lighting systems, appliances and equipment, through the internal AC low voltage grid the energy required to power the electrical components of the fresh and wastewater systems is also supplied, containing a submersible well pump (7), a water distribution system (8), a water storage tank (9) and the wastewater bio-treatment reactor (10). These systems are monitored to give a realistic value to the expectable output in the implementation location. The renewable-based thermal energy production uses systems presented in Fig. 6.

Fig. 6. Thermal energy equipment installed in the R&D Institute of the Transilvania University of Brasov: 1 - ground coupled heat pump, 2 - vertical geothermal heat exchanger, 3 - horizontal geothermal heat exchanger, 4 - flat plate solar thermal collector, 5 - evacuated tubes solar thermal collector, 6 - parabolic trough solar thermal collector, 7 - natural gas condensing boiler, 8 - natural gas reducing and metering station

12

I. Visa et al.

On each rooftop of seven buildings (L1, L2, L3, L4, L6, L8 and L10), two flat plate solar thermal collectors Buderus SKS4 (4) are installed and tilted at different angles (between 30° and 90°), to get the optimal angle in the implementation location; the collectors and coupled to 500 L storage tanks installed in each building, in the basement, in a technical room. On the rooftop of two laboratories (L5 and L9), two evacuated tubes solar thermal collectors Buderus SKR12 (5) are installed fixed, at 45° and 0° tilt angle respectively, and are coupled to 500 L storage tanks installed in the basement in each building’s technical room. On the L7 rooftop, two Phoenix Energy parabolic trough solar collectors (6) are installed, driving an 8 kW SorTech AG ACS08 adsorption chiller, part of an experimental solar cooling system. When this system is not active, the thermal energy provided by the parabolic trough collectors is used for DHW. Also on the building L7 rooftop, two PV/T modules Volther PowerTherm are installed in an experimental rig to evaluate the electrical and thermal efficiencies in different experimental conditions. In the L1 and L9 buildings, the low temperature heating/cooling system is supplied by 21 kW Viessmann ground coupled heat pumps (1). The geothermal energy is extracted for L1 building through a vertical geothermal heat exchanger (2) composed of four boreholes drilled down to 90 m below the ground level, one of which is monitored with temperature sensors installed each 5 m, and for the L9 building through a 1000 m2 horizontal geothermal heat exchanger (3) buried at 2.5 m below the ground surface. During the cold seasons the heat pumps work in direct mode and in summer in reversed mode (for cooling). Over the entire year, the heat pump systems provide DHW when the demand is not fully covered by the solar thermal collectors. As back-up source for heating and DHW, all the laboratory buildings have a natural gas condensing boiler (7) with an installed capacity of 63 kW; six of these are Hoval and the other six are Viessmann; each laboratory building is individually connected to an internal low pressure natural gas grid which is connected through a reducing and metering station (8) to the high pressure natural gas grid. The natural gas consumption is globally measured in the metering station (8), and for research purposes, individual gas meters are installed on the buildings L1, L7, L9 and L11 (Table 2 and Fig. 6). Table 2. Solar thermal collectors specifications Characteristic Type

M.U. Buderus SKS4 Flat plate

Buderus SKR12 Evacuated tubes 2070/1145/90 2080/1390/90 2.37 2.86 2.10 2.57 85.1 64.4 1779 1655

Length/Width/Height Gross area Absorber area Optical efficiency Thermal power Electrical power

mm m2 m2 % W W

Phoenix energy Volther PowerTherm Parabolic PVT trough 3860/1110/1350 870/1640/105 4.28 1.47 1.82 1.27 73–76 48.6 3600 680 190

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

13

Another utility that had to be insured in the Institute is the water; for all the regular consumption, water is supplied by a submersible pump (1), Fig. 7, which injects the natural ground water into the distribution system (2), from where each building is fed with the necessary amount of water. A water storage tank (3) insures a water reserve if the submersible pump is not working. A second circuit is for used/waste water, collected from each laboratory building and guided to the wastewater treatment plant, with a specific bio-treatment step. The treated water is reinserted in the environment through a discharge system that inserts this water into the soil, over the geothermal horizontal heat exchanger of the heat pump installed in the L9 laboratory building. The water consumption is centralized measured in the water distribution system (2) and in each building through individual water meters (6).

Fig. 7. The water supply system installed in the R&D Institute of the Transilvania University of Brasov: 1 - submersible well pump, 2 - water distribution system, 3 - water storage tank, 4 - wastewater treatment plant, 5 - treated water discharging system, 6 - individual water meter

5.1

Electrical Energy Production

As already reported for 2014 and 2015, [11], the nominal conversion efficiency in the implementation location has little variations on yearly basis for the mono- and poly-crystalline Si-PVs; larger variations (up to 13%) are observed for CIS and CdTe photovoltaic modules; among the thin film PVs, the CIGS ones have the best steadiness in the efficiency values over one year. Based on these monitoring results, the PV platform installed on L11 contains poly- and mono-crystalline silicon modules. The photovoltaic output during 2015 and 2016 is comparatively presented in Fig. 8. The average efficiency of the PV system installed on the L11 rooftop (considering the global solar energy in the horizontal plane) was 12.41% in 2015 and 11.97% in 2016. As expected, the lowest output and the lowest efficiencies are registered during the winter months (November, December and January) when snow and ice are covering

14

I. Visa et al.

Fig. 8. (a) Electrical energy produced by the PV string array on the L11 rooftop in 2015 and 2016 and (b) monthly conversion efficiency of the PV system

the photovoltaic surface limiting the access of solar radiation by a blocking effect (snow) or through reflection (ice), Fig. 8. During the summer months, the average efficiency of the PV system is about 12.5%, as result of the modules heating. The output follows the global horizontal solar radiation, Fig. 8a, thus well estimating the available solar radiation in the implementation location represents a compulsory path in the efficient design and energy management at community level. These monitoring results show that the electrical energy that can be provided by such a PV platform installed on the rooftop to meet the yearly needs of the testing laboratory building represents on average 33% from the total energy demand, estimated for building L7. This percentage is significantly fluctuating over the year as the data in Fig. 9 show: Considering a laboratory building rooftop for implementing PV systems, following issues have to be considered: – To give full use to the available solar radiation all over the year, thus avoiding reciprocal shading among the PV strings/platforms when the modules are optimally tilted. The optimal tilt angle in the implementation location varies over the year and the less favorable situation corresponds to winter time when, at about 30…35° tilt angle, a surface of 2.9 m2 is needed for each module (to avoid reciprocal shading

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

15

Fig. 9. The monthly coverage degree of the electrical energy consumption with the production of the PV platform on L11 rooftop

among the modules). The top of the buildings has an overall area of 450 m2 which can thus accommodate a maximum of 155 PV unshaded modules, corresponding to an yearly output of 55.8 MWh/year electrical energy for each rooftop. Alternatively, the modules can be horizontally mounted on the rooftop fully avoiding reciprocal shadowing, when a maximum of 281 modules that can be installed on the 450 m2 available rooftop area, corresponding to a yearly output of 70 MWh/year electrical energy for each rooftop. – To cover the energy need of the micro-community; the monitored amount of electrical energy required by one intensively used building (L7) was 36 MWh/year. Thus, there is no need to fully cover the rooftop of each building with PVs in any of the discussed situations (modules mounted horizontally or optimally tilted). It is to underline that the significant difference between the two mounting options is in the number of modules required to meet the energy demand: 144 modules horizontally mounted (230.4 m2) as compared to 100 modules optimally tilted (290 m2). 5.2

Thermal Energy Production

In the built environment, the thermal energy demand can be (partially) met by using solar-thermal systems with flat plate or with parabolic trough collectors as part of an energy mix also involving heat pumps and back-up systems based on biomass or fossil fuels, [12]. Following this assumption, on the L10 laboratory building the solar-thermal implemented system contains two flat plate collectors, with an overall surface of 4.2 m2. The monthly produced thermal energy during 2015 and 2016 is presented in Fig. 10. The overall thermal energy production was of 2693 kWh in 2015 and 2900 kWh in 2016. This quite significant variation (of about 7.2%) cannot be directly linked with the yearly input of solar radiation (higher in 2015 than in 2016) but it can be well correlated with the outdoor temperatures during the winter time, which were significantly lower during 2015 as the data in Fig. 11 show.

16

I. Visa et al.

Fig. 10. Thermal energy produced by the solar-thermal system on the rooftop of laboratory L10

Fig. 11. The monthly mean outdoor temperature in the implementation location

The thermal energy production of the solar-thermal collectors can cover about 65% of the need for domestic hot water in the building. In the testing building (L7) the monthly average thermal energy demand for preparing DHW was 353.68 kWh/month as the results in Fig. 12 show. A backup thermal energy system is required during September - May, with variable output (higher during winter and lower in the other month).

Fig. 12. Domestic hot water monthly demand in the L7 laboratory building

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

17

During the summer months, the results show an almost fully covered thermal energy demand using renewables thus, increasing the size of the solar thermal system, will not be followed by a linear increase in the share of the thermal energy demand satisfied by renewables, because during summer there will be an excess of thermal energy produced, Fig. 13.

Fig. 13. Monthly solar fraction in meeting the DHW energy demand in the L7 test building

This type of calculations is recommended to be done in the design of the solar-thermal systems implemented in the built environment for limiting the DHW storage equipment. Of course, the dimensioning has to consider the monthly demand and the available input solar energy in the location and this depends on the geographical coordinates (latitude especially) and the height of the implementation site. For the 45° latitude (as in the testing facilities under discussion), an average solar fraction of 65% can be considered as reasonable in the mountain climatic profile. To satisfy the entire thermal energy demand (for heating, cooling and DHW) the use of large solar-thermal systems is not entirely recommended in the temperate, rather cold climatic profile; as already mentioned in literature, [13], a coverage share of 30% is considered to be reasonable in the built environment and can be further coupled with biomass burners in a sustainable energy mix.

5.3

Sustainability Closure

Following these data it can be assumed that the share of energy is fully met using solar energy conversion systems over the year; according to the analyzed data the consumption consists of electrical and thermal energy consumed for DHW production. The results in Fig. 14 show a high monthly coverage degree with energy produced using the solar radiation input during summer (over 60%), the yearly average reaching 37%. If considering also the heating demand, currently covered by heat pumps in the laboratory buildings L9 and L1 and gas for the rest, the share of renewable energy out of the total energy consumed in the building decreases below 18%.

18

I. Visa et al.

Fig. 14. Share of renewable energy in the energy consumption of the L7 building

6 Sustainable Community Planning Two scenarios are proposed for further developing of this R&D community: • Scenario 1, with a share of 50% renewables covering the total energy demand, corresponding to a Nearly Zero Energy Community (nZEC); • Scenario 2, corresponding to a Net Zero Energy Community (NZEC), having 100% coverage of the total energy need with renewables. Scenario 1. Nearly Zero Energy Community (nZEC) Based on the registered input and output data for the already installed systems in/on the Institute’s buildings, the overall design of the renewable energy systems (RES) to be installed for meeting with renewable at least 50% of the total energy demand is synthetically presented in Table 3. Table 3. Energy demand in the community planned to be covered by RES Utility

Energy produced by RES Energy [MWh/year] demand [MWh/year]

Share of RES in meeting the energy demand [%]

DHW

50.928

63.4…68.33%

Heating and Cooling Total thermal energy Electrical energy consumed in the 12 buildings Electrical energy consumed to power the heat pumps Electrical energy for water treatment and distribution Total electrical energy Total energy at community level

552 602.928 432 125

32.4 (24 solar-thermal collectors) 447 (12 Heat pumps) 479.4 144 (using PVs and small wind turbines, installed on the buildings

80% 73% 25.85%

144 623.4

25.64% 53.53%

4.458 561.458 1164.438

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

19

As the results show, the chosen energy mix consists of: solar photovoltaic modules and small wind turbines installed on the building’s rooftops for electrical energy production and solar thermal collectors and heat pumps for meeting the thermal energy demand, along with natural gas as backup source. The micro-community represented by the R&D Institute has a higher electric energy consumption as compared with a regular residential community with buildings of the same type (Low Energy Buildings) due to the research testing rigs, thus a careful planning and the smart buildings design is expected to offer adequate implementation space for the renewables in this built environment. By installing PV platforms on each rooftop and small wind turbines a share of 25.85% renewable energy is used to meet the total electricity demand at micro-community level. The general management of the electrical energy is centralized at community level, giving primary use to the renewable electricity produced with the systems that are or can be mounted on the 12 buildings. The renewable thermal energy can be insured through geothermal systems and solar-thermal systems in the desired ratio. The heat pumps are used for heating and cooling the buildings and the solar thermal systems are used to obtain domestic hot water (DHW) in the buildings, Fig. 15. In all buildings, the low temperature heating/cooling system is supplied by ground coupled heat pumps (1). The geothermal energy is extracted through vertical geothermal heat exchangers (2) composed of four boreholes drilled down to 90 m below the ground level for each laboratory building and through a 2000 m2 horizontal geothermal heat exchanger (3) at 2.5 m below the ground surface for the L9 and L12 buildings. During the winter the heat pumps work in direct mode for heating and in summer in reversed mode, for cooling. During the entire year, the heat pump systems provide DHW when the demand is not covered by the solar thermal systems.

Fig. 15. The thermal energy for the renewable energy mix in the R&D Institute of the Transilvania University of Brasov: 1 - ground coupled heat pump, 2 - vertical geothermal heat exchanger, 3 - horizontal geothermal heat exchanger, 4 - solar thermal collectors, 5 - natural gas condensing boiler, 6 - natural gas reducing and metering station

20

I. Visa et al.

On each rooftop two solar thermal collectors (4) are installed fixed and tilted at the optimal angle (40°), further coupled to a 500 L storage tank installed in the basement of each building, in the technical room. As a back-up source for heating and DHW, a 63 kW natural gas condensing boiler (5) is installed in each building, individually connected to an internal low pressure natural gas grid which is connected through a reducing and metering station (6) to the high pressure natural gas grid. The natural gas consumption is globally measured for the entire community in the metering station (6), and individual gas meters are installed on each building. It is to notice that the practical application hereby discussed is one of an offices community that has rather low DHW consumption. For a residential area, this consumption may by higher and the solar-thermal surface need to be larger, according to the projected needs. It is to mention that the evacuated tubes collectors are more efficient and are recommended to be included for DHW production.

Table 4. Energy demand and energy produced at building and community levels

Yearly thermal energy demand Heating DHW for 40 persons Cooling Total thermal energy demand Yearly produced thermal energy using RES Heat pumps Solar thermal collectors Natural cooling Active cooling Total thermal energy produced by RES % of RES covering the thermal energy demand: 86.37% Yearly electrical energy demand Lighting and equipment Powering the heat pumps for heating Powering the heat pumps for cooling Fresh water system Wastewater system Back-up to fully cover the thermal energy demand (uncovered by RES) Total electrical energy demand Yearly produced electrical energy using RES Fixed, horizontal PV systems 44 kWp on the buildings Wind turbines systems of 1.8 kWp (3 turbines of 600 W) Infield platforms (8  2 kWp) Total electrical energy covered from RES % of RES covering the total electrical energy community demand % of RES covering the total energy demand at community level

At Building level [kWh/year]

At community level [kWh/year]

46413 4244 3986 50657

556956 50928 47832 607884

37075 2693 2106 1880 43754

444900 32316 25272 22560 525048

37474 10422 752 146.75 224.56 7044 55692

449688 125064 9024 1761 2694.72 84528 668304

45763.7 1245 19008 66016.7 115% 103.2%

549164 14940 228096 792200

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

21

Scenario 2. Net Zero Energy Community Considering the monitored values for the electrical and thermal energies consumption and production, the way how the demand can be balanced by the production is presented in Table 4: The data in Table 4 were calculated considering the following renewable energy systems: (a) For electrical energy production from: – string PV platforms (of 44 kWp each) installed on the rooftop of each of the 12 buildings; – three wind turbines (600 W  3 = 1800 W) installed on each rooftop. These systems can be implemented on the rooftops and as 8 additional ground installed platforms, as presented in Fig. 16.

Fig. 16. The complete electrical energy system planed for the R&D Institute of the Transilvania University of Brasov: 1 - distribution substation, 2 - 16 kWp ground installed photovoltaic platforms, 3 - 44 kWp photovoltaic platform installed on rooftop, 4 - 1.8 kWp wind turbines system, 5 - submersible well pump, 6 - water distribution system, 7 - water storage tank, 8 - wastewater treatment plant

Preliminary simulation results show that the electrical energy production exceeds the need by 15%. However, these data have to be matched with the monthly and daily need, and the eventual excess can be inserted in the national grid. (b) For thermal energy production, the energy mix is planed similarly to Scenario 1 and the thermal energy demand covered by this renewable energy mix (solar and geothermal) represents 86.37%.

22

I. Visa et al.

Thus, when finalizing the renewable energy systems implementation, the total community energy demand will be covered at about 103% (the excess electrical energy being inserted in the national grid).

7 Conclusions Implementing sustainable energy solutions in the built environment represents a trend widely approach in various extent. One of the most important issue that is tackled is related to satisfying the energy demand of the building stock by adopting feasible and affordable measures. This asks for a combined strategy for: • Increasing the energy efficiency of the buildings by using novel construction materials and novel design concepts; • Reducing the share of fossil fuels in meeting the energy demand of these buildings and using in a large extent the renewable energies. This concepts are matching the nZEB (Nearly Zero Energy Buildings) which are now very much investigated and, in many countries already implemented. However, taking one building at the time cannot solve fully the sustainability issue at community level or long time periods are required for this. Thus the implication of the community structures is required and will be accepted if there is an obvious gain. The paper analyses the newly formulated concept of Nearly Zero Energy Community (nZEC) which, besides residential buildings includes all the other parts of the building stock (administrative buildings, schools, hospitals, etc.). The main energy types that represent the consumption in a community are electrical and thermal energy. Many studies outline that the electricity production pattern can be preserved, and further using the already existing distribution infrastructure while changing only the energy source: instead of fossil fuels, the use of renewables is recommended on a large scale. The variability in the renewable energy sources potential can be better match with the variability in the energy demand if larger systems are developed targeting larger groups of users with a broader range of needs in time. Thus community energy management systems are recommended, as outlined also for the case study presented, of the R&D Institute of the Transilvania University of Brasov. The thermal energy demand is governed for almost any user of the built environment by a similar set of factors (geographical location, season, etc.). Additionally, the transport and distribution networks for thermal energy have significant larger losses than those for electricity and a shorter lifetime. This recommends in the sustainable energy transition the use of smaller thermal energy production and distribution systems, located e.g. at building level. Thus at community level, renewable based energy systems should accordingly be designed: • As centralized systems for electrical energy production, using photovoltaics, wind and small (or larger) hydros (if available the water potential);

Implementing Renewable Energy Systems in Nearly Zero Energy Communities

23

• As much smaller thermal energy production systems (solar-thermal, biomass, geothermal), designed to meet the demands for a small group of users, including houses, blocks of flats, etc. One significant issue when downscaling the existing thermal energy systems is related to the energy storage, for covering peak periods with high consumption and low available potential as e.g. during winter time. In any situation, the full energy demand in a community should be covered also with the production of backup sources, e.g. based on fossil fuels during periods of peak consumption or periods with lower renewable energy potential. The share of fossil fuels can be gradually decreased down to zero in a second stage, aiming at the transition from a Nearly Zero Energy Community towards the Net Zero Energy status. These concepts were implemented in the R&D Institute of the Transilvania University of Brasov, and the results of two years of monitoring are presented in the paper. The results show that using only solar energy conversion systems an overall share of 18% of the energy demand is covered by renewables. The results show that the electrical energy demand can be covered in a very large extent (during the summer months) by the installed systems on the buildings (if this was planned in the building step) but the thermal energy demand needs solar-thermal systems covering much larger available area or another source; this confirms the need for designing and implementing energy mixes, also including e.g. efficient geothermal or biomass systems and a smart energy management, beyond the building(s), towards the community. By adding geothermal systems (heat pumps) in the energy mix, for heating and cooling and using the top terraces of each building following the tested pattern to install solar energy conversion systems, about 53% of the total energy demand of the micro-community can be met, reaching thus the Nearly Zero Energy Community status. The simulated data show that the buildings and the nearby area can be used for implementing the components of the energy mix to fully cover the energy demand using renewables, thus complying with the Net Zero Energy status.

References 1. REN21. Renewable energy Policy Network for the 21st Century. Renewables 2014. Global Status Report (2016) 2. Hussain, A., Arif, S.M., Aslam, M.: Emerging renewable and sustainable energy technologies: State of the art. Renew. Sustain. Energy Rev. 71, 12–28 (2017) 3. Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings 4. Klein, S.J.W., Coffey, S.: Building a sustainable energy future. One community at a time. Renew. Sustain. Energy Rev. 60, 867–880 (2016) 5. Romero-Rubio, C., Ramon, J., Diaz, A.: Sustainable energy communities: a study contrasting Germany and Spain. Energy Policy 85, 397–409 (2015) 6. Renewables 2017. Global status of renewables, International Solar Energy Society (2017)

24

I. Visa et al.

7. Koening, R.: The three Ds of modern power. In: Power Engineering International, online version, May 2017 8. Visa, I., Duta, A.: The built environment in sustainable communities. In: Visa, I. (ed.) Sustainable Energy in the Built Environment - Steps Towards nZEB. Springer Proceedings in Energy, pp. 3–30 (2014) 9. Futcher, J., Mills, G., Rohinton, E., Korolija, I.: Creating sustainable cities one building at a time: towards an integrated urban design framework. Cities 66, 63–71 (2017) 10. Howell, S., Rezgui, Y., Hippolyte, J.-L., Jayan, B., Li, H.: Towards the next generation of smart grids: semantic and holonic multiagent management of distributed energy resources. Renew. Sustain. Energy Rev. 77, 193–214 (2017) 11. Visa, I., Burduhos, B., Neagoe, M., Moldovan, M., Duta, A.: Comparative analysis of the infield response of five types of photovoltaic modules. Renew. Energy 95, 178–190 (2016) 12. Moldovan, M., Visa, I., Duta, A.: Future trends for solar energy use in nearly zero energy buildings. In: Advances in Solar Heating and Cooling, pp. 547–569. Elsevier (2016) 13. Gajbert, H., Seds, J.: Apartment buildings in the cold climate, renewable energy strategy (in Sustainable Solar Housing, vol. 1, Strategies and Solutions), Solar thermal systems for building integration, pp. 207–225 (2008)

Refurbishment Solutions for Public Buildings Towards Nearly Zero Energy Performance Laura Aelenei(&) and Helder Gonçalves Laboratório Nacional de Energia e Geologia, Lisbon, Portugal [email protected]

Abstract. This study presents some results of an recent closed European Project, RePublic_ZEB [1], where an extensive analysis was conducted for identifying cost-optimal refurbishment solution an sets of solutions applied to exiting public buildings, towards nearly Zero Energy Buildings (nZEB) performance. The analysis was applied to 12 reference buildings identified in 8 countries participants in the project and for different building typologies. A cost-optimal solution sets matrix of the 12 buildings is presented together with the results of nZEB energy performance. Keywords: nZEB


Refurbishment
Public buildings
Cost-optimal

1 Introduction Nearly Zero Energy Buildings have gained more attention since the publication in 2010 of the EPBD recast [2]. EPBD recast requests all new buildings to meet higher levels of performance than before, by exploring more the alternative energy supply systems available locally on a cost-efficiency basis and without jeopardizing the comfort. To this end, beginning in 2020, all new buildings should become “nearly zero-energy”. A “nearly zero-energy building” refers to a high energy performance building of which annual primary energy consumption is covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby. The directive requires nearly zero energy buildings, but it does not give minimum or maximum harmonized requirements as well as details of energy performance calculation framework. Furthermore, the EPBD recast states that MS must ensure that minimum energy performance requirements for buildings are set with a view to achieving cost-optimal levels according to the Commission Delegated Regulation (EU) No 244/2012 of 16 January 2012 on the cost optimal methodology framework. In this context, MS implementation of the Regulation emphasized the cost-optimal analysis for the residential buildings, at the expense of all the other categories. The nZEB concept still does not seem to be easily applied in the member countries: the IEE programs past and current efforts clearly show that required investments and optimal integration of the technologies suitable for the buildings construction and/or renovation into nZEB are among the major barriers. Furthermore, the confidence both of the buildings industry and of the building owners in the real energy performance of © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_2

26

L. Aelenei and H. Gonçalves

the nZEBs and in the real risks associated to new technologies, seems one of the most strategic point. The resolution of which could possibly solve the problem related to the high investments required in the process.

2 RePublic_ZEB Project 2.1

About the Project

In this context and trying to respond as well to the European building legislation, RePublic_ZEB project started in 2014 focuses in the refurbishment of the public building stock towards nZEB in the countries of the South-East of Europe in line with the EU’s Energy Performance of Building Directive and its energy targets for 2019 and 2021. The project’s main objective is to support the participant countries to develop and promote on the market a set of concrete technical solutions for the refurbishment of the public building stock towards nZEB. To achieve this goal, RePublic_ZEB’s includes an assessment of the current public sector building stock and the determination of reference buildings. The expected output is the definition of cost optimal packages of measures for the refurbishment of the public buildings towards nZEB, which will be included in guidelines and the promotion activities addressed to national and regional authorities as well as construction industry, housing organizations, owners of large building stock and developers. The project plan was structured in 6 Working Packages (WP), from which two of them were related with project management activities (WP1) and project dissemination activities (WP6). Taking into account that two methodologies, the main streams of the project, were: one the cost-optimal methodology for calculating cost-effective packages of measures for refurbishment of public buildings and the other one the nZEB calculation approach, three of the WPs were dedicated to this development: WP2 was related with analysis of the public building stock in each country, definition and identification of reference buildings in each country and for each typology, WP3 was related with the identification of existing nZEB definitions and approach and proposing a common approach to be used in the project and for all participants and WP4 was related with the calculation of the cost-effective packages of measures for the identified reference buildings and nZEB common approach. WP5 was related with communication activities between the main actors and project guidelines development, including all the results from WP2, WP3 and WP4. In this paper, the refurbishment cost-effective solutions will be present, together with the matrix of these solution and set of solutions for 12 reference buildings and the energy performance of these buildings before the refurbishment and after applying the refurbishment solutions.

2.2

Methodologies

One of the main objectives of the RePublic_ZEB project was to propose a common framework and a harmonization methodology for the nZEB concept for existing public building”. To this aim, and considering the legislative context of each country, the

Refurbishment Solutions for Public Buildings

27

consortium has formulated the following definition: “Transformation of an existing public building to nZEB means to apply renovation technologies that reach a target share of RES and enables energy performances or CO2 emissions better than the optimal case but still cost effective.” As commonly defined in the framework of the project, a building is considered as nearly Zero Energy when the following requirements are met: • The EP is lower than the cost-optimal level (a nZEB has higher energy performance than the cost-optimal building); • The differential Global Cost (DGC) is negative (nZEB renovation is cost effective); • When available, the national minimum energy performance requirements for nZEBs are fulfilled. The proposed definition is coherent with the indicators proposed by the European Directive. The selected parameters to characterize the refurbishment toward nZEB are the followings: • Non-renewable primary energy consumption • Renewable energy ratio • Global costs. Based on these indicators, the cost-optimal methodology [3, 4] is used. Figure 1 represents an example of the effect of several retrofit measures (every dot) in terms of energy performance and differential global cost, in comparison with the existing building. The figure shows how the nZEB range is located between the cost-optimal package of measures and the measures with an equal or lower global cost than the existing building.

Fig. 1. Energy performance and differential global an example [5]

The economic indicator, global cost, is calculated following the European standard EN 15459:2008 Energy performance of buildings. Economic evaluation procedure for energy systems in buildings. The global cost method is the calculation of a present

28

L. Aelenei and H. Gonçalves

value of all the costs during a long period, taking into account the residual values of components with longer lifetimes. Basically, the costs can be divided in three main groups: energy costs, investment costs and running costs. Each of these costs is calculated for the established period in the study, in this case 30 years. The energy costs are composed of two terms: costs related to the consumed energy by the building (purchased energy) and the costs related to the produced energy in the building (sold energy). In both terms, the included costs can be: energy cost (€/kWh), additional values for purchase/sale (€/yr, as for example power fix term of the electrical contract), and environmental costs (€/CO2 emission). In this study, the environmental cost is not included because the perspective of the evaluation is microeconomic (financial). The investment cost of each retrofit option includes three terms: the initial investment cost, the replacement cost and the final value of the component. The total replacement cost and the final value of the component are related to the lifespan of the retrofit measures. Finally, the running cost includes the annual cost for the maintenance of the building and their systems, which is considered every year of the calculation period. The proposed nZEB definition wants to be useful for the countries in which nZEB has not been defined yet, and also for the countries that have already defined nZEB in detail, in order to help to better orientate the discussion on the matter and facilitate better future regulations.

3 Case Studies As mentioned previously, a methodology of defining the reference buildings based on the public building stock in each participant country has been developed. The reference building categories analyzed in the framework of the project were: residential buildings, office buildings, school buildings and hospitals, as these categories represent the highest fraction of primary energy consumption in all the countries. Furthermore, every building category has been analyzed in different countries and climates in order to compare which strategies are the most appropriate in each situation. Twelve examples of reference building for different categories were selected for the application of the refurbishment measures and solutions of public buildings towards nZEB: 4 buildings offices, 3 educational (schools), 3 hospitals and 2 residential (multifamily) buildings. It worth mentioned also regarding the location of these building that 5 large buildings (3 offices, 1 school and 1 hospital) are located in South Europe, 5 large buildings (1 office, 2 schools and 2 hopsitals) are located in Central-East Europe and 2 residential are located in Central-East Europe. The buildings are presented in the Fig. 2 together with the information about location, type of building, area and year of construction. A number of efficient cost-optimal solutions and set of solution were applied and tested according with the types of building, climate location, energy savings and costs.

Refurbishment Solutions for Public Buildings

29

Fig. 2. Case studies

3.1

Refurbishment Measures

For each kind of reference building a set of solutions have been simulated in order to identify those more cost-effective. The description of the final refurbishment solutions adopted for the 12 case studies are present in the Table 1. The solutions with the larger variety were those regarding building opaque envelope, representing 7 solutions of different external insulation for walls and roofs, 4 solutions for windows, 2 solutions for shadings device, 6 for efficient systems, 2 for lightening, 3 for renewable energy systems and one of district heating.

30

L. Aelenei and H. Gonçalves Table 1. Refurbishment solutions

M1 wall insulation

M2

M3 M4

M5 M6

M7

M1-1 M1-2 M1-3 M1-4 M1-5 M1-6 M1-7 windows M2-1 M2-2 M2-3 M2-4 shading M3-1 M3-2 energy efficient systems M4-1 M4-2 M4-3 M4-4 M4-5 M4-6 lighting M5-1 M5-2 RES M6-1 M6-2 M6-3 M7

Roof – External insulation (25–34 cm EPS) Roof – External insulation (15–22 cm XPS) Roof – External insulation (6–10 cm XPS) Wall – External insulation (20–22 cm EPS) Wall – External insulation (12–15 cm EPS) Wall – External insulation (3–9 cm EPS) Wall – External insulation (30 cm EPS) Window – Triple glass low-e filled with gas Window in PVC – Triple glass low-e Window in PVC – Double glass Window in aluminum – Double glass, low-e External movable shadings External fixed shadings Air source heat pump Ground or water source heat pump High efficient chiller Mechanical ventilation Heat recovery system Load management LED Linear fluorescent lamp T5, T8 Solar thermal systems Photovoltaic system (monocrystalline, polycrystalline) Biomass boiler District heating

The thermal transmittance of the building (external walls, roof, attic floor, ground or cellar floor slab) has a great influence on the heating and cooling demand. The thermal insulation of the building is one of the most expensive measures, but probably it has the biggest impact on heating energy saving. The best insulation is placed on the exterior of solid walls, so it enables the building to continue to benefit from the thermal mass of the walls and can easier reduce the effect of thermal bridges; however there are limitations for historic or protected buildings. The most common types of insulation are expanded polystyrene (EPS), extruded polystyrene (XPS), fiberglass and mineral wool. The air space of cavity walls can be filled with insulation materials such as cellulose insulation, glass wool and foam that can be blown into the cavity through suitably drilled holes. In all case studies the insulation was placed on the exterior of the walls and roofs. Windows have very high impact on the heating and the cooling demand, therefore the energy saving potential of changing or modernizing windows is significant. The required investment can be variable from moderate to high levels, depending on the type of refurbishment. The effect depends on the frame and the glazing of the windows:

Refurbishment Solutions for Public Buildings

31

the frame can be made of wood, PVC or aluminum. The aluminum frame must be designed with thermal breaks to avoid high thermal losses due to the high thermal transmittance of the material. There are three main characteristics to consider with glazing: the number of panes (double or triple), the filled gas (air, argon etc.) and its emissivity. Special coatings can reduce the infrared radiation transmission without compromising the amount of visible light that is transmitted. Solar shading is the term used to identify the systems to control the amount of heat and light from the sun admitted to a building. Solar shading devices can offer energy savings in different areas: they can reduce the amount of energy required for heating or cooling, can reduce the energy required for lighting, by optimizing the admittance of daylight, and enhance indoor comfort and stimulate productivity. Installation of solar shading devices is highly recommended in buildings exposed to the sun in summertime. Well-designed solar shading devices help to keep the building cool and comfortable, reducing the air-conditioning needs and, at the same time, taking benefits from solar gains in winter. The most efficient shading devices are placed outside the windows. In this way, the solar radiation is reflected to outside before reaching the window. When the protection is placed inside, only a fraction of the incoming solar radiation is reflected outside. The shading devices can be fixed or movable. For rooms exposed to the East or to the West, movable solar shading devices are better for an optimal operation in the different seasons. Regarding the energy efficient systems, the ground source heat pump transfers thermal energy stored within the soil to the building by means of an electric heat pump. The thermal energy is collected with closed horizontal or vertical loop coils. Horizontal collectors may be more economical but require a sufficient area near the building. The first 1.5 m layer of the ground is moderately influenced by the sun and the season variations. Deeper, the ground temperature is almost constant and warmer than the air temperature in winter and colder in summer. Horizontal ground collectors (coils or spirals) are buried below freezing depth over a certain surface area, depending on the heating/cooling demand. Vertical ground collectors (pipes or loops) are placed in bored wells that can reach 120 m or more in depth. The water source heat pumps use the heat energy available in water as a heat source. Water source heat pumps can operate with “open” or “closed” loop. Air source heat pumps use the outside air as a heat source. Air temperatures vary seasonally and moisture content fluctuates: an air source heat pump will always depend on the climate conditions. The colder the air temperature, the harder the heat pump must work to lift the temperature up to what is required for heating. Air source heat pumps use electricity to move heat from a cool space to a warm one, making the cool space cooler and the warm space warmer. During the heating season, heat pumps move heat from the outdoors into the building and during the cooling season, from the buildings to the outdoors. Chillers are part of centralized systems and are adopted for the cooling of the buildings. A vapour compression chiller produces chilled water by transferring heat from the chilled water circuit to the re-cooling circuit. The vapour compression cycle is driven by electrical energy supplied to the compressor. The main components of these machines are: electric compressor, condenser, thermal expansion valve and the evaporator.

32

L. Aelenei and H. Gonçalves

The objective of the ventilation is to guarantee a good air quality for the occupants. Adequate ventilation is needed for both the comfort and the safety of occupants, as it removes pollutants produced in the building. The air renovation depends on the number of occupants and the relevant activity. Mechanical ventilation is used where natural ventilation is not appropriate, like in cold climates. Air extraction produces a constant depression and the inlet air should be pre-conditioned to ensure an appropriate air quality (filters) and temperature. Mechanical ventilation must be combined with a control system to optimize its operation and reduce the energy consumption. The control can regulate the air flow according with the air temperature and quality inside the building (CO2 concentration, humidity etc.). Energy recovery takes energy from exhaust air and transfers it either to the supply air or to the domestic hot water. The heat recovered from exhaust air reduces the quantity of energy required for heating or humidifying the outdoor air in air ventilation systems. Several types of energy efficiency lighting technologies exist, such as T5 fluorescent lamps, compact fluorescent lamps (CFL) and light-emitting diodes (LED). All this types of lamps are suitable to replace old T8 fluorescent lamps and incandescent lamps. When continuous lighting is required, the application of energy efficient T5 fluorescent lamps is suggested. With intermittent lighting, the application of energy efficient LED lamps is suggested. LED lamps have long life spans even with frequent switching and generate much lesser heat compared to other lighting systems. To reduce the energy consumption of the lighting system, control strategies (M18) are required, like: occupant sensors, daylighting control, dimmer controllers. A Building Management System (BMS) is a computer-based controller network that controls and monitors the building’s mechanical and electrical equipment such as heating, cooling, ventilation, lighting, power supply, fire and security plants. Current generation BMS systems are based on open communication protocols and are WEB enabled allowing integration of systems and access from everywhere in the world. These systems incorporate sensors to monitor the use of the building and to control and regulate, through the actuators, the level and time of operation according with the set-point established. These systems make possible to collect information, guaranteeing an adequate operation and giving the possibility to detect and predict possible problems. District heating/cooling means the distribution of thermal energy from a central source to multiple buildings or sites through a network. Where water is used as heat transfer medium, heat exchangers and water flow meters are the only equipment needed to provide heating and cooling to the buildings. The advantage of these systems is the higher performance of the generation plants in comparison with individual systems. The production of domestic hot water can be achieved using a solar thermal panels. In some climate regions, the system is useful for heating as well. In summer, there is a possibility to feed absorption machines for cooling. The most common solar panels are of the following types: flat-plate collectors and evacuated tube collectors. PV panels convert solar energy to electricity. Even in cloudy, northern latitudes, PV panels can generate power to meet totally or partially the building’s electricity demand. PV is a flexible and versatile technology. Panels can be used on roofs, curtain walls and decorative screens. With Building-Integrated PV (BIPV) the photovoltaic components are used to replace part of the conventional building materials such as the roof covering and the external layers of facades.

Refurbishment Solutions for Public Buildings

3.2

33

Results Refurbishment Solutions Set Matrix

In order to understand common strategies and solutions adopted regarding building categories and also locations (different climates) a matrix of solution sets was developed in the following (Fig. 3). The methodology focused by the project Republic_ZEB is suitable for defining the packages of measures needed to refurbish the existing buildings towards optimal nZEBs.

Envelope solutions Energy Efficient systems solutions Renewable energy Systems solutions

RES_SL

RES_HU

Residential HP_SV

HP_ES**

HP_BG

Hospitals SC_RO

SC_BG

SC_IT

OF_HU*

Schools OF_GR*

OF_PT

OF_IT*

Office

M1-1 M4-1

M4-1

M4-1 M6-1

M1-2

M1-2 M4-2

M4-2

M6-2 M1-3

M1-2 M6-2

M6-2

M1-3

M6-2

M1-3 M4-3

M4-3 M6-3

M1-4

M1-4 M4-4

M1-5

M4-4

M4-4

M1-5

M4-5

M4-5 M1-6

M1-6

M4-6

M4-6 M1-7 M5-1

M5-1 M2-1

M2-1

M5-2

M5-2 M2-2 M2-3 M2-4

M2-4 M7

Fig. 3. Matrix of solution set for public building refurbishment toward nZEB

M2-2

34

L. Aelenei and H. Gonçalves

Despite all differences between the 12 analyzed case studies the type of construction and climate conditions, the strategies to achieve the nZEB criteria are nearly common. In fact, the measures that have been selected in most of the buildings are the following: (a) Envelope solutions (M1, M2, M3) (M1) Thermal insulation has been adopted in most of the buildings to: facade, walls and slabs separating conditioned and unconditioned rooms, roof and ground. Despite their high investment costs, this measure is the most effective in terms of energy demand reduction. The thermal insulation permits to reduce the heating, the cooling demand and the thermal bridges of the building. Its sizing is dependent on the climate (more insulation in colder climates). (M2) Efficient windows. This measure is one of the most effective measures. The investment cost is high but the benefits are significantly important. There are many types of efficient windows and the appropriate selection depends on the climate and the overall design of the building (heat gains, solar shading devices, daylighting control have to be considered). (M3) Shading devices as fixed or movable were used in some case studies. (b) Energy efficient systems (M4) (M4-6) Load management. To ensure a proper operation of the systems it is very important to manage the building with advanced tools, as building management systems and optimal control strategies. There are different levels of implementation, depending on the needs and features of the building. (M4-1) Air source heat pump. The air source electric heat pump has been chosen in several building categories and climates, in which more services have to be provided (only heating; heating and cooling; heating, cooling and hot water). The technical and economic feasibility and the reliability of the heat pumps are increasing and this makes the technology very flexible today. It is also an ideal technology to be combined with electric renewable generators. The use of geothermal (ground source) and water heat pumps (M4-2) depends on the location of the building and is less generalizable. (M4-4) Mechanical ventilation. The system permits to control the rate of air renovation guaranteeing the indoor air quality. However, the more interesting achievements in terms of energy savings require combining it with additional measures: advanced control systems (M18) and heat recovery systems (M13). (c) Efficient lighting (M5) The artificial lighting has a significant impact on the energy balance and the adoption of efficient lamps provides positive impact also from an economic point of view. The most common solutions are the LED technologies and fluorescent lamps T5, combined with control strategies. (d) Renewable energy systems (M6) (M6-1) Solar Thermal Systems were proposed as solution for the case studies school in Romania and hospital in Bulgaria.

Refurbishment Solutions for Public Buildings

35

(M6-2) Photovoltaic system. The PV system is the most adopted renewable energy system due to the simplicity of the installation and the benefits in terms of reduction of electric consumptions. Almost all case studies integrate the PV systems for generating electricity. (M6-3) Biomass boiler. This technology has been adopted in large buildings, where the heating and the sanitary hot water production must be covered by the boiler. This system is more adequate in cool climates or in buildings with high energy demand (for example, the hospital).

3.3

Results Energy Performance

The 12 case studies were simulated taking into account the real characteristics or the characteristic of the reference buildings considered for each category. Taking into account the considered solutions and set of solution identified for refurbishment towards nZEB, all case studies were simulated with the implemented solutions. The results of the energy performance of all case studies before and after refurbishment, can be observed in the Fig. 4 for residential and office buildings and Fig. 5 for schools and hospitals. It can be observed that generally, after the application of the refurbishment solutions, the primary energy consumption (non-renewable) is reduced after applying the refurbishment measures. In the same time, the use of renewable energy is also higher, as in some cases even before refurbishment the buildings were equipped with renewable energy systems (Hungary, Italy, Portugal). In which regards the general aspect and nZEB approach, there are some differences in the context of each country that could make difficult the comparison between the featured buildings. In particular: – In some countries there is no official definition of nZEB and the retrofit solutions have been selected just according to the project definition: a refurbished building is more energy efficient than the cost-optimal solution, but at the same time is cost effective. – The share of renewable energy regulated in each country is different. – The energy needs and the number of services considered in the final energy consumption are not the same for all the countries and for all the building categories. – Some countries have no official values for the primary energy factors, specifically regarding the renewable fraction of primary energy. – The chosen buildings are different as typologies, constructive characteristics and volume. – The climate and the occupation of the buildings are also different; these factors highly influence the energy consumption of the buildings.

L. Aelenei and H. Gonçalves

OF_HU

OF_GR

OF_PT

OF_IT

RES_HU

RES_SL

36

Fig. 4. Energy performance before and after refurbishment for residential and office buildings

HP_SL

HP_ES

HP_BG

SC_RO

SC_BG

SC_IT

Refurbishment Solutions for Public Buildings

Fig. 5. Energy performance before and after refurbishment for schools and hospitals

37

38

L. Aelenei and H. Gonçalves

4 Conclusions This study presents some results of an recent closed European Project, where an extensive analysis was conducted for identifying cost-optimal refurbishment solution an sets of solutions applied to exiting public buildings, towards nearly Zero Energy Buildings (nZEB) performance. The analysis was applied to 12 reference buildings identified in 8 countries participants in the project and for different building typologies. A cost-optimal solution sets matrix of the 12 buildings is presented together with the results of nZEB energy performance. As a final remark, it important to underline that the energy diagnosis and an overall assessment of the existing building are a very substantial step in the design of the retrofit measures. In fact, the transformation towards nZEB is, at the end, an energy and an economic issue based on the energy balance of the building. This means: reducing energy needs, improving efficiencies in general and increasing the use of renewables taking into considerations the characteristics of the building and the local climate. However, other aspects must be considered in refurbishments, like: the comfort, the rationalization of the use of the building, eventual artistic demands (often required in public buildings by the local regulation) and the eventual preservation of historic value (this is a very big issue in ancient cities and town) etc. Then, the consultation of these results should not make us forget the need to also analyse all these aspects. Acknowledgments. We hereby acknowledge the IEE Project RePublic_ZEB, Grant agreement no. IEE/13/886/SI2.674899.

References 1. Republic_ZEB. http://www.republiczeb.org/. Accessed June 2017 2. Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings (recast). http://eur-lex.europa.eu/legal-content/EN/TXT/ PDF/?uri=CELEX:32010L0031&from=en. Accessed June 2017 3. Aelenei, L., Paduos, S., Petran, H., Tarrés, J., Ferreira, A., Corrado, V., Camelo, S., Polychroni, E., Sfakianaki, K., Gonçalves, H., Salom, J., Riva, G., Murano, G.: Implementing cost-optimal methodology in existing public buildings. Energy Procedia 78, 2022–2027 (2015). doi:10.1016/j.egypro.2015.11.197 4. Corrado, V., Ballarinia, I., Paduos, S.: Assessment of cost-optimal energy performance requirements for the Italian residential building stock. Energy Procedia 45, 443–452 (2014). doi:10.1016/j.egypro.2015.11.197 5. Ortiz, J., Aelenei, L., Ferreira, A., Hartless, R.: Guidelines on best practice addressed to several stakeholders and target group such as: industries, housing organizations, owners of large building stocks, developers (2016). http://www.republiczeb.org/filelibrary/WP5/D5.2_ Guidelines_RePublic_ZEB-final.pdf. Accessed June 2017

Renewable Energy Management Using Embedded Smart Systems Viorel Miron-Alexe1(&), Iulian Bancuta1, and Nicolae Vasile2 1

2

Scientific and Technological Multidisciplinary Research Institute, Valahia University of Târgoviște, Târgoviște, Romania [email protected] Electrical Engineering Faculty, Valahia University of Târgoviște, Târgoviște, Romania

Abstract. This paper highlights the implementation possibility of automated embedded systems for energy management into insular clusters of homes or off-grid buildings that can harness multiple renewable energy sources. As the embedded technologies and the Internet of Things concept are starting to merge stronger and faster from one year to another, we can ow acknowledge the new possibilities for energy efficiency and energy harvesting that are becoming mainstream. Traditional worldwide companies that provides IT&C services and electronic products solutions, have now a mature portofolio for IoT data communication and devices automation. In this respect, Cisco predicted that by the year 2020, at least 50 billions of devices will share a common communication network, thus any electronic device will be able to communicate with another in an automated manner. If by this time we were talking about the “Internet of People”, where people communicated with other people, now the paradigm have changed into the “Internet of Things” which enables devices communicate with other devices. To no surprise, this is a natural evolutionary step that aims to minimise the human efforts, accelerate information transmission, processing and execution, optimise and correct human errors and even provide the best alternatives to complicated problems by the help of AI (Artificial Intelligence). Regarding the energy sector, these smart systems have the purpose of providing energy efficiency, components compatibility, low carbon footprint and further exploit the renewable energies potential to a higher degree by hybridization. Keywords: Hybrid renewable energy
Prosumers
Embedded systems Off-grid
Electrical sensors
Hydrogeneration
Photovoltaics




1 Introduction According to the International Renewable Energy Agency (IRENA) report [1], the Bloomberg report [2], the Sustainable Energy for All (SE4ALL) report [3] and the World Bank report [4], a number of over 1.16 billion people worldwide or 17% of the world population is still living off-grid or without access to electricity due to the poverty, equipment costs, remote locations or geopolitical factors. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_3

40

V. Miron-Alexe et al.

The analysis of the worldwide access to electricity statistics, reveals that Africa represents the top continent regarding the lowest electrification rate of communities, the population percent having access to electricity ranging only from 24% to 40%, depending on the country (Fig. 1).

Fig. 1. The 2014 World Bank report map over the global population percentage with access to electricity for each country [5]

The worldwide interest for the off-grid renewable energy development is slowly increasing in both emerging countries and developed ones alike because of the declining costs of the photovoltaics, wind turbines, hydroelectric installations, electricity control and storage equipment, technological improvements and market accessibility. In Romania there is a large potential for both solar and hydro energy to be harvested as a large number of remote villages and households live the off-grid mainly because of poverty, calamities or remote locations and where the national electrical distribution grid cannot reach due to high costs or inaccessible locations for infrastructure deployment. An analysis over the solar potential in Romania (Fig. 2) reveals that the Eastern region, the South-Eastern region, the South region, the West region and the Central region, all represent the most favored areas as solar irradiance levels. According to the annual measurements of the solar radiation in Romania, the average is about 3.56 kWh/m2 per day and giving the fact that almost 210 days per year are sunny days [6]. Regarding the hydrography of Romania, there are a total of 11 river basins spreaded equally all across the country, so without getting into unnecessary details, the hydrological potential both for groundwater, lakes, wells and rivers is clearly a large one (Fig. 3) [8].

Renewable Energy Management Using Embedded Smart Systems

41

Fig. 2. Global horizontal irradiation map for Romania between 2010 and 2016 [7]

Fig. 3. Hydrographic map of Romania with 11 river basins equally distributed across the country [9]

42

V. Miron-Alexe et al.

In this respect, the paper represents an overview of a constructive solution of multiple off-grid renewable energy sources used in autonomous buildings. The main renewable energy source for an off-grid prosumer is represented by a photovoltaic system with solar panels and energy storage battery bank, while the second renewable energy source is represented by a pico hydroelectric installation corroborated with a water source that acts like an electrical energy backup for the previously mentioned system. By design, the hydrogeneration system is meant to be flexible and energy efficient because of the multiple sources from which it can draw the water and also because the water tower can further extend it’s use for irrigation, washing or fire extinguishing. The water can be also efficiently reused by returning it to the same source effortlessly by using only gravity.

2 Brief Concept Design of the Hybrid Renewable Energy System The pico hydro system generates under 5 kW of power and it is comprised of a large water tower mounted near the prosumer building or residence that can be refilled from different water sources such as a lake, a well or a pool, by using a high speed water pump (Fig. 4).

Fig. 4. Descriptive cross section diagram of the pico hydrogeneration system, water sources and photovoltaic system: (a) lake, (b) well, (c) pool, (d) water tower, (e) hydroelectric group (water pump, water valve, hydrogenerator), (f) photovoltaic system

3 Embedded Energy Management System Description and Implementation The working regime of the pico hydro system is dictated by a schedule programmed into the embedded microsystem. The embedded microsystem is actually composed of two advanced microcomputers, one is represented by a programmable microserver platform (master unit) for monitoring the energy consumption which is displayed

Renewable Energy Management Using Embedded Smart Systems

43

online and offline to the prosumer, while the other is represented by a programmable electronic platform (slave unit) which reads the electrical current, voltage and water level sensors, controls the relays of the hydrogeneration system for the electrovalve and the water pump and also the relays of some appliances with a large power consumption (Fig. 5).

Fig. 5. Embedded microsystems used in our application: (a) Arduino MEGA slave unit, (b) Arduino YUN master unit - the two microsystems communicate via I2C protocol to SDA/SCL and GND pins with 4.7 kX pull-up resistors to 5 VDC for digital data transfer stability

All the electronic system’s execution algorithm was thought by us in order to make the entire renewable hybrid system as energy efficient as possible, where all the energy produced is wisely valued. We have developed in our laboratory a customised embedded stack-on adaptation board for the Arduino MEGA to simplify the sensors and relays connections. The board contains different connectors, op-amp filters for the current sensor signal, voltage dividers for current/voltage sensor that require a DC offset of the signal, a dedicated DC-DC 3A/5 V switching power supply for the relays that draw up to 460 mA and digital I/O pins for I2C communication, relays control, water level sensors and solar charge controller (Fig. 6). The ADC of the slave unit is of 10 bits which means it can read analog values between 0 VDC to 5 VDC domain with a resolution between 0 to 1023 numerical values. Offsetting the signal to 2.5 VDC is required for both voltage and current sensors as Arduino cannot read the negative values of a signal. The voltage sensor is already configured with a built-in offset of 2.5 VDC. The reference voltage that ADC needs to convert the analog signal voltage values to numerical values is the same as the supply voltage of 5 VDC, thus for a precise power reading, the power supply of the two embedded microsystems has to be stable and well filtered [10]. The master unit is configured as a microserver that displays realtime data on a local HTML page with values about voltage, current and watts extracted from the csv file generated on a 16 GB microSD card. The unit is also able to send in realtime, data to a remote online server as ThingSpeak that can be accessed from anywhere on the internet. After the csv file reaches 50 KB it is erased from the system and a new one is generated in order to avoid the lagging of the system due to large processing files.

44

V. Miron-Alexe et al.

Fig. 6. Prototyped shield for Arduino MEGA microsystem: (a) I2C connector to the Arduino YUN, (b) external power supply connector for the DC-DC 3 A/5 V module, (c) current sensor jack, (d) LM358 op-amp for filtering and offsetting the current sensor signal, (e) voltage/current sensor connector with voltage divider for offsetting, (f) voltage sensor connector, (g) other analog sensors connectors, (h) external 5 VDC header and GND for relays, (i) I/O digital pins for water level sensors, (j) external DC-DC 3 A/5 V switching power supply for relays, (k) other I/O digital pins

The master unit also records the date of the realtime monitoring and is highly flexible from programmability and customizability point of view, not to mention that it uses the Internet of Things (IoT) feature that makes it a cheap and powerfull tool for automation and data management (Fig. 7) [11]. The system measures the instantaneous power consumption which can be expressed as the average power in rel. (1): Pavg ¼

Vm Im cos u ¼ Vrms Irms cos u 2

ð1Þ

where Vm and Im are the maximum instantaneous values of voltage and current, cos u is the power factor that is equal to 1 in our experimental case because we have used a resistive load as a home appliance. We can also mention that the inverter is comparable to a synchronous machine that always tries to correct the power factor to be near 1. The slave unit reads the power consumption of the household by the voltage and current sensor then it sends the data to the master unit for displaying and logging. The system reads the signal from the solar charge controller when solar irradiation is present, then it reads the water level from the water tower and refills it during the day

Renewable Energy Management Using Embedded Smart Systems

45

Fig. 7. Descriptive block diagram with the hardware and software components of the Arduino YUN master unit where it is plotted online (ThingSpeak) and offline (HTML page) the active power consumption of the prosumer household

by the water pump while charging the battery bank aswell. At night, the battery bank provides the power for medium and low consuming appliances, but if high consuming appliances are used (washing machine or resistive plate), the system releases the water from the tower by the electrovalve to generate an extra percent of electricity for 3 h as long as the referred appliance is used (Fig. 8). When the referred appliance is turned on at nighttime, a relay sends a digital command to the slave unit which further acts on the hydroelectric system to be turned on for power generation. During the day, if the water from the tower has not been already used on the previous night, the slave system switches from loading the water tower, using solar energy, to running the appliance (washing machine). Considering that the peak sun-hours on a sunny day are between 11AM and 1AM, a RTC (real time clock) module has been used to trigger the water tower filling or large consuming appliance operation.

46

V. Miron-Alexe et al.

Fig. 8. Descriptive block diagram of the Arduino MEGA slave unit and the I/O sensors with hardware components control where: (a) Arduino MEGA slave unit, (b) current and voltage sensors that read power consumption of the household, (c) prosumer household, (d) relays for controlling the appliances and the water pump/valve, (e) solar charge controller output, (f) water tower with water level sensors, (g) large consumer appliance, (h) electrovalve, (i) water pump

To calculate the electrical power production of the hydroelectric system we have used rel. (2): Pthe ¼ g  h  q  q  g

ð2Þ

where Pthe is the theoretical electrical power output of the hydroelectric system, g is the gravity acceleration of 9.81 m/s2, h is the height of the water tower of 15 m, q is the water density of 1000 kg/m3, q is the water flow of 0.01 m3/s, η is the system efficiency in converting mechanical power to electrical power of 90% if using a Pelton turbine with spear-jets [12]. The water tower has a total capacity of 110 kl, while the 2.21 kW high speed water pump is rated at about 601 L/min pumping speed, in result the water tower is fully filled in 3 h, with a total electrical energy consumption of 6.63 kWh. On the other hand, the hydroelectric generator outputs a constant power of 1.3 kW to the inverter AC input. The hydroelectric system can be used for 3 h, so in result it produces a total electrical energy of 3.9 kWh. To calculate daily energy generation curve of the photovoltaic system we have used rel. (3):

Renewable Energy Management Using Embedded Smart Systems

47

Zt24 Eday ¼

Pp ðsÞds ¼ t24
Pavgday

ð3Þ

0

where Eday is the total solar energy production per day, t24 is the time cycle of 24 h, Pp(s) is the power variation according to time during the day while Pavg-day is the average power for one day period. The photovoltaic system is fixed and positioned on the South side at 67° angle, is comprised of 18 polycrystalline solar panels, with a maximum of 250 W each, configured in series-parallel, with a nominal power output of 4500 W (Fig. 9). Also the maximum inverter output power is of 5 kW/230 VAC. The battery bank is comprised of 12 lead-acid gel units, configured in series-parallel, with a 660 Ah capacity and 48 VDC output.

Fig. 9. ICSTM off-grid solar panels with polycrystalline cells and 4500 W power output

A three members home power scenario was generated based on the experimental off-grid photovoltaic platform from our research institute (ICSTM) (Fig. 10). The electrical energy consuming habits of the family cannot be predicted, nor the weather forecast for solar radiation, thus, the energy schedule scenario is a hypothetical one regarding a whole sunny summer day where we acknowledge the electrical energy production and consumption of the off-grid prosumer household. The peak solar hours are between 11AM and 1PM where we have the largest electrical energy generation. In this respect, harvesting the solar energy at peak hours, to run the water pump that fills the water tower is the main priority. The second priority is to charge the battery bank which is done in parallel with the water tower. The third priority is to run a preprogrammed washing machine or another large consumer that doesn’t need supervision only if the water tower is filled. The plotted scenario is based on the statistics about the solar radiation during a clear summer day, the household electrical energy needs of a

48

V. Miron-Alexe et al.

Fig. 10. Plot representation scenario of the prosumer household power production during the day hours by the photovoltaic system (green), the power consumption during day hours from the water pump and during the night hours from appliances (red), the permanent appliances connected to the grid as standby appliances or other appliances that are always consuming (fridge)

family at certain hours and the hydroelectric system sized accordingly to backup a large household load in order to reduce the DOD (depth of discharge) of the battery bank to prolong the life cycle.

4 Conclusions Extended research is yet conducted in order to find the best configuration of a hybrid renewable energy system for off-grid usage. Our system has the paramount advantage that it can be configured in multiple ways in order to increase energy efficiency of a native energy system such as a photovoltaic installation. Another possible configuration would be in respect to the state of charge (SOC) or depth of discharge (DOD) of the battery storage system. Giving the fact that most solar battery banks require a maximum DOD of 30–40% to keep the lifecycle as high as possible, a passive hydroelectric generation system could increase the energy efficiency up to 40–50% of that given system when used. Many current off-grid photovoltaic systems use an AC backup generator on fossil fuels that generate a lot of disadvantages over time and require rised costs.

Renewable Energy Management Using Embedded Smart Systems

49

The compatibilization of multiple renewable energy sources can lead to the development of a more efficient autonomous insular power grids but it also represents a good alternative to the on-grid power distribution infrastructure that is becoming redundant as the global power requirements rise proportionally with the anthropisation. Acknowledgments. We hereby acknowledge the doctoral coordinator professor Nicolae Vasile, professor Nicolae Olariu and research scientist Iulian Băncuță for support.

References 1. IRENA report (2015). http://www.irena.org/DocumentDownloads/Publications/IRENA_ Off-grid_Renewable_Systems_WP_2015.pdf 2. Bloomberg report (2016). https://about.bnef.com/blog/off-grid-solar-market-trends-report2016/ 3. SEE4ALL report (2016). http://www.se4all.org/sites/default/files/GTF-2105-Full-Report.pdf 4. World Bank Group report (2016). https://www.energynet.co.uk/webfm_send/1690 5. The World Bank, Global Tracking Framework 2017 - Progress toward Sustainable Energy report (2017). http://gtf.esmap.org/data/files/download-documents/eegp17-01_gtf_full_report_ for_web_0516.pdf 6. Romania solar map and data. http://www.instalatii-solare.eu/index.php/instalatii/ 7. Romania Solar Radiation Map, Statistics (2016). http://energystreet.ro/ro/wp-content/uploads/ 2011/08/harta-solara.jpg 8. Romania hydrographic map and data. https://www.romaniadigitala.ro/jurnalul-hartii/jurnalarhiva/retea-hidrografica/ 9. Romania Hydrographic Map, Statistics (2005). https://www.romaniadigitala.ro/jurnalulhartii/jurnal-arhiva/retea-hidrografica/ 10. Reverter, F., Areny, R.P.: Direct Sensor-to-microcontroller Interface Circuits: Design and Characterisation. Google books (2005) 11. Badra, M.: Internet of Things and Smart Cities: Security, Privacy and New Technologies Preface. Amsterdam, Netherlands. Ad Hoc Networks, Elsevier Science, BV (2017) 12. Kougias, I., Szabo, S., Monforti-Ferrario, F., Huld, T., Bodis, K.: A methodology for optimization of the complementarity between small-hydropower plants and solar PV systems. Renew. Energy 87(2), 1023–1030 (2016). Pergamon-Elsevier Science Ltd.

The Role of Energy Management Systems in nZEB and nZEC Bogdan Burduhos(&), Anca Duta, and Macedon Moldovan Renewable Energy Systems and Recycling Research Center, Transilvania University of Brașov, Brașov, Romania [email protected] Abstract. In the near future, buildings will have to meet strict energy consumption standards in order to get as close as possible to the concept of nZEB (nearly Zero Energy Building), which means that buildings need to produce to a very large extent (10% for Romania) of their energy demand using renewable systems (RES) mounted on or near them. These standards can be met by at least three paths, simultaneously implemented: (a) reducing buildings losses, (b) designing renewable energy systems (RES) according to the constructive and architectural restrictions of the implementation location and (c) optimally managing the energy consumed by the building so that all available renewable sources are used at their maximum potential and only a minimum amount is consumed from conventional sources (fossil fuels). Implementing all described RES at building level (in order to meet nZEB standards) can raise real problems due to space or renewable source limitations. On the other hand, at district or even at city level the solutions for implementing all types of RES are more diverse and may support the local inhabitants to directly benefit from the advantages of nearly Zero Energy Communities (nZEC), if appropriate energy management systems (EMS) are used. The paper describes the basic principles of EMS focusing mainly on electrical energy, presents the renewable energy systems available in a newly established research community and proposes a management algorithm able to efficiently use the produced electrical energy considering local restrictions. Keywords: Energy management systems – EMS
Renewable energy systems – RES
Nearly Zero Energy Building – nZEB
Nearly Zero Energy Community – nZEC

1 Introduction The fact that the total human population on Earth is increasing corroborated with the increasing percentage of the people who will live in cities, estimated by the United Nations Population Fund at 70% until 2050, indicates that cities will play a major role in the future development of the human society [1]. The problem of cities is their reliance on external resources because the large numbers of people who are living in a relatively small and confined area [2]. This situation is, on a large time scale, neither sustainable nor economically feasible due to increasing problems linked to energy and fresh water supply, wastes and wastewater management, air pollution and resources depletion. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_4

The Role of Energy Management Systems in nZEB and nZEC

51

The major problem is the energy supply to the cities, which currently consume approx. 40% of the European energy demand [3], because currently the energy production is based mainly on fossil fuels. Their non-equally distribution and the limited amounts on Earth are a permanent source of tension (and wars) between the countries and civilizations. This is why the necessity appeared for developing and improving the build environment, targeting a reduced or even zero fossil fuel consumption. Several concepts where developed to support a step-by-step transition to the new situation: – LEB = Low Energy Building; the term indicates a building with an annual energy consumption of 60–80 kWh/m2, being very dependent on the climatic conditions of the implementation location [4]; – nZEB = nearly Zero Energy Building; the term defines according to the Energy Performance of Buildings Directive (EPBD) [3] buildings which include both measures for higher energy efficiency and a very large extent of the energy produced from renewable energy sources; – NZEB = Net Zero Energy Building; the term defines a new level of buildings which are able to cover their entire annual energy demand using renewable energy systems; – nZEC, NZEC refer to nearly/Net Zero Energy Communities and are the next step in transforming the present energy pattern of cities in a more sustainable one. Communities are an obvious necessary step forward because the implementation of renewable energy systems at building level is limited by spatial, constructive and architectural constrains. All these concepts and terms are interconnected with the concepts called Smart Building and Green Building but should not be confused since a smart or green building is not necessary also a nZEB and opposite. Smart building refers mainly to the ability of the building to respond to external and internal stimuli while a green building refers especially to the biodegradable, emission-free materials used and the fitting into the landscape of the building [5]. This paper indicates the solutions available for producing and monitoring renewable energy installed on, in and near one nZEB building of the Research Institute of the Transilvania University of Brasov, Romania and proposes a general block diagram of the energy flow together with an energy management algorithm for the electrical energy production and consumption, which aims at increasing cost efficiency and use of renewable energy in the particular implementation conditions. The identified solutions and the proposed algorithm can be used and eventually adapted to other locations with similar meteorological and energy policy conditions.

2 Energy Management Systems After all design and construction steps [6] were covered, needed for developing or improving buildings to reach the standards of the above presented concepts, the final step is the implementation of the energy management system (EMS) and the design of the management algorithm able to minimize the energy cost and the energy produced from fossil fuels.

52

B. Burduhos et al.

The general definition of an EMS is a system of computer-aided tools used by operators of electric utility grids to monitor, control, and optimize the performance of the generation and/or transmission system. In a more restrictive sense, related to the subject of this paper, EMS can be also defined as the tools used by individual buildings or communities to monitor, measure and control all types of electrical or thermal loads, like heating, ventilation and air conditioning (HVAC) units and lighting systems [7]. An EMS is actually a set of several control systems able to influence the functioning of different processes. As all control systems, for functioning it needs at least the five main components presented in Fig. 1: (1) a process with at least one input parameter which may influence/control that process, (2) sensors for communicating the state of the process to the controller, (3) a software/hardware controller which determines the needed actions in order to obtain the targeted result from the process, (4) an amplifier for powering an actuating element and (5) the active actuating element able to modify the process.

Fig. 1. The main components of a control system (adapted after [8])

Control systems, in general, can be of two types: open-loop or closed-loop (Fig. 2). The first type, although very simple and cost-effective, is unable to compensate the noises which may add to the command signal of the controller (noise 1) or to the output signal of the process (noise 2). The closed-loop control type eliminates the mentioned disadvantages and is therefore the most used solution in practice and also in the case of EMS where rapid changes of inputs and disturbances may appear on all communication lines, [8].

Fig. 2. Block diagram of control systems with: (a) open loop, (b) closed loop (adapted after [8])

The Role of Energy Management Systems in nZEB and nZEC

53

The trend in implementing the nZEB concept is to create combined cooling heating and power (CCHP) micro-grids based on renewable energy systems and conventional energy systems, connected to the main grid [9, 10] and controlled by EMS for assuring a high percentage of renewable thermal/electrical energy and cost efficient solutions according to local energy policies and other specific constrains (Fig. 3). From the electrical point of view, micro-grids can be considered the Low-Voltage and MediumVoltage networks below the transformer points [6].

Fig. 3. Energy management of a micro-grid (adapted after [9])

Due to the requirements for high energy efficiency and the use of the energy from renewable sources in large extents, nZEBs or communities based on buildings with nZEB status need to be powered using hybrid energy systems, of renewable and traditional fossil-fuel energy systems. In order to ensure a buildings functioning (heating, lighting, water supply, wastewater treatment, operation of various electrical and electronic equipment, including RES) two energy types are basically required: electrical and thermal energy (Fig. 4), with correspondent storage facilities. Suppling renewable electrical energy can be done using photovoltaic (PV) modules, wind or hydro turbines, while thermal energy can be obtained from solar thermal (ST) collectors, geothermal heat pumps or biomass combustion boilers [6]. Supplying traditional energy can be done using Diesel, petroleum or natural gas combustion generators or connecting the building/community to the centralized electrical grid or gas network. In order to function according to the specific needs of the beneficiary, all energy production systems and consumers/loads (Fig. 5) need to be optimally managed by an EMS [11], whose control architecture (Fig. 6) may be, from the hardware point of view, centralized or distributed or combined (centralized and distributed) [12, 15]. Depending on the control type, the EMS may use a single controller for all processes or several controllers (one for each process) either equally ranked or having one master and the others being slave controllers.

54

B. Burduhos et al.

Fig. 4. Renewable energy systems types installable at nZEB or nZEC level (adapted after [6])

Fig. 5. Diagram with optimal energy flow obtainable using EMS (adapted from [11, 12])

The physical connections which allow the communication between the control system and all the other components of the building can be done using cables with different communication protocols (e.g. RS485, Modbus) or wireless communication protocols like Zigbee etc.

The Role of Energy Management Systems in nZEB and nZEC

55

Fig. 6. Energy management control architectures: (a) centralized, (b) distributed and (c) combined

EMS are mainly based on SCADA (Supervisory Control and Data Acquisition) systems with different complexity degree, were all information generated by the sensors is received, analyzed, stored and used for decision making [12]. From the software point of view, an EMS can be controlled using different algorithm strategies which depend on the complexity and type of the energy producers and consumers and on the needs of the end-user. Two main strategies are currently described in literature [12]: strategies based on linear programming which assume a step-by-step input analysis and decision making and strategies based on artificial intelligence (e.g. Fuzzy logic, artificial neural networks, genetic algorithms). Their role is to control the flow of energy among the components of the building or inside the community (energy sources, storage devices, and loads) and to reach at least one of the following objectives: (1) high level of system reliability and decreased time percentage of electricity interruptions, (2) high operational efficiency, (3) reduced cost of the generated energy, (4) increased lifetime of the components. The optimal strategy depends very much on the configuration of the building and the energy producers/ consumers [12].

56

B. Burduhos et al.

According to literature [9, 11, 13, 14] a general diagram which can insure the controlled production, consumption and monitoring of the electrical energy in an nZEB or nZEC is presented in Fig. 7. It includes both the AC/DC power lines (marked with continuous lines), needed for transferring the electrical power to consumers and the communication lines (marked with dotted lines) needed for sending control signals to individual components and receiving information about their functioning.

Fig. 7. General block diagram of the electrical power flow in a system containing conventional/renewable producers and DC/AC loads (adapted using [9, 11, 13, 14])

The idea behind the electrical energy management is to use two different power buses for DC and AC energy and to convert the energy from one type to the other only when the DC/AC electrical loads require it.

The Role of Energy Management Systems in nZEB and nZEC

57

3 Aspects in Implementing EMS in nZEB and nZEC Although the targets of nZEB, and correspondingly of nZEC, are well defined in the EPBD for all European geographical areas [16], the solutions and possibilities for achieving these targets very much depend on objective and subjective limitations of the location and of the residents which will be using the infrastructure [17]. The main limitations refer to the availability of local renewable sources and the physical space for implementing renewable systems. This is why the use of renewable energy systems needs to be optimized in order to diminish/eliminate traditional fuels and, at the same time to decrease the energy costs. This requires dedicated solutions for using the whole available renewable energy which includes the use of EMS, storage devices and measures for grid compatibility. The main aspects which should be considered when designing and implementing EMS in buildings and communities with low energy status result from the analysis of Fig. 3. 3.1

Estimating the Energy Demand

The energy demand pattern of a building/community is one of the most important parameters for the implementation of EMS into nZEBs and can be estimated based on the building types, local climate and residents’ habits. Along with the electrical and thermal energy estimation, the processes for fresh- and wastewater treatment and those of the community waste management need to be considered. 3.2

Estimating the Potential of the Renewable Energy Sources

To get the lowest cost for the renewable energy share specific to an nZEB, the renewable energy potential has to be accurately estimated. Five types of renewable sources can be mainly used in nZEBs, according to their availability in the implementation location: – Solar energy; the direct and diffuse irradiances, can be roughly estimated based on mathematical models, irradiance maps or prediction software tools; – Wind energy can be estimated using similar methods; – Hydro energy of possible nearby flowing rivers can be estimated using measurements from hydrological services; – Geothermal energy can be estimated based on the soil structure and underground waters; – Biomass energy can be estimated considering the forest/agricultural potential, the amount of waste and wastewater sludge, etc. Additionally, the aspects regarding transportation and storage have to be considered. Due to their daily/seasonal and annual variations, for obtaining best estimations of the solar, wind and hydro potential, local measurements for at least one full year should be considered.

58

3.3

B. Burduhos et al.

Identifying the Solutions for Energy Production and Storage

Based on the estimated renewable energy potential, correspondent systems should be available at the nZEB site. Implementing EMS for managing the systems should consider the functioning characteristics, limitations and weak points of the systems in order to minimize maintenance interventions. For stability reasons, due to the uncertain output of renewable energy systems, storage solutions should also be considered and applied to nZEC communities [18, 19] based on batteries [20], hydrogen, compressed air [21] or pumped water into reservoirs. 3.4

Identifying the Solutions for Energy Distribution

Implementing EMS should consider that thermal energy is recommended to be distributed in decentralized networks thus minimizing the transport losses. For distributing electrical energy the use of a regional/local centralized network is recommended which minimizes the costs of battery storage during high production periods of renewable energy. These networks, mounted generally after the power transformation points, include both generators and consumers and can be considered independent micro-grids [22] receiving energy from the grid only when needed [23–25]. Micro-grids require special protection solutions including relays with embedded signal processing techniques and two-way communication [26]. 3.5

Identifying the Objectives of the Systems Operation

The optimal combination of energy produced from different sources is completely dependent on the energy management system, whose main aim is to convert all the available renewable potential into useful forms of energy, when needed. Depending on the type of system (off-grid or grid-connected) and the financial perspectives for the produced energy, the action lines of an EMS may differ in an nZEB. For example, in case of an off-grid system, the EMS needs to firstly insure that all useful consumers are started when energy is produced; in this way only the extra energy has to be stored and the storage capacity of a specific location can be minimized. On the other hand, for a grid-connected system, where under most circumstance the produced renewable energy injected into the grid has a higher financial value than the energy taken from the grid, it is important to deliver as much as possible energy to the grid an consume energy from the grid during intervals with minimal prices. In both cases, the location where the EMS is implemented would need to have consumers able to be remotely switched on/off. This premise can be obtained using either a local wired/wireless network or, more easily, using the newly emerging Internet of Things concept which would allow the monitoring and control of devices based on an IP (Internet Protocol) address [27]. 3.6

Developing the Monitoring and Energy Management Systems

When all these aspects are known, the final step is the implementation of the EMS, including both hardware (controller, actuating devices and communication devices) and software (management algorithm) components.

The Role of Energy Management Systems in nZEB and nZEC

59

Energy management systems and correspondent algorithms are currently intensively studied since the needed equipment and approach varies very much with the aim of the installation. As an example, algorithms for managing and distributing power between various system components of off-line renewable-energy-based desalination and water pumps are analyzed [28, 29]. Even more studies are related to optimal algorithms and strategies for managing energy produced from renewable systems in micro-grids [12, 30–32], which mainly use dispatchable and non-dispatchable power sources and different order DC/AC power loads [33].

4 Case Study - R&D Institute of the Transilvania University of Brasov In order to adopt and eventually implement the two concepts of nZEB and nZEC at larger scales, examples with positive results are important. An example, of a sustainable community, is the Research and Development Institute of the Transilvania University in Brașov, Romania (ICDT), located in a mountain region of the temperate climate. Except the utilitarian aspects, which were at the base of its design, the Institute was developed considering complementary aspects specific to nZECs, allowing research and improvements in the competence fields of the academic community. 4.1

Estimating the Energy Demand

The Institute (Fig. 8) consists of 12 interconnected buildings with 3 levels (basement, ground and first floor) having each of them an overall surface of 1350 m2. All 12

Fig. 8. Plan of the R&D Institute with installed solar-thermal collectors (STC), photovoltaic platforms and string (PV), small wind turbines (WT), ground coupled heat pumps (HP)

60

B. Burduhos et al.

buildings contain offices, laboratories and dependences allowing all R&D Centers of the university to operate their research activities. The average yearly energy demands were identified without considering the energy consumption of the research equipment at: thermal energy 66.69 kWh/m2/year and total electric energy 10.02 kWh/m2/year [34, 35], indicating the LEB status of the Institute. The energy consumption pattern is specific to an office building with most energy consumed during the working time of a day (8:00–16:00). 4.2

Estimating the Potential of the Renewable Energy Sources

The solar energy potential was estimated using four sources: (1) irradiance measurements from the Brașov town, approx. 7 km away, obtained in the city location of the Renewable Energy Systems and Recycling Research Center using a Delta-T DLe2 weather station with SPN1 pyranometer, (2) irradiance maps based on satellite and interpolated measured data (Fig. 9a), (3) specific estimation software (Meteonorm, Fig. 9b) and (4) prediction models based on Meliss algorithm (Fig. 10) [36, 37]. All indicated an annual value of approx. 1200 kWh/m2/year.

Fig. 9. (a) Solar irradiance map of Romania on horizontal surface [38] and (b) User interface of Meteonorm 6.1 estimation software

When research equipment was installed, the estimated solar irradiance potential could be verified using two different devices: a Delta-T DLe2 automatic weather station (Fig. 11a) and a Kipp&Zonen Solys2 solar tracker (Fig. 11b) for monitoring the direct, diffuse and global components of the solar irradiance. Wind potential in the Institute area was identified using the same DLe2 weather station (Fig. 11a) and three ADCON data loggers which indicated very low wind speeds, of approx. 2.5 m/s during almost 75% of the time. Hydrological potential is not available in the area because there are no flowing rivers in the Institute neighborhood.

The Role of Energy Management Systems in nZEB and nZEC

61

Fig. 10. Solar irradiance estimated during summer solstice using Meliss mathematical model [39]

Fig. 11. Systems for estimating the renewable energy potential: (a) Delta-T weather station, (b) Kipp&Zonen Soly2 equipment

The geo-thermal potential was addressed by using in some of the Institute’s buildings heat pumps with vertical and horizontal collectors installed in the vicinity of the buildings. Their functioning is under analysis and will establish the amount of thermal energy able to be provided. 4.3

Identifying the Solutions for Energy Production and Storage

The building which hosts the Renewable Energy Systems and Recycling R&D Centre has the main types of renewable energy systems installed and monitored. The electrical energy is generated using photovoltaic modules (Figs. 12a and 13a) and small wind turbines. It is injected into the national electricity grid used for backup during no-production times and for storage/distribution to other buildings during times of high production.

62

B. Burduhos et al.

Different types of photovoltaic modules are used, made of different flexible or rigid materials (mono-Si, poly-Si, CIS, CIGS, CdTe etc.), installed fixed optimally-tilted, fixed horizontal, or single-axis or dual-axis tracked. The photovoltaic system was developed allowing individual module monitoring (Figs. 12b and 13b), allowing to perform wide research on the implementation and behavior of different solutions [40].

Fig. 12. (a) Rooftop installed PV systems with mono-, poly-crystalline and amorphous/flexible Silicon, fixed and tracked PV modules with a total installed power of 5 kWp, (b) SolarEdge interface for individually monitoring PV modules

For example, the comparative analysis between the annual energy produced by dual-axis and non-tracked (fixed) photovoltaic platforms (Fig. 14a) indicate that tracked solutions could produce under similar conditions with approx. 32% more electrical energy compared to the fixed ones. Furthermore, the annual comparative analysis of the energy produced by mono-Si, poly-Si, CIS, CIGS and CdTe photovoltaic modules installed on the same surface (Fig. 14b) indicate the poly-Si modules as the best solution for conditions similar to the temperate climate of Brașov, Romania with roughly 30% more energy produced compared to their CdTe counterparts.

The Role of Energy Management Systems in nZEB and nZEC

63

Fig. 13. (a) Tracked platforms installed near the institute (five platforms with mono- and poly-crystalline silicon, CIS, CIGS and CdTe PV modules, total installed power 9.5 kWp and (b) SolarEdge interface for individually monitoring the PV modules on the platforms

(a)

(b)

400 350

40 35 Eenrgy [kWh]

Energy [kWh]

300 250 200 150 100 fixed PV plaƞorm

50

30 25 20

poly-Si mono-Si CIGS CdTe CIS

15 10

dual-axis PV plaƞorm

5

0

0 1

2

3

4

5

6 7 Month

8

9

10

11

12

1

2

3

4

5

6 7 Month

8

9

10

11

12

Fig. 14. Annual energy produced by: (a) two 1.75 kWp PV platforms with/without dual-axis tracking and (b) different types of PV modules installed in the same plane

The PV installations summarizing 15 kWp roughly produce 17 MWh/year covering the entire annual energy of approx. 13 MWh/year needed for the functioning of one building. The wind turbines used are of horizontal type (HWAT), with low cut-in wind speeds and are installed in groups of 3 (300 Wp and 600 Wp) on different buildings of the Institute, assuring the lighting of the building’s surroundings with 100 W lamps based on LED technology. Thermal energy needed for heating/cooling the building is achieved using a heat pump, together with a natural gas boiler used as a backup source during peak cold days of the winter season. For cooling the building during hot summer days an adsorption

64

B. Burduhos et al.

chiller is used, powered with the energy produced by solar concentrating collectors. The domestic hot water (DHW) is produced in each building of the Institute using flat-plate or vacuum-tube solar thermal collectors installed at different angles, allowing a comparative analysis of their output. Moldovan et al. demonstrated in [34] that building L7 is able to cover 85% of its energy demand using the renewable energy systems mentioned above.

4.4

Identifying the Solutions for Energy Distribution

The Institute was constructed on an empty area near the city of Brașov, approx. 2 km away from the first city residences. Therefore it was developed as a separate community with all utilities separated from the rest of the town: – It has its own centralized distribution point for electrical energy from the national grid; the micro-grid created in this way allows the local consumption of the renewable energy produced by photovoltaic modules and wind turbines (Fig. 15);

PV tracking system

PV modules

Wind turbines

DC/AC Inverter

AC/AC converter

Connection to next building

Voltage transformation point AC electrical microgrid

Pumps for thermal equipment

Lighting

other electrical loads

Solar thermal collectors

Domestic hot water network

Geothermal Heat Exchanger

Heat pump

Gas boiler

Solar thermal concentrator

Chiller

Space heating / cooling network

One nZEB building

Fig. 15. General block diagram of the electrical and thermal energy flow in one nZEB building of the ICDT, which hosts the renewable energy systems and recycling center

The Role of Energy Management Systems in nZEB and nZEC

65

– Thermal energy is produced decentralized, in each building, using heat pumps with vertical and horizontal collectors and solar thermal collectors compensated during peak intervals with conventional natural gas condensing boilers (Fig. 15); – The fresh water, which is at the same time drinkable, is centralized extracted for the whole Institute from a depth of 132 m using a 2.2 kW electrical pump; – The wastewater generated by the whole Institute is centralized treated using a 6 kW biological plant and afterwards distributed on a large land surface in order the regenerate the thermal potential of the ground. 4.5

Identifying the Objectives of the Systems Operation

The energy management system (EMS) of the Institute and respectively of each individual building are currently under design and tune-up according to the results currently obtained from the renewable energy systems presented above. The EMS has to manage the injection of the electrical renewable energy produced into the grid in a most cost-efficient way. The consumed electrical energy is not subject of the management since it is consumed from the grid when needed and measured using a double-sense energy-meter. Renewable energy production is subsidized in Romania using green certificates whose value may vary between 120…200 Euro/MWh according to the certificate market conditions. Romanian legal frame on the electrical energy injection into the grid asks the producers to give an accurate estimation of the energy (Eest, Fig. 17) that will be injected the next day into the grid. If extra energy is injected there are no financial benefits, while in case less energy is injected the producer will be penalized. This is why injecting exactly the estimated amount of energy is of crucial importance for maximizing profit. Excepting the priority the EMS has to give to the different systems which produce renewable energy, it has also the role to insure optimal working conditions for the research community, with minimal energy consumption, considering both indoor and outdoor parameters. 4.6

Developing the Monitoring and Energy Management Systems

The monitoring system implemented in the R&D Institute allows the analysis of the following information: – The meteorological (external ambient) parameters of the area where the Institute is located using the devices already mentioned above; – The online electrical energy consumed at institute/building/floor level using the graphical interface presented in Fig. 16; – The level of occupancy for each building obtained from the control access system, which is important in determining the heating/cooling and fresh air demand according to the number of researchers which are in the building; – The number of free parking places and the activities around the Institute using the parking control access system and the video surveillance system.

66

B. Burduhos et al.

Fig. 16. Software interface used for monitoring the online consumption of electrical energy

Since the EMS of the buildings in the Institute is still under development a simplified algorithm is further proposed in Fig. 17, able to maximize the financial profit, considering the Romanian conditions for the injection of electrical energy into the grid, as previously discussed. Best financial results can be obtained using this algorithm if the Institute enrolls as a renewable energy producer and is able to obtain green certificates, which add extra value to the renewable energy produced. START

day = 0

PRES > 0

NO

YES

day = 1 NO

day = 1 YES NO

ERES < Eest. YES

STORE in Battery

ERES < Eest.

YES

INJECT from RES to Grid

NO

day = 0

INJECT from BATTERY to Grid

Fig. 17. Energy management algorithm for maximizing financial profit in Romania, 2017

The Role of Energy Management Systems in nZEB and nZEC

67

Eest. represents the estimated energy to be produced by a renewable installation during the day, while the parameter day is used for indicating if the estimated energy has been already produced during the present day on not. Also, preliminary monitoring data outline that adding a battery bank to the infrastructure is needed, with at least 7.5 kWh capacity (the equivalent of half-hour production of the 15 kWp PV installation), similar to [41].

5 Conclusions The implementation on a large scale of the nearly Zero Energy concept on buildings and communities largely depends on its acceptance at regional and national level, which is influenced by the payback time of the extra funds invested to achieve this status. The payback time can be minimized if optimal energy management systems are used, which have to consider the six aspects presented in this paper: local energy demand pattern, the available renewable sources potential, the characteristics of the installed renewable energy systems, local renewable energy policies, regulations and energy distribution limitations. A good example of a community developed to achieve the nZEC status is the research laboratory of the Renewable Energy Systems and Recycling R&D Centre located in the Research & Development Institute of the Transilvania University Brasov. For this building a general block diagram of the energy flow and an energy management algorithm is proposed in this paper which would allow not only the production of the maximal renewable energy but also financial benefits for the community in the particular implementation conditions. The identified solutions are useful for other locations with similar meteorological and energy policy conditions. Acknowledgments. This work was done in the frame of the project EMAX-BIPV, PNII-RUTE-2014-4-1763, contract no. 131/1.10.2015, financed by the Romanian National Research Council (ANCS, CNDI-UEFISCDI), within the Romanian Research Program: Human Resources - Research Projects for Young Research Teams, RU-TE-2014 Subprogram. The structural funds project PRO-DD (ID123, SMIS 2637, ctr. No. 11/2009) is gratefully acknowledged for providing the infrastructure mentioned in the paper.

References 1. UN, United Nations: World Urbanization Prospects: The 2007 Revision Population Database (2008). http://esa.un.org/unup. Accessed May 2017 2. Albino, V., Berardi, U., Dangelico, R.M.: Smart cities: definitions, dimensions, performance and initiatives. J. Urban Technol. 22(1), 3–21 (2015) 3. *** The directive 2010/31/EU of the European parliament and of the council of 19 May 2010 on the energy performance of buildings. Off. J. Eur. Union 53 (2010). http://eur-lex. europa.eu/legal-content/en/TXT/?uri=CELEX:32010L0031

68

B. Burduhos et al.

4. Ramesh, T., Prakash, R., Shukla, K.K.: Life cycle energy analysis of buildings: an overview. Energy Build. 42, 1592–1600 (2010) 5. http://fmlink.info/article.cgi?type=Sustainability&title=Smart%20Buildings%20versus% 20Green%20Buildings%3A%20Unfortunately%2C%20they%20are%20Talking%20Different %20Languages&pub=Linnean%20Solutions&id=44225&mode=source. Accessed May 2017 6. Visa, I., Burduhos, B.G, Duta, A.: The role of renewable energy systems in smart cities. In: Proceedings of XI-th Conference ASTR Academic Days, “Smart city”, Tîrgu Mures (2016) 7. http://blog.lnsresearch.com/bid/164624/A-Guide-to-Understanding-Energy-ManagementSystems. Accessed May 2017 8. Ogata, K.: Modern Control Engineering, 5th edn. Prentice Hall, Englewood Cliffs (2010) 9. Gu, W., Wu, Z., Bo, R., Liu, W., Zhou, G., Chen, W., Wu, Z.: Modeling, planning and optimal energy management of combined cooling, heating and power microgrid: a review. Int. J. Electr. Power Energy Syst. 54, 26–37 (2014) 10. Meng, L., Sanseverino, E.R., Luna, A., Dragicevic, T., Vasquez, J.C., Guerrero, J.M.: Microgrid supervisory controllers and energy management systems: a literature review. Renew. Sustain. Energy Rev. 60, 1263–1273 (2016) 11. Chauhan, A., Saini, R.P.: A review on Integrated Renewable Energy System based power generation for stand-alone applications: configurations, storage options, sizing methodologies and control. Renew. Sustain. Energy Rev. 38, 99–120 (2014) 12. Olatomiwa, L., Mekhilef, S., Ismail, M.S., Moghavvemi, M.: Energy management strategies in hybrid renewable energy systems: a review. Renew. Sustain. Energy Rev. 62, 821–835 (2016) 13. Krishna, K.S., Kumar, K.S.: A review on hybrid renewable energy systems. Renew. Sustain. Energy Rev. 52, 907–916 (2015) 14. Bajpai, P., Dash, V.: Hybrid renewable energy systems for power generation in stand-alone applications: a review. Renew. Sustain. Energy Rev. 16, 2926–2939 (2012) 15. Adil, A.M., Ko, Y.: Socio-technical evolution of Decentralized Energy Systems: a critical review and implications for urban planning and policy. Renew. Sustain. Energy Rev. 57, 1025–1037 (2016) 16. https://ec.europa.eu/energy/en/topics/technology-and-innovation/strategic-energy-technologyplan. Accessed May 2017 17. Shum, K.L.: Renewable energy deployment policy: a transition management perspective. Renew. Sustain. Energy Rev. 73, 1380–1388 (2017) 18. Parra, D., Stuart, A., Norman, Gavin S., Walker, M.G.: Optimum community energy storage for renewable energy and demand load management. Appl. Energy 200, 358–369 (2017) 19. Hemmati, R., Saboori, H., Jirdehi, M.A.: Stochastic planning and scheduling of energy storage systems for congestion management in electric power systems including renewable energy resources. Energy (2017, accepted manuscript) 20. Zhang, X., Yuan, Y., Hua, L., Cao, Y., Qian, K.: On generation schedule tracking of wind farms with battery energy storage systems. IEEE Trans. Sustain. Energy 8(1), 341–353 (2017) 21. Mohammadi, A., Ahmadi, M.H., Bidi, M., Joda, F., Valero, A., Uson, S.: Exergy analysis of a Combined Cooling, Heating and Power system integrated with wind turbine and compressed air energy storage system. Energy Convers. Manag. 131, 69–78 (2017) 22. Bendatob, I., Bonfiglioa, A., Brignonea, M., Delfinoa, F., Pampararoa, F., Procopioa, R.: Definition and on-field validation of a microgrid energy management system to manage load and renewables uncertainties and system operator requirements. Electr. Power Syst. Res. 146, 349–361 (2017)

The Role of Energy Management Systems in nZEB and nZEC

69

23. Muruganantham, B., Gnanadassa, R., Padhy, N.P.: Challenges with renewable energy sources and storage in practical distribution systems. Renew. Sustain. Energy Rev. 73, 125– 134 (2017) 24. Wang, Z., Chen, B., Wang, J., Begovic, M.M., Chen, C.: Coordinated energy management of networked microgrids in distribution systems. IEEE Trans. Smart Grid 6(1), 45–53 (2015) 25. Sandström, A., Söderholm, P.: Network management and renewable energy development: an analytical framework with empirical illustrations. Energy Res. Soc. Sci. 23, 199–210 (2017) 26. Casagrande, E., Woon, W.L., Zeineldin, H.H., Svetinovic, D.: A differential sequence component protection scheme for microgrids with inverter-based distributed generators. IEEE Trans. Smart Grid 5(1), 29–37 (2014) 27. Mazhar, R., Awais, A., Anand, P., Seungmin, R.: Urban planning and building smart cities based on the Internet of Things using Big Data analytics. Comput. Netw. 101, 63–80 (2016) 28. Smaoui, M., Krichen, L.: Control, energy management and performance evaluation of desalination unit based renewable energies using a graphical user interface. Energy 114, 1187–1206 (2016) 29. Ouachania, I., Rabhib, A., Yahyaouic, I., Tidhaf, B., Tadeo, T.F.: Renewable energy management algorithm for a water pumping system. In: 8th International Conference on Sustainability in Energy and Buildings, Turin, Italy (2016) 30. Kotur, D., Durisic, Z.: Optimal spatial and temporal demand side management in a power system comprising renewable energy sources. Renew. Energy 108, 533–547 (2017) 31. Naz, M.N., Mushtaq, M.I., Naeem, M., Iqbal, M., Altaf, M.W., Haneef, M.: Multicriteria decision making for resource management in renewable energy assisted microgrids. Renew. Sustain. Energy Rev. 71, 323–341 (2017) 32. Rahima, S., Javaida, N., Ahmada, A., Khana, S.A., Khanb, Z.A., Alrajehc, N., Qasimd, U.: Exploiting heuristic algorithms to efficiently utilize energy management controllers with renewable energy sources. Energy Build. 129, 452–470 (2016) 33. Ye, B., Zhang, K., Jiang, J.J., Miao, L., Li, J.: Towards a 90% renewable energy future: a case study of an island in the South China Sea. Energy Convers. Manag. 142, 28–41 (2017) 34. Moldovan, M.D., Visa, I., Neagoe, M., Burduhos, B.G.: Solar heating and cooling energy mixes to transform low energy buildings in nearly zero energy buildings. Energy Procedia 48, 924–937 (2014) 35. Visa, I., Moldovan, M.D., Comsit, M., Duta, A.: Improving the renewable energy mix in a building toward the nearly zero energy status. Energy Build. 68, 72–78 (2014). doi:10.1016/ j.enbuild.2013.09.023 36. Meliss, M.: Regenerative Energiequellen - Praktikum. Springer, Berlin/Heidelberg (1997) 37. Burduhos, B.G., Visa, I., Neagoe, M., Badea, M.: Modeling and optimization of the global solar irradiance collecting efficiency. Int. J. Green Energy 12(7), 743–755 (2015). doi:10. 1080/15435075.2014.884499 38. http://re.jrc.ec.europa.eu/pvgis. Accessed May 2017 39. Visa, I., Jaliu, C.I., Duta, A., Neagoe M., Comsit, M., Moldovan, M.D., Ciobanu, D., Burduhos, B.G., Saulescu, R.G.: The Role of Mechanisms in Sustainable Energy Systems. Ed. Universității Transilvania din Brașov (2015). ISBN 978-606-19-0571-3 40. Visa, I., Burduhos, B.G., Neagoe, M., Moldovan, M.D., Duta, A.: Comparative analysis of the infield response of five types of photovoltaic modules. Renew. Energy 95, 178–190 (2016) 41. http://www.renewableenergyworld.com/articles/2017/05/hybrid-wind-storage-project-startsup-in-spain.html. Accessed May 2017

EfDeN Prototype - A Sustainable and Low Energy Consumption House Presented at Solar Decathlon 2014 Tiberiu Catalina1(&), Mihai Baiceanu2, Eduard-Daniel Raducanu2, Mihai Toader Pasti2, and Claudiu Butacu2 1

2

Faculty of Building Services, Technical University of Civil Engineering, Bucharest Romania, Bucharest, Romania [email protected] Solar Decathlon Association Bucharest-EFdeN Project, Bucharest, Romania

Abstract. Within this article is presented a prototype house called EFDEN which is a research and educational project that represented Romania at Solar Decathlon Europe 2014 in Versailles France. The constructed solar house was built as a Positive Energy Building implementing multiple passive (phase change materials, greenhouse, solar shadings, heat recovery) and active (air-water heat pump for heating, cooling and hot water; vacuum tube collectors - for hot water and heating; cold water tank; heating water tank; hot water tank; heating/cooling coil; radiant panels-radiant heating and cooling in ceiling and walls; heat recovery unit - maximum efficiency above 90% for the fresh air treatment; BMS automation system, PV array for electric energy production) energy efficient strategies. The building total habitable surface is of 115 m2 and the total heated/cooled volume is 400 m3. Since 2014 the house was monitored in terms of the indoor climate parameters and energy consumption. It was found that indoor air quality is great with low values of CO2 (250 kg/m2. The variety of plants used is very large, it is possible to associate trees, shrubs and suburbs, annual and perennial flowers, garden furniture (benches, pergolas, luminaires, towers, pools), alleys of different materials, but always taking into account the concept, the design and the budget. It is a system generally used on roofs of the buildings with a high structural capacity and minimum slopes. Ideal for public access - they are real suspended gardens; thus traditional garden are practically relocated to the height with the help of structural engineers. It requires irrigation and regular maintenance. A world-famous example is the Roof Garden Rockefeller Center, New York on Fifth Avenue (Fig. 3).

Fig. 3. View of Roof Garden Rockefeller Center [12]

(b) The semi-extensive green roofs are an intermediate type between the extensive and the intensive systems. It is a type of green vegetated roof with small and medium sized plants (perennials, succulent plants, herbs of different heights). The substrate is intermediate to the two systems (intensive and extensive), more than 15 cm thick and can reach up to several tens of centimeters. It can be equipped with various flora, alleys, garden furniture, where people have the opportunity to rest, (Fig. 4) to relax, socialize and, to walk around. (c) The right system for our proposal is the extensive green roof. It is characterized by a low soil layer (2.5–15 cm), low weight (60–250 kg/m2), with minimal care needs, it does not require a great effort for plant growth and development. The system is recommended for plants that adapt easily to harsh conditions such as drought or strong winds. The recommended plants are the small ones such as succulents, sedums and crabs, grasses (decorative herbs) in general, foliage plants

Solutions to Reduce Energy Consumption in Buildings

183

Fig. 4. View of semi-extensive green roof [13]

(a)

(b)

(c)

(d)

Fig. 5. View of the extensive green roof: (a) protective geotextile layer, (b) land prepared for planting, (c) and (d) after planting [15]

of different colors, shapes, textures or mosses. Usually, their height does not exceed 20 cm, they are unpretentious and grow quickly. This type is the easiest to adopt in the case of building rehabilitation due to the thickness of the soil layer and the type of vegetation recommended [7, 8, 10, 11]. In this view, concrete examples have also been noticed in Romania, through projects belonging to the “Art of the Garden [14] “ team. Two of these implemented projects give a touch of elegance to the buildings where installed and a positive example at national level. A first project described The preparation of the extensive green roof on an area of about 400 sqm (Fig. 5) and benefited from waterproofing, drainage, soil substrates (a special mixture of up to 10–15 cm that does not make the structure too difficult), the installation of the drip irrigation system with the takeover of the meteoric water from a special basin arranged and, finally, from the effective planting with succulent plants and small grasses. The execution of this work lasted about 3 weeks, and the positive results were not delayed. Beneficiaries were delighted from the decorative (or aesthetic) point of view,

184

I. Nicolae and S. Petra

(a)

(b)

(c)

(d)

Fig. 6. View of extensive green roof: (a) installing the irrigation system, (b) and (c) waterproofing and antiriot membranes, (d) preparing the vegetal substrate [17]

and the advantages of applying this system were obvious: cooling inside the building during the summer, minimizing or avoiding the use of the air conditioner, lower energy bills, up to 25% both in summer and winter when the vegetation layer acts as insulator and prevents heat loss. Another interesting and unique project in Romania is designed and implemented in the village of Berca, Buzau County, within a mini-complex of 5 houses and a restaurant on which roof there is an area of 320 m2 of green space arranged [16]. The complex is called Cob Village, the houses are made of cob (mixture of clay, sand, straw and grass, which, manually modeled. The green roof project (Fig. 6) falls into the category of semi-intensive roofs because the designer played with the depth of the substrate, which in some cases exceeds 15 cm in the suspended garden ensemble, has embedded flower boxes and decorative elements with a modular structure, where the elegance and refinement of the materials used stand out not to break the monotony of the landscape, but to create diversity and continuity of the local landscape. Also, structure calculations have been made, to know how many layers of insulating and waterproofing material are needed, as well as calculations of installations for the irrigation system. With patience, the results have not been awaiting and the peak of the setup has created a perfectly integrated ecosystem in the area. In its realization, the idea of approaching nature was pursued (Fig. 7). At the establishment of the assortment, the plants belonging to the botanical family Crassulaceae, the so-called succulent plants, Sedum species were chosen, of various textures, shapes, colors and flowers - characteristic elements that reproduce the image of a perfect, naturally living picture (Fig. 8). Factors influencing the performance of these living green roof systems are ambient temperature, humidity, exposure, solar radiations, light, wind speed, limited nutrient supply, poor/low humidity due to reduced substrate.

Solutions to Reduce Energy Consumption in Buildings

(a)

(b)

(c)

(d)

185

Fig. 7. View of extensive green roof: (a) image processed, (b) and (c) images from execution, (d) picture after planting [18]

(a)

(b)

(c)

(d)

Fig. 8. View of extensive green roof: (a)–(c) details plants of sedum, (d) picture after planting [19]

Another example of an inverted roof/terrace (the project can be integrated into the extensive roofing category) was made at the top of a 5-floor building in Bucharest [20]. Throughout the design process (Fig. 9), we had to take into account three important issues linked to each other in order to achieve positive, quality and sustainable results. These are: the beneficiaries (the owners/occupants who will serve the space allocated), the products selected for implementation (structure, materials, equipment, services etc.) as well as the processes that follow the implementation (maintenance/ maintenance, performance). Both the project and the implementation have been carefully studied, respected and verified throughout the construction site. Images from the project phase, during implementation on stages of execution to the final form, are presented in Figs. 10, 11 and 12.

186

I. Nicolae and S. Petra

(a)

(b)

Fig. 9. (a) Three-dimensional personal project image, (b) image processed [21]

(a)

(c) (b)

Fig. 10. Personal archive images - implementation

(a)

(b)

(c)

(d)

Fig. 11. Personal archive images - implementation

Solutions to Reduce Energy Consumption in Buildings

(a)

187

(b)

(d)

(c)

Fig. 12. Personal archive images - implementation

The project, with a simple, elegant solution, focuses on the modern design, the colors of the vegetation in the gardens and the lawn surface creating a familiar atmosphere. 2.2

Advantages of a Green Roof

The green roof is an additional, thermal insulator that increases the lifetime of the roof; it uses plants which absorb toxins (including CO2) from the air, and support the balance between temperature and relative humidity. The main advantages outlined in literature are [2, 4, 9, 22, 23]: • Reduces the effect of the heat island (UHI) by renaturing green roofs; • Increases humidification of outdoor air due to plants that retain some of the meteoric water and which then return to the atmosphere through evapotranspiration; • The energy costs of the space at the last level decrease (by reducing the cooling load in the summer); • Using and reusing water in an efficient way - reduces the amount of meteoric water that gets into the city’s sewer system due to the fact that a significant share of the roof vegetation is retained, as well as the cost of collecting rainwater is reduced due to its use; • Increases the green area in the city, increases the habitat of birds, insects and animals within cities; • The vegetation freshens the air inside the cities, and by the humidity intake cools the air in the immediate vicinity of the roof, creating a much improved microclimate all around, reducing noise pollution, absorbing dust, etc.; • The aesthetic value of the green roof will vary continuously over time and seasonally. Improving the quality of life and the image of the urban-built fund; • Architectural accents can be considered in the urban landscape, landmarks and why not symbolic elements at the area or city level.

188

2.3

I. Nicolae and S. Petra

Disadvantages of a Green Roof

When designing is not conceived to withstand the weight of a landscape composition, discrepancies in the system may occur. If the project is related to an existing building, expertize can be done with a structural specialist and, after the report, there will be identify the specific weight (kg/m2) that will be supported and also the appropriate roof type (extensive, intensive or semi-intensive) [2, 4, 9, 22, 23]: • There are situations when the type of plants used is not always thought out for circulation; Can be thought of as a static living picture; • The costs of roof insulation systems are higher than the classic ones; • If these steps are not followed, unpleasant situations such as leaks, crashes, clogging due to weak and/or non-existent drainage, clogging due to poor maintenance, and inappropriate choices of the assortment of species used may occur; • There are situations when spontaneous, unplanned green areas appear, and if no action is taken, they can cause material damage, facilitate the installation of dampness, cracks on the roof, plasters and contribute to its degradation over time. 2.4

Benefits of Using Succulent Plants

The generous palette of studied plants offers sun shading through the foliage and evapotranspiration cooling. The latter is one of the important processes of heat transfer and mass transfer for the green roof: “Evaporation is the movement from the thermal energy from the surface of the water to the atmosphere, which involves a phase shift from liquid to vapor (thermodynamic) that is removed from the surface (aerodynamic). When solar radiation heats the atmosphere, it provides a surge of energy at the surface of the water, capable of increasing the flow of heat that drives the sweat from the leaves of the plants” [24]. Sedums are succulent plants, belonging to the family Crasulaceae and exceeding about 3000 species. These are found in North America, Europe and Asia. They are small plants, have low growth and can be planted both horizontally and vertically for the arrangement of living green walls. They cover very well the soil, they are not precious plants, do not require periodic maintenance, they easily cover the laid surfaces, they have a superficial root system and develop well in a low soil substrate (vegetative layer of at least 5 cm thick) (25–30 days between watering), tolerant to drought due to fleshy/succulent leaves, storing enough water to survive long summer droughts (25–30 days between watering), stress tolerance, surviving under extreme conditions and prevent the emergence and development of weeds, due to their compact growth. The latter is an important environmental benefit for situations where irrigation on the roof is limited or not possible. They are heliophile plants, but also have the ability to grow nicely, to survive in weather conditions, high/low temperatures, sun/shade, humidity, frost, precipitation, sunlight and drought excess [25, 26]. There also are environmental, economic, social and aesthetic benefits. The most important environmental benefit is cooling the air inside the city [7, 23]. The economic benefits derive from the environment. Retaining and using rainwater reduces the running costs of the drainage and urban sewerage systems;

Solutions to Reduce Energy Consumption in Buildings

189

Reducing bills is also found in energy saving (plant shading reduces climate stress on building envelope, plant layer becomes a buffer space that prevents heat exchange with the outside, and use of air conditioners is reduced or, in any cases, no longer used). Social and environmental benefits add value to cities by enhancing envelopes. They provide contrast associated with eliminating the overly built anthropic environment. We can take out of anonymity architecturally outdated buildings and, by greening them, can provide the locals with a sense of closeness to nature, help the population to be healthier (stress is eliminated, some people recover/cure certain diseases, generates some emotional, intellectual, social and physical benefits, for man are generated) can become city-level seasonal or symbolic signs. 2.5

Capturing, Managing and Using Meteoric Water

Water, a natural and renewable source, is a determinant factor in maintaining the ecological balance in the existence of life, and in the society in which we live water represents as a source of energy for the human activities [27]. The meteoric (pluvial) waters are waters from atmospheric precipitation that falls all over the earth, including the built environment. These are discharged from the building construction step through the public sewerage network and this is a major problem in urban areas due to under-dimensioning of sewers and to water loading with petroleum residues, oils, lead from various fuels, tire abrasion particles, automobile brake discs, etc. - factors affecting the public sewerage network, deteriorating it, requiring filtering and cleaning in the sewage treatment plant just like the other waste waters [27]. We can avoid all the problems using meteoric water for irrigation of green roofs. Thus, much of the rainfall is retained since the first fall and the surplus can be stored in containers specially arranged for storage [2]. Every technologic leap represents a step forward in introducing minimum energy performance standards in the construction sector. An example of a future concept house (Fig. 13) shows that there is the possibility of integrating the components (natural resources - water, vegetation, climate) so that the market of new and existing constructions develops according to the European Directive 31/2010/EU (RECAST EPBD, Article 9) with almost zero energy consumption (NZEB). The future living design should take into account resource creation and location. The role of natural resources in buildings is to optimize energy consumption. Using gravity, captured meteoric water can generate pressure and provide watering of the vegetal envelopment (rooftops and green walls). Because of the collection and reuse of rainwater, we eliminate a significant amount of water that does not enter the sewer system. The water-vegetation combination brings us direct benefits by humidifying the outdoor air due to the retention of the meteoric water that plants give to the atmosphere through the evapo-sweating process. At the same time, solar, wind and photovoltaic panels can provide energy through the wind and the solar system.

190

I. Nicolae and S. Petra

Fig. 13. Sustainable, water flow in a building [28]

2.6

Implementation of Sustainability Policies at District, City, Country Level

The building enveloped with succulent plants is a living skin that breathes and protects the construction against the solar radiation during hot summer periods, improves thermal comfort by cooling indoor spaces, reduces energy costs associated with air conditioning, improves air quality and helps the increase of biodiversity in urban space, reduces carbon dioxide in the atmosphere and produces oxygen through photosynthesis. Also, these systems can extend roof life, absorb and manage rainwater, and take over from the sewer system load, preventing floods in urban areas [9, 23, 29]. “Although innovative adaptation projects at local level are important to address the impact of climate change, they depend on the support of the highest levels of government. The framework should therefore foster dialogue between different levels as well as with EU citizens and private sector organizations [21]”. We have concrete examples in the world, with clear legislation in landscape policies. There are over 100 million m2 of green roofs in Europe. Many countries such as Germany, Austria, Switzerland, Canada and the United States have clear strategies in this perspective. As an example, in Switzerland, (Fig. 14), green roofs are required for all large commercial buildings by federal regulations requiring that any newly built roof of more

Solutions to Reduce Energy Consumption in Buildings

191

than 500 m2 be made using such a green system (The surface dislodged from the ground to be transposed on the roof).

Fig. 14. View of green roof in Switzerland, Basel [30]

In the north-west of Switzerland, flat roofs have been promoted in Basel since 1998, and since 2002 the greening of new roofs is mandatory. Several cantons provide subsidies to owners, between 1000 and 9000 Swiss francs (CHF) for a single dwelling with a green roof. 19 cantons of the 26 offer exclusive subsidies and require extensive roofs to be sown with native plants to provide habitats for invertebrates. Also in Switzerland, at the Basel Exhibition Hall, we meet the largest green roof with an area of approximately 16,000 m2. In Germany, policies on roof vegetation were promoted in 1997, with the help of technical guides provided by the municipality, when there were more than 11 million square meters of green roofs. The number has grown to 13.5 million in 2002, and this figure has now doubled by encouraging people by providing financial compensation or tax exemptions, all to reduce urban pollution. These policies provide the following to stakeholders, developers, customers, designers and other stakeholders: • Recognition on the international market for buildings with a low environmental impact; • Systems and materials that help reduce operating, maintenance and maintenance costs; • Creativity to find innovative and revolutionary solutions that minimize the impact on the environment; • The confidence that environmental practices have been tried and tested; • Stimulating efforts towards the corresponding requirements of sustainable buildings; • Standards demonstrating progress towards achieving environmental objectives; • Green roofs are considered by financiers, public administrations, design offices, managers of different consortia or real estate agencies, etc. useful as it promotes, sustains and researches environmental issues and sustainability, allows interested

192

I. Nicolae and S. Petra

people to demonstrate the green performance of live green buildings implemented by users. Therefore, these systems should be promoted, encouraged and implemented in Romania. 2.7

Energy Performance of Green Roof Terraces - Analysis Based on a Dynamic Simulation Model

The analysis of the energy performance of a green roof was made by determining two basic energy characteristics (intensive and extensive) of the terraces: • Outside virtual temperature [31]; • The energy input (heat) characteristic of the terrace that is adjacent to a living space whose resulting (operative) temperature [32] has the value of 27 °C (provided by the use of the air-conditioning of the living areas); • The climatic support is represented by cloudless calculus summer day, characteristic to the Timisoara Municipality [33]. The modeling of the heat transfer process between the external environment and the air-conditioned space considers the following constructive solutions of the terrace: (a) Current stage - the terrace characterized by corrected thermal resistance R′ = 1.1 m2K/W, the solar radiation absorption coefficient (short wave), = 0.88 and the maximum exposure relative to the direct component of the solar radiation (cs = 1). The external temperature and the intensity of the solar radiation, the direct and diffuse horizontal components, are used by the hourly values, ID(t) and Idif.(t) according to the values determined by processing the data provided by the National Meteorology Agency, ANM [33]; (b) The renovation stage with additional thermal protection, which leads to the corrected thermal resistance R′ = 5 m2K/W, without changing the absorption coefficient of the solar radiation = 0.88; (c) The major renovation stage leading to the corrected thermal resistance R′ = 5 m2K/W, associated with the modification of the absorption coefficient of the solar radiation to the value = 0.30; (d) The major renovation stage by transforming the terrace into a cool roof (maximizing the albedo of the covering surface, i.e. the external environment) characterized by the values: R′ = 5 m2K/W and the absorption coefficient of the solar radiation to the value = 0,05; (e) The green roof stage, which uses the structure of the renovated terrace [21] and the planting layer on the surface adjacent to the outside environment. The dynamic modelling of the thermal response of the terraces to climatic demand [34] was made using the INVAR dynamic calculation program, validated by the BESTEST solution (standards EN 15255, EN 13792, EN 15265). For each technical solution “j” the hourly values of the virtual outdoor temperature, were determined; depending on which the hourly values of the thermal flux taken in the inhabited space and evacuated in the external environment through the air conditioning system were determined:

Solutions to Reduce Energy Consumption in Buildings

0ev;j ðtÞ  0i;0 Q_ l ðtÞ ¼
AT 0 Rl

193

ð1Þ

where: #ev;j ðtÞ - outdoor virtual temperature of the terrace [°C]; #i;0 - the resulting indoor 0 temperature (operative) [°C]; Rl - corrected thermal heat resistance (with the effect of thermal bridges) [m2K/W]; AT - the heat transfer surface of the terrace (determined on the surface of the living space) [m2]; j - index specific to each of the above technical solutions (1…5). In the case of the green terrace, the following adjustments are required by the terraced operating regime in relation to the climatic parameters: • The surface heat transfer coefficient by convection changes according to the geometric characteristic of the external surface of the terrace. This is included within a surface with fins (grass wires) that generate the transfer of heat from/to the outside air; For the purposes of modeling, a density grass of 10,000 threads/m2 was considered; Each thread represents a fin which takes over/yields heat. The resulting global heat transfer coefficient at the wire heat level has a value of 8.16 W/m2K, lower than the coefficient of characteristic of a smooth horizontal surface. Depending on the ratio of the effective - grass wires (20 m2) and the geometric (1 m2) heat transfer surfaces, the equivalent heat transfer coefficient = 163,2 W/m2K; • The radiation process to the celestial vault (black body sky temperature in hours with clear sky) leads to reaching the temperature of the dew point at the surface of the wires and implicitly to the appearance of condensation on the surface covered with the vegetal mass. It results that in the boundary layer adjacent to the vegetal layer, the outdoor air temperature is lower than the outside calculation temperature. On the other hand, the condensation that infiltrates into the support layer of the vegetal layer takes over the thermal flux from the terrace area. This heat flux provides partial or total water evaporation. The thermal flow taken over ensures the latent heat of water vaporization and is manifested by the sensitive cooling of the support layer (which yields the sensitive heat flow to ensure the process of liquid phase change to vapor). Along with reducing the outside air temperature in the area of the terrace (based on sky radiation), the mass transfer process leads to a further reduction in outdoor temperature; • The resulting value is the equivalent outside temperature. The equivalent term refers to the effect on natural convection heat transfer in environments sensitive to the terraced: – outside air. In the case of the average hourly difference 0e  0e;ECH = 1.40 °C; – taking into account the characteristics of the heat and mass transfer processes presented, characteristic to the vegetation layer, the external climatic demand was corrected with the external temperature range and the external thermal . resistance was determined by the value hECH e The results of the dynamic modelling are shown graphically in (Figs. 15 and 16). In the case of the green terrace solution, the average daily outdoor temperature is 28.9 °C, lower than the daily average value of the daily outdoor temperature of 29.1 °C.

194

I. Nicolae and S. Petra Outside virtual temperature - green roof - computing summer day, City of Timisoara 52 50 48 46 44 Outside virt.temp. [°C]

42 40 38 36 34 32 30 28 26 24 22 20 0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

day hour [h] R'=5,0; abs.coeff.= 0,30

R'=5 cool roof

R'=5 green roof

R'=5,0; abs. coeff..=0,88

R'=1,1;abs.coeff.=0,88

te

Fig. 15. Hourly variation in virtual outdoor temperature

Daily thermal energy intake and technical solutions energy efficiency - terrace heat transfer surface A=400 sqm. - computing summer day, City of Timisoara. 160 150 140

Q [kWh/day], Energy efficiency [%]

130 120 110 95,37

100

96,45

90,25

90 78,38

80 70 60 50 40 30 20 10

0,00

0

Actual (1)

Renovated (2)

Renovated (3)

Cool Roof (4)

Green Roof (5)

Technical solution Intake energy [kWh/day]

Energy efficiency [%]

Fig. 16. Changing the amount of heat evacuated from the living space and the estimated (thermal) energy economy

It is emphasized that the virtual outdoor temperature includes the effect of solar radiation. Therefore, the provision of the vegetal layer onto the terraces is thermally equivalent to the cancellation of the absorption effect of the solar radiation during the hours of the day, to which an additional reduction of 0.2 °C is associated.

Solutions to Reduce Energy Consumption in Buildings

195

The above results are the energy footprint of the green terrace that can be the basis for addressing the economic efficiency of technical solutions. In relation to medium and long term climate forecasts, technical solutions can make a significant contribution to maintaining the quality of life through a low thermal comfort with no or very low energy consumption (by reducing the thermal energy demand by more than 96% at the level of the air conditioning of inhabited spaces - Fig. 16) as well as to the preservation of the natural environment as a result of the cooling of the inhabited spaces. These features, at the level of energy performance, recommend green envelops systems as solutions for Nearly Zero Energy Buidings (NZEB) or “with zero net energy consumption” (Zero Net Energy Buildings - ZNEB).

3 Conclusions and Recommendations Urban air quality can be improved through the extension of traditional vertical gardens (classical façade and roofing materials can be replaced by plant systems with plants that embrace building envelopes of all kinds). Selecting the species used can become a problem when there is a great interest in using a large variety of surviving plants with emphasis on shape, color and texture. The assortment of plants chosen must be carefully determined and must take into account not only the aesthetic, decorative aspects, but also the growth rythm, development, life span, ease of maintenance, climate and weather resistance, diseases and pests resistance, etc. Urban space is a degraded ecosystem, incapable of retaining, draining or directing rainwater due to excessive mineralization. The advantages of these green roof systems are: improving urban climate, biodiversity, aesthetic appreciation, rainwater retention, etc. We propose the development and promotion of city-level policies to support the envelope of vegetal constructions, based on technical legislation with guides and manuals for the realization and implementation of these green roof systems. In this respect, the target of Romania by 2018 and 2020 is to provide almost Nearly Zero Energy Buildings (NZBE) or Zero Net Energy Buildings (ZNEB), measured as a percentage of the total number of existing buildings and, relative to the total useful area. Also, the adoption of a clear scheme for defining and certifying ZNEB/NZEB of the current calculation methods developed through policies, incentives and national plans with specific targets and directions by category of buildings supports the purpose of European Directive 31/2010/EU (RECAST EPBD, Article 9) and requires the introduction of minimum energy performance requirements. At present, for our country, there is a certificate of energy performance useful for selling and renting new and existing constructions. The design of green tile energy management systems must be appropriate primarily for the types of existing buildings that will lead to an increase in the number of certified buildings with minimum energy consumption. This paper is intended to be a plea in support of the Directive with the solutions and recommendations presented. It is necessary to continue the research on the functional and structural analyses, the economic and environmental efficiency of the technical

196

I. Nicolae and S. Petra

solutions. The completion of these researches consists in forming a compendium of solutions with structural characteristics in different fields and areas of application at national level. Acknowledgement. Information support for green envelopment systems was provided by the benchmarking study developed within the Doctoral School of UAUIM - “Ion Mincu” University of Architecture and Urbanism Bucharest, with support from USAMVB - University of Agronomic Sciences and Veterinary Medicine, Faculty of Horticulture, Bucharest.

References 1. Rapport: Urban adaptation to climate change in Europe. EEA Report No. 2, 1-143. www. eea.europa.eu/publications/urban-adaptation-to-climate-change. Accessed Apr 2017 2. Nicolae, I.: The energy influence of plants in the building envelope. EMERG - Energy, Environment, Efficiency, Resources, Globalization Publishing AGIR, New series II (2016) 3. World Energy Outlook Special Report: Energy and Air Pollution, OECD/IEA (2016) 4. Nicolae, I.: Green facades, living walls - Space, Art, Architecture, Bucharest, article, Publishing Ed. Univ. “Ion Mincu” (2013) 5. Kim, M.J., Oh, M.W., Kim, J.T.: A method for evaluating the performance of green buildings with a focus on user experience. Energy Build. 66, 203–210 (2013) 6. Kibert, C.J., Hoinka, K.: Sustainable Construction: Green Building Design and Delivery, 3rd edn. Wiley, Hoboken (2012) 7. Dabija, A.M.: Green roof rehabilitation: an untapped opportunity in Romania. National Architectural Symposium “Problems of the architectural and urban rehabilitation”. Iaşi Bucharest, Romania (2007) 8. Dabija, A.M.: Green roof, a possibility to improve the environment, Architecture Technology - Ambient. In: UAUIM Symposiums at the International Fairs ConstructExpo and Ambient (2011) 9. Freed, E.C.: Green Building and Remodeling For Dummies. Wiley Published, Inc., Hoboken (2010) 10. Kingsbury, N., Dunnett, N.: Planting Green Roofs and Living Walls. Timber Press, Inc., Portland (2010) 11. Dabija, A.M., Petrovici, R., Georgescu, I.M.: Green Roof Design Guide. MDRT Technical Regulation (2011) 12. http://untappedcities.com/2014/05/01/daily-what-the-hidden-rooftop-gardens-of-rockefellercenter/. Accessed Apr 2017 13. http://www.odu.ro/de-ce-acoperis-verde-/de-ce-acoperis-semi-extensiv/73. Accessed May 2017 14. Samar, S., Nourhan, M.: The living walls as an approach for a healthy urban environment. Energy Procedia 6(1) (2015). Green Facades 15. https://www.artagradinilor.ro/galerie-foto/acoperi-uri-verzi/proiect-privat-7.html. Accessed Apr 2017 16. Anghel, C.: Founder at “Arta Gradinilor”, the promoter of green roofs and vertical gardens in Romania 17. http://i1.wp.com/adelaparvu.com/wp-content/uploads/2014/04/adelaparvu.com-despre-acoperisverde-la-Berca-gradina-pe-acoperis-design-si-executie-Arta-Gradinilor-10.jpg. Accessed May 2017

Solutions to Reduce Energy Consumption in Buildings

197

18. http://i0.wp.com/adelaparvu.com/wp-content/uploads/2014/04/adelaparvu.com-despre-acoperisverde-la-Berca-gradina-pe-acoperis-design-si-executie-Arta-Gradinilor-11.jpg. Accessed Apr 2017 19. https://www.artagradinilor.ro/galerie-foto/acoperi-uri-verzi/proiect-privat-27.html#pretty Photo, http://cobvillage.ro/galerie.html. Accessed Apr 2017 20. Project carried out in collaboration with Nicolae Bogdan - landscape architect 21. http://www.imsm.com/ie/wp-content/uploads/2015/02/green_roof_system.jpg. Accessed Apr 2017 22. Dover, J.W.: Green Infrastructure Incorporating Plants and Enhancing Biodiversity in Buildings and Urban Environments. Routledge, Abingdon (2015) 23. Grant, G.: Green Roofs and Facades. IHS Bre Press, Bracknell (2006) 24. Ouldboukhitine, S.E., Graig, S., Belarbi, R.: Impact of plants transpiration, grey and clean water irrigation on the thermal resistance of green roofs. Ecol. Eng. 67, 60–66 (2014) 25. https://www.dictio.ro/dex/involutie. Accessed May 2017 26. http://www.apaoltenia.ro/serviciile-publice-de-canalizare/apa-meteorica/. Accessed May 2017 27. Yudelson, J.: Reinventing Green Building, Why Certification Systems Aren’t Working and What We Can Do About It. New Society, Canada (2016) 28. http://www.yankodesign.com/2010/09/27/this-is-future-living/. Accessed Apr 2017 29. Montoya, M.: Green Building Fundamentals, 2nd edn. Pearson, London (2011) 30. https://livingroofs.org/swiss-green-roof-for-biodiversity/. Accessed Apr 2017 31. Constantinescu, D.: Thermal engineering treatise. In: Thermotechnics in Construction, vol. 1, cap. 1.4.2, pp. 44–49. Publishing House AGIR (2008) 32. Missenard, F.A.: Heating and Cooling by Radiation, Paris (1961) 33. The climatic parameters needed to determine the energy performance of existing and new buildings contr. INCERC nr. 483/2011 34. Constantinescu, D.: Elaboration of the design - sustainable reconfiguration of urban climate area, including the buildings Pr. PNCDI - REDBHI etapa 3, (Partener P2) (2016)

Solar Heating and Cooling in Buildings and Communities

Simulation-Based Investigation of the Air Velocity in a Naturally Ventilated BIPV System Rafaela Agathokleous and Soteris Kalogirou(&) Cyprus University of Technology, Limassol, Cyprus [email protected]

Abstract. A Building Integrated Photovoltaic (BIPV) façade is formed by PV panels integrated to a second skin forming an air gap between the two skins. The air gap is responsible for cooling the PVs and for removing the excess heat, to avoid building overheating. The ventilation of the air gap can be natural or mechanical. The system investigated in this study is a vertical, naturally ventilated system. This has a number of advantages, the most important being the avoidance of energy to power the fans, the operation with no noise and the avoidance of overheating which can happen when the fan stops in an active system. A BIPV system is designed in COMSOL simulations software in 3D geometry and tested by varying the temperature on the various surfaces of the system for different air velocities from 0.02 m/s to 2.5 m/s. Additionally, experimental tests are carried out to validate the model. The results show a good agreement between the simulated and measured values. Keywords: BIPV


Temperature influence on PV
Air velocity

1 Introduction During the past few years photovoltaic (PV) panels have been increasingly incorporated (or integrated) into the construction of buildings to generate electrical power. These are called Building Integrated Photovoltaic (BIPV) systems. The BIPV systems can be installed on building facades or on the roofs. BIPV systems as well as Double Skin Facades (DSF) have two skins. For the BIPV systems the first skin is the PV module and the second is the last building component on the façade or roof. The panels are integrated on the skin of the building with the use of various brackets and connectors. The integration of PV panels in a second skin creates heat behind the PVs. However, in order to prevent the overheating of the PVs and, accordingly, the loss of efficiency, the two skins are separated by an air gap. The air gap can reduce the PVs and also building overheating which may occur due to the hot surfaces around the skin. Fresh air passes through the air gap and cools the PVs. The heated air then can be either directly evacuated to the environment or it can be used to heat the interior of the building. If the latter option is implemented, the system is called Building Integrated Photovoltaic/Thermal (BIPV/T). The ventilation of the air gap can be naturally or © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_15

202

R. Agathokleous and S. Kalogirou

mechanically done. This study focuses on a naturally ventilated BIPV system. This has a number of advantages, the most important being: avoiding the consumed energy to power the fans, the operation with any noise and the avoiding overheating which can happen when the fan stops in an active system. The design of the system and the sizing of the air gap are very important for the building’s performance. The air in the duct affects the system whether it is a DSF or a BIPV. In DSF, the air may overheat the façade if it is not appropriately treated thus adding unwanted thermal loads to the building, and in BIPV systems the overheating of the PVs decreases their efficiency but also leads to overheating the building. Gan (2009) used a CFD method to assess the effect of the air gap between the PV modules and the building envelope on the performance of the system in terms of PV cell temperature for a range of roof pitches and panel lengths, of minimum air gap that is required to minimize the PV overheating. Initially, the air flow patterns and the images of the temperature distribution around the module, show that while the roof inclination increases, the velocity of the air increases and the PV temperature decreases. Various researchers tried to explain the heat transfer and the air flow between the two skins of the DSF and BIPV systems. There are numerous studies that have approached the analysis experimentally [1–6] or numerically, through simulations [7–10]. Studies can also be divided into investigations on the forced ventilated systems and studies about the naturally ventilated systems. An extensive review by Agathokleous and Kalogirou (2016) presented the various studies carried out for BIPV systems separated into naturally ventilated systems and mechanically, and studies which analyzed the system experimentally or theoretically. It was concluded that most researchers studied the systems with mechanical ventilation because of the flexibility to adjust the air flow in the duct to remove the heated air or drive it into the building. Additionally, natural ventilation systems are more complex in terms of the air flow behavior through the duct which is difficult to predict. ElSayed [11] carried out simulations for a BIPV model, and the results showed that the air flow behind PV modules in a ventilated gap and cell temperatures are complex due to the compilation of the internal space of the air gap and the dynamics of heat transfer. According to Wang et al. [12], BIPV has significant influence on the heat transfer through the building envelope because of the change of the thermal resistance by the various building elements. Consequently, it is important to find the configuration of the system that will increase the efficiency of the PVs without increasing the cooling loads of the building during summer. For the BIPV/T Systems it is important to keep both electrical and thermal efficiencies high throughout the year. According to [4] the most important variable to be fixed in the design of a PV cooling duct is the depth, and hence the hydraulic diameter of its cross section. As concluded by [13], researchers seem to agree that the optimum air gap between the PVs and the building façade ranges between 10 and 15 cm in order to keep the PVs temperature at low levels. The aim of this study is to investigate the effect of the air flow in the duct of a single PV BIPV system in terms of the air velocity. A model of a single PV module is constructed in COMSOL Multiphysics software in order to test the system under various air velocities ranging from 0.02 m/s to 2.5 m/s. The simulations were carried out to observe the thermal behavior of the system and the convective heat transfer

Simulation-Based Investigation of the Air Velocity

203

coefficients (CHTC). The analysis is carried out using real meteorological data for a selected typical summer day in Nicosia, Cyprus. The single parameter changed in every run was the velocity of the air inflow to the air gap.

2 Simulation Analysis As mentioned earlier, various studies attempted to investigate the PV facades and the DSF with simulation tools, [6, 8, 14, 15]. This study presents a CFD analysis of a naturally ventilated vertical single BIPV system for different values of air velocity in the air duct with weather data for a typical June day in Nicosia, Cyprus. For this study COMSOL Multiphysics 4.3b software is used, with 3D geometry. In COMSOL Multiphysics, the mathematical models are discrete functions obtained by the Finite Element Method (FEM) resulting in corresponding numerical models. 2.1

Model Geometry

In the FEM analysis, the geometry is set by connecting 3D surfaces in order to obtain real volumes. In the current study, the model has a simple geometry, but numerous physical parameters are considered for representing the in-field conditions to which a real system is exposed. The geometry of the BIPV model is shown in Fig. 1 and in

Air outflow AIR

WALL

Air passes through the air gap

PV

Air inflow

Fig. 1. The 3D model in COMSOL showing the PV panel, air gap and the building’s wall in the dimensions of a single PV panel, and the air path from the inlet to the outlet of the air gap

204

R. Agathokleous and S. Kalogirou

Table 1. The model consists of a single vertical PV module of 0.8 m width and 1.6 m length, an air gap with the same size and thickness of 0.1 m, and a thick wall (1.5 m) of the same dimensions. Thus, three volumes are designed considering different materials to represent the three domains. The two sides of the air domain are considered as adiabatic surfaces in order to avoid air leakage from the sides. Thus, it is considered that the ambient air enters the duct from the bottom opening and rises up being evacuated from the top opening. Table 1 shows the basic properties of the various parts of the system.

Table 1. Physical properties of the materials composing the model PV module Air 1500 q_air* Density, q (kg/m3) Thermal conductivity, k (W/mK) 0.36 k_air* Emissivity, e 0.95 – Heat capacity, Cp (kJ/kg K) 1760 1000 *Calculated for each temperature value of the air in the

Wall 2000 1.46 0.75 1500 duct

Finite element analysis requires that the model geometry and mesh of the solution points will allow the calculations to reach a possible result. The numerical model is complete when the mesh is created. In the system under investigation in this study, the different parts of the Computer Aided Design (CAD) geometry are meshed separately in order to focus on the important part of the system which is the air gap and limit the required computing power and time.

2.2

Weather Conditions

For the simulations, real weather data are imported into the mathematical model with equations. The purpose is to run the simulations using a typical summer day and to observe the effect of the air velocity in the air gap between the two skins on the temperature distribution of the system. Accordingly, a typical summer day is selected, namely the 15th of June, and the data needed to run the simulation in terms of real weather data are the solar radiation and the ambient temperature. The equations for radiation and ambient temperature were derived in Excel, from the weather data extracted from the Typical Meteorological Data (TMY) files of Nicosia, Cyprus, using the TRNSYS software. Then data are imported in COMSOL in the form of equations dependent on time. However, the orientation is one parameter that also needs to be specified in order to use the representative range of radiation. The solar radiation on a vertical surface in Nicosia, Cyprus is calculated under 4 orientations as shown in Fig. 2, in order to select the one with the largest range or the radiation that will show us the thermal behavior of the system in a larger range of radiation. As it can be observed, for each orientation except North, only the effective hours are plotted: for East 5:00–13:00, for South 6:00– 16:00 and for West 12:00–18:00. Looking at the graph in Fig. 2, it can be observed that

Simulation-Based Investigation of the Air Velocity

205

the East orientation has the largest range of radiation with maximum and minimum values of radiation through the day. Accordingly, this is the selected orientation to carry out the simulations and the time interval was selected as from 5:00 am to 13:00 pm for the vertical-oriented BIPV system. Radiation on Vertical Surface - Typical Summer Day - Cyprus

2

Solar Radiation (W/m )

1000 East South West North

800

600

400

200

0 5

6

7

8

9

10

11

12

13

14

15

16

17

18

Hour of the day

Fig. 2. Solar radiation on a vertical surface oriented East, South, North and West during a typical day in June in Cyprus

Both graphs showing the solar radiation and ambient temperature values are shown in Fig. 3.

3

35

800 30 600 25 400

2

y = -0.2431x + 6.6474x - 10.113 20 200

Ambient Temperature (deg C)

Solar Radiation (W/m2)

2

y = 3.2737x - 104.59x + 938.34x - 1624

1000

15

0 5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

Hour of the day

Fig. 3. Solar radiation on a vertical surface oriented East, and the temperature variation during a typical day in June in Cyprus

2.3

Model Physics

From a physical point of view, the boundary conditions and the initial data are often a natural part of the model. From a mathematical point of view, the boundary conditions

206

R. Agathokleous and S. Kalogirou

and the initial data are what singles out to be a unique solution among the infinitely many alternatives. This section presents the boundary conditions set in each part of the examined system as shown in Fig. 4. Convection hair_gap

Convection out Radiation

Conduction Wall

Conduction PV

Radiation out

Convection in

Q flow

Radiation in

Fig. 4. Heat transfer mechanisms taking place on the double skin BIPV system

The two skins of the BIPV system are exposed to different conditions, PV is facing the sun from the outer side and the duct from the inner side while the second skin is facing the duct from the outer side and the building indoors from the inner side. Consequently, they are facing different thermal conditions. Likewise, since there are several components comprising the systems, different heat transfer mechanisms are taking place. The exterior skin is subjected to incident solar radiation which increases the temperature of the skin while transferring heat in the duct and to the wall. As mentioned before, the air enters the duct from the bottom side of the BIPV with the same temperature as the ambient. The temperature of the outflow is dependent on the temperature distribution of the system when exposed to solar radiation. The air in the channel is in immediate contact with the front hot plate (the PV panel) and gets hotter, expands and becomes less dense than the surrounding air and thus experiences upward thrust until it exits from the top opening of the formed duct. The air velocity in the duct is the parameter that can give a better understanding of the effect of the air flow in the duct. Subsequently this is the parameter tested for various values. The simulations were carried out multiple times considering various velocities from 0.02 m/s to 2.5 m/s. To formulate the heat exchange process for a fluid flowing between the PV panel and the building’s wall, time dependent partial heat transfer differential equations (PDEs) are used and solved in COMSOL Multiphysics. The fundamental law governing all heat transfer actions is the first law of thermodynamics commonly referred as the law of conservation of energy. With respect to heat transfer problems, the basic law is written in terms of temperature T. For the heat transfer in fluids, ignoring viscous heating and pressure work and assuming that mass is always conserved, the heat equations is: Cp

@T þ qCp urT ¼ rðkrT Þ þ Q_ @t

ð1Þ

where t (s) is the time, T (K) is the temperature of the fluid, Cp (J/kg K) is the specific heat of the fluid at constant pressure, q (kg/m3) is the fluid density, u (m/s) is the flow

Simulation-Based Investigation of the Air Velocity

207

velocity, k (W/m K) is the thermal conductivity and Q (W/m3) includes the heat transfer sources with positive sign if the heat is added to the fluid volume and negative if it is extracted from the volume (for instance when there is heat loss to the environment). In the case of heat transfer in solids, the velocity is set to zero and the governing equation is thus the pure conductive heat transfer: Cp

@T  rðkrT Þ ¼ Q_ @t

ð2Þ

For steady state problems, the temperature does not change with time and the first term is null. The heat transfer interfaces use Fourier’s law of heat conduction, which states that the conductive heat flux q_ is proportional to the temperature gradient: k

@T ¼ q_ @x

ð3Þ

The convection is set to be natural and it is considered to exist in all areas of the system; at the front of the PV, at the back of the PV, at the front and at the back of the wall. The convective heat transfer coefficients (CHTC) were estimated each time with the appropriate equation because the conditions in each section of the system are different. The CHTC in the front surface of the PV and the back surface of the wall (facing indoors), are estimated by the use of empirical Nu number equation given by [16] for natural convection over vertical plates:

Nuout ¼

8 > < > :

0:825 þ h

1=6 0:387RaL

1 þ ð0:492=PrÞ

9=16

92 > = i8=27 > ;

ð4Þ

where: RaL ¼

gbðTs  T1 ÞL3c Pr m2

ð5Þ

where Lc is the characteristic length of the geometry (m), in this case the height of the system. The two Nu numbers (over the outer PV surface and over the inner wall surface), although estimated with the same correlation, are assumed to be different because of the different properties in the outside and inside and the different temperature of the vertical surface. The CHTC are then estimated by the following relationship considering L to be the height of the model in the y-direction: Nuout ¼

hout L k

ð6Þ

208

R. Agathokleous and S. Kalogirou

Regarding the CHTC in the duct, the estimation was challenging as there are no officially published correlations referring to this specific system or to similar conditions. As concluded in [13], the Nu correlation that describes best the thermal conditions of a BIPV system is the one given by [17] for natural convection in a vertical channel formed by a single isoflux plate and an insulated plate, based on the mid-height temperature difference: " Nugap

6 1:88 ¼ þ Ra00 ðRa00 Þ0:4

#0:5 ð7Þ

In the current case, the PV receives a constant heat flux from the sun whereas, due to its thickness, the building wall can be considered as adiabatic. According to [17], the modified channel Rayleigh number is given by: Ra00 ¼

q2 gbCp b5 q_ lLk 2

ð8Þ

where L and b are in the y and x dimensions respectively. In this case, the CHTC in the air gap is estimated by the following formula considering b the spacing between the two skins in the x-direction: Nugap ¼

hgap b k

ð9Þ

In order to better understand the thermal behavior of the system, four boundaries are selected to plot their temperature against the simulation time. The selected boundary surfaces are shown in Fig. 5 which are the outer and inner surfaces of the PV and the outer and inner surfaces of the wall.

Fig. 5. Boundary surfaces to plot the temperature against simulation time

Simulation-Based Investigation of the Air Velocity

209

3 Results from Simulations The results from the simulations show that the air flow plays an important role in the thermal behavior of the system since it affects the temperature distribution of all its components. The temperature at the four boundaries are shown in Fig. 5. Figures 6, 7, 8 and 9 show the temperature at the boundary at the outer surface of the PV, the inner surface of the PV, the outer surface of the wall, and inner surface of the wall respectively, during the day in the hour interval 5:00 to 13:00 for all the tested velocities. It should be noted that the initial temperature value of all boundaries for all parts of the system is set to ambient temperature.

u=0.02 m/s u=0.03m/s u=0.04m/s u=0.08m/s u=0.1m/s u=1m/s u=1.5m/s u=2.5 m/s

90 80

Tpv-out (deg C)

70 60 50 40 30 20 06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (Hour)

Fig. 6. Temperature at the boundary on the outer surface of the PV panel - Boundary 1

u=0.02 m/s u=0.03m/s u=0.04m/s u=0.08m/s u=0.1m/s u=1m/s u=1.5m/s u=2.5 m/s

80

Tpv - air gap (deg C)

70 60 50 40 30 20

05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00

Time (Hour)

Fig. 7. Temperature at the inner boundary surface of the PV facing the air gap - Boundary 2

210

R. Agathokleous and S. Kalogirou u=0.02 m/s u=0.03m/s u=0.04m/s u=0.08m/s u=0.1m/s u=1m/s u=1.5m/s u=2.5 m/s

25.5 25.4

Tair gap - wall (deg C)

25.3 25.2 25.1 25.0 24.9 24.8 24.7 24.6 24.5 05:00

06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (Hour)

Fig. 8. Temperature at the outer boundary surface of the wall facing the air gap - Boundary 3

Twall in the building (deg C)

u=0.02 m/s u=0.03m/s

25.00 u=0.04m/s 24.95 u=0.08m/s u=0.1m/s 24.90 u=1m/s 24.85 u=1.5m/s 24.80 u=2.5 m/s 24.75 24.70 24.65 24.60 24.55 24.50 24.45 24.40 24.35 24.30 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 Time (Hour)

Fig. 9. Temperature at the inner boundary surface of the wall facing the inside of the building Boundary 4

As can be observed, the higher the air velocity, the lower the temperature distribution of the boundaries. The amount of heated air removed from the duct is directly linked to the velocity of the air admitted to the duct. Figures 6 and 7 show that when the air velocity in the duct is the lowest, the maximum average temperature at the outer side of the PV reaches 86 °C and in the inner side reaches 76 °C. It is important also to observe the time at which the maximum temperatures occur. As it can be seen, this moment is around 8:00 o’clock when the solar radiation is near its maximum, and the ambient temperature increases. However, the reason for the difference in the temperature observed at the two sides of the PV is the fact that the outer surface is exposed to ambient air. Taking the maximum average temperature in the PV panel as a volume and not a surface, the maximum temperature of the PV reaches 69 °C for an air velocity of 0.02 m/s. From Figs. 8 and 9 it can be observed that while the higher air velocity leads to a decrease in the temperature of both sides of the wall, this reduction is very small.

Simulation-Based Investigation of the Air Velocity

211

It is also important to observe the temperature of the flowing air in the duct, since this is a significant parameter that affects the temperature distribution on the system’s surfaces. As it can be seen in Fig. 10 the graph has the same trend as the PV panel’s temperature distribution presented earlier in Figs. 6 and 7 and it is affected in a similar manner by the air velocity. Figure 11 shows the temperature of the air at the outlet of the duct from the top opening.

u=0.02 m/s u=0.03m/s u=0.04m/s u=0.08m/s u=0.1m/s u=1m/s u=1.5m/s u=2.5 m/s

55

50

Tair gap (deg C)

45

40

35

30

25

20 05:00

06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (Hour)

Fig. 10. Average temperature of the air in the air gap for all the tested velocities

55

u=0.02 m/s u=0.03m/s u=0.04m/s u=0.08m/s u=0.1m/s u=1m/s u=1.5m/s u=2.5 m/s

Tair outflow (deg C)

50 45 40 35 30 25

20 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00

Time (Hour)

Fig. 11. Temperature of the air at the outlet of the duct

Figures 12, 13 and 14 show the resulted CHTC in the air gap, over the outer surface of the PV panel and over the inner surface of the wall. The convective heat transfer was estimated at every step through the simulation procedure with the use of the equation showed earlier, assuming the PV panel to be an isoflux surface and the wall as an isothermal surface. As it can be observed, the heat transfer coefficient in the air gap ranges from 4.59 to 4.625 W/m2K while in the outer surface of the PV and inner side of the wall it ranges from 0.3–2.1 W/m2K and 0.975–1.007 W/m2K respectively.

212

R. Agathokleous and S. Kalogirou 4.630

4.620

2

CHTC in the air gap (W/m K)

4.625

4.615

u=0.02 m/s u=0.03m/s u=0.04m/s u=0.08m/s u=0.1m/s u=1m/s u=1.5m/s u=2.5 m/s

4.610 4.605 4.600 4.595 4.590 05:00

06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (Hour)

Fig. 12. Convective heat transfer coefficient in the air gap for all the tested velocities

u=0.02 m/s u=0.03m/s u=0.04m/s u=0.08m/s u=0.1m/s u=0.8 m/s u=1m/s u=1.5m/s u=2.5 m/s

CHTC over outer PV's surface (W/m2K)

2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (Hour)

Fig. 13. Convective heat transfer coefficient in the outer side of the PV panel for all the tested velocities

u=0.02 m/s u=0.03m/s u=0.04m/s u=0.08m/s u=0.1m/s u=0.8 m/s u=1m/s u=1.5m/s u=2.5 m/s

CHTC in the inner wall surface (W /m 2K)

1.010

1.005

1.000

0.995

0.990

0.985

0.980

0.975 06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (Hour)

Fig. 14. Convective heat transfer coefficient in the inner side of the wall for all the tested velocities

Simulation-Based Investigation of the Air Velocity

213

In order to observe the temperature distribution simultaneously at the four boundaries of the system, the four temperature distributions were plotted for the worst and best case scenarios. Figure 15 shows the temperature of the four boundaries when the air velocity in the duct is 0.2 m/s and Fig. 16 shows the temperature of the four boundaries when the air velocity in the duct is 2.5 m/s. The first observation is that the temperature of the PV outlet temperature is lower when using a velocity of 2.5 m/s which means that the higher the velocity, the lower the PV temperature and thus, the higher the electrical efficiency of the PV. Secondly, it can be observed that the two boundaries at the two sides of the wall remain in low temperatures in both cases. The boundary affected most is the one at the inner side of the PV, facing the air gap. When using an air velocity of 0.02 m/s, the temperature at the boundary between the PV and the air gap follows the same trend as the outer surface of the PV and it remains in high temperature because the heated air is not driven out of the duct due to the low air velocity. On the other hand, in the case of 2.5 m/s air velocity, the temperature at the

Temperature at the 4 boundaries when u=0.02 m/s 90

Tpv-out Tpv - air gap Tair gap -wall Twall in the building

Temperature (deg C)

80

70

60

50

40

30

20 05:00

06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (hour)

Fig. 15. Temperature distribution at the four boundaries of the system for u = 0.02 m/s

Temperature at the 4 boundaries when u=2.5 m/s

Temperature (deg C)

70

Tpv-out Tpv - air gap Tair gap -wall Twall in the building

60

50

40

30

20 05:00

06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (hour)

Fig. 16. Temperature distribution at the four boundaries of the system for u = 2.5 m/s

214

R. Agathokleous and S. Kalogirou

boundary PV-air gap is much lower. Due to the increase in the air velocity in the duct, the heated air is removed from the duct more efficiently and the temperature of the back side of the PV remains lower and thus it lowers the front surface’s temperature as well. However, taking the maximum average temperature in the PV panel as a volume and not surfaces, the maximum temperature of the PV in the case of 2.5 m/s air velocity reaches 56 °C but in the case of 0.02 m/s it reaches 69 °C. Another important observation is the high temperature of the air at the exit of the duct. It is strongly affected by the temperature of the PV in both cases. As it can be seen from Fig. 17, when the air velocity in the duct is 0.02 m/s the maximum temperature of the air at the exit reaches 52 °C (considering the air in the inlet at the ambient temperature with a maximum value of 35 °C). On the other hand, when the air velocity is 2.5 m/s the maximum air temperature at the exit of the duct remains quite close to that of the ambient (see Fig. 16). The air particles move faster and thus do not stagnate as much close to the high temperature PV.

55

Tfo

50

Temperature (deg C)

45

Ambient temperature 40 35 30 25 20 15 05:00

06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (Hour)

Fig. 17. The temperature of the air at the exit of the duct when air velocity is 0.02 m/s in comparison with the air at the inlet which is equal to the ambient temperature

4 Experimental Analysis Since the results presented earlier are based on simulation calculations, it is very important to investigate the accuracy of the results. Thus, an experimental procedure is carried out to measure the temperature of the photovoltaic panel in a typical summer day: the 15th of June 2016, the same used for the simulations (solar radiation and ambient temperature were taken from the TMY file). Although real weather data for ambient temperature and solar radiation were used from TMY files, the various physics applied to the model may cause differences in the thermal behavior of the system. The aim of the experimental analysis is to validate the simulation results. A custom made BIPV apparatus was built with one PV module 0.8 m wide and 1.6 m long, an air gap of 0.1 m thickness, and a brick wall of 0.15 m thickness. The apparatus was placed in vertical position in east orientation, from 7 am to 13:00 pm and

Simulation-Based Investigation of the Air Velocity

215

various thermocouples and data loggers were used to measure the temperature of the photovoltaic panel in various points on its outer surface. As mentioned before, for the simulations, real weather data from the TMY of Nicosia, Cyprus were used and imported in the mathematical simulation model with equations. In the experimental procedure, a pyranometer and thermocouples were used to measure solar radiation and ambient temperature. Figure 18 shows the measured weather data in Limassol, Cyprus, compared with the weather data from the TMY files for Nicosia, Cyprus used in COMSOL simulations. As it can be observed, the measured radiation is lower in the morning and reaches maximum at 9 o clock while the radiation from the TMY has the maximum early in the morning. Apart from this difference in radiation in the morning hours (between 7:00 and 8:00), from 8:00 and onward, the data are in a good agreement with a maximum relative error of 8% (from 8:00–13:00). TMY- Simulation Experimental 1200 36

Ambient Temperature (deg C)

2

Solar Radiation (W/m )

1000

800

600

400

200

34 32 30 28 26 24

0

07:00 08:00 09:00 10:00 11:00 12:00 13:00

07:00 08:00 09:00 10:00 11:00 12:00 13:00

Time (hour)

Time (hour)

Fig. 18. Ambient temperature and solar radiation used in the simulations and measured values from real experiment

After measuring the solar radiation and ambient air temperature experimentally one more run is carried out with the simulation model, using the real measured data for radiation and ambient air temperature, again imported in COMSOL model as equations. This is done in order to validate the model. Additionally, at this final run, the air velocity is considered to be 0.85 m/s which is the actual measured average air velocity in the duct during the experimental procedure. Figure 19 shows the average measured temperature of the photovoltaic panel on the 15th of June 2016, the simulation results for air velocity of 1 m/s in the duct (which is the closest simulated value to the measured one) with the TMY data and the simulation results with the real measured weather data and actual air velocity of 0.85 m/s.

216

R. Agathokleous and S. Kalogirou 75

Simulation with TMY 15 June, u=1 m/s Experimental Measured 15 June 2016 Simulation with measured data, u=0.85 m/s

70 65

Tpv (deg C)

60 55 50 45 40 35 30 25 20 07:00

08:00

09:00

10:00

11:00

12:00

13:00

Time (hour)

Fig. 19. Temperature of the photovoltaic panel from experimental procedure and simulation model

As it can be observed, the trend of the measured temperature values is the same with the simulation data trend for both simulations. However, the experimental data are closer to the simulation results obtained using the measured weather whereas the simulation results obtained using the TMY data, show a small deviation. This is because the TMY data are usually used for mean annual performance evaluation of thermal systems and do not necessarily coincide with the actual weather data for particular days. All measurements have an uncertainty between the measured or derived values and the true values. The absolute relative error of the parameters is calculated to reflect the accuracy of the estimated parameters using the following equation: DE ¼

Esimulated  Emeasured Emeasured

ð10Þ

The relative error difference between the experimental and the simulated with the experimental data results is 2% but between the experimental and the TMY simulated results it is 13%. Overall, the results are in a good agreement, and the differences between the experimental measurements regarding the temperature of the PV panel and the simulation results are due to: • The wind effect, which is not considered in the simulation model • The accuracy of the measurements carried out with thermocouples.

5 Conclusions This study presents a thermal simulation analysis performed on a single BIPV system using COMSOL Multiphysics software with finite element analysis method and computational fluid dynamics modeling. The most important outcomes of this study are summarized below:

Simulation-Based Investigation of the Air Velocity

217

• The higher the air velocity in the duct, the lower is the temperature of the various parts of the system. • The air gap plays an important role in the performance of the BIPV since it affects the various temperatures’ distribution of the system. • The wall (second skin) of the BIPV system is not significantly affected by the solar, since its temperature does not change dramatically during the exposure time (only 1–2 °C). • The model validation shows that the model is able to represent the temperatures of the system with an accuracy of less than 2%.

References 1. Brinkworth, B.: Estimation of flow and heat transfer for the design of PV cooling ducts. Sol. Energy 69, 413–420 (2000) 2. Brinkworth, B., Cross, B., Marshall, R., Yang, H.: Thermal regulation of photovoltaic cladding. Sol. Energy 61, 169–178 (1997) 3. Brinkworth, B.J., Marshall, R.H., Ibarahim, Z.: A validated model of naturally ventilated PV cladding. Sol. Energy 69, 67–81 (2000) 4. Brinkworth, B.J., Sandberg, M.: Design procedure for cooling ducts to minimise efficiency loss due to temperature rise in PV arrays. Sol. Energy 80, 89–103 (2006) 5. Kaiser, A.S., Zamora, B., Mazón, R., García, J.R., Vera, F.: Experimental study of cooling BIPV modules by forced convection in the air channel. Appl. Energy 135, 88–97 (2014) 6. Mei, L., Infield, D., Eicker, U., Fux, V.: Thermal modelling of a building with an integrated ventilated PV facade. Energy Build. 35, 605–617 (2003) 7. Eicker, U., Fux, V., Infield, D., Mei, L., Vollmer, K.: Thermal performance of building integrated ventilated PV façades. In: Proceedings of the ISES Solar World Congress (1999) 8. Gan, G.: Effect of air gap on the performance of building-integrated photovoltaics. Energy 34, 913–921 (2009) 9. Manz, H.: Numerical simulation of heat transfer by natural convection in cavities of facade elements. Energy Build. 35, 305–311 (2003) 10. Xamán, J., Álvarez, G., Lira, L., Estrada, C.: Numerical study of heat transfer by laminar and turbulent natural convection in tall cavities offaçade elements. Energy Build. 37, 787–794 (2005) 11. ElSayed, M.S.: Optimizing thermal performance of building-integrated photovoltaics for upgrading informal urbanization. Energy Build. 116, 232–248 (2016) 12. Wang, Y., Tian, W., Ren, J., Zhu, L., Wang, Q.: Influence of a building’s integratedphotovoltaics on heating and cooling loads. Appl. Energy 83, 989–1003 (2006) 13. Agathokleous, R.A., Kalogirou, S.A.: Double skin facades (DSF) and building integrated photovoltaics (BIPV): a review of configurations and heat transfer characteristics. Renew. Energy 89, 743–756 (2016) 14. Sanjuan, C., Sánchez, M.N., Heras, M.D.R., Blanco, E.: Experimental analysis of natural convection in open joint ventilated façades with 2D PIV. Build. Environ. 46, 2314–2325 (2011) 15. Sanjuan, C., Suárez, M.J., González, M., Pistono, J., Blanco, E.: Energy performance of an open-joint ventilated façade compared with a conventional sealed cavity façade. Sol. Energy 85, 1851–1863 (2011) 16. Churchill, S.W., Chu, H.H.S.: Correlating equations for laminar and turbulent free convection from a vertical plate. Int. J. Heat Mass Transf. 18, 1323–1329 (1975) 17. Bar-Cohen, A., Rohsenow, W.M.: Thermally optimum spacing of vertical, natural convection cooled, parallel plates. Int. J. Heat Mass Transf. (1984)

Design Aspects of Building Integrated Solar Tile Collectors Istvan Fekete1 and Istvan Farkas2(&) 1

2

College of Szolnok, PA University, Szolnok, Hungary Department of Physics and Process Control, Szent István University, Gödöllő, Hungary [email protected]

Abstract. This paper is dealing with the development of a shell-structured solar tile collector for the use of solar energy in buildings especially to make domestic hot water. The idea of the new type of collector based on its energetic usefulness, but also on the aesthetic considerations were seriously taking into consideration. During the modelling and simulation steps of the solar collector system the thermal efficiency issues were also studied. The temperature distribution on the collector surface was measured and validated by an infrared camera recording. The developed roof integrated tile elements can be recommended in the course of planning new building for the renovation of the existing buildings, as well. Keywords: Shell-structured collector
Thermal efficiency
Sensitivity study
Modelling
Infrared imaging List of symbols

At Ate Aw ct cw I kte kwt _ m mt mw qw T T_ kwt _ m mt mw qw

tile surface (m2) surface of the tile element in the direction of environment (m2) surface of the working fluid (m2) specific heat of tile material (J/kgK) specific heat of water (J/kgK) effective irradiation (W/m2) heat transfer coefficient between tile and ambient (W/m2K) heat transfer coefficient between tile and water (W/m2K) mass flow rate of the working fluid (kg/s) mass of tile (kg) mass of the working fluid (kg) density of water (kg/m3) temperature (°C) temperature difference (°C) heat transfer coefficient between tile and water (W/m2K) mass flow rate of the working fluid (kg/s) mass of tile (kg) mass of the working fluid (kg) density of water (kg/m3)

© Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_16

Design Aspects of Building Integrated Solar Tile Collectors

T _ m Vw w, h, l

219

temperature (°C) temperature difference (°C) volume of the working fluid (m3) geometric parameters of tile (width, length, thickness) (m)

Subscripts

a m in m out t w

ambient temperature medium temperature of working fluid inlet temperature of working fluid to the collector average temperature of working fluid outlet temperature of working fluid from the collector temperature of tile surface temperature of working fluid (water)

1 Introduction It is absolutely important to carry out with research and development activities to harness solar energy, which led to the birth and using novel equipment and systems, and to the emergence of commercially viable technologies in the past decades. Surveys studies show that people with solar collectors appreciate not only on the basis of their usefulness, but also by aesthetic considerations. This is the basic idea of the present study as well. Another issue is that, in addition to traditional collectors, how is justified a solution when the building components can also be used to capture solar energy. In terms of the energy view point, one might draw less efficient, but more surface available area. The proportion of use of the renewing energy resources in meeting the energy demands is only a few percent now in a country. To increase this proportion is of high importance and significance within the entire energy consumption from many points of view. There are significant subsidies to modernize the energy consumption, primarily for installation of the solar collectors, which could help the structural reform of the energy supply. The design of the present heat exploitation solar collectors has special structure in many cases, it uses special materials, therefore the expenses of this type of energy production can be considered high. Many studies have been performed that the temperature difference between urban areas and the surrounding suburban or rural areas can be as much as 5 °C [1, 5–8]. Nearly 40% of that increase is due to the prevalence of dark roofs, with the remainder coming from dark-coloured pavement. The heat island effect can be counteracted slightly by using white or reflective materials to build houses, roofs, pavements, and roads, thus increasing the overall albedo of the city. A cool roof made from a reflective material such as vinyl reflects at least 75% of the sun’s rays, and emit at least 70% of the solar radiation absorbed by the building envelope. Several solar collectors could reduce this effect. The literature review confirms that people select solar collectors based on their output and on aesthetic considerations. In our research this principle, has been built. In

220

I. Fekete and I. Farkas

addition to traditional solar collectors to examine this area, how is a viable solution when the building’s structural elements can also be used to capture solar energy. This is the basic idea presented in this study along with the traditional and the advanced design of the roof integrated solutions (Fig. 1).

Fig. 1. The traditional and the roof integrated design of solar collectors

2 Modelling of Solar Tile Collectors As a matter of fact, the roof integrated solar tile type of collectors convert also the solar irradiance into heat energy with certain amount of losses, which can be divided into optical and heat losses [2, 3]. The major energy factors (both the incoming and outgoing) are listed and drawn as it can be seen in Fig. 2. In the course of thermal behaviour of building integrated collector elements the goal is to increase and optimize the thermal efficiency of the integrated shell-structured collector bodies. The temperature of the solar tiles is mainly depending on the radiation intensity and the size of the absorber surface [9]. Additionally, the rest of the influencing factors are the following: effective irradiation (I), ambient temperature (Ta), average temperature of flowing working fluid (Tm), inlet temperature of working fluid to the collector (Tin). During the warming course of the working fluid, to calculate the outlet temperature _ a differential (Tout) and the tile temperature (Tt) according to the mass flow rate (m), equation based heat and mass transfer approach has to be developed.

Major energy factors: 1. Direct solar radiation 2. Diffused solar radiation 3. Reflection 4. Losses from convection 5. Wind, rain and snow convection 6. Conduction losses 7. Useful output

Fig. 2. The energy balance of the roof integrated solar collector

Design Aspects of Building Integrated Solar Tile Collectors

221

Fig. 3. The input/output of the solar tile element for realization

The input/output scheme of the solar tile element prepared for modelling can be seen in Fig. 3 [3, 4]. The heat transfer model of the tile element is given in Fig. 4, where the section by section calculation method is illustrated. During the modelling and simulation along with the governing equations several environmental variables must be entered in addition to the geometry data and the physical characteristics of the materials used. These items can be summarized, as follows [3, 4]: – – – – – –

surface of the tile element in the direction of environment, volume and mass of the tile element, the effective radiation intensity on the tile, the heat balance between the water and the tile, the heat balance between the element of the tile and environment, the water temperature inside of the tile.

The final governing equations for the Matlab coded simulations can be written in the following form: IAt þ kta Ata ðTa  Tt Þ  kwt Aw ðTt  Tout Þ T_ t ¼ ; ct m t

ð1Þ

_ w cw ðTout  Tin Þ kwt Aw ðTt  Tout Þ  m T_ out ¼ : cw qw Vw

ð2Þ

Establishment of solar collector’s outlet temperature of the working fluid by summarizing sequential thermal equilibrium state of the elementary particles can be observed. Based on Eqs. (1) and (2) derived from mathematical simulations the calculation scheme is shown in Fig. 5, the following simplification notations applied in the Matlab code: U[1] = T_ t ; U[2] = T_ out ; U[3] = Tin :

ð3Þ

222

I. Fekete and I. Farkas

Fig. 4. The structure and the heat balance scheme of tile element

Fig. 5. Matlab realization of the tile collector model

Design Aspects of Building Integrated Solar Tile Collectors

223

3 Calculation Results The Table 1 shows the parameter values used in the experiment and in the course of Matlab simulation. Table 1. Parameters values used in the experiments and for simulation Parameters l dw qt h kte

Values 2.5 m 0.005 m 2000 kg/m3 0.015 m 20 W/m2K

Parameters ct cw w I kwt

Values 900 J/kgK 4196 J/kgK 0.02 m 600 W/m2 150 W/m2K

Parameters _ m qw Ta Tin

Values 0.01 kg/s 1000 kg/m3 20 °C 18 °C

The temperature distributions in the shell-structured tiles calculated by simulations were first analysed. Figure 6 shows the warming process in some locations of the tile (A and B) until steady state is reached. (The locations of the A and B points are indicated in Fig. 7). Based on the afore-mentioned parameters, the maximum available tile surface temperature difference (DTt) is about 27 °C, the outlet fluid difference temperature (DTout) is about 25 °C over, and the inlet temperature (Tin) is 18 °C. Varying the pipe length, the simulation results show that when the built-in tube is longer, then the output temperature of the fluid is consequently higher. Surely, an unnecessarily increase in tube length is not economical as the tile collector reaches a maximum performance.

Fig. 6. Temperatures differences of tile and the outlet working fluid

Matching the calculated and measured temperature is shown in Fig. 7. The fluid enters at point A, and exit at the tile point B. Point C shows the maximum of tile surface temperature. The colour scale shows the approximate temperature values, along with an accuracy of 0.1 °C of the thermal imager software.

224

I. Fekete and I. Farkas

Fig. 7. Temperature distribution of tile element

Parameter Sensitivity Study The simulation results can also be effectively used in order to determine the additional influencing parameters and their operational values, which are required in the development of a new shell-structure type of solar collector shape. In Table 2, the parameters with the most influence are shaded along with some practical notes. Table 2. The list of the influencing parameters (most influence are shaded) Parameters

Notes

length of tube (l)

can be used for optimization of heat transfer, number of serial elements

diameter of tube (d

can be used for optimization of flow resistance, max. is about h/2 and w/2

mass flow rate of water

can be used for pump optimization

volume of tube (V

can be used for optimization of heat transfer

surface of tube (A

can be used for optimization of heat transfer

specific heat of working fluid (c

can be considered as other than water

density of working fluid (ρ

can be considered as other than water

4 Measurements Approach Applied For processing and evaluation of the large amount of data originated from the performed measurements an appropriate a data acquisition system along with analysis software were developed. The collector surface temperature distribution, as the most important feature, it is rather difficult exactly to measure using conventional temperature measuring devices.

Design Aspects of Building Integrated Solar Tile Collectors

225

Fig. 8. Measured surface temperature distribution of tiles

For that reason, the calculated temperature values were verified by infrared camera recordings. The accuracy of the infrared images software was about ±0.1 °C. Figure 8a shows some recording features. During the evaluation of thermal images the temperatures are identified according to radiation intensity levels. The modern infrared cameras setting can be chosen freely, but for detection purposes it is recommended to use the colour scale standard settings. Colour classification examples are shown in Fig. 8b.

5 Conclusions It is important to carry on research and development activities for the capture and utilization of solar energy that led to the birth of new equipment and commercially viable technologies. Beside the energetic reasons it is suggested to study the aesthetics impacts of the roof integrated solar collectors. The shell-structured solar tile collectors could be one of the way of such solutions. The validated simulation results and parameter sensitivity helped to optimally design the shape of the tile body. It is also recommend the use of such architectural elements for designing of new installation and also renovation of buildings, in order to increase the active utilization of solar energy and to meet the future standards.

References 1. Bougiatioti, F., Evangelinos, E., Poulakos, G., Zacharopoulos, E.: The summer thermal behaviour of “skin” materials for vertical surfaces in Athens, Greece as a decisive parameter for their selection. Sol. Energy 83(4), 582–598 (2009) 2. Farkas, I.: Solar energy applications. In: Kovács, R. (ed.) Hungarian Renewable Energy Handbook, pp. 32–34 (2011) 3. Fekete, I.: Building integrated shell-structured solar collectors. In: Thesis of Ph.D. Dissertation. Szent István University, Gödöllő, Hungary (2015)

226

I. Fekete and I. Farkas

4. Fekete, I., Farkas, I.: Application possibilities of building integrated solar tile collectors. In: Proceedings of First International Conference on Building Integrated Renewable Energy Systems, BRIES 2017, Paper No. 11, pp. 1–8 (2017) 5. Karlessia, T., Santamourisa, M., Apostolakisb, K., Synnefaa, A., Livadaa, I.: Development and testing of thermochromic coatings for buildings and urban structures. Sol. Energy 83(4), 538–551 (2009) 6. Kendrick, C.: Metal roofing on residential buildings in Europe: a dynamic thermal simulation study. Report 090903ECC, Oxford, September 2009 7. Kolokotroni, M., Giridharan, R.: Urban heat island intensity in London: an investigation of the impact of physical characteristics on changes in outdoor air temperature during summer. Sol. Energy 82(11), 986–998 (2008) 8. Kolokotsaa, D., Maravelaki-Kalaitzakib, P., Papantonioua, S., Vangelogloua, E., Saliaric, M., Karlessic, T., Santamourisc, M.: Development and analysis of mineral based coatings for buildings and urban structures. Sol. Energy 86(5), 1648–1659 (2012) 9. Pisello, A., Rossi, F., Cotana, F.: Increasing roof albedo: a retrofitting strategy for buildings and environment. In: 48° Convegno Internazionale AiCARR Baveno, Lago Maggiore (2011)

Modelling and Simulation of the Solar Biomass Base Heating System for Low Energy Buildings Developed for Rural Area Sándor Bartha1,2(&) and Boglárka Vajda2 1

Cercetare Silox LTD, 2 Aleea Centralei Street, 520063 St. George, Romania [email protected] 2 Green Energy Association, 4 Presei Street, 520064 St. George, Romania

Abstract. The present paper describes one theoretical model, used for designing the optimal structure of the one heating system, developed for new or thermal rehabilitated buildings. The model can be used for evaluating of the total heat demand for the building and to the establishing the optimal structure for bioenergy value chain, where the feedstock is the biomass wood chips produced on energy willow plantations. The studied model used in this design technique is for one high efficient type boiler, which is controlled by one PLC unit, creating in this way the autonomy of the system. The paper starts with the element of biomass and bioenergy value chain presentation. The second part is focused to presenting the theoretical algorithm for designed the optimal structure of the heating system and with the establishing the fuel needs and the used marginal land area where this type of feedstock can be produced. In finally is presented the cost benefits analyses for one model for sustainable biomass feedstock production on the short rotation plantation, which can be used and implemented in rural area for supplying the principal local authorities building with heat energy, produced by sustainable technology and creating in this way the first step to energy independency of the village. In this evaluation and modelling technique one solar thermal conversion unit are integrated in order to reduce the biomass consumption with 15–30%. Keywords: Bioenergy


Solar
Heating system
Cost benefits analysis

1 Introduction The European strategy for Nearly Zero Energy Buildings presents the definition of the “nZEB” and the targets for each member stats- which must to be achieved in National Action Plans. The Nearly zero energy building is a building that has a very high energy performance -the nearly zero or very low amount of energy required should be converted to a very significant extent by energy from renewable sources, including energy from renewable produced on site or nearby. The principal targets for the states members are presented in art. 9 of the Energy Performance of the Buildings Directive where member states shall ensure that: – by 31 December 2020 all new buildings will be categorized as nearly zero energy buildings, and © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_17

228

S. Bartha and B. Vajda

– after 31 December 2018 new buildings occupied and owned by the public authorities must to be are nearly zero energy buildings. The member’s states shall draw up national plans for increasing the number of the type of buildings and this plan need to established differentiated targets according to the category of the buildings. The concept and energy performance of the buildings are different and varies a lot of by the countries - in France this nZEB definition from the actual thermal regulation of the buildings the value of the energy consumption in residential new buildings must to be below than 50 kWh/m2/year. Today in Romania the final energy consumption per square meter is still very high (final energy consumptions of 175 kWh/(m2 year) for residential buildings and around 300 kWh/(m2 year) for non-residential buildings), a nZEB designed in Romania shall be characterized by the local climate zone and base of the primary energy use and in function of the type of buildings the minimum requirements for “nZEB” status are presented in Table 1 [1–3]. Base on statistical dates around half of the Romanian population live in country side and the usually heating system used in this area is based on woody biomass [4]. The energy sources are burned in low efficiency boiler and stoves and that bad quality burning of the feedstock has an important impact to the air quality. For implement the presented action plan target in the Central Region in Romania we established one sustainable model for producing the heat with biomass, resulted from short rotation energy plant plantation.

2 Biomass Base Heating System for Rural Area Feeds with Feedstock from SRCs Plantation In generally in rural area the energy performance of the building is not so high, the inhabitants and the local authorities building performance value, the useful “space heat demand” is around 150–350 kWh/m2/year, and the full power operation time in case of the Covasna County climatic area is 1600–1800 h/year [5]. Table 1. Proposed “nZEB” definitions for Romania and the minimum requirements Building type

Minimum requirements 2

Single family buildings Primary energy [kWh/m /yr] Renewable share [%] CO2 emissions [kgCO2/m2/yr] Multi-family buildings Primary energy [kWh/m2/yr] Renewable share [%] CO2 emissions [kgCO2/m2/yr] Office buildings Primary energy [kWh/m2/yr] Renewable share [%] CO2 emissions [kgCO2/m2/yr] Public office buildings Primary energy [kWh/m2/yr] Renewable share [%] CO2 emissions [kgCO2/m2/yr]

Year 2016 100 >20 20 600 °C) was reported by Cespedes et al. [22]. This solar selective absorber coating is of real interest since has one of the highest solar spectral selectivity (S = 54.5) reported so far. Table 2. The optical properties, spectral selectivity and average thickness (t) of alumina matrices and red coatings obtained by RSPD (according to [7]) Sample t [nm] A1 488 A1/Fe2O3 1218 A2 510 A2/Fe2O3 1384

as 0.13 0.51 0.13 0.53

eT 0.15 0.15 0.16 0.13

S 0.86 3.40 0.81 4.07

Development of Black and Red Absorber Coatings for Solar Thermal Collectors

271

3 Black (NiSx) and Red (Fe2O3) Solar Selective Absorbers Obtained via Sol-Gel Spraying Method Nickel sulphides, as semiconductor materials, show various crystalline phases such as NiS, Ni3S2, Ni7S6, Ni9S8, Ni3S4 and NiS2. Among these, the stoichiometric NiS is considered an attractive material with interesting electrical (electronic conduction), optical (band gap energy, Eg = 1.37 eV, matching solar spectrum) electrocatalytic, supercapacitive and magnetic properties, low toxicity, low cost and ease of preparation [37–39]. Considering these properties, NiS was used as cathode material in rechargeable lithium or secondary batteries [40], as supercapacitor (energy storage device) [38, 41], in dye-sensitized solar cells [42], in photoelectrochemical storage devices and as an improved Na- and Li-storage material [39]. Black nickel is an interesting, low-cost solar selective absorber material within the family of black metals which can be used for solar thermal collectors operating at low temperature. To achieve thermal stability of black nickel coatings electrodeposited on copper substrate, a metallic Ni interlayer is required. The cermet absorber coating exhibits a solar spectral selectivity of 10.22, slightly lower than that of black nickel coating directly electrodeposited on Cu substrate [10]. The first cermet absorber coatings containing Ni-Fe alloys with variable composition into porous alumina matrix (Al/Al2O3) were obtained and characterized by Santibanez et al. [26]. The electrodeposition technique was used to produce porous alumina nanostructures containing Ni-Fe nanorods and the binary (Fe2O3) and ternary (NiFe2O4) iron oxides enhanced the optical properties (as = 0.85 and eT = 0.12) of the Ni based solar absorber (as = 0.91 and eT = 0.17). One of the widely studied transition metal oxides is hematite (a-Fe2O3) due to its attractive and unique properties, such as good thermodynamic stability at high temperatures, chemical stability in oxidative environments, abundance, environment friendly and low cost. Moreover, it is known as a semiconductor material with bandgap energy Eg = 1.9–2.2 eV [43–45] and relative high refractive index, n = 1.7–2.2 [43]. The favorable optical band gap position in the Vis region, allows it to absorb considerable visible light (  40% of incident solar irradiation), therefore it has been extensively studied for many applications, including lithium ion batteries [46], gas sensors [43, 44, 47], photocatalysis [48–50], photo-oxidation of water [51, 52] and as magnetic materials [53, 54]. Hematite thin films have been prepared by a variety of techniques, such as physical vapour deposition [43, 47], electrochemical deposition [51, 52], spray pyrolysis [44, 51] and sol-gel spin coating deposition [53, 54]. In developing of black (NiSx) and red (Fe2O3) absorber coatings, as: Al/Al2O3ch/ (Al2O3sp)/NiSx/TiO2, respectively Al/Al2O3ch/(Al2O3sp)/Fe2O3/TiO2, several steps needed to be optimized, using spectral selectivity (S) as output property: (a) Substrate pre-treatment (Al/Al2O3ch); (b) Alumina matrix (Al/Al2O3ch/Al2O3sp); (c) Black and red absorber coatings obtained on alumina matrix by low temperature spraying; (d) Final absorber coating with anti-reflective (TiO2) layer.

272

L. Isac et al.

The black (NiSx) and red (Fe2O3) pigments are obtained as powders using the sol-gel technique and then were deposited on the substrate, respectively alumina matrix, by spraying, from a colloidal-based alcoholic dispersion, at low deposition temperature (*100 °C). The Al2O3 layer forms the alumina matrix by deposition of commercial c-Al2O3; similarly, TiO2 layers were obtained using TiO2-Degussa P25 powders, from alcoholic dispersions, at *100 °C.

3.1

Synthesis and Characterization

Recent research is focused on developing high selective and durable materials for solar absorber coatings which require cost-effective and environmental friendly preparation methods. In this context, sol-gel and spray pyrolysis meet these criteria and are highly promising techniques used for solar absorbers fabrication. Still, they are less common than the electrochemical or vacuum-based techniques, which are more costly. The sol-gel method is based on chemical processes involving precursors, generally in the form of a colloidal-based system, that are eventually transformed into a wide spread network of either discrete or continuously linked molecules to form particles [55]. Some of the main advantages of this technique are [55, 56]: – homogenous mixing of precursors at molecular scale; – ability to tailor the microstructure of the absorber film at low temperatures; – facile control of coating parameters such as chemical composition, particle size, particle size distribution, homogeneity etc.; – allows obtaining various materials, such as thin films, ceramic powders, fibers and nanocomposites; – requires low material (precursors) consumption and can be manufactured at ambient pressure; – is low-cost and efficient in energy consumption; – shows good potential for scaling up to an industrial scale. The possible limitations of sol-gel method are [56]: – high-cost of some precursor materials; – the potential toxicity of some organic solutions/additives used in the synthesis process; – high contraction rate during processing; – extensive time required; – difficulties regarding property foreseeing, reproducibility and processing. In this work, for the sol-gel synthesis of NiSx and Fe2O3 pigments, all reagents used were of analytical purity, as received from commercial sources, without further purification. The NiSx precursor gel synthesis started with mixing together stoichiometric amounts of NiCl2
6H2O 0.5M and thioureea 0.6M aqueous solutions. The targeted solution pH of 8.3 was reached by adding NaOH 10M solution, drop by drop, under continuous stirring, at room temperature. Further on, the solution was aged for 24 h.

Development of Black and Red Absorber Coatings for Solar Thermal Collectors

273

After removing the supernatant liquid separated through decantation, the denser solution was evaporated at 100 °C, for 4 h. The prepared gel was carefully dried in a furnace at 115 °C in air, for 20 h. Dried gel was grounded and calcined at 500 °C in air, for 5 h. The grey powder that resulted was annealed at 350 °C, for 3 h, when the powder becomes black. The Fe2O3 pigment was prepared starting from an aqueous - ethanolic (W:Et = 1:1) solution of FeCl3
6H2O 1M in which it was drop-wise added a NH4OH 10% solution, under continuous stirring, at room temperature. After reaching pH = 7, the solution was aged for 24 h. Further on the solution was concentrated by continuous stirring and evaporation at 80–90 °C, for 5 h. The obtained gel was carefully dried in a furnace at 115 °C in air, for 20 h. Dried gel was grounded and calcined at 500 °C in air, for 5 h, resulting a fine dark-red powder. The substrate pre-treatment and optimization consisted in: – degreasing and conditioning in alkaline solution the commercial Al substrate (99.5% Beofon, thickness 0.7 mm); – immersion the alkali treated substrates in H2SO4 (c = 200 g/L) and HNO3 (HNO3: H2O = 1:1) solutions for 0.5 h, 1 h, 2 h, 12 h and 24 h; – samples of 3 cm  5 cm were used as substrates in the spray deposition of the NiSx and Fe2O3 layers from the dispersions. The optimized substrate Al/Al2O3ch (S = 0.5), obtained by immersion in HNO3 solution for 12 h, was nominated as A. The alumina matrix was obtained by the deposition of Al2O3 layer via robotic spraying from an alumina sol prepared from commercial c-Al2O3 powder in isopropyl alcohol 10%, followed by stirring in an ultrasonic bath, for 2 h. The concentrations of the prepared sol were 1–2%, and DTAB 100 (1-Dodecyl)trimethylammonium bromide), TODA 100 (2-[2-(2-Methoxyethoxy)ethoxy]acetic acid) and PVP 25 (Polyvinylpyrrolidone) were used to stabilize the sol; the optimized alumina matrix Al/Al2O3ch/Al2O3sp, obtained from a 2% dispersion with TODA 100, was further nominated as A/AO. The NiSx, respectively the Fe2O3 dispersions were prepared by mixing the NiSx/ Fe2O3 pigment with isopropyl alcohol 10% aqueous solution, followed by stirring in an ultrasonic bath, for 2 h. The concentrations of the prepared dispersions were varied from 1% to 5% (for NiSx), and 1–8% for Fe2O3. The influence of stabilizing agents DTAB 100, PEG 400, TODA 100 or PVP 25 on the spectral selectivity response was investigated and DTAB was found to be more suitable. For the NiSx and Fe2O3 films deposition by spraying onto the substrate/the alumina matrix, dispersions with 4%, respectively 5% concentrations were used. Spray pyrolysis is a generic process for producing particles by decomposing precursor molecules at high temperature [57]. It is well-known that, among chemical deposition techniques, spray pyrolysis is considered one of the most attractive and low-cost method used for the preparation of efficient and inexpensive thin films, with various applications, at industrial scale. By pyrolysis, the technique also involves the chemical transformation of some of the components; without pyrolysis, spray deposition is a usual, controllable technique to deposit particles on a given substrate. The ability to control the morphology,

274

L. Isac et al.

homogeneity, uniformity and thickness of deposited films are essential requirements to consider the spray deposition technique as reproducible and applicable for obtaining suitable coatings for solar thermal applications. In this work, the dispersions previously prepared were sprayed at low temperature (T = 100 °C) onto the alumina matrix, using 40 spraying sequences, with 40 s break between two pulses. Air was used as carrier gas at 1.2 atm and the distance between nozzle and substrate was kept at 20 cm. On the top of these layers, the anti-reflective TiO2 film was sprayed, from dispersion, at T = 100 °C, with 5 spraying sequences, in the same working conditions. The TiO2 sol was prepared by mixing commercial TiO2 Degussa P25 with ethylic alcohol 10%, followed by stirring in an ultrasonic bath, for 0.5 h. The concentration of the prepared dispersion was 5%. It should be mentioned that a better spectral selectivity (S = 2.04) showed the NiSx layer deposited on the alumina matrix (A/AO), while lower spectral selectivity (S = 1.72) was obtained for the layer deposited directly onto the substrate A. On the contrary, higher spectral selectivity (12.8) was obtained for Fe2O3 layer deposited directly on the substrate A, compared to the much lower value (S = 5.75) showed by the film deposited on the alumina matrix. To have an overall view on these thin films, the layers used for further investigations are: (a) (b) (c) (d) (e) (f)

Al/Al2O3ch/NiSx nominated as A/NiSx; Al/Al2O3ch/Al2O3sp/NiSx nominated as A/AO/NiSx; Al/Al2O3ch/Al2O3sp/NiSx/TiO2 nominated as A/AO/NiSx/TiO2; Al/Al2O3ch/Fe2O3 nominated as A/Fe2O3; Al/Al2O3ch/Al2O3sp/Fe2O3 nominated as A/AO/Fe2O3; Al/Al2O3ch/Fe2O3/TiO2 nominated as A/Fe2O3/TiO2.

The crystalline structure and the layers composition were evaluated by X-Ray Diffraction (XRD, Bruker D8 Discover Diffractometer with Cu Ka1 line) using the locked-couple technique in the 2h range from 10° to 70°. The surface morphology of the alumina substrate and absorber layers was investigated using Scanning Electron Microscope (SEM 3500N, Hitachi). The surface elemental composition of the coatings was identified by SEM equipped with an energy dispersive spectrometer (EDS). The optical properties of NiSx and Fe2O3 based absorber coatings (as, eT) were evaluated using Fourier Transform Infrared Spectroscopy (FTIR, Bruker Vertex 70) and UV-VIS-NIR spectrophotometry (Perkin Elmer Lambda 950). 3.2

Results and Discussion

The X-Ray diffraction spectra (Figs. 3 and 4), show that both absorber coatings have polycristalline structures. Besides crystalline phases of Al2O3, aluminum oxyhydrogenated compounds, AlOOH and Al(OH)3, from the substrate/alumina matrix and nonstoichiometric sulphides (hexagonal NiS1.03 and orthorhombic NiS1.125) along with surprisingly hydrated Ni(ClO4)2 (hexagonal, PDF 00-026-1285), as predominant phase, were found in the composition of the black coating. In the red coating, rhombohedric Fe2O3 (PDF 01-087-1165) is the only predominant phase.

Development of Black and Red Absorber Coatings for Solar Thermal Collectors

275

Fig. 3. XRD patterns of substrate A and black absorber coatings: A1 - A/NiSx, A2 A/AO/NiSx, A3 - A/AO/NiSx/TiO2; inset in the upper left corner: elemental composition graphs

Fig. 4. XRD patterns of substrate A and red absorber coatings: A4 - A/Fe2O3, A5 A/AO/Fe2O3, A6 - A/Fe2O3/TiO2; inset in the upper left corner: elemental composition graphs

The Cl-based Ni compound in the black layer is due to the chemical reactions between NiSx pigment and/or the traces of unreacted precursor (NiCl2) with substrate components, in open air atmosphere. This composition has as result the alteration of coating properties, especially optical ones, proving the chemical instability of NiSx based coating. The composition of the crystalline phases and the overall crystallinity degree (estimated using the device software EVA 1.4) are presented in Table 3. The deposition results in relative thin layers, slightly thicker for Fe2O3, as the XRD show a strong signal coming from the aluminum substrate. No significant changes in the crystallinity degree are observed for NiSx based coatings (80–88%), even though the composition is not the expected one. For red samples, the crystallinity degree varies from 70% (A/AO/Fe2O3) to 92.5% (A/Fe2O3), which demonstrates that the presence of Fe2O3 crystalline phase (100%) in coating composition does not necessarily lead to increased crystallinity and consequently to the improvement of the absorber coating properties. Therefore, the differences in the

276

L. Isac et al.

pigment composition and structure of the investigated absorber coatings may have influence on the optical properties. Table 3. The crystallinity and estimative phases composition in the NiSx and Fe2O3 based absorber coatings obtained by sol-gel spraying Crystalline phase

A

A/NiSx A/AO/NiSx A/AO/NiSx/ TiO2

A/Fe2O3 A/AO/Fe2O3 A/Fe2O3/ TiO2

Crystallinity [%] Al(OH)3 AlOOH Al2O3 Al2O3
H2O NiS1.03 NiS1.125 Ni(ClO4)2
6H2O Fe2O3

93 32.04 51.20 10.58 6.11 – – – –

80 10.82 12.22 – – 13.56 7.38 56.02 –

92.5 4.51 6.27 – – – – – 89.22

87.9 2.13 2.17 – 0.65 21.98 11.94 61.13 –

87.7 2.32 4.34 – 1.51 16.82 9.94 61.69 –

70 – – – – – – – 100

83.4 – – – – – – – 100

The elemental composition analyzed by EDS, also represented in Figs. 3 and Fig. 4, offers information on the surface composition and consequently on the growth and adherence among layers, allowing to accurately design of the final absorber coating. It is interesting that in the coatings with sprayed alumina layer (AO), the increase of the oxygen content is not observed, as expected. Even more, the black coatings shows a decrease of the O content from 60% (weight) in the A/NiSx sample to 45% (in A/AO/NiSx/TiO2). However, for the investigated absorber coatings, the differences registered in the XRD composition are confirmed by EDS results, and the TiO2 crystalline phase is confirmed both by the XRD and EDS (4%Ti) results, for black coating, but is confirmed only by EDS (1.5% Ti) for the red coating, because the layer is so thin that it is not detected by X ray diffraction. In addition to the composition and crystalline structure, surface morphology represents another important property with consequences on the optical properties of an absorber material. As it was already reported [58], porous materials have been introduced as one of the most efficient and affordable solution to improve the heat transfer and energy efficiency in solar coatings. Therefore, the highly porous substrate/alumina matrix represents a good host for further infiltration with pigment layers to develop efficient solar selective absorber coatings, for thermal collectors. According to the SEM images in Fig. 5, the morphologies of the absorber samples are quite different and more or less significantly influenced by the substrate morphology (Fig. 5g). The results confirm that Fe2O3 pigment grains are mostly well infiltrated in the alumina matrix surface pores, but also some large agglomerates are grown (Fig. 5f, sample A/Fe2O3/TiO2) on the thin film. For coating A/AO/Fe2O3 (Fig. 5d), the intermediary sprayed alumina layer seems to favor the formation of smaller Fe2O3 aggregates on it. As result, the reflections of light on this surface are reduced and an increase of thermal emittance value is expected.

Development of Black and Red Absorber Coatings for Solar Thermal Collectors

277

Fig. 5. SEM images of absorber coatings: (a) A/NiSx, (b) A/Fe2O3, (c) A/AO/NiSx, (d) A/AO/Fe2O3, (e) A/AO/NiSx/TiO2, (f) A/Fe2O3/TiO2 and (g) A

Black samples show a lower infiltration with the pigments, because of the very large aggregates of NiSx and Ni(ClO4)2 phases formed on the substrate. This highly fractured morphology along with the composition and structure, obviously influence the optical properties of the black coating, especially by increasing the thermal emittance. For all investigated coatings, these less infiltrated aggregates are likely to leach from the absorber plate during functioning, reducing the durability and causing color deterioration. To assess the solar selectivity of the studied absorber coatings, reflectance spectra registered in the UV-Vis-IR wavelength range (k = 0.28–20 lm) of the substrate, black and red samples are presented in Figs. 6 and 7.

278

L. Isac et al.

Fig. 6. Reflectance spectra in UV-Vis-IR range of NiSx absorber coatings

Fig. 7. Reflectance spectra in range of Fe2O3 absorber coatings

UV-Vis-IR

It can be observed that a significant change in the reflectance spectra is obtained for the absorber layers, comparing with the substrate, inducing a decrease of the reflectivity in the UV-Vis-NIR region, more noticeable for black coating (higher absorption) than for red, as is expected. In IR range, the reflectance increases of about 35–45% for red coatings and about 25% (samples A/AO/NiSx and A/AO/NiSx/TiO2) for black samples, according to the variation of thermal emittance values: lower for red coatings comparing with those for black coatings. As it was expected, from reflectance spectra of the samples and confirmed by Table 4, higher solar absorptance values are obtained for black (as = 0.84–0.95) and good for red (as = 0.64–0.70) coatings. The thermal emittance values are eT = 0.05– 0.12 for red coatings, lower than those of the alumina substrate (eT = 0.22), and much lower than those of the black coatings (eT = 0.41–0.54), in agreement with the lower reflectivity registered in the IR region. According to the crystalline phases composition and surface morphology, the best optical results are obtained for red absorber coatings (S = 5.36–12.8), with higher content of pigment partially infiltrated in the substrate/alumina matrix pores, while for black coatings the spectral selectivity is in the range 1.72–2.04. Table 4. Optical properties for NiSx and Fe2O3 based absorber coatings obtained by sol-gel spraying Sample A A/NiSx A/AO/NiSx A/AO/NiSx/TiO2 A/Fe2O3 A/AO/ Fe2O3 A/Fe2O3/TiO2

as 0.11 0.93 0.84 0.95 0.64 0.69 0.70

eT S 0.22 0.50 0.54 1.72 0.41 2.02 0.52 1.82 0.05 12.8 0.12 5.36 0.12 5.83

Development of Black and Red Absorber Coatings for Solar Thermal Collectors

279

This is an important result, as there already are mature technologies for black coatings (allowing better selectivity) but much less technologies are reported for red coatings. The lab technology hereby outlined (sol-gel synthesis of colored powder pigments + spray deposition) can be further applied for various colored pigments.

4 Conclusions The development of novel solar thermal collectors is now recognized as a proven technology in terms of reliability, cost-benefit and low environmental impact. Besides increasing the efficiency and durability, the architectural integration of solar thermal collectors represents an important research topic, colored solar collectors being aesthetically preferred to black or dark blue ones. A review of the different types (intrinsic, semiconductor-metal, multilayer and cermet composite) of selective absorber coatings reported for black and colored solar thermal collectors obtained world-wide is presented, along with the results obtained by the group active in the R&D Centre Renewable Energy Systems and Recycling. The development and optimization of black and colored absorber coatings, based on infiltration of NiSx, respectively Fe2O3 sol-gel pigments from dispersions sprayed on the substrate/alumina matrix is presented in detail. The results reporting a spectral selectivity of 12.8 for the red coating, show the suitability and affordability of these absorber coatings as promising materials for novel, market-acceptable solar thermal collectors, with increased architectural acceptance, for facades integration in Nearly Zero Energy Buildings. Acknowledgments. We hereby acknowledge the structural founds project PRO-DD (POS-CCE, O.2.2.1., ID 123, SMIS 2637, No 11/2009) for providing the infrastructure used in this work and the project EST IN URBA, PN-II-PT-PCCA-2011-3.2-051, in the frame of the Program: Cooperation in Priority Fields - PNII, developed with the support of ANCS, CNDI-UEFISCDI, Romania.

References 1. Zhang, K., Hao, L., Du, M., Mi, J., Wang, J.-N., Meng, J.: A review on thermal stability and high temperature induced ageing mechanisms of solar absorber coatings. Renew. Sustain. Energy Rev. 67, 1282–1299 (2017) 2. Colangelo, G., Favale, E., Miglieta, P., Risi, A.: Innovation in flat solar thermal collectors: A review of the last ten years experimental results. Renew. Sustain. Energy Rev. 57, 1141– 1159 (2016) 3. Sun, X.-Y., Sun, X.-D., Li, X.-G., Wang, Z.-Q., He, J., Wang, B.-S.: Performance and building integration of all-ceramic solar collectors. Energy Build. 75, 176–180 (2014) 4. Fernandes, J.C.S., Nunes, A., Carvalho, M.J., Diamantino, T.C.: Degradation of selective solar absorber surfaces in solar thermal collectors - an EIS study. Sol. Energy Mater. Sol. Cells 160, 149–163 (2017)

280

L. Isac et al.

5. Visa, I., Moldovan, M.D., Comsit, M., Neagoe, M., Duta, A.: Facades integrated solar-thermal collectors - challenges and solutions. Energy Procedia 112, 176–185 (2017) 6. Dan, A., Chattopadhyay, K., Barshilia, H.C., Basu, B.: Colored selective absorber coating with excellent durability. Thin Solid Films 620, 17–22 (2016) 7. Isac, L., Nicoara, L., Panait, R., Enesca, A, Perniu, D., Duta, A.: Alumina matrix with controlled morphology for colored spectrally selective coatings. Environ. Eng. Manag. J. 16(3), 715–724 (2017) 8. Bermel, P., Ghebrebrhan, M., Chan, W., Yeng, Y.X., Araghehini, R.H., Marton, C.H., Jensen, K.F., Soljačić, M., Joannopoulos, J.D., Johnson, S.G., Celanovic, I.: Design and global optimization of high-efficiency thermophotovoltaic systems. Opt. Express 18, A314– A334 (2010). https://doi.org/10.1364/OE.18.00A314 9. Zhu, D., Zhao, S.: Chromaticity and optical properties of colored and black solar-thermal absorbing coatings. Sol. Energy Mater. Sol. Cells 94, 1630–1635 (2010) 10. Estrella-Gutiérrez, M.A., Lizama-Tzec, F.I., Arés-Muzio, O., Oskam, G.: Influence of a metallic nickel interlayer on the performance of solar absorber coatings based on black nickel electrodeposited onto copper. Electrochim. Acta 213, 460–468 (2016) 11. Voinea, M., Ienei, E., Bogatu, C., Duta, A.: Solar selective coatings based on nickel oxide obtained via spray pyrolysis. J. Nanosci. Nanotechnol. 9, 4279–4284 (2009) 12. Katumba, G., Olumekor, L., Forbes, A., Makiwa, G., Mwakikunga, B., Lu, J., Wäckelgård, E.: Optical, thermal and structural characteristics of carbon nanoparticles embedded in ZnO and NiO as selective solar absorbers. Sol. Energy Mater. Sol. Cells 92, 1285–1292 (2008) 13. Barshilia, H.C., Kumar, P., Rajam, K.S., Biswas, A.: Structure and optical properties of Ag-Al2O3 nanocermet solar selective coatings prepared using unbalanced magnetron sputtering. Sol. Energy Mater. Sol. Cells 95, 1707–1715 (2011) 14. Balakrishnan, G., Tripura Sundari, S., Ramaseshan, R., Thirumurugesan, R., Mohandas, E., Sastikumar, D., Kuppusami, P., Kim, T.G., Song, J.I.: Effect of substrate temperature on microstructure and optical properties of nanocrystalline alumina thin films. Ceram. Int. 39, 9017–9023 (2013) 15. Murali, K.R., Thirumoorthy, P.: Characteristics of sol-gel deposited alumina films. J. Alloy. Compd. 500(1), 93–95 (2010) 16. Olarinoye, I.O., Ogundare, F.O.: Optical and microstructural properties of neutron irradiated RF-sputtered amorphous alumina thin films. Optik 134, 66–77 (2017) 17. Kathirvel, P., Chandrasekaran, J., Manoharan, D., Kumar, S.: Deposition and characterization of alpha alumina thin films prepared by chemical bath deposition. Optik – Int. J. Light Electron Optics 126, 2177–2179 (2015) 18. Duta, A., Isac, L., Milea, A., Ienei, E., Perniu, D.: Coloured solar-thermal absorbers - a comparative analysis of cermet structures. Energy Procedia 48, 543–553 (2014) 19. Wu, S., Cheng, C.-H., Hsiao, Y.-J., Juang, R.-C., Wen, W.-F.: Fe2O3 films on stainless steel for solar absorbers. Renew. Sustain. Energy Rev. 58, 574–580 (2016) 20. Sudagar, A.J., Subasri, R.: Fabrication and characterization of silver/nickel sulphide solar absorber coatings on stainless steel by chemical bath deposition. Mater. Chem. Phys. 163, 478–484 (2015) 21. Bermel, P., Lee, J., Joannopoulos, J.D., Celanovic, I., Soljačić, M.: Selective solar absorbers. Ann. Rev. Heat Transfer 15, 231–254 (2012). doi:10.1615/AnnualRevHeatTransfer. 2012004119. Chap. 7 22. Céspedes, E., Wirz, M., Sánchez-García, J.A., Alvarez-Fraga, L., Escobar-Galindo, R., Prieto, C.: Novel Mo-Si3N4 based selective coating for high temperature concentrating solar power applications. Sol. Energy Mater. Sol. Cells 122, 217–225 (2014)

Development of Black and Red Absorber Coatings for Solar Thermal Collectors

281

23. Joly, M., Antonetti, Y., Python, M., Gonzalez, M., Gascou, M., Scartezzini, J.-L., Schüler, A.: Novel black selective coating for tubular solar absorbers based on a sol-gel method. Sol. Energy 94, 233–239 (2013) 24. Barshilia, H.C., Selvakumar, N., Rajam, K.S., Biswas, A.: Spectrally selective NbAlN/NbAlON/Si3N4 tandem absorber for high temperature solar applications. Sol. Energy Mater. Sol. Cells 92, 495–504 (2008) 25. Gaouyat, L., He, Z., Colomer, J.F., Lambin, P., Mirabella, F., Schryvers, D., Deparis, O.: Revealing the innermost nanostructure of sputtered NiCrOx solar absorber cermets. Sol. Energy Mater. Sol. Cells 122, 303–308 (2014) 26. Santibãnez, A., Herrera-Trejo, M., Oliva, J., Martinez, A.I.: Electrochemical deposition of Ni-Fe alloys into porous alumina for solar selective absorbers. Superlattices Microstruct. 100, 972–983 (2016) 27. Ziabari, A.A., Khatibani, A.B.: Optical properties and thermal stability of solar selective absorbers based on Co-Al2O3 cermets. Chin. J. Phys. 1–10 (2017). https://doi.org/10.1016/j. cjph.2017.02.015 28. Purghel, E., Voinea, M., Isac, L., Duta, A.: Optical properties of Ni/NiOx as infiltration agent in cermet solar Ir absorber. Rev. Chim. 59, 469–471 (2008) 29. Dudita, M., Isac, L., Duta, A.: Influence of solvents on properties of solar selective coatings obtained by spary pyrolysis. Bull. Mater. Sci. 35, 997–1002 (2012) 30. Wu, Y., Zheng, W., Lin, L., Qu, Y., Lai, F.: Colored solar selective absorbing coatings with metal Ti and dielectric AlN multilayer structure. Sol. Energy Mater. Sol. Cells 115, 145–150 (2013) 31. Xiao, X., Miao, L., Xu, G., Lu, L., Su, Z., Wang, N., Tanemura, S.: A facile process to prepare copper oxide thin films as solar seletive absorbers. Appl. Surf. Sci. 257, 10729– 10736 (2011) 32. Boström, T.K., Westin, G., Wäckelgård, E.: Optimization of a solution-chemically derived solar absorbing spectrally selective surface. Sol. Energy Mater. Sol. Cells 91, 38–43 (2007) 33. Geng, Q., Zhao, X., Gao, X., Yu, H., Yang, S., Liu, G.: Optimization design of CuCrxMn2-xO4-based paint coatings used for solar selective applications. Sol. Energy Mater. Sol. Cells 105, 293–301 (2012) 34. Isac, L., Eneșca, A., Mihoreanu, C., Perniu, D., Duță, A.: Spectrally solar selective coatings for colored flat plate solar thermal collectors. In: Visa, I. (ed.) Sustainable Energy in the Built Environment - Steps Towards nZEB part II, pp. 279–298. Springer, Cham (2014). http://link. springer.com/book/10.1007/978-3-319-09707-7 35. Milea, C.A., Ienei, E., Bogatu, C., Duta, A.: Sol-gel Al2O3 powders - matrix in solar thermal absorbers. J. Sol-Gel. Sci. Technol. (2013). doi:10.1007/s10971-013-3056-z 36. Ienei, E., Milea, A.C., Duta, A.: Influence of spray pyrolysis deposition on the optical properties of porous alumina films. Energy Procedia 48, 97–104 (2014) 37. Chate, P.A., Sathe, D.J.: Structural, electrical and thermoelectrical analysis of nickel sulphide thin films. Appl. Phys.: A Mater. Sci. Process. 122, 600 (2016). doi:10.1007/ s00339-016-0117-5 38. Yang, J., Guo, W., Li, D., Wei, C., Fan, H., Wu, L., Zheng, W.: Synthesis and electrochemical performances of novel hierarchical flower-like nickel sulfide with tunable number of composed nanoplates. J. Power Sources 268, 113–120 (2014) 39. Yin, P., Han, X., Zhou, C., Xia, C., Hu, C., Sun, L.: Large-scale synthesis of nickel sulfide micro/nanorods via a hydrothermal process. Int. J. Miner. Metall. Mater. 22(7), 762–769 (2015). doi:10.1007/s12613-015-1132-9 40. Nagaveena, S., Mahadevan, C.K.: Preparation by a facile method and characterization of amorhous and crystalline nickel sulfide nanophase. J. Alloy. Compd. 582, 447–456 (2014)

282

L. Isac et al.

41. Patil, A.M., Lokhande, A.C., Chodankar, N.R., Kumbhar, V.S., Lokhande, C.D.: Engineered morphologies of b-NiS thin films via anionic exchange process and their supercapacitive performance. Mater. Des. 97, 407–416 (2016) 42. Boughalmi, R., Rahmani, R., Boukhachem, A., Amrani, B., Driss-Khodja, K., Amlouk, M.: Metallic behavior of NiS thin film under the structural, optical, electrical and ab initio investigation frameworks. Mater. Chem. Phys. 163, 99–106 (2015) 43. Al-Kuhaili, M.F., Saleem, M., Durrani, S.M.A.: Optical properties of iron oxide (a-Fe2O3) thin films deposited by the reactive evaporation of iron. J. Alloys Compd. 521, 178–182 (2012) 44. Goyal, R.N., Kaur, D., Pandey, A.K.: Growth and characterization of iron oxide nanocrystalline thin films via low-cost ultrasonic spray pyrolysis. Mater. Chem. Phys. 116, 638–644 (2009) 45. Kayani, Z.N., Khan, E.S., Saleemi, F., Riaz, S., Naseem, S.: Optical and magnetic properties of iron oxide films. Mater. Today: Proc. 2, 5568–5571 (2015) 46. Gao, G., Zhang, Q., Wang, K., Song, H., Qiu, P., Cui, D.: Axial compressive a-Fe2O3 microdisks prepared from CSS template for potential anode materials of lithium ion batteries. Nano Energy 2, 1010–1018 (2013) 47. Saleem, M., Durrani, S.M.A., Saheb, N., Al-Kuhaili, M.F., Bakhtiari, I.A.: The effect of annealing on structural and optical properties of a-Fe2O3/CdS/a-Fe2O3 multilayer heterostructures. Appl. Surf. Sci. 320, 653–657 (2014) 48. Mishra, M., Chun, D.-M.: a-Fe2O3 as photocatalytic material: A review. Appl. Cathalysis A: Gen. 498, 126–141 (2015) 49. Zhang, M., Pu, W., Pan, S., Okoth, K.O., Yang, C., Zhang, J.: Photoelectrocatalytic activity of liquid phase deposited a-Fe2O3 films under visible light illumination. J. Alloy. Compd. 648, 718–725 (2015) 50. Cheng, L., Qiu, S., Chen, J., Shao, J., Cao, S.: A practical pathway for the preparation of Fe2O3 decorated TiO2 photocatalyst with enhanced visible-light photoactivity. Mater. Chem. Phys. 190, 53–61 (2017) 51. Vanags, M., Sutka, A., Kleperis, J., Shipkov, P.: Comparison of the electrochemical properties of hematite thin films prepared by spray pyrolysis and electrodeposition. Ceram. Int. 41, 9024–9029 (2015) 52. Jang, J.T., Ryu, H., Lee, W.J.: The growth of hematite by electrochemical deposition for PEC applications. J. Alloy. Compd. 638, 387–392 (2015) 53. Akbar, A., Imran, M., Riaz, S., Naseem, S.: Study of phase transition in iron oxide thin films. Mater. Today: Proc. 2, 5405–5409 (2015) 54. Velásquez, A.A., Marín, C.C., Urquijo, J.P.: Growth of magnetite films by a hydrogel method. J. Magn. Magn. Mater. 432, 190–197 (2017) 55. Amri, A., Jiang, Z.T., Pryor, T., Yin, C.-Y., Djordjevic, S.: Developments in the synthesis of flat plate solar selective absorber materials via sol-gel methods: a review. Renew. Sustain. Energy Rev. 63, 316–322 (2014) 56. Covei, M., Gartner, M., Mihaiu, S.: Transparent Conducting Oxides in Solar Energy Conversion. Transilvania University Publishing House, Lexington (2016) 57. Yung, D.S., Park, S.B., Kang, Y.C.: Design of particles by spray pyrolysis and recent progress in its application. Korean J. Chem. Eng. 27(6), 1621–1645 (2010). doi:10.1007/ s11814-010-0402-5 58. Rashidi, S., Esfahani, J.A., Rashidi, A.: A review on the applications of porous materials in solar energy systems. Renew. Sustain. Energy Rev. 73, 1198–1210 (2017)

A New Approach on the Protection Against Overheating of Flat Plate Solar-Thermal Collectors Mircea Neagoe, Ion Visa, Anca Duta, and Nadia Cretescu(&) Renewable Energy Systems and Recycling Research Center, Transilvania University of Brasov, Brasov, Romania [email protected]

Abstract. A large variety of methods and techniques are nowadays used to protect the flat plate solar-thermal collectors against overheating occurring during stagnation periods. The overheating leads to increased temperatures in the collector over the design values and negative effects on the absorber plate conversion efficiency, fast aging of system components and heat thermal fluid degradation can be involved, reducing the collector durability, safety and reliability. Many of the known solutions for avoiding overheating are applied only after the heat was generated and thus the thermal stress is still acting on the collector. The authors proposes the new approach of inverse tracking that allows to minimize the input solar radiation coming into the collector in stagnation, consequently limiting the heat production and implicitly the collector’s temperature. The procedure of inverse tracking is proved in the paper as an efficient and affordable solution for protecting against overheating the already tracked collectors, based on theoretical results well complying with experimental data registered in an outdoor testing setup. Keywords: Solar thermal collector Inverse tracking




Stagnation




Overheating protection




1 Introduction A flat plate solar-thermal collector (FPSTC) comes into stagnation when the produced thermal energy is no longer removed by the heat carrier, i.e. no flow of the heat transfer fluid (HTF) is carried out from the collector [1, 2]. The solar circuit pump may be out of work in different circumstances, in the normal operation mode when the maximum allowed temperature of the heat storage tank is reached, as well as in abnormal situations like pump failure, power supply blackout, failure of other equipment component, etc. [3, 4]. A solar-thermal collector is overheated if, under the action of the received solar radiation, the temperatures of its critical components - the absorber plate and HTF exceed the design threshold values and their degradation may occur [5]. For this reason, the design of a solar-thermal system has to consider specific technical solutions to efficiently cope with the stagnation effects and to avoid overheating. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_21

284

M. Neagoe et al.

The main negative overheating impacts on the solar-thermal systems can be classified as follows: (a) Absorber plate: permanent deformation of the thin absorber plate under thermal expansion due to the contour mechanical constraints [6]; micro-cracks in the ceramic coatings [7], leading to decreasing the collector efficiency and lifetime; (b) Anti-freeze HTF: chemical decomposition into corrosive substances damaging in time the solar circuit components [8, 9]; (c) System components (pipes, valves, vents, membrane type expansion vessels, pumps, rubber seals, non-metal components, heat exchangers, etc.): formation of vapor bubbles and water-hammer effect occurring when the HTF is evaporated and superheated [3], the penetration of the vapour into the solar circuit can damage the system components [6]; (d) Environment pollution: when the HTF vapours escape into atmosphere [10]. An impressive number of solutions to avoid overheating have been reported in literature and implemented in practice. All these measures act on different levels of intervention (Fig. 1) in correlation with the components of an FPSTC, aiming at: (a) Reducing the amount of incident solar radiation (Gn) on the absorber plate (level I); thus, the production of excess heat and implicitly the additional measures for heat removal from the collector are avoided; (b) Reducing the conversion efficiency of the solar radiation Gn into thermal energy by interventions on the absorber coating in stagnation (level II); (c) Limiting the heat transfer to HTF (level III), a measure designed to limit the HTF temperature; (d) Removing the heat stored in the HTF and implicitly reducing its temperature (level IV). The paper presents in the first part a brief description of the most common and efficient protection methods against overheating, according to the previous systematization of the intervention levels (Fig. 1), followed by the analytical modeling of the time evolution of the HTF temperature in stagnation. In the second part of the paper the efficiency of the inverse tracking procedure is theoretically and experimentally investigated, as a level I method in the protection of the flat plate solar-thermal collectors with liquid HTF.

2 Methods for Protection Against Overheating The received global solar radiation, noted as Gn in Fig. 1, is the main responsible factor for the rapid change in the collector’s temperature during stagnation and fast access to overheating. Several methods were identified in literature aiming at decreasing the amount of solar energy reaching the collector absorber (Fig. 1, level I) and thus diminishing the temperature on the absorber and thus the temperature of the carrier fluid.

A New Approach on the Protection Against Overheating of Flat Plate Solar-Thermal

285

Sun Limiting level

Intervention level

A I

Gn

Glazing

B C Absorber

II

D

Gn Q

III Q HTF

IV

Heat transfer fluid (HTF)

E

Flow tubes

F

Remove Q from HTF Insulation

G

Housing

H

Fig. 1. The components of a flat plate solar-thermal collector and the levels of protection against overheating during stagnation

The simplest method used to limit the access of the solar radiation into the collector, especially of the direct irradiance, is to cover or shade the collector during stagnation periods (Fig. 1, level A). Manual coverage with a protective casing is reported in domestic accessible applications, with the drawback of human intervention

286

M. Neagoe et al.

whenever the case. Automatic systems to partially or totally cover the collector were proposed in literature [6], but these can be expensive and inefficient in snowing areas. A total collector coverage can block approximatively 90% of the solar radiation [9]. A recent and very much investigated method applied for passive overheating protection is to cover the collector with thermotropic materials or changing the glazing materials (Fig. 1, level B). The thermotropic materials are able to significantly modify their transmittance and reflectance at high temperature [11, 12], as the solar transmittance can vary from >85% in the clear state to 68°) and significant decrease of the time interval in which the direct radiation is received (*8:00–16:00) are also highlighted (Fig. 3b). The maximum HTF average temperature still reaches higher values (*107°), but below the thermal cracking threshold. An approach with higher efficiency in reducing the thermal stress of the collector in stagnation by inverse tracking is to additionally apply a counter-phase diurnal movement (Fig. 3c): • the HTF temperature is maintained below 90 °C for a limited stroke Wn = ±45° (scenario 2); • for a larger stroke, Wn = ± 90° in scenario 3, the amount of received direct radiation becomes null as the incidence angle is greater than 90° throughout the day. Consequently, only the diffuse radiation acts on the collector and the HTF temperature registers values with *10 °C higher than the ambient temperature. According to these results, inverse tracking is theoretically proved as an effective protection method against overheating, in particular by applying the maximum counter-phase orientation to allow high incidence angles, ideally m > 90° for the entire period of stagnation.

A New Approach on the Protection Against Overheating of Flat Plate Solar-Thermal

(a) Global solar irradiance [W/m2]

1100

291

Summer sols ce (N=172)

1000 900 G Gn(αn=45°, Ψn=0°) Gn(αn=0°, Ψn=0°) Gn(αn=0°, Ψn=±45°) Gn(αn=0°, Ψn=±90°)

800 700 600 500 400 300 200

ts [h]

100 0 4

Incidence angle [°]

(b)

HTF temperature [°C]

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 υ(αn=45°, Ψn=0°) υ(αn=0°, Ψn=0°) υ(αn=0°, Ψn=±45°) υ(αn=0°, Ψn=±90°)

180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

ts [h] 4

(c)

5

5

190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20

Ta Tf(αn=45°, Ψn=0°) Tf(αn=0°, Ψn=0°) Tf(αn=0°, Ψn=±45°) Tf(αn=0°, Ψn=±90°)

ts [h] 4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20

Fig. 3. Comparative simulated results of inverse tracking vs. fixed tilt collectors for summer solstice (N=172), Brasov, Romania: a variation of the available (G) and received (Gn) global solar irradiances, b variation of the incidence angle (m), c estimated variation of the HTF temperature in stagnation for a given evolution of the ambient air temperature (Ta)

292

4.2

M. Neagoe et al.

Experimental Validation

The experimental research of the FPSTC thermal behaviour in stagnation was carried out on an outdoor testing rig installed at the RESREC Research Centre within the R&D Institute of the Transilvania University of Brasov, Romania. This stand (Fig. 4) has two flat plate solar-thermal collectors connected to a heat storage tank by independent hydraulic circuits and a dual-axis tracking system able to position the FPSTC in a quasi-vertical configuration (an = 10°…90°) and to get a large diurnal stroke DWn = 200° (±100°), by using a rotary actuator (pos. 5a in Fig. 4b, for diurnal motion Wn) and two linear actuators for the elevation motion an (pos. 5b, Fig. 4b). The experimental rig allows to register the collector inlet and outlet temperatures as well as the global irradiance measured in the collector plane.

Fig. 4. Experimental outdoor rig of RESREC R&D Center: dual-axis tracking system with two FPSTCs (an = 10°…90°, Wn = −100°…+100°): a front side, b back side (1 - FPSTCs; 2 pyranometers; 3, 4 - temperature sensors; 5 - actuators)

The numerical simulation and the experimental tests were performed for June 1st, 2016, a mostly clear sky day, by applying a maximum inverse tracking algorithm (i.e. Wn = ±100° and an = 10°) and considering the actual values of the ambient air temperature Ta recorded by the RESREC Centre weather station. The theoretical results (Fig. 5a) show that a variation of the HTF average temperature close to the ambient temperature is estimated in this case, Tm = Ta + (0…13 °C), except for a short time range at solar noon when the incidence angle lowest values are recorded (m = 84° … 90° in the time range [11:36–12:24]), accompanied by a rapid increase in the received global radiation and HTF temperature. Also, the transition at solar noon from the stationary position during the morning (Wn = −100°) to the one in the afternoon (Wn = +100°) causes the collector to be exposed to a higher radiation for about 1–2 min.

A New Approach on the Protection Against Overheating of Flat Plate Solar-Thermal

293

The experimental data depicted in Fig. 5b highlight a qualitative and quantitative evolution of the represented parameters similar to the values estimated by theoretical modeling. Thus, there is a good match between the shape and level of variation of the received global radiation Gn and HTF average temperature Tm. However, the estimated peak temperature Tm at noon is experimentally confirmed in this case study only

(a)

T [oC]

G [W/m2]

100

1000

90

900 Gh

80

800

70

700

60

600

Τm

50 40

500 400

Τa

30

300

20

200 Gn

10

100 ts [h]

0

0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

(b)

T [oC]

G [W/m2]

100 90

1000 900

Gh

80

800

70

700

60 50 40

600

Τm

500 400

Τa

30

300

20 10 0

200 Gn

100 ts [h]

0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Fig. 5. Modeled vs. registered data on 01.06.2016, Brasov, Romania (an = 10°, Wn = ±100°): a modeled results with measured Ta values, b registered experimental data (Gh - global irradiance measured in the horizontal plane)

294

M. Neagoe et al.

partially, the recorded data showing a sharp decrease in the Tm temperature, correlated with a Gn decrease due to significant fluctuations in the available radiation during this time period.

5 Conclusions Avoiding overheating of FPSTC in stagnation is a critical design requirement, given the possible negative effects of this phenomenon on the solar-thermal system appropriate functioning and lifetime. This requirement imposes the identification and implementation of additional measures able to be activated when the solar thermal system comes into stagnation. Based on the selected review solutions, the paper proposes and investigates the efficiency of the inverse tracking method in protecting the tracked FPSTC as an approach allowing to reduce the amount of the received solar radiation - the main input factor that causes rapid variations in HTF temperature during stagnation. This approach aims at avoiding the heat production by solar energy conversion in stagnation and does not entail additional investment costs for solar thermal systems that have already implemented solar tracking systems, requiring only an additional command-control system configuration complying with the stagnation management requirements. The results show that, theoretically, by maximum inverse tracking it is possible to reduce down to zero the received direct irradiance Bn and to significantly decrease the amount of received diffused irradiance Dn. Experimental investigations show that in this situation, the collector temperature follows closely (with differences of about +10°) the ambient air temperature and thus ensures a minimal thermal load of the collector and implicitly an increased lifetime of the system. Acknowledgments. This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI-UEFISCDI, project no PN-III-P2-2.1PED-2016-0338, within PNCDI III.

References 1. Weiss, W.: Solar Heating Systems for Houses. A Design Handbook for Solar Combisystems. James & James, London (2003) 2. Hausner, R., Fink, C.: Stagnation behaviour of thermal solar systems. A report of IEA SHC task 26, Solar Combysystems (2002). http://task26.iea-shc.org. Accessed June 2017 3. Thiesen, S.: Simple and safe solar heating: a whole systems approach. Pacific J. Sci. Technol. 10(1), 117–122 (2009) 4. Marken, C.: Overcoming Overheating. Home Power Review, vol. 142 (2011). http://www. homepower.com/articles/solar-water-heating/domestic-hot-water/overcoming-overheating. Accessed June 2017 5. Frank, E., Mauthner, F., Fischer, S.: Overheating prevention and stagnation handling in solar process heat applications, Technical Report A.1.2, IEA SHC Task 49 (2015). http://task49. iea-shc.org. Accessed June 2017

A New Approach on the Protection Against Overheating of Flat Plate Solar-Thermal

295

6. Harrison, S., Cruickshank, C.A.: A review of strategies for the control of high temperature stagnation in solar collectors and systems. Energy Procedia 30, 793–804 (2012) 7. Neagoe, M., Visa, I., Burduhos, B.G., Moldovan, M.D.: Thermal load based adaptive tracking for flat plate solar collectors. Energy Procedia 48, 1401–1411 (2014). doi:10.1016/j. egypro.2014.02.158 8. Hausner, R., Fink, C.: Stagnation behaviour of thermal solar systems. EUROSUN, Copenhagen, Denmark (2000) 9. Overheating Protection for Solar Collectors. www.radiantcompany.com/system/solar/ heatdump/. Accessed April 2017 10. Streicher, W.: Minimising the risk of water hammer and other problems at the beginning of stagnation of solar thermal plants - a theoretical approach. EUROSUN, Copenhagen (2000) 11. Gladen, A., Davidson, J., Mantell, S.C.: Selection of thermotropic materials for overheat protection of polymer absorbers. Sol. Energy 104, 42–51 (2014) 12. Muehling, O., Seeboth, A., Ruhmann, R., Eberhardt, V., Byker, H., Anderson, C., De Jong, S.: Solar collector cover with temperature-controlled solar light transmittance. Energy Procedia 48, 163–171 (2014) 13. Resch, K., Wallner, G.M.: Thermotropic layers for flat-plate collectors - a review of various concepts for overheating protection with polymeric materials. Solar Energy Mater. Solar Cells 93, 119–128 (2009) 14. Weber, A., Resch, K.: Thermotropic glazings for overheating protection. Energy Procedia 30, 471–477 (2012) 15. Resch, A., Wallner, G., Hausner, R.: Phase separated thermotropic layers based on UV cured acrylate resins - Effect of material formulation on overheating protection properties and application in a solar collector. Sol. Energy 83, 1689–1697 (2009) 16. Gladen, A., Davidson, J., Mantell, S.C., Zhang, J., Xu, Y.: A model of the optical properties of a non-absorbing media with application to thermotropic materials for overheat protection. Energy Procedia 30, 116–124 (2012) 17. Paone, A., Geiger, M., Sanjines, R., Schüler, A.: Thermal solar collector with VO2 absorber coating and V1-xWxO2 thermochromic glazing - Temperature matching and triggering. Sol. Energy 110, 151–159 (2014) 18. Slaman, M., Griessen, R.: Solar collector overheating protection. Sol. Energy 83, 982–987 (2009) 19. Paone, A., Schüler, A.: Advanced switchable selective absorber coatings for overheating protection of solar thermal collectors (2011). http://www.bfe.admin.ch/php/modules/enet/ streamfile.php?file=000000011297.pdf&name=000000291055. Accessed June 2017 20. Heat pipes in solar collectors - thermodynamic fundamentals and evaluation plus new approaches of application. www.isfh.de/institut_solarforschung/waermerohre-in-sonnenkolle ktoren.php?_l=1. Accessed June 2017 21. Goswami, D.J.: Principles of Solar Engineering, 3rd edn. CRC Press, USA (2015) 22. Kalogirou, S.A.: Solar thermal collectors and applications. Progress Energy Combust. Sci. 30, 231–295 (2004) 23. Duffie, J.A., Beckman, W.A.: Solar Engineering of Thermal Processes, 4th edn. Wiley, Hoboken (2013). ISBN 978-0-470-87366-3 24. Visa, I., Jaliu, C., Duta, A., Neagoe, M., Comsit, M., Moldovan, M., Ciobanu, D., Burduhos, B., Saulescu, R.: The role of mechanisms in sustainable energy systems. Transilvania University Publishing House, Brasov (2015) 25. Meliss, M.: Regenerative Energiequellen - Praktikum. Springer, Berlin (1997) 26. Burduhos, B.G., Visa, I., Neagoe, M., Badea, M.: Modeling and optimization of the global solar irradiance collecting efficiency. Int. J. Green Energy 12(7), 743–755 (2015)

Numerical Assessment of a Dynamic Daily Heating Unit Using Both Solar Collector and Heat Pump Coupled in a Dynamic Working Mugurel-Florin Talpiga(&), Eugen Mandric, and Florin Iordache Faculty of Building Services, Technical University of Civil Engineering of Bucharest, Bucharest, Romania [email protected]

Abstract. Solar energy is commonly used in heating systems as unconventional heat source. Assuming that in low solar radiation day, temperature obtained from collectors haven’t desired value for space heating, presented paper reveal the solution of a heat pump system, to satisfy heating demand, using the heat accumulated in active collectors period. The system considered work in both hypotheses, firstly in two distinct periods, charging and discharging of accumulated energy, and secondly in a mixt activity when the heat pump can start working in same time with heat accumulation due to collectors running. Day parameters, in terms of solar radiation and external ambient temperature, will be used to simulate the system functioning and different results are presented to reveal the working conditions, the energy balance between solar and electrical energy used by heat pump and advantages of such system. High COPCD for 2 March was obtained, with values greater than 7.85 for 120 L/m2 specific volume. Keywords: Solar assisted
Heat pump
Hybrid
Dynamic working
Heating unit

1 Introduction The solar energy used in systems that combined solar collectors and heat pump, conduct to high coefficient performance and reduce the primary energy demand [1–4]. Solar energy represents the highest available and clean energy that enter into earth atmosphere day by day, satisfying energy necessity for life support but also to heat up the planet. Commonly named solar irradiance, the energy is transferred to our planet due to temperature differences between Sun and Terra surfaces. Until today, the solar energy trapped in fossils was intensively used as primary heat source for space heating. An increasing trend to use alternative energies is a top priority today in space heating. Technologies that use alternative energy such solar radiation are subjected to research and development for efficiency improvement, decrease of installation cost and innovative technology mixing to assure the heating demand. To achieve this purpose

© Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_22

Numerical Assessment of a Dynamic Daily Heating Unit

297

researchers have a lot of possibilities, generally being used theoretical analyse of physical models, experimental results or numerical simulation of known systems. One of commonly used strategy is to define a numerical model, for simulation purpose, based on a theoretical study of the system considered. Heat source for daily hot water preparation, in temperate area, composed from solar collectors and heat accumulator, are generally not used in winter, intermediary period autumn-winter and winter-spring or in winter sunny days due to less amount of solar radiation available correlated with low number of daily hours. This is an energy loss due to no work of installed system but in general, temperature obtained inside accumulator is not sufficient to sustain the heating even on low temperature heating systems. The heat gained, when system work in assumed periods, can be used if the temperature is increased. In this paper both, solution and methodology to be used for numerical simulation are proposed. The mathematical model for simulation will be described and final equations will be provided and used to create the results for specific warm and cold days for comparison. Simulation results are based on mathematical model of the system and with input data climatic values of solar radiation and external ambient temperature for temperate areas. The model is a dynamic approach due to variable climatic data used. Analyze of simulation data will be focused on thermal parameters, specific energy performance and thermal behavior of involved system components.

2 Material In cold sunny days periods such transition between autumn and winter, winter and spring or even in winter, sun can increase the temperature of the thermal agent used in solar collectors systems installed on residential buildings, but not used due to low temperature assumption. The heat accumulated is a resource lost if not used. This paper presents the method to take all that heat and used in the heating system of the building, over the night. By suction due to evaporator boiling of the heat pump, the heat is transferred to the heating system using specific refrigerator driven by the heat pump compressor. In this way, the heat accumulated in charging period is used to increase the temperature of thermal agent at the condenser. Different solutions for hybrid systems are presented today in R&D, solar collectors and heat-pumps being used to prepare the thermal agent or hot water for heating purpose. In (Fig. 1) is presented schematically the hydraulic functioning of the system supposed. The solution is built from flat panel solar collector 1 through which a thermal agent is drive by the pump 2. Additionally are used the expansion tank 3 to keep the pressure of fluid at intended value and the immersed coil 4 used for discharging the heat from thermal agent. In tank 5 the heat is accumulated over the sunny days and used in the discharging period by heat pump 7, with evaporator 6 immersed, through which the refrigerant is circulated at low pressure state. Because of this, heat is discharged directly by the immersed evaporator, to increase efficiency, and the heat obtained at condenser of the heat pump is used in a low temperature heating system.

298

M.-F. Talpiga et al.

Fig. 1. System diagram

3 Method 3.1

Solar Collector and Tank Accumulator

Solar collector is commonly described by absorption of solar radiation through glass film, where a part of radiation is reflected to the ambient and remaining radiation absorbed by the plate surface. The thermal agent driven inside solar collector will increase his temperature due to this effect, and a part of transferred energy is lost to the environment because of heat transfer coefficient of the collector. The Eq. (1) synthesizes all those as such called equivalent temperature [5] were is tacked into account solar radiation and external ambient temperature, together with physical properties of solar panel: tE ¼

as I þ te kc

ð1Þ

where, tE is equivalent temperature which contain solar radiation data I and external ambient temperature te. Physical properties of solar collector are a absorptivity, s transparency coefficient and kc solar collector heat transfer coefficient. The thermal balance of solar collector is done by Eq. (2) were tT is exit temperature of thermal agent passing collector, tR is inlet temperature and EC is thermal module of collector, defined with Eq. (3) [6]: tT ¼ EC
tR þ ð1  EC Þ
tE
 F 0
k C
SC EC ¼ exp  G
q
c

ð2Þ ð3Þ

where, F′ is surface correction factor of solar collector, SC is solar collector surface.

Numerical Assessment of a Dynamic Daily Heating Unit

299

The thermal agent flow G with its physical properties density ⍴ and heat capacity c take the absorbed heat and discharge it internal accumulator tank through the immersed coil. The thermal balance between coil and tank is given by Eq. (4), were ES is thermal module of the coil, tank temperature h and already known input and output temperatures of solar collector: tR ¼ ES
tT þ ð1  ES Þ
h
 k S
SS ES ¼ exp  G
q
c

ð4Þ ð5Þ

In Eq. (5) we do not have any more a correction factor and the thermal agent is the same. Now, we should make the correlation of mathematical model using the surface of immersed coil Ss and its thermal heat transfer coefficient kS. If we include Eq. (4) in Eq. (2) and after small adaption we’ll obtain the mathematical relation between thermal agent temperature, equivalent temperature and tank temperature by Eq. (6): tT ¼

EC
ð1  ES Þ 1  EC
hþ
tE 1  EC
ES 1  EC
ES

ð6Þ

tR ¼

ES
ð1  EC Þ 1  ES
tE þ
h 1  EC
ES 1  EC
ES

ð7Þ

After replacement of tT with Eq. (6) in Eq. (4), was obtained the equation for tR where we have same variable parameters tE and tank temperature ϴ. To resolve this mathematical model we use the thermal balance between thermal agent and tank liquid with Eq. (8): G
qcðtT  tR Þ ¼ G
qc
ECS
ðtE  hÞ

ð8Þ

In the Eq. (8), ECS is thermal module of system composed by collector and immersed coil; this have the expression given by Eq. (9): ECS ¼

ð1  EC Þð1  ES Þ 1  EC ES

ð9Þ

To be able to describe a dynamic behaviour of temperature inside tank, time should be considered. In a period of time, the temperature inside tank is increased due to heat carried by agent flow from solar collector. Equation (10) show us that the volume V of tank receive an amount of heat in a desired time period: G
qcðtT  tR Þ
ds ¼ V
qc


dh ds ds

ð10Þ

300

M.-F. Talpiga et al.

This equation is simply resolved as ordinary differential equation, ODE, and the solution is given by Eq. (11): hðsÞ ¼ tE ðsÞ þ ðh0  tE ðsÞÞ
Ecs

ð11Þ

where,


G Ec ¼ exp 
ECS V

 ð12Þ

The parentheses coefficient of Eq. (12) can be noted CT or time constant of the system, which help us to define easily the numerical model of the solution. Will be used in this paper the Eq. (11) as the recurrence relation in numerical simulation of system made from solar collector and heat accumulator.

3.2

Heat Pump

The energy consumption of buildings is responsible for a fair percentage of the primary energy used in Europe [7]. Heat pumps are that systems which use two different temperature environments to carry in or out the heat. This paper aim is to find a mathematical model of a heat pump which take the heat from the tank and transfer it to the building heating system with the refrigerant agent circulated by a compressor. Commonly used coefficient of performance, is a term which describes the heat obtained at condenser when an amount of electrical energy is used or the heat absorbed from evaporator environment. Both are named coefficient of performance of condenser or evaporator. System (13) define both relations, where PCD, PVP and PEL are condenser power, evaporator power and respectively, electrical power: COPCD ¼ COPVP

PCD PEL

PVP ¼ PEL

ð13Þ

In reversible Carnot cycle both, coefficients of performance are described using the temperature values of vaporisation and condensing of refrigerant, tVP, respectively tCD with system Eq. (14) [8]: COPCD ¼ COPVP

tCD þ 273:15 tCD  tVP

tVP þ 273:15 ¼ tCD  tVP

ð14Þ

Temperatures of refrigerant inside evaporator and condenser should be lower, respectively higher than environments to be possible the heat transfer. Tacking all this

Numerical Assessment of a Dynamic Daily Heating Unit

301

into account and with simple adoption of Eqs. (13) and (14), we obtain the relation between thermal powers with Eq. (15): PVP ¼

h  DVP þ 273:15
PCD hCD þ DVP þ 273:15

ð15Þ

where, DVP and DCD, are temperature differences between environment and refrigerant, at evaporator respectively condenser and h, hCD are tank temperature respectively condenser environment temperature. With right notation, we can wrote a simple equation helping us describe the thermal behaviour of heat pump by Eq. (16): PVP ¼ a
h þ b

ð16Þ

here, the notation a and b, given by relation (17), are coefficient rearranged from Eq. (15) used to provide a simple differential equation, where vaporisation power and tank temperature are direct linked in dynamic behavior: a¼

PCD hCD þ DVP þ 273:15

273:15  DVP
PCD b¼ hCD þ DVP þ 273:15

ð17Þ

The variation of temperature internally tank, depends on immersed evaporator power, known by relation 16. If we apply a thermal balance between tank and evaporator, we conduct to an ordinary differential Eq. (18). The negative sign of right terms are due to the fact the energy is tacked out from tank: V
qc

dh ¼ a
h  b ds

ð18Þ

This type of equation, can be solved using ordinary equation solution, and if we consider equal periods of time, and initial condition, we can wrote a recurrence Eq. solution (19):
 B B hðsÞ ¼  þ h0 þ
expðA
sÞ A A

ð19Þ

The coefficient A and B are same as a respectively b, but now divided trough constant Vqc: A¼

1 PCD
V
qc hCD þ DVP þ 273:15

1 ð273:15  DVP Þ
PCD
B¼ V
qc hCD þ DVP þ 273:15

ð20Þ

302

M.-F. Talpiga et al.

If we resolve, the solution is given by recurrent Eq. (21), were ED is exponential function of coefficient A: h1 ¼ EDDs
h0  ð1  EdDs Þ


B A

ð21Þ

Ed ¼ expðAÞ

Equation (21) is used for discharge period and with Eq. (11) we have a system for both charge and discharge periods. An important analyse it is also presented for charging period, were solar radiation is present but also a heating demand to condenser is active, and the considered space for heating required an amount of heat. For this possibility, in [9] is presented a new method for both, charge and discharge are considered in system, when from solar collectors is provided power and at heat pump is demanded energy to be used in warm up the space. To write the correct relation, a thermal balance is considered between tank, solar collectors and immersed evaporator and equation obtained is given by (22): PCS  PVP ¼ ECS G
qc
ðtE  hÞ  ða
h þ bÞ ¼ V
ðqcÞ


dh ds

ð22Þ

Relation (22) can be resolved easily with using ordinary differential equation solution for first order linear Eq. (23): dhVP 1 1 ¼  00
hVP  00
t00 CT CT ds C00 ¼

V
qc ECS
G
ðqcÞ þ a

ECS
G
ðqcÞ
tE  b t ¼ ECS
G
ðqcÞ þ a

ð23Þ

ð24Þ

00

To solve relation (23) using coefficients given by the system (24) we have to make few consideration. Periods of integration should be equal, and the external function tʺ, representing equivalent temperature for charging period, is constant over the integration period (Ds). In this situation we will resolve the relation (23) by a recurrent Eq. (25), easily implemented in a mathematical modelling software as Scilab or Mathlab: Ds Ds 00 hn ¼ Ecd
hn1 þ ð1  Ecd Þ
tn1;n

ð25Þ

where Ec−d, in this modelling, is given by relation (26):
 1 Ecd ¼ exp  00 CT

ð26Þ

Numerical Assessment of a Dynamic Daily Heating Unit

303

Temperature is obtained by a mean value between resulting temperatures at moment n and before with one step, as relation (27): 00 tn1;n ¼

 1  00
tn1 þ tn00 2

ð27Þ

With all those equation, we can wrote an entire program to calculate the temperature inside tank, when solar radiation is present over the day and heat demand is required in the evening and night, first only after the charging is elapsed and secondly when also a heating demand it is supposed over the charging periods. 3.3

House

Space heating represent today a big amount of studies and researches, different methodologies and modelling technics being developed. To know how much heat is needed to keep the internal ambient comfort in residential or office buildings is a direct indicator of the system capacity to be used in heating or cooling the space. Houses and buildings are subjected to be influenced by cardinal orientation when the heat demand is estimated, generally, the cardinal position of the windows and wall have big or small influence if are North or South oriented. In (Fig. 2) is presented the building model, oriented in correlation with the cardinal points. To heat the living space we have to consider heat transferred through building boundaries between inside ambient and outside weather parameters. Secondly, the heat gain by building through windows and due to internal release is a part of heat won by house considered. The amount of heat transferred to exterior is estimated by thermal flow between an internal comfort temperature and outside temperature by a thermal loss coefficient [9], as in relation (28): Qloss ¼ H
ðhi  he Þ
t

ð28Þ

Fig. 2. House position and solar direction in a cardinal orientation of the model considered

304

M.-F. Talpiga et al.

where, Qloss is the entire heat loss in a period of time equal t, ϴi is internal comfort temperature, ϴe is external temperature and H is thermal loss coefficient. The amount of heat captured by building from solar radiation through a window is done by Eq. (29): Ucaptured ¼ I
ða
tÞ
ðFT
FS Þ
AFE

ð29Þ

In relation (29) I represent the solar radiation, a is absorptivity coefficient of surface, t is window transparency coefficient, FT is window frame factor, FS is shading coefficient and window surface is noted AFE. Internal release is also a heat which can be added as heat contribution and is in general a specific heat demand per square meter of internal space. The entire relation of calculation is now (30) were also a time dependant factors are considered as solar radiation and external temperature: UT ¼ H
ðhi  he ðsÞÞ 

X

Ij ðsÞ
ða
tÞ
ðFT
FS Þ
AFE j  Usp
S

ð30Þ

j

In relation (30) we have the entire flow which is needed to keep the internal temperature of considered space to a constant comfort value. Different notation are changed due to time dependant values of external weather condition and different solar radiation present on distinct windows cardinal orientation surface, coefficients Ij(s) and specific surface for each one AFEj. UT and Usp are total thermal flow and respectively internal specific heat release per square meter. Internal surface of space considered is S and is used to evaluate the entire heat flow dissipated by internal sources. Radiation I(s) represent the radiation on each surface according cardinal orientation; for this study, each orientation solar radiation have a specific value, calculated using a cardinal coefficient; for North is 7%, South represent 20%, West and East each 11%, all those values being applied to total solar radiation. Two special remarks, for this study, the shading coefficient is not considered time dependant and the heat flow due to air change between interior and exterior is included in the global heat transfer coefficient H. 3.4

Solar Radiation and External Temperature

In a solar collector numerical simulation, entry data are significant information that conduct to a good approach of real behaviour of model. Basically, real capture of outside weather data such radiation and temperature can be a good method to create entry information for computational model. In other cases mean values of radiation and outside temperature are correlated and achieved as statistical database for each day of the year. The purpose of this paper is to evaluate the possible usage of low solar radiation in a cold day of transition season like spring and autumn. For this type of day we can imagine a dynamic solar radiation and outside temperature as in (Fig. 3) for a spring day. Those data are imagined for 2 of March, when the external temperature can reach negative values over the night and a maximum below 10 °C in the day. The solar radiation represents direct and diffuses together in 45° plan. Normally, a dynamic

Numerical Assessment of a Dynamic Daily Heating Unit

305

1,200

15

1,036

1,000

9.26

10

800

5

600

0

400 200

-8.11

-5 -10

0 09:00

12:00

15:00

18:00

Solar Radiation

21:00

00:00

03:00

06:00

Temperature [oC]

Solar Radiation [W/m2]

behaviour is imagined, when radiation is starting to growth until a maximum is achieved at middle of day, and external temperature with a maximum at 15:00 o’clock, when start to fall down. This data are used in computational algorithm to calculate the equivalent external temperature in relation (1).

hh:mm

Outside Temperature

Fig. 3. Solar radiation, direct and diffuse, and outside temperature for 2 March

3.5

Solar Collectors and Tank

Different solar collector area will be considered in simulation to understand the behaviour of system when surface area is varied. Also, tank volume will be varied to trace the correlation between tank volume and system performances. The tank is supposed to have the same temperature on entire volume when the simulation is carried. The heat loss in pipes between solar collectors-tank and tank aperture heat loss are neglected. The mass-flow in charging system is considered constant, without interruption of flow pump, and hydraulic losses in system are also neglected. The surface of solar collectors is considered to be the surface needed to heat up the water tank used to serve the daily hot water for a considered space. That’s why the capacity installed for daily hot water demand cannot be used in space heating but because of low capacity compare with heating needs. For simulation, a set of parameters are defined as: dtI as kc ks F′ Ss Sc G V ϴ q c

-

charging time 8 h, coefficient of absorptivity and transparency 0.81, solar collector thermal losses coefficient 3 W/m2 K, thermal transfer coefficient of immersed coil 60 W/m2 K, correction factor of solar surface 0.9, specific surface of immersed coil 0.1 m2/m2, solar collector surface 8 m2, specific flow of solar collector thermal agent 60 L/m2h, tank volume in m3, tank temperature in °C, water specific density 1000 kg/m3, water specific heat capacity 4180 J/Kg K.

306

3.6

M.-F. Talpiga et al.

Heat Pump

Heat Pump simulation in computational modeling assumes that we should know the capacity of space heated. In relation (21) and relation (25) two functionality supposition are considered. The model will calculate at each period the new temperature of liquid inside tank when the pump is working in the same time with solar collector system and also when is working separately after the tank is charged by solar collectors in the day. For the convenient temperature differences between evaporator and tank liquid or between refrigerant at condenser state and condenser ambient temperature, the heat pump will discharge the heat from the tank to provide the heat demanded by heated space. Heating system of the space considered is chose being low temperature heating system like floor heating or forced convection units which use thermal agents with low temperature values. At each time, heat pump is able to vary the condenser heat demand by inverter technology, when the electrical power applied to compressor is directly controlled, a bigger power demand being available at condenser, when needed, due to increased refrigerant flow as a consequence of motor drive speed. Today technology provide higher efficiency of electrical motor drive with values under the interval 0.65 to 0.72. Regarding the necessary heat pump condenser power at each iteration period i, the system is able to provide only a part of total heat flow calculated with relation (30). The heat provided by the system at condenser power is considered to be a proportion of the total building heat flow, and is established using a sharing coefficient nHP. The heat flow at heat pump condenser is described by relation (31): PCDi ¼ UTi
nHP

ð31Þ

Because the solar collector surface used in summer, to provide the heat for daily hot water demand, cannot provide a thermal agent with enough temperature for heating purpose is imagine for simulation a part of the total building needs to be delivered by system. That’s why in cold transition periods the system proposed to heat up the thermal agent can only provide a shared value from the total need. For this study, the thermal inertia of model building is not tacked into account. Each time period heat flow become a demand for the heat pump, and, because of the sharing coefficient only a percent from entire heat flow is provided at condenser. Heat pump is modeled using the mentioned relations and the all other parameters inside the formulas are described below: Δϴcd Δϴvp ϴcd Pcd nHP

-

temperature difference at condenser ambient 6 °C, temperature difference at heat pump evaporator 6 °C, condenser ambient temperature 50 °C, condenser heat demand in W, shared coefficient of heat demand 25%.

Numerical Assessment of a Dynamic Daily Heating Unit

3.7

307

Building Heat Demand

Carbon dioxide (CO2) is the most important anthropogenic greenhouse gas, whose rapid increase in emission rate is attributed to the increase in civil and industrial activities over the last few decades [10]. A specific part is also produced due to building heating demand. Today, it is possible to make a brief study about what are the heating needs of a considered space. Just by knowing the materials, geographic place and cardinal direction we are able to determine the heat needs of any space or building. With method described we are able to generate, at each time, the heat demand by the space, using relation (30) where, solar radiation and external temperature are given by data considered in (Fig. 3). The model building considered have the orientation with vertical walls according cardinal directions N, S, E, W. Window distribution surfaces and the other parameters described below: AFS AFN AFE AFW a t H FT FS Usp S ϴi

-

South orientation window surface 2.43 m2, North orientation window surface 2.43 m2, East orientation window surface 16.2 m2, West orientation window surface 0.42 m2, absorptivity coefficient 0.33, transparency coefficient 0.9, thermal losses coefficient 240 W/K, window frame factor 0.8, window shading factor 0.55, specific heat release 8.61 W/m2, floor surface 63.18 m2, internal temperature 21 °C.

With all those data we are now able to make the calculation for the entire heat demanded, to keep constant the value of internal temperature to 21 °C. 7,000

Heat Flow [W]

6,000 5,000 4,000 3,000 2,000 1,000 9 10 11 12 13 14 15 16 16 17 18 19 20 21 22 23 24 1 2 3 4 5 6 6 7 8

0 Daily Hour[hh]

Φt

Pcd

Fig. 4. Model building heat flow and shared heat at heat pump condenser for 2 March

308

M.-F. Talpiga et al.

In (Fig. 4) both heat flow of model building and the heat flow provided by heat pump condenser. If compared with (Fig. 3) we can obviously see, for the minimum outside temperature, the maximum heat flow need is around 6:00 o’clock AM. A maximum value for heat flow at condenser is around 1610 W from a total of 6443 W required by the model building at same time. As imagined, no thermal inertia is considered, the heat pump is supposed to give at each time a share coefficient from total building needs and is calculated as instantaneous shared value from building requirement according relation (30). With this specification will be evaluated the performances and all parameters of the system in next (Sect. 4).

4 Results and Discussions In this paper was presented the entire methodology to simulate a dynamic behavior of a hybrid system that use a heat pump to drive a shared percentage of heating demand in a heating unit. The entire methodology is based on a mathematical modelling using Scilab 5.2.2 software, were all data describe in Sect. 4 were implemented. Different approach is given to tank volume to establish a right specific volume per square meter. To be able to analyze the energetically behavior of system, a set of data were simulated, in which tank volume for a specific surface of one square meter was varied to understood their correlation between tank temperature rising from the minimum to maximum obtained inside and COPCD average values. The analyze start with searching for the right volume of tank accumulator, comparing with solar collector surface. The collector surface is supposed 10 m2 and all other parameters defined in (Sect. 4.2). Varying the volume from 60 to 180 L/m2 we obtain the values of temperature differences between start temperature and the maximum inside tank, the COPCD average vary as shown in (Fig. 5). Temperature [oC] 30.0

COP[-] 20.00 18.00 16.00 14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00

25.0 20.0 15.0

12.00

10.0

9.41

8.40

5.0

7.85

7.50

7.26

7.09

0.0 -5.0 -10.0

60

80

100

120

140

160

180

Specific Volume[l/m2] COPcd Average

Δθ

Fig. 5. Tank temperature difference between start and final charging time and average COPCD for different specific volumes

Numerical Assessment of a Dynamic Daily Heating Unit

309

From the (Fig. 5) we can see the variation of tank temperature, Dh, between beginning and finish of charging period, obtained in 2 March considering the beginning temperature is the same with the temperature after discharging period. We can see that when we have big temperature variation inside tank also COPCD have high variation and low average COPCD is obtained for lowest variation of tank temperature over the day. The best is to use a big volume but this will influence in system cost and also in summer can conduct to low temperatures with improper value for daily hot water demand. We can see higher COPCD is obtained no matter the value of specific volume, but this is a normal situation because the tank temperature is close to condenser ambient temperature, considered 50 °C in simulation. For next analyses a specific volume of 120 L/m2 is selected. The influence of volume is significant also to trace the COPCD during all computation period of charging and discharging period when heat pump work on both stages but also to see how is influenced the behaviour of the system when heat pump work only on discharging period. Because the building considered have heat flow requirements all day time, as shown in (Fig. 4), the simulation method, when heat pump work also in the morning and evenings, is chose. This is actually a normal behaviour of the building in middle season of autumn or spring, when such system can work to provide a part of building heating requirement. In transition period, the heating is also needed in the day, even the solar radiation is present and outside temperatures reach positive values. The thermal behaviour of the building, in term of heat transfer rate between inside and outside, have a direct impact in heating of the building, when the lower outside temperatures influence the space, which required much more heat to be kept constant the internal comfort temperature value. Temperature [oC] 30

P [W] 1600

25 20

1400

15

1200

10

1000

5

800

0 -5

600

-10 -15 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 0 1 2 3 4 5 6 7 8

400

Pcd

Pvp

te

Daily Time[hour]

Fig. 6. Condenser and evaporator heat rate and outside temperature when heat pump work entire day, for 2 March

310

M.-F. Talpiga et al.

This fact is obviously an important quantity indicator showed very accurate in (Fig. 6) where, the power demanded at heat pump condenser is a direct consequence of outside temperature drop between evening and morning. If we look more in detail, on (Fig. 6) we can read an increasing of heat flow, after 15:00 o’clock, when solar radiation start to fall down, and after no solar radiation is present, a constant ramp is achieved, following the outside temperature curve.

Temperature [C]

2 March

2 April

15 October

Solar RadiaƟon [W/m2]

40 35 30 25 20 15

10.71

10

4.62

5

0.56 9 10 11 12 13 15 16 17 18 19 20 21 22 23 0 2 3 4 5 6 7 8

0

630 610 590 570 550 530 510 490 470 450

Day Time[hour]

I

02.mar

02.apr

15.oct

te

Fig. 7. Tank temperature, average solar radiation and average external temperature for 2 March, 2 April and 15 October

In (Fig. 7) we can see the obtained tank temperature in 3 different days, were only the outside weather parameters are changed. When high solar radiation is present the tank temperature reach also the biggest value in the middle of day if read on 2 March tank temperature value but this is not sufficient for night period when, since the temperature is the lowest comparing with 2 April and 15 October, the tank temperature in the morning reach a temperature value below the starting point. What is important to see is that a highest solar radiation is not sufficient to sustain the model building needs. Also we can conduct to an important factor to satisfy the heating of the house is the external temperature. An equilibrium exist between the value of tank temperature in the morning and outside weather parameters to obtain sufficient heat inside tank to satisfy the building needs. To do this, 3 simulations was conducted, to see what tank temperature is it necessary to have, when sun start to rise on sky, reaching sufficient heat inside tank to satisfy building needs. Based on this, a graph (Fig. 8) is created and show the distribution of temperature obtained inside tank. The starting values of tank temperature at 9:00 o’clock in the morning, signify an important behaviour of the system. For lowest values of solar

Numerical Assessment of a Dynamic Daily Heating Unit

311

radiation, high values of starting temperature inside tank are required. With this, the solar collectors are not so performant, this is obviously in low temperature differences obtain between starting and finish of charging period. In the same time, the heat pump achieve a high COP due to low temperature differences between evaporator and condenser. The distribution of tank temperature over the day, when both value in the morning and after the night are equal, show that no additional heat is required, and electrical power of heat pump and the heat obtained from solar radiation are sufficient to satisfy the shared coefficient. Condenser heat demand is a directly influence factor for electrical power consumption at heat pump compressor. On the heat pump evaporator and condenser the thermal behaviour is similar with the specification that COP obtained is higher in case of heat pump consideration. This is also a normal behaviour due to the fact that at the heat pump condenser the temperature is always higher comparing with evaporator ambient temperature at the same moment of time. The COPCD obtained at heat pump condenser, when all three days are simulated, with a starting temperature equal in all cases with 23 °C, is shown in (Fig. 9). Values obtained for coefficient of performance are in a good range and energy consumption over the entire day which is also traced in column view, indicate values between 1.6 kWh and 3.6 kWh. The higher electric energy consumption, 3.6 kWh, is obtained for 2 March, a day with big COPCD but with high heat flow required at heat pump condenser. Temperature [oC] 60 55 50 45 40 35 30 25 20 9 10 11 12 12 13 14 15 16 17 18 19 19 20 21 22 23 24 1 1 2 3 4 5 6 7 8 8

15

2 March

2 April

15 October

Daily Time[hour]

Fig. 8. Tank temperature for 2 March, 2 April and 15 October when no additional heat is required

312

M.-F. Talpiga et al. COP [-]

Energy [W·h]

2 March 10 9.5 9 8.5 8 7.5 7 6.5 6 5.5

2 April

15 October 3800 3300 2800 2300 1800

2569.61

1624.59

1300

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6 7 8

3601.07

Energy

2 March

2 April

15 October

Fig. 9. COPCD, and electric energy consumption when heat pump work entire day

5 Conclusions In this paper was presented the entire methodology to simulate a dynamic behaviour of a heating systems using solar collectors and heat pump coupled in an indirect expansion heat pump. The conclusions obtained after numerical simulation reveal the fact that such systems are able to support a quarter of the heating demand for considered model building. Average COPCD obtained through heat pump was 7,85 for 2 March. Electric energy consumption for 15 October was 1.625 kWh when 10.7 °C is average external temperature. With future research in functional validation of this model will be gained the needed parameter values of the hybrid system to serve the building heat demand.

References 1. Cai, J., et al.: Numerical simulation and experimental validation of indirect expansion solar-assisted multi-functional heat pump (2016). http://www.sciencedirect.com/science/ article/pii/S0960148116301811 2. Wang, Q.: Development and experimental validation of novel indirect-expansion solar-assisted multifunctional heat-pump. Energy Build. 43, 300–304 (2011) 3. Youssef, W.: Effects of latent heat storage and controls on stability and performance of a solar assisted heat pump system for domestic hot water production. Sol. Energy 150, 394–407 (2017) 4. Bellos, E.: Energetic and financial sustainability of solar assisted heat pump heating systems in Europe. Sustain. Cities Soc. (2017). http://dx.doi.org/10.1016/j.scs.2017.05.020 5. Iordache, F.: Absorption flat panel. Dynamic and stationary working condition of thermal process transfer. In: Thermal System Installation and Equipment Energetics, pp. 49–55 (2010). Chap. 7

Numerical Assessment of a Dynamic Daily Heating Unit

313

6. Iordache, F., Talpiga, M.: Solar collectors and heat pump system. In: Equipment and Thermal Systems Energetic and Functional Evaluation Methods, pp. 99–113 (2017) 7. Fumagalli, M.: Monitoring of gas driven absorbtion heat pumps and comparing energy efficiency on primary energy, 1 (2016) 8. Iordache, F., Dragne, H.: Dynamic thermal modelling for a system that uses a compression heat pump. In: CLIMA 2016 - Proceedings of the 12th REHVA World Congress, vol. 3 (2016). Paper 87 9. Energetic Performances Calculation Breviary of Buildings and Apartments – 4rd Part. Calculation Methodology for Building Energetic Performances, Chapter III, 20 10. Sheng, X.: Energy Saving Factors Affecting Analysis on District Heating System with Distributed Variable Frequency Speed Pumps. Dalian University of Technology, Liaoning (2017)

Solar Power in Buildings and Communities

Optimized Management for Photovoltaic Applications Based on LEDs by Fuzzy Logic Control and Maximum Power Point Tracking Dan Craciunescu1, Laurentiu Fara1,2(&), Paul Sterian1,2, Andreea Bobei1, and Florin Dragan1 1

Polytechnic University of Bucharest, Bucharest, Romania [email protected] 2 Academy of Romanian Scientists, Bucharest, Romania

Abstract. This work takes into account the implementation and analysis of a Fuzzy Logic Controller (FLC) based on Maximum Power Point Tracking (MPPT), in order to optimize the output parameters and efficiency of a photovoltaic system (PV), as well as its integration in specific applications of LED lighting. The obtained results prove the effectiveness of the FLC and MPPT able to reduce fluctuations in terms of output parameters and to have a quick response for electrical load against variations of solar radiation. By this approach the complex PV system behavior was analyzed on short, medium and long term. Keywords: PV system
MATLAB/Simulink FLC applications
Stability
Security and optimization




MPPT




LED lighting

1 Introduction Nowadays, one of the most convenient sources of renewable energy is represented by solar energy. The importance of studying PV systems comes from the need for consumer-related applications, ranging from power supply of isolated areas to complex and expensive consumers for medical applications, efficient lighting and solar vehicles [1–3]. The difficulty of using solar energy for electricity production comes from several reasons, such as: very high initial cost of purchasing PV components, the fluctuations in meteorological parameters or the energy supply in accordance with the conditions imposed by the power grids [4]. Currently, in order to use PV systems at a higher capacity, the maximum power needs to be extracted under the given operating conditions, in order to increase their electrical efficiency [5–7]. To achieve this goal, different techniques are applied, the most commonly used and efficient method being Maximum Power Point Tracking (MPPT) [8–10]. In order to guarantee the overall stability and distribution of power in the PV system, it is necessary to implement a controller which regulates the loading/unloading function of the storage devices and the stabilization of the load voltage. In terms of the use of solar radiation characterized by non-linearity, high uncertainty and rapid fluctuations, intelligent technologies, such as ‘fuzzy’ algorithms, have proved to be more effective than conventional controllers, like © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_23

318

D. Craciunescu et al.

the Proportional-Integral-Derivative (PID) [11, 12]. The main drawbacks of conventional PID-type techniques are: (1) the fluctuations around the optimum power point and the inability to detect the real point of maximum power in a rapid manner; (2) they do not work correctly in nonlinear systems with multiple inputs and outputs; (3) under high fluctuations and variable input conditions, conventional connectors frequently require calibration and adjustment of parameters in order to generate the desired performance [13]. In order for a PV system to provide stable electrical power, both peak power tracking and power system adjustment must be maintained in all meteorological conditions. Currently, by implementing and using Fuzzy Logic Controller (FLC) algorithms and MPPT techniques, the exploitation of PV systems can be as efficiently as possible, compared to the conventional methods [14, 15]. Mukesh Kumar, S.R. Kapoor, Rajkumar Nagar and Amit Verma obtained interesting results by using FLC algorithms and MPPT techniques for PV systems in the work Comparison between IC and Fuzzy Logic MPPT Algorithm Based Solar PV System using Boost Converter [16–20]. G. Balasubramanian and S. Singaravelu proposed and implemented in Matlab/Simulink a FLC and MPPT controller, by which they studied the I-V and P-V characteristics of a PV system at fluctuating solar irradiation and at different temperatures. The model was validated experimentally and resulted in very good performance for the analyzed PV system [8, 21, 22]. In the present paper, the authors implement in the Matlab/Simulink work environment an algorithm that uses FLC for the MPPT technique. In order to analyze the complex PV system, two MPPT methods are used, namely: (1) the direct method, that considers the PV system in load conditions, respectively in the open circuit (the simulations occur during the system operation in order to direct it to the maximum MPPT values), and (2) the temperature gradient control (TG) method, which depends on the variation of the open circuit voltage, as function of the PV system’s temperature [23]. Thus, using the FLC and MPPT methods, an efficient response is provided under conditions of large fluctuations of the meteorological parameters for the electrical characteristics of the system. MPPT is implemented using an incremental algorithm and a FLC. The incremental algorithm compares the real power of the PV system with an estimated value for maximum reference power with the help of the Fuzzy Logic Controller at equal time intervals [24–27]. The authors also perform a simulation of the PV system integrated into a specific LED lighting application, analyzing the performance of the complex photovoltaic system, which indicates the degree of capability and stability of the final consumer’s power supply. The main objective of the present work is the operational optimization of a complex photovoltaic system and its operation in different meteorological conditions in order to increase its electrical efficiency for a given application. The relevant contributions highlighted in this paper are as follows: (1) Modeling and simulation of a PV system by integrating a FLC control algorithm in order to track the maximum power point (MPPT) using the Matlab/Simulink work environment for a LED lighting application; (2) Modeling and simulation of the LED lighting system; (3) Determining the electrical performance of the complex PV system.

Optimized Management for Photovoltaic Applications Based on LEDs

319

2 Methodology of Modeling and Simulation of a PV System and a LED Lighting System 2.1

Main Concepts

The development of a model, which simulates the performances of the analyzed PV system, is proposed, based on a fine agreement between the Matlab/Simulink simulation program and the methods using the MPPT and FLC algorithms. Investigations on the two methods indicate that they are efficient and suitable both for PV systems, regardless of complexity, and for their optimization. A detailed overview of the main features of the Matlab/Simulink software tool and the MPPT and FLC methods is furthermore provided. 2.2

Matlab/Simulink Software Tool

The MATLAB/Simulink software could be used to enhance the understanding of all characteristics for PV systems and has the following features [28, 29]: • It is a basic tool for professionals and researchers to accurately predict the PV characteristics; • It is considered as a design aid for users to build actual PV systems and to study their stability; • It is used to study the effect of array configuration on the output power, as well as to develop and validate the new MPPT schemes. 2.3

MPPT Techniques

The non-linear characteristic of the I-V curve for a PV panel results in unequal power distribution during its operation. Figure 1 shows the relationship between power, voltage and current for a PV panel [30]. It can be noticed that there is a point associated with certain values of voltage and current that have the highest power. When the PV panel corresponds to the maximum power point, its maximum available power (Pmax) is provided. The values of the current and voltage at the Maximum Power Point are called the maximum power point current (Imp) and the

Fig. 1. I-V and P-V characteristics for a PV panel, highlighting MPPT [30]

320

D. Craciunescu et al.

Fig. 2. The P-V characteristic of the PV panel for different levels of solar irradiation at a temperature of 25 °C [31]

maximum power point voltage (Vmp). When operating conditions such as temperature and solar radiation change, the Pmax, Vmp and Imp values change as well. Figure 2 shows changes in the Maximum Power Point depending on variations in solar irradiation for 25 °C [31]. Maximum Power Tracking Techniques (MPPT) are algorithms that find the maximum power point in any operating state of the PV panel/system. They represent inputs for a controller that connects to the rest of the system. The output signal of the controller is directed to a modulation technique called Pulse Width Modulation (PWM), which generates control pulses that allow the system to operate at the maximum values.

2.4

Fuzzy Logic Controller

Intelligent methods for tracking the maximum power point provide a much improved performance in varying weather conditions and rapidly changing uncertainties. The main intelligent methods for MPPT are: Fuzzy algorithms, genetic algorithms and neural networks. The Fuzzy Logic Controller (FLC) can detect the sudden changes and heuristic variables, making it very effective for power control system applications. It also updates quickly to input data. The FLC algorithm is suitable for use in photovoltaic systems, highly non-linear, and characterized by fluctuations of meteorological parameters [32]. Intelligent control methods based on FLC and used in PV systems, which also contain the MPPT function, are discussed. The fuzzy logic, which interprets qualitative information in mathematical relationships, was first introduced by Zadeh in 1965 [17]. It allows explanation of unpredictable behavior of systems that cannot easily be modeled. Fuzzy variables are expressed by functions or curves between 0 and 1 or other ranges. To define the fuzzy set, it is necessary to specify both the set values and the weights of these values. Fuzzy logic operations are used to link fuzzy sets [33]. The main operations of fuzzy sets are: membership functions and fuzzy rules. In conclusion, Fuzzy Controllers have provided effective responses for both MPPT tracking and power regulation of photovoltaic systems. Also, fuzzy logic based MPPT applications in PV systems have the advantage of robustness, fast response and are easy to project. The use of fuzzy logic allowed to obtain performances as high as possible for PV systems, as well as improving their stability [33–36].

Optimized Management for Photovoltaic Applications Based on LEDs

2.5

321

LED Lighting System

The development of LEDs is a challenge today and requires the elaboration and implementation of new techniques for manufacturing, use and control. Research in the field includes analyzes and applications of LED lighting systems integrated into photovoltaic applications, characterized by LED hybrid PV systems [15, 37–39]. The study of the electrical characteristics and performance of LED hybrid PV lighting systems, in terms of their efficiency and stability, is based on the following: (1) modeling and simulation of the hybrid PV system with LEDs, (2) obtaining information and data regarding its behavior, efficiency and stability in photovoltaic applications, and (3) implementation of a FLC controller capable of efficiently using the energy consumed by the LED lighting system by adjusting it according to the intensity of the natural lighting. Effective lighting involves a correlation between artificial and natural illumination. An efficient lighting system using FLC algorithms can save energy compared to its use under conventional conditions.

3 Simulation, Results and Performances of the PV System on Short Term 3.1

Main Concepts

The authors have developed the structure, modeling, simulation and performance for a PV system and for a specific lighting application, which is the hybrid LED system. The components of the considered complex PV system are represented by: (1) the PV system (which defines the photovoltaic generator), the MPPT system and the power and control system (characterized by the FLC controller); (2) the LED lighting system. The fluctuation of the input power was achieved by the variation of the solar radiation in the range 600–1000 W/m2. The analysis of a PV system based on preliminary LED lighting application was developed using the simulation approach on short term (a span time from 60 s to maximum one hour). The obtained results took into account the input data and the load of the LED lighting system. The power required to supply the lighting system was also varied in the range 500–800 W. Figure 3 presents the structure of the complex PV system,

Fig. 3. Block diagram of the PV complex system implemented in MATLAB/SIMULINK

322

D. Craciunescu et al.

proposed for a given lighting application, which envisages the implementation of the FLC algorithm and MPPT determination. The results obtained by modeling and simulation will determine the capability of the PV system, in order to meet the consumer’s load with high safety and functionality. 3.2

Determining the Characteristics of the PV Generator

For the modeling and simulation of the photovoltaic generator, there will be used the specific parameters of the analyzed PV generator, based on polycrystalline silicon cells, produced by Suntech [40]. It was conducted the implementation and simulation of the PV generator with the MATLAB/Simulink software, thus being obtained its characteristics and performance. In Fig. 4, the electric layout of the complex PV system developed in Matlab/Simulink is presented.

Fig. 4. Block diagram of the PV complex system implemented in MATLAB/SIMULINK

The characteristics of the PV generator studied were achieved under the following conditions: (1) For a temperature range of 15–85 °C (Fig. 5a and b); (2) For different solar irradiation values ranging from 100–1000 W/m2 (Fig. 6a and b). The obtained simulated results allow the implementation of the FLC algorithm and the determination of the maximum power point (MPPT) for the PV generator. 3.3

Analysis of Components for the Studied Complex PV System

(a) DC-DC Converter. The DC-DC converter used is intended to reduce or increase the input voltage according to the operating cycle. The system voltage control is

Optimized Management for Photovoltaic Applications Based on LEDs

323

Fig. 5. Simulated characteristics of the analyzed PV generator using Matlab/Simulink for different values of temperature: (a) I-V characteristics, (b) P-V characteristics (a time span of three days)

Fig. 6. Simulated characteristics of the analyzed PV generator using Matlab/Simulink for different values of solar irradiance: (a) I-V characteristics, (b) P-V characteristics

carried out with the help of a pulse generator or a PWM modulator, which generates signals depending on the output of the controller; (b) Storage system. In order for the studied PV system to function efficiently and steadily, in addition to controlling the maximum power tracking operation, there must be ensured an efficient and stable source of power supply, as well as the control of the operation of battery’s charging and discharging cycles under different variation conditions. A process that allows this to be accomplished is the use of the MPPT controller by adjusting the battery charging/discharging system; (c) Load power control system. The considered PV system provides electrical power at DC charge for a specific LED lighting application. To function efficiently, the PV system must be able to maintain power at steady charge under all operating conditions and also to adapt to sudden load and power changes. A FLC controller is used for the proper functioning of the load control system.

324

3.4

D. Craciunescu et al.

Simulation Approach for MPPT and FLC Algorithms

(a) MPPT and FLC controller configuration for PV system. The maximum power point tracking is implemented using an incremental algorithm and a fuzzy logic controller. The incremental algorithm compares the actual power of the PV system (PPV) with an estimated maximum power (reference power) (Pr) through the FLC controller at equal time intervals. The output of the FLC controller is used to direct the reference power to a new level, which is added to the previous value of each range. The highest power value can be considered as the maximum power. The output signal from the FLC controller is directed to a PWM to control the functioning cycle of the DC-DC voltage converter. The DC-DC converter raises the voltage to the value at which the PV system can operate at full power. Figure 7 shows the configuration of the MPPT controller based on FLC, with the following notations: PPV is the real power of the PV system, IPV represents the current in the system, VPV represents the system voltage, Pr is the estimated maximum rated power and S represents the signal from the FLC controller.

Fig. 7. MPPT controller configuration based on FLC

In the implementation diagram of the FLC algorithm in the Matlab/Simulink simulation software (see Fig. 8), the input to the FLC controller is represented by the estimated reference power (Pr) and the real power of the PV system (PPV), while the output of the controller is represented by the command signal (S). Each input variable is represented by three triangular membership functions: small, medium and large. The output variable is represented by a singleton function with three variables: small (Sm), medium (M) and large (B). In Fig. 9 are represented the input functions for two cases: (a) the reference power (Pr) and (b) the real power of the system (PPV), based on FLC and MPPT. The purpose of the FLC controller is to force the control signal (PWM) to increase the real power (PPV) as close as possible to the maximum reference power (Pr). When the real power is much lower than the reference power, the control signal triggers the increase in real power. The value of the output signal from the FLC depends very much on the variation between the two power values, Pr and PPV. In the following, the Fuzzy rules are resented, the meanings of the FLC incremental algorithm parameters being indicated:

Optimized Management for Photovoltaic Applications Based on LEDs

325

Fig. 8. Flow chart of control algorithm for its implementation in Matlab/Simulink

Fig. 9. FLC functions for MPPT: (a) Fuzzy input membership function Pr, (b) Fuzzy input membership function PPV

(1) (2) (3) (4) (5) (6)

If If If If If If

Pr Pr Pr Pr Pr Pr

is is is is is is

small and PPV is small, then S is small; average and PPV is low, then S is average; average and PPV is average then S is small; high and PPV is small then S is high; high and PPV is average, then S is average; high and PPV is high then S is average.

(b) Controller configuration based on FLC for battery regulator. Battery charging and power transfer operations occur under fast variations. That is why it can be stated that the battery controller’s command operation is essential for the efficiency and stability of the PV system. The functioning of the battery in order to control the total power distribution and load charging/discharging, with the help of the FLC control algorithm, can be described as it follows: (1) Charge mode: The PV generator power is higher than the load requirements (PPV > PL). Battery power is the difference between the two powers (PPV - PL);

326

D. Craciunescu et al.

(2) Discharge mode: The power delivered by the PV generator is less than the load requirements (PPV < PL). The battery is discharged (PL - PPV) to ensure load demand when the system cannot meet the consumer ‘s requirements; (3) Standby mode: load demand is equal to or nearly equal to the power delivered by the PV generator (PPV = PL). There is no need to discharge the battery. Figure 10 shows the configuration of the FLC controller with the following specifications: the input power to the FLC controller (PPV) is the difference between the desired power (Pd) and the actual battery power (PB). The desired power can be found in the difference between the power of the consumer (PL) and the power of the PV generator (PPV). The output signal from the controller (I0 ) is compared to the actual battery current (IB) and then directed to the PWM. PWM generates the signal that determines the duty cycle of the DC-DC converter. It changes the current in order to charge and discharge the battery according to the operating conditions of the PV system.

Fig. 10. Battery control units

The battery’s charging/discharging operation, required to simulate the complex PV system, is shown in the diagram from Fig. 11. (c) Configuration of load voltage controller based on FLC. In any load specification, there are certain current, voltage and power values that need to be supplied correctly to the consumer during the operation of the complex PV system. Voltage and charge current control is achieved by implementing a MPPT-based FLC algorithm in the Matlab/Simulink work environment for power control. Through the control method used, the voltage, current and output power are adjusted and stabilized at the optimum load value. In Fig. 12 it is presented the configuration of the load controller, with the following notations: (VL) represents the actual voltage of the load, (VLd) represents the desired load voltage, (I”) represents the reference current and (IL) is the load current.

Optimized Management for Photovoltaic Applications Based on LEDs

327

Fig. 11. Flow chart of the battery operation

Fig. 12. Load voltage control

3.5

Results and Comments

MPPT methods based on various controllers generate relatively stable results. Taking this into account, there was conducted a comparison between the MPPT FLC-based method (proposed in this article) and MPPT method based on conventional controller, in order to identify the optimum solution. The results obtained from simulation highlighted a greater efficiency of the MPPT FLC-based method, compared to the conventional method (as can be seen in Fig. 13). From this reason the FLC controller was selected, its method being fundamental for the analysis of the considered complex PV system. Following the simulations performed with the Matlab/Simulink software and the MPPT and FLC algorithms, interesting results on the behavior, stability and

328

D. Craciunescu et al.

Fig. 13. Efficiency comparison between FLC controller and conventional controller (considering the temporal evolution of the two controllers’ efficiencies)

performance of the complex studied PV system were obtained. The input data considered for the analysis of the complex PV system, as well as for the implementation of the MPPT FLC-based method, were represented by solar irradiance and temperature. These data were considered for the modeling and simulation of the studied PV panel, without being taken into account any experimental data (see Sect. 3.2). Figure 14(a–d) shows the behavior of the voltage related to the components of the complex PV system. In Fig. 14a it can be seen that the PV generator voltage is fluctuating, with a sudden drop after about 20 s. In Fig. 14b it can be seen that the load voltage is stabilized around 18 V after about 10 s. Figure 14c shows that the charge voltage drives the battery to a maximum capacity of 50 V over the simulated range (60 s) by the MPPT intervention which causes the reach of maximum operating point (see Fig. 14d). Figure 15 shows the behavior of the current through the components of the complex PV system. More specifically, Fig. 15a shows the behavior of the current through the PV generator but its fluctuations are much more visible than in the case of voltage, the variations being determined by the degree of solar irradiation. Figure 15b shows the current through the battery, which exhibits some small fluctuations compared to the PV generator, which exhibits much higher fluctuations. There is a slight increase in battery current in the first 30 s, followed by a small decrease in the second part of the analyzed range. In Fig. 15c, it is noted that the load current is practically constant over the entire analysis time (60 s) with the same voltage as the system load voltage. Figure 16(a, b) defines the voltage and current response for the three components of the complex PV system. In this way, both current and voltage evolutions can be simultaneously viewed, which allows an understanding of the behavior on different segments of the complex PV system, both from the consumer’s point of view and the system stability’s point of view.

Optimized Management for Photovoltaic Applications Based on LEDs

329

Fig. 14. The voltage response in the complex PV system’s components: (a) PV generator voltage, (b) load voltage, (c) battery voltage, (d) MPPT voltage

Fig. 15. The current response for the complex PV system: (a) PV generator current, (b) battery current, (c) load current

330

D. Craciunescu et al.

Fig. 16. The behaviour of PV system: (a) current and (b) voltage vs time for different input and output parameters of the PV system (solar irradiance, load voltage, battery voltage)

4 Simulation, Results and Performances for the Complex PV Based on LEDs Lighting System on Medium and Long Term The potential for reducing energy consumption by using LED lighting systems is the basis for integrating the photovoltaic system into the considered LED lighting application. Also, the LED lighting systems have a number of advantages over conventional ones, such as: (1) higher brightness, (2) longer life, (3) increased flexibility, and (4) much easier handling. These aspects help to increase the stability of the complex PV system, as well as to reduce the energy consumption, without reducing the comfort of the consumer. However, although LED-based lighting systems powered by PV systems are a promising alternative, they are not widely used in lighting applications because of the specific DC power generated by the PV system. For this reason, the study highlighted the capability of the PV system to generate stable and optimal DC power for supplying the LED lighting application (see Fig. 20). The performance and results of the PV system, analyzed in the previous chapter, aimed at determining the electrical parameters of the system and its behavior under different operating conditions, in order to determine its capability and stability to deal with the rapid input variations, as well as its ability to satisfy the consumer’s task. The results obtained are not conclusive to determine the exact behavior of the system, as the time interval considered does not allow knowledge of the system’s performance in the medium term (several hours, respectively several days) and long (several months) respectively. This is why the simulation of the electrical performances of the complex PV system was performed using the HOMER software [41]. The behavior of the complex PV system has been studied by conventional method in two cases: (1) using the solar power supply; (2) using the electrical storage system (Fig. 17). This method does not allow accurate determination of the share of electricity allocated to the consumer, provided by the PV generator, respectively by the electric battery.

Optimized Management for Photovoltaic Applications Based on LEDs

331

Fig. 17. Time behaviour of a PV complex system based on LED lighting application defined by the conventional method (no MPPT and FLC) using: (1) solar resources; (2) electrical battery

For a fair assessment of the situation of the electric consumer’s stiuation, a case study (PV generator + LED lighting system) was implemented; it uses the two studied methods, MPPT and FLC, which ensure the stability and control of the complex PV system. The state of the photovoltaic generator structured on four PV panels with a total power of 1200 W was analyzed. For the lighting system, an electrical load of about 800 W was considered. Figure 18 shows the charging/discharging status of the system (PV generator + electric storage system) for a three-day period. It is noted that the maximum operating power, determined by MPPT with FLC, allows the battery to be charged and discharged without sensitive fluctuations, especially during the second day of the considered interval.

Fig. 18. State of charge/discharge of PV complex system for a medium term analysis

In order to accurately highlight the operation of the complex PV system, its efficiency for the time interval 6:00–9:00 is presented in Fig. 19, which shows the behavior and the continuous functionality, both for the PV generator (which includes the electric battery), and for the consumer, represented by the LED lighting system. It is

332

D. Craciunescu et al.

Fig. 19. Efficiency of a complex PV system (for the main two components: (1) PV generator + battery and (2) electrical load) on medium term

noted that the efficiency of the PV system is characterized by rapid time fluctuations and the efficient use of consumer electricity is constant over the entire time interval considered. This is due to the use of the two MPPT and FLC methods, which, in conditions of rapid fluctuations in the input parameters of the complex PV system (especially solar irradiance), contribute to transmission of a constant energy to the consumer, maintaining its efficiency at an average value of about 85%. Figure 20 shows the final analysis of the complex PV system over a 5-months period (on long term). High power fluctuations of the PV generator, slower fluctuations in battery efficiency and efficiency constant of the electric consumer (also determined by using the FLC and MPPT methods) are highlighted.

Fig. 20. Efficiency of a complex PV system (for the main three components: (1) PV generator (2) battery and (3) electrical load) on long term

Optimized Management for Photovoltaic Applications Based on LEDs

333

It is thus concluded that MPPT and FLC methods are very effective in both situations (medium and long term), being able to determine as accurately as possible the maximum power of the complex photovoltaic system (by tracking the maximum power point), contributing to a dimensioning of the system as accurate as possible, by fully satisfying the requirements of the electrical consumer (stability, continuity and high electrical parameters of the system).

5 Concluding Remarks The study conducted using the Matlab/Simulink software and the MPPT & FLC methods, in order to optimize the performance of a complex photovoltaic system, correlated with an application of an LED lighting system, led to the following results: – Determining the behavior of the electrical characteristics of the studied PV generator, the storage system, the electric consumer, and the MPPT controller over a considered time frame; – Response to rapid fluctuations of solar irradiation, as well as how the complex PV system is affected; – Optimizing and stabilizing the electric consumer; – Analysis of the behavior, performance and stability of the complex PV system on three distinct time intervals defined by: (1) short term, (2) medium term, and (3) long term; – Highlighting the maximum power of the complex PV system by tracking the maximum power point with respect to consumer satisfaction, regardless of system fluctuations. The results were in line with those established by other authors in the literature, regarding the efficiency of using the two methods (MPPT and FLC) for PV systems [1, 10, 15]. The original contributions achieved by the authors, based on the approach proposed in the paper, can be considered as follows: – Development of conceptual schemes of the MPPT and FLC controller and their integration into the Matlab/Simulink interface for their use in the study of the PV system for specific applications; – Realizing a unified approach of a LED lighting system, correlated with a PV system, in order to establish the performance, stability and security in the power supply, regardless of the conditions inherent; – Proposing a model analysis of the complex PV system’s behavior for three time intervals (short, medium and long term). For the best valorisation and development of the approach proposed by the authors in this paper, based on the MPPT and FLC methods, it is envisaged to use hybrid systems like solar + wind or other similar configurations that lead to stability and increased security in supplying the final consumer with electricity.

334

D. Craciunescu et al.

The study of the complex PV system introduced in the present work can be further developed by connecting the system to a smart grid, in order to reduce the perturbations that it determines into the electrical grid, thus contributing to the optimization of the performance of both the system and the smart grid.

References 1. Coyle, E.D., Simmons, P.A.: Understanding the Global Energy Crisis. Prdue University Press, Indiana (2014) 2. Fara, L., Yamaguchi, M.: Advanced Solar Cell Materials, Technology, Modelling, and Simulation. IGI Global Publishing House, USA (2013). doi:10.4018/978-1-4666-1927-2 3. Sterian, P.E.: Photonics (in Romanian). Printech, Romania (2000) 4. Fara, L., Diaconu, A., Dragan, F.: Trends, challenges and opportunities in advanced solar cells technologies and PV market. J. Green Eng. 5, 157–186 (2016). doi:10.13052/jge19044720.5350 5. Zeman, M.: Introduction to Photovoltaic Solar Energy. Delft University of Technology, Netherlands (2012) 6. Fara, L., Craciunescu, D.: Output analysis of stand-alone PV systems: modeling, simulation and control. Energy Procedia 112, 595–605 (2017). doi:10.1016/j.egypro.2017.03.1125 7. Diaconu, A., Fara, L., Sterian, P., Craciunescu, D., Fara, S.: Results in sizing and simulation of pv applications based on different solar cell technologies. J. Power Energy Eng. 5(1), 63 (2017). doi:10.4236/jpee.2017.51005 8. Subudhi, B.: A comparitive study on maximum power point tracking techniques for photovoltaic systems. IEEE Trans. Sustain. Energy 4(1), 89–98 (2013). doi:10.1109/TSTE. 2012.2202294 9. Taheri, H., Salam, Z., Ishaque, K., Syafaruddin: A novel maximum power point tracking control of photovoltaic system under partial and rapidly fluctuating shadow conditins using differential evolution. In: IEEE Symposium on Industrial Electronics and Applications, Penang, Malaysia (2010). doi:10.1109/ISIEA.2010.5679492 10. Onat, N.: Recent developments in maximum power point tracking technologied for photovoltaic systems. Int. J. Photoenergy 245316, 1–11 (2010). doi:10.1155/2010/245316 11. Passino, K.M., Yurkovich, S.: Fuzzy Control. Addison Wesley Longman Inc., California (1998) 12. National Instruments. Improving PID Performance. National Instruments (2014) 13. Zhang, H.: Constant voltage control on DC bus of PV system with Flywheel Energy Storage Source (FESS). In: The International Conference on Advanced Power System Automation and Protection, vol. 300072, pp. 1723–1727 (2011). doi:10.1109/APAP.2011.6180648 14. Sharma, D.: Designing and modeling fuzzy control systems. Int. J. Comput. Appl. 16(1), 0975–8887. doi:10.1.1.206.2882 15. Shiau, J.K., Wei, Y.C., Lee, M.Y.: Fuzzy controller for a voltage-regulated solar-powers MPPT system for hybrid power system application. Energies, 8, 3292–3312 (2015). doi:10. 3390/en8053292 16. Letting, L.K., Munda, J.L., Hamam, Y.: Optimization of fuzzy logic controller design for maximum power point tracking in photovoltaic systems. Soft Comput. Green Renew. Energy Syst. 269, 233–260 (2011). doi:10.1007/978-3-642-22176-7_9 17. Zadeh, L.A.: Toward a theory of fuzzy information granulation and its centrality in human reasoning and fuzzy logic. Fuzzy Sets and System 90, 111–127 (2007). doi:10.1016/S01650114(97)00077-8

Optimized Management for Photovoltaic Applications Based on LEDs

335

18. Lilly, J.H.: Fuzzy Control and Identification. Wiley, Hoboken (2010). doi:10.1002/ 9780470874240 19. Omar, A., Ali, A., Sumait, B.S.: Comparison between the effects of different types of membership functions in fuzzy logic controller performance. Int. J. Eng. Res. Technol. 3(3), 2349–4395 (2015) 20. Touil, S., Attous, D.B.: Effect of different membership functions on fuzzy power system stability for synchronous machine connected to infinite bus. Int. J. Comput. Appl. 71(7), 0975–8872 (2013) 21. Chaturvedi, D.K.: Modeling and Simulation of System Using Matlab and Simulink. Taylor & Francis Group, US (2010) 22. Hong, H.E., Li, Y., Zhang, Z.H., Xu, X.: Fuzzy PID Control System in Industrial Environment. In: Information Technology and Mechatronics Engineering Conference (ITOEC 2015), Tianjin, China (2015) 23. Dubey, S., Sarvaiya, J.N., Seshadri, B.: Temperature dependent photovoltaic (PV) efficiency and its effect on PV production in the world - a review. In: PV Asia Pacific Conference, Singapore (2012). doi:10.1016/j.egypro.2013.05.072 24. Amarnath, K., Suresh, R.: Simulaton of incremental conductance MPPT with direct control method using cuk converter. Int. J. Res. Eng. Technol. 2(9), 557–566 (2013) 25. Safari, A., Mekhilef, S.: Incremental conductance MPPT method for PV systems. In: 24th Canadian Conference on Electrical and Computer Engineering (CCECE), pp. 345–347 (2011). doi:10.1109/CCECE.2011.6030470 26. Ping, W., Hui, D., Changyu, D., Shengbiao, Q.: An improved MPPT algorithm based on traditional incremental conductance method. In: International Conference on Power Electronics Systems and Applications, Hong Kong (2011). doi:10.1109/PESA.2011. 5982914 27. Ranjani, K., Raja, M., Anitha, B.: Maximum power point tracking by ANN controller for standalone photovoltaic systems. Int. J. Electr. Comput. Energ. Electron. Commun. Eng. 8 (3), 615–619 (2014). doi:scholar.waset.org/1999.5/9998096 28. Modelling and Simulation of Fuzzy Systems Using Matlab and Simulink. Tailor and Francis Group, U.S.A (2010) 29. Bequette, B.W.: Process Control. Modelling, Design and Simulation. Prentice Hall, New Jersey (2003) 30. Davis, S.: Solar System Efficiency: Maximum Power Point Tracking is Key (2015). http:// powerelectronics.com/solar/solar-system-efficiency-maximum-power-point-tracking-key. Accessed May 2017 31. Solar365. http://www.solar365.com/green-homes/windows-doors/clerestory-windows-passi ve-solar-homes. Accessed May 2017 32. Essefi, R.M., Souissi, M., Abdallah, H.H.: Maximum power point tracking control using neural networks for standalone photovoltaic systems. Int. J. Mod. Nonlinear Theory Appl. 3, 53–65 (2014). doi:10.4236/ijmnta.2014.33008 33. Mallika, S., Saravanakumar, R.: Genetic algorithms based MPPT controller for photovoltaic systems. Int. Electr. Eng. J. (IEEJ) 4(4), 1159–1164 (2014) 34. Bogdan, Z.S.: Fuzzy Controller Design: Theory and Applications. Taylor & Francis, Abingdon (2005) 35. Kaufman, H., Barkana, I., Sobel, K.: Direct Adaptive Control Algorithms: Theory and Applications. Springer, NY (1998) 36. Dadios, E.: Fuzzy Logic - Controls, Concepts, Theories and Applications. InTech, Croatia (2012) 37. Vieira, J.A.B., Mota, A.M.: A High-Performance Stand-Alone Solar PV Power System for LED Lighting. ISRN Renewable Energy, pp. 1–10 (2013). doi:10.1155/2013/573919

336

D. Craciunescu et al.

38. Islam, M.A., Merabet, A., Beguenane, R., Ibrahim, H.: Power Management Strategy for Solar Stand-alone Hybrid Energy System. Int. J. Electr. Robot. Electron. Commun. Eng. 8 (6), 783–787 (2014) 39. Alternative Energy. http://www.alternative-energy-tutorials.com/solar-power/stand-alone-pvsystem.html. Accessed April 2017 40. Suntech website. http://www.solar-facts-and-advice.com/Suntech.html. Acessed May 2017 41. Homer Software website. http://homerenergy.com/HOMER_pro.html. Accessed May 2017

Characterizing the Variability of High Resolution Solar Irradiance Data Series Robert Blaga(&) and Marius Paulescu Faculty of Physics, West University of Timisoara, Timișoara, Romania [email protected]

Abstract. Since the transient effects produced by clouds are manifest at sub-minute intervals, the accurate assessment of the performance of photovoltaic and solar-thermal systems requires high temporal resolution solar irradiance data. Different statistical quantifiers that describe the variability in solar irradiance time-series have been developed for characterizing the solar radiative regime over a given time interval. In this paper, two improved quantifiers for characterizing the stability of the solar radiative regime are proposed and assessed in relation to the traditional ones. A comparative study on the ability of these indicators to classify the days according to their stability is performed. The conclusions are illustrated with measurements performed on the Solar Platform of the West University of Timisoara, Romania at equal time intervals of 15 s. Keywords: Solar irradiance
Radiative regime
Statistical indicators
Clouds

1 Introduction The development of a Near-Zero Energy Community (NZEC) mandatorily involves renewable energies, like solar, wind and micro-hydro. Such projects typically include solar converters. In order to design an efficient photovoltaic system and/or a solar-thermal converter, in addition to quantitative information about the available solar energy, also information about its variability is required. There are many ways of classifying the days from the point of view of the solar radiative regime. The traditional quantifiers are defined in relation with the state-of-thesky. The total cloud cover amount C, which represents the fraction of the celestial vault covered by clouds, is the most common measure for the state-of-the = sky, usually reported by the meteorological stations. A second quantifier is the relative sunshine r, which represents the fraction of the day length with bright sunshine. These simple indicators encapsulate only limited information about solar radiative regime variability. For example, a daily average value C = 1/2 means that on the average half of the celestial vault was covered by clouds in that day. However, this value says nothing about the transient effects in solar irradiance time-series produced by clouds: a value C = 1/2 can be recorded in a stable solar radiative regime (bright sunshine in the morning and overcast afternoon) as well as in highly variable radiative regime. Thus, in order to classify the days from the point of view of the stability (or its counterpart the variability) of the solar radiative regime specific quantifiers have been developed. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_24

338

R. Blaga and M. Paulescu

Maafi and Harrouni [1] introduced fractal dimension of the solar irradiance time-series as specific quantifier for daily solar irradiance variability, aiming to classify the days into three classes: clear sky, partly cloudy and overcast. Tomson and Tamm [2] uses criteria based on the notion of increment for characterizing a given time interval as stable or unstable. An increment is defined as the absolute value of the difference between two subsequent data in the global solar irradiance series. Paulescu and Badescu [3] introduced a binary parameter, namely the sunshine stability number, for assessing the stability of the solar radiative regime. Basically, the sunshine stability number counts how many times the sun is covered (or uncovered) by clouds in a given time interval. Thus the sunshine stability number appears as a natural quantifier for the stability in solar radiative regime. In this paper, two improved quantifiers for characterizing the stability of the solar radiative regime are proposed and assessed in relation to the traditional ones. The first quantifier, the stability index, is defined on basis of the increment concept [4] while the second one, the sunshine number index, is defined in terms of the fractal dimension theory [5]. Section 2 is dedicated to introducing the quantifiers. Section 3 contains a description of the relevant data used in this study. A comparative study on the ability of these indicators to classify the days according to the solar radiative regime stability is reported in Sect. 4. The main conclusions are summarized in Sect. 5.

2 Quantifiers for the Variability of the Solar Radiative Regime 2.1

Stability Index

This quantifier is based on the solar irradiance measurements series. Following [2] we calculated the increments of the clearness index time-series. An increment defined as the magnitude of the difference between subsequent measurements. In Ref. [2] the increments are calculated for the solar irradiance time-series. We decided to work with clearness index because it isolates the fluctuations the series and removes the deterministic diurnal variation. The increments are thus defined as:

dkt;i ¼
kt;i þ 1  kt;i


ð1Þ

where kt ¼ GG represents the clearness index. G is the global solar irradiance measured ext at the ground level, while Gext is the solar irradiance estimated at the top of the atmosphere (for a detailed definition of clearness index, see e.g. Chap. 5 from [6]). We can either consider the individual increments, or we can sum over a number of measurements in order characterize the variability over a given time interval. For example, the increments over a 10-min time interval are obtained as: dkt ¼

XN i¼1

dkt;i

ð2Þ

Characterizing the Variability of High Resolution

339

N is the number of data measured in the considered time interval, which in our case is N ¼ 10  4 ¼ 40 measurements (Chap. 3 gives detailed information about the data used in this study). In order to classify a day as being stable or unstable, we introduced a critical value of the increment. If in a given time-interval dkt is greater than the critical value the time-interval is considered as being unstable. Adopting directly from [2], we estab¼ 1, for a 10-min interval. From lished empirically the critical value equal to k10min c this, the critical value for the instantaneous increments becomes kc ¼ 0:025. The stability index is defined as the fraction of increments that are unstable throughout a day. SI ¼



N X Ni ; N i¼1 day

Ni ¼

1; if dki [ kc 0; otherwise

ð3Þ

Nday is the number of the 10-min intervals within a day. A day is categorized as being stable/unstable if the value of SI is below/above a threshold value. According to [2] we set the threshold for a stable day at SIstable ¼ 0:1, and for an unstable day at SIunstable ¼ 0:5.

2.2

Sunshine Stability Number

Sunshine number n is a binary operator indicating whether the Sun is covered or not by clouds [7]. The sunshine number takes the value 1 when the Sun is shining and 0 when it is covered. In practice, we use the convention of the World Meteorological Organization (WMO) to designate when the Sun is shining. This occurs when the direct-beam solar irradiance Gb exceeds 120W=m2 [8]. Thus, the sunshine number is defined as:  n¼

1; 0;

W if Gb [ 120 m 2 otherwise

ð4Þ

Only global and diffuse solar irradiance are usually measured by the radiometric stations. Thus, the direct-beam solar irradiance is computed as: Gb ¼

G  Gd sin h

ð5Þ

where h represents the solar elevation angle. The sunshine stability number [3] counts the number of transitions in the sunshine number series. By convention we only count the changes that have the same sign (i.e. only when the Sun gets covered or comes out from behind the clouds). The equation of for the sunshine stability number can be written in a compact form as:  fi ¼

1; 0;

if eðni  ni1 Þ [ 0 ; otherwise

 e¼

1; 1;

if n1 ¼ 0 if n1 ¼ 1

ð6Þ

340

R. Blaga and M. Paulescu

The parameter e ensures that only the one-way transitions are taken into account. In the following we will consider the average of the sunshine stability number values over an entire day as a natural indicator of the stability of the solar radiative regime.

2.3

Fractal Dimension

Regular shapes like a circle or a tetrahedron have dimensions given by natural numbers. Some objects however, like fractals, can have fractional dimensionality. There are various ways of mathematically defining the dimension, one such quantity being the Minkowsky-Bouligand (MB) dimension [9]. This method was applied in Ref. [1] for characterizing the shape of the solar irradiance time series. The function G(t) is analytical because all physical processes are continuous. In practice, due to the discrete nature of the measured solar irradiance time-series, the mathematically calculated dimension takes a value between 1 and 2. In order to compute the fractal dimension, we first need to obtain the quantity: SDt ðAÞ ¼

N X

jAðtn þ DtÞ  Aðtn ÞjDt

ð7Þ

n¼0

The notation A stands for any time-series for which we wish to evaluate the fractal dimension. N represents the size of the sample, which depends on the sampling interval Dt. Following [4] we compute the fractal dimension of the curve as follows: 1 0  SDt ðAÞ ln 2 B C Dt h i C DðAÞ ¼ lim B @ A Dt!0 ln D1t

ð8Þ

Since the time-series is discrete, the limit cannot be taken exactly. However, D can be approximated as the slope of the linear equation: ln

    SDt ðAÞ 1 þc ffi D ð A Þ
ln Dt2 Dt

ð9Þ

In order to apply Eq. (9) we have to evaluate the left- and right-hand-side of the equation for different values Dt. Then the slope D is evaluated with a least-squares estimation. The values of Dt should range between the minimal length, given by the sampling frequency of the data series, up to a value which should not be larger than half of the whole data set (half of a day length in our case) [1]. The more values we take for Dt, the more accurate the result will be. In this study we applied the MB method both to the solar irradiance series (as in [1]), but also to the sunshine number time series. The latter is a novel approach.

Characterizing the Variability of High Resolution

341

Fig. 1. Variation of solar irradiance (G) and sunshine number (SSN) in five days of August 2010: (a) 14, (b) 16, (c) 22, (d) 28 and (e) 30

342

R. Blaga and M. Paulescu

3 Database Global and diffuse solar irradiance recorded during August 2010 on the Solar Platform of the West University of Timisoara are used in this study [10]. Measurements are performed all day long at equal time intervals of 15 s. DeltaOHM LP PYRA 02 first class pyranometers which fully comply with ISO 9060 standards and meet the requirements defined by the World Meteorological Organization are employed. The sensors are integrated into an acquisition data system based on National Instruments PXI Platform including a PXI-6259 data acquisition board optimized for high accuracy. Series of clearness index values have been calculated from measurements according to the definition given in Sect. 2. Series of sunshine number values have also been calculated by means of Eq. (4). Figure 1 shows the variation of solar irradiance and sunshine number in five days of 2010 with very different solar radiative regimes. Figure 1a (day 14) shows a generic bell shape of solar irradiance, typical for a stable radiative regime. Figure 1d (day 28) shows the opposite case of a typical day with highly unstable radiative regime. The days 16, 22 and 30 are intermediary, the solar irradiance profiles being characterized by different levels of variability. The variation of the sunshine number in these five days is also presented in Fig. 1. It can be seen that sunshine number accurately converts the solar irradiance series into a binary series. The transitions between the two states quantify the variability of the solar irradiance time series. Visual inspection of Fig. 1 illustrates that the days with a stable radiative regime are characterized by a small number of transitions in the sunshine number series, while the days with an unstable radiative regime have high number of transitions.

4 Classification of the Days Passing clouds induce high variability in the collectable solar irradiance in a given day. Tomson [11, 12] has shown that most of these fluctuations occur at sub-minut time scales. The sunshine stability number is able to capture the presence of large variations in solar irradiance series. Hence, we use the sunshine stability number on the highest sampling frequency data available (1/15 s) as our reference quantifier in classifying the days. We compare the other quantifiers introduced in Sect. 2, against the sunshine stability number. Furthermore, we look at how the quantifiers perform when the sampling frequency decreases.

4.1

Dependence on the Sampling Frequency

Although solar irradiance data series measured with a sample rate below 1 min are becoming more and more prevalent, their accessibility is still reduced at the present time. On the other hand, data measured at intervals of 1 min or above are already widespread and publicly available. The most notable example of such data is the open

Characterizing the Variability of High Resolution

343

access data bank of the BSRN network [13]. One might justly wonder how the performance of the different quantifiers in classifying the days is affected by the temporal resolution. Obviously quantifiers applied on such data cannot capture the cloudinduced transient effects, which are manifest on the sub-minute domain. However, the relative rankings of days in terms of variability may remain unchanged, allowing us to reliably diagnose the radiative regime. The four panels in Fig. 2 show the results obtained by applying the quantifiers discussed in Sect. 2 to data measured in the days of August 2010 at Timisoara. We have represented the quantifiers values at four different sampling intervals (15 s, 1 min, 2 min and 5 min). The magnitude of the stability index and of the daily mean of the sunshine stability number, respectively, depends on the sampling rate. The fractal dimension of the solar irradiance time-series and of the sunshine number time-series maintains roughly the same profile. In order to quantify this behavior, for each quantifier we evaluate the determination coefficient R2 of the 1, 2 and 5 min sampling interval series, in respect to the 15 s series. The results are listed in Table 1.

Fig. 2. Variation of: (a) stability index, (b) sunshine stability number, (c) fractal index of solar irradiance and (d) fractal index of sunshine number, of all the days in the month of August.

344

R. Blaga and M. Paulescu

Table 1. Determination coefficient R2 of the considered four quantifiers at different sampling rates with respect to the 15 s series. Quantifier SI (Stability index) f (Sunshine stability number) D(G) (Fractal dimension of solar irradiance) D(n) (Fractal dimension of sunshine number)

1 min 0.959 0.954 0.994 0.984

2 min 0.920 0.911 0.979 0.936

5 min 0.842 0.860 0.945 0.844

The fractal dimension of the solar irradiance time series performs remarkably well for all sample rates, with a correlation coefficient as high as R2 ¼ 0:94 for 5 min sampling rate as compared to the 15 s series. The other three indicators perform less well as compared to the fractal dimension of the irradiance series and comparably amongst themselves, with a good overall performance. For all the quantifiers, the value of the determination coefficient decreases sharply as the sampling interval is increased.

4.2

Comparative Analysis

The studied quantifiers have different domains of values. In order to compare their performances, we need to project the natural domain of values of every quantifier onto a given domain. The procedure is similar to the normalization procedure of distributions in statistics: we subtract the mean and divide by the standard deviation of the quantifier values over days of August 2010. The normalized quantifiers, generically denoted by Q, applied on the 15-s time series, are shown superimposed in Fig. 3. The horizontal lines in Fig. 3 represent the two limiting values: Q þ , above which a day is classified as highly unstable, and Q below which a day is marked as stable. We set these limits to Q ¼ 0:6. This classifies roughly 27% of the days as being stable

Fig. 3. The four quantifiers presented in Sect. 2, applied on the 15 s sampling interval time-series measurements in all days of August.

Characterizing the Variability of High Resolution

345

Table 2. The limits for stable and unstable days in absolute values of the four quantifiers

Qþ Q

SI (Stability index) 11.64 3.81

f (Sunshine D(G) (Fractal dimension of D(n) (Fractal dimension of stability number) solar irradiance) sunshine number) 51.25 16.95

1.63 1.38

1.69 1.51

Table 3. Correlation coefficients R2 of the quantifiers with respect to the sunshine stability number, applied on the 15 s time series f SI 0.916 D(G) 0.602 D(n) 0.519

(Q\Q ), 27% as being highly unstable (Q [ Q þ ), and 45% as being in the transition regime (partly cloudy, Q \Q\Q þ ), which is a reasonable distribution for a summer month in Romania (temperate climate, labeled as Cfb in the Geiger-Köppen climate classification system). The limits converted back into absolute values of the quantifiers are listed in Table 2. Note that the classification of SI is consistent with that in Ref. [2], while the classification of D(G) is consistent with that introduced in Ref. [1]. The correlation coefficients of the other three quantifiers as compared to the sunshine stability number, are shown in Table 3. The results clearly suggest that only the stability index contains the same information about the variability of a times series as the sunshine stability number. The fractal index characterizes well the long-term variability of the series (which is why it performs well on smaller sampling frequency data sets, as we have seen), but it is not sensitive to the large sudden fluctuations. In order to obtain the most accurate characterization of the radiative regime of a day, we conclude that the best way is to look at several different indicators. We propose the following procedure for the classification. First we establish the limits Q . We consider a day as being highly unstable if it is classified as such Q [ Q þ by all but one of the indicators. In our case this means that at least 3 of the 4 indicators show the given day as being unstable. Similarly, we classify a day as being stable when all but one of the quantifiers rank it as such Q\Q þ . The days that do not fall into either of the categories are assigned to the transition class. These are partly cloudy days with different types of cloud covers. One could further classify the transitional days into subcategories according to whether or not the day is ranked by all quantifiers as being partly cloudy. Using these criteria, the days from August 2010 are classified as follows: 9 out of the 31 days are classified as being highly unstable. These are the days: 4, 7–9, 20, 25, 28, 29 and 31. Similarly, 8 out of the 31 days are designated as being stable. These are the days: 6, 10, 14, 21, 23, 24, 26 and 27. The remaining 14 days (1–3, 5, 11–13, 15– 19, 22, 30) are marked as transitional.

346

R. Blaga and M. Paulescu

5 Conclusions In this paper, we have introduced two new quantifiers for characterizing the solar radiative regime: the stability index, defined on the basis of the clearness index increments and the fractal dimension of a sunshine number time series. We have investigated the ability of these quantifiers along with other two from the literature to classify the days according to the stability of their solar radiative regime. We have studied the effect of increasing the sampling interval on the results and we performed a comparative analysis of the quantifiers amongst themselves, when applied to the highest available sampling frequency data. We have introduced a procedure relying on information from all quantifiers, for classifying the days into stable, unstable, and transitory radiative regime categories. The procedure was illustrated on a set of 15 s measurements performed in Timisoara during August 2010. Based on our analysis, we recommend the sunshine stability number to be used for characterizing the stability of the radiative regime over a given time interval. When high temporal resolution data are not available, as is sometimes the case in NZECs, the fractal dimension of the solar irradiance should be applied. If several quantifiers are available, we suggest the use of our procedure for classifying the days. Acknowledgments. This work was supported by the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI - UEFISCDI, project number PN-III-P2-2, 1-PED2016-0592.

References 1. Maafi, A., Harrouni, S.: Preliminary results of the fractal classification of daily solar irradiances. Sol. Energy 75, 53–61 (2003) 2. Tomson, T., Tamm, G.: Short-term variability of solar radiation. Sol. Energy 80, 600–606 (2006) 3. Paulescu, M., Badescu, V.: New approach to measure the stability of the solar radiative regime. Theor. Appl. Climatol. 103, 459–470 (2011) 4. Tomson, T., Russak, V., Kallis, A.: Dynamic behavior of solar radiation. In: Badescu, V. (ed.) Modeling Solar Radiation at the Earth Surface, pp. 257–281. Springer, Berlin (2008) 5. Harrouni, S.: Fractal classification of typical meteorological days from global solar irradiance: Application to five sites of different climates. In: Badescu, V. (ed.) Modeling Solar Radiation at the Earth Surface, pp. 29–54. Springer, Berlin (2008) 6. Paulescu, M., Paulescu, E., Gravila, P., Badescu, V.: Weather Modeling and Forecasting of PV Systems Operation. Springer, London (2013) 7. Badescu, V., Paulescu, M.: Statistical properties of the sunshine number illustrated with measurements from Timisoara (Romania). Atmos. Res. 101, 194–204 (2011) 8. World Meteorological Organization: Guide to Meteorological Instruments and Methods of Observations, No. 8, 7th edn. (2008) 9. Bouligand, G.: Ensembles impropres et nombre dimensionnel. Bull. Sci. Math. 11(53), 185 (1929)

Characterizing the Variability of High Resolution

347

10. Solar Platform: Solar Platform of the West University of Timisoara (2017). http://solar. physics.uvt.ro/srms. Accessed May 2017 11. Tomson, T.: Fast dynamic processes of solar radiation. Sol. Energy 84, 318–323 (2010) 12. Tomson, T.: Transient processes of solar radiation. Theor. Appl. Climatol. 112, 403–408 (2013) 13. BSRN: Baseline Surface Radiation Network (2017). http://bsrn.awi.de/. Accessed May 2017

Semiconductor Graphenes for Photovoltaics Doru Buzatu1, Marius Mirica1, and Mihai Putz1,2(&)

2

1 Laboratory of Renewable Energies-Photovoltaics, R&D National Institute for Electrochemistry and Condensed Matter-INCEMC-Timisoara, Timisoara, Romania [email protected], [email protected] Laboratory of Structural and Computational Physical-Chemistry for Nanosciences and QSAR, Biology-Chemistry Department, West University of Timisoara, Timisoara, Romania

Abstract. Graphene as a single-atom-thick honeycomb lattice of carbon atoms has extraordinary optical and electrical features like high electron mobility (100 times greater than silicon). This makes it an attractive material for applications in photovoltaic devices. However, such extremely conductive quality negatively impacts on life-time efficiency in photovoltaics’ life cycle, when accordingly incorporated. The present challenge is to design and exploit semiconductorgraphene (SG), with controlled conductivity that assuring the desired energy conversion also maintains the long life using photovoltaics. Accordingly, two new forms of graphene are studied and employed, as new classes of n-doped, and p-doped semiconductors, so producing the so called, e-SG (electron-type semiconductor graphene, based on topological defective Graphene, as appeared by inherent Stone-Wales topological rotations in pristine Graphene 0-G) and h-SG (hole-type semiconductor graphene, when the structurally defective graphene is present), see figure. This way, the new controlled photovoltaic systems may be composed from various layers of pristine and semiconductor graphenes, passing from the fashioned generation of i-/p-/n-semiconductor based heterojunctions photovoltaics to the new generation of e-/h-SG controlled photovoltaics based on defective semiconductor graphenes - for a long-life use. The efficiency of photovoltaic materials with 0-G, e-SG, and h-SG heterojunctions may be explored by using computational quantum chemistry methods. Keywords: Defective graphenes
Heterojunctions’ i/p/n-semiconductors
Energetic alignment

photovoltaics




1 Introduction 1.1

Graphenes at a Glance

The new promising trend for graphene is to replace, or just complete the use of semiconductors in micro- and nanoelectronics. It is determined by the following factors: the 2D nature of the graphene, which involves a facile processing and a direct control of the charge carriers, the possibility of rapid electronic excitation (quasi-relativistic) yielding a high mobility (l, approximately equal to the electrons and © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_25

Semiconductor Graphenes for Photovoltaics

349

the holes) - both at room temperature (RT) and low temperature T, and high j-dielectrics’s constant. In the case of graphene crystals, there are two well-established allotropes: the single layer graphene (SLG) and the bilayer graphene (BLG). In SLG charge carriers resemble relativistic Dirac particles [1], and the absence of a gap is supplemented by the high symmetry of the honeycomb lattice. In the case of BLG, electrons exhibit some Dirac-like properties, but they present a parabolic dispersion [1]. They are more versatile due to the fact that a transverse electric field may open a gap, [2–4] and the modality to change qualitatively its low energy band structure is by strain [5]. According to these considerations the use of both SLG and BLG has both advantages and disadvantages, which must be controlled and used in order to build functional devices. A very large range of 2D crystals are to be found in nature, for example several layered materials (LMs), stable in form of monolayer, and have complementary properties with the graphene. Layered structures are present in the case of transition metal oxides (TMOs) and in the case of transition metal dichalcogenides (TMDs) [6]. Within each layer the atoms are bound by covalent bonds, and the layers are hold together by van der Waals (vdW) forces [6]. In the case of LMs a lot of systems behaving very interestingly could be mentioned, such as: systems acting as semi-metals - NiTe2 and VSe2 [6], as semiconductors - WS2, WSe2, MoS2, MoSe2, MoTe2, TaS2, RhTe2, PdTe2 [6], as insulators - h-BN, HfS2 [6], as superconductors - NbS2, NbSe2, NbTe2, and TaSe2 [6]. Some LMs exhibit thermoelectric properties, such as Bi2Se3, Bi2Te3 [6] and may behave as topological insulators (TIs) [7]. By mechanic or liquid-phase exfoliation process, layers of atomic dimensions could be obtained from these materials [8]. The current complementary metal oxide semiconductor (CMOS) technology, is nowadays the main technology used for integrated circuits fabrication, as the miniaturizing of circuits has reach its limitations. It will be eclipsed in the future by the new emerging technologies including those based on graphene - according to International Technology Roadmap for Semiconductors (ITRS) [9]. At present the technology of producing graphene circuits is emerging; a low power device based on graphene which complies with all the CMOS technology requirements is not quite settled, and the growth of large area films with improved electrical properties on flat dielectric surfaces is also in its infancy. According to Sun et al. [10] and Yan et al. [11] new architectures based on graphene ribbons, or other types of graphene systems must be designed and developed in the near future. Since the thickness of the graphene layer has the dimension of a single atom, graphene is the perfect material for a novel generation of flexible electronic devices [11]. As for the production costs, the electronics on plastic or paper are cost effective [12, 13]. Due to the “all-surface” nature of the graphene, it is possible to modify its properties by surface treatments, for example by chemical functionalization [14]. In this regard graphene could be converted into a band-gap semiconductor, i.e. hydrogenated graphene or “graphane” [14] or into an insulator, i.e. fluorinated graphene, or “fluorographene” [15]. In the case of transistors, the use of graphene is an opportunity to complete and extend the present Si technology. In order to obtain logic devices by using graphene,

350

D. Buzatu et al.

one must create a controllable band gap. The key to the limited on/off current ratio (ION/IOFF) could be found using the modulation of the work function of the graphene [16], by injecting a graphene carrier into a fully-gaped semiconductor [17]; by getting control over vertical transport through various barriers (preferably against planar transport) [18]; or by using graphene as a gate, as an electrode, or as an interconnection. In this context, the present approach advances the idea of using topological and structural defective graphenes to produce heterojunctions with semiconductor controlled properties - so opening a new fruitful application of graphenes in moletronics. Moreover their conduction properties are eventually described by electron pairing quantum quasi particles (the bondons), as in the sequels described. 1.2

Defective Graphenes

With the graphene, the Stone-Wales (SW) structural rearrangements are isomeric and reversible. The SW7/7 represents the inverse rotation of SW6/6, and according to Ori et al. [19] SW7/7 annihilates the 5|7 defects transforming the two 5|7 pairs in four hexagons, as shown in (Fig. 1). From the topological point of view, by applying an arbitrary number of SW6/7 rotations, the extension of the graphene region intersected by the diagonal diffusion of the 5|7 pairs could be infinitely increased. According to Cataldo et al. [21] the simplest propagation diagonal mechanisms available for the 5|7 pairs was named the SWwave. It shows the following diagonal diffusion mechanism: for a 5|7 pair - that originates by a SW6/6 transformation - the SW6/7 operator rotates the vertical bond which in the case of graphene dual lattice ensures the connection between the 7-node of the pair to an adjacent 6-node. It determines the diagonal swap of the 5|7 pair with a 6|6 pair with the creation of a new horizontal hexagon-hexagon bond, as shown in (Fig. 2) [22].

Fig. 1. The action of the basic Stone-Wales rotations in both the direct and dual graphene lattice representations is shown. SW6/6 flips the arrowed central bond of the four shaded hexagons originating two 5|7 pairs in gray [19]

Semiconductor Graphenes for Photovoltaics

351

Fig. 2. (a) Dual representation of the graphene lattice armchair orientated, the direct lattice being also represented. The dashed region individuates the lattice supercell along the diagonal direction, (b)–(c) Dual representation of the SW mechanisms (a, b) given (Fig. 1). Hexagons, pentagons, heptagons are represented by white, shaded, black circles respectively. The dashed SW6/7 operator represents the next available rotation [22]

The above mentioned propagation mechanism determines in the graphene plain a diagonal or a vertical extended dislocation dipole. In the particular case of single graphene layers, the presence of in situ formation of 5|7 pairs was experimentally proven in studies conducted on single-walled carbon nanotubes, through transmission electron microscopy (TEM) [20]. Graphene lattice shows subtle and significant isomerization phenomena, i.e. the creation and the wave-like propagation of the Stone-Wales topological defects [22], determining countless isomeric re-tessellations of the hexagonal mesh, such as the pentagon-octagon-pentagon defect, whose pure topological nature has been recently proved [23]. In other words topological-based techniques represent a novel tool in

352

D. Buzatu et al.

order to model the diffusion processes taking place in graphenic structures or similar extended systems. The topologic rearrangements of graphene layers determined by the Stone-Wales rotations lead to 5|7 structural defects, which were diffused in the graphene layer. Further research studies are necessary in order to make understandable the effects of charge and defects inhomogeneities, to develop new doping techniques, to understand better the influence of different dielectric substrates or overgrown insulators, and to improve the devices performance. For example, for FET (Field Effect Transistor) applications, research must be made to analyze the transport regimes and the optoelectronic effects in gapped BLG. If an electrically induced gap in BLGs for quantum dots (QDs) and engineered QDs-based circuits (for example for quantum information processing) [24] could be utilized, it is necessary to better understand the influence of disorder and Coulomb interaction on the T dependence of conductivity. The nature of variable range hopping in gapped BLGs must be taken into consideration. It is generically described by an exponential increase of resistance, according to Eq. (1) [25]: R ¼ exp½ðT0 =T Þp

ð1Þ

where T0 is a constant depending on the localization length and density of states; the exponent is given by: p = 1/2 for the Efros-Shklovskii mechanism [26], and p = 1/3 for the Mott hopping regime [25]. According to Mott, the dominating regime depends on the material [25]. However, it is clear that the chemical bonding propagation may be regarded as the key concept in graphene dual regime (pristine vs. topologically defective); from dual behavior to double/bi-layer graphenic regime (BLF) there is only one step. The present chapter advocates for the BLF with allotropic topologically defective structures first, see the Sect. 2, and then with the structurally defective structures, as will be in the Sect. 3 further revealed.

2 Methods 2.1

Quantum Behaviour of Graphene

The double behavior of the graphene, as a metal or as a semiconductor [27] determines the occurrence of novel nanodevices which could be build directly over the carbon honeycomb, where the “active” hexagonal units could be controlled by molecular deposition/zipping/synthesis, meanwhile investigating the bondonic linkage/breakage mechanisms, see Putz and Ori [28, 29]. In the case of pristine honeycomb lattices the structural isomeric transformations could be considered topological expressions of bondonic entanglement among the involved junctions of the bonding. These allows employing the associate bondons of the involved breaking/transformed bonds in teleporting experiments aiming at detecting the specific bondons of the SW cell at a certain distance on the graphene sheet.

Semiconductor Graphenes for Photovoltaics

353

Fig. 3. The main conceptual and experimental tools of entangled quantum chemistry: (a) graphene and its 5/7 Stone-Wales (SW) bonding transformation, after Ori et al. [22]; Putz and Ori [28, 29], (b) the SW wave propagation on honeycomb group-IV systems with bondonic raised signal (best for C-graphene) starting from the next and beyond nearest neighboring (NN…) steps as revealed by pristine-to-topological defect phase transition in terms of caloric capacity in fourth order quantum path integral, after Putz and Ori [29]

It was predicted by Putz and Ori [28, 29] by modeling the bondonic “pulses” of the SW junction propagating on graphene nanoribbons, (Fig. 3). This provides the theoretic prediction for experiments with entangled bondons on graphenic lattices. On the other hand, if the graphene’s transport properties are properly understood, its behavior in the presence of a strong - quantizing - magnetic field must be also considered. Due to the fact that graphene is a 2D electron system, it exhibits the fundamental phenomenon of quantum Hall effect (QHE) [30–34], consisting of a very precisely quantization of Hall resistance of the device [34]. In this case, integer and several fractional QHE (FQHE) states were noticed, [30, 32, 35]. Regarding the FQHE state, a very high crystalline quality and pure material is needed [35] as the Coulomb interactions between electrons may become very strong, thus determining the formation of correlated states of matter [36]. Nevertheless, due to the QHE robustness in SLG a new possibility occurs aiming at exploring what was an impossible regime until recently of quantum transport in the case of solid-state materials, i.e. the interaction between QHE and superconductivity in a hybrid device made from graphene and a superconductor presenting high critical magnetic field, such as NbTi alloy [37]. Furthermore, the special robustness of QHE in graphene on the Si towards SiC [38], which is not yet completely explained [39]. It makes it an appropriate platform for a new type of resistance standard [38]. Moreover, the BLG system is once more seen as a controlled quantum gate system for the graphenic contained systems, while exhibiting controlled quantum resistance and thus the observed current, with the direct application to the quantum photovoltaic systems, will be presented in next subchapter.

354

2.2

D. Buzatu et al.

Bondonic Heterojunction Propagation on Graphene’s PV

The special features of electrons in SLG, such as their similitude with the relativistic Dirac particles, determine a p-n junction in graphene transparent to electrons arriving at normal incidence [40, 41]. This effect is known as Klein tunneling [41] and it determines a difficult way to achieve a complete pinch-off of electric current, if chemical modifications or patterning are not done [42]. But, at the same time this effect determines a unique possibility to create ballistic devices and circuits (here the electrons go through focusing by one or several p-n interfaces) [43]. If such devices are developed, techniques of non-invasive gating are needed [44]. In order to improve the graphene quality Bolotin et al. [44, 45] suggested a different method, i.e. suspending it over electrodes (also used as support), followed by a cleaning process by current annealing. In this case highly homogeneous carrier densities and micron-long mean free paths are obtained. They allow detailed investigations of electronic properties at very low excitation energies [45]. According to Heiblum et al. [46] other methods are focused on the development of a hot electron transistor, similar to those from semiconductor electronics. Thin transistors of a few atoms, based on a 2D tunneling barrier and graphene, reveal an increased quality. They were appropriate for subsequent applications. The transit time through such sandwiches is expected to be much less than 1 ps [46], whereas there are no limits for scaling down in the lateral dimension to real nm sizes. The metal/h-BN/SLG/h-BN/SLG system (considered that the thickness of the active part of the device must be smaller than 10 atoms, approx. 3 nm), allows a ballistic current controlled by the central graphene electrode. If 2D crystals are assembled into superstructures, stacks of several transistors in series (metal/h-BN/SLG/h-BN/SLG)N are built in a vertical integrated architecture. The photovoltaic photocurrent is generated through the separation of photogenerated e-h pairs by built-in electric fields at junctions between negatively (n-type) and positively (p-type) doped regions of graphene or between differently-doped sections in general as presented in [47–49]. If a source-drain bias voltage is applied, determining an external electric field, the same effect is achieved. In the case of graphene, as it is a semi-metal and generates a high dark current, such effect is generally avoided. In order to generate the built-in field, it must be doped, which could be achieved by local chemical doping [50], electrostatically, using two (split) gates [48, 51], or using the work-function difference between graphene and a contacting metal [49, 52, 53]. In the first case, depending on the applied gate voltages, the doping process could be tuned to be p or n. In the second case of graphene-metal junctions, the doping in the contact area is set, which is typically p-type for metals with a work function higher than the work function of intrinsic graphene (4.45 eV) [54] while the graphene channel can be p or n. The PV photocurrent direction is not influenced by the overall doping level, and it depends only on the direction of the electric field. It switches sign, when going from p-n to n-p, or from p-p+ to p+-p, where p+ means stronger p-type doping besides p.

Semiconductor Graphenes for Photovoltaics

355

Urich et al. [55] estimated a lower bound (about 2 ps.) on the intrinsic response time of SLG based MGM PDs, by an ultrafast optical correlation technique. Whereas the photogenerated carriers in graphene reach very high values for l, the transit time of these carriers will not limit the photodetection speed, which will be reached only by the RC (resistance multiplied by capacitance) characteristics of the detector [56]. Both response time and photo-detection efficiency depend on the ultrafast scattering processes. According to some authors [57–59] e-e scattering may determine the conversion of one high energy e-h pair into multiple e-h pairs of lower energy [59–61]; it is also called carrier multiplication. It could improve the overall photo-detection efficiency. From another point of view, the electron-phonon scattering process transfers electron energy to the phonons, and it could determine bolometric effects [62–65]. In this context, the bondonic forms of electronic pairings either as topologically defective graphene, as an electron-donor system, vs. defective graphenic form, as an electron-accepting form (equivalent of p-doped system), through the intermediate pairing recombination form of structurally genuine (pristine) form, may be employed in various functionalized forms (including the graphene-oxide form) to produce the photovoltaic mechanism in a mixed heterojunction tandem, (Fig. 4). However, much of the experimental testing can be saved by appropriate computationally testing of the alignment energetic HOMO-LUMO condition required the photovoltaic mechanism can be triggered, as in (Fig. 4). It is depicted in various forms of graphenic systems, either as topological (equivalent of e-doped) or structurally defective (equivalent of p-doped) nano-carbonic forms. Further discussions on these systems are included in the next section.

Fig. 4. Schematic representation of the photovoltaic photocurrent generation mechanism by donor-interlayer-acceptor heterojunction on the graphene base using the isomorphic forms of topologically defective graphene vs. structurally defective graphene states recombined in the inter-layer region by the pristine graphene, respectively

356

D. Buzatu et al.

3 Discussions Nowadays graphene systems evolution has a long-term objective which is the possibility to use graphene for both classical and quantum information processing, after CMOS systems. The use of graphene as an active component (as interconnect, or transparent gate) in the classical information processing area, refers to the development of vertical transistors and atomic scale metal-semiconductor field effect transistor (MESFETs). In quantum information processing area, in order to develop monolayer and bilayer QD qubits, readouts, and their scalable circuits, one must exploit the long-lived spin coherence of electrons in graphene. A major problem in transistor applications (mainly in case of integrated circuits (ICs) as potential Si replacement) is the zero bandgap of graphene. The new graphene device concepts, as well as the tunnel FETs (TFETs) and bilayer pseudospin FETs (BISFET) [66] will be studied in order to develop and optimize several design options. According to Banerjee et al. [66], BiSFET function is determined by the electrical properties of two layers of graphene placed in proximity. Consequently the electrons from one layer can pair with holes (both Fermions) from the opposite layer and e-h-pairs/excitons (Bosons) will occur, which afterwards can condense [66]. This condensation process modifies the quantum wavefunctions in the bilayer structure, and the isolated states from one of the two layers, will be converted into states that are a coherent linear combination of top and bottom layer components [67]. As a consequence of such a qualitative exchange, the tunnel resistance decreases from a higher value to a value which is only limited by the contacts [66]. This decreasing in tunnel resistance is applied only for small interlayer bias, due to the fact that the condensate is destroyed in the presence of high currents [67]. The performances are increased in the presence of the CMOS FETs, as BiSFET uses the I-V nonlinearities associated with this maximum tunnel current, and determines lower values for voltage or power [66]. An important step in graphene electronics development is represented by the integration of graphene systems with the present CMOS technology. From the literature on metal and semiconductors, today it is thought that two main mechanisms may occur in graphene. The first is the Elliot-Yafet (EY) mechanism [68, 69] and the other is Dyakonov-Perel (DP) mechanism [70]. The former refers to the electron spin which has a finite probability to flip during each scattering event off impurities or phonons [68, 69]. The latter mechanism is driven by the precession of electron spins along effective magnetic field orientations, depending on the momentum; direction and frequency of precession is changing at each scattering event [70]. According to Ochoa et al. [71] one of the recent theoretical derivation in SLG (taking into account the Dirac cone physics) reports a spin relaxation time which depends proportionally with the transport time; this represents a typical behavior of the EY-relaxation. One of the main objectives in order to obtain high quality graphene devices is to elucidate the real nature of the dominant mechanism, which will determine the spin relaxation time and the spin relaxation length. Spin transport in graphene was demonstrated by various research groups, but spin dynamics and relaxation are not

Semiconductor Graphenes for Photovoltaics

357

completely elucidated and theoretical predictions or generalization of EY and DP relaxation mechanisms do not handle the experimental reality [72]. According to Dlubak et al. [73] this situation could be improved by a precise tuning of the contact resistance between graphene and magnetic electrodes. Still the implications for large scale room temperature (RT) devices must be clarified. In this respect it is necessary to explore the spin relaxation mechanisms from a theoretical perspective beyond the conventional perturbative treatments. These parameters - spin relaxation time and the g factor (or dimensionless magnetic moment) - must be evaluated in terms of the relevant scattering processes close-to and away-from the Dirac point (such as short and long range scatterers, e-e and e-photon interaction, etc.). They depend on the intrinsic and extrinsic nature of the scattering sources. Regarding the materials, they depend on the relevance for RT operability. Since perturbation may have a direct influence on the graphenic resistance, and thus on its conductibility and photovoltaic conversion power, it can also be regarded as the series of topological (Stone-Wales) isomorphic forms for the e-donor systems, in general, and even as the e-pairing in the form of bondon donors in special (the so-called e-semiconductor graphene, e-SG). Another state of perturbation may consider the bonding vacancies themselves, in which case the structural graphenic defects induce the hole-semiconductor graphene, h-SG. When coupled they may be explored under the BLG transistor with topo-structural defects, and it should be explored in both theoretical and experimental sides. On the other hand, when combined with the inner-semiconductor system, the pristine graphene or intrinsic (semi)conductor graphene, 0-SG, one may build the photo-voltaic mechanism, when the energetic alignment is ensured, as shown in (Fig. 4). However, their interrelation may be physical-chemically established as in (Fig. 5): one may use the un-bonding in adjacency (for instance by TEM bombarding) to obtain

Fig. 5. Conceptual and structural inter-relation of three forms of graphene used in binding the photovoltaic systems, as in Fig. 4 revealed, however here with emphasising on the physical-chemistry operations bringing one form to another

358

D. Buzatu et al.

the p-SG from 0-SG; the chemical bonding addition (eventually by bondonic accepting) under an externally or by in-building applied or formed potential function may produce either the back-pristine graphenic cell or, when the “colored topological” action is undertaken (for instance by graphenic relating fullerene system is employed or when the magnetic field is applied for changing the aromaticity) towards the e-SG, respectively, (Fig. 5). Various couples and heterojunctions of 0-, e- and h-SG may trigger respective bondonic flux and producing the enhanced or damped photovoltaic effects when the appropriate anode and cathode contacts are applied. Such attempts will bring more eco-friendly photovoltaics as well as the moletronics in the attempt to turn the Si-based electronics to the carbon based nano-tehnology in electronics.

4 Conclusions The future of the eco-nano-technology of graphene for the next twenty years is focused on the transformation of graphene transistors, from outstanding tools to probe the transport properties of this material, to competitive devices which will replace or integrate state-of-the-art Si and compound semiconductor electronics. It is important to develop new ways for the design and the fabrication of graphene-based digital electronics in order to thoroughly use the potential of this material and to bring the semiconductor industry beyond the 7.4 nm node, which the ITRS expects to be reached by 2025 [9]. According to Liu et al. [74] by electrostatically controlled Pauli-blocking of optical transitions and controlled damping of plasmon propagation, the possibility to achieve ultra-high bandwidth electro-optical modulators, optical switches, and other devices is largely possible. Other authors [75] concluded that graphene is an outstanding candidate for high-gain photo-detection using the photo-gating effect; due to its 2D nature and its very high value of l, graphene’s conductance has a higher dependence on electrostatic perturbation determined by the photo-generated carriers in the proximity of the surface. Its special properties, such as for example the absence of a band-gap, which may be an obstacle for uses in electronic devices, are friendly for photonics and optoelectronics. It could have some positive effects, such as: allowing ultra-wideband accessibility ensured by the linear electronic dispersion, and allowing an efficient, gate controllable, e-h pair generation at all wavelengths, in contrast with other semiconductors. On the other hand, as reported in the innovative studies devoted to 1D graphenic nanoribbons, at the typical space-scale of 15–30 Å, relevant long-range bonding contributions arise from the action of the bondons B [28, 29]. However further effects in terms of “caloric capacity” signal of bondonic propagation on honey-comb lattices was identified paralleling the increasing of induced vacancies in the nanoribbons [76]: the presence of delocalized bondons (along graphene sheets) provide universal long-range electronic interactions able to guarantee the appearance of vacancy accumulation and self-healing effects in graphene and non-carbon honeycomb systems.

Semiconductor Graphenes for Photovoltaics

359

However, accordingly the main road-map for graphene functionalizing towards electronics and photovoltaic technology may include the critical research-developing steps: • redefining the entire photovoltaics (PV) based on semiconductors to photovoltaics (PV) based on graphene (Fig. 5); • generalization of PV-semiconductor junctions to hybrid junctions with 0-SG, e-SG, and h-SG, respectively; • designing the graphene-based transistor, with potential applications in electronics, nanoelectronics and moletronics; • the increase of the greening degree of the photovoltaic conversion systems by using the graphene, based exclusively on carbon, beside the exclusive use of oxides in photovoltaics based on semiconductors; • the conduction degree improvement of the hybrid semiconductors based on graphene (because of the ultra-high conduction properties of graphene). • developing the quantum theory of chemical interactions by bondons in molecules [77] and by bondots in stacked nanosystems [78], so advancing the field of designing intelligent materials (as PVs) with fast and pairing electrons and quantum dots on graphenes. In all these endeavours the computational study is a compulsory pre-requisite for monitoring the energetic alignment conditions as in (Fig. 4) to ensure the photovoltaic mechanism by avoiding experimental trial-and-errors testing. Acknowledgments. Authors hereby acknowledge the research project PED123/2017 of UEFISCDI-Romania.

References 1. Geim, A.K.: Graphene: status and prospects. Science 324, 1530–1534 (2009). doi:10.1126/ science.1158877 2. McCann, E., Fal’ko, V.I.: Landau level degeneracy and quantum Hall effect in a graphite bilayer. Phys. Rev. Lett. 96, 86805 (2006). doi:10.1103/PhysRevLett.96.086805 3. Oostinga, J.B., Heersche, H.B., Liu, X., Morpurgo, A.F., Vandersypen, L.M.K.: Gate-induced insulating state in bilayer graphene devices. Nat. Mater. 7, 151–157 (2007). doi:10.1038/nmat2082 4. Zhang, Y., Tang, T.T., Girit, C., Hao, Z., Martin, M.C., Zettl, A., Crommie, M.F., Shen, Y.R., Wang, F.: Direct observation of a widely tunable bandgap in bilayer graphene. Nature 459, 820–823 (2009). doi:10.1038/nature08105 5. Mohiuddin, T.M.G., Lombardo, A., Nair, R.R., Bonetti, A., Savini, G., Jalil, R., Bonini, N., Basko, D.M., Galiotis, C., Marzari, N., Novoselov, K.S., Geim, A.K., Ferrari, A.C.: Uniaxial strain in graphene by Raman spectroscopy: G peak splitting, Gruneisen parameters and sample orientation. Phys. Rev. B 79, 205433 (2009). doi:10.1103/PhysRevB.79.205433 6. Wilson, J.A., Yoffe, A.D.: The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties. Adv. Phys. 18, 193–335 (1969). doi:10.1080/00018736900101307

360

D. Buzatu et al.

7. Kane, C.L., Mele, E.J.: Quantum spin hall effect in graphene. Phys. Rev. Lett. 95, 226801 (2005). doi:10.1103/PhysRevLett.95.226801 8. Novoselov, K.S., Jiang, D., Schedin, F., Booth, T., Khotkevich, V., Morozov, S., Geim, A. K.: Two-dimensional atomic crystals. Proc. Nat. Acad. Sci. USA 102, 10451–10453 (2005). doi:10.1073/pnas.0502848102 9. http://www.itrs.net. Accessed 2017 10. Sun, D.-M., Liu, C., Ren, W.-C., Cheng, H.-M.: A review of carbon nanotube- and graphene-based flexible thin-film transistors. Small 9, 1188–1205 (2013). doi:10.1002/smll. 201203154 11. Yan, C., Cho, J.H., Ahn, J.-H.: Graphene-based flexible and stretchable thin film transistors. Nanoscale 4, 4870 (2012). doi:10.1039/c2nr30994g 12. Rogers, J.A., Bao, Z.J.: Printed plastic electronics and paperlike displays. J. Polym. Sci., Part A: Polym. Chem. 40, 3327–3334 (2002). doi:10.1002/pola.10405 13. Steckl, A.J.: Circuits on cellulose. IEEE Spectr. 50, 48–61 (2013). doi:10.1109/MSPEC. 2013.6420146 14. Elias, D.C., Nair, R.R., Mohiuddin, T.M.G., Morozov, S.V., Blake, P., Halsall, M.P., Ferrari, A.C., Boukhvalov, D.W., Katsnelson, M.I., Geim, A.K., Novoselov, K.S.: Control of graphene’s properties by reversible hydrogenation: evidence for graphane. Science 323, 610–613 (2009). doi:10.1126/science.1167130 15. Nair, R.R., Ren, W., Jalil, R., Riaz, I., Kravets, V.G., Britnell, L., Blake, P., Schedin, F., Mayorov, A.S., Yuan, S., Katsnelson, M.I., Cheng, H.-M., Strupinski, W., Bulusheva, L.G., Okotrub, A.V., Grigorieva, I.V., Grigorenko, A.N., Novoselov, K.S., Geim, A.K.: Fluorographene: a two-dimensional counterpart of Teflon. Small 6, 2877–2884 (2010). doi:10.1002/smll.201001555 16. Giovannetti, G., Khomyakov, P., Brocks, G., Karpan, V., Van den Brink, J., Kelly, P.: Doping graphene with metal contacts. Phys. Rev. Lett. 101, 26803 (2008). doi:10.1103/ PhysRevLett.101.026803 17. Avouris, P.: Graphene: electronic and photonic properties and devices. Nano Lett. 10, 4285– 4294 (2010). doi:10.1021/nl102824h 18. Britnell, L., Gorbachev, R.V., Jalil, R., Belle, B.D., Schedin, F., Mishchenko, A., Georgiou, T., Katsnelson, M.I., Eaves, L., Morozov, S.V., Peres, N.M.R., Leist, J., Geim, A.K., Novoselov, K.S., Ponomarenko, L.A.: Field-effect tunneling transistor based on vertical graphene heterostructures. Science 335, 947–950 (2012). doi:10.1126/science.1218461 19. Ori, O., Cataldo, F., Graovac, A.: On topological modeling of 5|7 structural defects drifting in graphene. In: Putz, M.V. (ed.) Carbon Bonding and Structures: Advances in Physics and Chemistry, Carbon Materials: Chemistry and Physics, vol. 5, pp. 43–55. Springer Science +Business Media B.V. (2011). doi:10.1007/978-94-007-1733-6_3 20. Hashimoto, A., Suenaga, K., Gloter, A., Urita, K., Iijima, S.: Direct evidence for atomic defects in graphene layers. Nature 430, 870–873 (2004). doi:10.1038/nature02817 21. Cataldo, F., Ori, O., Graovac, A.: Graphene topological modifications. Int. J. Chem. Model. 3(1–2), 45–63 (2011) 22. Ori, O., Cataldo, F., Putz, M.V.: Topological anisotropy of stone-wales waves in graphenic fragments. Int. J. Mol. Sci. 12, 7934–7949 (2011). doi:10.3390/ijms12117934 23. Ori, O., Putz, M.V.: Isomeric formation of 5|8|5 defects in graphenic systems. Fuller Nanotub Carbon Nanostruct. 22(10), 887–900 (2014). doi:10.1080/1536383X.2012.749454 24. Fal’ko, V.: Graphene: quantum information on chicken wire. Nat. Phys. 3, 151–152 (2007). doi:10.1038/nphys556 25. Mott, N.F.: Conduction in glasses containing transition metal ions. J. Non-Cryst. Solids 1, 1–17 (1968). doi:10.1016/0022-3093(68)90002-1

Semiconductor Graphenes for Photovoltaics

361

26. Efros, A.L., Shklovskii, B.I.: Coulomb gap and low temperature conductivity of disordered systems. J. Phys. C: Solid State Phys. 8, L49 (1975) 27. Neto, A.C., Guinea, F., Peres, N.M.R., Novoselov, K.S., Geim, A.K.: The electronic properties of graphene. Rev. Modern Phys. 81, 109–162 (2009). https://doi.org/10.1103/ RevModPhys.81.109 28. Putz, M.V., Ori, O.: Bondonic characterization of extended nanosystems: application to graphene’s nanoribbons. Chem. Phys. Lett. 548, 95–100 (2012). https://doi.org/10.1016/j. cplett.2012.08.019 29. Putz, M.V., Ori, O.: Bondonic effects in group-IV honeycomb nanoribbons with Stone-Wales topological defects. Molecules 19, 4157–4188 (2014). doi:10.3390/ molecules19044157 30. Novoselov, K.S., Geim, A.K., Morozov, S., Jiang, D., Grigorieva, M.I.K.I.V., Dubonos, S., Firsov, A.: Two-dimensional gas of massless Dirac fermions in graphene. Nature 438, 197–200 (2005). doi:10.1038/nature04233 31. Zhang, Y., Small, J.P., Amori, M.E.S., Kim, P.: Electric field modulation of galvanomagnetic properties of mesoscopic graphite. Phys. Rev. Lett. 94, 176803 (2005). doi:10.1103/ PhysRevLett.94.176803 32. Zhang, Y., Tan, Y.W., Stormer, H.L., Kim, P.: Experimental observation of the quantum Hall effect and Berry’s phase in graphene. Nature 438, 201–204 (2005). doi:10.1038/ nature04235 33. Novoselov, K.S., McCann, E., Morozov, S., Fal’ko, V.I., Katsnelson, M., Zeitler, U., Jiang, D., Schedin, F., Geim, A.K.: Unconventional quantum Hall effect and Berry’s phase of 2p in bilayer graphene. Nat. Phys. 2, 177–180 (2006). doi:10.1038/nphys245 34. Klitzing, K.V., Dorda, G., Pepper, M.: New method for high-accuracy determination of the fine-structure constant based on quantized hall resistance. Phys. Rev. Lett. 45, 494–497 (1980). doi:10.1103/PhysRevLett.45.494 35. Du, X., Skachko, I., Duerr, F., Luican, A., Andrei, E.Y.: Fractional quantum Hall effect and insulating phase of Dirac electrons in graphene. Nature 462, 192–195 (2009). doi:10.1038/ nature08522 36. Bolotin, K., Ghahari, F., Shulman, M.D., Stormer, H.L., Kim, P.: Observation of the fractional quantum Hall effect in graphene. Nature 462, 196–199 (2009). doi:10.1038/ nature08582 37. Komatsu, K., Li, C., Autier-Laurent, S., Bouchiat, H., Gueron, S.: Superconducting proximity effect in long superconductor/graphene/superconductor junctions: from specular Andreev reflection at zero field to the quantum Hall regime. Phys. Rev. B 86, 115412 (2012). doi:10.1103/PhysRevB.86.115412 38. Tzalenchuk, A., Lara-Avila, S., Kalaboukhov, A., Paolillo, S., Syväjärvi, M., Yakimova, R., Kazakova, O., Janssen, T., Fal’ko, V., Kubatkin, S.: Towards a quantum resistance standard based on epitaxial graphene. Nat. Nanotechnol. 5, 186–189 (2010). doi:10.1038/nnano.2009. 474 39. Janssen, T., Tzalenchuk, A., Yakimova, R., Kubatkin, S., Lara-Avila, S., Kopylov, S., Fal’ko, V.: Anomalously strong pinning of the filling factor m = 2 in epitaxial graphene. Phys. Rev. B, 83, 233402 (2011). https://doi.org/10.1103/PhysRevB.83.233402 40. Cheianov, V.V., Fal’ko, V.I.: Selective transmission of Dirac electrons and ballistic magnetoresistance of n-p junctions in graphene. Phys. Rev. B 74, 041403 (2006). doi:10. 1103/PhysRevB.74.041403 41. Katsnelson, M., Novoselov, K.S., Geim, A.K.: Chiral tunneling and the Klein paradox in graphene. Nat. Phys. 2, 620–625 (2006). doi:10.1038/nphys384

362

D. Buzatu et al.

42. Cresti, A., Nemec, N., Biel, B., Niebler, G., Triozon, F., Cuniberti, G., Roche, S.: Charge transport in disordered graphene-based low dimensional materials. Nano Res. 1, 361–394 (2008). doi:10.1007/s12274-008-8043-2 43. Cheianov, V.V., Fal’ko, V., Altshuler, B.: The focusing of electron flow and a Veselago lens in graphene p-n junctions. Science 315, 1252–1255 (2007). doi:10.1126/science.1138020 44. Bolotin, K.I., Sikes, K., Jiang, Z., Klima, M., Fudenberg, G., Hone, J., Kim, P., Stormer, H.: Ultrahigh electron mobility in suspended graphene. Solid State Commun. 146, 351–355 (2008). doi:10.1016/j.ssc.2008.02.024 45. Du, X., Skachko, I., Barker, A., Andrei, E.Y.: Approaching ballistic transport in suspended graphene. Nat. Nanotechnol. 3, 491–495 (2008). doi:10.1038/nnano.2008.199 46. Heiblum, M., Nathan, M.I., Thomas, D.C., Knoedler, C.M.: Direct observation of ballistic transport in GaAs. Phys. Rev. Lett. 55, 2200–2203 (1985). doi:10.1103/PhysRevLett.55. 2200 47. Mueller, T., Xia, F., Freitag, M., Tsang, J., Avouris, P.: The role of contacts in graphene transistors: a scanning photocurrent study. Phys. Rev. B 79, 245430 (2009). doi:10.1103/ PhysRevB.79.245430 48. Peters, E.C., Lee, E.J.H., Burghard, M., Kern, K.: Gate dependent photocurrents at a graphene p-n junction. Appl. Phys. Lett. 97, 193102 (2010). doi:10.1063/1.3505926 49. Rao, G., Freitag, M., Chiu, H.-Y., Sundaram, R.S., Avouris, P.: Raman and photocurrent imaging of electrical stress-induced p-n junctions in graphene. ACS Nano 5, 5848–5854 (2011). doi:10.1021/nn201611r 50. Farmer, D.B., Golizadeh-Mojarad, R., Perebeinos, V., Lin, Y.M., Tulevski, G.S., Tsang, J.C., Avouris, P.: Chemical doping and electron-hole conduction asymmetry in graphene devices. Nano Lett. 9, 388–392 (2009). doi:10.1021/nl803214a 51. Lemme, M.C., Koppens, F.H.L., Falk, A.L., Rudner, M.S., Park, H., Levitov, L.S., Marcus, C.M.: Gate-activated photoresponse in a graphene p-n junction. Nano Lett. 11, 4134–4137 (2011). doi:10.1021/nl2019068 52. Mueller, T., Xia, F., Avouris, P.: Graphene photodetectors for high-speed optical communications. Nat. Photonics 4, 297–301 (2010). doi:10.1038/nphoton.2010.40 53. Freitag, M., Low, T., Xia, F., Avouris, P.: Photoconductivity of biased graphene. Nat. Photonics 7, 53–59 (2013). doi:10.1038/nphoton.2012.314 54. Sherpa, S.D., Kunc, J., Hu, Y., Levitin, G., de Heer, W.A., Berger, C., Hess, D.W.: Local work function measurements of plasma-fluorinated epitaxial graphene. Appl. Phys. Lett. 104, 081607 (2014). doi:10.1063/1.4866783 55. Urich, A., Unterrainer, K., Mueller, T.: Intrinsic response time of graphene photodetectors. Nano Lett. 11, 2804–2808 (2011). doi:10.1021/nl2011388 56. Wolf, S., Chtchelkanova, A.Y., Treger, D.: Spintronics - a retrospective and perspective. IBM J. Res. Devel. 50, 101–110 (2006). doi:10.1147/rd.501.0101 57. Tomadin, A., Brida, D., Cerullo, G., Ferrari, A.C., Polini, M.: Non-equilibrium dynamics of photo-excited electrons in graphene: collinear scattering, Auger processes, and the impact of screening. Phys. Rev. B 88, 035430 (2013). doi:10.1103/PhysRevB.88.035430 58. Kim, R., Perebeinos, V., Avouris, P.: Relaxation of optically excited carriers in graphene. Phys. Rev. B 84, 075449 (2011). doi:10.1103/PhysRevB.84.075449 59. Malic, E., Winzer, T., Bobkin, E., Knorr, A.: Microscopic theory of absorption and ultrafast many-particle kinetics in graphene. Phys. Rev. B 84, 205406 (2011). doi:10.1103/ PhysRevB.84.205406 60. Brida, D., Tomadin, A., Manzoni, C., Kim, Y.J., Lombardo, A., Milana, S., Nair, R.R., Novoselov, K.S., Ferrari, A.C., Cerullo, G., Polini, M.: Ultrafast collinear scattering and carrier multiplication in graphene. Nat. Commun. 4, 1987 (2013). doi:10.1038/ncomms2987

Semiconductor Graphenes for Photovoltaics

363

61. Winzer, T., Knorr, A., Malic, E.: Carrier multiplication in graphene. Nano Lett. 10, 4839– 4843 (2010). doi:10.1021/nl1024485 62. Ferrari, A.C., Basko, D.: Raman spectroscopy as a versatile tool for studying the properties of graphene. Nat. Nanotechnol. 8, 235–246 (2013). doi:10.1038/nnano.2013.46 63. Ferrari, A.C., Meyer, J.C., Scardaci, V., Casiraghi, C., Lazzeri, M., Mauri, F., Piscanec, S., Jiang, D., Novoselov, K.S., Roth, S., Geim, A.K.: Raman spectrum of graphene and graphene layers. Phys. Rev. Lett. 97, 187401 (2006). doi:10.1103/PhysRevLett.97.187401 64. Breusing, M., Ropers, C., Elsaesser, T.: Ultrafast carrier dynamics in graphite. Phys. Rev. Lett. 102, 086809 (2009). doi:10.1103/PhysRevLett.102.086809 65. Lazzeri, M., Piscanec, S., Mauri, F., Ferrari, A.C., Robertson, J.: Electron transport and hot phonons in carbon nanotubes. Phys. Rev. Lett. 95, 236802 (2005). doi:10.1103/ PhysRevLett.95.236802 66. Banerjee, S.K., Register, L.F., Tutuc, E., Reddy, D.A., MacDonald, H.: Bilayer pseudospin field-effect transistor (BiSFET): a proposed new logic device. IEEE Electron Device Lett. 30, 158–160 (2009). doi:10.1109/LED.2008.2009362 67. Su, J., MacDonald, A.H.: How to make a bilayer exciton condensate flow. Nat. Phys. 4, 799–802 (2008). doi:10.1038/nphys1055 68. Elliott, R.: Theory of the effect of spin-orbit coupling on magnetic resonance in some semiconductors. Phys. Rev. 96, 266 (1954). doi:10.1103/PhysRev.96.266 69. Yafet, Y.: g Factors and spin-lattice relaxation of conduction electrons. Solid State Phys. 14, 1 (1963). doi:10.1016/S0081-1947(08)60259-3 70. Jeong, H.Y., Kim, J.Y., Kim, J.W., Hwang, J.O., Kim, J.-E., Lee, J.Y., Yoon, T.H., Cho, B. J., Kim, S.O., Ruoff, R.S., Choi, S.-Y.: Graphene oxide thin films for flexible nonvolatile memory applications. Nano Lett. 10, 4381–4386 (2010). doi:10.1021/nl101902k 71. Ochoa, H., Castro Neto, A.H., Guinea, F.: Elliot-Yafet mechanism in graphene. Phys. Rev. Lett. 108, 206808 (2012). doi:10.1103/PhysRevLett.108.206808 72. Han, W., Kawakami, R.K., Gmitra, M., Fabian, J.: Graphene spintronics. Nat. Nanotechnol. 9, 794–807 (2014). doi:10.1038/nnano.2014.214 73. Dlubak, B., Martin, M.-B., Deranlot, C., Servet, B., Xavier, S., Mattana, R., Sprinkle, M., Berger, C., De Heer, W.A., Petroff, F., Anane, A., Seneor, P., Fert, A.: Highly efficient spin transport in epitaxial graphene on SiC. Nat. Phys. 8, 557 (2012). doi:10.1038/nphys2331 74. Liu, M., Yin, X., Ulin-Avila, E., Geng, B., Zentgraf, T., Ju, L., Wang, F., Zhang, X.: A graphene-based broadband optical modulator. Nature 474, 64–67 (2011) 75. Konstantatos, G., Badioli, M., Gaudreau, L., Osmond, J., Bernechea, M., De Arquer, F.P.G., Gatti, F., Koppens, F.H.L.: Hybrid graphene-quantum dot phototransistors with ultrahigh gain. Nat. Nanotechnol. 7, 363–368 (2012). doi:10.1038/nnano.2012.60 76. Ori, O., Cataldo, F., Putz, M.V., Kaatz, F., Bultheel, A.: Cooperative topological accumulation of vacancies in honeycomb lattices. Fullerenes, Nanotubes, Carbon Nanostruct. 24(6), 353–362 (2016). doi:10.1080/1536383X.2016.1155561 77. Putz, M.V.: The bondons: the quantum particles of the chemical bond. Int. J. Mol. Sci. 11(11), 4227–4256 (2010). doi:10.3390/ijms11114227 78. Putz, M.V., Tudoran, M.A., Mirica, M.C.: Quantum dots searching for bondots: towards sustainable sensitized solar cells. In: Putz, M.V., Mirica, M.C.: (eds.) Sustainable Nanosystems Development, Properties, and Applications. IGI Global, Pasadena (2016). doi:10.4018/978-1-5225-0492-4. Chap. 9

Deployable Mobile Units Concepts for Photovoltaic and Solar Thermal Arrays Mihai Comsit(&), Macedon Moldovan, and Mircea Neagoe Renewable Energy Systems and Recycling Research Center, Transilvania University of Brasov, Brasov, Romania [email protected]

Abstract. One of the greatest concerns nowadays is the growth of the world population. This is the main reason for the continuously increase of the electrical and thermal energy demand and consumption. It is a fact that the reserves of fossil fuels are limited and the exponentially pollution expansion imposes the development and the implementation of renewable based energy production technologies. Thus, the solar energy use represents one of the most promising of the available answers. The solar energy conversion into electricity or heat for remote area applications with different functionalities imposes the design and implementation of transportable (mobile) based on stand-alone photovoltaic modules and solar thermal systems. The paper evaluates the availability of the solutions for this type of products. The research formulates a set of design criteria through constructive and functional design quality requirements meant to generate novel concepts for mobile solutions. The paper proposes several concepts for deployable mobile units for photovoltaic and solar thermal conversion systems. The concepts of mechanisms suitable for deployable PV and solar thermal arrays are developed through embodiment design by using 3D CAD tools. The analysis and the conceptual design process results lead to the conclusion that the use deployable/transportable systems is covering a wide range of applications starting with telecommunication systems up to domestic lighting, heating etc., washing facilities and several concepts are proposed in the paper. Keywords: Deployable mobile units


PV arrays
Solar thermal arrays

1 Introduction The solar energy conversion to electricity and heat by using photovoltaic (PV) and respectively solar thermal collectors (STC) it’s becoming one of the most promising options for fulfilling the energy demand worldwide, as the fossil fuel use for energy production represents a serious problem having the direct effect the environmental pollution. Both solar energy conversion technologies, were rapidly growing in the past decades and they should be considered a reliable an answer to the environmental issue. Even though the solar energy conversion technology is now mature, when referring to the technical and commercial development, the currently installed photovoltaic capacities provide only 0.1% of world total electricity generation and has an unbalanced distribution [1, 2], while solar thermal systems are facing challenging times too [3]. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_26

Deployable Mobile Units Concepts for PV and ST Arrays

365

This concerning phenomena is reflected by the continuous shrinkage of the annually installed solar collectors capacity. The expansion of installed capacity declined from 18% (2010–2011) to 5% in the period 2015–2016 [3]. Regarding the power production, the global targets are set by 2020 to an estimated 4% of the global electricity generation and even three times higher by 2030 [4]. In this context, the scientific reviews and the reports on the market show that the average growth of PV systems installations is 40% [4]. PV markets emerged and developed initially in northern countries despite their lack of solar potential while population in the Sunbelt region (between 30° N and 30° S Latitude) representing about 78% of the world population that could also benefit from off-grid and on-grid PV systems. The data show that PV had a more than double growth in 2010, continued with almost 30% increase in 2011 and a further 11% in 2012. The end of 2013 marked a cumulative global generation PV electricity capacity of 140 GWp. Most of the cumulative installed capacity is represented by 80.7 GWp in EU which is still a leader in terms of global capacity installation. Nowadays, China became world’s leading manufacturer of solar PV modules and ST collectors [5]. The vast majority of the total solar thermal capacity in operation was installed in China (289.5 GWth) which represent the about 71% of the world installation [6–8]. However the installed PV and capacity is far behind its producing capacity. While China and Taiwan are yearly producing about 54 GWp, China installed in 2014 only about 12–14 GWp. Meanwhile, China and Europe, the traditional mass markets of small-scale solar water heating systems for detached single family houses and apartment buildings are under market pressure from heat pumps and photovoltaic systems [7, 8]. The most dramatic development was observed in China. For the third year in a row, the 2016 market declined. After −17% in 2014 and also in 2015 the year 2016 continued this trend with −9% [4]. The reports of International Energy Agency (IEA) [9, 10] rings the bell regarding the energy availability and social equality revealing that from about 22% of the world population which has no access to electricity and to proper hygiene conditions up 78% lives in rural areas. In this context, solar energy conversion systems, including PV technologies and ST technologies provide options for remote and unfavorable areas and for rural electrification and proper hygienic conditions in a sustainable way, as compared to fossil fuel based solutions. There are three main paths to bring heat, hot water and electricity and in the remote areas: (a) extending national grids (long term and expensive development); (b) implementing stand alone PV and ST solutions (short and medium-term and accessible options); (c) development of mini-centralized units with hybrid solutions (PV, ST and Diesel) which are short and medium term options but not 100% clean and sustainable). Eradication of poverty and social inequity by ensuring clean and secure energy sources does not represent the complete solution, but it is a reliable way to improve the quality of life for communities located in less favored, remote areas. Development of

366

M. Comsit et al.

PV and STC powered engineered solutions meant to fulfill the needs of such communities may find an answer in the design of mobile, compact, reliable and multifunctional facilities. In this context the objective of this paper is focused on defining a general set of criteria regarding the design process of stand-alone deployable PV/ST arrays and on development of design concepts for this kind of products. Following the product design algorithm, two concepts of systems suitable for deployable PV/ST arrays are proposed and developed by embodiment design methods, through 3D CAD models. Thereby, novel possible solutions for mobile deployable units that integrate both STC and PV modules are proposed. The versatility of these units regarding the possibility of utilization it is remarkable because they can cover a wide range of applications.

2 Problem Formulation An important step towards development and progress of humanity is represented by the access to electricity, sanitation facilities and decent hygiene conditions. When referring to progress, United Nations defined a set of targets by the Millennium Development Goals (MDG) [11] focused on the progress of rural communities and not only, that includes: (a) (b) (c) (d) (e) (f) (g) (h)

reduction of starvation (ensuring the cold food storage); access to potable water (by pumping and decontamination systems); improving education (lighting and communication devices); reducing mortality and the incidence of diseases (by refrigeration of medication, modern medical equipment and facilities, personal hygiene facilities); providing clean power and domestic hot water DHW to remote or unpredicted communities (by the use of non-pollutant technologies of any kind); ensuring gender equality (releasing women from some housing tasks by water pumping, DHW sources and access to electronic household products); access to information (by media channels and internet); ensuring primary education (by civilized facilities and equipments).

In order to reach the most of these goals, common features are identified – the necessary systems and facilities refer to electricity and domestic hot water (DHW). The solution of extending the national grids has to consider that many countries are prevented from such development because of the huge cost of extra-capacity generation. Hence, stand alone PV based systems and/or ST systems represents a competitive solution for fulfilling the energy demand of communities in remote or unfavorable areas [10]. Solar energy is available in its active or passive use in various forms, concepts and innovative designs are expected to emerge in order to provide answers to energy needs of the community as electric energy for lighting, refrigeration, power for common appliances, medical equipment, telecommunications, decontamination, water pumping etc., and thermal energy for washing or even heating in special circumstances. In this context the market already provides solutions for these needs in different applications.

Deployable Mobile Units Concepts for PV and ST Arrays

367

As the mobile off grids systems destined for remote or unfavorable areas should answer to a wide variety of application like telecommunications, IT, domestic lighting, camp security, emergency relief, refugee camps, medical facilities, sanitation facilities, washing facilities, street lighting, learning facilities, water pumping, decontamination units, refrigeration, military application etc., transportable/deployable PV and ST systems should be considered as a reliable option for the requirements of emergency relief, refugee camps or remote communities [11, 12].

Fig. 1. The pillars of the design quality of the system

A set of criteria for the design strategy is necessary to be formulated, as the development of an adaptable and versatile mobile and deployable PV/ST system is limited by the broad variety of application. The complexity of the deployable/transportable PV systems design imposes two pre-requisites to be met, as presented in Fig. 1: • functionality (meeting the energy demand, folding/deploying capability, option for tracking etc.); • constructive quality (meeting the embodiment design exigencies of a mechanical system reliable for the above described areas of implementation).

3 Design Prerequisites and Criteria for Transportable and Deployable PV/STC Arrays The solutions for transportable and deployable systems for solar energy conversion devices have been explored nowadays by several companies which already placed on the market a wide variety of products mainly PV based [12, 13]. Mainly, off-grid PV systems are extensively investigated [14–16] in the last decades and the design and the optimization of the large majority of these systems was developed accordingly to the built environment implementation and integration criteria. Reliable solutions adapted to various applications (power production, lighting, small appliances, etc.) are already in the market but the literature regarding the ST or combined PV/ST solutions is scarce. In the case of mobile deployable PV/ST based units, the following customer pre-requisites can be considered in a realistic scenario: • Power supply based on renewable energy sources for a range of remote applications (e.g. motors, pumps, generators, lighting) with up to 1.5 kW nominal power; • Off-grid electrical loads;

368

M. Comsit et al.

• Empowering the appliances for up to 8 h per day, including cloudy sky or rainfall; • The electrical loads can be both of direct current (24/12 VDC) and alternative current (230 VAC); • DHW supply based on renewable energy source - STC; • DHW up to 400 L/day, storage included; • Mobility of the systems in-between the operational points can be performed on various types of roads, including bumpy and rough roads, even off-roads; • Quick and easy operation at location switch; • Simplicity in operation with no need of specialized staff; • Reliability and safety in operation, even at high wind speeds or rough weather; • Effective cost and quality. The product design specifications (known also as product planning) are formulated in the first step of any design process, in a multi-disciplinary and specialized activity for converting a certain social need into a list of external and internal requirements; these are associated to the designed product, along with a set of evaluation criteria and are completed with milestones [17, 18]. The product design specifications are stated by describing key properties [19], accompanied by essential qualitative and quantitative data, using various parameters of different types (e.g. geometry, kinematics, material, energy, safety, quality control, maintenance, recycling, costs, etc.). Considering the customer pre-requisites, a simplified but compact set of design specifications of an off-grid mobile and deployable PV/ST unit is proposed, structured in functional and constructive requirements. While the mobile systems destined for remote or unfavorable areas can find solutions by implementation in transportable/deployable concepts, the compact engineered solutions for these units represent an asset. Thus, from engineering point of view, the development of deployable PV arrays destined for remote areas has to be based on a set of design criteria approaching functional and constructive aspects of such systems. Considering the analysis of the already implemented solutions and the overview on the possible area of applications, the functionality of a deployable transportable PV/ST array have to rely on the following functional criteria (Table 1):

Table 1. Functional criteria for PV respectively ST mobile systems Functional Criterion

For PV system

For ST system

(F1)

PV based system;

ST based system

(F2)

versatile- AC/DC output;

DHW output;

(F3)

built-in inverter min 1.5 kW;

built-in boiler;

(F4)

built-in storage unit (1400 Ah);

built-in storage unit ;

(F5)

PV source ≥ 1.5 kWp;

Flat solar thermal collectors

(F6)

deployable system;

(F7)

tilt angle adjustment;

(F8)

integrated power management unit;

(F9)

mobile system (on wheels).

flexible connections;

Deployable Mobile Units Concepts for PV and ST Arrays

369

The constructive quality of the design for a transportable/deployable PV/ST array it is also determined by the following aspects (Table 2):

Table 2. Constructive criteria for PV respectively ST mobile systems Constructive criterion C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12

For PV system and ST system Modularity of the system able to adapt to a diverse area of application Compact solution for stowed PV and ST array Integrated driving system on the mobile unit Built-in power unit (conversion, storage, management and control) Built-in power unit (conversion, storage, management and control) Reliable and efficient driving solutions (rotary or linear actuators) Possibility for sun-tracking (at least seasonal adjustment of the array) Efficient and cost effective PV modules and STC Protection capacity for the modules and STCs Lightweight structures for the deployable arrays Low cost manufacturing Durability and easy maintenance

In order to find an answer to fulfill these criteria novel concepts are expected to be developed for transportable/deployable PV/ST arrays.

4 Novel Concepts for Mobile Deployable PV/ST Arrays Being an essential part in the design process (Fig. 2), the concept development process has a strong connection with the creativity of the designers. In most of the cases this creativity seems to be an uncontrolled process bound to the intuition and sensitivity of the designer.

Fig. 2. The design process

370

M. Comsit et al.

In the context of a competitive market, where the product developers have to provide reliable and cost effective products, the design process evolved developing methods that come to confirm that the creativity in design is a mind controlled process characterized by a very logical structure. This synthesizing feature is meant to organize the intellectual and the emotional resources of the designer. The most significant step in the development of a product is represented by the phase of the concept development. The design process is mainly based on the three major stages: the concept generation phase, the concept development and the design strategy. These major phases may be divided into specific steps that provide a detailed approach of the new product or of the product that has to be developed. Considering these steps and accordingly to the requirement list previously defined, novel concepts for transportable/deployable PV/ST array units were developed. Concept 1 consists of a trailer able to be transported and optimally oriented (to South) by using common vehicles, a storage unit based on gel batteries (8 pieces), a DC/AC inverter and a control unit necessary for the management of the charging/discharging of the batteries, a solar thermal array (4 pieces of STC) and a storage tank.

Fig. 3. The folded and unfolded state of the PV/ST array - Concept 1

The installed power of 1.5 kWp covers a 12 m2 area (unfolded) and is able to provide DC or AC electricity, according to the applications (motors, pumps, fans, lightning systems, etc.) and the collectors surface covers 6 m2 and is able to provide DHW through a built-in storage tank, Fig. 3. Considering the functional-constructive criteria, the deployable unit uses a screw based mechanism (Fig. 4), solution (point E and D) driven by rotary actuators in order to operate the deploying system (Fig. 5), by pushing the PV arrays through the exterior. By using this mechanism, the sliding motion of the solar energy conversion array it is ensured and the system has a self lock capacity to the loads (Fig. 6). The simplicity of the solution is given by the use of a linear actuator for the elevation motion which may adjust the tilt angle of the array by varying the distance between point C and point B. This choice ensures a low maintenance system with a reduced complexity degree and a compact solution for the stowed configuration of the deployable array. The second variant proposed for the deployable system is also based on 2 rows of PV modules flanking a middle row of STCs. The main difference consists of a different approach of the unfolding principle of the PV array.

Deployable Mobile Units Concepts for PV and ST Arrays

371

Fig. 4. The tilt state of the PV/ST array - Concept 1

Fig. 5. The components of the mobile unit - Concept 1

Fig. 6. The structural scheme of the deployable array and the working principle of Concept 1

The solution is also based on a automated system using a linear actuator for the adjustment of the elevation angle and uses a rotary driven actuator system for unfolding the array which allows the stowing/un-stowing of the 3 rows one over the other (Fig. 7). The advantage brought by this solution consists of a higher protection in the folded state of all the conversion systems (against mechanical shock or dust).

372

M. Comsit et al.

Fig. 7. The folded and unfolded state of the PV/ST array - Concept 2

Fig. 8. The tilt state of the PV/ST array - Concept 2

Fig. 9. The tilt state of the PV/ST array - Concept 2

The whole structure can be transported using a common trailer, suitable for any type of car equipped with a hook, because this solution provides a lightweight configuration able to ensure a broad mobility degree. Like the previous solution, this unit includes a storage unit for electricity, DC/AC inventor, and DHW storage tank. This solution is compact and doesn’t require complex implementation solutions for driving the deployable array (Fig. 8), providing a compact configuration with low costs and low maintenance (Fig. 9).

Deployable Mobile Units Concepts for PV and ST Arrays

373

Fig. 10. The tilt state of the PV/ST array - Concept 2

Compared to the first solution, unfolding the side rows of PV modules may require an extra effort for the motion, as the rotation implies a bigger force than in first case. However, the rotational joints A, E and D (Fig. 10), may consist of common hinges which are more reliable than a sliding mechanism (proposed in Concept 1). Considering the list of requirements and the constructive-functional criteria, these mobile/deployable systems represent integrated parts of two novel concepts able to meet the energy needs for a broad range of applications. Further development will consider these two concepts for the dimensional synthesis optimization, through embodiment design, to provide ready to market solutions as an answer to the identified needs regarding mobile energy providers in agriculture.

5 Conclusions Reliable and clean solutions could be provided by stand alone PV/ST systems implemented in remote or unfavorable areas. The analysis on the market leads to the conclusion that deployable/transportable systems are covering a wide range of applications starting with telecommunication systems up to domestic lighting and domestic hot water production. This diversity imposes various solutions. The variety of solutions biases from the energy production capacity diversity to the size and mechanical configuration particularities which are directly connected with the area of application. Thus the paper defined a general set of design criteria regarding the functional and constructive quality of the mobile deployable PV/ST based systems. Based on the defined criteria two novel solutions for mechanisms reliable for deployable/transportable PV/ST array units suitable remote areas applications were proposed and described. In addition the embodiment approaches were presented by developing CAD models for each of the variant. By this approach, the paper opens new opportunities in the research on the development of deployable/transportable PV/ST arrays and imposes further studies regarding the mechanisms structural, kinematical and dynamical and also dimensional synthesis on the mechanical systems suitable for this type of application. Acknowledgments. We hereby acknowledge the work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI-UEFISCDI, project number PNII-RU-TE-2014-4-1763, within PNCDI II.

374

M. Comsit et al.

References 1. Razykov, T.M., Ferekides, C.S., Morel, D., Stefanakos, E., Ullal, H.S.: Solar photovoltaic electricity: current status and future prospects. Sol. Energy 85, 1580–1608 (2011) 2. International energy agency: Technology roadmap-solar photovoltaic energy (2010). http:// www.iea-pvps.org. Accessed June 2017 3. Weiss, W., Spork-Dur, M., Mauthner, F.: Global market in 2017. Detailed market figures 2015. Solar Heat Worldwide. Steinhuber Infodesign, Graz, Austria (2017) 4. Tyagi, V.V., Rahim, N.A.A., Rahim, N.A., Jeyraj, A., Selvaraj, L.: Progress in solar PV technology: research and achievement. Renew. Sustain. Energy Rev. 20, 443–461 (2013) 5. European Photovoltaic Industry Association: The solar photovoltaic electricity empowering the world, EPIA Report, Solar generation 6 (2011). http://www.greenpeace.org/international/ Global/international/publications/climate/2011/Final%20SolarGeneration%20VI%20full %20report%20lr.pdf 6. Green, M.A., Emery, K., Hishikawa, Y., Warta, W., Dunlop, E.D.: Solar cell efficiency tables (version 44). Prog. Photovoltaics: Res. Appl. 22, 701–710 (2014) 7. Visa, I., Moldovan, M.D., Comsit, M., Duta, A.: Improving the renewable energy mix in a building toward the nearly zero energy status. Energy Build. 68, 72–78 (2014). doi:10.1016/ j.enbuild.2013.09.023 8. Fraunhofer institute for solar energy systems ISE, Photovoltaics Report, Freiburg, October 2014 9. United Nations. The Millennium Development Goals Report, New York (2014) 10. International Energy Agency. World Energy Outlook 2014 (2014) 11. International Energy Agency. World Energy Outlook 2013 (2013) 12. Weiss, W., Spork-Dur, M., Mauthner, F.: Markets and contribution to energy supply. Solar Heat Worldwide. Steinhuber Infodesign, Graz, Austria (2016) 13. Jäger-Waldau, A.: European Commission, DG Joint Research Centre, Institute for Energy and Transport, Renewable Energy Unit, PV Status Report 2014 (2014) 14. Wiemann, M., Ng, L., Lecoque, D.: Best practices for Clean Energy Access in Africa Fourth edition, Alliance for Rural Electrification (2014) 15. Macharia, E., Gupta, G., Tsan, M.: Solar Lighting for the Base of the Pyramid - Overview of an Emerging Market, Lighting Africa (2010). http://www.ifc.org/wps/wcm/connect/ a68a120048fd175eb8dcbc849537832d/SolarLightingBasePyramid.pdf?MOD=AJPERES 16. Franceschi, J., Rothkopb, J., Miller, G.: Off-grid solar PV power for humanitarian action: from emergency communications to refugee camp micro-grids. Proc. Eng. 78, 229–235 (2014) 17. Comsit, M., Visa, I.: Integrated prototyping platform for a tracked PV system. In: 24th EU PVSEC – 23rd European Photovoltaic Solar Energy Conference and Exhibition, Hamburg, Germany (2009) 18. Moldovan, M., Visa, I., Saulescu, R., Comsit, M.: Four-bar linkages with linear actuators used for solar trackers with large angular diurnal strokes. In: The 11th IFToMM International Symposium on Science of Mechanisms and Machines, pp. 411–423. Springer International Publishing, Switzerland (2014). ISBN: 978-3-319-01844-7 19. Chinda, D.H.: The industrial design esthetical form crisis of the XXI century. The Ion Mincu University Publishing House, Bucuresti (2009)

Recycling Silicon-PV Modules in Composites with PVC, HDPE and Rubber Wastes Mihaela Cosnita(&), Cristina Cazan, Anca Duta, and Ion Visa Renewable Energy Systems and Recycling Research Center, Transilvania University of Brasov, Brasov, Romania [email protected]

Abstract. The paper focuses on the sustainable recycling of siliconphotovoltaic (Si-PV) modules by developing innovative composites entirely based on wastes of plastic materials (PVC, HDPE) and rubber, through low cost compression molding technique. In the first part of this study low amount of Si-PV modules powder (up to 3% mass weight) is embedded in polymer matrix and the interfacial and mechanical properties are investigated; two series of samples being obtained, the first Si-PV module without glass and the second one with all Si-PV modules (so including the glass cover of the PV module). The results have proved that the samples series with all Si-PV module powder exhibits higher mechanical performance (2.4 N/mm2 in tensile strength, Young’s modulus of 17 N/mm2) than Si-PV module without glass. In the second part of this study, up to 45 wt% of all Si-PV modules is incorporated in the polymer matrix. The output properties were measured in terms of tensile, compression and impact strength. The structural and conformational modification were evaluated by using Fourier Transform Infrared Spectroscopy (FTIR), the crystalline structure with X-ray diffraction (XRD), while surface morphology was studied by AFM and SEM techniques. The best mechanical properties were recorded for sample with 30% Si-PV with tensile strength of 2.02 N/mm2 and 45% Si-PV composite with compression strength of 39.35 N/mm2. Therefore, novel mechanical performance composites with recycled Si-PV modules could be designed for specific applications. Keywords: Photovoltaic modules recycling adhesion
Mechanical strength




Polymer matrix




Interfacial

1 Introduction In the current global scenario of environment pollution, avoiding global warming [1] and Energy Crisis asks for certain actions as the development and implementation of renewable energy systems (low carbon energy sources) which are imperative. The most widespread renewable energy technology is based on photovoltaics (PV) systems and generates electricity directly from the sun. The end of life PV modules rise significant environmental issues, but sustainable and market-accepted ways for recycling them are still not developed. The International Renewable Energy Agency estimates that waste modules will appear in large amounts by the early 2030 s and by 2050, they will reach a total of total 78 million tones [2]. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_27

376

M. Cosnita et al.

The market of PV modules consist of: Si based (crystalline. polycrystalline and amorphous Si); copper - indium sulphides as CIS or as the CIGS group which consists of CuInSe(S), or CuInGaSe(S); CdTe; the amorphous Si/crystalline Si thin layer tandem; crystalline Si in thin layer [3–5] being dominated by the crystalline silicon PVs with the market share exceeding 80% [6]. Disposing PV modules in municipal landfills is not environmental friendly because of the hazardous materials (e.g. Cd, Pb, In, Ga, Se) content [7, 8]. State-of-art to PV modules recycling reports on: mechanical separation, laminated glass recycling, chemical and/or mechanical treatment thermal separation, waste incineration, smelters [9], in cement matrix [10]. Currently, crystalline Si PV and mono- crystalline Si-PV modules, containing high purity Si, can be re-used if a cost effective technology is developed; there is no literature about the recycling process of amorphous Si modulus, although purifying the Si is quite complex [11]; Cyntia et al., report also on recycling of silicon PV panels by physical and chemical processes (acid leaching and electrolysis) [12] the EVA, polymer used to protect the PV elements from humidity and impurities raises difficulties in the recycling of silicon PV panels [6]. There is used a micro-emulsion in order to remove completely the lamination foil land the semiconductors coatings from the glass [13], without more information of the process and its environmental implications. Recycling CdTe from PVs (PVCdTe), or CuInSe2 (PVCIS) (PVCIGS) from thin films modules have environmental risks and target the recovery of critical materials (In, Ga, Ag). A different way of PV modules recycling is reported by Fernandes et al., embedding it in cement matrix, in low amount of 5%, but the mechanical strength was decreased [10]. Some authors reported that the chemical treatment implied in PV recycling processes involve toxic substances, as NO, fluorides, acids and additionally are energy intensive [2] making recycling an unsustainable process. Therefore, in the current sustainable development frame, there is a real need for implementing sustainable recycling processes. Therefore, the paper proposes incorporating of the shredded and milled PV modules wastes directly in another waste plastic blend (PVC, rubber, HDPE) using common mixing processes. Polyvinyl chloride (PVC) was used because of its low cost and high performance. Annually, the demand for plastic (mainly poly-olefins and PVC) exceeds tens of million tones. In recent years, the question on the waste PVC and rubber disposal has gained increasing importance in the scientific world, resulting from the rapid growth of these wastes amounts. PVC is an extremely inert and very stiff polymer that is widely used in construction. Its mechanical properties such as tensile strength and Young modulus are much better than those of commodity olefin plastics. By PVC addition to the composite, strength and rigidness is the target, while rubber provides a better toughness. The reuse of PVC in composites could become an important green alternative instead of more environmentally hazardous techniques like energy recovery or even land filing. Rubber wastes can be chosen because of the large waste amounts discarded every year, but due to its properties and versatile structure containing inorganic alongside organic phase, therefore being a potential candidate for supporting organic-inorganic interfaces in the polymer composite systems. The key issue in developing organic-inorganic composites is related to the interfacial adhesion. The factors that influence the interfaces formation are: the chemical composition of the composite components, the transition temperature (Tg - glass

Recycling Silicon-PV Modules in Composites

377

transition and Tm - melting temperatures), the crystallinity and the crystallite size and shape, the structural homogeneity, the processing temperature which influences the interface energy, and the adhesion between materials. Inorganic fillers have high surface energy, thus they cannot be dispersed in the polymer matrix or they can be wetted only with high energy consumption. Too much additives could have negative effects due to their low viscosity and insufficient wetting. Previous research proved the possibility of composites development with organic-inorganic interfaces, by inserting metal oxides (in low amount) in the rubber matrix, as CaO, TiO2, fly ash [14–16]. These studies outlined the formation of new stronger interfaces, thus increasing the stability of organic-inorganic composites fully based on waste. Relevant studies showed that by inserting inorganic filler (SiO2, TiO2, CaO, ZnO) in the polymeric matrix, inorganic/organic interfaces are formed, leading to complex optimization of the composites: strength, Young modulus, dimensional stability and heat resistance [17, 18]. The increase of glass transition temperature in composites was reported by Chen et al., when inorganic nanoparticles were introduced in polymeric blends [19]. This behavior is due to the reduced mobility of the polymeric chains when interacts with nanoparticles. Composites with SiO2 in the polymeric matrix were reported as having an increase in the Young modulus value (27% upon 6 wt% SiO2 addition) [20, 21]. The addition of such fillers, coming also from the wastes stream, could be a path for controlling the properties of the wastes based composites (improving the tensile strength, Young modulus and impact strength). Thus, the concept of organic-inorganic interfaces could be extended by recycling Si-PV modules in composites with waste rubber-plastics matrix. The paper aims at presenting the results of recycling significant amount of Si-PV powder waste, which contain organic and inorganic phases, in waste polymer blend (PVC, rubber, HDPE), thus extending the organic-inorganic interfaces. The plastic wastes of PV modules: ethylene-vinyl acetate copolymer (EVA), polyvinyl butyral (PVB) and polyvinyl fluoride (PVF) alongside HDPE synergistically will lead to the increase of composite’ components compatibility.

2 Experimental 2.1

Materials

The materials used for obtaining the composites were: • Polyvinyl chloride (PVC) flakes, (from Silnef SRL, Brasov); • high density polyethylene (HDPE) flakes, (from Silnef SRL, Brasov); • tire rubber powder (which consists in four different types of rubber: natural-, styrene-butadiene-, polybutadiene- and butyl-rubber) from Granutech Recycling Suceava; • Si-PV modules waste (waste from ICDT of Transilvania University of Brasov). The PVC and HDPE flakes were milled using Centrifugal mill ZM 200 (Retsch) to obtain powder with the grains diameter less than 1 mm.

378

M. Cosnita et al.

The dismantling of the end-of-life Si-PV modules (poly-crystalline Si-PV modules) was performed manually and aluminum frame and junction box were removed to be sent to specialized recycling companies. The remained Si-PV module waste (glass+Si wafer+EVA+metals+polymer material) was selected to manufacture the novel composites based on PV, -rubber and HDPE waste. Si-PV waste material was prepared by shredding and then the scraps were milled, Fig. 1.

Fig. 1. Preparation of the Si-PV powder

2.2

Composite Preparation

The “all waste” composites were obtained by compression in the laboratory mold using for final processing an oven with thermostat (type ECv 200–300). The composites compositions were: PVC: tire rubber: HDPE: Si-PV module = (60 − x): 35: 5: x (% wt). The components blends were thermally processed for 30 min at 220 °C temperature, the processing parameters were selected considering the Tg and Tm of all polymeric components. Two composites series were prepared (in these conditions: T = 220 °C, curing duration of 30 min), the first Si-PV module free glass and the second one with all Si-PV modules (so including the glass component). Five samples of each type were mechanically tested in terms of tensile, compressive and impact strength. The first stage of the study was conducted to check the effect of the low Si-PV powder and the effect of glass from module on the interface and on the mechanical properties of polymer blends (rubber, PVC and HDPE). For deep research, there have been prepared two sets of composites, by inserting into the polymer matrix Si-PV powder without glass (set I) and other samples with all Si-PV powder (set II). For both sets of samples, the Si-PV powder amount has been set in the range of 0.5–3% wt, with a 0.5% wt step. Further, in the second stage, because the main target of our work

Recycling Silicon-PV Modules in Composites

379

is to recycle Si-PV module in novel composite materials fully based on wastes, with good mechanical performance, the Si-PV module waste was added as filler in large amount (10%…45%) into the polymer blend. It was found that the Si-PV module waste visibly improves the mechanical properties of the composite. These composite materials can be used for indoor applications, but further studies upon this aspect will be done. 2.3

Characterization

2.3.1 Si-PV Module Waste Powder Characterization The powder obtained from Si-PV module waste will be characterized by using FTIR, XRD and SEM-EDX analysis to correlate the milling parameters (speed, duration, load) with specific parameters of the Si-PV powders (grain size and specific area) as key issues in developing the interfacial adhesion between inorganic-organic composite components. 2.3.2

Rubber: Plastic: Si-PV Module Composites Characterization

Mechanical Tests Tensile tests were carried out using an Z020, Zwick/Roell equipment at room temperature and constant cross-head speed of 100 mm/min. The speed of the gripping arm has been chosen following several tests, being in line with the speed of movement for plastic specimens (1 mm/min, according to SR EN ISO 527-2: 2000) and the speed of displacement Rubber specimens (500 mm/min, according to SR ISO 37: 1997). Young‘s modulus, ultimate tensile stress and strain-to-break of composites were measured. The fracture surface of the composites was analyzed by a Hitachi, S3400N, type II field emission scanning electron microscope (SEM). The determination of the compression resistance (RC) was recorded SR EN ISO 604:2004 using Z020, Zwick Roell equipment and impact resistance (RI) was evaluated with the IZOD method based on the SR EN ISO 180: 2001 standard and using the impact test equipment Galdabini Impact. Surface Properties and Composition of the Composites Surface morphology was determined by scanning with electron microscopy (SEM. Hitachi, S3400N, type II) and with atomic force microscopy (AFM, NT-MDT model NTEGRA PRIMA EC). The AFM images were recorded in semi-contact mode with “GOLDEN” silicon cantilever (NCSG10 force constant 0.15N/m tip radius 10 nm). The surface energy was determined based on contact angle measurements performed with an OCA-20 Contact Angle System (Data Physics Instruments), by using the sessile drop method. Surface energies were calculated using Owens, Wendt, Rabel and Kaelble (OWRK) method [22] using two testing liquids: water (rH2O ¼ 72:10 mN=m: rpH2O ¼ 52:20 mN=m and rdH2O ¼ 19:90 mN=m) and glycerol (rglycerol ¼ 73:40 mN=m: rpglycerol ¼ 37:00 mN=m and rdglycerol ¼ 36:40 mN=m); the total surface energy of the composites (rSV) and liquids (rLV), and their polar (rpSV : rpLV ) and the dispersive (rdSV : rdLV ) components were obtained as follows:

380

M. Cosnita et al.

rSL

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ rSV þ rLV  2 rdSV
rdLV þ rpSV
rpLV

ð1Þ

The 5 lL sessile drop volume was kept constant during all contact angle measurements, by using a microsyringe. For accuracy, the measurements were performed in five different surface zones on the same sample. Measurement of the contact angle with up to 2 liquids ensures maximum accuracy when determining the SFE (OWRK method). Fourier Transforms Infrared Spectroscopy (FTIR) analysis was performed using a Spectrum Bruker spectrophotometer to outline the chemical transformation during molding, with a focus on the composition and interfaces; the spectra were recorded in reflectance mode, in the 500 to 4500 cm−1 range, after 16 scans with a resolution of 4 cm−1. Crystallinity data were collected using a Bruker Advanced D8 diffractometer (XRD, CuKa1 radiation, with 1.5406 Å wavelength at 40 kV. 20 mA) over 2h = 10 – 70° in the fixed time mode, with a step interval of 0.01°, at 25º.

3 Results and Discussion 3.1

Rubber: PVC: HDPE: Si-PV Powder Composite with Low Si-PV Module Content 0.5−3% wt

3.1.1 Si-PV Module Waste Powder Characterization FTIR analysis was used to monitor the changes in the Si-PV module structures before and after removing glass, Fig. 2. The FT-IR curve of all Si-PV module shows a characteristic stretching peak between 1060–1002 cm−1 corresponding to Si-O-Si bond (around 1100 cm−1), the same and the 585 cm−1 band and around 900 cm−1 band for Si-OH. These bands are strong and mask the characteristic bands for the groups/blends: the bands at 1740 and 1094 cm−1 were associated to C = O and C-O stretching vibrations;

Fig. 2. FTIR spectra for Si-PV module powders

Recycling Silicon-PV Modules in Composites

381

the band at 846 cm−1 was assigned to C-C stretching; the band at 1241 cm−1 was related to H-C-H bending mode in -CH3 species; the band at 720 cm−1 was assigned to H-C-C bending mode in -CH2-groups. These bands are found in the spectrum of the Si-PV module free of glass. On the wavelengths from 1300 to 4000 cm−1, the FTIR spectra of the two powders indicate the same types of potential bands of different intensities. EDS analysis of Si-PV module with and without glass reveals the main components: C, O, Si and Al, Table 1. Carbon and oxygen coming from the polymer sheet of ethylene vinyl acetate (EVA) and possible polyvinyl fluoride (PVF) of the Si-PV module. Table 1. Components of Si-PV module from EDS analysis Component of PV module C Si O Al Glass free Si-PV 0.11 63.57 29.75 6.57 All Si-PV 34.46 27.14 26.12 12.08

3.1.2

Composites Characterization

Mechanical Tests Mechanical performance of any composite system is strongly depending on the interfacial adhesion between the components of the composite. Interfacial adhesion of a composite system heavily depends on the processing temperature and duration, on the fillers wetting, on the components dispersion in the matrix, on the mechanical characteristics of each component and so on. Outstanding mechanical strength can be reached when chemical bonds or at least mechanical-chemical bonds are formed between the composite’s components. Usually a compatibility agent is used in a composite system, to support the interfacial adhesion. In developing novel composite materials, organic-inorganic blends were prepared by mixing waste PV modules powder, rubber, PVC - waste HDPE, the last playing the role of compatibility agent. Five species of each type were mechanically tested in terms of tensile, compressive and impact strength, the mean value being summarized in Figs. 3 and 4, compared with the standard specimen (without Si-PV addition). Knowing that the higher the interfacial strength the higher the tensile strength value, the following analysis was done for the tensile strength: • Within the first composites series prepared with Si-PV powder, glass free, that with an insertion of 2 wt% Si-PV powder exhibits the best tensile strength and Young Modulus (2.34, 14.24 N/mm2 respectively), Fig. 3. It can be note that by increasing the glass free- Si-PV amount, the tensile strength and Young Modulus decreased, supporting thus probably the known explanation in the field, that of filler agglomeration. This effect, in turn, led to the interface weakening and further worsening the tensile strength and Young Modulus. In fact, the fillers agglomeration acts as a barrier and hampers the stress transfer from matrix to the composite’ components. Further the all Si-PV modules were inserted in polymers blend to

382

M. Cosnita et al. 3.0

2.5

2.5

2

Ei [kJ/m ] 2

2.0

Rc[N/mm ]

1.5

E [N/mm ] 2 σtr [N/mm ]

2

1.0 0.5 0.0 0

5

10

15

20

25

30

35

40

Mechanical properties value

Fig. 3. Mechanical properties for the samples with low content of Si-PV module free of glass (Ei - impact strength; Rc - compression resistance; rtr - tensile resistance; E - Young modulus)

Samples with low content of all Si-PV module

Samples with low content of Si-PV module free glass

3.0

2.0 1.5 2

Ei [kJ/m ] 1.0

2

Rc[N/mm ] 2

E [N/mm ]

0.5

2

σtr [N/mm ]

0.0 0

5

10

15

20

25

30

35

40

Mechanical properties value

Fig. 4. Mechanical properties for the samples with low content of all Si-PV module (Ei impact strength; Rc - compression resistance; rtr - tensile resistance; E - Young modulus)

study what influence will give the larger silica amount (coming from the glass component) in the polymers blend; • The second composites series, with all Si-PV module (including glass), exhibits a slightly different mechanical behavior when compared with the first one; it can be note, that the higher the inorganic powder amount in the polymeric matrix, the higher mechanical performance are recorded, tensile resistance of 2.36 N/mm2 and Young modulus of 17.16 N/mm2 for a Si-PV powder amount of 3 wt%, Fig. 4. The glassy components bring more toughness to the novel composites, due to the increased silica ratio in polymer blend and more likely a better dispersion in the polymer blend is achieved. There is well acknowledged that the silica filler has positive effect on the static and dynamic mechanical performance of a polymer blend, [23, 24]. Considering the compression strength, by comparing the results of the both composites series, the mechanical tests outlined the best compression strength in case of the second series, 28.54 N/mm2 for Si-PV powder of 3% wt, Fig. 4; therefore the insertion of all Si-PV powder (with glass) improved the overall mechanical strength of novel composite, due to the toughness brought by the insertion of the Si-PV’ glassy components. The higher impact resistance, 12.89 kJ/m2, corresponds also to the 3% all Si-PV powder of the second series, Fig. 4, due to the same reasons aforementioned; additionally due to the silica in glassy components displaying more affinity and interact to the rubber component, thus enhancing the absorbed energy potential of the composite. It is possible that by using more than 3% PV as a filler, better mechanical properties of the composite material will be obtained, due to the large amount of EVA and PVF alongside the silica. This will be presented in the second section of this paper.

Recycling Silicon-PV Modules in Composites

383

The results clearly reflect the positive effect of all Si PV on the performance of the novel composite; it can be concluded that: • all Si-PV insertion in the polymer blend increased the mechanical performance of the novel composites: Si-PV powder-PVC-rubber- HDPE; • the increased silica amount of all Si-PV module determines the development of a dense interface in novel composites, probably due to the main interaction between rubber and silica; • an economic benefit is meet by recycling all Si-PV module (including the glass) in novel composites composition, the process cost will be lowered; there will be no need to separate the glass from the Si-PV module. Contact Angle Measurements. Surface Energies of the Si-PV Composites The species behavior in contact with various liquids was investigated by contact angle measurements. This behavior is very important, especially when specimens are designed to be used as products in outdoor applications. By measuring the contact angle, the surface energies of the novel composites were calculated. Composites having low surface energies values are requested for out-door applications (incomplete or non-wetting, H > 90°; in case of H < 90° good wetting). This condition is reached if there is a high contact angle between sample surface and the testing liquid droplet. The contact angle is strongly influenced, mainly by: the interaction between the sample’s surface and the testing liquid, the chemical nature of the sample, the test liquid type and the surface porosity (voids). The polar and dispersive components of the surface energies were calculated considering the initial contact angle values, Figs. 5, 6, 7 and 8.

Fig. 5. Contact angle value for samples with low content of Si-PV module glass free

Fig. 6. Surface tension for samples with low content of Si-PV module glass free

By comparing the surface energies of both composite sets (with and without glass of PV), it can be note that the values of the second series (with glass) are lower than of first series (without glass), Figs. 5, 6, 7 and 8, suggesting a more compact structure in all Si-PV specimens. The compact structure of the second series is determined by their stronger and extended interfaces, probably due to the new linkages formed between the

384

M. Cosnita et al.

all Si-PV component and the polymeric components of the blend. By inserting all Si-PV in the polymer blend, the inorganic filler amount is increased, determining in their vicinity the polymer chains constraining, reducing the mobility of the macromolecular chains. This behavior confirms the mechanical tests results, which outlined higher compression strength of all Si-PV composites than that of the first series (glass free).

Fig. 7. Contact angle value for samples with low content of all Si-PV module

Fig. 8. Surface tension for samples with low content of all Si-PV module

It is also to note that the surface energy of 3 wt% all Si-PV specimen, Fig. 8, exceeds 50 mN/m, but with a prevalent share of dispersive component (over 90%), outlining a better inorganic dispersion and consequently the interface strengthening. It may be concluded, that the reduced wetting behavior of all Si-PV composites leads to the possibility of their use in products for outdoor applications, as paving slabs, carpets for covering the playgrounds, pockets for pillars from parking spaces, but future research will be done in this way. Further the chemical modifications and the likelihood of the new interfaces formation or the extending of the existing interface will be investigated by FTIR spectroscopy. FTIR Analysis The most representative samples of both composites series (with and without glass) were investigated by FTIR spectroscopy, to outline the chemical changes or new interfaces that were developed between the organic -inorganic components, during the molding processing. The characteristics bands of the samples of 1 series without glass (of 2–3 wt% Si-PV) and the specimen with 3 wt% Si-PV powder of the 2 series (with glass) are presented below, Table 2. The mechanical performance of a composite is determined rather by the covalently bonded interface than that developed by means of the Van der Waals interactions. The FTIR spectra revealed a set of changes in the structure of the analyzed specimens of the both composites series, as follows: • the bands of 1423 cm−1 and that of 448 cm−1 (Si-O-R) has been recorded at lower wave number in 3 wt% all Si-PV composites than the others one (with 2–3 wt%

Recycling Silicon-PV Modules in Composites

385

Si-PV specimens), suggesting an interface flexibilization. This fact is more likely through the interface linkage extending, implying the Si-PV groups; • the Si-O groups band of 858 cm−1 has not been longer recorded in the 3 wt% all Si-PV specimens, unlike the other specimens where it is present, confirming thus the new interface formation, involving the all Si-PV component; • the disappearance of the 1010 cm−1, band specific to rubber, PVC and HDPE in all specimens. • missing of the 1532 cm−1 attributed to the C=C group from rubber Table 2. The main FTIR bands of the components in the Si-PV composites

The disappearance of the bands of 1010 cm−1, 1506 cm−1 and of 1532 cm−1 in all specimens, clear are confirming the development of new interfaces/the interfaces extending through Si-PV and polymer components interaction (mainly rubbery component). In the next section the morphologies of the more representative specimens of each series (without and all Si-PV module) will be investigated.

386

M. Cosnita et al.

SEM Investigations The fracture surface morphologies of the representative samples coming from both composites series were investigated by scanning electron microscopy and the SEM images are given in Fig. 9. It is clearly shown that the 2.5% glass free Si-PV sample revealed the largest amount of voids and delamination in its surface morphology, by comparing with the others ones. All three SEM images have indicated the high affinity of the PV particles to rubber phase, as also reported by Cazan et al. [25]. The SEM micrograph of 3% all Si-PV samples clearly shows the highest degree of interfacial adhesion, when comparing with the other two.

Fig. 9. SEM images of fractured Si-PV composites with/without glass: (a) 2% glass free; (b) 2.5% glass free; (c) 3% with glass

The insertion in the polymer blend of all Si-PV led to a tight adhesion between the composite’s components, Fig. 9c; this in turn has improved the mechanical properties of the 3% all Si-PV composite, as mechanical tests has already recorded. The 3% all Si-PV more homogenous surface fracture suggests rather a ductile failure, by comparing with the 2.5% Si-PV whose failure seems to be of brittle pattern, Fig. 9b. Therefore, the fracture morphology of 3% all Si-PV will be further studied by AFM technique. AFM Characterization The 3% all Si-PV composite AFM image of an interfacial region on the fracture (obtained after tensile test) is shown in Fig. 10.

Recycling Silicon-PV Modules in Composites

387

Fig. 10. AFM images of 3% all Si-PV fracture surface (different zones)

The AFM fracture images are clearly revealed that prior breaking the composite tears, the structural plans sliding being noticed, proving thus the development of mechanic-chemical interface between composite components [26], as the FTIR data has already suggested. 3.2

Rubber Plastic Composites with Increased Si-PV Powder Amount

Mechanical Tests Increasing the PV modules amount in the polymer blend would contribute to the increase of the composites strength. This result could be expected because the PV modules contain polymer phases, which can better bind the components and also because of their inorganic components (glass, metal oxide, metals). The mechanical characteristics of the all Si-PV high content composites are presented in Fig. 11. The results of the mechanical tests show that by increasing the all Si-PV content over 30% wt in the polymeric blend, the interface weakens, leading to the decrease of the mechanical properties, as outlined in Fig. 11. This behavior is due to the filler-filler interaction and their agglomeration because of their high surface energies. The clusterizing of the filler determines a poor dispersion/distribution of the Si-PV powder in the polymer matrix, consequently hindering the stress transfer from the matrix to filler. However the Si-PV content increase in the polymer blend does not dramatically reduce the impact strength of the composites. Thus, high Si-PV content composites could be developed with good impact strength behavior, which could find their application as protective barriers, sleeves for pillars used in parcking spaces, and so on. An optimal combination of mechanical properties and of increased Si-PV content in the polymer blend was noticed for 30% all Si-PV composite. This sample has exhibited a tensile strength of 2.02 MPa, impact strength of 25.06 MPa and a compressive strength of 31.90 MPa, suggesting the formation of an optimal interface bonding. This aspect will be further investigated by FTIR spectroscopy.

388

M. Cosnita et al.

45

Samples

40

Ei [kJ/m2 ] Rc [N/mm2 ]

30

E [N/mm2 ] σtr [N/mm2]

20

10 0

10

20

30

40

50

60

Mechanical properties value Fig. 11. Mechanical properties of the 10–45% all Si-PV module samples. Ei - impact strength Rc - compression resistance; rtr - tensile resistance; E - Young modulus

Contact Angle Measurements Contact angle measurements on the novel composites with increased amount of all Si-PV module (10–45 wt%) powder was done to investigate the surface energies and properties; considering that a densification of composite could be obtained, giving larger contact angles, practically lead to a hydrophobic behavior. Overall, the surface energies of high content Si-PV composites are lower than that of low Si-PV content composites, confirming thus a densification in their structure. The composites with 40 and 45% all Si-PV amount exhibited the highest contact angles and in turn the lowest surface energies values, results that are in good agreement with the mechanical testing which has recorded the highest compression strength in the case of these samples. The 30% all Si-PV composite seems to be of particular behavior having the highest surface energy, but this could be explained by a larger amount of polar components on its surface, as polar component share confirms, Fig. 12b. Taking into account that the mixing procedure of organic and inorganic phases was manually, this result could well happen. Overall, the surface energies of high content Si-PV composites are lower than that of low Si-PV content composites. FTIR Investigations The bands corresponding to the methyl/methylene groups in the polymers from rubber tires and the double bonds (1390–1457 and 875 cm−1) are affected by the Si from Si-PV module. Over the same period, an increase in silane bands was observed at 1260, 1095 and 815 cm−1, indicating the participation of this group in the interactions with the rubber and HDPE, Table 3. Good interaction of rubber silane means an compatibility effect because the coupling agent used in this studied in terms of HDPE-silane interactions with positive results. For all samples, the band specific to PVC (672 cm−1)

Recycling Silicon-PV Modules in Composites

(a)

389

100

Contact angle, θ [degree]

θwater θsalt

90

80

70

60

0

10

20

30

40

45

(b)

Surface energy, their components [mN/m]

Composite with high content of all Si-PV module

60 Surface energy polar component dispersive component

50

40

30

20

10

0 0

10

20

30

40

50

Composite with high content of all Si-PV module

Fig. 12. Wetting characteristics of increased all Si-PV composites: (a) contact angles; (b) surface energies

Table 3. Bands involved in interactions between tire rubber, silane, PVC Band [cm−1] 672 610 815 871–875 1017–1104 1240–1256 1415–1435

Assignation Cl-Cl stretch H2C=CSi-C stretch -C=C-H in plane C-H bend Si – O – C stretch Si – CH3 -C=C – H in plane C – H

Component PVC EVA, HDPE Si-PV module, rubber Silane, rubber Silane, rubber Silane Silane, rubber

and bands specific Si-PV module (610 cm−1 and 1530 cm−1) disappeared due to the interaction between the composite components when forming a new interface. Samples with 30% and 40% Si-PV module has several differences and bands changes that suggest interactions with the participation of the groups assigned to these bands. The 1014–1017 cm−1 band include the specific bands of the components Si-PV

390

M. Cosnita et al.

Fig. 13. FTIR spectra for the 10–45% all Si-PV module samples

module, rubber and HDPE as a result of the interaction between these components, Fig. 13. This band in case of samples with 40% Si-PV module is larger with a high intensity than samples with 30%, due to the formation of stronger interface between components, result confirmed by the mechanical testing. XRD Analysis The XRD measurements were performed to assess the influence of the high content of Si-PV particles on the novel composite interface and to determine the crystalline structure. The crystalline degree of 30 and 45% all Si-PV composites were determined, and compared with that without any Si-PV content, Fig. 14.

Si-PV

Crystallinity

[%]

[%]

0

63.3

30

36.8

45

31.8

Fig. 14. Crystallinity of composites with increased all Si-PV amount

Recycling Silicon-PV Modules in Composites

391

The crystallinity of the samples with 30, 45% all Si-PV, compared with that without all Si-PV, is 50% lower. This suggests that the all Si-PV particles addition in PVC-rubber-HDPE blend disturbs the macromolecular chains order in the matrix, leading to a lower ordered composite structure, as presented in Fig. 14. It is interesting that the lower crystallinity of 45% all Si-PV compared to 30% all Si-PV, does not necessarily led to a lower compression resistance. The mechanical tests result has recorded the highest compression strength within the all series, in the case of 45% all Si-PV, 39.35 N/mm2. SEM Morphologies Surface aspect characterization of the best tensile strength sample was performed using scanning electron microscopy. The SEM micrographs of fractured surfaces of composite with 30% all Si-PV module are given in the Fig. 15(a–c), outlining that the inorganic filler is very well enveloped in the polymer phases. The micrographs confirm the multi-component composition at the surface morphology of the blends, which could promote interfacial adhesion between the fillers and polymer components, due to the formation of chemical interfaces between components. It is to note that the fractured surface SEM image displays a ductile like failure of the composite with 30% all Si-PV module powder; these images suggests that tear occurs in the close vicinity of the neck interface region before the sample failure. Therefore, SEM micrographs outline the development of strong interfacial bonding between the reinforcement and the polymer components, which in turn could favor a

Fig. 15. SEM images of 30% Si-PV fracture surface in different zones on the same fractured sample, EDX

392

M. Cosnita et al.

good load transfer between the matrix and the reinforcing fillers, as mechanical tests has registered the highest tensile strength in case of 30% Si-PV composite. In this way the output properties of the composites could be enhanced, as confirmed by the highest tensile and impact strength obtained in case of 30% all Si-PV, 2.02 N/mm2 and 25.06 N/mm2 respectively.

4 Conclusions Recycling Si-PV modules by developing novel composites materials based on PVC-rubber-HDPE is reported. The recycling of all Si-PV modules has positive influence on the interfaces and mechanical properties of the novel composites, when comparing with Si-PV module without glass components. The recycling of all Si-PV modules brings an economic advantage, as there is no need for removing the glazing from Si-PV module. The FTIR, SEM and AFM data outlined the development of the mechanic-chemical interfaces in the novel composites with all Si-PV module powder, Si-PV module powder proved to have high affinity for the rubber phase. Unlike the Si-PV module without glass, the all Si-PV modules powder due to the inorganic larger amount results in a better strength in the composite. The best combination of mechanical performance and large amount of all Si-PV module powder embedded in polymer blend was found in the 30 and 45% all Si-PV module composites. The first exhibited the best tensile and impact strength and the latter showed a very good compression resistance. Thus the Si-PV modules can be sustainable recycled by mixing with other polymer wastes. The products that can be obtained will be tested in the near future for indoor and outdoor applications.

References 1. Jeongeun, S., Jongsung, P., Nochang, P.: A method to recycle silicon wafer from end-of-life photovoltaic module and solar panels by using recycled silicon wafers. Sol. Energy Mater. Sol. Cells 162, 1–6 (2017) 2. Huang, W.H., Shin, W.J., Wang, L., Sun, W.C., Tao, M.: Strategy and technology to recycle wafer-silicon solar modules. Sol. Energy 144, 22–31 (2017) 3. Baneto, M., Enesca, A., Mihoreanu, C., Lare, Y., Jondo, K., Napo, K., Duta, A.: Effects of the growth temperature on the properties of spray deposited CuInS2 thin films for photovoltaic applications. Ceram. Int. 41(3), 4742–4749 (2015) 4. Corcelli, F., Ripa, M., Leccisi, E., Cigolotti, V., Fiandra, V., Graditi, G., Sannino, L., Tammaro, M., Ulgiati, S.: Sustainable urban electricity supply chain-Indicators of material recovery and energy savings from crystalline silicon photovoltaic panel end-of-life. Ecol. Indic. 5 April 2016. https://doi.org/10.1016/j.ecolind.2016.03.028 5. Wong, J.H., Royapoor, M., Chan, C.W.: Review of life cycle analyses and embodied energy requirements of single-crystalline and multi-crystalline silicon photovoltaic systems. Renew. Sustain. Energy Rev. 58, 608–618 (2016)

Recycling Silicon-PV Modules in Composites

393

6. Dias, P., Javimczik, S., Benevit, M., Veit, H., Bernardes, A.: Recycling WEEE: extraction and concentration of silver from waste crystalline silicon photovoltaic modules. Waste Manag. 57, 220–225 (2016) 7. Youn, K.Y., Kim, H.S., Tran, T., Kil Hong, S., Kim, M.J.: Recovering valuable metals from recycled photovoltaic modules. J. Air Waste Manag. Assoc. 64, 797–807 (2014) 8. Goe, M., Gaustad, G.: Identifying critical materials for photovoltaics in the US: a multi-metric approach. Appl. Energy 123, 387–396 (2014) 9. Tao, L., Yu, S.: Review on feasible recycling pathways and technologies of solar photovoltaic modules. Sol. Energy Mater. Sol. Cells 141, 108–124 (2015) 10. Fernandez, L., Ferrer, R., Aponte, D.F., Fernandez, P.: Recycling silicon solar cell waste in cement based systems. Sol. Energy Mater. Sol. Cell 95, 1701–1706 (2011) 11. McDonald, N.C., Pearce, J.M.: Producer responsibility and recycling solar photovoltaic modules. Energy Policy 38, 7041–7047 (2010) 12. Cynthia, E.L., Latunussa, F.A., Blengini, G.A., Mancini, L.: Life cycle assessment of an innovative recycling process for crystalline silicon photovoltaic panels. Sol. Energy Mater. Sol. Cells 156, 101–111 (2016) 13. Kim, H., Fthenakis, V.M.: Comparative life-cycle energy payback analysis of multi junction a-SiGe and nanocrystalline/a-Si modules. Prog. Photovoltaics Res. Appl. 19, 228–239 (2011) 14. Cosnita, M., Cazan, C., Duta, A.: Interfaces and mechanical properties of recycled rubber-polyethylene terephthalate-wood composites. J. Compos. Mater. 48, 683–694 (2014) 15. Vladuta, C., Voinea, M., Purghel, E., Duta, A.: Correlations between the structure and the morphology of PET- rubber nanocomposites with different additives. Mater. Sci. Eng. B 165, 221–226 (2009) 16. Cazan, C., Duta, A.: Rubber/thermoplastic blends: micro and nano structure. In: Advances in Elastomers-I: Their Blends and Interpenetrating Networks. Springer, Heidelberg (2013). ISBN 978-3-642-2092417. Bhat, G., Hegde, R.R., Kamath, M.G., Deshpande, B.: Nanoclay reinforced fibers and nonwovens. J. Eng. Fibers Fabr. 3, 22–34 (2008) 18. Uddin, N.: Developments in Fiber-Reinforced Polymer (FRP) Composites for Civil Engineering. Woodhead Publishing Series in Civil and Structural Engineering, Alabama, USA 2013, vol. 45 (2013) 19. Chen, K., Wilkie, C.A., Vyazovkin, S.: Nanoconfinement revealed in degradation and relaxation studies of two structurally different polystyrene-clay systems. J. Phys. Chem. B 111, 12685–12692 (2007) 20. Chrissafis, K., Paraskevopoulos, K.M., Papageorgiou, G.Z., Bikiaris, D.N.: Thermal and dynamic mechanical behavior of bionanocomposites: fumed silica nanoparticles dispersed in poly(vinyl pyrrolidone), chitosan, and poly(vinyl alcohol). J. Appl. Polym. Sci. 110, 1739– 1749 (2008) 21. Aso, O., Eguiazábal, J.I., Nazábal, J.: The influence of surface modification on the structure and properties of a nanosilica filled thermoplastic elastomer. Compos. Sci. Technol. 67, 2854–2863 (2007) 22. Fowkes, F.M.: Treatise on Adhesion and Adhesives. Marcel Dekker, New York (1967) 23. Xu, T., Jia, Z., Li, J., Luo, Y., Jia, D., Peng, Z.: Study on the dispersion of carbon black/silica in SBR/BR composites and its properties by adding epoxidized natural rubber as a compatilizer. Polymer Composite (2016). http://dx.doi.org/10.1002/pc.23946 24. Vijay, V.R., Anitha, A.M., Menon, A.R.R.: Studies on blends of natural rubber and butadiene rubber containing silica-organomodified kaolin hybrid filler systems. Polymer 89, 135–142 (2016)

394

M. Cosnita et al.

25. Cazan, C., Cosnita, M., Visa, M., Duta, A.: Novel rubber-plastics composites fully based on recycled materials. In: Sustainable Energy in Built Environment - Steps Towards nZEB, Part of the series Springer Proceedings in Energy, pp. 503–519 (2014) 26. Zou, Y., Sun, Y., He, J., Tang, Z., Zhu, L., Luo, Y., Liu, F.: Enhancing mechanical properties of styrene-butadiene rubber/silica nanocomposites by in situ interfacial modification with a novel rare-earth complex. Compos. Part A: Appl. Sci. Manuf. 87, 297–309 (2016)

Sizing and Optimization of Cost-Efficient PV Generator System at Residential Buildings in the Region of Ruse, Bulgaria Katerina Gabrovska-Evstatieva, Boris Evstatiev, Ognyan Dinolov, and Nicolay Mihailov(&) Faculty of Computer Science and Faculty of Electrical Engineering, Ruse University “Angel Kanchev”, Ruse, Bulgaria [email protected]

Abstract. In this study a method for cost-efficient investments in PV generators at residential buildings has been presented. It takes into consideration all the initial investment and maintenance costs as well as the potential benefits, based on the mean hourly solar energy production for each month of the year in Ruse, Bulgaria. The variation of the net present value as well as the return on the investment are investigated for different scenarios, using a typical daily energy consumption distribution at residential buildings. The obtained results show that for properly sized installations the investment could pay off for approximately 8 years. On the other hand the annual money loses from oversized investments increase significantly and could be approximated with a quadratic equation. Keywords: Sizing Cost-efficient




Optimization




PV generators




Residential buildings




1 Introduction Undoubtedly, the photovoltaic energy sources are an alternative to the conventional power generation. As a result of the targeted European measures and policies, the development of these systems has reached such a level that their construction is already considered a common and acceptable practice. The sources have found different applications - such as alternative power supply to industrial plants, as additional power sources in power grids, as local power systems for supplying residential buildings and remote sites, and others. The permanent increase in the energy price for end-users, the lower cost of photovoltaic modules, the poor reliability of existing power supply, especially in some remote areas, and other factors make the PV systems application in residential buildings especially appropriate and up-to-date. The current trend impels consumers to proceed and invest in construction of systems to cover their power demands. Against the backdrop of the weak practices in Bulgaria for selling the excess energy, many of the projects become oversized and/or do not contain information about the actual payback periods, as most often, scientifically-based methods and research are not applied. This, in turn, is crucial for making effective investments, real positive

© Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_28

396

K. Gabrovska-Evstatieva et al.

energy and environmental balances, energy security and sustainable economic development of the regions. According to some authors, the cost-effective sizing is related to the probability of a small shortage of generator power at certain periods. This principle is used in a comprehensive study [1], in which an optimization model is proposed, taking into account factors like the electrical load of the building, solar radiation, temperature, full investments and others. The authors argue that the model is applicable to any particular site which can be expected in the context of the presented case study in Nigeria. In this case, the economic efficiency of the photovoltaic system is undoubtedly justified. A similar work is presented in [2]. In the study, a simulation method using an optimization iterative algorithm has been developed. Economic parameters related to inflation and others processes, are considered. It is believed that the method gives more accurate results compared to the existing developments. Information has been provided that the method is applicable to Malaysia. The use of intelligent algorithms for optimal sizing of stand-alone PV systems components has been developed at a high level in [3]. The developed practical approach is nearly twice as fast as the existing ones. Regarding the investments effectiveness and the payback period, a number of more particular studies are presented in literature. In an interesting study by Hartner et al. [4], the possibility of deploying roof installations in residential buildings in Austria has been analyzed. The systems are connected to the power grid, which allows the utilization of the entire roof space. The results show that this approach leads to larger systems that generally have lower specific cost and better economic returns. The economic profitability of roof on-grid residential systems is discussed in detail in another study [5] that take into account the levels of the price tariffs for selling the surplus energy. The calculations were made for sites primarily in the United States. Another interesting issue related to the impact of the energy network on the profitability of investments has been investigated in [6] through a developed calculation algorithm. Under a growing invasion of PV systems in the UK, the authors point out that buying up the excessive energy is not always guaranteed. A new approach to assessing the cost-effectiveness of roof installations is developed [7]. The authors take into account not only the investment in the generator system itself but also in the building on which the system is located. The studies concern a number of European cities. There is also research related to the evaluation of the economic efficiency of backup supply PV systems [8] as in [9], an aggregate methodology for investments feasibility assessment in on-grid systems in Poland is presented. In addition to the initial investments, in certain cases, the economic benefits from emissions trading are also taken into account when determining the price of the photovoltaic energy [10]. It is proved that for sites in India and setting an optimum panels orientation, these benefits reduce the energy cost by (16…25) % as the greater effect is being observed for building-integrated systems. The subject of this work is to propose a cost-effective investment method tailored to the specifics of the renewable energy market conditions in Bulgaria, and to justify its applicability for the region of Ruse, Bulgaria.

Sizing and Optimization of Cost-Efficient PV Generator System

397

2 Materials and Methods 2.1

Modelling the Energy Production and Consumption

The energy consumption and production of a PV-hybrid residential building could be described with: ECONS ¼ ECONV þ EPVðUSEDÞ ð1Þ where ECONS is the consumed electrical energy in kWh, ECONV is the energy from conventional sources in kWh and EPV(USED) is that part of the PV energy which was actually used for own needs in kWh. The total produced PV energy in kWh consists of consumed and excess energy EPV(EXC): EPV ¼ EPVðUSEDÞ þ EPVðEXCÞ

ð2Þ

In the present study we assume two types of mean hourly information arrays are available: the energy consumption of the apartment/house for each month of the year (ECONS) and the energy production from the PV modules for each month of the year (EPV), both in kWh. The model used to estimate the excess energy is presented with a simplified diagram in Fig. 1.

Fig. 1. Simplified energy production-consumption model

2.2

Modelling of the Financial Costs and Benefits

Two types of expenses, related to the investment in PV energy sources could be used: the initial investment and the monthly maintenance expenses. The initial expenses CINV could be estimated with: ð3Þ where CPV is the price for 1 kWp peak power in €/kWp, PRP is the installed peak power in kWp and CEQ are the additional expenses for equipment, related to the investment in

398

K. Gabrovska-Evstatieva et al.

€. In the present study the monthly maintenance expense CMN, related to the PV generator, are estimated with: ð4Þ where CMN0 is the monthly expenses for maintenance of 1 kWp installed PV power in €/kWp. The financial benefits could have two components: benefits from not buying conventional energy and benefits from selling the excess energy. The daily financial benefits CFIN.BEN could be expressed with: ð5Þ where CCONV is the selling price of energy from conventional sources in €/kWh and CPV is the buying price of energy from PV sources in €/kWh. The daily money flow Ci(t) for the ith day is: ð6Þ and the net money flow for the kth month is: ð7Þ Two financial indicators are used to evaluate the investment: the net present value (NPV) and the return on investment (ROI). The NPV of the invested money in Euro is estimated with: ð8Þ where the cost of capital r is obtained with: r¼

nr  inf 1 þ inf

ð9Þ

nr is the monthly nominal rate of return and inf is the monthly inflation. The second indicator, ROI in percent, is estimated with: P ROI ¼ 2.3

Ci ðtÞ
100; % CINV

ð10Þ

Optimality of the Investment

In Bulgaria the buying price of PV energy for small power plants under 30 kWp has been reduced to 0.13 € from 2017, which is lower than the selling price of conventional energy. However, it should be taken into consideration that in recent years, surpluses of

Sizing and Optimization of Cost-Efficient PV Generator System

399

energy in the power grid are observed, which obstructs the excess energy sale. Additionally connecting a small power plant to the grid in Bulgaria is related with a relatively complicated procedure, which introduces additional expenses. For this reason in the present study we assume that the investment is optimal when there is no excess PV energy for all 12 months of the year: 12 X

EPVðEXCÞ ðtÞ ¼ 0;

ð11Þ

t¼1

Obviously there is more than one solution to this problem, however we also try to maximize the installed power, so a second criteria is added: PRP ¼ MAX

ð12Þ

In other words in the present study the criteria for optimal investment is to max out simultaneously the installed PV power as well as the financial benefits for the residential customer/investor.

Fig. 2. Average load profile for each month of the year

400

K. Gabrovska-Evstatieva et al.

3 Results and Discussion The object of the investigation is a typical apartment in Ruse (Bulgaria) with central heating in the winter months. The energy profile of the apartment have been presented as average hourly consumption for each month of the year using the average normalized load profile reported by Ghaemi and Brauner in 2009 [11]. The data is presented in a graphical form in Fig. 2. The lowest energy consumption is in August, which is probably due to the holiday season. Another anomaly is noticed in November, which is explained with the fact that the central heating in Ruse usually doesn’t get started until the middle of the month, which implies the need to use electrical energy for heating. Similarly the mean hourly energy production from the Zita Ruse PV power plant, located in Ruse (Bulgaria), have been estimated for each month of the year. The information was obtained from [12] for a 4 years period from 2012 to 2016 and is presented in Fig. 3 in kWh per kW peak power.

Fig. 3. Average hourly PV energy production per 1 kWp

Sizing and Optimization of Cost-Efficient PV Generator System

401

Table 1. Other parameters of the simulation analysis Parameter Value Price for 1 kW installed PV power, €/kWp [13, 14] 1500 Life expectancy, years 25 Price of conventional energy, €/kWh [15] 0.14 Annual nominal rate of return, % 1 Annual inflation, % 3

Table 2. Results from the analysis Installed Life expectancy unused NPV payoff power kWp PV energy kWh time years

ROI after 25 years %

NPV after 25 years €

Annual losses from overpowered plants €

0.1 0.4 0.5 0.7 1.0 1.5 2.0 3.0

279 279 278 271 248 201 167 123

392 1570 1954 2649 3329 3632 3506 2661

0 0 0.24 3.02 18.34 69.45 133.80 280.96

0 0 43 539 3275 12401 23893 50172

8.25 8.25 8.25 8.33 9.167 10.08 13 17

Fig. 4. Annual losses in NPV money from overpowering the installation

The other parameters of the performed analysis are presented in Table 1. In this study we assume zero monthly maintenance fee, since this is a small power plant and maintenance includes clearing the PV modules’ surface. The experimental data has been analysed using the presented method for different installed power of the PV plant from 0.1 kW to 3.0 kW and the results are presented in Table 2. The annual losses in NPV money from oversized installation in Euro have also been presented graphically in Fig. 4. It can be seen they could be well approximated by a quadratic equation.

402

K. Gabrovska-Evstatieva et al.

Fig. 5. Load profile and power production for each month of the year with 0.7 kWp installed power

Sizing and Optimization of Cost-Efficient PV Generator System

403

The obtained results show that the residential PV installations should be very well sized in order to provide optimal benefits from the investment. A second option appears if the excess energy is sold. In 2017 the buying price of energy from small power plants decreased from 0.20 €/kWh to 0.13 €/kWh and in the future is expected to decrease more. This means that even if the excess energy is sold, the return on the investment would still decrease if the installation is overpowered. In the present study the load profile has a minimum in August (Fig. 5), which limits the optimal installed PV power to 0.5 kW. On the other hand if the consumption in August doesn’t differ significantly from July, the optimal installation could be increased to 0.7 kW and still keep the optimal ROI. However even with the reduced consumption in August, ROI decreases with only 8% from 279% to 271%, which is a loss of only 3 Euro annually. Such difference is insignificant and could be well ignored. This also means that when sizing the optimal installation, single month anomalies could be ignored, in order to increase the installed PV power. In Fig. 5 are presented the results of the hourly production and consumption for each month of the year for 0.7 kW installed PV power. It could be seen that the average PV production would exceed the average consumption only in August, but it doesn’t influence the investment significantly.

4 Conclusions In the present study a method for evaluating the effectiveness of investments in residential PV systems is proposed by which a sizing and optimization analysis has been performed on a typical apartment in Ruse, Bulgaria. The method reflects the specifics of the renewable energy market conditions in Bulgaria. The analysis relies on mean hourly data of the power load and of the PV energy production for every month of the year. The optimality is assessed using the NPV and ROI of the investment as well as the payoff time. The obtained results showed that in Bulgaria small PV power plants, used to partially power residential buildings, should be properly sized in order to provide optimal investment efficiency. Oversized installations increase the annual losses significantly and could be approximated with a quadratic equation. The results also showed that single month anomalies do not influence the investment return significantly and could be ignored in order to increase the installed rated PV power. If there are no changes in the price of conventional energy, the optimal investment would payoff for approximately 8 years. For the life expectancy of the PV modules, the ROI is expected to reach 271% to 279%. The obtained experimental results justify the performance and the practical applicability of the proposed method. It is considered that it can be applied to sites in other regions of the country. This would provide valuable information and allow for sound and targeted sustainable investments, better strategies and policies for the potential areas in the field of lowering the residential building energy demand.

404

K. Gabrovska-Evstatieva et al.

References 1. Okoye, C.O., Solyalı, O.: Optimal sizing of stand-alone photovoltaic systems in residential buildings. Energy 126, 573–584 (2017). doi:10.1016/j.energy.2017.03.032 2. Ibrahim, I., Khatib, T., Mohamed, A.: Optimal sizing of a standalone photovoltaic system for remote housing electrification using numerical algorithm and improved system models. Energy 126, 392–403 (2017). doi:10.1016/j.energy.2017.03.053 3. Aziz, N., Sulaiman, S.I., Shaari, S., Musirin, I., Sopian, K.: Optimal sizing of stand-alone photovoltaic system by minimizing the loss of power supply probability. Sol. Energy 150, 220–228 (2017). doi:10.1016/j.solener.2017.04.021 4. Hartner, M., Mayr, D., Kollmann, A., Haas, R.: Optimal sizing of residential PV-systems from a household and social cost perspective: a case study in Austria. Sol. Energy 141, 49–58 (2017). doi:10.1016/j.solener.2016.11.022 5. Comello, S., Reichelstein, S.: Cost competitiveness of residential solar PV: the impact of net metering restrictions. Renew. Sustain. Energy Rev. 75, 46–57 (2017). doi:10.1016/j.rser. 2016.10.050 6. Pillai, G., Putrus, G., Pearsall, N., Georgitsioti, T.: The effect of distribution network on the annual energy yield and economic performance of residential PV systems under high penetration. Renew. Energy 108, 144–155 (2017). doi:10.1016/j.renene.2017.02.047 7. Vimpari, J., Junnila, S.: Evaluating decentralized energy investments: Spatial value of on-site PV electricity. Renew. Sustain. Energy Rev. 70, 1217–1222 (2017). doi:10.1016/j. rser.2016.12.023 8. Pillai, G., Hodgson, J., Insaurralde, C.C., Pinitjitsamut, M., Deepa, S.: The techno-economic feasibility of providing solar photovoltaic backup power. In: IEEE International Symposium on Technology and Society, Trivandrum, India, pp. 62–67 (2016). DOI:10.1109/ ISTAS.2016.7764051 9. Pstraś, L.: The methodology of PV investment profitability analysis [Metodyka analizy rentowności inwestycji fotowoltaicznych]. Rynek Energii 110(1), 129–139 (2014) 10. Arulmurugan, R., Suthanthiravanitha, N.: Investment cost evaluation and sizing approach of isolated residential PV scheme. Int. J. Simul. Syst. Sci. Technol. 14(3), 42–53 (2013). doi:10.5013/IJSSST.a.14.03.06 11. Ghaemi, S., Brauner, G.: User behavior and patterns of electricity use for energy saving. Internationale Energiewirtschaftstagung an der TU Wien, IEWT (2009) 12. https://www.sunnyportal.com. Accessed 3 May 2017 13. http://www.motto-engineering.com/bg/produkti/solarni-sistemi/mrezhovi-solarni-sistemi/ mrejova-fotovoltaichna-sistema-3kwp-153-detail. Accessed 3 May 2017 14. http://ecosolar-bg.com/network-photovoltaic-powerplants. Accessed 3 May 2017 15. https://www.energo-pro.bg/bg/Dejstvashti-ceni-na-elektroenergiyata-Bitovi-klienti. Accessed 3 May 2017

Modular Electrochemical Reactivity for Photovoltaics’ Machines Mirela Iorga1, Marius Mirica1, and Mihai Putz1,2(&) 1

2

Laboratory of Renewable Energies-Photovoltaics, R&D National Institute for Electrochemistry and Condensed Matter-INCEMC-Timisoara, Timisoara, Romania Laboratory of Structural and Computational Physical-Chemistry for Nanosciences and QSAR, Biology-Chemistry Department, West University of Timisoara, Timisoara, Romania [email protected], [email protected]

Abstract. The paper presents the idea of an extensive study, starting on the one side from the main features of molecular machines and on the other side from the applicability of Fredholm integral in electrochemistry. To this aim, the chemical reactivity could be expressed as a link between electronegativity (v), number of exchanged/carried/transported electrons/charges (N) and the total energy of the system, dynamically evolving under potential V, respectively through the differential equation v ¼ ð@E=@N ÞV and/or by its integral form R E ¼  vðN ÞV dN. This way, the complementary electrochemistry processes, i.e. electrode interfaces’ processes (such as deposition, corrosion, oxidation, reduction processes, etc.) and the electrolyte solution phenomena (diffusion, dispersion, recombination processes, etc.), may be either interchanged and/or separately controlled. In this context, one may employ the conceptual mix between electronegativity (chemical reactivity) driving the charge transfer in an electrochemical cell with the molecular machine’s inner conversions and light activated features, the so called modular electrochemical reactivity laws are established. Remarkably, such modular controlling of electrochemical processes applied to self-organized molecular machines may control and eventually enhance the life-cycle of photovoltaics, by designing the appropriate electromolecular modular photovoltaics machine with the inner electrochemistry modularly controlled. Keywords: Electronegativity  Reactivity Fredholm integral equation in electrochemistry

 Electro-photo-chemistry   Molecular machines

1 Introduction 1.1

Electronegativity

The electronegativity is a fundamental chemical concept implied both in structure and in reactivity [1]. It evaluates the tendency to receive or donate electrons, combining the quantum and the electromagnetic duality, acting on particle charges, and initiating a reaction on the nuclear or electric field of the particle. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_29

406

M. Iorga et al.

The electronegativity and the chemical hardness play an important role in the reactivity concept [2], and they could be expressed as differential equations and as integral equations. They play also a special role in modeling chemical reactivity and chemical bonding through the association between the fundamental principles and the computational quantum methods in the case of multi-electronic and multi-nuclei system. The expression through differential equation of the electronegativity, v, also called the negative of the chemical potential [3, 4] it is as follows:  v ¼ l ¼ 

@E @N

 V ðrÞ

ð1Þ

and establishes the energetic median position. Chemical hardness [5], η, has the following expression:     1 @v 1 @2E g¼ ¼ 2 @N V ðrÞ 2 @N 2 V ðrÞ

ð2Þ

and establishes the energetic interval between the electronic accepting tendency of the chemical system - on LUMO, and the electronic donating tendency - from HOMO. The five main physical-chemical principles [2] regarding the electronegativity are: • • • • •

the the the the the

electronegativity equalization principle (v = 0); chemical action principle; minimum electronegativity principle; hard and soft acids and bases principle; maximum hardness principle.

If the valence state is implied, the electronegativity should be calculated taking into account the perturbation factor, k, according to formula: vk ¼ 

@ hEk i @ hEk i @k ¼ @qk @k @qk

ð3Þ

The integral expression of electronegativity according to March [2, 6] is: vðN; Z Þ ¼ 

   Z  1 1 ¼ qðN; Z; r Þ dr ¼ CACoulombic jr j jr j

and the chemical action will have the expression [2, 7]: Z CA ¼ qðr Þ V ðr Þdr

ð4Þ

ð5Þ

Modular Electrochemical Reactivity for Photovoltaics’ Machines

407

Some more general forms expressed by integral equations [2, 8, 9] are: 1 vA ¼  2

gA ¼ 

1 2

NZ0 þ 1

dEN

ð6Þ

dvD

ð7Þ

N0 1 NZ0 þ 1

N0 1

In what follows, the basic equations of electrochemistry will be overviewed, so that their differential-integral forms as a counterpart of those of the chemical reactivity become obvious.

1.2

Electrochemistry

Electrochemistry studies the physical-chemical processes occurring near/at the interfaces between electronic conductors (such as: metals, semiconductors, conductive polymers, etc.) and/or ionic conductors (such as: liquid electrolytic solutions, solid electrolytes, electrolytic gels, etc.), as well as at liquid/liquid interfaces [10]. Of main interest are charge transfer processes at the interfaces, where the electric charge could be transferred by electrons or ions; a difference of the electric potential between the two phases takes place. The most common interface is considered the solid-liquid one. The main laws and terms specific to electrochemistry could be written as differential equations or as integral equations. One of the first examples is Gibbs-Helmholtz equation [11], expressed as a differential equation:   DH D@E E¼ þT zF @T P

ð8Þ

where E represents the voltage; F - electrochemical equivalent; DH - reaction heat; T - temperature. In the case of an electrode reaction [12]: A þ ze ! Az

ð9Þ

Faraday’s law could be written as follows: R MQ M Idt m¼ ¼ ve F ve F

ð10Þ

408

M. Iorga et al.

and in case of a general electrode reaction: vs S þ ve e ! vp P

ð11Þ

it could be formulated as: mp ¼

vp M p ve F

Z Idt

ð12Þ

Its division by Mp and its differentiation with respect to t, yields the production point rate: dnp vp ¼ I dt ve F

ð13Þ

dmp vp Mp ¼ I dt ve F

ð14Þ

Due to the fact that the rates of such reactions are always proportional to the interfacial area, the electrochemical reaction rate depends on the electrode area, Ae, and the current density, i, could be deduced from formula: vp I vp 1 dnp ¼ i ¼ Ae dt ve F Ae ve F

ð15Þ

0

The real current efficiency, Uep , at time t, known as differential or point current efficiency, is defined as: 0

Uep ¼

dnp dt

ve F vp A e i

ð16Þ

In the case of an electrochemical reaction: A þ ve e  $ B

ð17Þ

the electrochemical conversion rate, r, is determined by the applied current: r¼

dNA Ue I ¼ ve F dt

ð18Þ

so the current density, i, could be obtained from the equation: i¼

I 1 dN ¼ ve FUe1 A A dt

ð19Þ

Modular Electrochemical Reactivity for Photovoltaics’ Machines

409

In order to calculate the mass of an electrochemically generated product, mj,prod., the previous equation will be integrated over the t time, and dN=dt will be multiplied by the molecular weight: Z  idt ð20Þ mj;prod: ¼ A  Mj Ue =Fve;j The activation energy for electrochemical reactions, at constant overvoltage, could be determined from the differential equation: 

d ln i d ð1=T Þ



d aa;c gF RT g AEi0 aa;c gF d ln i0  ¼  ¼ R d ð1=T Þ d ð1=T Þ R g



ð21Þ

The reaction order, ni,j is defined as:  ni;j ¼

d ln i d ln ci

 ð22Þ cj

In the case of metal electrodeposition the important factors are the fluid dynamic conditions - i.e. the mass transport: M z þ þ ve e ! M

ð23Þ

The most general expression for the mass transfer diffusion is given by Fick’s first law: n ¼ D

  @c @y y¼0

ð24Þ

In this case the current density, i, could be expressed as:   @c ve F i ¼ n0 v e F ¼ D @y y¼0

ð25Þ

where y = 0 means the boundary condition on the electrode surface. D

  dc i ¼ dy y¼0 ve F

ð26Þ

and the change of concentration profile near the electrode is described by the Fick’s second law: @c @c2 ¼D 2 @t @y

ð27Þ

410

M. Iorga et al.

Fick’s second law in two coordinates, x (flowing parallel to the electrode), y (diffusive mass transfer due to the metal deposition - perpendicular to the electrode surface) could be expressed as following: @c @ 2 c @ ðwcÞ ¼0¼D 2 @t @y @x

ð28Þ

The Laplace equation defining the divergence of the electrical field strength as zero, in charge-free space is: Du ¼

@2u @2u @2u þ 2 þ 2 ¼0 dx2 dy dz

ð29Þ

and Ohm’s law is expressed as: @u @u @u ~ 1 þ þ ¼ ij dx dy dz

ð30Þ

or div i ¼ jDu ¼ j

 2  @ u @2u @2u þ þ dx2 dy2 dz2

ð31Þ

The theoretical modeling of transient experiments in electrochemistry could be analyzed by a specific mathematical approach, known as integral equation method [10]. An important feature of the integral equation method is the profound mathematical insight concerning the models, resulted from the necessity of the partial analytical solutions [13, 14]. The integral equations method could facilitate the obtaining of the analytical formulas for some limit cases of the models [15]. The equation describing the kinetics of an electrode redox reaction is: O þ ne $ R

ð32Þ

and could be considered as a Volterra type integral equation [16, 17] (a particular case of the Fredholm integral equation): Zt i ðt Þ ¼ k

K ðt; uÞiðuÞdu þ f ðtÞ

ð33Þ

0

where k = −1; i(u), i(t) - faradic current densities at u < t, respectively t; K(t, u) - the integral equation kernel and f(x) have explicit expressions containing kinetic parameters of the electrode reaction, concentrations, diffusion coefficients of the electrochemical active species, times t and u, overvoltage at time t.

Modular Electrochemical Reactivity for Photovoltaics’ Machines

411

Depending on how the overvoltage is applied, different forms of the Eq. (33) are obtained. Out of equation’s solutions different forms of the studied interface response are obtained. These equations have unique solutions for any k, therefore the first of Fredholm alternative is applied. By studying reaction (32) through unsteady techniques, the kinetic parameters of the electrode redox reaction and the diffusion coefficients (or concentrations) of both electrochemical active species may be determined. Thus, only the limitation by charge and mass transfer (by unsteady diffusion) of these two species must be ensured. The conclusion is that any electrochemical technique could be grounded starting from the basic Eq. (33) which is an integral equation (Volterra type). All the equations describing electrochemical unsteady techniques could be obtained through the same mathematical procedure, because they all imply solving of the same type of integral equations. Since electrochemistry has as one of its most famous application photoelectrochemistry, in the following subchapter we will have a brief presentation so as to introduce the vanguardist stage of electro-photo-chemistry.

1.3

Photo-Electrochemistry

The main energy source is the solar energy [18–20] and all the vital mechanisms of all forms of life are based on the photosynthesis, the process that converts solar energy in high energy substances which are further processed by the body in order to ensure all biological functions. In nature, solar light photons play a double role [21]: first they are involved as energy quanta in photosynthesis, and secondly they behave as information elements in the processes supplied by solar light. One of the main parameters in electro-photo-chemistry is the exchange current density, J0, which can be determined from Tafel equation [22–24]: J0 ¼

RT NFRct

ð34Þ

where: R represents the gas constant; T - temperature; n - number of electrons involved in the counter-electrode reaction; F - Faraday constant; Rct - charge transfer resistance at the interface. By means of electro-photo-chemistry studies [22] it has been determined that the open circuit voltage, Voc, and the short-circuit current, Isc, are directly proportional to the conversion energy. The maximum value for Voc is obtained if the difference between the HOMO-LUMO gap of the donor and of the acceptor could determine efficient charge generation [25]. The photoinduced energy and charge transfer reactions could be used in order to connect the energy provided by the light with the mechanic, electrical, and optical functions of devices and machines [26, 27].

412

M. Iorga et al.

The actual challenge is to find the proper molecular environment in which photo-electrochemistry can also take place. Hopefully, such innovative molecules have just been the reason why the Nobel Prize was awarded for Chemistry in 2016, the so-called molecular machines. A brief introduction of the topic will be made in the next subchapter.

1.4

Molecular Machines: The Photo-Driving Molecules

Nowadays the extension at the molecular level of device and machine concept, both for nanoscience and nanotechnology practical applications and for fundamental research have become very important [28, 29]. Science and technology have moved from micro to nano-world with the advent of the bottom-up (chemical) approach. Depending on the nature of the inputs (that could be light or chemical) they have moved from electronics to photonics and chemionics. The chemical molecule-by-molecule bottom-up approach gives unlimited possibilities for nanoscale supramolecular structures design and construction [19, 20, 30]. Most of the artificial molecular machines designed so far are based on interlocked molecular species such as rotaxanes, catenanes, and related species [18, 28, 30–33]. The main interactions in the case of rotaxanes and catenanes are: charge transfer capacity, hydrogen bonding, hydrophobic-hydrophilic character, p-p stacking, electrostatic forces, metal-ligand bonding [18, 33, 34]. As a consequence of the nanoscale phenomena occurring from the quantum mechanics laws - the Brownian motion of the molecules, the electromagnetic interaction between molecules, and the size of the molecules (much smaller than the light wavelengths for energy supply or information receiving) - the molecular devices and the molecular machines have some specific and intrinsic properties [30]. In order to operate, the molecular devices and machines need energy, and from the three main alternatives (chemical, electrochemical or photochemical reactions) [35–38] the best alternative is represented by the photochemical reactions [39–46], where the energy is conferred to a chemical system by photons [47]. Due to the fact that light is a clean reactant containing energy and no mass [21, 48], no waste products are generated, and these reactions are endergonic and reversible. In case of some supramolecular systems [49] designed to fit, photo-induced reactions [18, 26] could lead to large displacements of molecular components. Thus, nanoscale devices and machines empowered by light could be designed and built. In the case of pseudorotaxane the noncovalent interactions between the ring and the axle, which stabilize the supramolecular structure, may be modulated by light. Thereby it controls the threading and dethreading of the molecular components, a motion that reminds of the mechanical movement of a piston in a cylinder [18, 50], e.g. the thread-like species trans-1, containing a p-electron rich azobiphenoxy unit, and the p-electron deficient macrocycle, which through self assembling gave a pseudo-rotaxane, stabilized by electron donor-acceptor interactions [51], as presented in (Fig. 1).

Modular Electrochemical Reactivity for Photovoltaics’ Machines

413

Fig. 1. Threading-dethreading of a pseudorotaxane containing an azobenzene-type unit; redrawn after [51]

2 Methods Hereby we are advancing an innovative mechanism by which the photo-electrochemistry and the electrochemistry in general can be enriched by the use of molecular machines. This ensures a continuous closed charge transfer in the electrochemical cell, even under the open-circuit or under the light-off conditions. To this aim, few conceptual steps are necessary, and they will be described in what follows. 2.1

Modular Electrochemical Reactivity

The first module of an electrochemical machine is conceptually described in (Fig. 2). Accordingly, two processes are identified, i.e.: • The interface reactions, modeled by the differential (gradient-like) equations as the surface (interface) layer between the electrode and electrolyte; it should be noted that at this stage the chemical kinetics is applied, which is chemical reactivity in its limited form, at the electrode;

414

M. Iorga et al.

Fig. 2. Module 1 in an electro-photo-chemical sample: the correspondence of the differential with the integral formulation of the chemical reactivity driven by the electronegativity

• The electrolyte diffusion, mainly governed by physicochemical dynamics, with charge being transferred through the space of the electrochemical cell, eventually triggered by light or catalysts’ activating electrodes’ species. It is eventually connected to the quantum effects related to the ionic species wave-functions interferences as caused by scattering and recombination in solution or even by charge activation at distance by spin-waves transmissions (spintronics), depending on the light and molecular species (including molecular magnetism) involved.

2.2

Modular Electrochemical Machine

The second module of an electrochemical molecular machine is conceptually drawn in (Fig. 3) as based on the molecular machine cycle presented in (Fig. 1). In (Fig. 3), two states are identified, namely: • The molecular machine (MM) state I, placed at anode of an electrochemical cell supporting the threaded pseudorotaxane unit in a trans form, with a faster chemical kinetics, so being able to trigger the chemical reactivity and charge transfer in the electrochemical cell, upon further light activation (see below); • The molecular machine state II (MM II), at the cathode when its intra-conversion rate is slower than in the MM state I. Thus it is able to record the charge accumulation at different life-span than the anode and thus generating an electrochemical potential, even in an open-circuit (no external voltage applied).

Modular Electrochemical Reactivity for Photovoltaics’ Machines

415

Fig. 3. Module 2 in an electro-photo-chemical sample: application of electrochemical chemical reactivity integral code to cyclic molecular processes modelling

Both molecular machines’ states are crucial in building a modular photovoltaic machine, in the third stage of this mechanism, which will be described in what follows. 2.3

Modular PV Machine

The third module of an electrochemical molecular machine is conceptually drawn in (Fig. 4) as based on the molecular machine states presented in (Fig. 3). Finally, (Fig. 4) reveals two types of processes, related to the previously mentioned molecular machine’s electrochemical phenomenology, i.e.: • When the electrode is activated by light, the molecular machine in state I - in (Fig. 3) - migrates (or is quantumly transferred through the electrolyte induced potential gap) to the counter-electrode, with the corresponding charge transfer accumulation, eventually enhancing the ordinary photo-electrochemical processes. They may appear under proper photovoltaic cell preparation; shortly one can have an enhanced photovoltaic effect by the synergetic molecular machine cycle superimposed in its photo-activated cell; • When the electrode is not light activated the molecular machine in state II at counter-electrode - in (Fig. 3) - migrates to the electrode (anode), due to the inner potential formed in between electrode/counter-electrode at the time of the light activated previous process, now “refilling” the anode with the molecular machine at

416

M. Iorga et al.

Fig. 4. Integration of modules 1 & 2 of Figs. 2 and 3 in an electro-photo-chemical sample

states I, with the recording of an electrical charge flux, with lower velocity, yet with persistence even under open-circuit (and in the absence of light activation) conditions; briefly, in this case one can have a molecular machine electrochemical activated (or a photovoltaic cell) even in the absence of light (for a certain period of time, depending on the circuit total impedance) or in an open-circuit electrochemically condition, enhancing the ordinary dark current.

3 Discussions The three modules of a photovoltaic machine, previous presented and illustrated in (Figs. 2, 3 and 4) are in (Fig. 5) presented as integrated in a possible flexible (controlled) system. One, therefore may bear in mind the following integrated message: • Chemical reactivity is a versatile conceptual-analytical tool, by which one may understand the charge transfer, either at electrodes by local gradients, or by diffusion processes in electrolytes by integral forms susceptible to include quantum phenomena acting from a distance, of wave function interference, especially by the transition amplitude known as (path) integral; • Electrochemical processes at electrodes may involve molecular machine states which by their inner nature thread and unthread with different rates, eventually producing the electrode potential difference in an innovative way, and this is presented in this paper for the first time;

Modular Electrochemical Reactivity for Photovoltaics’ Machines

417

Fig. 5. Integrated modular electro-photo-chemical phenomenon by chemical reactivity driving charge transfer triggered by the action of light on molecular machines in an electrochemical cell

• The photo-activated processes may in turn link the states of the electrodes, and the molecular machines modules in this case, to either enhance the photovoltaic effect, or diminishing the dark current to the limit where the photovoltaic cell may function also in the dark with performance depending of the induced impedance by the molecular machine system optimization. This way the molecular machine insertions in PV systems may assure the cell operating also in the absence of photo-action; when experimentally realized, we anticipate it as a truly breakthrough in PV generations, this time with molecular machines sensitizers; however, both further theoretical and experimental prototype of such a system are by the actual research group envisaged, and for the medium-long term to be reported. Our present endeavor may open a new research direction, with possible new electrochemical achievement of the photovoltaics, this time under the photovoltaic machines. Such researches are currently unfolding by the authors of this paper and will be submitted in subsequent studies.

4 Conclusions We may conclude by underlining that designing a functional photovoltaic machine involves certain analytical and technical preparation stages such as: • by rewriting the fundamental laws of electrochemistry in terms of electronegativity, one can establish the correspondence between the differential laws expressing the chemical reactivity and the differential laws in electrochemistry;

418

M. Iorga et al.

• applying the same rules in the case of integral equations, starting for example from expressing the electrochemical processes using Fredholm integrals, and rewriting it in terms of chemical reactivity, quantum electrochemical models could be set up, and further on they could be used for various applications; • by correlating these rules to quantum electrochemical models; • by establishing correlation rules and quantum electrochemical models which could be applied to molecular machines study, due to the fact that most of the molecular machines (MM) have a cyclic operation (based on reversible or renewable processes); in this case the electrochemical - chemical reactivity integral code could be used to model the cyclic molecular processes. As a logical consequence, the electrochemical - chemical reactivity integral code could be applied to cyclic molecular processes modeling, in case of molecular machines - cyclic working - based on reversible, renewable reactions. Moreover, the electro-photo-chemical phenomenon could be studied, analyzing the light action on an activity segment of the studied molecular circuit, in case of molecular machines - cyclic working - operated by photochemical energy. Acknowledgments. We hereby acknowledge the research project PED123/2017 of UEFISCDIRomania.

References 1. Putz, M.V.: Chemical reactivity and electromagnetic field. In: Putz, M.V. (ed) Advances in Chemical Modeling. Nova Science Publishers, pp. 9–14 (2011) 2. Putz, M.V.: Electronegativity and chemical hardness: different patterns in quantum chemistry. Curr. Phys. Chem. 1, 111–139 (2011) 3. Iczkowski, R.P., Margrave, J.L.: Electronegativity. J. Am. Chem. Soc. 83, 3547–3551 (1961) 4. Parr, R.G., Donnelly, R.A., Levy, M., Palke, W.E.: Electronegativity: the density functional viewpoint. J. Chem. Phys. 68, 3801–3808 (1978) 5. Parr, R.G., Pearson, R.G.: Absolute hardness: companion parameter to absolute electronegativity. J. Am. Chem. Soc. 105, 7512–7516 (1983) 6. March, N.H.: The ground-state energy of atomic and molecular ions and its variation with the number of elections. Struct. Bond. 80, 71–86 (1993) 7. Putz, M.V.: Chemical Action and Chemical Bonding. J. Mol. Struct. (Thoechem) 900, 64– 70 (2009) 8. Putz, M.V., Russo, N., Sicilia, E.: Atomic radii scale and related size properties from density functional electronegativity formulation. J. Phys. Chem. A 107, 5461–5465 (2003) 9. Putz, M.V.: Systematic formulation for electronegativity and hardness and their atomic scales within density functional softness theory. Int. J. Quant. Chem. 106, 361–389 (2006) 10. Bieniasz, L.K.: Modeling Electroanalytical Experiments by the Integral Equation Method. Springer Verlag, Berlin (2015) 11. Murgulescu, I.G., Radovici, O.M.: Introducere in Chimia Fizica. Electrochimia. Bucharest: Ed. Acad (1986)

Modular Electrochemical Reactivity for Photovoltaics’ Machines

419

12. Wendt, H., Kreysa, G.: Electrochemical engineering: science and technology in chemical and other industries. Springer, Heidelberg (1999) 13. Jerri, A.J.: Introduction to Integral Equations with Applications. Wiley, New York (1999) 14. Rahman, M.: Integral Equations and their Applications. WIT Press, Southampton (2007) 15. Ramm, A.G.: A simple proof of the Fredholm alternative and a characterization of the fredholm operators. Am. Math. Monthly 108, 855–860 (2001) 16. Bonciocat, N.: Electrochimie și aplicatii. Dacia Europa-Nova, Timisoara (1996) 17. Bonciocat, N.: Alternativa Fredholm în Electrochimie. Mediamira, Cluj-Napoca (2005) 18. Balzani, V., Credi, A., Venturi, M.: Molecular Devices and Machines. Concepts and Perspectives for the Nanoworld. Wiley-VCH, Weinheim (2008) 19. Credi, A., Venturi, M.: Molecular machines operated by light. Cent. Eur. J. Chem. 6, 325– 339 (2008) 20. Balzani, V., Credi, A., Venturi, M.: Light powered molecular machines. Chem. Soc. Rev. 38, 1542–1550 (2009) 21. Balzani, V., Bergamini, G., Ceroni, P.: Light: a very peculiar reactant and product. Angew. Chem. Int. Ed. 54, 11320–11337 (2015) 22. Putz, M.V., Tudoran, M.A., Mirica, M.C.: Bondonic electrochemistry: basic concepts and sustainable prospects. In: Putz, M.V., Mirica, M.C. (eds.) Sustainable Nanosystems Development, Properties, and Applications. IGI Global, Hershey Pasadena, USA, pp. 328– 411 (2017) 23. Wang, M., Anghel, A.M., Marsan, B., Ha, N.L.C., Pootrakulchote, N., Zakeeruddin, S.M., Gratzel, M.: CoS supersedes Pt as efficient electro-catalyst for triodide reduction in dye-sensitized solar cells. J. Am. Ceram. Soc. 131, 15976–15977 (2009) 24. Wu, M., Lin, X., Wang, Y., Wang, L., Guo, W., Qi, D., Ma, T., et al.: Economical Pt-free catalysts for counter electrodes of dye-sensitized solar cells. J. Am. Ceram. Soc. 134(7), 3419–3428 (2012) 25. Kooistra, F.B., Knol, J., Kastenberg, F., Popescu, L.M., Verhees, W.J.H., Kroon, J.M., Hummelen, J.C.: Increasing the open circuit voltage of bulk-heterojunction solar cells by raising the LUMO level of the acceptor. Org. Lett. 9(4), 551–554 (2007) 26. Balzani, V., Bergamini, G., Marchioni, F., Ceroni, P.: Ru(II)-bipyridine complexes in supramolecular systems, devices and machines. Coord. Chem. Rev. 250, 1254–1266 (2006) 27. Ceroni, P., Credi, A., Venturi, M.: Light to investigate (read) and operate (write) molecular devices and machines. Chem. Soc. Rev. 43, 4068–4083 (2014) 28. Balzani, V., Credi, A., Raymo, F.M., Stoddart, J.F.: Artificial molecular machines. Angew. Chem. Int. Ed. 39, 3348–3391 (2000) 29. Edwards, S.A.: The Nanotech Pioneers: Where Are They Taking Us?. Wiley-VCH, Weinheim (2006) 30. Balzani, V., Credi, A., Venturi, M.: Molecular devices and machines. Nanotoday 2, 18–25 (2007) 31. Raymo, F.M., Stoddart, J.F.: Organic template-directed syntheses of catenanes, rotaxanes, and knots. In: Sauvage, J.P., Dietrich-Buchecker, C. (eds) Molecular Catenanes, Rotaxanes and Knots. Wiley-VCH, Weinheim (1999) 32. Abendroth, J.M., Bushuyev, O.S., Weiss, P.S., Barrett, C.J.: Controlling motion at the nanoscale: rise of the molecular machines. ACS Nano 9, 7746–7768 (2015) 33. Venturi, M., Credi, A.: Electroactive [2] catenanes. Electrochim. Acta 140, 467–475 (2014) 34. Cao, D., Amelia, M., Klivansky, L.M., Koshkakaryan, G., Khan, S.I., Semeraro, M., Silvi, S., Venturi, M., Credi, A., Liu, Y.: Probing donor-acceptor interactions and co-conformational changes in redox active desymmetrized [2] catenanes. J. Am. Chem. Soc. 132, 1110–1122 (2010) 35. Goodsell, D.S.: Bionanotechnology - Lessons from Nature. Wiley, New York (2004)

420

M. Iorga et al.

36. Ballardini, R., Balzani, V., Credi, A., Gandolfi, M.T., Venturi, M.: Artificial molecular-level machines: which energy to make them work? Acc. Chem. Res. 34, 445–455 (2001) 37. Kaifer, A.E., Gomez-Kaifer, M.: Supramolecular Electrochemistry. Wiley-VCH, Weinheim (1999) 38. Balzani, V., Credi, A., Venturi, M.: Molecular machines working on surfaces and at interfaces. Chem. Soc. Rev. 9, 202–220 (2008) 39. Balzani, V., Bergamini, G., Ceroni, P.: From the photochemistry of coordination compounds to light-powered nanoscale devices and machines. Coord. Chem. Rev. 252, 2456–2469 (2008) 40. Balzani, V., Ceroni, P., Juris, A.: Photochemistry and Photophysics. Concepts Research Applications. Wiley-VCH, Weinheim (2014) 41. Barber, J.: Photosynthetic energy conversion: natural and artificial. Chem. Soc. Rev. 38, 185–196 (2009) 42. Blankenship, R.E.: Molecular Mechanism of Photosynthesis. Blackwell Science, Oxford (2002) 43. Balzani, V., Clemente-Leon, M., Credi, A., Ferrer, B., Venturi, M., Flood, A.H., Stoddart, J. F.: Autonomous artificial nanomotor powered by sunlight. Proc. Natl. Acad. Sci. U.S.A. 103, 1178–1183 (2006) 44. Ragazzon, G., Baroncini, M., Silvi, S., Venturi, M., Credi, A.: Light-powered autonomous and directional molecular motion of a dissipative self-assembling system. Nat. Nanotech. 10, 70–75 (2015) 45. Ashton, P.R., Ballardini, R., Balzani, V., Credi, A., Gandolfi, M.T., Menzer, S., Pérez-García, L., Prodi, L., Stoddart, J.F., Venturi, M., White, A.J.P., Williams, D.J.: Molecular meccano. 4. The self-assembly of [2] catenanes incorporating photoactive and electroactive #-extended systems. J. Am. Chem. Soc. 117, 11171–11197 (1995) 46. Balzani, V., Carassiti, V.: Photochemistry of Coordination Compounds. Academic Press, London (1970) 47. Venturi, M., Iorga, M.I., Putz, M.V.: Molecular devices and machines: hybrid organic-inorganic structures. Curr. Org. Chem. (2017). Accepted 48. Irie, M.: Photochromism: memories and switches introduction. Chem. Rev. 100, 1683–1684 (2000) 49. Brouwer, A.M., Frochot, C., Gatti, F.G., Leigh, D.A., Mottier, L., Paolucci, F., Roffia, S., Wurpel, G.W.H.: Photoinduction of fast, reversible translational motion in a hydrogen-bonded molecular shuttle. Science 291, 2124–2128 (2001) 50. Balzani, V., Credi, A., Venturi, M.: Controlled disassembling of self-assembling systems: Toward artificial molecular-level devices and machines. Proc. Natl. Acad. Sci. U.S.A. 99, 4814–4817 (2002) 51. Balzani, V., Credi, A., Marchioni, F., Stoddart, J.F.: Artificial molecular-level machines. Dethreading-rethreading of a pseudorotaxane powered exclusively by light energy. Chem. Commun. 11, 1860–1861 (2001)

The Efficiency and the Profitability of the Photovoltaic Panels as Generator for Household Electricity in the Region of Banat/Romania Stefan Pavel1(&), Ioan Silviu Dobosi2, Daniel Stan3, and Gabriel Fischer Szava4 1

ICER - Renewable Energy Research Institute, Politehnica University of Timisoara, Timisoara, Romania [email protected] 2 S.C. Dosetimpex SRL Timisoara, Timisoara, Romania 3 Universitatea Politehnica Timisoara, Timisoara, Romania 4 State Inspectorate for Buildings, Bucharest, Romania

Abstract. An objective and more accurate assessment of a photovoltaic (PV) electric system efficiency can be achieved through continuous monitoring of electrical parameters of this for a long period of time (at least one year) and correlating the results with the local particular conditions such as the geographic position (solar irradiance and incidence angle of the radiation flux, day length, number of hours of sunshine on the sky) but also other random weather conditions and, finally, taking into account all the technical-economic details specific for the domain. According to the results presented in the paper, a PV system with 50 kW nominal power, installed in the area of Banat/Romania may provide a considerable amount of energy (55629 kWh/year) that can cover largely the consumption of the building under study. For the summer months, from May to September, the system was able to ensure the whole energy for household consumption. The conclusions drawn in the paper could be extended to all regions from Romania benefiting from solar energy at radiation intensity over 1300 kWh/m2/year. Keywords: Photovoltaic
Solar radiation intensity Conversion yield
Efficiency
Profitability




Household electricity




1 Introduction Throughout the history, the man has always been concerned about the exploitation of natural available resources, for using them to improve his daily living. Solar energy has been shown to be useful not only for agriculture, food or habitat warming but also other less conventional applications. In the modern times, the discovery of the photoelectric effect has launched the idea of using the solar energy for electricity generation. The research on photosensitive materials as source of energy has been spectacularly imposed during the cold war © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_30

422

S. Pavel et al.

(1960–1970’s) by the technological competition mainly in high-tech domains and military: space industry, aviation, marine. Later, Japanese and American research teams have developed several manufacturing technologies for civil use as photovoltaic panels, [1], and in 1975 Robert E. Lucier obtained the patent for the technical solution of a tower-generator powered by solar energy, [2]. The solar energy flux reaching the Earth’s surface represents a few thousand times greater amount than the current use of primary energy at global scale, [3]. Beside the wind-, hydro energy, the potential of this resource could turn it in the future into the main component of the “green strategy” based on a renewable energy portfolio, aimed at reducing the global emissions of greenhouse gasses into the atmosphere, [6, 7]. However, and even though the deployment of photovoltaic systems has been increasing steadily for the last 20 years, solar technologies still suffer from some drawbacks that make them poorly competitive on the energy market dominated at this moment by fossil fuels: (still) high capital cost, (still) modest conversion yield, irregular and DC output, [8]. The technology for solar cells manufacturing is relatively expensive but the evolution of the costs in the last ten years reveal a reliable constant decreasing trend, [1–5]. The solar cells energetic efficiency, a convenient and cheapest technical solution for the storage of the produced energy and the conversion of the output DC energy into AC current for the end user are nowadays the main challenges for the researchers working for solar energy conversion into energy, key requirements for enabling the development of the solar energy technologies at a large scale, tasks and targets for the scientists. The use of solar energy for the production of electricity is used in Romania for only a few years and all the important solar plants are situated in the south of Romania and in Banat region, west of the country. The cumulated installed power was about 1220 MW at the end of the year 2014, Table 1. Table 1. History of the PV deployment in Romania, [9, 10] Year Total output power, (MW) 2006 0.19 2007 0.30 2008 0.45 2009 0.64 2010 1.94 2011 3.5 2012 51 2013 1.151 2014 1.219

The Efficiency and the Profitability of the Photovoltaic Panels

423

The first two industrial scale solar power plants in the country, each at 1 MW, were the Singureni Solar Park (south, Giurgiu county) completed in December 2010 and the Scornicesti Photovoltaic Park (south, Olt county) completed 27 December 2011, [9]. Nowadays, the most important solar plant connected to the national grid are: – the Covaci Solar Park (west, Banat region), the largest solar power plant at completion having a total of 480,000 solar panels with a combined capacity of 35 MW, – the Gura Ialomitei Solar Park (south, Ialomita county) which have a capacity of 10 MW. A 32 MW project in four sections of 8 MW each is planned for Gataia (west, Banat region) and a 48 MW solar park is planned for Segarcea (south, Dolj county). The paper aimed to evaluate the potential of a fixed solar electric system placed in the region of Banat and to provide reference data for investments in photovoltaic electrical systems in the region. We considered that the results of the study could be extrapolated for the regions from Romania with similar parameters of solar flux and weather conditions.

2 Geographical Location and Particularities of the Solar Energy in Timisoara and Banat Region Timisoara is the main city in Banat, the west side of Romania, at an altitude of 90 m from the sea level and, as location on the globe [11], it has the following coordinates: 45° 44’ 58 “North, 21° 13’ 38” East, benefiting consequently by a moderate continental climate characterized by diversity, in terms of irregularly atmospheric conditions, [12]. According to the data from the Table 2, the number of hours of sunshine in the sky for the Banat area (Timisoara and surroundings), cumulated for the entire year 2016 when the study was conducted, was at about 2124 h. As expected, it is obvious and relevant in this timetable the influence of the vernal/autumn equinox and of the summer/winter solstice. After a gradually increase in the number of monthly sunshine hours, from January and with a peak in July, then the available solar energy decreases in the next five months until December. As Table 2 show, the months of May, June, July, August and September provides the highest Table 2. Statistic data for atmospheric conditions for the year 2016, in Banat/Timisoara, [12] Month of the year I II III IV V VI VII VIII IX X Sunshine hours 72 92 155 184 242 262 300 280 217 177 (*) Sunshine index, at 0.36 0.4 0.57 0.57 0.66 0.68 0.75 0.77 0.71 0.63 noon Daily average −1.5 0.6 5.7 11.1 16.3 19.6 21.5 20.9 16.8 11.2 temperature, [°C] (*) sunshine index = hourly average shining at noon, between 11:30 and 12:30 h

XI XII 86 57 0.39 0.37 5.7

1.2

424

S. Pavel et al.

brightness of the sun on the sky, with an hourly average shining index greater than 0.66 at noon (between 11:30–12:30 h), and, as the results presented in chapter 3 reveal, the electricity produced by photovoltaic panels during this five month period was more than 34000 kWh (average value greater than 6800 kWh/month) for a generator system with 50 kW instaled power as described in Table 3. Also, the data from the Table 2 show that, for this five months, the west side of Romania and Banat region benefits from more than 200 and up to 300 h of sunshine/month, circumstance that argues the initiatives in electricity generation with PV installations and creates investment opportunities. The charts for the atmospheric conditions in Timisoara during the year 2016, Figs. 1 and 2, with data from Table 2 and the time limits of efficiency established in chapter 3 (from May to September) allow the setting of the following indicative limits for satisfactory operation of the photovoltaic panel system in the study: not less than 200 sunshine hours/month and for a hourly average shining index greater than 0.66. At first, the experiment aimed the efficiency of the PV electric system described in Table 3 by comparing the output supplied energy, as independent variable in the study, by comparing with the electrical consumption of the building in the study. The PV panels with fixed position in the network presented in the paper were produced by Kyocera (type KD240 GH-2 PB, Table 3), available on the market, and through this experimental approach where the supplied energy of the electric system was considered as single independent variable, the influence of all the other dependent variables referring to the daily and seasonal variations of solar flux energy (intensity, incidence angle, weather conditions, ambient temperature, variations of the PV cell conversion yield and periodic maintenance of these) are reflected in the final result.

Fig. 1. Charts for sunshine hours/month in Timisoara during the year 2016

The Efficiency and the Profitability of the Photovoltaic Panels

425

Fig. 2. The average shining index in Timisoara and surroundings during the year 2016

The use of an automatic adjustment device (robot) for the continuous or periodic orientation of photovoltaic panels, for tracking the position of the sun on the sky for an incidence angle of 90° (±5°) of the energy flux on the panel, could increase the output electric energy of PV converters and provide a higher conversion yield of solar energy into electricity, [13–15]. For the moment, the cost of these facilities is relatively high, situation which leads to the conclusion that, for the current technological and market context, it would be preferable to invest in photovoltaic panels with fix position. Despite of this conclusion, and as encouragement for the future, on the market are available, as serial products, few variants of solar panels systems, certainly more performant in terms of efficiency, with conical collector and/or rotating facilities, [15, 16], or with PV vacuum tube and mirror, [17].

3 Network of Photovoltaic Panels. Case Study A photovoltaic system can supply continuous current (VDC), which is then converted to alternating current (AC) by an inverter. After this important step, the electricity is passed through the electrical distribution panel and it is available for consumers connected to the electrical system of the building, Fig. 3. The photovoltaic panels (1), generators of electricity, are connected to the inverter (3) is protected by an electrical protection device (2). The inverter (3) convert the DC electricity generated by the photovoltaic panels (1) into AC electric power [18, 19]. The electric panel (5) contains more protection devices (4) (for overload due to the atmospheric electricity peaks, for faulty operating of the network), the specific devices for electric energy production monitoring and, optionally, for data transmission (electrical control parameters) to a computer. The electric panel (5) is connected upstream of the switchboard (6), intermediate for the electric consumers (9).

426

S. Pavel et al.

1 - photovoltaic panels 2 - protection device 3 - inverter 4 - protection device 5 - electric panel 6 - switchboard 7 - counter 8 - electrical power distributor 9 - consumers

Fig. 3. Basic configuration of the photovoltaic system as domestic electricity supplier

Electrical power distributor (8) provides regularized electrical power by the counter (7) which is connected to the switchboard (6). At the selection of the inverter type it is necessary to take into account the compatibility requirements between the inverter input voltage and the maximum voltage generated by the photovoltaic system. A primary sizing of the system requires the successive solving of the following steps [20–23]: – – – – – –

settlement of the required output; decision on the type of the photovoltaic panels; establish the number of panels in the system; ascertain the configuration of the system; set out the necessary components and indicative cost for these; find suppliers and the most advantageous offer, [24–26].

Fig. 4. Rows of solar panels, inverters and electric panel of the photovoltaic electric system

European Investment Bank finances projects aimed at achieving energy efficiency and energy from renewable sources for buildings in urban areas, [27]. For the photovoltaic system with 50 kW installed power, in Timisoara, Fig. 4, the estimated costs are presented in Tables 3, 4 and 5.

The Efficiency and the Profitability of the Photovoltaic Panels

427

Table 3. Costs of the materials for the photovoltaic system in study, in the year 2016 Feature(s)

m.u.

Quantity

Cost per unit, [RON] (*) 1800

Expenditure, [RON] (*) 360000

Unit 200 Photovoltaic panels, Kyocera, type KD240 GH-2 PB, 990  1662 mm, max. power: 240 W at 1000 W/m2 and 25 °C, efficiency: 14.4% Frame structure Unit 4 12400 49600 Cables and connectors Meter 700 15 10500 Inverter Unit 4 5800 23200 Electric switchboard fully equipped Unit 1 2790 2790 (1) Total costs for components and consumables aquirement 446090 (2) Transport expenditure, 2.5% 11152 (*) official conversion rate, Romanian National Bank, for the year 2016: 4,4908 RON = 1 EURO

Table 4. Labour costs for the manufacturing of the photovoltaic system, in the year 2016 Required labour [hours] Average hourly rate, [RON/hour] (*) Value, [RON] (*) (3) 169 50 8450 (4) Fees relating to labour costs, 30% 2535 (*) official conversion rate, Romanian National Bank, for the year 2016: 4,4908 RON = 1 EURO

Table 5. Estimated manufacturing costs and sale price (for the year 2016) Total material and workmanship costs, (1) + (2) + (3) + (4) Overheads, 10% of (5) Profit, 10% of (5) + (6) Manufacturing price VAT, 20% from the manufacturing price (in 2016) Sale price (*) official conversion rate, Romanian National Bank, for the 4,4908 RON = 1 EURO

(5)

468227 46823 51505 566555 113311 679866 year 2016: (6)

In terms of specific intensity of solar energy (distributed per unit area), Timisoara is placed in a favorable position, with a yearly average between 1300 and 1350 kWh/m2/ year, Fig. 5. Estimated amount of energy able to be produced by the photovoltaic system used in the study, Fig. 4, for the atmospheric conditions from the Table 1, for the number and characteristics of the PV panels in use (Table 3), and for an average solar energy intensity at 1325 kW/m2/year, Fig. 5, is around of 55500 kWh, close to the experimentally determined value from the Table 6 (55629 kWh), with a monthlydistribution shown in Fig. 6.

428

S. Pavel et al.

Table 6. Balance of the electric energy for the year 2016 and the building in the study Month of the year

Consumed energy, [kWh]

Recorded sunshine lasting hours, in Timisoara

January February March April May June July August September October November December Cumulated, for the year 2016:

7838 7667 6816 7358 7214 5803 7990 7418 4509 7224 7354 7900 85091 kWh

72 92 155 184 242 262 301 280 218 177 86 57 2128 h

Energy produced by the PV system in study, [kWh] 1887 2410 4062 4820 6336 6857 7858 7324 5685 4635 2258 1487 55629 kWh

Fig. 5. Map with the distribution of solar energy intensity in Romania [9, 26]

The Efficiency and the Profitability of the Photovoltaic Panels

429

The money equivalent of the produced energy in the year 2016, of the 55629 kWh, at the rate of the local energy distributor (ENEL, 0.58 RON/kWh), was at 32265 RON, results that indicate a yearly recovery rate of the sale price estimated in the Table 5 at around 5%. The results presented in this paper synthesizes the data obtained from the monitoring, during the year 2016 and demonstrate the energy efficiency of such an alternative system from May to September and for the areas marked in orange and red in the map from Fig. 5 (intensity of solar energy > 1300 kWh/m2/year).

cumulated consumed energy = 32934 kWh energy produced by the PV system = 34060 kWh

kWh

(from May to September, according to the data from Table 6)

9000 8000 7000 6000 5000

consumed energy

4000

produced energy

3000 2000 1000 0 1

2

3

4

5

6

7

8

9

10

11

12

month of the year

Fig. 6. Balance of the electric energy for the buiding in study, for the photovoltaic electric system presented in the paper, in the region of Banat/Romania for the year 2016

4 Considerations on the Cost of the Photovoltaic (PV) Systems The total installed cost of PV systems can vary widely within individual countries, and between countries and regions, [5]. These variations in costs reflect the maturity of domestic markets, the variations of the local labor and manufacturing costs, as in Tables 3 and 4, the national and even local incentive policy and structures, and more other factors. While different PV technologies have different PV module costs, the overall PV system cost also depends on the size of the system (due to the economies of scale with large utility-scale projects), and on whether the system is ground- or roof-mounted [19, 21, 23]. To analyse costs, PV systems can be grouped into four main end-use markets [5]: • Residential PV systems typically do not exceed 20 kW and are usually roof mounted, [18, 23];

430

S. Pavel et al.

• Large-scale building PV systems typically do not exceed 1 MW and are placed on large buildings or complexes, e.g. commercial buildings, schools, hospitals, universities; • Utility-scale PV systems are larger than 1 MW and are generally ground-mounted; • Off-grid applications vary in size from small systems for remote beacons or relay stations to mid-size systems for homes or businesses not connected to the grid, all the way up to large-scale PV systems that provide electricity to off-grid communities. Despite the impressive declines in PV system costs, the leveled cost of electricity (LCOE) from PV remains high. The LCOE of residential systems without storage, assuming a 10% cost of capital, was in the range 0.25 up to 0.65 USD/kWh in 2011. When electricity storage is added as option, the cost range increases to 0.36… 0.71 USD/kWh, [5].

5 National Legislation for Renewable Energy Romanian legislation [28] was adapted to European standards and demands in the domain in order to encourage initiative and to support the investments for energy generation from the so called renewable sources, by solar-, wind- and geothermal ower stations, biomass reactors, small hydropower plants: • Government decision (GD) no. 1535/2004, The strategy for the capitalization of the renewable resources; • Law 134/2012 for establishing the promotion system for the generation of electricity from renewable energy sources; • GD 553/2007 amending and supplementing the Regulations for the granting of licenses and authorizations in the electricity sector, approved by GD no. 540/2004; • Government ordinance (GO) no. 22/2008 on energy efficiency and promotion for the use of the renewable energy sources at the end-users; • GD 750/2008 for the approval of the state regional aid plan on the capitalization of renewable energy resources; • Order no. 28/2010 for the endorsement of the technical connection approvals; • Order no. 04/2012 on the updating of the trading values for the green certificates and on the value of a not acquired green certificate, applicable for the year 2012; • Order no. 37/2012, amending and supplementing the Rules of accreditation of the producers of electricity from renewable energy sources, for the application of the green certificates promotion system. The green certificates (GC) are documents in electronic format issued by the official network operator, the National Company TRANSELECTRICA in Romania’s case. The GC system was designed and implemented as a support mechanism to impel the electricity production from renewable energy sources (RES) that aims at increasing the

The Efficiency and the Profitability of the Photovoltaic Panels

431

interest in producing electricity from renewable energy sources and applies to electricity generated from: – hydro energy used in the power stations with installed power is less than 10 MW, – wind, solar, geothermal or waste fermentation power plants with installed power over 1 MW. In 2014, the Romanian laws and regulations for energy required energy providers and energy-intensive businesses to obtain 14% of their electricity from renewable sources. If they did not achieve the required quota, they were obliged to purchase “green certificates” at a price of 110 EUROS (144 USD) each to cover the shortfall. And this quota was rising by 1% year each year with a target, for 2019, of 19.5% “green energy” in the national economy, [29]. On the other hand, each producer of electricity from RES receives, depending by the type of RES, a number of green certificates which is proportional to the energy supplied to the grid. For the period 2008–2025, the trading value of the green certificates on the market was established in the range of a minimum trading between 27 and 55 EUROS/GC, [30]. So that, the system has a double effect, combining the compulsory quotas with the green certificate trading but is not applicable for small entrepreneurs and private initiatives.

6 Conclusions As the results presented in the paper prove, for the atmospheric conditions from the Table 2, for the nominal power of the system at 50 kW and the characteristics of the PV cells from the Table 3, in the year 2016 the photovoltaic electric generator system in use in Timisoara, Banat region, was able to cover about 65% from energy consumption of the building in the study (55629 kWh produced energy versus 85091 kWh consumed, Table 6). This balance demonstrates the effectiveness and the profitability of this type of energy generation. For the summer months, from May to September, the system was able to ensure the whole energy for household consumption, Fig. 6, for a hourly average shining index, at noon, not lower than 0.66, Fig. 2, for more than 200 sunshine hours/month, Fig. 1, and for a daily average temperature greater than 16°C (Table 2). The conclusion of this study could be extended to all regions from Romania marked in orange and red on the map from Fig. 5, benefiting from a specific intensity of solar energy at an average value over 1300 kWh/m2/year. At present, for the current technological and for the market context, the cost for manufacturing, Tables 3 and 4, or for purchasing a photovoltaic system, Table 5, is relatively high and prohibitive so that, the 5% yearly recovery rate demonstrated in our study could be considered as being modest. The Romanian legislation, [28–30], encourage the initiative and support the investments in “green energy” combining the compulsory production quotas with the green certificate trading but these incentive measures are not addressed to the small entrepreneurs and private initiatives.

432

S. Pavel et al.

For the moment, the financial support from EU funding for green energy (partially or fully non-refundable) could be incentive for the private investors and such an initiative.

References 1. Renewable energy in the world. https://en.wikipedia.org/wiki/Renewable_energy. Accessed Mar 2017 2. Solar & thermal energy - Stecasolar site. www.stecasolar.ro/energie-solara/Energie-solaratermica-:-Istoric–a714.html. Accessed Mar 2017 3. An Assessment of Solar Energy Conversion Technologies and Research Opportunities, vol. GCEP Energy Assessment Analysis Summer 2006, issued by Global Climate & Energy Project. Stanford University. http://gcep.stanford.edu. Accessed May 2017 4. Janssen, R.: Towards Energy Efficient Buildings in Europe. The European Alliance of Companies for Energy Efficiency in Buildings, London (2004) 5. Renewable energy technologies: Cost analyses of solar photovoltaics. Power Sector - Solar Photovoltaics, vol. 1(4/5). IRENA International Renewable Energy Agency, Abu-Dhabi (2012) 6. Patel, R.: Wind and Solar Power Systems. CRC Press, Boca Raton (1999) 7. Priambodo, P.S., Poespawati, N.R., Hartanto, D.: Solar cell technology. INTECH Open Access Publisher (2011) 8. Green, M.A.: Solar Cells. Operating Principles Technology and System Applications. Prentice Hall, Upper Saddle River (1982) 9. Review on Solar power in Romania, Wikipedia. https://en.wikipedia.org/wiki/, Solar_ power_in_Romania. Accessed May 2017 10. Romanian National Institute of Statistics. http://www.insse.ro/cms/. Accessed May 2017 11. Official site of the Timisoara municipality, Geographic data and atmospheric conditions. www.primariatm.ro/timisoara/index.php?meniuId=2&viewCat=44&viewItem=286. Accessed April 2017 12. Geography, meteorology and environment, Romanian Statistical Yearbook, p. 19. https://ro. wikipedia.org/wiki/Timi%C8%99oara#Clim.C4.83. Accessed April 2017 13. Loomis, R.S., Connor, D.J.: Crop Ecology. Cambridge University Press, Cambridge (1992) 14. Vartanian, R.: Design & implementation of movable photovoltaic array with two-degrees of freedom to study of increment in absorbed solar energy in compare with fixed one. In: M.Sc. thesis. Isfahan University of Technology (2001) 15. Vartanian, R., Moghbelli, H.: Implementation of the movable photovoltaic array to increase output power of the solar cells. In: Proceedings of the International Conference on Renewable Energy for Developing Countries-2006 (2006) 16. Burgess, P.: Variation in light intensity at different latitudes and seasons, effects of cloud cover, and the amounts of direct and diffused light. Presentation to Continuous Cover Forestry Group (CCFG) Scientific Meeting, 29 September 2009, Westonbirt Arboretum, Gloucestershire. www.ccfg.org.uk/conferences/downloads/P_Burgess.pdf. Accessed May 2017 17. SOLYNDRA photovoltaic tubes. www.solideas.com/GlassTubes.html. Accessed May 2017 18. Shrestha, G.B., Goel, L.: A study on optimal sizing of stand-alone photovoltaic stations. IEEE Trans. on Energy Convers. 13(4), 373–378 (1998)

The Efficiency and the Profitability of the Photovoltaic Panels

433

19. Beshr, M.H., Khater, H.A.: Modelling of a residential solar stand-alone power system. In: Proceedings of 1st International Nuclear and Renewable Energy Conference (INREC10), Amman, Jordan, pp. 1–6 (2010) 20. Hua, C., Shen, C.: Control of DC/DC converter for solar energy system with maximum power tracking. In: IECON 23rd International Conference on Industrial Electronics, Control and Instrumentation, Vol. 2, pp. 827–832 (1997) 21. Gow, J.A., Manning, C.D.: Photovoltaic converter system suitable for use in small scale stand-alone or grid connected applications. IEE Proc-Electric Power Appl. 147(6), 535–543 (2000) 22. Bhim, N.A., Vyas, A.L.: Design and control of small power standalone solar PV energy system. Asian Power Electron. J. 6(1), 17–24 (2012) 23. Anilkumar, P.P.: Effective and passive utilization of solar energy for energy efficient buildings: an application perspective. Int. J. Emerg. Technol. Adv. Eng. 3(3), 311–315 (2013). ICERTSD 2013 24. Solar energy businesses in Romania. http://energy.sourceguides.com/businesses/byGeo/ byC/Romania/Romania.shtml. Accessed May 2017 25. Sunshine solar energy in Romania, The steps necessary for project implementation. http:// www.sunshinesolarenergy.com/. Accessed May 2017 26. SOLARGIS Data and maps. http://solargis.com/products/maps-and-gis-data/?_ga=2.19509 6940.1133455138.1497583098–1817779692.1497583098, Solar radiation chart for Romania. Accessed Apr 2017 27. Knapp, K., Jester, T.: Empirical investigation of the energy payback time for photovoltaic modules. J. of Solar Energy 71(3), 165–172 (2001) 28. ECOMOVE Consulting site, Green energy legislation in Romania. http://e-panouri.eu/ energie-verde-legislatie. Accessed Mar 2017 29. Hardesty, L.: Green certificates’ make solar an investment vehicle in Romania (2013). www. energymanagertoday.com/green-certificates-make-solar-an-investment-vehicle-in-romania091664/. Accessed May 2017 30. Green certificates support mechanism (2014). www.rets-project.eu/UserFiles/File/pdf/resp edia/10%20Green%20certificates%20support%20mechanism/10-Green-certificates-supportmechanism_EN.pdf. Accessed May 2017

Extracting the I-V Characteristics of the PV Modules from the Manufacture’s Datasheet Andreea Sabadus1(&), Marius Paulescu1, and Viorel Badescu2 1

Faculty of Physics, West University of Timisoara, Timisoara, Romania [email protected] 2 Candida Oancea Institute, Polytechnic University of Bucharest, Bucharest, Romania

Abstract. Proper knowledge of the I-V characteristics of a PV module is a key requirement for accurate estimation and forecast of energy production. By using the scarce information provided in the manufactures’ datasheet (short circuit current, open circuit voltage and the maximum power point), the mathematical description of the I-V characteristic is always a challenge. In this paper two procedures for extracting the I-V characteristics in standard test conditions (STC) are discussed. The procedures, based on the Taylor’s series expansion of the current equation, are developed within the frame of the one diode model. The results are assessed by using the datasheets of four different crystalline PV modules, commercially available. The estimated parameters are also compared with the ones previously reported for the same PV modules. Generally, the results show that while the models reproduce accurately the I-V characteristics, the parameters values experience a large dispersion. Keywords: Solar cells


I-V characteristics
One-diode model

1 Introduction The current-voltage (I-V) characteristic of a photovoltaic (PV) module represents a superposition of the I-V characteristics of its constituent solar cells. Most models of the solar cells have as starting point the Shockley theory of the illuminated p-n junction (see e.g. [1]). As a result, the equivalent circuit of the solar cell is described at different levels of approximation. The one-diode model (Fig. 1) is the most popular approximation. The photocurrent IL is produced by a source of current, primarily depending on solar irradiance. The diode D, characterized by the saturation current IS and the diode ideality factor m, models the dark current losses. The parallel resistance RP accounts for the current loss caused by the increasing conductivity at cell edges. The series resistance RS captures all the resistive losses in the cell. Different procedures were developed in the last decades for extracting the five parameters (IL, IS, m, RS and RP) of the one-diode model. Reference [2] reported a comprehensive review of 34 different procedures developed to extract the one-diode model parameters. The authors stratified the procedures in three categories: (1) based on the theoretical analysis of the I-V curve (e.g. non-linear regressions), (2) dealing with the graphical analysis of the measured I-V characteristics and (3) a mix of the first two categories. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_31

Extracting the I-V Characteristics of the PV Modules

435

Fig. 1. One-diode model of a solar cell: the electric circuit. RL is a load attached to the solar cell terminals

The PV modules are usually delivered by manufactures accompanied by datasheets listing three notable points on the I-V characteristic. These points (the short circuit current, the open circuit voltage and the maximum power point -MPP) are measured in standard test conditions (STC). This standard specifies a global solar irradiance of 1000 W/m2 at normal incidence with a spectral distribution AM1.5G and the solar cell operation temperature of 25 °C. Using only the information encapsulated by these three notable points, the mathematical description of the I-V characteristic becomes always a challenge. A turning point in the history of the one-diode model was the report of De Soto et al. [3], where the authors demonstrated that the five-parameter model is a reliable tool for estimating the PV module output power. Reference [4] proposed an interesting procedure for estimating the I-V characteristic of a PV module within the frame of the five-parameter model. However, in addition to the three notable points from the I-V characteristic, the method needs the slopes of the I-V characteristic at short-circuit current and open circuit voltage, respectively. Reference [5] reported a different procedure, which is based on the analysis of either the I-V characteristic supplied by manufacturer or the user-obtained experimental I-V curve. Basically, the procedure combines the solution of an algebraic system of equations with an optimization algorithm. In order to extract the parameters of the one-diode model, an unusual approach based on the adaptive differential evolution technique is proposed in [6]. Reference [7] discusses a comparison between gradient descendent techniques (based on the classic Newton-Raphson method) and genetic algorithms applied to the parameters extraction of the one diode-model. The results showed that the error obtained with the Newton-Raphson method was significantly lower than the error for the genetic algorithms. This implies that the Newton-Raphson method can be considered favorable over other methods, even if it is less convenient in terms of convergence. In this paper two procedures for extracting the I-V characteristics within the frame of the one diode model at STC are discussed. The procedures, based on the Taylor series expansion of the current equation, require for running only the three notable points. The results are evaluated against data provided by manufactures for four different crystalline PV modules. The estimated parameters are also compared with the ones previously reported by other studies focused on the same PV modules.

436

A. Sabadus et al.

2 Equations for the One-Diode Model The one-diode model (Fig. 1) is widely used in practice due to its simplicity and accuracy. The most popular I-V equation developed within the frame of the one-diode model is [8]:

  eðV þ IRS Þ V þ IRS I ðV Þ ¼ IL  IS exp ð1Þ 1  mkB T RP Equation (1) is known as the five-parameter model. Sometimes, in practice, the number of the parameters is reduced to four, assuming a high value for the parallel resistance, i.e. RP ! 1. In this case, the I-V equation reads:

  eðV þ IRS Þ I ðV Þ ¼ IL  IS exp 1 ð2Þ mkB T Equation (2) represents the so-called four-parameter model. Two procedures for extracting the parameters of the four- and five-parameter models are proposed next. 2.1

The Four-Parameter Model

By applying Eq. (2) in the three notable points (short circuit, I ¼ ISC ; V ¼ 0; open circuit, V ¼ VOC ; I ¼ 0 and MPP V ¼ VM ; I ¼ IM ), we obtain the equations:

  eISC RS f1 ðIL ; IS ; RS ; mÞ  ISC þ IL  IS exp 1 ¼ 0 mkB T

  eVOC f2 ðIL ; IS ; RS ; mÞ  IL  IS exp 1 ¼ 0 mkB T

  eðVM þ IM RS Þ f3 ðIL ; IS ; RS ; mÞ  IM þ IL  IS exp 1 ¼ 0 mkB T A fourth equation can be obtained by imposing the condition IS mkeB T exp



eðVM þ IM RS Þ mkB T



dP  dV M ¼

ð3bÞ ð3cÞ

0 at MPP:



  VM 1 þ IS RS mkeB T exp eðVMmkþBITM RS Þ 
  eðVM þ IM RS Þ  IS  IS exp 1 ¼ 0 mkB T

f4 ðIL ; IS ; RS ; mÞ  IL 

ð3aÞ

ð4Þ

In order to find the approximate solution of the system of Eqs. (3c–4) we applied the Newton - Raphson method. The specific method used here is briefly described next. Denoting x ¼ ðIL ; IS ; RS ; mÞ, the system of equations can be written in a matrix form as follows:

Extracting the I-V Characteristics of the PV Modules

1 f 1 ð xÞ B f ð xÞ C ¼ 0 f ð xÞ  @ 2 f 3 ð xÞ A f 4 ð xÞ

437

0

ð5Þ

By expanding f(x) in Taylor series, an iterative solution can be derived [8]:     xðn þ 1Þ ¼ xðnÞ  Jf1 xðnÞ f xðnÞ

ð6Þ

where Jf is the Jacobian matrix of the first partial derivatives function f: 0 @f

@f1 @IS @f2 @IS @f3 @IS @f4 @IS

1

B @IL B B @f2 B B @I B L Jf ð xÞ ¼ B B @f3 B B @IL B @ @f 4 @IL The guess value xð0Þ ¼



@f1 @RS @f2 @RS

@f3 @RS @f4 @RS

@f1 1 @m C C @f2 C C @m C C C @f3 C C @m C C @f4 A @m

ð7Þ

 ð0Þ ð0Þ ð0Þ IL ; IS ; RS ; mð0Þ required for starting the numerical

algorithm is given by the following equations:
 eVOC ð0Þ ð0Þ ; IL ¼ ISC ; IS ¼ ISC exp  ð0Þ m kB T   VM IISC  1 þ VOC VM M I

ð0Þ RS

¼

ln 1I M

SC

ISC  IM þ  IM  ln

;

m

ð0Þ

ð8Þ

¼ 1:5

I 1I M SC

The algorithm stops when the necessary precision is reached. 2.2

The Five-Parameter Model

The specific parameters of the five-parameter model ðIL ; IS ; m; RS ; RP Þ are evaluated using the Newton-Raphson method for function optimization. Similar to the four-parameter model we denote by x the vector ðIL ; IS ; m; RS ; RP Þ. According to [7], the following iterative solution can be derived:   xðnÞ ¼ xðn1Þ  Hf1 ð xÞF xðn1Þ ð9Þ where F is a column vector containing the partial derivatives of f ðxÞ and H is the Hessian matrix of the objective function:

438

A. Sabadus et al.

f ð xÞ ¼

N X

Ikexp  Ikth

2

ð10Þ

k¼1 th is the kth sample out of N experimental current data sample and Ith Iexp k is the k k sample of the estimated current [7]:


exp  e Vk þ Ikexp RS V exp þ Ikexp RS ¼ IL  IS exp 1  k mkB T RP 

Ikth

ð11Þ

Each element of the Hessian matrix is calculated as: 0

@2f B @I 2 B L B 2 B @ f B B @I @I B S L B 2 B @ f Hf ðxÞ ¼ B B @m@I L B B 2 B @ f B B @RS @IL B B @ @2f @RP @IL

@2f @IL @IS

@2f @IL @m

@2f @IL @RS

@2f @IS2

@2f @IS @m

@2f @IS @RS

@2f @m@IS @2f @RS @IS

@2f @m2 @2f @RS @m

@2f @m@RS @2f @R2S

@2f @RP @IS

@2f @RP @m

@2f @RP @RS

1 @2f @IL @RP C C C @2f C C @IS @RP C C C @2f C C @m@RP C C C 2 @ f C C @RS @RP C C C A @2f

ð12Þ

@R2P

  ð0Þ ð0Þ ð0Þ ð0Þ The guess value xð0Þ ¼ IL ; IS ; RS ; mð0Þ ; RP required for starting the numerical algorithm is given by the following equations: ð0Þ IL

¼

ð0Þ ISC ; IS

ð0Þ

RP

¼

ISC  VOC ð 0Þ RP  

ð0Þ

; RS ¼ 




OC exp meV 1 ð 0Þ k T B
1 @I  ¼ ; mð0Þ ¼ 1:5 @V V¼VOC

 @I 1 @V I¼ISC

ð13Þ

The numerical algorithm searches for that set of parameters which minimizes the objective function.

3 Results and Discussions The numerical experiments reported here were conducted on the basis of the datasheets of four crystalline PV modules, commercially available (Table 1). The computer algorithms were developed following the two procedures discussed above. The values of the short circuit current, open circuit voltage and MPP of a single cell were used as

Extracting the I-V Characteristics of the PV Modules

439

Table 1. Electrical parameters, of the PV modules used in this study, measured at STC by the manufactures and provided in the accompanied datasheets. NS represents the number of the cells connected in series. P represents the nominal power of the PV module. Module ID P (W) NS VM (V) IM (A) VOC (V) ISC (A) Source #1 #2 #3 #4

175 265 36 60

48 60 36 36

0.491 0.515 0.458 0.475

7.42 8.48 2.18 3.50

0.608 0.631 0.594 0.586

8.09 9.11 2.30 3.80

www.kyocerasolar.com www.canadiansolar.com www.proyectodeenergiarenovable.com www.solarelectricsupply.com

inputs. In each case, the solution was identified by comparing the estimated I-V characteristic with the measured one. The fit of the two curves was measured using three statistical indicators: the determination coefficient r2 , root mean square error (RMSE) and mean bias error (MBE). The determination coefficient r2 is a measure of how well a model fits a set of data: PM r ¼ 1  Pi¼1 M 2

ð m i  ci Þ 2

i¼1 ðmi

 lÞ 2

ð14Þ

where c and m refer to the computed and measured values, respectively, while M is the sample size. RMSE and MBE are often used as indicators of accuracy in PV modeling. They are defined as: " #1=2 M 1X 2 RMSE ¼ ð ci  m i Þ ð15Þ M i¼1 MBE ¼

M 1X ð ci  m i Þ M i¼1

ð16Þ

The estimated parameters obtained with the proposed procedures are also compared with the ones reported previously by other studies [4, 9–11]. For extracting the parameters, in addition to the three notable points, the procedure proposed in [4] needs as inputs the slopes of the I-V characteristic at ISC and VOC. Reference [9] reports a generalization of the algorithm from [4], proposing an empirical method for estimating the slopes on basis of the notable points. The main contribution of [10] is the simplification of the current equation, in which only four parameters are required. Reference [11] reports an explicit procedure for estimating the I-V characteristic of a solar cell based on Pade approximants. Table 2 shows the results. The computer code was developed within the mathematical software MathCAD [12] while the I-V curve from the PV module datasheet was digitized using GetDataGraph tool [13]. Looking at the proposed procedures, the determination coefficient r2 falls in the range 0.995–0.999 demonstrating that the fourand five-parameter models approximate very well the measured I-V characteristic. Generally, r2 falls in the range 0.971–1.0 showing that all the models reproduce accurately the I-V characteristics. This is confirmed visually in Fig. 2.

440

A. Sabadus et al.

Table 2. The one-diode model parameters and its accuracy in the fitting of the experimental I-V characteristics of the considered PV modules. The results are evaluated in standard test conditions r2

RMSE MBE

– 3.114 2.006 2.276 – 3.111 1.695 – 3.353 –

0.996 0.998 1 0.991 0.999 0.998 0.984 0.998 0.996 0.995

0.146 0.110 0.036 0.223 0.075 0.139 0.386 0.034 0.043 0.051

0.049 −0.007 −0.004 0.155 0.011 −0.002 −0.218 −0.029 0.007 −0.045

12.96

0.999 0.024

−0.007

3.8 3.833 3.803

3.078∙10−11 0.894 0.015 – 8.561∙10−7 1.49 0.0091 4.478 9.094∙10−8 1.3 0.0041 6.350

0.995 0.08 0.999 0.032 0.971 0.19

−0.062 0.001 −0.120

3.82

2.424∙10−10 0.973 0.011

0.987 0.127

−0.076

Module ID

Method

IL (A)

IS (A)

m

RS (Ω) RP (Ω)

#1

This work 4-param This work 5-param Reference [4] Reference [9] This work 4-param This work 5-param Reference [9] This work 4-param This work 5-param Reference [10] 4-param Reference [10] 5-param This work 4-param This work 5-param Reference [10] 5-param Reference [11]

8.09 8.125 8.092 8.106 9.11 9.307 9.135 2.3 2.373 2.3

7.902∙10−7 9.852∙10−7 9.602∙10−12 8.01∙10−9 2.226∙10−9 6.671∙10−7 7.67∙10−15 1.262∙10−8 3.947∙10−7 4.32∙10−8

1.47 1.495 0.868 1.142 1.11 1.492 0.708 1.219 1.486 1.3

0.0032 0.0027 0.0058 0.0044 0.0046 0.0027 0.0047 0.02 0.013 0.014

2.301

9.733∙10−9

1.2

0.02

#2

#3

#4

4.061

Fig. 2. Measured and estimated I-V characteristics of four commercial PV modules (see Table 1 for details): (a) #1, (b) #2, (c) #3 and (d) #4

Extracting the I-V Characteristics of the PV Modules

441

Fig. 3. The dispersion of the saturation current estimated by different procedures in case of four commercial PV modules (see Table 1 for details): (a) #1, (b) #2, (c) #3 and (d) #4. The values of the saturation current are marked on the graphs

Looking again at Table 2, it can be seen that for each PV module the estimated parameters experience a large dispersion, while the I-V characteristics are roughly overlapping (Fig. 2). The saturation current IS experienced the largest dispersion, covering several orders of magnitude. Figure 3 captures this behavior. The values of the diode ideality factor, the serial resistance and the shunt resistance have a smaller dispersion, but also significant. For example, in case of the PV module #2, m takes values between 0.708 and 1.492, while r2 takes values between 0.984 and 0.999. Taking into account the large dispersion of IS and the high sensibility of the I-V characteristic at m [8], the accurate reproduction of the measured characteristic shows that Eq. (1) has multiple solutions.

4 Conclusions In this study two procedures for extracting the I-V characteristics of a PV module at STC were discussed. The procedures, based on the Taylor’s series expansion of the current equation, are developed within the frame of one diode model. One procedure solves the four-parameter model while the other solves the five-parameter model. The results were assessed against the measured I-V characteristic provided by manufactures in the datasheets of four different PV modules. The estimated parameters were also compared with the ones previously reported for the same PV modules. Generally, the results show that while the models reproduce accurately the I-V characteristics, the parameters experience a large dispersion. This shows that the Shockley equation of a PV module may have multiple solutions.

442

A. Sabadus et al.

From a broader perspective, the results raise a question mark on the ability of the current procedures used for extracting the one-diode model parameters. Generally, the procedures were developed aiming to model the output power delivered by a PV module to different external loads. As the present paper shows (and also all the quoted papers), this target was reached at different levels of accuracy, depending on the procedure peculiarities. The extracted parameters are generally tabulated and presented under the guarantee that the corresponding Shockley equation accurately reproduces the I-V characteristic of the PV module at STC. However, the results reported here show that even if a procedure accurately reproduces the I-V characteristics, this does not guarantee the accurate identification of the parameters. Substantial efforts are still required to identify a procedure for solving the one-diode model that unequivocally guarantees high accuracy for the estimated parameters. Acknowledgments. We hereby acknowledge the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI - UEFISCDI, project number PN-III-P2-2,1-PED2016-0592.

References 1. Nelson, J.: The Physics of Solar Cells. Imperial College Press, London (2003) 2. Cotfas, D.T., Cotfas, P.A., Kaplanis, S.: Methods to determine the dc parameters of solar cells: a critical review. Renew. Sustain. Energy Rev. 28, 588–596 (2010) 3. De Soto, W., Klein, S.A., Beckman, W.A.: Improvement and validation of a model for photovoltaic array performance. Sol. Energy 80, 78–88 (2006) 4. Lo Brano, V., Orioli, A., Ciulla, G., Di Gangi, A.: An improved five-parameter model for photovoltaic module. Sol. Energy Mater. Sol. Cells 94, 1358–1370 (2010) 5. Lineykin, S., Averbukh, M., Kuperman, A.: An improved approach to extract the single-diode equivalent circuit parameters of a photovoltaic cell/panel. Renew. Sustain. Energy Rev. 30, 282–289 (2014) 6. Chellaswamy, C., Ramesh, R.: Parameter extraction of solar cell models based on adaptive differential evolution algorithm. Renew. Energy 97, 823–837 (2016) 7. Appelbaum, J., Peled, A.: Parameters extraction of solar cells - a comparative examination of three methods. Sol. Energy Mater. Sol. Cells 122, 164–173 (2014) 8. Paulescu, M., Paulescu, E., Gravila, P., Badescu, V.: Weather Modeling and Forecasting of PV Systems Operations. Springer, London (2013) 9. Mares, O., Paulescu, M., Badescu, V.: A simple but accurate procedure for solving the five-parameter model. Energy Convers. Manag. 105, 139–148 (2015) 10. Ishaque, K., Salam, Z., Taheri, H.: Simple, fast and accurate two-diode model for photovoltaic modules. Sol. Energy Mater. Sol. Cells 95, 586–594 (2011) 11. Lun, S., Du, C., Yang, G., Wang, S., Guo, T., Sang, J., Li, J.: An explicit approximate I-V characteristic model of a solar cell based on pade approximants. Sol. Energy 92, 147–159 (2013) 12. PTC - MathCAD - Engineering Calculations Software. http://www.ptc.com/products/ mathcad/. Accessed December 2016 13. GetDataGraph - Tool for digitizing graphs and images. http://getdata-graph-digitizer.com. Accessed Dec 2016

PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application Codruta Jaliu, Radu Saulescu, Daniela Ciobanu(&), and Florin Panaite Renewable Energy Systems and Recycling Research Center, Transilvania University of Brasov, Brasov, Romania [email protected]

Abstract. Part of the renewable energy systems (based on solar, wind or hydroelectric power) generates electricity in an intermittent way, depending on the weather conditions that are difficult to predict and control. These disadvantages can be overcome by integrating two or more renewable sources that can counterbalance each other. In this case, the hybrid systems based on combinations of renewable energies are preferred to meet the required energy. These systems are often used in remote areas, but their design and analysis are difficult to be performed due to the variability of the renewable sources. A possible option for the off-grid systems can be the combination/operation of PV modules (PV platform) with one or more wind turbines in parallel. The paper presents two algorithms for the design and operation of an off-grid hybrid system, whereby electric energy is obtained from the conversion of solar and wind energy, with a conventional generator as a backup source. The algorithm is exemplified in the case study: the energy supply of a photoreactor used for wastewater treatment. Further, conclusions and recommendations for the design of PV-wind hybrid systems are formulated based on the previous results. Keywords: Renewable system


Wind
PV
Off-grid
Algorithm

1 Introduction Nowadays, a great part of the world’s energy requirements, being in an exponential growth, is provided from conventional energy sources. However, these sources are in a rapid decrease, while increasing the greenhouse gas emissions, which led to the development of efficient, cost-effective and environmentally friendly solutions for producing the required energy, i.e. the use of renewable energy sources. Each type of renewable source (solar, wind, hydraulic, biomass, wave or geothermal) has its own advantages that make it usable for certain applications, depending on the onsite potential. In general, the use of solar energy and wind energy are preferred among all the available options of renewable energy generation, due to the availability and inexhaustible nature of these resources. However, they have the disadvantages of being unpredictable and dependent on the site weather conditions and climate change. Therefore, the energy production on renewable basis does not fully meet the consumer’s energy demand at every moment. The variable nature of these resources can be © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_32

444

C. Jaliu et al.

overcome by integrating the mentioned resources into an appropriate hybrid combination that will provide the necessary energy. This impediment represents a challenge in the design of hybrid solar-wind systems, which have to consider many parameters, such as network availability, electricity cost and onsite weather conditions. A solution consists in connecting the hybrid system to the electric grid (Fig. 1a), the consumers taking over the necessary energy from the grid, which also covers the sub-production periods of the hybrid system [1]. In case of overproduction, the amount of energy that exceeds the required energy is sold to the network owner at a predetermined price. The grid-connected renewable energy systems that are designed to meet the local energy requirements are mainly used in the urban areas. The absence of an electric grid in the isolated regions and the high connection costs due to the large distances and the hilly relief lead to the use of alternative solutions, i.e. the autonomous hybrid systems. Renewable energy systems that are not connected to the grid require a back-up source such as batteries and/or diesel generators to meet consumer requirements under all conditions (Fig. 1b). However, the batteries short lifecycle, the high maintenance costs and the environmental damaging content are constraints for their use in autonomous applications [2–4]. The current cost of these systems prevents widespread implementation and, therefore, research and development are mainly focused on cost reduction and efficiency increase through an optimal design regarding the component selection, and system sizing and operation. The optimal dimensioning of the autonomous hybrid systems requires a detailed analysis of the given location due to the influence of different site-dependent variables such as solar radiation, wind speed and air temperature and their implications on the system cost.

Fig. 1. The structure of a hybrid system: (a) grid-connected system and (b) autonomous system

PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application

445

The efficient design of a hybrid system involves the identification of the optimal combination between the two subsystems so as to ensure the energy demand required by the consumer, using the available area for mounting the photovoltaic modules and producing energy at the lowest price. Various techniques that allow selection and sizing of the hybrid system components based on optimization algorithms (genetic algorithm, particle swarm optimization, etc.) or some dimensioning tools such as Hybrid Optimization Model for Renewable Sources (HOMER) are presented in the literature [5]. The design of a hybrid system for an isolated location should take into account the fluctuating aspect of resources. Different algorithms for the selection and design of hybrid systems are presented in the literature, but they are limited to specific applications or locations [2, 3, 6–10]. Most of these applications use a diesel generator as a back-up source, which starts when the energy in the storage system reaches the minimum level. The paper presents two general algorithms for the design and operation of an autonomous PV-wind hybrid system, which consider covering the required energy based on two optimization criteria: the system cost and the implementation area.

2 The Design Algorithm of an Autonomous Hybrid System The proposed method and algorithm for the design of the hybrid system (consisting of photovoltaic modules PV and wind turbines WT) consider covering the required energy for an autonomous application based on energy consumption, the onsite meteorological data and the technical and economic evaluation of the obtained variant. The daily energy requirement can be calculated using rel. (1): Ereq ¼

n X

Pi ti

kWh/day,

ð1Þ

i¼1

where: ti represents the functioning time of consumer i during a day, expressed in hours, and Pi is the power of consumer i. By taking into account the meteorological data, the specifications of the main components of the hybrid system and the load variation mode for any location, the algorithm provides the possible configurations that can fully cover the energy needs for isolated consumers. The wind potential and the solar radiation data are used to select the components of the hybrid system. The optimization criteria considered in the proposed algorithm consist in providing the total energy requirement, in minimizing the system implementation area and the system cost, on the basis of which the system optimal configuration can be obtained. The design algorithm is presented in Fig. 2 as a logical diagram. The possible configurations of the PV-wind hybrid system are analyzed based on the input data in the design algorithm (variable wind and solar radiation data, ambient temperature, system components specifications and energy requirements), the area used by the hybrid system, and the system economic evaluation. A list of preferred photovoltaic modules and wind turbines is drawn up based on the meteorological data of the considered location, the energy requirements and

446

C. Jaliu et al.

Fig. 2. The design algorithm of the hybrid system

components costs. The type of batteries to be used is selected by taking into account their performances, and the costs they incur (taking also into account the costs of replacing them). The algorithm also sets the period for which the autonomy should be ensured with the battery bank. The algorithm starts by choosing the first PV module and the first WT from the list. It is then initialized by choosing a single PV module without using wind power. Subsequently, the algorithm enters in a repetitive loop that calculates the energy produced by the hybrid system, the surface occupied by the PV modules, and the cost of the produced energy. The loop implies increasing the number of photovoltaic modules by one unit until the available area is exceeded, or until the energy needs are covered. If the available area is exceeded, a wind turbine is added (if the WT number is lower than the maximum number previously set, which is imposed by the system cost), the number of PV modules is reset to zero, and the loop is resumed. If the maximum number of WT is reached, and all variants of PV modules and WT have been tested, then a diesel generator will be dimensioned and the final configuration will be saved. If not all types of PV modules or WT have been tested, then the next module and turbine will be selected and the algorithm will be resumed again. When the energy requirement is covered, the algorithm compares the cost of the energy with the maximum energy cost (initially, the maximum cost is given by the cost of the energy produced by the diesel generator), and if the cost is lower, it will be set as the maximum cost for the following configurations and the last generated configuration is saved.

PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application

447

In operation, in case of weather conditions that are unfavourable for energy production (seasonal variations of renewable sources), the sub-production of the hybrid system is covered by the energy storage system (battery bank), which also has the role of facilitating the system control and operation by the ability to smooth electricity fluctuations [3, 10]. 2.1

The Selection of Hybrid System Components

The selection of the components is made based on the wind potential and the solar radiation data. The output power of each selected component (PV and WT) is further established. The model describing the output power of the PV module is more difficult due to the non-linear dependence between illumination and temperature. A simplified model can be used to estimate the PV output power [3]: PPV ¼ gPV APV Gb ;

ð2Þ

where ηPV is the conversion efficiency of the PV module (%), APV is the module surface (m2) and Gb is the direct solar radiation (W/m2), which is assumed to be orthogonal to the PV module surface. At least 4 types of PV modules (mono and polycrystalline, of different powers) are selected, for each of them the following specifications being known: maximum power, conversion efficiency, price and dimensions. The data of the selected modules are ordered from smallest to largest power in order to be integrated into the hybrid system. The wind turbine produces energy when the wind speed v is in the range vCI  v  vCO, according to the power curve associated to each WT (Fig. 3). The WT power can be obtained either from the power curve or with relation (3) [3, 11–13]: 1 PWT ¼ cp qa Av3 g; 2

ð3Þ

where qa is the air density; Cp - the power coefficient; A - the rotor swept area; v - the mean wind speed (v > vCI), and η - the WT efficiency. Power Rated power

Wind speed

Fig. 3. The power curve of a wind turbine

448

C. Jaliu et al.

The relationship between WT power and the wind speed can be expressed in a simplified way, by considering a linear dependence between the two parameters in the variation range (vCI, vr) [2, 12, 14]:

PWT ðvÞ ¼

8 > ðvr vci Þ

:

PWT

vci  v  vr

;

ð4Þ

vr  v  vco

where vci, vco and vr are the cut-in, cut-off and rated speeds; PWT is the WT rated power. For most of the WT, vCI takes values in the range 2.5–3.5 m/s, while vco between 20 and 25 m/s. Another important aspect is the dependence of wind speed on the altitude. Thus, the wind velocity v at a height h can be estimated according to the Justus equation as a function of the measured wind speed v1 at an altitude h1 [2, 11, 13, 15]: v ¼ v1

 a h ; h1

ð5Þ

where the exponent a depends on the site topography and weather data [13]. A typical 1/7 value is used for surfaces with low roughness and well-exposed areas. The reference height is considered to be of 2 m. In the case of mounting the WT on the roof terrace, the height at which the turbine will be installed will be equal to the height of the building + the height of the supporting tower. A minimum number of 4 types of wind turbines (vertical and horizontal axes) are selected, the technical data being ordered from smallest to largest nominal power. The minimum requirements for evaluation are: the power curve or equivalent data (cut-in, cut-off, rated speeds, rated power and power values for different wind speeds, cost). The energy generated by the WT for the given location during a day is determined based on relations (3–5) or on the power curve and wind speeds frequency chart. If the obtained configuration of the hybrid system cannot meet the energy requirement and surface criteria, a new PV-WT combination is generated, which follows the same evaluation and optimization steps until the criteria are met. The design algorithm considers changing the wind turbine type and also modifying the number of identical components (PV and WT). The number of wind turbines, NWT, cannot be high due to the cost of this component. The number of photovoltaic modules, NPV, may be limited by the available surface for the hybrid system implementation Atotal. The energy generated by each component of the hybrid system (EPV, EWT) can be obtained in a simplified way as the product of the delivered power and the number of operating hours of each subsystem (tPV and tWT): EPV ¼ PPV NPV tPV ; E ¼ EPV þ EWT :

EWT ¼ PWT NWT tWT

where PPV and PWT are the power of a single PV and a single WT, respectively.

ð6Þ

PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application

449

In order to be able to choose the best combination of PV modules and WT, the cost of the produced energy will be used for comparison between the obtained configurations. A simplified version will be used to calculate this cost: Cost of produced energy ¼

System costs : Produced energy

ð7Þ

This calculation is made for the system entire life of about 25 years [13]. The system costs are: cost of components (PV modules, wind turbines, batteries, inverter), installation costs of PV modules (20% of modules cost [6, 16]) and of WT (40% of the turbines cost [6, 16]), cost of components replacement (batteries have a life of 5 years, so they will be replaced 4 times, and the inverter has a service life of 10–15 years, so it will be replaced once), maintenance costs (1% of PV modules cost/year and 3% of the cost of wind turbines/year). The algorithm takes into account the management of the energy balance (the energy generated by the hybrid system, E, is compared to the required energy, Ereq). Thus, one of the criteria for optimizing the hybrid system is to minimize the difference DE between the generated energy E and the needs Ereq:     DE ¼ E  Ereq  ¼ NPV PPV tPV þ NWT PWT tWT  Ereq :

ð8Þ

The energy surplus (the difference between generated energy and energy demand at time t), if any, is stored in batteries: Ebat ðtÞ ¼ E ðtÞ  Ereq :

ð9Þ

The batteries are connected in series to give the desired rated DC voltage (Vbus) and are connected in parallel to achieve the system desired storage capacity. Thus, the number of serially connected battery (NBAT, s) depends on the voltage of the DC port (Vbus) and of the nominal voltage of each individual battery (VBAT, nom) [7]: NBAT; s ¼

Vbus : VBAT; nom

ð10Þ

It is recommended to use 12 V batteries for energy requirements of less than 150 kWh/month, 24 V or 48 V for energy requirements between 150 kWh/month and 700 kWh/month and 48 V batteries for an energy demand of more than 700 kWh/month [8]. The number of parallel connected batteries (NBAT, p) that determines the storage system capacity is the design variable of the hybrid system. The total number of batteries (NBAT) can be determined by relation (11) [7]: NBAT ¼ NBAT; s NBAT; p :

ð11Þ

The storage capacity can be determined using relation (12) [2] by taking into account the number of storage days. According to Diafa [6], the optimum storage time is of two days:

450

C. Jaliu et al.

h Storage capacity ½Ah=day ¼ No: of storage days

Energy demand; Nec

Wh day

i

Battery nominal voltage ½V  ð12Þ

If the hybrid system does not cover the energy need and the batteries have reached the minimum energy, the algorithm provides the use of a diesel generator. For this purpose, it is selected a locally available generator with the closest power to the application energy requirements. The diesel generator operates with maximum efficiency when it is at 80–90% of rated power and becomes less efficient as the load drops down. The nominal power (PD, rated) of the diesel generator should be at least equal to the maximum load demand (Ppload) [7]: 

   PD; rated  Ppload :

ð13Þ

The operation of the hybrid system is based on the complementarity of the two renewable energy systems (wind and photovoltaic), generating the required energy (or a large part of it) during the days with low solar radiation and wind of medium intensity, but, also, in days with clear sky and no wind. The energy of the two systems is summed up and compared with the consumer’s energy demand. 2.2

Operation of the Autonomous Hybrid System

The autonomous hybrid system operates as follows (Fig. 4):

Fig. 4. The algorithm for the operation of the hybrid system

PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application

451

(a) if the hybrid system produces more energy than it is required to feed the consumer (in conditions of good potential), the surplus will be stored in the batteries until they are fully charged (when the batteries are fully charged, the rest of the energy is lost); (b) if the hybrid system produces the required amount of energy, the system will feed the consumer directly; (c) if the hybrid system cannot produce sufficient energy to supply the consumer, then the energy deficit may be covered from the batteries and/or a backup source (e.g. a conventional gasoline, diesel, wood or coal generator, Fig. 1b). The generator starts when the batteries charge status drops to the minimum level, Ebat min or the batteries have not stored all the required amount of energy.

3 Case Study The application of the previous algorithms is exemplified on a case study: the design of an autonomous PV-WT hybrid system that has to supply energy to a photoreactor used for the wastewater treatment at the Research and Development Institute of the Transilvania University of Brasov. The photoreactor has a nominal power of 0.9 kW and treats 20 l of water in 24 h. As presented in the previous algorithms, the following weather data were used to dimension the PV modules and to find out the number of wind turbines that can provide the required energy for the photoreactor: the direct solar radiation and the wind speed which were recorded at the meteo station located on the roof of L7 laboratory of the Renewable Energy System and Recycling Research Centre, at a height of 10 m. The average daily wind speeds recorded every minute for four months in 2016 (February, March, July and August) are presented in Fig. 5, while the average values for the direct incident solar radiation (recorded every minute) are illustrated in Fig. 6. The analysis of the measured weather data highlights that March is the best month in terms of wind potential, and the worst is August, while for solar radiation, the best month is August and the unfavourable - March (see Fig. 6). Therefore, the solar radiation data recorded in March 2016 (the most unfavourable month) will be used to size the PV system. The available amount of direct solar radiation received by the PV module is presented in Fig. 7. This radiation was determined for the annual equivalent day [13]. The values of solar radiation for the annual equivalent day were obtained from the average values of solar radiation corresponding to every 15 min interval. The amount of solar radiation captured by the solar module per m2 is given by rel. (14): X E¼ Gb ti ½kWh/m2 ; ð14Þ where Gb is the direct solar radiation received by a square meter of the PV module [W/m2]; ti is the time between the measurements (15 min) [h]. For the considered equivalent day it was obtained E = 2.897 kWh/m2.

452

C. Jaliu et al.

Fig. 5. Average values of daily wind speed for: (a) February, (b) March, (c) July and (d) August

The amount of solar energy captured by the solar module is obtained by using rel. (15): ER ¼ EAPV [kWh],

ð15Þ

PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application

453

Fig. 6. The monthly average values of recorded direct solar radiation

Fig. 7. Direct solar radiation received by PV modules in the equivalent day

where ER is the solar radiation captured by the PV module [kWh/m2]; APV is the PV module area [m2]. The next step in the hybrid system design consists in selecting 4 different types of PV modules that can be found on the market, with the technical data systematized in Table 1 [17]: Table 1. The technical data of 4 types of PV modules Type Power Efficiency Dimensions Cost

Si - Polycrystalline 260 W 16% 1640  992 mm 220.15 €

Si - Monocrystalline 265 W 16% 1640  992 mm 223.15 €

Si - Polycrystalline 275 W 17% 1640  990 mm 233.04 €

Si - Monocrystalline 295 W 18% 1640  992 mm 280.84 €

According to rel. (14), the obtained captured solar energy is ER = 4.713 [kWh]. In order to find out the energy produced by the PV module EPV, the minimum value of the efficiency is considered (16%, see Table 1): EPV ¼ ER gPV ¼ 0:754 [kWh]:

ð16Þ

454

C. Jaliu et al.

The relation used to determine the number of photovoltaic modules that ensure the energy demand of the photoreactor is the following: NPV ¼

Ereq ¼ 29:6 EPV

ð17Þ

where: NPV - represent the number of PV modules; Ereq - energy need (Ereq = 0.9 24 = 21.6 kWh/day); EPV - represent the energy produce by the PV module. The application needs 30 PV modules. According to the dimensions from Table 1, the area of the 30 PV modules is of 48.8 m2, and can be placed on the laboratory terrace (with an area of 450 m2) in two strings. The PV modules can be oriented towards sun by using a tracking system. The number of batteries required to ensure the energy demand for a 2-day period is further determined. According to rel. (12), the needed storage capacity for the photoreactor is 1800 Ah/day. Two types of batteries are further considered: (a) a battery of 24 V, 100 Ah and 2.6 kWh, with the price of 3200 € [18]. Eight batteries are needed in this case, the cost being of 25600 €; (b) a battery of 24 V, 180 Ah, with the price of 5000 € [19]. In this case, there are necessary 5 batteries and their total price is of 25000 €. In terms of price, the chosen variant is the battery of 24 V and 180 Ah. Besides the PV modules, the system has to contain an invertor and a regulator. The characteristics of the selected invertor are: power of 1000 W, voltage of 24 V [20]. For this application, one invertor has to be used, the price being of 5200 €. Thus, the cost of the entire PV system, consisting of PV modules, batteries, invertor is of 120110.5 €. In case of WT, the manufacturers evaluate their turbines in terms of providing a certain power at a certain wind speed; however, it is unlikely to use the actual energy output as an indicator in its assessment. For most of the people living in urban areas, the installation of WT on or near their buildings, at wind speeds of less than 5 m/s is probably not a realistic proposal. In this case, the electricity production will be disappointing and, besides, reimbursement periods will likely decrease in the distant future. Yet, a case study suggesting a wind turbine that produces about 7 kWh/day of electricity (about the third part of the total required energy) is taken into account: 0:9 kW
24 h ¼ 21:6 kWh : 3 ¼ 7:2 kWh=day

ð18Þ

The case study considers for the design of the WT the same month as for the solar system, March 2016. From the data provided by the low-capacity WT manufacturers, this type of turbines do not produce energy up to a wind speed of 2.5 m/s. Therefore, the wind speeds have to be arranged as indicated in Table 2 and Fig. 8 for the evaluation of the onsite wind potential (the data are recorded every minute). The average daily value is obtained by dividing the no. of recordings during a given period to the number of days included in that period of time. Thus, Fig. 9 illustrates the frequency chart for the average daily value.

PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application

455

Table 2. Wind speeds for March 2016 Wind 0_2.5 2.5_3.5 3.5_4.5 4.5_5.5 5.5_6.5 6.5_7.5 7.5_8.5 8.5_9.5 9.5_15 speeds m/s No of 469.80 115.56 59.71 30.62 20.46 14.70 9.59 11.74 4.77 recordings The average 15.15 3.72 1.92 0.98 0.66 0.47 0.30 0.37 0.15 value/day

Fig. 8. Wind speed frequency chart for March 2016 considering the total no. of recordings

Fig. 9. Wind speed frequency chart for March 2016 considering the average daily values

The selection of WT is made according to the power curve and the onsite values of wind speed with high frequency; thus, the wind speed values below 2.5 m/s are eliminated in the analysis and the average values are considered for the rest of the intervals (e.g. for the interval v = 2.5–3.5, the average value is v = 3 m/s, except for the last interval for which the average speed is v = 10 m/s); therefore, for this case study, wind turbines that can produce approx. 7 kWh/day starting at a wind speed of 3 m/s will be selected.

456

C. Jaliu et al.

Fig. 10. Theoretical power curve for a WT [21]

According to the theoretical power curve (Fig. 10) and the wind speed frequency chart (Fig. 9), the wind speed of 3 m/s is recorded for 4 h during a day, for which the turbine produces 20% of the rated power, while at the wind speed of 4 m/s for 2 h the turbine can produce 30% of its installed capacity; thus, a 6 kW wind turbine is needed to get an energy of approx. 7 kWh/day. According to Fig. 10, for the wind speed of 3 m/s (Fig. 10) the turbine power is 1.2 kW (20% of 6 kW), generating in 4 h an energy of 4.8 kWh/day, while for 4 m/s the WT power is 1.8 kW (30% of the rated power) and the energy generated in the 2 h is 3.6 kWh/day. By summing up the energy generated during the 6 h of the day with wind speeds over 3 m/s it is obtained a total energy of 8.4 kWh/day, which exceeds the required energy. Several wind turbines producing energy at lower wind speeds are selected for the considered application (Table 3): Table 3. Examples of WT of low rated power WT model/rated power WT type Wind speed [m/s] 3 4 5 Power [kW] Nova-wind 6/6 kW HAWT 0 0.27 0.74 Ampair 6000/6 kW HAWT 0.05 0.3 0.5 Proven 6/6 kW HAWT 0.2 0.5 1 Aeolos/5 kW VAWT 0.2 0.4 0.6

The comparative analysis of the WT technical data presented in Table 3 highlights the optimal turbine, Proven 6, whose power curve is presented in Fig. 10. The daily energy generated by the Proven 6 WT (Table 4) is obtained based on the values from Fig. 11.

PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application

457

Power Output [W]

Wind speed [m/s]

Fig. 11. The power curve of the Proven 6 WT [22]

Table 4. The energy produced by Proven 6 WT for the wind speeds frequency chart from Fig. 9 Average wind 3 4 5 6 speed [m/s] 3.73 1.93 0.98 0.66 No. of hours in which the speed was recorded Power [kW] 0.2 0.5 1 1.5 Energy [kWh] 0.745 0.02 0.987 0.990 Total energy produced by a turbine during a day [kWh]

7

8

9

10

0.47

0.30

0.38

0.15

2.1 0.995

3 0.928

4 1.515 6.935

5 0.769

In order to assure the entire energy demand for the photoreactor with wind turbines, 4 units are needed: NWT ¼

Nec ¼ 3:11 EWT

ð19Þ

According to the proposed algorithm, the cost of the hybrid system for this application is 136713 €.

4 Conclusions A general algorithm for a PV-wind hybrid system is developed in this paper by taking into account the available renewable energy potential, the area needed for mounting the photovoltaic modules and the cost of the produced energy. This algorithm is exemplified on a case study in which it is necessary to provide the electrical energy for a 0.9 kW photoreactor, which will be located at the Research and Development Institute of the Transilvania University of Braşov and works continuously for 24 h/day.

458

C. Jaliu et al.

The sizing of the photovoltaic system was made for the weather data recorded during the most unfavourable month of the year in terms of solar radiation. Four variants of PV modules of different powers were selected; the number of PV modules for the considered application is established at 30, the area for mounting them being of approx. 50 m2. To ensure the electricity requirement for 2 days with low solar and wind potential, the system must contain one inverter and 5 batteries. The cost of the entire solar system is of 120110.5 € and its lifetime is 25 years. The onsite wind potential for the same month, March 2016, was considered in sizing the wind turbines. March is the month with the best wind potential in the year 2016. The wind speed is ordered in a frequency chart and average values are calculated for each interval. Four wind turbines are selected based on the cut-in speed and the onsite wind potential. The WT for the considered application is found out by using its power curve and the average values of wind speed in each interval of the frequency chart. Thus, the energy generated by the WT can be calculated and compared to the energy demand. The WT that generates at least the required energy is chosen among the four different types. Then, the cost of the wind turbines and of the hybrid system are calculated. In the case study, four WT are required to get the energy demand (1/3 of the photoreactor need of energy), the cost being of 136713 €. The cost of the energy produced by the PV modules in this case is of 0.609 €/kWh, and 0.693 €/kWh for the wind system. Thus, the PV- wind hybrid system for the considered application should be mainly based on the photovoltaic conversion due to the lower cost of the produced energy, the onsite weather potential and the available implementation area. Acknowledgments. This paper was realized within the Partnerships Programme in priority domains-PN-II, which runs with the financial support of MEN-UEFISCDI, Project no. 217/2014.

References 1. Hina Fathima, A., Palanisamy, K.: Optimization in microgrids with hybrid energy systems a review. Renew. Sustain. Energy Rev. 45, 431–446 (2015) 2. Kaabeche, A., Ibtiouen, R.: Techno-economic optimization of hybrid photovoltaic/ wind/diesel/battery generation in a stand-alone power system. Sol. Energy 103, 171–182 (2014) 3. Smaoui, M., Abdelkafi, A., Krichen, L.: Optimal sizing of stand-alone photovoltaic/wind/ hydrogen hybrid system supplying a desalination unit. Sol. Energy 120, 263–276 (2015) 4. Zhao, B., Zhang, X., Chen, J., Wang, C.: Operation optimization of stand-alone microgrids considering lifetime characteristics of battery energy storage system. IEEE Trans. Sustain. Energy 4(4), 934–943 (2013) 5. Erdinc, O., Uzunoglu, M.: Optimum design of hybrid renewable energy systems: overview of different approaches. Renew. Sustain. Energy Rev. 16(3), 1412–1425 (2012) 6. Diafa, S., Belhamelb, M., Haddadic, M., Louchea, A.: Technical and economic assessment of hybrid photovoltaic/wind system with battery storage in Corsica Island. Energy Policy 36, 743–754 (2008)

PV-Wind Hybrid System for the Energy Supply of an Off-Grid Application

459

7. Dhanalakshmi, R., Palaniswami, S.: ANFIS based neuro-fuzzy controller in LFC of wind-micro hydro-diesel hybrid power system. Int. J. Comput. Appl. (0975 - 8887), 42(6), 28–35 (2012) 8. Hongxing, Y., Wei, Z., Chengzhi, L.: Optimal design and techno-economic analysis of a hybrid solar-wind power generation system. Appl. Energy 86, 163–169 (2009) 9. Ma, T., Yang, H., Peng, J.: Optimal design of an autonomous solar-wind-pumped storage power supply system. Appl. Energy 160, 728–736 (2015) 10. Yang, H., Lu, L., Zhou, W.: A novel optimization sizing model for hybrid solar-wind power generation system. Sol. Energy 81, 76–84 (2007) 11. Manwell, J.F., McGowan, J.G., Rogers, A.L.: Wind Energy Explained. Wiley, Hoboken (2005) 12. Poggi, P., Notton, G., Cristofari, C., Muselli, M.: Wind hybrid electrical supply system: Behaviour simulation and sizing optimization. Wind Energy 4(2), 43–59 (2001) 13. Visa, I., Jaliu, C., Duta, A., Neagoe, M., et al.: The Role of Mechanisms in Renewable Energy Systems. Transilvania University Publishing House, Brasov (2015) 14. Mesquita, F.G.G.: Design optimization of stand-alone hybrid energy systems, dissertation (2010) 15. Elistratov, V.V.: Hybrid system of renewable energy sources with hydro accumulation. In: Proceedings of World Wind Energy Association, online (2008) 16. Arulmurugan, R., Suthanthiravanitha, N.: Investment cost evaluation and sizing approach of isolated residential PV scheme. IJSSST 14(3), 42–53 (2006) 17. https://www.victronenergy.ro/upload/documents/Datasheet-Lithium-ion-and-Lynx-Ion-EN. pdf. Accessed 29 May 18. http://www.claytonpower.com/products/lithium-ion-batteries/. Accessed 15 June 19. http://shop.pkys.com/Victron-Lithium-Ion-Battery-24V180Ah_p_2844.html. Accessed 15 June 20. http://energie-eco.eu/invertoare-off-grid/invertor-1000W-unda-pura.html. Accessed 30 May 21. www.greenspec.co.uk/building-design/small-wind-turbines. Accessed 26 May 22. https://cdn.hepn.com/Content/files/renewables/meromWind_proven.pdf. Accessed 15 May

Large Conversion Ratio DC-DC Hybrid Converters for Renewable Energy Applications Nicolae Muntean(&), Octavian Cornea, and Dan Hulea Department of Electrical Engineering, University POLITEHNICA Timişoara, Timisoara, Romania [email protected]

Abstract. Renewable energy conversion systems require high performance DC-DC power converters, for power flow control between the primary energy sources, storage elements, different DC buses and loads. For high conversion voltage ratio, new hybrid structures can be used for energy conversion in single or bidirectional power flow, obtained by introducing commutated inductive and capacitive cells in the buck and boost DC-DC converters. In these new configurations, the voltage conversion ratio is larger, at the same duty cycle, compared with the classical converters. In the same time, some advantages are obtained regarding the active components voltage and current stresses. The paper presents a synthesis of the author contributions in two DC-DC hybrid converters structure study and implementation. PV and wind energy conversion systems and DC microgrids, are the applications where these converters were implemented in order to prove the proposed structures viability. Circuit diagrams, analytical descriptions, and experimental results are presented, regarding the analyzed hybrid converters and their applications. Keywords: DC-DC converters Energy conversion and storage




Hybrid converters




Renewable energy




1 Introduction Power electronics technology evolution, together with intelligent control strategies, makes renewable energy systems more efficient and controllable in order to achieve a better and flexible integration with the input sources, loads and grid [1–6]. In many renewable energy conversion systems, DC-DC converters, in conventional or dedicated structures, play an important role. Voltage conversion ratio, high efficiency, quality of the control algorithms etc. are important goals in this research field. A large number of converter topologies with higher voltage conversion ratios obtained from classical DC-DC converters (without power transformers) by adding additional components, have been presented in the literature [7–13]. New topologies with increased voltage conversion ratio can be obtained by inserting switching- capacitor or switching- inductor cells into the simple step-up and step-down converters (Figs. 1 and 2) [14–18]. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_33

Large Conversion Ratio DC-DC Hybrid Converters L1

(a)

D1

(b)

(c) D1

D2

C1

461

D2

L2

L1

D12 C2

D1

L2

D2

Fig. 1. Step-down switching cells: (a) Down 1, (b) Down 2, (c) Down 3

C1

D1

(a)

(b) C1

C2

(c) D1

D2

L1

D2

D12 D1

D2

L2

C2

Fig. 2. Step-up switching cells: (a) Up 1, (b) Up 2, (c) Up 3

The presented switching cells can be inserted in the structure of the classical Buck, Boost, Buck-Boost, Củk, Sepic and Zeta converters according to Table 1. In the following sections, two DC-DC hybrid converters structures are described analytically. The converters are integrated in energy conversion and storage systems related to renewable energy applications. Selected experimentally results will give details how the converters work in laboratory and in real exploitation conditions.

Table 1. Hybrid converters obtained with the L/C insertion in classical structures C/L circuit converter Buck Boost Buck-Boost Cuk Sepic Zeta

Down 1 Down 2 Down 3 Up 1 Up 2 Up 3 • • • • • • • • • • • • • • • • •

462

N. Muntean et al.

2 Hybrid Buck Switched-Inductor DC-DC Converter (HBDC-L) 2.1

Analytical Description

The circuit diagram of the HBDC-L converter and the corresponding topologies during ton and toff (ton and toff are the switching time intervals of the transistor T commutation period Ts) are presented in Fig. 3. L1

T

A

(a) D1

Vin

D2

Cout

Rout

Cout

Rout

+ Vout -

Cout

Rout

+ Vout -

B L2 L1

T

iout=iL1=iL2

(b)

iL1 D1

D2

Vin

iL2 L2 L1

T

(c) Vin

iout=iL1+iL2

D1

D2

iL1

iL2

L2

Fig. 3. (a) HBDC-L circuit diagram, (b) ton state, (c) toff state

For given values of the input and output voltages (Vin and Vout), the duty cycle is determined using the following expression [19]: D¼

ton 2
Vout ¼ Ts Vin þ Vout

ð2:1Þ

Using Eq. (2.1) the expression of the voltage conversion ratio is: Vout D ¼ 2D Vin

ð2:2Þ

Large Conversion Ratio DC-DC Hybrid Converters

463

It can be seen that the voltage conversion ratio is (2-D) times higher in comparison with the classical buck converter. This means that for the same voltage ratio, the duty cycle is higher and the converter can be better controlled. An extensive converter analytical description and the comparison with the classical Buck structure are presented in [19]. 2.2

HBDC-L Application in a 5 kW, Off-Grid, Wind Turbine System

The converter was tested in laboratory and real condition. The system structure, in both cases, is presented in Fig. 4. The input electric power is provided by a PMSG driven directly by the wind turbine. Using a six diode bridge rectifier (DB), the 3-phased AC power is rectified. An overvoltage relay (KA1) supervises the rectified voltage, after the DB, in order not to exceed the upper limit of 380 [V]. HBDC-L works in current control mode, with the current reference given by a Fuzzy-Logic controller, in order to achieve the maximum power point (MPP) of the wind turbine, depending on the wind and turbine speed [20]. The converter charge a Maxwell supercapacitor (SC), used as a bumper with the ability to handle high instantaneous power values. The SC energy is transferred through a Xantrex Solar Charge Controller (CHG) used to charge the battery bank (BAT). The experimental setup also contains a Xantrex Inverter/Charger-XW6048 (INV) which is used to supply the loads. The INV can interface with the grid, supply the loads and charge the battery bank from the grid, if a grid connection is available. In off-grid situation the inverter is used to supply the loads from the stored energy in the battery bank. If the input voltage is in the range of 120–380 [V], the HBDC-L converter starts operating. If the voltage across the SC (or at the input of the CHG) rises above the upper limit 100 [V], measured with KA3 overvoltage relay, a 2 [Ω] resistor is inserted in the circuit in order to reduce the voltage (to a 60 [V] limit).

Fig. 4. The wind system configuration

464

N. Muntean et al.

KA2 overvoltage relay also measures the voltage across the SC. If the upper limit of 120 [V] across the SC is reached, KA2 commands the contactors K1 and K2 to disconnect for protection reasons. The specifications of the HBDC-L prototype (Fig. 5) are presented in Table 2:

Fig. 5. HBDC-L prototype

Table 2. HBDC-L specifications Parameter Value Rated power 5 [kW] L1, L2 (switching cell inductors) 200 [µH] Input voltage range (150–400) [V] Output voltage range (0–120) [V] PWM frequency 10 [kHz]

In the laboratory setup a hardware-in-the loop (HIL) emulator for the wind turbine is used (Fig. 6) [21]. The HIL uses an induction motor (IM) with a gearbox (GB) fed by a DTC ABB inverter (the physical part), controlled by a Control Desk dSpace platform (who implements the wind turbine equation). The IM produces at the (real) PMSG shaft the same torque as the real turbine produces, as a function of the wind speed, in steady state and dynamic regimes. The same energy conversion and storage control system is used in a experimental platform, in real exploitation conditions. The wind turbine (Fig. 7) parameters, emulated in the laboratory setup, are presented in Table 3.

Large Conversion Ratio DC-DC Hybrid Converters

PMSG IM

GB

Fig. 6. The laboratory setup with wind turbine HIL

Fig. 7. The experimental platform

465

466

N. Muntean et al. Table 3. Wind turbine specifications Parameter Rated power Rated wind speed Maximum speed Turbine inertia Blade swept area Radius of the turbine blade Maximum coefficient of power conversion

Value 5 [kW] 11 [m/s] 126 [rpm] 140 [kg
m2] 19.6 [m2] 2.5 [m] 0.42

Fig. 8. Experimentally results: (a) wind speed, (b) HBDC-L input power, (c) the SC voltage

Large Conversion Ratio DC-DC Hybrid Converters

2.3

467

Experimental Results

The wind energy conversion and storage control system was first tested in the laboratory. After the control was validated in this way, the solutions were transferred in the platform. Some experimental results, in real exploitation conditions, are presented in Fig. 8.

3 Hybrid Bidirectional Switched-Capacitor DC-DC Converter (HBDC-C) 3.1

Analytical Description

The hybrid converter, presented in Fig. 9, consists of a simple boost converter followed by a C switching cell which allows a bi-directional current flow by adding T1 and T2 switches in parallel to D1 and D2. The operating depends on the action of the C switching cell. The switching cell capacitors are charged in parallel and discharged in series for the boost mode, and they are discharged in parallel and charged in series for the buck mode [22]. IL1

L1

(a) VS SC

VL1 Ci

T1

IL2

T2 D2 D1

VL2 VC

C1

L2

C2

VC

CO

VO

CO

VO

CO

VO

D3 T3 IL1

L1

L2

IL2

(b) SC

Ci C1

L1

C2

IL1

L2

IL2

(c) SC

Ci

C1

C2

Fig. 9. (a) HBDC-C circuit diagram, (b) ton state (step down mode), (c) toff state (step down mode)

468

N. Muntean et al.

As it can be seen from the two states (ton and toff) only one driving signal is needed for the three transistors. The PWM signal drives the T1 transistor directly, and it is inverted to drive T2 and T3. From the duty cycle expression: D¼

V0  Vs V0 þ Vs

ð3:1Þ

Using (3.1), the voltage conversion ratio can be written as: Vo 1 þ D ¼ Vs 1  D

ð3:2Þ

It can be seen that the voltage conversion ratio is (1 + D) times higher in comparison with the classical converter. This means that for the same voltage ratio, the duty cycle is higher and the converter can be better controlled. An extensive converter analytical description and the comparison with the classical structure are presented in [22, 23]. 3.2

HBDC-C Application in a DC Microgrid Structure

HBDC-C is integrated in a DC microgrid, as an interface between the DC bus and a supercapacitor (SC) used for a fast control of the DC voltage, where are connected the input sources (PV panels and wind/hydro generators) and the AC grid connection (Fig. 10) [24]:

PV panels

Wind/Hydro turbine AC

DC DC

DC

AC Grid

AC DC

DC Bus BidirecƟonal DC converter DC Supercapacitor

Fig. 10. HBDC-C used as bidirectional power flow control between the DC bus and the SC

Large Conversion Ratio DC-DC Hybrid Converters

469

The specifications of the HBDC-C prototype (Fig. 11) are presented in Table 4.

Fig. 11. HBDC-C prototype

Table 4. Nominal parameters of the HBDC-C prototype Parameter Rated power (step-down mode) Rated power (step-up mode) C1, C2 (switching cell capacitors) L1 inductor L2 inductor PWM frequency Supercapacitor

3.3

Value 2 [kW] 6 [kW] 1410 [lF] 200 [lH] 2500 [lH] 20 [kHz] 63 [F]

Experimental Results

The prototype was used in a microgrid laboratory [25]. The converter uses a novel nonlinear droop control strategy, as a function of the DC bus voltage, in order to charge/discharge the SC, Fig. 12 [24]. A valley current mode controller can also be used [26].

470

N. Muntean et al.

Fig. 12. Nonlinear droop current control characteristic

Experimental results for charging and discharging the SC are presented in Fig. 13.

Fig. 13. Discharge (IL2 > 0)/charge (IL2 < 0) variation: IL2 current of ±5 A, 40% duty cycle

4 Conclusions A synthetic presentation of two hybrid DC-DC converters and their applications was the subject of this paper. The hybrid converters, with no insulation between their input and output (without power transformer), can obtain a higher voltage conversion ratio which is necessary in many applications, including renewable energy conversion and storage systems. In both presented cases, the converters work with supercapacitor energy storage. The voltage across the supercapacitor depends on the stored energy, and varies in an extended range. From this reason, a high voltage conversion ratio is needed. The

Large Conversion Ratio DC-DC Hybrid Converters

471

presented converters use current mode control, proper for the applications. In order to be capable to work in decentralized modes, in complex systems (without a master application control), nonlinear droop and valley current controls were proposed. The future work will be oriented in increasing the efficiency of the studied hybrid converters, using high performance switching devices, simultaneous with the increasing of the commutation frequency, reducing the sizes and the weights.

References 1. Bose, B.: Global energy scenario and impact of power electronics in 21st century. IEEE Trans. Ind. Electron. 60(7), 2638–2651 (2013) 2. Blaabjerg, F., Iov, F., Terekes, T., Teodorescu, R., Ma, K.: Power electronics - key technology for renewable energy systems. In: IEEE Power Electronics, Drive Systems and Technologies Conference (PEDSTC 2011), pp. 445–466, Tehran, Iran (2011) 3. Blaabjerg, F., Chen, Z., Kjaer, S.B.: Power electronics as efficient interface in dispersed power generation systems. IEEE Trans. Ind. Electron. 19(5), 1184–1194 (2004) 4. Blaabjerg, F., Liserre, M., Ma, K.: Power electronics converters for wind turbine systems. IEEE Trans. Ind. Appl. 48(2), 708–719 (2012) 5. Blaabjerg, F., Ma, K.: Future on power electronics for wind turbine systems. IEEE J. Emerg. Sel. Top. Power Electron. 1(3), 139–152 (2013) 6. Wang, H., Liserre, M., Blaabjerg, F.: Toward reliable power electronics: challenges, design tools, and opportunities. IEEE Ind. Electron. Mag. 7(2), 17–26 (2013) 7. Middlebrook, R.D.: Transformerless DC-to-DC converters with large conversion ratios. IEEE Trans. Power Electron. 3(4), 484–488 (1988) 8. Maksimovic, D., Ćuk, S.: Switching converters with wide DC conversion range. IEEE Trans. Power Electron. 6(1), 151–157 (1991) 9. Yuanmao, Y., Cheng, K.W.E.: A family of single-stage switched capacitor-inductor PWM converters. IEEE Trans. Power Electron. 28(11), 5196–5205 (2013) 10. Wei, Q., Dong, C., Cintron-Rivera, J.G., Gebben, M., Wey, D., Peng, F.: A switched-capacitor DC-DC converter with high voltage gain and reduced component rating and count. IEEE Trans. Ind. Appl. 48(4), 1397–1406 (2012) 11. Hsieh, Y.-P., Chen, J.-F., Liang, T.-J., Yang, L.-S.: Novel high step-up DC-DC converter with coupled-inductor and switched-capacitor techniques. IEEE Trans. Ind. Electron. 59(2), 998–1007 (2012) 12. Cortez, D.F., Waltrich, G., Fraigneaud, J., Miranda, H., Barbi, I.: DC-DC converter for dual voltage automotive systems based on bidirectional hybrid switched-capacitor architectures. IEEE Trans. Ind. Electron. 62(5), 3296–3304 (2015) 13. Wu, B., Li, S., Smedley, K.M., Singer, S.: Analysis of highpower switched capacitor converter regulation based on charge-balance transient-calculation method. IEEE Trans. Power Electron. 31(5), 3482–3494 (2016) 14. Axelrod, B., Berkovich, Y., Ioinovici, A.: Switched-capacitor switched-inductor structures for getting hybrid step-down Cuk/Zeta/Sepic converters. In: IEEE ISCAS, pp. 5063–5066, Kos, Greece (2006) 15. Axelrod, B., Berkovich, Y., Ioinovici, A.: Hybrid switched-capacitor Ćuk/Zeta/Sepic converters in step-up mode. In: Proceedings of the IEEE International Symposium on Circuits and Systems (ISCAS), pp. 1310–1313, Kobe, Japan (2005)

472

N. Muntean et al.

16. Axelrod, B., Berkovich, Y., Ioinovici, A.: Switched coupled-inductor cell for DC-DC converters with very large conversion ratio. In: IEEE IECON, pp. 2366–2371, Paris, France (2006) 17. Axelrod, B., Berkovich, Y., Tapuchi, S., Ioinovici, A.: Steep conversion ratio Ćuk, Zeta and Sepic converters based on a switched coupled-inductor cell. In: IEEE PESC, pp. 3009–3014, Rhodes, Greece (2008) 18. Axelrod, B., Berkovich, Y., Ioinovici, A.: Switched-capacitor/switched-inductor structures for getting transformerless hybrid DC-DC PWM converters. IEEE Trans. Circuits Syst. 55(2), 687–696 (2008) 19. Cornea, O., Pelan, O., Muntean, N.: Comparative study of buck an hybrid buck switched inductor DC-DC converter. In: Proceedings of the 13th Conference on Optimization of Electrical and Electronic Equipment (OPTIM), pp. 853–858 (2012) 20. Petrila, D., Blaabjerg, F., Muntean, N., Lascu, C.: Fuzzy logic based MPPT controller for a small wind turbine system. In: Proceedings of the 13th Conference on Optimization of Electrical and Electronic Equipment (OPTIM), pp. 993–998 (2012) 21. Muntean, N., Tutelea, L., Petrila, D., Pelan, O.: Hardware in the loop wind turbine emulator. In: Proceedings of the International Aegean Conference on Electrical Machines and Power Electronics and Electromotion Joint Conference, pp. 59–64 (2011) 22. Cornea, O., Andreescu, G.D., Muntean, N., Hulea, D.: Bidirectional power flow control in a DC microgrid through a switched-capacitor cell hybrid DC-DC converter. IEEE Trans. Ind. Electron. 64(4), 3012–3022 (2017) 23. Cornea, O., Guran, E., Muntean, N., Hulea, D.: Bi-directional hybrid DC-DC converter with large conversion ratio for microgrid DC busses interface. In: International Symposium on Power Electronics, Electrical Drives, Automation and Motion, (SPEEDAM), pp. 688–693 (2014) 24. Hulea, D., Cornea, O., Muntean, N.: Nonlinear droop charging control of a supercapacitor with a bi-directional hybrid DC-DC converter. In: Proceedings of the 16th International Conference on Environment and Electrical Engineering (EEEIC), pp. 1–6 (2016) 25. Pătraşcu, C., Muntean, N., Cornea, O., Hedeş, A.: Microgrid laboratory for educational and research purposes. In: Proceedings of the 16th International Conference on Environment and Electrical Engineering (EEEIC), pp. 1–6 (2016) 26. Hulea, D., Muntean, N., Cornea, O.: Valley current mode control of a bi-directional hybrid DC-DC converter. In: Proceedings of the International Aegean Conference on Electrical Machines and Power Electronics and Electromotion Joint Conference, pp. 1–6 (2015)

Life Cycle Assessment of the Romanian Electricity Mix: Impacts, Trends and Challenges George Barjoveanu, Carmen Teodosiu(&), and Daniela Cailean (Gavrilescu) Department of Environmental Engineering and Management, Gheorghe Asachi Technical University of Iasi, Iasi, Romania [email protected]

Abstract. Considering the recent pressures in the energy sector at global level, in close relation with the conventional fuel availability, climate change, public interest and the overall debate for more sustainable energy sources, there is an acute need for instruments, capable to identify and measure in a coherent framework how various changes in the energetic systems lead to progress/ challenges, in terms of environmental impacts and sustainability. In this context, Life Cycle Assessment (LCA) is a standardized methodology, capable of analysing complex systems, as well as to identify and quantify various environmental impacts of products for their entire life cycles. The main objectives of this study are to perform a life cycle evaluation of the Romanian energy sector for electricity production, in order to identify, quantify and update the associated environmental impacts and to investigate the sustainability of future scenarios. The LCA is focused onto 1 kWh of electricity produced in Romania, considering the indigenous resources mix: coal and gas-fired power plants, hydropower, wind turbines, nuclear power, solar panels and biomass, as well as imports and exports. The assessment is based on the ReCiPe impact assessment methodology, which enables the use of 18 environmental impact categories. By applying the LCA methodology, the Romanian energy mix environmental impact profiles can be compared for 4 years: 1990 (reference year), 1997, 2010 and 2015. Furthermore, the 2030 and 2050 scenarios were analysed. The results show how the changes in the electricity production mix have positive changes in the environmental profile. Keywords: Life Cycle Assessment Environmental impacts




Electricity mix




Carbon footprint




1 Introduction The energy sector of a country is considered to play a strategic role in the national development, being closely linked to an improved economic status, a better life quality and the impact on natural resources. According to the European Union, an advanced economy cannot be competitive without a reliable and sustainable energy sector. As a response to economic and societal challenges, in the entire European Union, in 2014, © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_34

474

G. Barjoveanu et al.

the total net electricity generation was estimated at 3.03 million GWh. There are several main aspects related to the energy sector that the European policies have struggled to overcome: price volatility of the carbon dependent markets (oil and gas); difficulties in energy transportation (imports/exports); issues related to the nuclear energy; the environmental impact, directed in particular to greenhouse gas (GHG) emissions from fossil fuel combustion [1]; the ageing process of the conventional power plant infrastructure [2]. In the last years, the energy sector received an increased interest from the sustainability point of view. Researchers have focused on analyzing the current situations in various countries and on the development of decision support systems that would allow the formulation of policies and strategies for future developments. The life cycle assessment studies of electricity generation for various countries include: Japan [3], Singapore [4], Belgium and Spain [5], Mexico [6], Nigeria [7], the United Kingdom [8]. More recently, studies have been updated and extended by considering developments and targets in the energy sector and the reduction of greenhouse gas emissions. For example, Santoyo- Castelazzo and Azapagic [9], have suggested a five step decision support framework to analyze the energy profile in Mexico, by applying the life cycle methodology on a “cradle to grave” approach. Their assessment is based on 10 environmental impact indicators, 4 social indicators and 3 economic indicators to evaluate in an unitary manner the existing situation as well as future scenarios based on Mexico energy drivers and climate change targets for 2050. Stamford and Azapagic [10], have performed a study that give information on future energy scenarios in United Kingdom, for a timeframe as long as 2070. The researchers started from the current situation of the British energy mix, based mostly on fossil fuels (87%) and build up scenarios on the energy mix decarbonisation. The 36 indicators values, from environmental, social and economic categories, provided information on challenges and implications of the energy policies. The main conclusion of the study is that the degree of decarbonisation of the energy mix strongly influences the outcomes and compromises should be addressed, because none of the analyzed scenarios can be considered as a “best case” scenario. Developing countries such as Mauritius have also been recently analyzed from the point of view of energy sector sustainability [11]. The main objective of the study was to inform the stakeholders in the energy sector on the current impacts and the major environmental impacts associated to the rapid development in the area. The Mauritius current energy mix, based extensively on coal and natural oil (77%) has a significant environmental impact for 10 indicators, while the renewables: bagasse and wind power contribute up to 12% to the environmental impacts. In Mauritius’ case, the main recommendation is that more emphasis should be put on the renewable share, mainly wind farms and solar energy harvesting, while investing in increasing the fossil power plants performances. Recently, the rapid development of United Arab Emirates (UAE) in terms of electricity production was studied by Treyer and Bauer [12]. The authors assessed the energy sector environmental footprint, based on LCA methodology. Six environmental indicators were used to characterize the actual status of the UAE energy sector and future scenarios. Until 2009, the energy was produced entirely from natural gas and oil, with significant consequences in terms of GHG emissions. The diversification of

Life Cycle Assessment of the Romanian Electricity Mix

475

energy mix such as: nuclear, renewables and the improvements of existing natural gas plants technologies will diminish the environmental footprint of the energy sector, by comparison with the reference scenario. In Turkey, a life cycle analysis of the national energy sector was realized by Atilgan and Azapagic [13], mainly focused on renewable energy sources (RES), which account for approximately 27% of the country’s energy mix. In 2010, the Turkish RES was based extensively on hydropower plants (93%), while the rest includes wind farms, geothermal and other renewables and waste. The evaluation comprises a set of 11 environmental indicators applied for energy production systems such as: large and small reservoirs, run-of-river, onshore wind and geothermal power. An increased percentage of RES in the energy mix should be approached. Nanaki et al. [14], have investigated the environmental impact of the energy produced from coal in Greece. The contribution of lignite and fuel oil to Greek energy mix was 64% in 2009. By using the Eco-indicator ‘99 and ‘95 methods, the environmental impact of lignite and fuel in the energy mix and also future scenarios that envisage an increased input from RES were assessed. The occurrence in literature of a combination of Life Cycle and Data Envelopment Analysis (LC+DEA) used in the assessment of energy systems, was investigated by Martin-Gamboa et al. [15]. The LC+DEA allows the modelling of energy scenarios by integrating life-cycle indicators and ranking energy scenarios, based on sustainability criteria. Coupling multi-criteria decision analysis (MDCA) with LCA was proposed by Santos et al. [16], in order to evaluate the Brazilian power sector. The energy mix in Brazil is currently based on RES with 77% hydro, 7% biomass and 1% wind power. Fifteen criteria from economic, social and environmental categories were selected to investigate 5 suggested scenarios. The most important findings are the following: the RES share is expected to increase in the energy mix and the wind power, currently under-exploited, and it should be considered as a feasible option. Another methodology found in literature used to analyze a part of the Portuguese energy sector namely hydropower generation is a partial equilibrium bottom-up optimization model (TIMES_PT). This framework allow the modelling of future energy scenarios up to 2050 and provides information on costs and GHG emissions [17]. Besides the evaluation of national energy systems, sustainability indicators have been suggested for smaller systems like municipalities e.g. Ormoz (Slovenia), a study performed by Kostevsek et al. [18]. The proposed Locally Integrated Energy Sector (LIES) concept considers besides environmental, economic and social indicators, some specific energy indicators. Another investigated system may be a region, like in the case of Martire et al. study, [19] which investigated the alpine area of Lake Como (Italy), by using Sustainability Impact Assessment, or the case of Ding et al. who focused on 31 regions in China, the evaluation being made based on LCA [19]. Furthermore, the versatility of LCA methodology allows the investigation of technologies like Power-to-Gas technologies like in the case of a recent study of Zhang et al. [20]. Romania is one of the European Union (EU) member states in which the latest statistics show increases in electricity generation, in contrast with most of the member states that have recorded a decline in electricity generation.

476

G. Barjoveanu et al.

In 2014, Romania has recorded the largest annual increase in electricity production ar European level, followed by Slovenia and Bulgaria [1]. In this context, the following research questions may be formulated: (a) Which are the main environmental issues/impacts related to this sector in Romania? and (b) How sustainable is the Romanian growing energy sector for electricity production? This study has as main objective the identification and quantification of the environmental impacts related to the energy production system in Romania, by using the Life Cycle Assessment (LCA) methodology. To the best of our knowledge this is the first study that: applies a life cycle approach to scenario analysis of electricity production in Romania; considers a wider range of environmental aspects, going beyond the traditional link between energy sector and greenhouse gas emissions, in a coherent and unitary manner so as to reflect current and future scenarios for the Romanian energy profile, and discusses the futures energy generation options. The LCA approach uses ReCiPe impact assessment methodology, included in the SimaPro software package.

2 Romanian Electricity Production System The Romanian energy mix (electricity and heat production) is based mostly on indigenous resources. In 2015, the energy production mix had the following profile: 28% coal (lignite), 27% hydropower, 18% nuclear, 13% natural gas, 11% wind power, 2% photovoltaic and 1% biomass. Approximately 41% of the energy production comes from renewable resources, 60% from the mix is considered to be with “zero” GHG emissions, while 75% of the mix has low CO2 emissions [21]. The Romanian electricity production system is still largely carbon-based, but also hydro- and nuclear sources represent an important part in the energy mix. Also, renewable sources are becoming more and more important in terms of share, as presented in Table 1. Table 1. Romanian electricity mix for 1990, 1997, 2010, 2015 Year Sources\Units Hydro Solar Wind Biofuels Biogas Nuclear Coal Oil Gas

1990 GWh 11,411 0 0 0 0 0 18502 11823 22573

1990 % 17.7% 0.0% 0.0% 0.0% 0.0% 0.0% 28.8% 18.4% 35.1%

1997 GWh 17,509 0 0 11 0 5400 16862 6863 10084

1997 % 30.9% 0.0% 0.0% 0.0% 0.0% 9.5% 29.7% 12.1% 17.8%

2010 GWh 20,603 0 306 110 1 11623 20681 475 7516

2010 % 33.6% 0.0% 0.5% 0.2% 0.0% 19.0% 33.7% 0.8% 12.3%

2015 GWh 17,381 1982 7063 463 61 11640 18125 203 9738

2015 % 26.1% 3.0% 10.6% 0.7% 0.1% 17.5% 27.2% 0.3% 14.6%

Life Cycle Assessment of the Romanian Electricity Mix

477

Table 2. Energy balance for the years: 1990, 1997, 2010, 2015 Energy balance, GWh Gross production Imports Exports Distribution losses Energy available for final consumption

1990 64,309 9,476 0 5,929 54,236

1997 56,729 777 556 6,600 38,714

2010 61,315 767 3,041 7,058 41,468

2015 66,656 4,492 11,220 7,161 43,134

In this evolution, it is important to pinpoint the appearance of the nuclear sources in the mix in 1997 and the rise of the renewables in the last period, all of which have led to changes in the environmental profile of Romanian electricity production systems. The energy available for final consumption is mainly based on internal production, however, in time, the ageing of the infrastructure leads to an increase in distribution losses (Table 2). 2.1

Combined Heat and Power Plants

Approximately 80% of the combined heat and power (CHP) plants, have been installed in 1970–1980, operating longer than the usual expected lifespan. In general, the literature considers a technical lifetime for coal power plants to be around 40 years [2]. With few exceptions, the plants performance is reduced to 30% due to the old technologies. The rehabilitated CHP plants (on coal) have a performance around 33%. In 2009, from a total installed power of 4900 MW, 53% come from CHP plants older than 30 years, 30% is produced in installations 20–30 years old, while the remaining 17% comes from plants under 20 years. Most of the CHP plants lack proper gas treatment installations and have a significant impact in terms of SO2 and NOX emissions (higher than the maximum values set out by EU). In the last 10 years, the CHP plants technologies have been updated, representing 10% of the installed power, with efforts directed towards the fulfilment of environmental requirements [22]. 2.2

Centralized Heating Systems

The centralized heating systems have low technical performance (heat and steam generation) and register heavy losses in terms of transportation and distribution (between 10–50%). Also the disappearance of industrial steam and hot water industrial consumption has led to unsustainable operating regime, reflected in higher energy production and distribution costs, low quality services and increased bills for average consumers, [22].

478

2.3

G. Barjoveanu et al.

Hydroelectric Power Plants

The hydroelectric power plants (HPP) have been in use longer than the usual lifespan and sum up an installed power of 6450 MW (31% of the total installed power). After 2000, the modernization of HPPs has been considered systematically with the scope of achieving approximately 1/3 of their installed power (2400 MW) by 2020, [22]. 2.4

Nuclear Power Plant in Cernavoda

Since 2007, the Nuclear power plant (NPP) in Cernavoda has 2 operating units with an installed production capacity of 700 MW each and an average contribution to the energy production mix of 20%. The Cernavoda NPP uses the Canadian Deuterium Uranium Technology (CANDU 6), based on natural uranium as fuel and deuterium as moderator and cooling agent [23]. In 10 years, the assumed lifetime of a nuclear power plant, the First Reactor Unit will exceed the usual lifespan [2]. 2.5

Natural Gas Production

In Romania, there are 2 key players, Romgaz and Petrom, both having 98% of the natural gas production, the remaining 2% belonging to other companies [22] (Romanian Energy Strategy for 2007–2020, revised for 2011–2020). The gas power plants have an expected technical lifetime of 34 years [2]. 2.6

Wind Power

Romania has a significant potential in energy production from wind power, being classified as the second country within EU member states. According to several authors [24, 25], energy production from wind power has registered a significant increase in 2010 of up to 462 MW as compared with 2009, with just 14 MW. By the end of 2015, 75 wind farms with 1200 onshore wind turbines were in use in Romania, with a power range varying from 0.08 to 600 MW and an average of 40 MW. These windfarms are distributed mainly in the Dobrogea Plateau (78% of the total power installed) and Barlad Plateau. 2.7

Solar Energy and Photovoltaics

As in the case of wind power, Romania exhibits a great potential for further developments in terms of energy production from solar energy. However, the first projects and investments in solar energy harvesting started in 2009–2010. By the end of 2012, statistics show 25 installed projects in solar energy based on photovoltaics, with 8 areas having operational solar parks, summing up an installed power of 51 MW. By the end of 2014, the installed capacity of solar power was 1219 MW. The same report shows records of the following installed projects: 1222 wind; 409 microhydro, 2 biogas and 34 biomass [26, 27].

Life Cycle Assessment of the Romanian Electricity Mix

2.8

479

Romanian Objectives and Targets in the Energy Sector for 2016–2030

As an EU member state, Romania has to fulfil targets related to: energy efficiency, energy production from renewable resources and GHG emissions. Energy efficiency is estimated based on the primary energy demand reduction. The target for 2020 is set at 20%, a target already exceeded by Romania. The value achieved, estimated at 36%, exceeds the target and is considered to remain constant up to 2030. In 2015, Romania has achieved a 54% reduction of the GHG emissions, as compared to 1990, exceeding both the 2020 and 2050 targets. This situation was possible due to the transformations (reduction) of the Romanian industry, the former larger energy consumer. It is assumed that 60–63% reduction of GHG emissions (reference year 1990) will be possible by 2030. The 2020 target, namely 24% of the gross final energy consumption that is supposed to come from renewables was already achieved in 2015. It is expected that this percentage will slightly increase, starting with 2020. Also, it is possible that Romania will introduce a supporting mechanism for the development of energy production from biomass that will increase the contribution of this RES in the energy production mix [21].

3 Methodology The LCA analysis performed in this research has followed the ISO 14040 structure of an LCA study in 4 steps: goal and scope definition, inventory analysis, life cycle impact assessment, and interpretation of results. 3.1

Goal and Scope Definition

The life cycle analysis performed in this research approaches the primary energy sources and processes used for the production of electricity in Romania in four different years (1990- as reference year; 1997- the year when the 1st reactor of Cernavoda NPP became operational; 2010, 2015- as years after Romania entered EU and renewable energy sources usage increased). The main drivers for this research endeavor are motivated by the need to identify and quantify the extent of various environmental impacts of electricity production and to analyze how different changes have impacted and how future changes may affect the performance of this system. The analysis takes into consideration multiple conventional sources, as well as renewable resources. From an LCA point of view, the analysis considers the corresponding shares of primary sources to one kilowatt-hour of electricity. 1990 is used as reference year for comparing changes in the mix, as well as to project a series of scenarios for the future, as 1990 has also been selected as reference year for measuring the GHG emissions reduction efforts at global level (Kyoto protocol). This LCA considers the gross-electricity production and it also accounts for the heat produced by various co-generation systems.

480

G. Barjoveanu et al.

3.2

Life Cycle Inventory

Data collection and analysis represents a major challenge for any LCA study, and this is even more important in complex systems, such as the energy sector where there are so many different processes and uncertainty sources. Thus, to allow for a credible analysis, systematic, comprehensive and complete data sources are always required to ensure a low uncertainty of the results. To achieve this goal for high quality data, a top-to-bottom approach for data collection has been implemented, and so, this analysis is based onto data sourced from the Eurostat database for energy production and the Romanian National registry of GHG emissions for the air emissions. The Eurostat data is based on the data collection methodology described at the following link: www.wc.europe.eu/eurostat, [1] while the National Registry for GHG emissions considers the IEA Energy Statistics Manual [28], thus ensuring a unitary platform for data collection. The life cycle inventory of this study considers the inputs (fuels consumption by year and type corresponding to 1 kWh gross electricity, as presented in Table 3) and outputs (polluting streams) (see Table 4) and the overall operational phase of electricity production infrastructure. The analysis does not take into consideration the construction and decommissioning electricity production infrastructure. Although construction and decomissioning of large infrastructure can have important impacts, they were not considered given the large time span of the analysis and the data availability. Furthermore, the output fluxes of electricity production was sourced from the Ecoinvent 3.0 data base and were updated with quantities relative to 1 kWh electricity corresponding to their source. Data for the specific pollution streams is presented in Table 3 and it mainly concerns the carbon-based fluxes and was sourced from the National GHG inventory (2012 emission). Data summarized in Table 3 presents the total fuel consumption (and calorific data) for the electricity production, considering the fuel types and the studied years. Table 3. Fuel consumption data for electricity produced in Romania, in various years Fuel type Liquid fuels Refinery gas (not liq.) Net calorific value Gas-diesel Oil Net calorific value Transport diesel Net calorific value Residual fuel oil Net calorific value Solid fuels Lignite/brown coal, Net calorific value Sub-bituminuous coal

Unit

1990

1997

2010

2015

t 10^3 kJ/kg t 10^3 kJ/kg t 10^3 kJ/kg t 10^3 kJ/kg

0 42435 0 42435 0 42485 6492 39350

59 42435 3 42435 3 42485 3427 39350

95 42435 5 42435 5 42485 200 39350

0 42435 0 42435 0 42485 1 39350

t 10^3 33856 MJ/t 7507 t 10^3 0

30235 7513 1173

29813 8297 379

25918 7805 196 (continued)

Life Cycle Assessment of the Romanian Electricity Mix

481

Table 3. (continued) Fuel type Net calorific value Bituminous coal Net calorific value Natural gas Gross calorific value

Unit MJ/t t 10^3 MJ/t Mm3 kJ/m3

1990

1997 18932 3098 0 24442 11112036 5305203.9 37613 37126

2010 24585 0 2822749.5 36959

2015 24586 0 948.53216 36959

Table 4. Specific emission factors Fuel type

Liquid fossil Gas/diesel oil Residual fuel oil Refinery Gas Solid fossil Other bituminous coal Sub-bituminous coal Lignite Blast furnace gas Gaseous fossil Natural gas (dry) Biomass Solid biomass Liquid biomass Gas biomass Other biomass & wastes

3.3

CH4 CO g/kWh

Carbon content, t/TJ

CO2 kg/kWh 1990– 2010– 1997 2015

20.2 21.1 18.2 25.8

0.266 0.278 0.240 0 0.340

0.011 0.018 0.2619 0.286 0 0 0.004 0.407 0.341

26.2

0.345

0

27.6 66.0

0.364 0.871 0 0.201 0 0.394 0.263 0.403

0.347 0 0 0.201 0 0 0 0

15.3 29.9 20.0 30.6

NMVOC N2O

0.00288

SO2

0.0022 1.656 1.746

0.00612

0.0051 6.415

2.952

0.004 0.140

0.0054

0.0004 0.001

0.108

0.0144

0.108 3.5999 0.18

0.0144 0.04

Life Cycle Impact Assessment (LCIA)

The LCIA has been performed using the updated Recipe 1.12 methodology, which considers the impact categories presented in Table 5. For data validation, an additional analysis was performed by using the CML 2000 baseline methodology. One of the main advantages of the LCA methodology in evaluating the environmental impacts is represented by the possibility of depicting a complex environmental

482

G. Barjoveanu et al. Table 5. ReCiPe 1.12 Impact categories No Impact category

Sym. Unit

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

CC OD TA FE ME HT POF PMF Ttox Ftox Mtox IR ALO ULO NLT WD MD FD

Climate change Ozone depletion Terrestrial acidification Freshwater eutrophication Marine eutrophication Human toxicity Photochemical oxidant formation Particulate matter formation Terrestrial ecotoxicity Freshwater ecotoxicity Marine ecotoxicity Ionising radiation Agricultural land occupation Urban land occupation Natural land transformation Water depletion Metal depletion Fossil depletion

kg CO2 eq kg CFC-11 eq kg SO2 eq kg P eq kg N eq kg 1,4-DB eq kg NMVOC kg PM10 eq kg 1,4-DB eq kg 1,4-DB eq kg 1,4-DB eq kBq U235 eq m2 a m2 a m2 m3 kg Fe eq kg oil eq

Normalization values Europe set Local set 0.0000707 1 45.4 1 0.0309 1 2.41 1 0.0988 1 0.00286 1 0.0176 1 0.0671 1 0.121 1 0.091 1 0.132 1 0.000485 1 0.000221 1 0.00246 1 6.19 1 0 1 0.0014 1 0.000643 1

profile which comprises other impact categories beside the traditional global warming potential. In this context, the Recipe methodology is very useful as it uses 18 impact categories which include aspects like climate change, ecosystem related impacts (toxicity, eutrophication, acidification, photochemical oxidation potential), human related impacts (toxicity, land use) and resources-related impacts. Life cycle impact assessment consists in impact classification (impact identification, which is automatically done by the LCIA method by correlating various environmental impacts with the fluxes in the life cycle inventory), impact characterization (using the life cycle inventory values and method specific characterization factors which enable impact quantification and impact correlation among various contributors). To be able to compare the environmental impacts across different impact categories, an additional normalization step is required to reduce the impacts to the same reference. In Table 5, the normalization values for the Recipe 1.12 method are presented which show the corresponding impact weights for the 18 impact categories for the European weighting set. To better represent the local environmental impacts, a local set of normalization weights has been developed in which all impact categories have the same importance.

Life Cycle Assessment of the Romanian Electricity Mix

483

4 Results and Discussion 4.1

Environmental Profiles of the Electricity Mixes

Figure 1 presents annual environmental profiles of the Romanian electricity mixes after the characterization step of the LCIA, by considering the impact categories as designated in Table 5 (the impact categories abbreviations are used subsequently for all figures). The results in Fig. 1 present a comparison of environmental impacts for the evaluated period (1990, 1997, 2010 and 2015) and show that for 8 of the 18 impact categories, the environmental impacts have decreased. However, to be able to compare impacts across impact categories, one must refer to normalized results. In Fig. 2, normalized results using a weighting set show that only in a few categories the impacts are higher. In the context of this study, the European normalization set (Table 5) is not useful, because the aim is to analyze the evolution of the Romanian electricity production and not to compare it with other European energy systems. Because of this, a

Fig. 1. Romania’s environmental profile (characterization step)

Fig. 2. Comparative environmental profile (weighted normalized results)

484

G. Barjoveanu et al.

Fig. 3. Comparative environmental profile (non-weighted normalized results)

non-weighted normalization of results was performed and the results are presented in Fig. 3 which point out the impact categories with the highest impacts: Climate change, Ionizing radiation, Fossil depletion, Human toxicity, Freshwater and Marine Eco-toxicity, which reflect the structure of the electricity mixes, and the corresponding entries in the life cycle inventories. If we refer to the yearly environmental profiles, the contributors to each impact category may be observed in Figs. 4, 5, 6 and 7. These results point-out the vast contribution of fossil-based fuels to most of the impact categories, except the Ionizing radiation (IR), where the nuclear electricity production has the largest contribution and the Agricultural land occupation where the bio-based fuels generate higher impacts in 2010 and 2015.

Fig. 4. 1990 environmental profile

These results showcase how the structure of the Romanian electricity mix influence its environmental profiles, and indicate a few impact categories that need a more in-depth analysis.

Life Cycle Assessment of the Romanian Electricity Mix

Fig. 5. 1997 environmental profile

Fig. 6. 2010 environmental profile

Fig. 7. 2015 environmental profile

485

486

4.2

G. Barjoveanu et al.

Climate Change Impacts

As presented in Fig. 8, the Climate changes impacts, have constantly decreased from 1990 to 2015 due to changes in the quantities of fossil-fuels used in the electricity production (see Table 1). If 1990 is used as a base to compare GHG emissions, until 2015 a 45% reduction was recorded for the Romanian electricity mix. This was possible due to the changes in the electricity mix (in 1996 the first nuclear reactor was started and in 2007, another one started to operate).

Fig. 8. Evolution of climate change impacts

Coal (solid fuels) make about half of the emitted GHG emissions which, in conjunction with the relative constant proportion of the coal in the mix induces a high dependence of the carbon footprint to the solid fuel use. Although, the targets set by the Kyoto protocol for Romania have already been met and overcome (20% reduction assumed, 45% realized), an additional decrease of the GHG emissions seems only possible by further decreasing the fossil fuels and coal in particular. 4.3

Future Scenarios

The previous analysis of the Romanian electricity mix in this study has enabled the identification of its characteristics in terms of major impacts, contributors, and has pointed out some aspects to be further analyzed. Two future scenarios have been considered in order to analyze the future environmental impacts of the Romanian electricity mix, as presented in Table 6, with reference to 2015. The 2030 scenario considers a light increase in electricity production (to 73 TWh) and some optimistic changes in the electricity mix (13% and 7% decrease of coal and respectively gas use, a 13% increase of nuclear electricity and a 11% increase of the renewable energy sources), in accordance with the Romanian Energy Strategy, 2016– 2030, with an outlook to 2050.

Life Cycle Assessment of the Romanian Electricity Mix

487

Table 6. Electricity mix scenarios Energy source % Hydro Solar Wind Biofuels Nuclear Coal Gas Gross production, TWh

2015 26 3 11 1 17 27 15 66.56

2030 24 7 16 1 30 14 8 73

2050 24 10 20 2 20 16 8 67.89

The data for the 2050 scenario was derived from a provision document which considers the primary energy production (not electricity) for the 2030–2050 period which considers changes related to the decommissioning of some of the nuclear reactors, and an increase in the renewables. The impact profiles are presented in Fig. 9, where it may be observed that the impact structure is similar with the 1990–2015 period. Changes of the impact values are due to changes in the production mix, being more visible in the climate change and ionizing radiation impact categories. A tradeoff between the reduction of GHG emissions between 2015 (reference year) and 2030 scenario is compensated by an increase in the Ionization Radiation category due to the increase of the nuclear electricity production.

Fig. 9. Future scenarios impacts

5 Conclusions The main objective of this study was the identification and calculation of the overall environmental impacts associated to electricity in Romania by means of Life Cycle Assessment (LCA). This was performed by developing an LCA study according to the

488

G. Barjoveanu et al.

ISO 14040 methodology. A top-down approach for data collection was used as data was collected from Eurostat for energy production mix structures and the national inventory for GHG emissions. The results have demonstrated the utility of LCA to depict complex environmental impacts, evolutions and trends. In the Romanian context, this analysis has pointed out how the changes in the electricity production mix have had positive changes in the environmental profile (expressed mainly as a 45% decrease of the GHG emissions for the 1990–2015 period) and how future changes may affect this evolution. This analysis has also pointed out some aspects that need a more in-depth analysis, especially to include the infrastructure-related processes in the LCA analysis, considering the dynamic future evolution of the Romanian electricity production system (new renewable sources e.g. wind farms and solar farms, future construction and decommissioning of the nuclear reactors at Cernavoda, the dynamics of the hydro system, etc.). Furthermore, the dependence of the environmental profile structure and dimension to the carbon-based energy source needs to be further investigated, in correlation with changes of the other electricity production options.

References 1. www.wc.europe.eu/eurostat 2. Farfan, F.J., Breyer, C.: Structural changes of global power generation capacity towards sustainability and the risk of stranded investments supported by a sustainability indicator. J. Clean. Prod. 141, 370–384 (2017). http://dx.doi.org/10.1016/j.jclepro.2016.09.068 3. Hondo, H.: Life cycle GHG emission analysis of power generation systems: Japanese case. Energy 30, 2024–2056 (2005). doi:10.1016/j.energy.2004.07.020 4. Kannan, R., Leong, K.C., Osman, R., Ho, H.K.: Life cycle Energy, emissions and cost inventory of power generation technologies in Singapore. Renew. Sustain. Energy Rev. 11, 702–715 (2007). doi:10.1016/j.rser.2005.05.004 5. Foidart, F., Oliver-Solá, J., Gasol, C.M., Gabarrell, X., Rieradevall, J.: How important are current energy mix choices on future sustainability? Case study: Belgium and Spain projections towards 2020–2030. Energy Policy 38, 5028–5037 (2010). doi:10.1016/j.enpol. 2010.04.028 6. Santoyo-Castelazo, E., Gujba, H., Azapagic, A.: Life cycle assessment of electricity generation in Mexico. Energy 36, 1488–1499 (2011). doi:10.1016/j.energy.2011.01.018 7. Gujba, H., Mulugetta, Y., Azapagic, A.: Power generation scenarios for Nigeria: an environmental and cost assessment. Energy Policy 39, 968–980 (2011). doi:10.1016/j.enpol. 2010.11.024 8. Stamford, L., Azapagic, A.: Life cycle sustainability assessment of electricity options for the UK. Int. J. Energy Res. 36(14), 1263–1290 (2012). http://dx.doi.org/10.1002/er.2962 9. Santoyo-Castelazzo, E., Azapagic, A.: Sustainability assessment of energy systems: integrating environmental, economic and social aspects. J. Clean. Prod. 80, 119–138 (2014). http://dx.doi. org/10.1016/j.jclepro.2014.05.061 10. Stamford, L., Azapagic, A.: Life cycle sustainability assessment of UK electricity scenarios to 2070. Energy Sustain. Dev. 23, 194–211 (2014). http://dx.doi.org/10.1016/j.esd.2014.09. 008

Life Cycle Assessment of the Romanian Electricity Mix

489

11. Brizmohun, R., Ramjeawon, T., Azapagic, A.: Life cycle assessment of electricity generation in Mauritius. J. Clean. Prod. 106, 565–575 (2015). http://dx.doi.org/10.1016/j.jclepro.2014. 11.033 12. Treyer, K., Bauer, C.: The environmental footprint of UAE’s electricity sector: combining life cycle assessment and scenario modeling. Renew. Sustain. Energy Rev. 55, 1234–1247 (2016). http://dx.doi.org/10.1016/j.rser.2015.04.016 13. Atilgan, B., Azapagic, A.: Renewable electricity in Turkey: life cycle environmental impacts. Renew. Energy, 89, 649–657 (2015). http://dx.doi.org/10.1016/j.renene.2015.11. 082 14. Nanaki, A.E., Koroneos, C.J, Xydis, G.A.: Environmental impact assessment of electricity production from lignite. Environ. Prog. Sustain. Energy (2016, in press). http://dx.doi.org/ 10.1002/ep 15. Martin-Gamboa, M., Iribarren, D., García-Gusano, D., Dufour, J.: A review of life-cycle approaches coupled with data envelopment analysis within multi-criteria decision analysis for sustainability assessment of energy systems. J. Clean. Prod. 150, 164–174 (2017). http:// dx.doi.org/10.1016/j.jclepro.2017.03.017 16. Santos, M.J., Ferreira, P., Araújo, M., Portugal-Pereira J., Lucena, A.F.P., Schaeffer, R.: Scenarios for the future Brazilian power sector based on a multicriteria assessment. J. Clean. Prod. (2017, in press), http://dx.doi.org/10.1016/j.jclepro.2017.03.145 17. Teotónio, C., Fortes, P., Roebeling, P., Rodriguez, M., Robaina-Alves, M.: Assessing the impacts of climate change on hydropower generation and the power sector in Portugal: a partial equilibrium approach. Renew. Sustain. Energy Rev. 74, 788–799 (2017). http://dx. doi.org/10.1016/j.rser.2017.03.002 18. Kostevsek, A., Klemes, J.J., Varbanov, P.S., Cucek, L., Petek, J.: Sustainability assessment of the Locally Integrated Energy Sectors for a Slovenian municipality. J. Clean. Prod. 88, 83–89 (2015). http://dx.doi.org/10.1016/j.jclepro.2014.04.008 19. Ding, N., Liu, J., Yang, J., Yang, D.: Comparative life cycle assessment of regional electricity supplies in China. Resour. Conserv. Recycl. 119, 47–59 (2017). http://dx.doi.org/ 10.1016/j.resconrec.2016.07.010 20. Zhang, X., Bauer, C., Mutel, C.L., Volkart, K.: Life cycle assessment of power-to-gas: approaches, system variations and their environmental implications. Appl. Energy, 190, 326–338 (2017). http://dx.doi.org/10.1016/j.apenergy.2016.12.098 21. Romanian Energy Strategy 2016–2030, with an outlook to 2050 22. Romanian Energy Strategy for 2007–2020, revised for 2011–2020 23. http://www.nuclearelectrica.ro/cne/ 24. Dragomir, G., Șerban, A., Năstase, G., Brezeanu, A.I.: Wind energy in Romania: a review from 2009 to 2016. Renew. Sustain. Energy Rev. 64, 129–143 (2016). http://dx.doi.org/10. 1016/j.rser.2016.05.080 25. Colesca, S.E., Ciocoiu, C.N.: An overview of the Romanian renewable energy sector. Renew. Sustain. Energy Rev. 24, 149–158 (2013). https://doi.org/10.1016/j.rser.2013.03.042 26. Romanian Photovoltaic Industry Report (2012) 27. http://www.iea-pvps.org/index.php?id=32. International Energy Agency - Photovoltaic Power Systems Programme, 30 March 2015, 15 28. http://www.iea.org

Developing Modified Hydrodynamic Rotor for Flow Small Hydro Ion Bostan, Viorel Bostan, Valeriu Dulgheru(&), Oleg Ciobanu, Radu Ciobanu, and Vitalie Gladis Technical University of Moldova, Chisinau, Moldova [email protected]

Abstract. An efficient conversion of kinetic energy of river water into mechanical or electrical energy without building barrages is provided by micro-hydropower stations. Increased efficiency is achieved by an optimum position of the blades with hydrodynamic profile. The micro hydro power plant is posted in the river water flow. The position of blades compared to the water level is ensured by the Archimedes forces that react on the floating blades. The efficiency of the micro-hydro power stations as conversion systems of renewable energy sources kinetic energy of flowing river depend mostly on profiles of the hydrofoils used in the rotor’s construction for interaction with fluid. The main goal of this paper consists in the elaboration of the modified hydrodynamic blades with modular structure, and based on them of the turbines with increased conversion efficiency. According to the opinion of authors, the constructive solutions of the micro hydro power plant presented in this work correspond to a great extent to the requirements advanced to the performance hydrodynamic rotor. This fact imposes the designing and execution of some experimental prototypes, which would validate the expectations. The industrial models of micro hydro power plant with modified hydrodynamic rotor and with indicated power of 4 kW have been projected, and fabricated. In present the hydro power plant are in testing stage. Keywords: Hydrodynamic blade


Turbine
Water kinetic energy

1 Introduction Hydraulic energy is the oldest form of renewable energy used by man and has become one of the most currently used renewable energy sources, being also one of the best, cheap and clean energy sources. Hydraulic energy as a renewable energy source can be captured in two extra power forms: • potential energy (of the natural water fall); • kinetic energy (of the water stream running). Both extra power forms can be captured at different dimensional scales. Floating micro hydro power plants are of special interest. In terms of costs, floating micro hydro power plants are efficient because they do not include essential costs related to civil engineering [1]. The analysis of hydraulic energy conversion systems © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_35

Developing Modified Hydrodynamic Rotor for Flow Small Hydro

491

has demonstrated the opportunity for the development of water kinetic energy conversion systems compared to potential energy conversion systems. A number of advantages are observed obviously. Technical advantages: relatively simple hydraulic energy conversion systems. Economic advantages: the cost of civil engineering works is reduced considerably. Ecological advantages: absence of dams and storage basins. The analysis of existing micro hydroelectric power plants for river water kinetic energy conversion has pointed that there are reserves to increase the efficiency of the utilized turbines. Betz coefficient, equal to 0.59, represents the maximum theoretical efficiency of the hydraulic energy conversion. The majority of the existing systems provides an output factor (coefficient) for water kinetic energy in the value range of 0.2. Only certain modern systems exceed the efficiency by over 30%. In this respect there are sufficient reserves to increase the efficiency of the flow hydraulic turbines, which become more and more attractive to the engineers and inventors in the field. Insistent searches of authors have lead to the design and licensing of some advanced technical solutions for outflow micro hydroelectric power plants. They are based on the hydrodynamic effect, generated by the hydrodynamic profile of blades and by the optimal blades’ orientation towards water streams with account of energy conversion at each rotation phase of the turbine rotor [2]. To achieve this, it was necessary to carry out considerable multicriteria theoretical research on the selection of the optimal hydrodynamic profile of blades and the design of the orientation mechanism of blades towards the water streams.

2 Theoretical Justification of the Hydrodynamic Profile Selection of the Blade in Normal Section Considering the symmetrical profile of the blade placed in a uniform water stream with ! velocity V 1 (Fig. 1) [2, 3]. In the fixing point O′ of the symmetrical blade with lever OO′ let consider three coordinate systems, namely: the O′xy system with axis O′y ! oriented in the direction of the velocity vector V 1 , and axis O′x normal to this direction; the O′x′y′ system with axis O′y′ oriented along the lever direction O′O, and axis O′x′ normal to this direction, and finally the O′x′′y′′ system with axis O′x′′ oriented along the profile’s chord toward the trailing edge and axis O′y′′ normal to this direction. Points A and B correspond to the trailing and the leading edges, respectively. The angle of attack a is the angle between the profile’s chord AB and the direction of the velocity ! vector V 1 , and the positioning angle u is the angle formed by the velocity vector direction and lever O′O. ! The hydrodynamic force F has its components in directions O′x and O′y, named the lift and drag forces, respectively given by: 1 2 FL ¼ CL qV1 Sp ; 2

ð1Þ

1 2 FD ¼ CD qV1 Sp ; 2

ð2Þ

492

I. Bostan et al.

Fig. 1. Hydrodynamic profile blade

where q is the fluid density, V∞ is the flow velocity, Sp = ch (c is the length of chord AB, and h is the blade height) represents the lateral surface area of the blade, and CL and CD are dimensionless hydrodynamic coefficients, called the lift coefficient and drag coefficient. The hydrodynamic coefficients CL and CD are functions of the angle of attack a, the Reynolds number Re and the hydrodynamic shape of the blade profile. The components of the hydrodynamic force in the coordinate system O′x′y′ are: Fy0 ¼ FL sin u þ FD cos u; Fx0 ¼ FL cos u þ FD sin u:

ð3Þ

The torque developed by blade i at the rotor spindle OO′ is: Tr;i ¼ Fx0
jOO0 j;

ð4Þ

and the total torque developed by all blades is: TrR ¼

Npal X

Tri ;

ð5Þ

i¼1

where Npal is the number of rotor blades. Generally, the hydrodynamic force does not have application point in the origin of the blade axes system O′ so that it produces a resultant moment. The produced moment is determined with respect to a certain reference point. As a reference point there is

Developing Modified Hydrodynamic Rotor for Flow Small Hydro

493

considered the point located at distance ¼ of the chord length measured from the leading edge B. Similarly Eqs. (1) and (2) the moment, called the pitching moment, is computed according to formula: 1 2 M ¼ CM qV1 cSp ; 2

ð6Þ

where CM is the hydrodynamic moment coefficient. The shape of the hydrodynamic profile is chosen from the library of NACA 4 digits aerodynamic profiles. The standard NACA 4 digit profiles are characterized by three shape parameters measured in percents of the chord’s length: maximum value of camber Cmax, location of the maximum camber xC,max and maximum thickness Gmax. For example, the NACA 5416 profile has a 5% maximum camber located at 40% from the leading edge and has a maximum thickness of 16%. The profile coordinates are obtained by combining the camber line and the distribution of thickness [2]. Since the considered blades will have a symmetric shape, the camber is null (Cmax = 0, xC,max = 0) and the camber line will coincide with x-axis.

3 Reducing the Turbulence of the Water Currents in the Depth of Immersion of the Blade To justify the constructive and functional parameters, additional numerical modeling and simulations were performed. The computer simulations of the flow-blade interaction of the micro-hydro power station have been performed in the academic version of the commercial CFD packages ICEM CFD and ANSYS CFX. In this study three-dimensional simulations have been conducted for a hydrofoil with NACA 0016 profile placed in a waterstream at an angle of attack of 18o with chord length c = 1.3 m and height h = 1.5 m. The computational domain is a box ABCDEFGH presented in Fig. 2. The Inlet is defined at ABCD. The no-slip boundary condition is imposed on the surface of each hydrofoil, the streamwise flow boundary conditions with initial velocity of 1 m/s and medium turbulence intensity (5%) are imposed on the upstream boundary (inlet), the free-slip boundary conditions are imposed on the lateral sides, while on the downstream boundary (outlet) a constant zero averaged pressure condition is enforced. The geometry and mesh discretisation of the domain have been conducted in ICEM CFD. The mesh is a hybrid mesh containing tetraedras and very fine prism elements for modelling the boundary layer near blade walls as presented in Fig. 3. The hydrofoil surface was discretised using a total of 15000 nodes. A total number of 16 prism element layers have been used to model the boundary layer. The first boundary layer has a height of 0.00025 m. The corresponding y+ is bounded 2  y+  8, where

yþ

rffiffiffiffiffi sw y q ; ¼ m

ð7Þ

494

I. Bostan et al.

Fig. 2. Computational domain

Fig. 3. Mesh in vicinity of the trailing edge

with sw being the wall shear stress, q the fluid density, y the wall normal distance and m the fluid viscosity. A sufficient boundary layer resolution should satisfy the condition y+ = O(1) in order to describe correctly the boundary layer behaviour. A total number of approx. 1 000 000 elements for the entire computational domain. Spatial convergence tests identified this discretisation as sufficient for convergence and optimal for computational costs.

Developing Modified Hydrodynamic Rotor for Flow Small Hydro

495

The steady CFD simulations have been performed in CFX. The fluid was chosen as water at 25°C. For the turbulence model the SST k - x model was chosen. This model was chosen since SST k - x simulates quite well separated boundary layers, a phenomena happening at high angles of attack, angles characteristic to the discussed setting. The post-processing of the numerical results have revealed that the separation of the boundary layer from the hydrofoil surface, and as consequence the increase in the turbulence intensity will affect the conversion efficiency. It can be observed from results presented in Fig. 4 that the separation of the boundary layer progresses toward the leading edge as the depth increases. Also, the endpoint of the hydrofoil will contribute towards the earlier separation. In order to control the separation of the boundary layer it was proposed a partition of the hydrofoils surface with transversal ribs. In the Fig. 5a is presented the proposed solution of the blade with separation of the boundary layer [4]. The ribs (Fig. 5b) consequently will decrease the reciprocal influence of the adjacent boundary layers and also will allow a modular assembly of the hydrofoils fabricated from composite materials. Also, the modular construction will allow the variable hydrofoil heights in dependence of the terrain conditions, such as the river depth.

Fig. 4. Streamlines and velocity distribution for angle of attack 18o

496

I. Bostan et al.

Fig. 5. (a) Hydrofoil with 3 sections and transversal ribs and (b) modular assembly of the hydrofoils fabricated from composite materials

4 Design of the Micro Hydro Power Station for Pumping Water Necessary for the Irrigation of Terrains The micro hydro power station designed modularly, allow change of destination and of functional characteristics by replacing some units with others (generator, pump, blades with other hydrodynamic profile, 3- and 5- blade rotor) (see Fig. 6 [5]). The designed new variant of the micro hydro power station possesses more resistance in structure construction, calculated for strength and rigidity to dynamic applications. For good maintenance of hydrodynamic impeller immersed in water the platform is made of two parts connected articulated (Fig. 7). One part of platform, which include the hydrodynamic rotor, is lifted from the water with a winch. The relative degree of instability of micro hydro power station platform is minimised by supplementary plastic pontoon installed opposite the other two (Fig. 7 [5]). Buoyancy and maintenance of hydropower plant rotor axis perpendicularity at variable river water level is ensured by patented technical solutions [5]. Continuous orientation mechanism of the blades at the constant entering angle relative to the direction of fluid stream contains Know-how elements and is not described here. The main working body, which depends mainly on the amount of kinetic energy converted into useful energy, is the blade with hydrodynamic NACA 0016 profile, developed on the basis of carried theoretical research. On the basis of the conceptual diagram designed above, technical documentation was developed and industrial prototype of micro-hydro power plant for river water

Developing Modified Hydrodynamic Rotor for Flow Small Hydro

497

Fig. 6. The new design of the micro hydro power station for pumping water

Fig. 7. The micro hydro power station with hydrodynamic rotor out of the water

kinetic energy conversion into electrical and mechanical energy was manufactured (Fig. 8) and installed for testing on the Prut river. Thus, micro-hydro power plant MHCF D4  1,5 ME provides conversion of up to 73.6% and 67% of useful energy for electricity production and for water pumping from the energy potential of flowing water entrapped by the hydrodynamic rotor.

498

I. Bostan et al.

Fig. 8. Industrial prototype of micro-hydro power plant with modular blades [4]

5 Conclusions The proposed mycrohydro power plant for river water kinetic energy conversion has a high degree of novelty and stage of achievement. It is characterized by the following advantages: • Exclusion of dam construction and of the negative impact on the environment, implicitly; • Lowest cost; • Simplicity of construction and operation; • Increased reliability at dynamic overload in operating conditions; • Resistant composite materials, including conditions of high humidity; • Automatic adjustment of the micro hydropower plant platform position in conditions of water level changing.

References 1. Curtis, D.: Going with the flow: small-scale water power, CAT 1999 (1999) 2. Bostan, I., Gheorghe, A., Dulgheru, V., Sobor, I., Bostan, V., Sochirean, A.: Resilient energy systems. renewables: wind, solar, hydro. Springer. VIII, (2013). ISBN 978-94-007-4188-1 3. Popovici, D., Ionescu, C.M.: Principiile Zborului (Aerodinamica Zborului), Bucureşti (2009)

Developing Modified Hydrodynamic Rotor for Flow Small Hydro

499

4. Bostan, V., Ciobanu, O., Dulgheru, V., Sochireanu, A., Vaculenco, M., Gladîş, V.: Hydraulic turbine. Patent 4235MD CIB F03B 3/12 // F03B 3/14, Technical University of Moldova. Publ. BOPI Nr 6/2013 (2013) 5. Bostan, I., Dulgheru, V., Bostan, V., Ciobanu, O., Sochireanu, A., Gladîş, V.: Floating hydraulic station. Patent 601Y(MD) CIB F03B7/00 // F03B13/00, Technical University of Moldova. Publ. BOPI Nr 2/2013 (2013)

Development of a Horizontal Axis Wind Turbine for the Production of Thermal Energy Viorel Bostan, Ion Bostan, Ion Sobor, Valeriu Dulgheru(&), and Vitalie Gladis Technical University of Moldova, Chisinau, Moldova [email protected]

Abstract. The wind energy conversion systems could play a significant role in the production of mechanical, electrical and thermal energy in the Republic of Moldova, in particular for providing the individual consumer with energy using wind turbines of low power (until 30 kW). In order to redress the situation of the energy sector, the Government of the Republic of Moldova, through the agency of the Supreme Council for Science and Technological Development (Academy of Sciences of Moldova), initiated several National Programs, addressing the elaboration of renewable energy conversion systems as well. This paper describes some research and application of the industrial prototypes of horizontal axis wind microturbines with power of 10 kW, which include some new elements comparative to the already existing systems (wind orientation mechanism, thermal generator). These wind turbines are intended to be installed in different geographic areas of the Republic and tested. Some results are included in this paper. Keywords: Blade


Turbine
Wind energy

1 Introduction Wind energy has been used by mankind over thousands of years. For over 3000 years the windmills have been used for pumping water or grinding (milling). And nowadays, in the century of information technologies, nuclear energy and electricity, thousands of windmills are used for pumping water and oil, for irrigation and production of mechanical energy to drive low-power mechanisms on different continents. Electricity can be obtained using different methods, but absolutely all require fuel, in most cases fossil fuels - coal, natural gas, oil or uranium 235 and plutonium 239 in thermonuclear plants. By burning or nuclear fission the primary energy embedded in the fuel is converted into thermal energy (heat). The turbine, designed specifically for each type of fuel, drives the generator that produces electricity. In this context, the electricity produced from the wind is not differing from the electricity produced from fossil or nuclear fuels. The wind as a fuel is essentially different - it is free of charge and does not pollute the environment. Nowadays, the phrase “use of wind energy” means, primarily non-pollutant electrical energy produced at a significant scale by modern “windmills” called wind turbines, a term that attempts to outline their similarity to steam or gas turbines, which are © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_36

Development of a Horizontal Axis Wind Turbine

501

used for producing electricity, and also to make a distinction between their old and new destination. With the launch of the European Technology Platform on wind energy issues the EU Commissioner Piebalgs said [1]: “Wind energy technology is certainly one of the fastest growing and plays an important role, contributing to create a sustainable and competitive energy policy in Europe”. In 2014, the wind industry installed 11.791 MW in the EU - more than gas and coal combined. Today wind energy can meet 10.2% of Europe’s electricity demand with a cumulative capacity of 128.8 GW at the end of 2014 [2]. The wind provides electricity to more than 35 million households in the EU, but very few know it - a symptom which indicates a lack of knowledge about this technology. Globally, by 2020 about 12% of the produced electricity will be of wind origin. In this context G7 Agreement provide: reduce global greenhouse gas emissions at the upper end of a range of 40% to 70% by 2050; committed to raising $100bn in annual climate financing by 2020 from public and private sources; decarbonise the global economy in the course of this century [3]. China, which installed 23 GW in 2016, is a leader of all markets. China’s newly installed wind power capacity reached a record high in 2015 amid increasing efforts from the government to boost clean energy. The new wind power capacity jumped to 32.97 GW last year, more than 60% higher than 2014. Wind energy represented 3.7% of China’s electricity use in 2015, up from 2.8% in 2014 [3]. Wind turbines can be classified into four major groups, depending on the power developed at the wind rated speed, which is between 11 and 15 m/s. Micro turbines cover powers between 0.05 and 3.0 kW. Low-power wind turbines range from 3 to 30 kW and medium power turbines range between 30–1000 kW. Both micro turbines and low power turbines are designed to operate in autonomous mode; these turbines supply electricity to territorially dispersed consumers that are not connected to the public power grid. To examine what the market for small power wind turbines in the US is about, one should consider the following. The number of small wind turbines sold in the US in 2006 was 6807 units, of which 6639 (about 98%) produced in the USA, with a total installed capacity of 17543 kW (including 16093 kW of US produced units). In 2006 outside US, 9502 turbines were sold having a total installed capacity of 19483 kW [4]. Presently, in the world there are a number of companies producing a wide range of small wind turbines rated less than 1 kW and up to 100 kW. The USA became the largest producer of small wind turbines. The American Wind Energy Association (AWEA) has made a compilation of companies manufacturing and selling wind turbines for residential applications, industrial/commercial and farms use. Small wind turbines produced in the USA are currently employed in over 140 countries. For example, the most popular product of the company Bergey Windpower Co. - Bergey Excel-S 10 kW turbine, have a cost of 21450 USD [5]. The leaders in the production of small wind turbines are: Gazelle Wind Turbines Ltd, UK [6]; Iskra Wind Turbine Manufacturers Ltd [7]; WestWind, J.A. Graham Renewable Energy Services [8]; TairuiWindpower CO [9] and Hefei Hummer Dynamo CO, Ltd in China [10].

502

V. Bostan et al.

2 Characteristics and Parameters of the Wind Energy Wind serves as “fuel” for wind power plants. Taking into account that the wind power density is proportional to the cube of the wind speed it is very important to know the wind energy resources over the whole country, the wind sources of the region and the site where possibly the wind power plant will be built. Typically, the wind energy resources are explained by two main characteristics of the wind - the wind speed and its power density, which determines the wind energy potential of the location. For policy makers at central level, it is important to know the wind energy resources for strategic planning; in this regard the following questions should be answered [11]: • What are the wind energy resources and how are they spread across the regions? • What is the share from the total electricity consumption that can be covered by the wind energy? • How can we exploit this potential? At the local level or for an investor in the wind energy at the initial stage of implementing a project, it is important to know the answers to the following questions: • What is the wind energy potential on a certain site? • How much electricity will be produced in one year by a turbine with specified technical characteristics? • What will the cost price of wind power be? • What is the period of return on investments? • What is the annual and diurnal variation of the wind speed, and respectively, of the wind power density? The correct answers can be obtained as a result of measurements of wind characteristics at the given site at the height of the turbine axis of rotation for a minimum of one year period. But this way is expensive and requires a long period of time. Countries with a high degree of wind energy use have chosen a different way computer modelling of the wind speed for large areas, using special software that would consider the orography and the land surface characteristics, the obstacles, etc. In these models, the so-called historical wind data are applied collected from the weather stations across the country or region. As a result, the Wind Atlas (WA) is developed, which includes information about the speed and wind power density in the form of a contour or graded map. The Wind Atlas can be produced at a global, country or region level, but it does not substitute the need for instrumental measurements; it only identifies the region where to focus investigations and to indicate the location where necessary to perform the measurements. At the next phase of investigations, a virtual wind turbine with known technical characteristics may be located in a certain geographical point and, using the WA data, it can determine the amount of electricity that can be produced in a certain period - a month or a year, etc. Obviously, there are constraints that limit or make it difficult to use mathematical models to estimate the wind energy resources. First of all, we refer to the availability of reliable primary data on wind and digital topographic maps for the

Development of a Horizontal Axis Wind Turbine

503

Fig. 1. An example of wind variation for 24 h

scale required. No less important is the availability of wind data measurement characteristics - speed and direction, carried out at least 50 m height above the ground in order to validate the results obtained by calculation. The wind speed and direction are the main characteristics of wind for a certain location. At meteorological stations the wind speed is measured by cup anemometers, which are also fitted with wind vanes to determine the wind direction. According to the standards, the wind speeds have been obtained as a result of every three hours records, respectively, at 0, 3, 6, 9, 12, 15, 18, 21 o’clock. The wind speed for each three hours interval is considered the average fixed velocity for an interval of 10 min, i.e. between 000–010, 300–310, etc. The weather stations measure wind characteristics at a height of 10–12 m above the ground. The wind is characterized by a pronounced change in both its speed and direction and, in order to obtain accurate information, the primary data for a minimum period of 10 years is necessary. Figure 1 shows an example of the variation in the wind speed over a period of 24 h, at a height of 50 m above the ground. The diagram shows the processed results of the wind speed collected every 3 s. As a result of the speed measurement, the average speed over a period of time equal to 10 min (the arithmetic average of 200 measurements) is considered. Thus, we will have 144 results in 24 h. We state that the average wind speed for 10 min intervals varies in 24 h from 0 to 8.71 m/s. Obviously, we can determine the average speed for an interval bigger than 10 min, for example, for an hour, a day, a month or even for a year. But the information about the average wind speed for a certain interval is not sufficient to consider the potential of the wind energy. To demonstrate this assertion, we calculate the average wind power density for the above example, i.e. for a period of 24 h. Average Wind Power Density. It is measured in W/m2 and characterizes the wind energy potential of the location. Average arithmetic speed in the example above, within

504

V. Bostan et al.

24 h is equal to 4.49 m/s (see the line parallel with x-axis in Fig. 1). Then the average wind power density will be:
P ¼ 0:5qV 3 ¼ 0:5
1:225
4:493 ¼ 54:5W m2

ð1Þ

where q is the air (atmospheric) density; V is the average wind velocity. But the wind velocity is a variate and it should be characterised in terms of probability theory. Such a term is the probability density function of the wind velocity, F (V), which is defined as the fraction of time for which the average wind velocity falls within a specified interval ΔVi. In other words, the probability density function of the wind velocity characterizes the share of velocity in the range of Vmin and Vmax obtained during the measurements. To determine the probability density function of the wind velocity for the example above (Fig. 1), let us proceed as follows: • The velocity variation range during the measurements is determined. In our case Vmin = 0.0 and Vmax = 8.71 m/s; • The velocity variation range is divided into n equal intervals, usually between 0.1 and 1.0 m/s. It was chosen ΔVi = 1.0 m/s. The speed of calculation for each period is equal to the average velocity. For example, within the interval 6 velocities between 5 and 6 m/s are enclosed, the average speed of calculation is considered equal to 5.5 m/s; By considering the probabilistic nature of the wind velocity, the power density is calculated by formula p ¼ 0:5q

X9 k¼0

Vi3 F ðVi Þ ¼ 83:9W=m2

ð2Þ

and is 54% higher than the power density calculated above, using only the average wind velocity for 24 h. The largest rate of power density belongs to the velocity range between 6 and 7 m/s and is 35.5%. However, the highest rate of velocity belongs to the speed range between 3 and 4 m/s. Modern turbine start-up speed is equal to or bigger than 4 m/s. It results that, for the analysed period (24 h), the lucrative velocities duration (  4 m/s) is about 60%. Turbulence. It refers to fluctuations in the wind velocities over a short period of time, usually less than 10 min. Turbulence is caused by two phenomena: first, the friction between the airflow and the Earth surface, often magnified by topographical features, such as valleys, hills and mountains; the second is related to thermal effects which cause vertical movement of air masses. Turbulence has a negative influence on the turbine rotor, as mechanical stress caused by short gusts of wind increases, the material from which the propeller is made exhausts and it may fail. Simultaneously with height increasing, the turbulence is reduced. One of the indicators characterizing the turbulence is turbulence intensity defined as the ratio of standard deviation r and the average velocity for a period of time equal to or less than 10 min. Figure 2 presents the variation of turbulence intensity for a period equal to 24 h. The smaller is the average velocity for a 10 min period, the bigger is the intensity of

Development of a Horizontal Axis Wind Turbine

505

Fig. 2. Variation of wind velocity and turbulence intensity: period of observations - 24 h; number of measurements - 144

turbulence. To draw conclusions about the turbulence it is necessary to have the results of wind velocity measurements for less than 10 min for periods of 10 years, at least. Extreme Winds. Wind turbines must be designed so as to withstand the extreme winds or gusts of wind. If the wind velocity is bigger than 25 m/s the wind turbine is broken or taken out from under the wind action.

3 Small Power Wind Turbines Designed at the Technical University of Moldova Small wind turbines should be mostly robust and simple, have maximal resistance and little maintenance, and optimal wind energy conversion efficiency. Given the topical interest and relatively high costs of imported wind turbines, a team of authors developed two types of small power wind turbines. The wind turbines with servo motors have the ability to track wind direction and remove the bladed rotor out of the wind action at wind speeds exceeding 15–25 m/s. The advantages of these turbines compared to vane wind turbines are: • angular positioning stability of the bladed rotor at dynamic fluctuations of air currents direction; • bladed rotor protection from overloads, caused by wind speeds exceeding the highest allowed values.

3.1

Wind Turbine with Mechanical Orientation to Wind Direction

Based on the study of wind energy potential and specific orographic terrain surface of Moldova, characterized mainly by gorges oriented along North-South direction, the

506

V. Bostan et al.

authors developed the concept of a three-bladed rotor with asymmetric aerodynamic profile. Theoretical research on the developed rotor was carried out using modern software ANSYS CFX5.7 and Autodesk Motion Inventor. As a result, the basic parameters of the aerodynamic profile characterizing the efficiency of wind energy conversion by the rotor blades were determined. Taking into account that across the gorges the wind prevails on North-South direction with minor fluctuations, the authors have designed a prototype wind turbine facing the wind by means of a windrose wheel. This turbine has a simple construction and requires neither kinematic wind guidance devices nor devices for the protection of turbine rotor from the excessive wind action. Construction simplicity of the wind turbine with vane leads to about 20–30% cost reduction compared to turbines with servo motors. The choice of three blade rotor scheme provides a greater dynamic stability, minimizing related vibrations and sonic background, thus resulting a longer life period of all components. Direct connection of the rotor to the generator ensures rotor start up at lower wind speeds, production of a larger amount of energy, requires less demanding maintenance compared to turbine multiplier case. Specially designed permanent magnet generator combines efficiency with the simplicity of construction. Figure 3 shows a wind turbine with mechanical orientation to wind, developed by a team of authors [12]. Both wind direction rotor orientation and its removal out of the action of air currents is done by means windrose wheels 21 which performs the kinematical liaison of gondola 5 with tower (Figs. 3 and 4). When the wind direction is changed the windrose wheels performs an angular re-positioning of gondola 5. Overloading protection of turbine is realised by swinging the rotor against the horizontal plane by means hydraulic cylinder 15 and mechanical transmission 20.

3.2

Permanent Magnet Eddy Current Heater for Wind Energy Conversion

In Moldova is reasonable to convert wind mechanical energy direct into heat using Joule machine or permanent magnet eddy current heater. In the 3…50 kW power range, i.e. rotation speed 400…100 rpm, is appropriate to use the eddy current heater. The power generated by permanent magnet eddy current heater is proportional to the square root of the cubic of rotational speed. Heater efficiency exceeds 90%. The direct method to convert wind energy into heat is based on the principle of the Joule machine [13]. A heater based on this principle is a mixer installed into a tank filled with heat transfer liquid. Due to friction among molecules of the mixing liquid, mechanical energy is converted into heat energy. The heated liquid then transfers heat to a heating system. The main advantages are: simple construction, available and inexpensive materials, the characteristic P(n) of the heater is a cubic function and ideally corresponds to similar characteristics of the wind turbine for different wind speeds. At the same time, the heater, whose operation is based on the use of friction forces, has a critical drawback - the exploitation period is small, the density of the thermal power generated will be 4…6 times smaller than for the eddy current heater.

Development of a Horizontal Axis Wind Turbine

507

Fig. 3. (a) Rotor orientation systems with windrose and (b) overloading protection by swinging the rotor against the horizontal plane

The disadvantages listed above are excluded from the permanent magnet eddy current heater. Here, the frictional forces disappear, respectively, disappear the pieces which are subject to mechanical stress; the heat is generated by eddy currents induced in a solid conductor material due to the effect of electromagnetic induction. Figure 5a shows the wind driven eddy current heater according to the invention UK2207739, 1989. The heater comprises a magnet (1) mounted on the rotating shaft (2), which is driven by wind turbine. As the magnet rotates inside the solid iron cylinder (3) all the available wind energy is converted to heat in the cylinder due to the generated eddy currents. The cold water to be heated enters in the water jacket (4) through the right side inlet and hot water leaves from the left side outlet. A prototype (Fig. 5) of permanent magnet eddy current heater has been recently realized by Electromechanical and Metrology Department and several tests are carried out. Compared to permanent magnet electric generator, the eddy current heater contains

508

V. Bostan et al.

Fig. 4. (a) Assembling process, (b) wind turbine with mechanical orientation to wind and (c) wind rotor with windrose wheel

no copper windings, no electrical insulation, and no electrical sheet steel. As a result the cost decreases, and the conversion efficiency of wind energy into heat increases. To ensure an intensive transfer of heat from massive steel, the armature comprises a special maze, which makes the water flow to be turbulent. Efficiency was determined for the constant rotational speed of 400 rpm. Thermal power was measured with multifunctional thermal energy meter and for verification it was calculated using the relation

Development of a Horizontal Axis Wind Turbine

509

Fig. 5. (a) A diagram of permanent magnet eddy current heater and (b) permanent magnet eddy current heater prototype

P¼

mCW ðTT  TR Þ t

ð3Þ

where: m is the average water mass, [kg], flowing through the heater during period of time t; CW = 4.173  103 J/°C kg is the heat capacity of water; TT - water temperature in the tour circuit; TR - water temperature in the retour circuit. To determine the average water mass it was measured the pump flow, Q, [L/h], and it was calculated using the relation m¼

Q t 60

ð4Þ

The difference between the value measured by multifunctional thermal energy meter and the calculated one, using relation (1) does not exceed 5.1%. The wind turbine project, developed by authors, was implemented at the Scientific Technical Centre for Implementation of Advanced Technologies at the Technical University of Moldova in cooperation with companies INCOMAS SA, Chişinău, ELECTROMAŞ SA, Tiraspol, Reupies SRL and SA Topaz from Chişinău etc. Figure 4a presents the assembling stage of the component of the wind turbine. The team developed the manufacturing technology for blades and gondola parts from composite material reinforced with glass fibre. The rotor blades and gondola cone were made of composite materials in the Laboratory of New Technologies within the Centre for Renewable Energy Conversion Systems Development (CRECSD), Technical University of Moldova. The wind turbines with servo motor, shown in Fig. 4, are installed at the Râşcani campus of the Technical University of Moldova and is designed for lighting and irrigation system of the adjacent dendrologic park.

510

V. Bostan et al.

4 Conclusion The Vindros wheel system provides rotor orientation to the wind direction and overloading protection without mechatronic systems. by swinging the rotor against the horizontal plane. Consumer prices and state policies are the most important components in supporting and developing the small power wind turbine market. Geopolitical, climate and economic forces shall further increase the market demands.

References 1. Piebalgs, A.: Wind energy for future. Mesagerul Energ. J. 66, 14–16 (2007) 2. Wind energy: the facts. An analysis of wind energy in the EU-25. http://www.ewea.org/ index.php?id=91. Accessed June 2017 3. Wu, G.: Wind matters: China’s role in the future of wind. Goldwind (2015). http://www. worldwindconf.net/wp-content/uploads/2015/11/Wu-Gang.pdf. Accessed June 2017 4. AWEA Small Wind Turbine Global Market Study. American Wind Energy Association 5. http://www.bergey.com. Accessed June 2017 6. https://www.edie.net/8832/d/Gazelle-Wind-Turbines-Ltd. Accessed June 2017 7. http://www.iskrawind.com. Accessed June 2017 8. Westwind wind turbines. Information pack. http://www.enviko.com/pdf/Westwind%20Broc hure.pdf. Accessed June 2017 9. Home wind turbine- wholesale suppliers. http://www1.nb-tairui.com. Accessed June 2017 10. Humer wind generator. https://manualzz.com/doc/7265895/manual-wind. Accessed June 2017 11. Bostan, I., Gheorghe, A., Dulgheru, V., Sobor, I., Bostan, V., Sochirean, A.: Resilient Energy Systems. Renewables: Wind, Solar, Hydro. VIII, p. 507. Springer (2013). ISBN 978-94-007-4188-1 12. Bostan, I., Dulgheru, V., Bostan, V., Sobor, I., Sochirean, A.: Wind turbine with horizontal axis. Patent MD 4219, BOPI nr. 4/2013 (2013) 13. Chakirov, R., Vagapov, Y.: Direct conversion of wind energy into heat using joule machine. In: International Conference on Environmental and Computer Science IPCBEE, 19, IACSIT Press, Singapore, pp. 12–16 (2011)

Solar Energy for Water Re-use

Sustainable Autonomous System for Nitrites/Nitrates and Heavy Metals Monitoring of Natural Water Sources (WaterSafe) Mariuca Gartner1(&), Carmen Moldovan2, Marin Gheorghe3, Anca Duta4, Miklos Fried5,6, and Ferenc Vonderviszt7 1

Institute of Physical Chemistry, “Ilie Murgulescu” of the Romanian Academy, Bucharest, Romania [email protected] 2 National Institute for Research and Development in Microtechnologies, 077190 Bucharest, Voluntari, Romania 3 NANOM MEMS SRL, Râșnov, Romania 4 Transilvania University of Brasov, Brașov, Romania 5 Institute for Technical Physics and Materials Science, Centre for Energy Research (MFA), Budapest, Hungary 6 Institute of Microelectronics and Technology, Óbuda University, Budapest, Hungary 7 Research Institute of Biomolecular and Chemical Engineering, University of Pannonia, Veszprém, Hungary

Abstract. The project sets to develop a new energy autonomous system based on electrochemical sensors for detection of different ionic species in natural water sources and ultra-thin solar cells (UTSC). It focuses on three directions: high efficiency, new materials in solar energy harvesting and fabrication of small UTSC and the power stabilizing device able to supply the needed voltage to the sensors and electronic module; new microsensors for detection of nitrites/ nitrates and heavy metals in water; low cost autonomous energy system integration and fabrication. The harvester will include a UTSC ( TODA > DTAB > PEG > PVP, suggesting different stabilization mechanisms. These consider the types and strength of the interactions developed by the stabilizers molecules with the particle surface functional groups, forming architectural structures with different stabilities, depending on the particle surface charge in the

Design and Development of TiO2 Based Dispersions for Photocatalytic Fabrics

541

Fig. 13. Stability of Degussa P25 and u.s sol-gel TiO2 dispersions

working conditions (pH, continuous medium composition). Changes in the particle double layer thickness and charge are expected in the alcohol presence and due to the stabilizer adsorption. Depending on the dispersion composition (concentration, additives, and continuous medium) electrostatic, steric or combined stabilization mechanisms may occur. The particle size and the dimensional homogeneity is also critical for dispersion stability. At the working pH (pH < PZC, as previously presented [16, 35]), titania surface is positively charged, thus electrostatic interactions with charged stabilizer molecules are likely. In the DTAB stabilized dispersions, considering the positive charge of both titania particles surface and surfactant, van der Waals/London dispersion forces are developed. This leads to a nonpolar physical adsorption of the DTAB molecules onto the titania particles, leaving the positive heads oriented to the solvent. As consequence, electrostatic repulsions between stabilized particles, but also steric hindrances (that may occur at pH close to the PZC), prevent particles agglomeration. When using the nonionic PEG surfactant, typical steric stabilization occurs by physical adsorption via hydrogen bonding, forming complexes between O from ethylene oxide groups and the hydroxyl groups on the TiO2 surface [23, 34]. Similar mechanism is followed by PVP as previously described [16]. In the case of TODA stabilized dispersions, anchoring mechanism occurs, via strong and complex interactions between the TODA carboxyl and carbonyl groups and the titania surface (oxygen or hydrogen from the hydroxyl groups) [32]. The higher stability is supported by strong repulsions between the capped particles. Electrosteric stabilization was reported in TiO2 dispersions prepared with chitosan. The adsorption of long-chain chitosan molecules on the dispersed particles via hydrogen bond between its polar groups and TiO2 hydroxyl surface creates energetic barriers against aggregation. These are accompanied by strong repulsions between the stabilized particles due to the presence of NH3þ on the adsorbed chain, leading to highly stable dispersions, as observed. It was reported that even after agglomeration, titania-chitosan dispersion could be easily re-dispersed under mixing or ultra-sonication [12]. Similar electrosteric mechanism is expected in the PAA stabilized dispersions. The lower stability compared to chitosan can be explained considering the influence of pH (almost neutral in the working condition, Table 4) on the polymer conformation

542

C. Bogatu et al.

and ionization degree, leading to weaker electrostatic repulsion between the particle. Bridging flocculation is also possible to occur depending on the polymer concentration [18, 34]. In conclusion, chitosan and TODA are the best stabilizers and can be recommended as stabilizing agents for TiO2 based dispersions. Competitive results are also obtained when DTAB and PEG are used. In practical applications, including photocatalysis based titania dispersions, preserving particles photocatalytic activity in the stabilized dispersions is a critical requirement. The adsorption of stabilizers at the particle surface by strong interactions, favorable in the stabilization, may negatively affect the photocatalytic activity. In our recently reported studies [16] the photocatalytic activity of selected stabilized dispersions was evaluated using MB 4 ppm as test pollutant and simulated solar radiation (85% VIS and 15% UV). The process efficiency (removal, adsorption, and photocatalysis) after 6 h of irradiation for the investigated dispersions are comparatively presented in Fig. 14.

Fig. 14. Photocatalytic efficiency of Degussa P25 and u.s sol-gel TiO2 dispersions [16] (MB photocatalysis = MB removal − MB adsorption for 1 h in dark conditions)

The reported results show that more efficient MB removal/photodegradation occurs on Degussa P25 dispersions (code “D”), but competitive values are obtained for the PEG stabilized dispersions. This is mainly related to specific surface properties of the two types of investigated photocatalysts. The lower adsorption and removal efficiencies reported for the most stable dispersions prepared with TODA can be explained considering the strong anchoring of TODA molecules on the TiO2 particle, partially blocking the available surface active centres in the process [16]. On the other hand, despite the lower stability compared to DTAB and TODA dispersions, PEG stabilized dispersions provide the best photocatalytic activity. The favourable effect in photocatalysis of PEG is in agreement with other the literature data [55]. Thus, in the development of TiO2 dispersions for photocatalytic fabrics, the type and amount of stabilizers must be optimized with a compromise between the dispersion stability and functionality.

Design and Development of TiO2 Based Dispersions for Photocatalytic Fabrics

543

The most stable dispersions prepared with chitosan, TODA, DTAB and the more photocatalytically active PEG stabilized dispersion were further used for deposition onto fabrics.

4 Photocatalytic Fabrics A sustainable, versatile, technique with very good control of the parameter over deposition, suitable for photocatalytic dispersion deposition is room temperature spraying. Through a carefully control of the deposition parameters including carrier gas pressure, deposition temperature, the break between sequences, the number of deposited layer, thin films with controlled morphology and surface properties adapted to different application can be obtained. In this study the optimized TiO2 dispersions were sprayed on commercial woven cotton fabrics by using previously optimized deposition parameters: 10–30 spraying sequences, 300 s break between the sequences, temperature T = 50 °C, 1.2 bar carrier gas pressure (air). The investigated samples of coated fabrics were nominated by using the dispersion code followed by the number of deposited sequences. A high photocatalytic activity and good stability/durability are critical requirements in the selection of photocatalytic fabrics for practical applications. The photocatalytic properties of the coated fabrics deposited from dispersion based US1.5 h TiO2 powders were tested considering methylene blue as reference pollutant dye. The photodegradation efficiencies are compared with previously reported results [16] in Fig. 15. The titanium dioxide thin film deposited on the highly hydrophilic cotton substrate is favored by its loose structures. The embedment of particles between and around the fibers is allowed, resulting in large available active surface with active sites that can be involved in the adsorption “the shadowed active sites” (parts of the substrate with

Fig. 15. Photocatalytic efficiency of coated fabrics obtained by RT spraying of Degussa P25 and u.s sol-gel TiO2 dispersions, (MB photocatalysis = MB removal − MB adsorption)

544

C. Bogatu et al.

Fig. 16. Stability of the coated fabrics based TiO2 (Degussa P25 and u.s. sol-gel) dispersions

nanoparticles inserted in the fabric that are not directly exposed to irradiation) or/and photocatalysis (under irradiation). Additionally, the migration of adsorbed MB molecules through the large surface voids towards the irradiated active sites significantly improves the removal efficiency. Thus, all samples exhibit good removal/photocatalytic efficiencies, with better results for the coated fabrics deposited from dispersions based u.s. sol-gel TiO2 powders obtained at 1.5 h of ultra-sonication. The results are in agreement with the highest photocatalytic activity of the US1.5 h powder as previously presented. By increasing the number of sequences (20, 30 sequences) for the deposition process, larger amounts of photocatalytic material remains on the fibers leading to an increase in the available active sites exposed to irradiation as compared to the shadowed ones. Consequently, higher amount of pollutant is photodegraded as the increase of MB photocatalysis efficiency for samples sprayed with 20 or 30 sequences show, while lower adsorption is registered for the 10 sequences deposited samples. For the less covered samples, deposited with 10 sequences, larger amount of MB molecules are bonded to the coated fabrics, increasing the adsorption efficiency. This is in agreement with recently reported results [7]. Therefore, a number of 20 sequences is recommended for the deposition of photocatalytic fabrics. Related to the influence of the stabilizers on the photocatalytic process, a positive effect of PEG on the MB removal is confirmed, while TODA, DTAB, more efficient stabilizers may partially clog the photocatalyst surface, leading to lower process efficiencies [16, 35]. Similar effects of dispersion stabilizers on the decomposition of mustard gas (HD) on TiO2 coated fabrics were observed, as previously reported [35]. Photocatalytic fabrics deposited from PEG stabilized dispersions exhibit removal efficiency higher than 90% after 10 min of UV irradiation under water aerosols. Promising, competitive results were obtained for the new photocatalytic fabrics deposited from the highly stable dispersions prepared with chitosan. The stability of the photocatalytic fabrics was investigated by monitoring the conductivity, the total dissolved solids (TDS) and pH of the resulted waters after samples immersion for 72 h. The variation of conductivity for selected photocatalytic fabrics is presented in Fig. 16.

Design and Development of TiO2 Based Dispersions for Photocatalytic Fabrics

545

The values indicate a slow variation of the conductivity, but no significant modifications are observed after 72 h of immersion. Similar trend was found for the TDS variation too. This corresponds to good stabilities in time of the deposited TiO2 thin film indicating strong interactions of the TiO2 nanoparticles with the hydrophilic cotton fabric. Slightly better results correspond to the samples deposited using DTAB stabilized dispersions compared to the coated fabrics obtained with PEG or chitosan additive. Considering the results on the stability and photocatalytic activity of both TiO2 based dispersions and coated fabrics, it can be concluded that chitosan and PEG meet better the compromise regarding the stability and functionality of photocatalytic fabrics required in practical applications.

5 Conclusions The results obtained in the development of photocatalytic fabrics with TiO2 were detailed presented following the concept “from material to product”. The corresponding steps in the photocatalytic fabrics design and development were identified and the critical related issues were outlined and discussed; recommendations were formulated for each stage, as it follows: • Design and development of the photocatalytic particles: the ultrasound assisted sol-gel method with an accurate control of the ultra-sonication duration was outlined as suitable for the synthesis of TiO2 particles with optimized properties in terms of size, structural and surface properties (charge and photocatalytic activity) adapted to the application. The sample, US_1.5h, obtained at 1.5 h ultra-sonication best meet these requirements; • Design and development of the photocatalytic dispersions considering as key properties: the dispersion stability (evaluated based on transmittance spectra, DT30) and the photocatalytic properties. Chitosan was identified as the best stabilizers (DT30 = 15%) followed by TODA, and DTAB for aqueous or slightly alcoholic dispersion based on optimized u.s. sol-gel TiO2 powders, while dispersion stabilized with the less efficient PEG best preserve the photocatalytic activity of the dispersed particles; • Design and development of the photocatalytic fabrics by room temperature spraying of the stabilized dispersions on fabrics. The photocatalytic activity and the stability of the coated fabrics were set as selection criteria for practical applications. It was outlined that a compromise must be accepted between the photocatalytic activity, the fabrics functionality and the dispersion stability. Chitosan and PEG stabilizers were selected, as TODA, DTAB better stabilizers compared to PEG may hinder the photocatalytic activity of the coated fabrics. The development of photocatalytic fabrics by room temperature spraying of dispersion based on u.s. sol-gel TiO2, stabilized with chitosan and PEG represent a viable and sustainable solution for applications involving photocatalysis (wastewater treatment, self-cleaning fabrics) in nZEC communities as it uses low energy intensive synthesis method/techniques for both powders and coated fabrics and environmentally friendly materials, solvents and additive.

546

C. Bogatu et al.

Acknowledgments. We hereby acknowledge the project CBPhotoDeg, 282/2014, for providing the founds that supported this work and the project PRO-DD (POS-CCE, O.2.2.1, ID 123, SMIS 2637, No 11/2009) for providing the infrastructure used in this work.

References 1. Malato, S., Fernandez-Ibanez, P., Maldonado, M.I., Blanco, J., Gernjak, W.: Decontamination and disinfection of water by solar photocatalysis: recent overview and trends. Catal. Today 147, 1–59 (2009). http://dx.doi.org/:10.1016/j.cattod.2009.06.018 2. Fujishima, A., Rao, T.N., Tryk, D.A.: Titanium dioxide photocatalysis. J. Photochem. Photobiol. C: Photochem. Rev. 1, 1–21 (2000). https://doi.org/10.1016/S1389-5567(00)00002-2 3. Wang, Y., He, Y., Lai, Q., Fan, M.: Review of the progress in preparing nano TiO2: An important environmental engineering material. J. Environ. Sci. 26, 2139–2177 (2014). https://doi.org/10.1016/j.jes.2014.09.023 4. Han, Z., Chang, V.V.C., Zhang, L., Tse, M.S., Tan, O.K., Hildeman, L.M.: Preparation of TiO2 coated fiber filters by sopray coating and its photocatalytic degradation of gaseous formaldehyde. Aerosol Air Qual. Res. 12, 1327–1335 (2012). http://dx.doi.org/10.4209/ aaqr.2012.05.0114 5. Choi, H., Stathatos, E., Dionysiou, D.D.: Synthesis of nanocrystalline photocatalytic TiO2 thin films and particle using sol-gel method modified with nonionic surfactants. Thin Solid Films 510, 107–114 (2006). https://doi.org/10.1016/j.tsf.2005.12.217 6. Pasqui, D., Barbucci, R.: Synthesis, characterization and self- cleaning properties of titania nanoparticles grafted on polyester fabrics. J. Photochem. Photobiol. A: Chem. 274, 1–6 (2014). http://dx.doi.org/10.1016/j.jphotochem.2013.08.017 7. Frunza, L., Diamandescu, L., Zgura, I., Frunza, S., Ganea, C.P., Negrila, C.C., Enculescu, M., Birzu, M.: Photocatalytic activity of wool fabrics deposited at low temperature with ZnO or TiO2 nanoparticles: methylene blue degradation as a test reaction. Catal. Today (2017, in press). https://doi.org/10.1016/j.cattod.2017.02.044 8. Radetić, M.: Functionalization of textile materials with TiO2 nanoparticles. J. Photochem. Photobiol. C: Photochem. Rev. 16, 62–76 (2013). http://dx.doi.org/10.1016/j.jphotochemrev. 2013.04.002 9. Ortelli, S., Blosi, M., Albonetti, S., Vaccari, A., Dondi, M., Costa, A.L.: TiO2 based nano-photocatalysis immobilized on cellulose substrates. J. Photochem. Photobiol. A: Chem. 276, 58–64 (2014). http://dx.doi.org/10.1016/j.jphotochem.2013.11.013 10. Selishchev, D.S., Karaseva, I.P., Uvaev, V.V., Kozlov, D.V., Parmon, V.N.: Effect of preparation method of functionalized textile materials on their photocatalytic activity and stability under UV irradiation. Chem. Eng. J. 224, 114–120 (2013). http://dx.doi.org/10. 1016/j.cej.2012.12.003 11. Landi Jr., S., Carneiro, J., Ferdov, S., Fonseca, A.M, Neves, I.C., Ferreira, M., Parpot, P. Soares, O., Pereira, M.: Photocatalytic degradation of Rhodamine B dye by cotton textile coated with SiO2-TiO2 and SiO2-TiO2-HYcomposites. J. Photochem. Photobiol. A: Chem. (2017, accepted manuscript). http://dx.doi.org/doi:10.1016/j.jphotochem.2017.05.047 12. Goyal, N., Rastogi, D., Manjeet, J., Agrawal, A.K.: Chitosan as a potential stabilizing agent for titania nanoparticle dispersions for preparation of multifunctional cotton fabric. Carbohyd. Polym. 154, 167–175 (2016). http://dx.doi.org/10.1016/j.carbpol.2016.08.035 13. Grandcolas, M., Sinault, L., Mosset, F., Louvet, A., Keller, N., Keller, V.: Self-decontaminating layer-by-layer functionalized textiles based on WO3-modified titanate nanotubes. Application to the solar photocatalytic removal of chemical warfare agents. Appl. Catal. A: General 391, 455–467 (2011). doi:10.1016/j.apcata.2010.05.028

Design and Development of TiO2 Based Dispersions for Photocatalytic Fabrics

547

14. Yuranova, T., Laub, D., Kiwi, J.: Synthesis, activity and characterization of textiles showing self-cleaning activity under daylight irradiation. Catal. Today 122, 109–117 (2007). doi:10. 1016/j.cattod.2007.01.040 15. Fasaki, I., Siamos, K., Arin, M., Lommens, P., Van Driessche, I., Hopkins, S.C., Glowacki, B.A., Arabatzis, I.: Ultrasound assited preparation of stable water-based nanocrystalline TiO2 suspensions for photocatalytic applications of ink-jet printed films. Appl. Catal. A 411–412, 60–69 (2012). https://doi.org/10.1016/j.apcata.2011.10.020 16. Bogatu, C., Perniu, D., Duta, A.: Challenges in developing photocatalytic inks. Powder Technol. 287, 82–89 (2016). http://dx.doi.org/10.1016/j.powtec.2015.09.018 17. Fagan, R., McCormack, D., Dionysiou, D.D., Pillai, S.C.: A review of solar and visible light active TiO2 photocatalysis for treating bacteria, cyatoxins and contaminants of emerging concern. Mater. Sci. Semicond. Process. 42, 2–14 (2016). http://dx.doi.org/10.1016/j.mssp. 2015.07.052 18. Karakas, F., Celik, M.S.: Mechanism of TiO2 stabilisation by low weight NaPAA in reference to water-borne paint suspensions. Colloids Surf. A 434, 185–193 (2013). https:// doi.org/10.1016/j.colsurfa.2013.05.051 19. Witharana, S., Palabiyik, I., Musina, Z., Ding, Y.: Stability of glycol nanofluids - the theory and experiment. Powder Technol. 239, 72–77 (2013). https://doi.org/10.1016/j.powtec.2013. 01.039 20. Tkachenko, N.H., Yaremko, Z.M., Bellmann, C., Soltys, M.: The influence of ionic and non-ionic surfactants on aggregative stability and electrical surface properties of aqueous suspensions of titanium dioxide. J. Colloid Interface Sci. 299, 686–695 (2006). https://doi. org/10.1016/j.jcis.2006.03.008 21. Farrrokhi-rad, M., Ghorbani, M.: Stability of titania nano-particles in different alcohols. Ceram. Int. 38, 3893–3900 (2012). https://doi.org/10.1016/j.ceramint.2012.01.04 22. Guiot, C., Spalla, O.: Stabilization of TiO2 nanoparticles in complex medium through a pH adjustment protocol. Environ. Sci. Technol. 47, 1057–1064 (2013). doi:10.1021/es3040736 23. Fazio, S., Guzman, J., Colomer, M.T., Salomoni, A., Moreno, R.: Coloidal stability of nanosized titania aqueous suspensions. J. Eur. Ceram. Soc. 28, 2171–2176 (2008). https:// doi.org/10.1016/j.jeurceramsoc.2008.02.017 24. Sahu, M., Suttiponparnit, K., Suvachittanont, S., Charinpanitkul, T., Biwas, P.: Characterization of doped TiO2 nanoparticles dispersions. Chem. Eng. Sci. 66, 3482–3490 (2011). https://doi.org/10.1016/j.ces.2011.04.003 25. Suttiponparnit, K., Jiang, J., Sahu, M., Suvachittanont, S., Charinpanitkul, T., Biswas, P.: Role of surface area, primary particle size, and crystal phase on titanium dioxide nanoparticle dispersion properties. Nanoscale Res. Lett. 6, 27 (2011). doi:10.1007/s11671-010-9772-1 26. Neppolian, B., Wang, Q., Jung, H., Choi, H.: Ultrasonic-assisted sol-gel method of preparation of TiO2 nano-particles: characterization, properties and 4-chlorophenol removal application. Ultrason. Sonochem. 15, 649–658 (2008). https://doi.org/10.1016/j.ultsonch. 2007.09.014 27. Prasad, K., Pinjari, D.V., Pandit, A.B., Mhaske, S.T.: Phase transformation of nanostructured titanium dioxide from anatase-to-rutile via combined ultrasound assisted sol-gel technique. Ultrason. Sonochem. 17, 409–415 (2010). https://doi.org/10.1016/j.ultsonch. 2009.09.003 28. Prasad, K., Pinjari, D.V., Pandit, A.B., Mhaske, S.T.: Synthesis of titanium dioxide by ultrasound assisted sol-gel technique: effect of amplitude (power density) variation. Ultrason. Sonochem. 17, 697–703 (2010). https://doi.org/10.1016/j.ultsonch.2010.01.005 29. Pinjari, D.V., Prasad, K., Gogate, P.R., Mhaske, S.T., Pandit, A.B.: Synthesis of titanium dioxide by ultrasound assisted sol-gel technique: effect of calcination and sonication time. Ultrason. Sonochem. 23, 185–191 (2015). https://doi.org/10.1016/j.ultsonch.2014.10.017

548

C. Bogatu et al.

30. Singh, B.P., Nayak Samal, S., Bhatttacharjee, S., Besra, L.: The role of poly (methacrylic acid) conformation on dispersion behaviour of nano TiO2 powder. Appl. Surf. Sci. 258, 3524–3531 (2012). https://doi.org/10.1016/j.apsusc.2011.11.107 31. Garnweiter, G., Ghareeb, H.O., Grote, C.: Small-molecule in situ stabilization of TiO2 nanoparticles for the facile preparation of stable colloidal dispersions. Colloids Surf. A 372, 41–47 (2010). https://doi.org/10.1016/j.colsurfa.2010.09.024 32. Bosch-Jimenez, P., Yu, Y., Lira-Cantu, M., Domingo, C., Ayllón, J.: Solution processable titanium dioxide precursor and nanoparticulated ink: application in dye sensitized solar cells. J. Colloid Interface Sci. 416, 112–118 (2014). https://doi.org/10.1016/j.jcis.2013.11.013 33. Tkachenko, N.H., Yaremko, Z.M., Bellmann, C., Soltys, M.: The influence of ionic and non-ionic surfactants on aggregative stability and electrical surface properties of aqueous suspensions of titanium dioxide. J. Colloid Interface Sci. 299, 686–695 (2006). https://doi. org/10.1016/j.jcis.2006.03.008 34. Farrokhpay, S.: A review of polymeric dispersant stabilisation of titania pigment. Adv. Coll. Interface. Sci. 151, 24–32 (2009). https://doi.org/10.1016/j.cis.2009.07.004 35. Bogatu, C., Perniu, D., Sau, C., Iorga, O., Cosnita, M., Duta, A.: Ultrasound assisted sol-gel TiO2 powders and thin films for photocatalytic removal of toxic pollutants. Ceram. Int. 43, 7963–7969 (2017). https://doi.org/10.1016/j.ceramint.2017.03.054 36. Liao, D.L., Wu, G.S., Liao, B.Q.: Zeta potential of shape-controlled TiO2 nanoparticles with surfactants. Colloids Surf. A 348, 270–275 (2009). https://doi.org/10.1016/j.colsurfa.2009. 07.036 37. Nakata, K., Fujishima, A.: TiO2 photocatalysis: design and applications. J. Photochem. Photobiol. C: Photochem. Rev. 13, 169–189 (2012). https://doi.org/10.1016/j.jphotochemrev. 2012.06.001 38. Brinker, C.J.: Sol-gel Science, The Physics and Chemistry of Sol-Gel Science. Academic Press Inc., San Diego (1990) 39. Peng, Y., Ji, J., Zhao, X., Wan, H., Chen, D.: Preparation of ZnO nanopowder by a novel ultrasound assisted non-hydrolytic sol-gel process and its application in photocatalytic degradation of C.I. Acid Red 249. Powder Technol. 233, 325–330 (2013) 40. Eskandarloo, H., Badiei, A., Behnajady, M.A., Ziarani, G.M., Patil, M.N., Pandit, A.B.: Ultrasonic-assisted sol-gel synthesis of samarium, cerium co-doped TiO2 nanoparticles with enhanced sonocatalytic efficiency. Ultrason. Sonochem. 26, 281–292 (2015). http://dx.doi. org/10.1016/j.ultsonch.2015.02.001 41. Patil, M.N., Pandit, A.B.: Cavitation - a novel technique for making stable nano-suspensions. Ultrason. Sonochem. 14, 519–530 (2007). https://doi.org/10.1016/j.ultsonch.2006.10.007 42. Mahata, S., Mondal, B., Usha, K., Mandal, N., Mukherjee, K.: Chemical modification of titanium isopropoxide for producing stable dispersion of titania nano-particles. Mater. Chem. Phys. 151, 267–274 (2015). https://doi.org/10.1016/j.matchemphys.2014.11.065 43. Mutuma, B.K., Shao, G.N., Kim, W.D., Kim, H.T.: Sol-gel synthesis of mesoporous anatase-brookite and anatase-brookite-rutile TiO2 nanoparticles and their photocatalytic properties. J. Colloid Interface Sci. 442, 1–7 (2015). https://doi.org/10.1016/j.jcis.2014.11. 060 44. You, Y.F., Xu, C.H., Xu, S.S., Cao, S., Wang, J.P., Huang, Y.B., Shi, S.Q.: Structural characterization and optical property of TiO2 powders prepared by sol-gel method. Ceram. Int. 40, 8659–8666 (2014). https://doi.org/10.1016/j.ceramint.2014.01.083 45. Mandzy, N., Grulke, E., Druffel, T.: Breakage of TiO2 agglomerates in electrostatically stabilized aqueous dispersions. Powder Technol. 160, 121–126 (2005). https://doi.org/10. 1016/j.powtec.2005.08.020 46. Veronski, N., Andreozzi, P., La Mesa, C., Sfiligoj-Smole, M.: Stable dispersions for nanocoating preparation. Surface, Coating technology 204, 1445–1451 (2010)

Design and Development of TiO2 Based Dispersions for Photocatalytic Fabrics

549

47. Myers, D.: Surfaces, Interfaces, and Colloids: Principles and Applications, 2nd edn. Wiley, New York (1999) 48. Tadros, T.: Dispersion of Powder in Liquids and Stabilisation of Suspensions. Wiley VCH, Hardcover (2012) 49. Leong, Y.-K., Ong, B.-C.: Polyelectrolyte-mediated interparticle forces in aqueous suspensions: molecular structure and surface forces relationship. Chem. Eng. Res. Des. 101, 44–55 (2015). https://doi.org/10.1016/j.cherd.2015.07.001 50. Bakshi, M.S., Sachar, S., Singh, K., Shaheen, A.: Mixed micelle behavior of Pluronic L64 and Triton X-100 with conventional and dimeric cationic surfactants. J. Colloid Interface Sci. 286, 369–377 (2005). https://doi.org/10.1016/j.jcis.2004.12.044 51. Duta, M., Perniu, D., Duta, A.: Photocatalytic zinc oxide thin films obtained by surfactant assisted spray pyrolysis deposition. Appl. Surf. Sci. 306, 80–88 (2014). https://doi.org/10. 1016/j.apsusc.2014.02.132 52. Ismay, M., Doroodchi, E., Moghtaderi, B.: Effects of colloidal properties on sensible heat transfer in water-base titania nanofluids. Chem. Eng. Res. Des. 91, 426–436 (2013). https:// doi.org/10.1016/j.cherd.2012.10.005 53. Kosmulski, M.: The pH-dependent surface charging and points of zero charge V. Update. J. Colloid Interface Sci. 353, 1–15 (2011). https://doi.org/10.1016/j.jcis.2010.08.023 54. Suarez-Meraz, K.A., Ponce-Vargas, S., Trinidad-Lopez-Maldonado, J., Manuel-CornejoBravo, J., Teresita-Oropeza-Guzman, M.: Alberto-Lopez-Maldonadoelectro, E.: Ecofriendly innovation for nejayote coagulation-flocculation process using chitosan: evaluation through zeta potential measurements. Chem. Eng. J. 284, 536–542 (2016). http://dx.doi.org/ 10.1016/j.cej.2015.09.026 55. Colleoni, C., Massafra, M.R., Rosace, G.: Photocatalytic properties and optical characterization of cotton fabric coated via sol-gel with non-crystalline TiO2 modified with poly (ethylene glycol). Surf. Coat. Technol. 207, 79–88 (2012). https://doi.org/10.1016/j.surfcoat. 2012.06.003

Sustainable Wastewater Treatment for Households in Small Communities Alexandru Enesca(&), Luminita Andronic, Anca Duta, and Ion Visa Renewable Energy Systems and Recycling Research Center, Transilvania University of Brasov, Brasov, Romania [email protected]

Abstract. The paper is a comprehensive review on the wastewater treatment processes focused on the energy performance and energy efficiency. Extensive studies reported in literature, including results from our Renewable Energy Systems and Recycling R&D Center, are selected to give a clear view on the advantages and disadvantages of traditional and advanced wastewater treatment processes, from the energy consumption perspective. The challenges in terms of energy saving, process optimization and sustainable materials are presented. The traditional processes used in the wastewater plants have limited efficiency for removing the new organic pollutants and usually require environmental aggressive procedures (e.g. chlorination). Advanced wastewater treatments using common raw materials and renewable energy sources represent a sustainable answer to the problem raised by the resilient organic pollutants. So, the paper outlines that advanced wastewater treatment represents a suitable part of the strategy for planning nearly zero energy communities (nZEC). Keywords: Advanced wastewater treatments
Energy performance energy
Photocatalysis
Photoactive heterostructures


Saving

1 Introduction Wastewater treatment and sanitation have to comply with certain criteria that are crucial for protecting the public health and the environment. These criteria are established at national and international levels and focus on the main pollutants, [1]: suspended solids, chemical oxygen demand (COD) used to quantify the organic compounds in water, nitrogen containing compounds, sulfides, detergents, cyanides, chlorides and heavy metals. In EU the national legislation has to be amended based on the European Union recommendations for the member states. Water and wastewater systems are significant energy consumers, requiring onsite energy for keeping a constant flow (pumping), continuous aeration and processing but also offsite energy for additional processes such as materials and chemicals production and transport. Relevant studies [2, 3] show that in countries like Germany and Italy the energy consumption required for wastewater treatment can easily exceed 1% of the overall energy consumption including the industrial activity, which represents a significant cost from the annual budged. There are other studies [4, 5] which show that in the developing countries the energy required for wastewater treatment is significantly © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_39

Sustainable Wastewater Treatment for Households in Small Communities

551

higher and can reach 3% of the total electric energy consumption. The United States also have a high energy demand (around 4%) for wastewater treatment [6], but in this particular case much of the spending is spread over the desalination area and advanced treatment. Considering that the number of wastewater treatment plants increases significantly [7, 8] due to the expansion of the urban areas and the effluent quality criteria’s become more severe [9], the problems related to energy efficiency and sustainable development are now more tackled, aiming at a sustainable future. Thus, the water agencies, non-governmental organizations and wastewater treatment plant operators show an increased interest in the development and use of tool, methods, and strategies aiming to reduce the energy consumption, [10, 11]. This paper gives an insight into the energy aspects involving wastewater treatment as well as the main novel methods used to increase the energy efficiency of the wastewater treatment plants. The paper aims to highlight the energy problems related to the traditional wastewater treatment methods as well as the barriers encounter in the implementation of new advanced methods such as heterogeneous photocatalysis. Aspects related to energy saving, energy performance and optimization, and the environmental impact are also considered (with a specific focus on the Romania as case study).

2 Wastewater Issues in Romania The analysis of the wastewater situation in Romania is quite difficult to accurately develop because only since 2006 statistical data, able to be used in scientific studies, are reported and, unfortunately, not all wastewater treatment plants operators kept and communicate this information. Based on the available data from water suppliers the average price (see Fig. 1) for the drinking water has increased with more than 100% between 2010 and 2017 (from 2.5 Ron/m3 up to 5.5 Ron/m3) and the wastewater price registered an increase of 280% in the same period (from 1.19 Ron/m3 up to 3.42 Ron/m3). It is important to mention that these are average yearly prices used by the water supplier’s operators from various Romanian regions. Considering these aspects the price for a cubic meter can vary depending on the corresponding month and the geographical area. For example in 2017 the highest price for drinking water was 7.8 Ron/m3 in Constanta area [12] (SE part of the country) and the lowest price was 3.01 Ron/m3 in Ploiesti area, in the central Romania [13]. As the graphs in Fig. 1 show, the average price trend of the cost of drinking water and wastewater is almost similar till 2013, and afterwards the cost of drinking water rises much faster. These are rather worrying data and indicate an upward trend in wastewater treatment costs which is closely related to the energy consumption required to reach high quality standards. Mousel et al. [14] show that the overall electric and thermal energy consumption has a significant impact on the wastewater treatment costs and this trend will continue to raise when involving new treatment steps. In Romania the investment in wastewater treatment is an important economical aspect considering that the country has adopted the EU Water Directives assuming to double the storage and treatment capacities. An overall estimation presented by Frone et al. [15] indicates that the

552

A. Enesca et al.

Fig. 1. The price evolution for drinking water and wastewater in Romania

required investment for the Romanian water sector between 2007–2013 was around 12 billion Euro (almost half of them represented by the EU funds). Based on the Priority axis 1 - “Extension and modernization of water and wastewater systems” of SOP Environment, the EU founds are focused on local or regional water suppliers and asks to improve and modernize the network distribution and wastewater treatment technologies. Thus, when building nZECs, it is important to adopt wastewater treatment processes based on energy saving technologies and renewable energies.

3 Energy Performance Indicators A literature review [2, 16–19] shows that there are various methods to calculate the energy performance of different wastewater treatment processes. Among these, three indicators have reached global acceptance and are used in the assessment of the process feasibility and in the research activity: electric energy consumption ½kWh=m3  volume of treated wastewater

ð1Þ

electric energy consumption ½kWh=PE year served population equivalentðPEÞ

ð2Þ

EP1 ¼ EP2 ¼

EP3 ¼

Sustainable Wastewater Treatment for Households in Small Communities

553

electric energy consumption ½kWh=kg CODremoved  chemical oxigen demand ðCODÞ load removed

ð3Þ

The energy efficiency has a significant improvement potential for large wastewater treatment plants (exceeding 100,000 PE) based on the following reasons, [20–22]: (1) Higher operation stability by eliminating the energy-intensive transitional periods and ensuring regular operation of mechanical and electromechanical equipments; (2) Advantage of scale economies due to the involvement of efficient pumps and compressors which are usually the highest energy consumers; (3) Increasing the automation control systems at various stages of wastewater treatment process, thus decreasing the human interventions and the associated human resources required for plant operation; (4) Professional management staff ready to implement the technological and legislative modifications and to improve the working conditions. The smaller wastewater plants can also improve their energy efficiency by adapting the modern technologies for using renewable energies sources [23, 24], and lower amounts of chemicals. The most important energy consumers in the wastewater treatment plants are presented in Fig. 2. It is important to mention that not all these processes are involved in all wastewater plants. Each treatment plant chooses the processes best suited to the wastewater pollutants types, according to the scale of the plant, its facilities and the quality of the treated water. Usually, advanced treatment processes, if provided, are designed after the traditional processes.

Fig. 2. Main energy consumers in wastewater treatments

554

A. Enesca et al.

Due to the significant increase of the water resource stress, in various parts of the world the energy used for water supply and treatments will be higher. The nearly zero energy communities will be focused on decreasing the wastewater treatment specific consumption, implementing energy saving technologies, reducing the costs but keeping or even improving the water quality. These are essential criteria to be considered for the improvement of the overall energy performance of the wastewater treatment, [25]. Updated legislation and government support, are focused on the implementation of new and modern technologies at an important step in reducing the energy consumption, [26]. Beside the technical and financial issues, environmental aspects represent a common problem when considering the selection of wastewater treatment techniques, [27, 28]. Therefore, the life cycle assessment represents a useful tool to evaluate the environmental impact of the treatment processes, [29]. Additionally, the life cycle assessment can compare and integrate various treatment processes considering the environmental aspects. Based on the life cycle assessment it is possible to further optimize and improve the wastewater treatment efficiency using experimental and quantitative data, [10]. The life cycle assessment requires several impact categories (see Fig. 3) such as: emissions, raw materials involved in different processes, wastes released during the entire wastewater treatment chain, [30]. In practice, the life cycle assessment is based on a methodology regulated by ISO 14040 specifications which define the mains inputs and outputs of this process. Thus, the LCA contains four main steps: (1) (2) (3) (4)

Definition of goal and scope which act as a study planning; Inventory analysis responsible for data collection and analysis; Impact assessment; Results interpretation, [31].

The LCA considers several parameters including the energy use, the available infrastructure, the sewage related system, etc. allowing to have a complete image on how and what is important in implementing sustainable wastewater treatment in nZECs, [32]. This concept can be further expanded to larger scale if the necessary tools are properly used.

Fig. 3. Categories used to define LCA environmental impact

Sustainable Wastewater Treatment for Households in Small Communities

555

4 Energy Requirements for the Traditional Wastewater Treatment Processes Except the environmental problems, the energy-related issues (energy saving, increasing the efficiency of the traditional wastewater treatment and seeking for new alternatives such as using renewable energy sources), represents a common pursuit of nZEC and global sustainable development. In a traditional wastewater treatment plant the operating costs due to the energy consumption may vary from 25% up to 40% depending on the technological updates, [33, 34]. Additionally, the traditional wastewater treatment processes rise many questions related to the greenhouse gas emissions, [35, 36]. A short description is required in order to have a comprehensive view of the energy consumption in traditional wastewater treatment plants and the need of using advanced wastewater treatment processes. Currently, the wastewater treatment process is divided in three main steps (primary, secondary and tertiary) and an additional one (sludge treatment) which is relevant considering the energy approach of this paper. It is important to underline that the preliminary step (representing wastewater pumping from the network, screening, grit removal) was not included due to the inconsistent data required for assessing the energy consumption. However, based on Yang et al. [37] the preliminary step can be responsible for 2.5% of the total energy consumption: (1) Primary treatment consists mostly of physical processes such as separation step in circular settling tanks containing mechanized scrapers. According to Longo et al. [2], this step requires between 4.3  10−5 up to 7.1  10−5 kW h/m3, which is just a small part of the total energy use. (2) Secondary treatment includes various processes that are energy intensive as the biological processes (requiring extensive aeration). Some of the processes that correspond to this stage are: aeration, sludge separation, mixing in anoxic reactors, etc. Table 1 contains the average specific energy consumptions related to these processes, [38–42]; these data vary according to the plant size, pollutant concentrations, periodical maintenance and technological updates. Table 1. The main energy consuming processes from the secondary treatment step Process name Aeration Primary sludge separation (settling) Secondary sludge recirculation Mixing (anoxic reactors)

Average energy consumption (kWh/m3) 0.51 (45 up to 75% of the energy costs in the plant) 0.6 • 10−2 (max. 1.5% of the energy costs in the plant) 2.5 • 10−2 (max. 3.5% in the plant energy costs) 0.11 (can vary according to the tank size)

Aeration represents an important process in the wastewater treatment plants and can be improved by providing a suitable match between the aeration system and the oxygen demands of the process. The sludge separation takes place in two steps: the first is gravitationally induced in decanters equipped with mechanized

556

A. Enesca et al.

scrapers (lower energy consuming) and the second requires pumping for sludge recirculation (higher energy consuming). Finally, the mixing is required in different stages (depending on the wastewater plant) such as in the anoxic reactor to maintain a homogeneous working environment. (3) Tertiary treatment includes various processes (physical, biological, and chemical processes) depending on the plant size and legislation, such as dosage of chemicals (aluminum salts, chlorinated reagents, etc.), UV disinfection or tertiary filtration. The average energy consumption for this step can vary from 2.7  10−3 kWh/m3 for tertiary filtration up to 4.5  10−2 kWh/m3 for UV disinfection, [2]. (4) Sludge treatment (at all stages) and its disposal can have an important impact on the economic and energy balance of the wastewater plants no matter the size. One of the highest energy consumer stages is the aerobic sludge stabilization. The most cost effective and an energy efficient option is the use of the sludge anaerobic digestion, which can add supplementary benefits in terms of revenue for the wastewater plants. Sludge dewatering is another energy consuming process due to the mechanical centrifugation. The average energy consumption is estimated at 0.12 kWh/m3, [43, 44].

5 Energy Requirements for the New Wastewater Treatment Processes Elimination of organic micro-pollutants (OMP), such as pharmaceuticals and household chemicals, in local wastewater treatment plants represents an important environmental issue, solved through intensive research in the past years. Based on their toxicity for the aquatic environment and the difficulty to get complete removal by traditional methods [45], advanced wastewater treatment steps were considered as a suitable approach. Thus, the concept of Nearly Zero Energy Community, nZEC, has to be accordingly extended on the wastewater treatment plants by using energy efficient processes. An energy efficient wastewater treatment usually has an energy demand that can be produced on-site by employing renewable energy sources or other energy production methods (with low or no pollutant emissions), [46]. To achieve these concepts two aspects must be considered: (1) periodical technological upgrading which supports an increase in the energy savings and (2) the use of renewable energy sources or other type of energy sources produced by the wastewater plant (such as chemical energy, heat etc.). It is important to underline that even wastewater is considered as an energy source based on the organic matter content. Consequently, the wastewater plant can produce a significant amount of biogas by using the digesters. In this case the biogas is considered as an environmental friendly energy sources allowing the insertion of a material considered as waste into the production circuit, [47]. There are also other energy conversion sources available at the wastewater treatment plant that can be considered (as e.g. the fuel cells). Several advanced treatment processes which are suitable for the concept of nZEC are presented in the next paragraphs. The number of these processes is significantly higher and most of them have never been tested at large or even at pilot scale.

Sustainable Wastewater Treatment for Households in Small Communities

557

Microbial fuel cell (MFC) is a technology that converts the chemical energy (from the sludge) into electrical energy. It can be applied to large or smaller plants due to the simple technology allowing direct conversion in electric energy. This technology is considered as advanced because allows the energy production from the wastewater sludge without the involvement of additional processes. The consequence is the increase of the plant’s energy independence and economic efficiency. The conversion efficiency of microbial fuel cell is about 40%, [48]. Algal-based wastewater treatment and biofuel production is a method involving the use of natural biological wastewater treatment based on microalgae. These methods can be applied only for small or medium sized communities and require large land areas. The method is not suitable for wastewater with high content of pharmaceutical or petroleum products. Even if the algal-based wastewater treatment requires longer periods comparing to the traditional methods it allows saving more than 50% of the energy usage due to algal photosynthesis [49]. The by-product resulted from the algal-based wastewater treatment can be successfully used for biofuel production. Mehrabadi et al. calculated a production of 800–1400 GJ/ha/year energy by using these methods [50]. Ozonation is also considered as an advanced treatment method, highly efficient in the degradation of pharmaceutical product such as carbamazepine, sulfamethoxazole and diclofenac. Because it is an unstable gas, the ozone (O3) is produced directly in the wastewater treatment plant by using liquid oxygen. This type of treatment induces a partial mineralization of the organic pollutants and has to be accompanied by other processes (usually biologically active post-treatment), [51]. Photocatalytic wastewater treatment is considered an important topic in the scientific community due to the possibility of inducing a complete pollutant mineralization by employing common raw materials and UV-Vis radiation. The photocatalytic efficiency is influenced by the catalyst ability to generate electron-hole pairs, [52]. The charge carriers are responsible for the free radicals formation (such as hydroxyl radicals •OH) which will start secondary oxidation reactions: – In the homogenous photocatalysis both reactant and photocatalyst are in the same phase. The reaction mechanism includes a photo-Fenton system (such as Fe+ and Fe+/H2O2) and ozone, [53]. The process has several limitations such as the use of UV radiation, high amounts of chemicals and sludge, and potential polluting by-products resulted in the end. – On the other hand, the heterogeneous photocatalysis has overcome most of the homogeneous photocatalysis problems. In the heterogeneous photocatalysis the photocatalyst is in a different phase compared to the reactants. The photocatalyst is usually represented by semiconductors but other materials have been used as well (polymers [54], composites [55], wood based product [56], etc.). The first major challenge in promoting the heterogeneous photocatalysis as a feasible and energy efficient, advanced wastewater treatment suitable for nZEC is represented by the possibility to generate charge carriers only by sun light irradiation. In order to achieve this goal, the materials properties have to be tailored to use both the UV and Vis spectral wavelength of the light spectrum. The second challenge is to generate enough oxidative species to induce a complete mineralization of the organic

558

A. Enesca et al.

pollutant. In this case not only the photocatalyst properties but also the environmental conditions are important. There are studies [57, 58] showing that the involvement of H2O2 is beneficial for increasing the concentration of oxidative species. Titanium oxide (TiO2) is one of the mostly reported materials used in the photocatalysis studies [57] due to the high chemical stability in water and photosensitive properties. However, a major disadvantage of TiO2 is represented by the limited light absorbance in the Vis region, [58]. In order to surpass this problem two methods have been used to enhance the photocatalytic properties: (1) Using tandem systems of wide band gap semiconductors (TiO2, ZnO, WO3, SnO2) able to reduce the charge recombination and to increase the number of hydroxyl radicals. (2) Inserting narrow band gap semiconductors (CuxS, CuInS2) able to directly extend the absorbed spectral range to the visible region. Tandem Systems with Wide Band Gap Semiconductors The structures obtained by coupling semiconductors represent highly promising candidates for photocatalytic applications where the solar energy conversion for the degradation of organic compounds is targeted. By coupling two different semiconductor materials such as TiO2/SnO2, SnO2/WO3 and WO3/TiO2, the charge separation is improved, allowing an accumulation of the charge carriers (electrons and/or holes) from both semiconductor films with the suppression of charge recombination, [59]. Choosing the semiconductors that compose the tandem structure is done after a rigorous study on the values corresponding to the energy levels of each material. Two possibilities are presented in Fig. 4: (a) the correct choice of the semiconductors (TiO2/SnO2) allowing the mobility of the charge carriers and (b) the incorrect choice of the materials (TiO2/Cu2O) which does not allow the free movement trough the structure.

Fig. 4. Tandem structures composed of (a) TiO2/SnO2 and (b) TiO2/Cu2O

Considering the working tandem system during irradiation, in Fig. 4a, charge carriers are generated into the semiconductors and the electrons from tin oxide valence band are promoted on the titanium valence band which is the closest energy level. In terms of electrical conductivity, the electrons flow into the SnO2 under-layer, while

Sustainable Wastewater Treatment for Households in Small Communities

559

holes oppositely diffuse into the TiO2 over-layer. Consequently, enhanced charge separation in the coupled film is obtained based on the fast electron-transfer process from the conduction band of TiO2 to that of SnO2. In these tandem systems the photocatalytic efficiency is about 70%, [58]. Using the second example in Fig. 4b, where the materials have an unsuitable disposition of the energy levels, the photocatalytic activity is still possible but the two materials act independently and the efficiency will be significantly decreased. UV-Vis Photoactive Heterostructures The UV-Vis photoactive heterostructures were obtained by inserting narrow band gap semiconductors such as CuxS or CuInS2 into the tandem structure. The aim was to maximize the light absorption spectra used during the photocatalytic degradation. Several attempts were done to produce different photoactive heterostructures, among them the most promising were Cu2S/SnO2 [60] and CIS/TiO2/SnO2 [52]. As presented in Fig. 5 it was possible to increase the absorption range from 380 nm to up to 700 nm which represents a significant gain. The morphology of the TiO2/SnO2 tandem is granular and porous compared with the CIS/TiO2/SnO2 which is denser allowing a uniform interpenetration between the layers. The most important difference between these structures is represented by the photocatalytic efficiency (in methylene blue decomposition): 40% for Cu2S/SnO2 and 96% for CIS/TiO2/SnO2.

Fig. 5. The absorption range and morphology of the heterostructures

The energy consumption in the photocatalytic processes calculated by Al-Bastaki [61] was 4.0 kWh/m3 which is considerable higher compared to the traditional wastewater treatments. However, this value can be significantly reduced (up to 90%) if: (1) the photocatalyst is activated only using the sun light (without any artificial light),

560

A. Enesca et al.

(2) the system use only common raw materials and (3) the mechanical mixer and pump use energy produced by photovoltaic systems. The photocatalytic processes have the potential to further expand from wastewater treatment to air decontamination, [62]. Additionally, the photocatalytic processes have the particularity to induce complete mineralization of very resilient organic pollutants which are not decomposed by traditional methods [52]. Now-a-day the advanced wastewater treatment processes are still expensive due to several factors: (1) plant operators reluctance to new and innovative wastewater treatments; (2) lack of infrastructure investments required to implement these processes and (3) problems related to the transition from research to large scale application. The comparison of the energy costs in the traditional and the advanced techniques is irrelevant if the environmental aspects and the use of common raw materials is not considered. Another key factor is the development of manufacturing technologies able to provide the materials flow required in the advancement wastewater treatments. These materials have various compositions (ceramics, carbon, wood, polymers, metal oxides, composites, etc.) in different forms (powder, granules, membrane, thin films, pallets, etc.). In a wastewater treatment plant there are also other ways to increase the energy efficiency such as process optimization usually requiring low investments and short payback times. A relevant example of energy saving was registered in Netherlands where the energy consumption was reduced with 15% [63] by regulating the mixed liquor suspended solids concentration based on activated sludge temperature. Also considerable savings in energy where obtained by decreasing the number of mixers used in the biological processes based on a retrofit of the designed plant [64]. A very important energy consumer in the wastewater treatment plants are the pumps. Adopting energy-efficient pumps along with changes of the design conditions can contribute to energy saving.

6 Conclusions In the last years, household wastewater contains increasingly large amounts of complex pollutants (pharmaceutical compounds, dyes, cleaning products). This paper shows that the traditional methods of wastewater treatments have several limitations in terms of efficiency and cost. In the context of developing a nZEC the implementation of advanced wastewater methods such as photocatalysis for medium and large wastewater treatment plants should be considered as a suitable solution. The study shows that heterogeneous photocatalysis requires prior optimization from the economical and technological perspective before large scale implementation. Considering the environmental issues, using advanced wastewater processes can bring benefits such as (1) the involvement of renewable energy sources and (2) the complete degradation of organic pollutants. The heterogeneous photocatalysis using photoactive heterostructures is able to give useto both, UV and Vis, spectral ranges of the light and induce high mineralization of resilient organic compounds. Energy saving by updating the wastewater plant technologies, process optimization and periodical maintenance has to be considered. The

Sustainable Wastewater Treatment for Households in Small Communities

561

advanced wastewater treatment brings high energy efficiency and environmental benefits, as required for the development of the nZEC. Acknowledgments. We hereby acknowledge the project Photocat Flow, PN-III-P2-2.1-PED2016-0514, for providing the founds that supported this work.

References 1. Romanian Government decision according with HG. Nb. 188 from 2002 2. Longo, S., Antoni, B.M., Bongards, M., Chaparro, A., Cronrath, A., Fatone, F., Lema, J.M., Mauricio-Iglesias, M., Soares, A., Hospido, A.: Monitoring and diagnosis of energy consumption in wastewater treatment plants. A state of the art and proposals for improvement. Appl. Energy, 179, 1251–1268 (2016). http://dx.doi.org/10.1016/j.apenergy. 2016.07.043 3. Foladori, P., Vaccari, M., Vitali, F.: Energy audit in small wastewater treatment plants: methodology, energy consumption indicators, and lessons learned. Water Sci. Technol. 72, 1007–1015 (2015). http://dx.doi.org/10.2166/wst.2015.306 4. Chowdhury, S., Jafar Mazumder, M.A., Al-Attas, O., Husain, T.: Heavy metals in drinking water: occurrences, implications, and future needs in developing countries. Sci. Total Environ. 569–570, 476–488 (2016). http://dx.doi.org/10.1016/j.scitotenv.2016.06.166 5. Zhang, D.Q., Jinadasa, K.B.S.N., Gersberg, R.M., Liu, Y., Ng, W.J., Tan, S.K.: Application of constructed wetlands for wastewater treatment in developing countries - a review of recent developments (2000–2013). J. Environ. Manag. 141, 116–131 (2014). http://dx.doi.org/10. 1016/j.jenvman.2014.03.015 6. Goldstein, R., Smith, W.: Water & Sustainability: US Electricity Consumption for Water Supply & Treatment-the Next Half Century, vol. 4. Electric Power Research Institute, Palo Alto (2012) 7. Liu, H.Q., Lam, J.C.W., Li, W.W., Yu, H.Q., Lam, P.K.S.: Spatial distribution and removal performance of pharmaceuticals in municipal wastewater treatment plants in China. Sci. Total Environ. 586, 1162–1169 (2017). http://dx.doi.org/10.1016/j.scitotenv.2017.02.107 8. Barbu, M., Vilanova, R., Meneses, M., Santin, I.: On the evaluation of the global impact of control strategies applied to wastewater treatment plants. J. Clean. Prod. 149, 396–405 (2017). http://dx.doi.org/10.1016/j.jclepro.2017.02.018 9. Wang, Q., Wei, W., Gong, Y., Yu, Q., Li, Q., Sun, J., Yuan, Z.: Technologies for reducing sludge production in wastewater treatment plants: state of the art. Sci. Total Environ. 587– 588, 510–521 (2017). http://dx.doi.org/10.1016/j.scitotenv.2017.02.203 10. Ebrahimi, M., Gerber, E.L., Rockaway, T.D.: Temporal performance assessment of wastewater treatment plants by using multivariate statistical analysis. J. Environ. Manag. 193, 234–246 (2017). http://dx.doi.org/10.1016/j.jenvman.2017.02.027 11. Dong, X., Zhang, X., Zeng, S.: Measuring and explaining eco-efficiencies of wastewater treatment plants in China: an uncertainty analysis perspective. Water Res. 112, 195–207 (2017). http://dx.doi.org/10.1016/j.watres.2017.01.026 12. RAJA Constanta local operator. www.rajac.ro 13. ApaNova Ploiesti local operator. www.apanova-ploiesti.ro 14. Mousel, D., Palmowski, L., Pinnekamp, J.: Energy demand for elimination of organic micropollutants in municipal wastewater treatment plants. Sci. Total Environ. 575, 1139– 1149 (2017). http://dx.doi.org/10.1016/j.scitotenv.2016.09.197

562

A. Enesca et al.

15. Frone, S., Frone, D.F.: Factors and trends of economic efficiency in the water/wastewater sector. Procedia Econ. Finan. 3, 1018–1024 (2012). http://dx.doi.org/10.1016/S2212-5671 (12)00267-5 16. Yang, L., Zeng, S., Chen, J., He, M., Yang, W.: Operational energy performance assessment system of municipal wastewater treatment plants. Water Sci. Technol. 62, 1361–1370 (2010). http://dx.doi.org/10.2166/wst.2010.394 17. Krampe, J.: Energy benchmarking of South Australian WWTPs. Water Sci. Technol. 67, 2059–2066 (2013). http://dx.doi.org/10.2166/wst.2013.090 18. Balmer, P.: Operation costs and consumption of resources at Nordic nutrient removal plants. Water Sci. Technol. 41, 273–279 (2000) 19. Mizuta, K., Shimada, M.: Benchmarking energy consumption in municipal wastewater treatment plants in Japan. Water Sci. Technol. 62, 2256–2262 (2010). http://dx.doi.org/10. 2166/wst.2010.510 20. Carlsson, M., Lagerkvist, A., Morgan-Sagastume, F.: Energy balance performance of municipal wastewater treatment systems considering sludge anaerobic biodegradability and biogas utilisation routes. J. Environ. Chem. Eng. 4, 4680–4689 (2016). http://dx.doi.org/10. 1016/j.jece.2016.10.030 21. Henriques, J., Catarino, J.: Sustainable value - an energy efficiency indicator in wastewater treatment plants. J. Clean. Prod. 142, 323–330 (2017). http://dx.doi.org/10.1016/j.jclepro. 2016.03.173 22. Kumar, M., Singh, R.: Performance evaluation of semi continuous vertical flow constructed wetlands (SC-VF-CWs) for municipal wastewater treatment. Bioresour. Technol. 232, 321– 330 (2017). http://dx.doi.org/10.1016/j.biortech.2017.02.026 23. Kollmann, R., Neugebauer, G., Kretschmer, F., Truger, B., Kindermann, H., Stoeglehner, G., Ertl, T., Narodoslawsky, M.: Renewable energy from wastewater - practical aspects of integrating a wastewater treatment plant into local energy supply concepts. J. Clean. Prod. 155, 119–129 (2017). http://dx.doi.org/10.1016/j.jclepro.2016.08.168 24. Hickman, W., Muzhikyan, A., Farid, A.M.: The synergistic role of renewable energy integration into the unit commitment of the energy water nexus. Renew. Energy 108, 220– 229 (2017). http://dx.doi.org/10.1016/j.renene.2017.02.063 25. Wang, H., Yang, Y., Keller, A.A., Li, X., Feng, S., Dong, Y., Li, F.: Comparative analysis of energy intensity and carbon emissions in wastewater treatment in USA, Germany, China and South Africa. Appl. Energy 184, 873–881 (2016). http://dx.doi.org/10.1016/j.apenergy. 2016.07.061 26. Fernández-Arévalo, T., Lizarralde, I., Fdz-Polanco, F., Pérez-Elvira, S.I., Garrido, J.M., Puig, S., Poch, M., Grau, P., Ayesa, E.: Quantitative assessment of energy and resource recovery in wastewater treatment plants based on plant-wide simulations. Water Res. 118, 272–288 (2017). http://dx.doi.org/10.1016/j.watres.2017.04.001 27. Rashidi, H., Hoseini, A.G., Sulaiman, N.M.N., Tookey, J., Hashim, N.A.: Application of wastewater treatment in sustainable design of green built environments: a review. Renew. Sustain. Energy Rev. 49, 845–856 (2015). http://dx.doi.org/10.1016/j.rser.2015.04.104 28. Wieck, S., Olsson, O., Kümmerer, K.: Possible underestimations of risks for the environment due to unregulated emissions of biocides from households to wastewater. Environ. Int. 94, 695–705 (2016). http://dx.doi.org/10.1016/j.envint.2016.07.007 29. Teodosiu, C., Barjoveanu, G., Robu Sluser, B., Ene Popa, S.A., Trofin, O.: Environmental assessment of municipal wastewater discharges: a comparative study of evaluation methods. Int. J. Life Cycle Assess. 21, 395–411 (2016). http://dx.doi.org/10.1007/s11367-016-1029-5 30. Bustamante, M., Liao, W.: A self-sustaining high-strength wastewater treatment system using solar-bio-hybrid power generation. Bioresour. Technol. 234, 415–423 (2017). http:// dx.doi.org/10.1016/j.biortech.2017.03.065

Sustainable Wastewater Treatment for Households in Small Communities

563

31. Pintilie, L., Torres, C.M., Teodosiu, C., Castells, F.: Urban wastewater reclamation for industrial reuse: an LCA case study. J. Clean. Prod. 139, 1–14 (2016). http://dx.doi.org/10. 1016/j.jclepro.2016.07.209 32. Barjoveanu, G., Comandaru, I.M., Rodriguez-Garcia, G., Hospido, A., Teodosiu, C.: Evaluation of water services system through LCA. A case study for Iasi City, Romania. Int. J. Life Cycle Assess. 19, 449–462 (2014). http://dx.doi.org/10.1007/s11367-013-0635-8 33. Demirbas, E., Kobya, M.: Operating cost and treatment of metalworking fluid wastewater by chemical coagulation and electrocoagulation processes. Process Saf. Environ. Prot. 105, 79– 90 (2017). http://dx.doi.org/10.1016/j.psep.2016.10.013 34. Ioannou-Ttofa, L., Michael-Kordatou, I., Fattas, S.C., Eusebio, A., Ribeiro, B., Rusan, M., Amer, A.R.B., Zuraiqi, S., Waismand, M., Linder, C., Wiesman, Z., Gilron, J., Fatta-Kassinos, D.: Treatment efficiency and economic feasibility of biological oxidation, membrane filtration and separation processes, and advanced oxidation for the purification and valorization of olive mill wastewater. Water Res. 114, 1–13 (2017). http://dx.doi.org/10. 1016/j.watres.2017.02.020 35. Andreo-Martínez, P., García-Martínez, N., Quesada-Medina, J., Almela, L.: Domestic wastewaters reuse reclaimed by an improved horizontal subsurface-flow constructed wetland: a case study in the southeast of Spain. Bioresour. Technol. 233, 236–246 (2017). http://dx.doi.org/10.1016/j.biortech.2017.02.123 36. Wang, X., Ratnaweera, H., Holm, J.A., Olsbu, V.: Statistical monitoring and dynamic simulation of a wastewater treatment plant: a combined approach to achieve model predictive control. J. Environ. Manag. 193, 1–7 (2017). http://dx.doi.org/10.1016/j.jenvman. 2017.01.079 37. Yang, Y., Zhou, Z., Lu, C., Chen, Y., Ge, H., Wang, L., Cheng, C.: Treatment of chemical cleaning wastewater and cost optimization by response surface methodology coupled nonlinear programming. J. Environ. Manag. 198, 12–20 (2017). http://dx.doi.org/10.1016/j. jenvman.2017.05.009 38. Ruiz-Rosa, I., García-Rodríguez, F.J., Mendoza-Jiménez, J.: Development and application of a cost management model for wastewater treatment and reuse processes. J. Clean. Prod. 113, 299–310 (2016). http://dx.doi.org/10.1016/j.jclepro.2015.12.044 39. Theregowda, R.B., Vidic, R., Landis, A.E., Dzombak, D.A., Matthews, H.S.: Integrating external costs with life cycle costs of emissions from tertiary treatment of municipal wastewater for reuse in cooling systems. J. Clean. Prod. 112, 4733–4740 (2016). http://dx. doi.org/10.1016/j.jclepro.2015.06.020 40. Eggimann, S., Truffer, B., Maurer, M.: Economies of density for on-site waste water treatment. Water Res. 101, 476–489 (2016). http://dx.doi.org/0.1016/j.watres.2016.06.011 41. De Gisi, S., Lofrano, G., Grassi, M., Notarnicola, M.: Characteristics and adsorption capacities of low-cost sorbents for wastewater treatment: a review. Sustain. Mater. Technol. 9, 10–40 (2016). http://dx.doi.org/10.1016/j.susmat.2016.06.002 42. Kårelid, V., Larsson, G., Björlenius, B.: Pilot-scale removal of pharmaceuticals in municipal wastewater: comparison of granular and powdered activated carbon treatment at three wastewater treatment plants. J. Environ. Manag. 193, 491–502 (2017). http://dx.doi.org/10. 1016/j.jenvman.2017.02.042 43. Silva, C., Rosa, M.J.: Energy performance indicators of wastewater treatment - a field study with 17 Portuguese plants. Water Sci. Technol. 72, 510–519 (2015). http://dx.doi.org/10. 2166/wst.2015.189 44. Laitinen, J., Moliis, K., Surakka, M.: Resource efficient wastewater treatment in a developing area - climate change impacts and economic feasibility. Ecol. Eng. 103, 217–225 (2017). http://dx.doi.org/10.1016/j.ecoleng.2017.04.017

564

A. Enesca et al.

45. Mujtaba, G., Lee, K.: Treatment of real wastewater using co-culture of immobilized Chlorella vulgaris and suspended activated sludge. Water Res. 120, 174–184 (2017). http:// dx.doi.org/10.1016/j.watres.2017.04.078 46. Gu, Y., Li, Y., Li, X., Luo, P., Wanga, H., Robinson, Z.P., Wangc, X., Wuc, J., Li, F.: The feasibility and challenges of energy self-sufficient waste water treatment plants. Appl. Energy (2017, accepted for publication). doi:10.1016/j.apenergy.2017.02.069 47. Xue, S., Jin, W., Zhang, Z., Liu, H.: Reductions of dissolved organic matter and disinfection by-product precursors in full-scale wastewater treatment plants in winter. Chemosphere 179, 395–404 (2017). http://dx.doi.org/10.1016/j.chemosphere.2017.02.106 48. Ahn, Y., Logan, B.E.: Effectiveness of domestic wastewater treatment using microbial fuel cells at ambient and mesophilic temperatures. Bioresour. Technol. 101, 469–475 (2010). http://dx.doi.org/10.1016/j.biortech.2009.07.039 49. Craggs, R.J., Lundquist, T.J., Benemann, J.R.: Wastewater treatment and algal biofuel production. In: Algae for Biofuels and Energy, pp. 153–163. Springer (2013). doi:10.1007/ 978-94-007-5479-9_9 50. Mehrabadi, A., Craggs, R., Farid, M.M.: Wastewater treatment high rate algal ponds (WWT HRAP) for low-cost biofuel production. Bioresour. Technol. 184, 202–214 (2015). http://dx. doi.org/10.1016/j.biortech.2014.11.004 51. Soltermann, F., Abegglen, C., Tschui, M., Stahel, S., von Gunten, U.: Options and limitations for bromate control during ozonation of wastewater. Water Res. 116, 76–85 (2017). http://dx.doi.org/10.1016/j.watres.2017.02.026 52. Enesca, A., Baneto, M., Perniu, D., Isac, L., Bogatu, C., Duta, A.: Solar-activated tandem thin films based on CuInS2, TiO2 and SnO2 in optimized wastewater treatment processes. Appl. Catal. B: Environ. 186, 69–76. http://dx.doi.org/10.1016/j.apcatb.2015.12.053 53. Trapido, M., Tenno, T., Goi, A., Dulova, N., Kattel, E., Klauson, D., Klein, K., Viisimaa, M.: Bio-recalcitrant pollutants removal from wastewater with combination of the Fenton treatment and biological oxidation. J. Water Process Eng. 16, 277–282 (2017). http://dx.doi. org/10.1016/j.jwpe.2017.02.007 54. Liu, F., Jamal, R., Wang, Y., Wang, M., Yang, L., Abdiryim, T.: Photodegradation of methylene blue by photocatalyst of D-A-D type polymer/functionalized multi-walled carbon nanotubes composite under visible-light irradiation. Chemosphere 168, 1669–1676 (2017). http://dx.doi.org/10.1016/j.chemosphere.2016.11.068 55. Enesca, A., Isac, L., Duta, A.: Charge carriers injection in tandem semiconductors for dyesmineralization. Appl. Catal. B: Environ. 162, 352–363 (2015). http://dx.doi.org/10. 1016/j.apcatb.2014.06.059 56. Nagarajan, S., Skillen, N.C., Fina, F., Zhang, G., Randorn, C., Lawton, L.A., Irvine, J.T.S., Robertson, P.K.J.: Comparative assessment of visible light and UV active photocatalysts by hydroxyl radical quantification. J. Photochem. Photobiol. A: Chem. 334, 13–19 (2017). http://dx.doi.org/10.1016/j.jphotochem.2016.10.034 57. Enesca, A.: Influence of precursor composition on optoelectric and photocatalytic properties of TiO2 and WO3 film. Environ. Eng. Manag. J. 10, 1191–1196 (2011) 58. Enesca, A., Andronic, L., Duta, A.: The influence of surfactants on the crystalline structure, electrical and photocatalytic properties of hybrid multi-structured (SnO2, TiO2 and WO3) thin films. Appl. Surface Sci. 258, 4339–4346 (2012). http://dx.doi.org/10.1016/j.apsusc. 2011.12.110 59. Enesca, A., Andronic, L., Duta, A.: Optimization of opto-electrical and photocatalytic properties of SnO2 thin films using Zn2+ and W6+ dopant ions. Catal. Lett. 142, 224–230 (2012). http://dx.doi.org/10.1007/s10562-011-0762-4

Sustainable Wastewater Treatment for Households in Small Communities

565

60. Enesca, A., Isac, L., Duta, A.: Hybrid structure comprised of SnO2, ZnO and Cu2S thin film semiconductors with controlled optoelectric and photocatalytic properties. This Solid Films 542, 31–37 (2013). http://dx.doi.org/10.1016/j.tsf.2013.06.008 61. Al-Bastaki, N.M.: Performance of advanced methods for treatment of wastewater: UV/TiO2, RO and UF. Chem. Eng. Process.: Process Intensif. 43, 935–940 (2004). http://dx.doi.org/ 10.1016/j.cep.2003.08.003 62. Enesca, A., Yamaguchi, Y., Terashima, C., Fujishima, A., Nakata, K., Duta, A.: Enhanced UV-Vis photocatalytic performance of the CuInS2/TiO2/SnO2 hetero-structure for air decontamination. J. Catal. 350, 174–181 (2017). http://dx.doi.org/0.1016/j.jcat.2017.02.015 63. Brandt, M., Middleton, R., Wang, S.: Energy efficiency in the water industry: a compendium of best practices and case studies-global report. Water Intell. 11, 9781780401348 (2012) 64. Sharma, A.K., Guildal, T., Thomsen, H., Jacobsen, B.: Energy savings by reduced mixing in aeration tanks: results from a full scale investigation and long term implementation at Avedoere wastewater treatment plant. Water Sci. Technol. 64, 1–5 (2011). http://dx.doi.org/ 10.2166/wst.2011.546

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents Ileana Manciulea1(&), Lucia Dumitrescu1, Cristina Bogatu1, Camelia Draghici1, and Dora Lucaci2 1

2

Renewable Energy Systems and Recycling Research Center, Transilvania University of Brasov, Brasov, Romania [email protected] National Institute for Research and Development in Forestry “Marin Dracea”, Brasov, Romania

Abstract. Recycling the biodegradable waste by composting represents a sustainable solution for developing new ecological compost-type substrates, useful both as biofertilizers and as sorbents for the removal of heavy metals from wastewaters. By this paper we aim to present an overview of our studies related to using composted biomass from biodegradable wastes, as viable solution for biofertilizers or sorbents for heavy metals removal from the environmental. The novelty of our studies consists of the new materials that were prepared by composting together different biomass wastes. Aerobic fermentation was used to obtain sixteen different composts from vegetables waste, sewage sludge, beech sawdust and beech ash, in different mixing ratio, and the composting process was monitored. Based on their composition, three of these mature and stable composts were selected, while their capacity as nutrients and suitability as bio-fertilizers were analyzed in terms of C/N ratio, germination tests. Furthermore, one of these composts was also demonstrated to be suitable as low-costs sorbent, specifically to remove heavy metals from polluted waters. For this application the topography and morphology of compost substrates were determined, before and after sorption of metal cations. The sorption parameters (contact time, ratio of wastewater volume: sorbent compost mass) were optimized. Both, kinetic and thermodynamic sorption mechanisms were discussed and the results were further correlated with the structural properties of the compost substrate. The advantaged of biodegradation wastes by composting different raw biomaterials for preparation of ecological soil fertilizers and sorbents to remove heavy metals from contaminated waters, as low cost and environmental friendly solutions were also discussed. Keywords: Biomass wastes
Compost
Biofertilizer
Sorbent
Heavy metals removal

1 Introduction World Comission on Environment and Development in “Our Common Future Circular” known as Brundtland Report, defines [1]: “Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. It contains within it two key concepts: © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_40

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

567

• the concept of needs, in particular the essential needs of the world’s poor, to which overriding priority should be given; • the idea of limitations imposed by the state of technology and social organization on the environment’s ability to meet present and future needs”. The implementation in practice of the principles of sustainable development for agricultural and non-agricultural soils fertilization as well as for wastewater treatment imposes identification of clean technologies, based on products provided by waste recycling, with low prices. Clean technologies may also involve biological processes that can be used to solve environmental protection needs, such as for soil fertility or remediation, and for wastewater treatment. Municipal organic wastes production is growing continuously, imposing development of waste recycling technologies, as an alternative for wastes disposal or incineration [2]. Composting is an efficient method for reducing, reusing and recycling biodegradable wastes [3]. In this respect, local authorities are responsible for waste management, by treating the municipal biodegradable wastes as valuable row material, not only as ordinary disposed wastes. Therefore we consider that this study has a great relevance for Romanian municipalities that have to manage yearly, large quantities of biodegradable wastes. For example, Brasov municipality managed during 2015, a quantity of 80226 tones of domestic wastes, 4646.29 tones sawdust and 4700 tones sewage sludge co-incinerated and more than 6040 tone sewage sludge were disposed [4]. The amount of composted waste from public parks and gardens in urban area of Brasov county, starting with 2012 is still low (Fig. 1). The present study aims to present an overview of our studies related to composting biomass used as recycling biodegradable wastes solution, especially as biofertilizers or as sorbents. As a novelty of our studies, new materials were prepared by composting together different biomass wastes, mixtures with different composition, selected so as to meet the required properties of biofertilizer and sorbents. Sixteen different composts were prepared by aerobic fermentation from vegetables waste, as basic biomass, composted together with sewage sludge, beech sawdust and beech ash, in different mixing ratio (%). The composts were characterized to demonstrate their ability to contribute to plants growth (as fertilizers) or to remove heavy metals (Cu2+) from contaminated wastewaters (as low cost sorbents).

Fig. 1. Waste quantities composted in Brasov county (Environmental protection agency Brasov report, 2015)

568

I. Manciulea et al.

2 Composting Biomass Wastes According to the Directive 2009/28/CE, “biomass means the biodegradable fraction of products, waste and residues of biological origin from agriculture (including vegetal and animal waste), forestry and related industries including fisheries and aquaculture, as well as the biodegradable fraction of industrial and municipal waste” [5]. Following the above mentioned definition, the main sources of biomass are grouped in crops and residues from agriculture and forestry, residues from industrial, urban and farming activities (Fig. 2). Composting is a biological process of decomposition by biological oxidation of organic constituents and is applied for transformation and valorization of organic waste in a stabilized, hygienic compost/humus, similar with soils, rich in humic compounds [6]. Therefore, composting needs special conditions regarding the optimum values of temperature, humidity, aeration degree, pH, C/N ratio, for optimal biological activity, in different stages of the process [7, 8].

Fig. 2. Selection of sources for biomass

The main products of aerobic composting are: gases (carbon dioxide, ammonia), water vapors, minerals with different non-toxic metals (Na2+, Ca2+, Mg2+, Fe2+) and recycled organic matter, compost (Fig. 3) [9]. Some of the mostly relevant characteristics of composting are: environmentally friendly process; environment preservation; reducing the recycling unfriendly wastes. From industrial and agricultural or forestry activities, there are several wastes recommended for composting: forestry waste (bark, chipped wood/sawdust), agricultural waste (vegetable, animal dejections, straw, corn cobs, pruning), marc grape, olive mill waste, food processing waste, garden waste, organic fraction of municipal solid waste, from source separation, sludge from anaerobic digestion, waste by products from bioenergy production (bioethanol, biodiesel), wood ash and coal fly ash.

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

569

Fig. 3. Schematic description of composting process

From household wastes, composting may be processed from fruits and vegetable peels, tea bags and leafs or plants from infusions, coffegrounds, coffee paper and waste, paper towels and bags, decay flowers, as from garden waste, dry leafs and plants, cut grass and branches, hay and straws, manure from herbivourous may be used. It is important to underline that there are also types of household wastes not recommended and thus, not used for composting due to their particular properties: • processed food - have overheating effects and produce strong and unpleasant smells; • inorganic materials (aluminium foil, glass, plastics, metals) - are not biodegradable; • chemicals (herbicides, pesticides) - are not biodegradable; • printed paper - the ink contains heavy metals and other toxic compounds; • coal ash - contains iron and sulfur, causing damages for plants; • diseased plants - diseased organisms are not distroyed during composting; • pets manure - may contain diseased organisms. Composting is a very complex process of degrading organic substrate easy fermentable (poliglucides, proteins, complex lipids) by microorganisms, and producing organic matter partially transformed and stabilized (monoglucides, amino-acids, and simple lipids). The process occurs in three stages (Fig. 4). The first stage (mezophilic phase) occurs with excess of oxygen, in order to allow microorganisms to biodegrade organic compounds (exotherm reactions), and to maintain hygienic conditions for biodegradation. The second stage (thermophilic phase) takes place in less oxidative conditions (avoiding extreme mineralization of organic substrate) and allows the obtaining the biodegradation compounds specific to the compost. During curing stage (maturation), when the biological process is slow, the oxygen demand is low (5%), the temperature decreases and the mature compost is obtained [10, 11]. Considering the (bio)chemical reactions involved in composting, the following physical-chemical parameters influencing the microbial activity, composting rate and good quality products can be monitored [12]: pH, conductivity, nutrients content

570

I. Manciulea et al.

Fig. 4. Schematic description of composting stages

(C/N ratio, N, C, P, K, Na, monoglucides, enzymes), heavy metals content, composting temperature, biomass humidity, particles size, biological aspects of composting (microorganisms activity). For composts with low heavy metals content, bio-availability is controlled by compost chemistry. Heavy metals in traces can’t present toxicity and bioaccumulation, being chemically bound on the active centers on the compost surface [13]. Due to their physical and chemical properties, composts are used as biofertilizers or ecological sorbents for pollutants removal from wastewaters or of contaminated air and soil [14–17]. Composts are also contributing to natural resources protection by: improving soil nutritional quality, texture and fertility; improving the nutrients and water retention in soil and crops; decreasing infiltration of levigate in underground water; decreasing soil erosion; decreasing the amount of waste in landfill and also the emission of toxic gases in atmosphere [18]. As a consequence, the main users of composts are: agricultural farms, horticulture and forestry, soil improvement workers, landscape companies, local authorities involved in parks administration. In many European countries, compost factories add new values to theirs products by producing mixtures and special types of compost, according to clients’ and market demands [19]. It should be mentioned that composting at industrial scale have also disadvantages [20]: • involves high production costs, due to specialized management, equipment, and labour; • requests proper marketing - contact potential clients, advertising, packaging, transport in sale point; • involves a large terrain for raw material storage, composting procedure and finite compost;

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

571

• composting is influenced by weather conditions; • releases in air unpleasant smells, at least in the composting first stage.

3 Application of Compost Used as Fertilizer and Sorbent For our study we prepared three different composts, by aerobic fermentation of vegetables biomass waste (carrots, potatoes, cabbage, bananas and apples) composted with sewage sludge (from the wastewater treatment plant) and with woody biomass waste such as beech sawdust and beech ash. The composts were subject of specific tests to demonstrate their properties to be used both as ecological biofertilizers and as sorbents in advanced treatment of wastewaters polluted with Cu2+ (Fig. 5).

Fig. 5. Raw materials for composts substrates used as biofertilizer and sorbent

3.1

Characterisation of Raw Materials and Compost

The raw materials used for composting are characterised in terms of their chemical composition. Sawdust, especially beech sawdust is a by-product obtained in large quantities during wood processing activity, having a complex inorganic and organic composition (Table 1) [21]. Table 1. Chemical composition of beech sawdust Characteristic Cellulose Hemicellulose (pentosans) Lignin Hot water extractable substances Extractables with NaOH 1% Extractables with ethyl ether Ash

% 43.61–49.96 10.95–20.19 18.25–24.75 0.83–3.80 12.05–20.27 0.09–0.58 0.19–0.52

572

I. Manciulea et al.

Of interest from the inorganic compounds are those considered nutrients, like nitrogen containing compounds (nitrate, nitrite, and ammonium salts), or phosphorus containing compounds (P2O5, phosphate), but also those involved in the metabolic process, like CaO, MgO, K2O. The organic compounds (cellulose, hemicellulose and lignine) have structural functional groups, mostly phenolic and alcoohlic hydroxyl, thus allowing heavy metals bonding, when using the compost as sorbent. Beech ash also contains chemical elements of special interest for plants growth, as micronutrients source (Table 2) [22]. Table 2. Chemical composition of beech ash Characteristic Phosphorus Potassium Calcium Magnesium % 0.8–3.0 2.8–8.6 14–28 0.8–2.8

According to European Directive 86/278/EEC, sewage sludge is the sludge from domestic or urban wastewater treatment plants, septic tanks and similar sewage treatment plants. Different way of storage and valorizations of sludge are applied: incineration, landfilling (with or without biogas synthesis), composting (for covering agricultural and roads surfaces). All over the world, legislation became more and more restrictive for sludge storage, and ground surfaces available for landfilling is reduced. This leads to intense research in sludge valorization [23, 24], directly spread on agricultural soils, or composted and used as fertilizer [25, 26]. Sewage sludge is considered as a source of pollutants, but after decontamination, it can be also used as a source of nutrients, containing nitrogen and phosphorous mineral and organic compounds. For our studies, vegetable wastes and sewage sludge were characterized (Table 3) before composting. Sixteen different composts were prepared, as lab scale experiment, by mixing the above presented raw materials (vegetable waste, sewage sludge, beech sawdust and beech ash), following the methodology already presented [23, 27–32], and further characterised in terms of their nutrient [30] and sorbent capacity [33]. Three of these Table 3. Chemical characteristics of vegetable wastes and sewage sludge [27] Characteristics Vegetable wastes Sewage sludge pH 4.076 7.812 EC (mS/cm) 0.649 2.59 Kexch 105 (g/L) 8.97 2.82 Caexch 105 (g/L) 0.5 11.5 Zn (mg/L) 0.3224 7.072 Ni (mg/L) ND* 0.2639 Cd (mg/L) ND* 0.0363 Cu (mg/L) ND* ND* Pb (mg/L) ND* 0.3661 *ND - not detected

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

573

Fig. 6. Raw materials used as biomass for composting

composts were now selected (C1, C2, C3), and their properties were investigated in relation with possible use as fertilizers and/or sorbents (Fig. 6). Monitoring the aspect of biomass during the composting process, the different stages of biodegradation are visible (Fig. 7). At the beginning, the samples had natural aspects and smells, while next days, specific smells were noticed, due to the volatilization of alcohols, carboxylic acids from lipids, ammonia salts during the aerobic fermentation. In the same time, the surfaces of the compost samples showed microorganisms films (Fig. 7a). While advancing the composting process, microorganisms’ colonies increased (Fig. 7b) until the decomposition and biochemical transformation of composted waste turn into a paste like organic matter with specific smell (Fig. 7c). At the end of composting, the decomposed organic matter have changed the colour and reduced the volume at over 70% (compared with the first day of composting), becoming an homogenous dark brown coloured product, odour free, like soils (Fig. 7d). The compost structure and morphology were investigated by Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques (Fig. 8). The FTIR spectra confirmed the biodegradation of complex compounds such as proteins, poly carbohydrates etc. into simpler, biological active compounds, like carboxylic acids, alcohols, phenols, amines and their salts, amides, proving the viability of the process based on wastes composting [27, 28, 30].

3.2

Compost Applications as Biofertilizer

Using compost as fertilizer has some advantages and disavatages compared with mineral fertilizer (Table 4) [34]. Of interest for using the composts as biofertilizer are the carbon/nitrogen (C/N) ratio, germination tests, as percent of seeds germinated (PSG) and germination index (GI). C/N Ratio The C/N ratio is an important parameter in the composting process, because microorganisms need both: (i) carbon, constituent of biochemical specific compounds (glucides, lipids, protides), acting as energy source for the metabolic processes;

574

I. Manciulea et al.

C1

C2

C3

(a)

(b)

(c)

(d)

Fig. 7. Composts samples, visually monitoring in time: (a) Composts after the first week of composting, (b) Composts after the third week of composting, (c) Composts after the fifth week of composting and (d) Composts after the seventh week of composting

(ii) nitrogen, constituent of protides/proteins, involved in the biosynthesis of microorganisms, acting in waste biodegradation of biomass [7]. The initial optimum C/N ratio is 35:1, when microorganisms develop and the final optimum is considered to be between 20  35, to be used as biofertilizer. Higher values of C/N ratio inhibit growing microorganisms, and lower values accelerate microbial growing, and the the decomposition process. A higher concentration of nitrogen in compost can create a toxic medium for microbial populations, inhibiting the composting process [35].

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

C1

C2

C3

42 nm

41 nm

45 nm

575

(a)

(b)

Fig. 8. AFM and SEM images of the composts: (a) AFM and (b) SEM.

Table 4. Advantages and disadvantages of compost versus chemical fertilizers Materials Compost fertilizer

Chemical fertilizers

Advantages • Improve soil structure • Efficient control of soil erosion • Supply large types of nutrients • Improve microorganism activity in soil • Low cost of transport and application • Good response of crops

Disadvantages • Difficult application (specialized equipment) • Higher C/N ratio leads to nitrogen quantity decrease in soil

• Easily contaminates the soils and groundwater • In excess, leads to soil erosion • Supplies only major nutrients (P, N and K)

Germination Tests The germination test represents the most sensitive parameter for evaluating the nutritive quality, the toxicity and the degree of maturation of the compost. GI higher than 85% or PSG higher than 60% are indicators of a mature compost, without phytotoxins [36, 37]. For our study, the germination processes was performed with 3 cabbage samples (20 seeds) and 3 radish samples (20 seeds) grown during 7 days, in a mixture of compost and soil (1/5, w/w). Two control samples, with cabbage and radish seeds, grown only in soil were also used (Fig. 9). The germination test represents the most important parameter to evaluate the nutritional quality and maturation degree of the compost [38–40]. The germination indexes for 7 days combines relative seed germination and relative root growth for soil

576

I. Manciulea et al.

Fig. 9. Cabbage and radish growth: (a) Cabbage growth in 3 days, (b) Radish growth in 3 days, (c) Cabbage growth in 7 days and d Radish growth in 7 days

cultivated with Raphanus sativus and Brassica oleracea, comparable with the control sample (Eqs. 1 and 2). It is considered that a mature compost, without fitotoxines has GI > 85% or PSG > 60%. GI ð%Þ ¼

number of germinated seeds x average root length of compost sample  100 ð1Þ number of germinated seeds x average root length of control sample

PSGð%Þ ¼

number of seeds germinated in compost sample  100 number of seeds germinated in control sample

ð2Þ

All our compost showed good GI for both radish and cabbage seeds, the best results were obtained for compost C1 obtained from biomass, sewage sludge and sawdust which have enriched content in nutrients and biocatalysts enzymes (Fig. 10a and b). An average of GI and PSG obtained from both cabbage and radish growth in the mixed compost/soil is considered to be relevant information for using our composts for other cultures too (Table 5). The low content of monoglucides (G) and amino acids (AA) confirms that the biodegradation process was completed, and the compost is mature. Our results classify all three composts (C1, C2, C3) as suitable fertilizers, all the tested parameters being in accordance with optimum values.

3.3

Compost Applications as Sorbent for Heavy Metals Removal

High quantities of wastes are released in the environment, most of them also containing heavy metals (Cu2+, Ni2+, Zn2+, Cr3+, Cr6+, Pb2+, Sn2+, Cd2+), known as being persistent in soil and groundwater and dangerous due to their non-biodegrability, generating important health problems. Due to the fact that these types of pollutants are water

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

577

Fig. 10. Germination test for the compost samples, after 7 days: (a) GI and (b) PSG

Table 5. Characteristics of compost used as biofertilizer Compost C1 C2 C3 Optimum values [41] pH 6.452 6.555 7.545 6  9 EC (mS/cm) 2.23 3.43 2.05 2.0  3.5 C/N 27.76 25.76 32.45 20  35 GI 176.7 129.35 149 >85 PSG 80 81.75 76 >60 G (reported for 1 g solid compost, %) 0.152 0.136 0.168 – AA (reported for 1 g solid compost, %) 0.274 0.226 0.265 – * Content on monoglucides (% G), Content on amino acids (% AA)

soluble, heavy metals cations are involved in trophic chain, and in long term generate severe illnesses at brain, digestive system, liver and kidney level [42]. Several techniques are already known for heavy metals removal from wastewaters and sludge, sorption being one of the mostly applied. In order to avoid using expensive sorbents (activated charcoal) and to increase the efficiency in reducing traces of heavy metals, new cheaper materials are studied and proposed, based on agricultural wastes [43–46], sewage sludge [47], sawdust [48–53], ash, composts [54–56]. Heavy metals removal from wastewaters by biosorption is a relatively new approach, still under investigation [57]. This method is recommended especially for wastewaters with low

578

I. Manciulea et al.

heavy metals content, or when final effluent request a very low heavy metal concentration in order to be recirculated [58]. In the last two decades, different agricultural and food industry wastes were studied, and used as sorbents for copper and nickel removal, like cereals waste [59, 60] and peels of onion, oranges and almonds [53, 61–64]. Compost C1, with 70% vegetable wastes, 20% beech sawdust and 10% sewage sludge, was further selected to present its properties that qualifies if as sorbents for copper ions removal from wastewaters, as being the compost obtained from three different biomass wastes [33]. Before sorption tests, cooper ions content in the compost substrates was analysed by AAS, following a previously presented method for samples preparation [48]. Composts C1 contained no Cu2+, result allowing us to easy evaluate the metal cations sorbed by the composts. In order to demonstrate the sorbent capacity of our selected compost (C1), the methodology followed the steps: • compost surface characterization; • sorption parameters determination: (i) contact time (t), (ii) ratio of wastewater volume: sorbent compost mass (v/mss); for the optimum t and mss, sorption isotherms were plotted; • thermodynamic investigation: Langmuir and Freundlich models were used to fit the experimental data and to describe the sorption mechanisms; • kinetic models investigation: pseudo-first-order, pseudo second-order and intra particle diffusion were used also to establish the sorption mechanisms; • correlation of the thermodynamic and kinetic models with the composts surface properties, determined after sorption. For the Cu2+ content (mg/L) determination during soption, amounts of substrate composts were added into 100 mL of Cu2+ solutions (250 mg/L), at room temperature (21–23 °C), and at natural pH (5.1  6) and under magnetic stirring. There was no physical or chemical treatment applied on the compost, thus keeping the sorption based treatment at low costs. Qualitative evaluation of Cu2+ sorbed on C1 compost surface was possible by studding its morphology and topography. Therefore, SEM and AFM analysis after adsorption were performed to get information on the changes induced by the heavy metal sorption. The presence of bright spots in the SEM images give evidence of a change in the compost surface morphology (Fig. 11), which can be attributed to the sorption of Cu2+ on the compost surface. The AFM analyses indicate large aggregates with different dimensions on C1 surface, and an increase in the average roughness (from 42 to 51 nm), certifying the adsorption process of Cu2+ only on specific sites on the compost surface. The sorption efficiencies (η, in %) were evaluated based on Eq. (3): g¼

c0  ce
100 c0

ð3Þ

where: co - copper ions concentration in the initial solution [mg/L]; ce - copper ions concentration at sorption equilibrium [mg/L].

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

579

Fig. 11. AFM and SEM images after adsorption of Cu2+ on C1 compost

The adsorption capacity (q, in mg/g) was calculated according to Eq. (4): q¼

ð c0  ce Þ
V mss

ð4Þ

where: V - volume of the copper ions solution [mL]; mss - mass of sorbent substrate [g]. In order to optimise the contact time, 0.5 g of compost sorbents were stirred for 1 min  48 h, then the sorbents were removed by vacuum filtration and the supernatant was analyzed by AAS (kCu = 324.75 nm). At the determined contact time, the V/mss ratio was optimised, working with different quantities of sorbents (0.5–3 g). With the optimised contact time and v/mss ratio, the sorption isotherms were plotted, at different Cu2+ concentration (1.5–250 mg/L). The optimum contact time and sorbent mass were determined based on the sorption efficiency variation in time (Fig. 12a and b). We determined the optimum time to be 30 min, and the sorbent optimum mass was 1.5 g. Based on optimised parameters, the adsorption isotherm, q = f(ce), was plotted (Fig. 11c) and the linear form of Freundlich model is given by Eq. (5): 1 log q ¼ log ce þ log k n

ð5Þ

where: k and n - Freundlich equilibrium constant and exponent, respectivelly; 1/n parameter giving information about the sorption intensity. The Langmuir model was not able to describe the copper ions sorption on C1 compost, for the whole range of tested Cu2+ concentrations, but, Freundlich parameters were calculated and gave information about the sorption mechanism (Table 6). In order to have more complete information on the adsorption process, kinetics studies were developed, and we found that the most suitable one was the pseudo

580

I. Manciulea et al.

Fig. 12. Sorption tests: (a) Cu2+ immobilization efficiency vs. contact time, (b) Cu2+ immobilization efficiency vs. compost mass, (c) Sorption isotherm of Cu2+ on compost, (d) Sorption efficiency versus initial Cu2+ concentration on compost

second-order kinetic model for the entire process duration of copper sorption on composts. The equation for pseudo-second order kinetic model is given by Eq. (6) [65]: t=qt ¼ 1=k2  q2e þ t=qe

ð6Þ

The kinetic parameters were calculated and also gave information about the sorption mechanism (Table 6). Table 6. Freundlich parameters and the kinetic parameters (pseudo second order) for copper ions sorption Compost Freundlich model Pseudo second order 1–30 min k2 [g/mg min] qe [mg/g] R2 k [mg/g] 1/n R2 C1 0.0378 1.009 0.9757 0.033 16.2 0.991

The values of the Freundlich parameters (especially 1/n > 1) support the cooperative adsorption of copper ions onto compost-type substrates. This is specific for substrates/surfaces with high heterogeneity degree in composition/structure, high energy and randomly distribution of the active sites with different affinities, like C1 is. The main interactions involve the partially dissociated –OH and –COOH functional groups from the composts surfaces and the positively charge copper ions, but also unspecific physical interactions [66, 67]. Pseudo second order kinetic model proved to be valid for C1 compost, for the studied process duration (3–120 min), being characteristic to substrates with concentration of active sites comparable with the concentration of copper ions. The process is more rapid (k2) in the first moments (3–30 min), being controlled by the number of copper ions that reach the composts surface. The other two tested models fit well the

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

581

data only in a limited time interval indicating that parallel/complex mechanisms are likely within this range, on the highly heterogeneous substrate [68–71]. In practical applications, like wastewater treatment based sorption, information on the sorption efficiency for different initial copper load are essential for the optimal functioning of the process (Fig. 11d). We concluded that C1 compost is efficient sorbent in advanced wastewater treatment for Cu2+ removal at concentration in the range of 7 to 125 mg/L, with maximum efficiency (98%) at 62.5 mg/L of Cu2+.

4 Conclusions Mature and stable composts were prepared from vegetable wastes, mixed with sewage sludge, beech sawdust and beech ash, by aerobic fermentation, up to their final state of humification. Our overviewed study demonstrated the possibility of obtaining, by recycling/composting of biomass waste, new, ecological and low costs biofertilizer materials, also having sorbent properties, to be used in advanced treatment of wastewaters polluted with heavy metals. A recent study demonstrating the sorbent capacity of two other composts was submitted for publication. For perspective development, other composts are prepared and ready for measurements to investigate their properties that qualify them either as biofertilizers or as sorbent substrates used for pollutants removal from contaminated environment. We consider that such studies can contribute to the development of “Nearly Zero Energy Communities”, by proposing sustainable solutions for all types of identified problems that characterize the environment nowadays.

References 1. IISD - International Institute for Sustainable Development site. http://www.iisd.org/topic/ sustainable-development. Accessed May 2017 2. Teresa, M., Herrero, E., Bescos, B., López, M.: LIFE + MANEV - evaluation of manure management systems and treatment technologies in Europe. In: Körner, I. (ed.) RAMIRAN 2015 - 16th International Conference Rural-Urban Symbiosis Proceedings book, 8th–10th September 2015, pp. 598–602. Hamburg University of Technology, Germany (2015). doi: urn:nbn:de:gbv:830-88213742 3. Neugebauer, M., Sołowiej, P.: The use of green waste to overcome the difficulty in small-scale composting of organic household waste. J. Clean. Prod. 156, 865–875 (2017). http://dx.doi.org/10.1016/j.jclepro.2017.04.095 4. Environmetal Protection Agency, Report on the state of the environment in Brasov county for 2015 (Raport privind starea mediului în judeţul Braşov, pentru anul 2015, in Romanian) site. http://www.anpm.ro/web/apm-brasov/rapoarte-anuale1 5. Directive 2009/28/CE site. http://eur-lex.europa.eu/legal-content/RO-EN/TXT/?uri=CELEX: 32009L0028&fromTab=ALL&from=EN 6. Wei, Y., Li, J., Shi, D., Liu, G., Zhao, Y., Shimaoka, T.: Environmental challenges impeding the composting of biodegradable municipal solid waste: a critical review. Resour. Conserv. Recycl. 122, 51–65 (2017). doi:10.1016/j.resconrec.2017.01.024

582

I. Manciulea et al.

7. Haug, R.T.: The Practical Handbook of Compost Engineering. Lewis Publishers, Boca Raton (1993) 8. Liu, N., Zhou, J., Han, L., Ma, S., Sun, X., Huang, G.: Role and multi-scale characterization of bamboo biochar during poultry manure aerobic composting. Bioresour. Technol. 241, 190–199 (2017). http://dx.doi.org/10.1016/j.biortech.2017.03.144 9. Rynk, R., et al.: On Farm Composting Handbook. Northeast Regional Agricultural Engineering Service, Ithaca (1992). Available from NRAES, Cooperative Extension, 152 Riley-Robb Hall, Ithaca, NY 14853-5701, (607) 255-7654 10. Dumitrescu, L.: Cercetari privind posibilitatile de recuperare şi valorificare superioara a deseurilor menajere prin compostare, Raport de cercetare - Grant: CNCSIS 602/2004, Universitatea Transilvania, Brasov (2004) 11. Chiumenti, A.: Complete nitrification-denitrification of swine manure in a full-scale, non-conventional composting system. Waste Manag 46, 577–587 (2015). http://dx.doi.org/ 10.1016/j.wasman.2015.07.035 12. Woodbury, P., Breslin V.: Key Aspects of Compost Quality Assurance. Cornell Waste Management Institute (1993) 13. Dumontet, S., Pontonio, M., Basile, G., Marino, P.: Effect of cadmium-bearing sewage sludge on crop plants and microorganisms in two different soils. Agric. Ecosyst. Environ. 181–194 (1998). https://doi.org/10.1016/0167-8809(88)90110-7 14. Bielská, L., Kah, M., Sigmund, G., Hofmann, T., Höss, S.: Bioavailability and toxicity of pyrene in soils upon biochar and compost addition. Sci. Total Environ. 595, 132–140 (2017). http://dx.doi.org/10.1016/j.scitotenv.2017.03.230 15. Huang, M., Zhu, Y., Li, Z., Huang, B., Luo, N., Liu, C., Zeng, G.: Compost as a soil amendment to remediate heavy metal-contaminated agricultural soil: mechanisms, efficacy, problems, and strategies. Water Air Soil Pollut. 227, 359 (2016). http://dx.doi.org/10.1007/ s11270-016-3068-8 16. Amin, M.M., Rahimi, A., Nourmoradi, B.B., Hassanvand, M.S.: Biodegradation of n-hexane as single pollutant and in a mixture with BTEX in a scoria/compost-based biofilter. Process Saf. Environ. Prot. 107, 508–517 (2017). http://dx.doi.org/10.1016/j.psep.2017.03.019 17. Rene, E.R., Kar, S., Krishnan, J., Pakshirajan, K., Lopez, M.E., Murthy, D.V.S., Swaminathan, T.: Start-up, performance and optimization of a compost biofilter treating gas-phase mixture of benzene and toluene. Biores. Technol. 190, 529–535 (2015). http://dx. doi.org/10.1016/j.biortech.2015.03.049 18. ASCP Guidelines: Quality Criteria for Composts and Digestates from Biodegradable. Waste Management. Association of Swiss Compost Plants (ASCP) (2001). http://www.biophyt.ch/ documents/vks_english_000.pdf 19. Zmora-Nahum, S., Hadar, Y., Chen, Y.: Physico-chemical properties of commercial composts varying in their source materials and country of origin. Soil Biol. Biochem. 39, 1263–1276 (2007). doi:10.1016/j.soilbio.2006.12.017 20. US. EPA: Decision Makers Guide to Solid Waste Management, vol. II, 2nd edn. EPA530-R-95-041 (1997). http://regulationbodyofknowledge.org/wp-content/uploads/2014/ 06/EPA_Decision_Makers.pdf 21. Simionescu, C., Grigoras, M., Cernatescu-Asandei, A.: Chimia Lemnului din RPR. Editura Academiei RPR, Bucuresti (1964) 22. Griffin, G., Oregon, F.: Beneficial use determination application (2012). http://www. humeseeds.com/ashes.htm 23. Zaha, C., Dumitrescu, L.: Sludge recycling needs and trends. Bull. Transilv. Univ. Brasov Ser. I 1(50), 299–305 (2008). ISSN 2065-2127 24. Fabregat, A., Bengoa, C., Font, J., Stueber, F.: Reduction, Modification and Valorisation of Sludge. IWA Publishing, London/New York (2011)

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

583

25. Worwag, M., Rorat, A., Brattebo, H., Almås, A., Singh, B.R.: Sewage sludge disposal strategies for sustainable development. Environ. Res. 156, 39–46 (2017). http://dx.doi.org/ 10.1016/j.envres.2017.03.010 26. Suleiman, H., Rorat, A., Grobelak, A., Grosser, A., Milczarek, M., Płytycz, B., Kacprzak, M., Vandenbulcke, F.: Determination of the performance of vermicomposting process applied to sewage sludge by monitoring of the compost quality and immune responses in three earthworm species: Eisenia fetida, Eisenia andrei and Dendrobaena veneta. Bioresour. Technol. 241, 103–112 (2017). doi:10.1016/j.biortech.2017.05.104 27. Zaha, C., Sauciuc, A., Dumitrescu, L., Manciulea, I.: Aspects regarding recycling sludge by composting. Environ. Eng. Manag. J. 10, 1589–1594 (2011) 28. Zaha, C., Manciulea, I., Sauciuc, A.: Reducing the volume of waste by composting vegetable waste, sewage sludge and sawdust. Environ. Eng. Manag. J. 10, 1415–1423 (2011) 29. Dumitrescu, L., Manciulea, I., Isac, L.: Recycling waste by composting. Bull. Transilv. Univ. Brasov 14, 679–684 (2007) 30. Dumitrescu, L., Manciulea, I., Zaha, C., Sauciuc, C.: Recycling biomass waste to compost. In: Visa, I. (ed.) Sustainable Energy in the Built Environment - Steps Towards nZEB, pp. 229–241. Springer, Berlin (2014). doi:10.1007/978-3-319-09707-7 31. Dumitrescu, L., Manciulea, I., Sauciuc, A., Zaha, C.: Obtaining fertilizer compost by composting vegetable waste, sewage sludge and sawdust. Bull. Transil. Univ. Braşov. 2, 117–122 (2009). Transilvania University Press, Brasov, Romania 32. Zaha, C., Sauciuc, A., Manciulea, I., Dumitrescu, L.: Sustainable development by recycling waste as biofertilizer compost. In: Proceedings of 1st International Conference on Quality and Innovation in Engineering and Management, pp. 535–538, Cluj-Napoca, Romania (2011) 33. RAMIRAN 2015 Conference Site. http://ramiran2015.de/wp-content/uploads/2016/01/ RAMIRAN2015_Abstract-Book.pdf. Accessed May 2017 34. Hogg, D., Lister, D., Barth, J., Amlinger, F., Favoino, E.: Frameworks for Use of Compostin Agriculture (2009). http://www.wrap.org.uk/sites/files/wrap/Eunomia%20compost%20in% 20agriculture%20in%20Europe%20report.pdf 35. Howarth, W.R., Elliott, L.F., Churchill, D.B.: Mechanisms regulating composting of high carbon to nitrogen ratio grass straw. Compost Sci. Util. 3(3), 22–30 (1995) 36. Oleszczuk, P.: The toxicity of composts from sewage sludges evaluated by the direct contact tests phytotoxkit and ostracodtoxkit. Waste Manag. 28, 1645–1653 (2008). doi:10.1016/j. wasman.2007.06.016 37. Rajbanshi, S.S., Endo, H., Sakamoto, K., Inubushi, K.: Stabilization of chemical and biochemical characteristics of grass straw and leaf mix during in-vessel composting with and without seeding material. Soil Sci. Plant Nutr. 44, 485–495 (1998) 38. Stylianou, M.A., Inglezakis, V.J., Moustakas, K.G., Loizidou, M.D.: Improvement of the quality of sewage sludge compost by adding natural clinoptilolite. Desalination 224, 240– 249 (2008). doi:10.1016/j.desal.2007.06.009 39. Zucconi, F., Bertoldi, M.: Composts specifications for the production and characterization of composts from municipal solid waste. In: Bertoldi, M., Ferranti, M.P., L’Hermite, P., Zucconi, F. (eds.) Compost: Production, Quality and Use, pp. 30–50. Elsevier Applied Science, London (1987) 40. Fuentes, A., Lloréns, M., Sáez, J., Aguilar, M.I., Ortuño, J.F., Meseguer, V.F.: Phytotoxicity and heavy metals speciation of stabilized sewage sludges. J. Hazard. Mater. A108, 161–169 (2004). https://doi-org.am.e-nformation.ro/10.1016/j.jhazmat.2004.02.014 41. Boulter-Bitzer, J.I., Trevors, J.T., Bolanda, G.J.: A polyphasic approach for assessing maturity and stability in compost intended for suppression of plant pathogens. Appl. Soil. Ecol. 34, 65–81 (2006). doi:10.1016/j.apsoil.2005.12.007

584

I. Manciulea et al.

42. World Health Organisation (WHO): Guidelines for the Safe Use of Wastewater, Excreta and Greywater. Excreta and Greywater Use in Agriculture, vol. 4, Geneva, Switzerland (2006). ISBN 92 454685 9 43. Morosanu, I., Teodosiu, C., Paduraru, C., Ibanescu, D., Tofan, L.: Biosorption of lead ions from aqueous effluents by rapeseed biomass. New Biotechnol. (2016, in press). http://dx.doi. org/10.1016/j.nbt.2016.08.002 44. Tofan, L., Teodosiu, C., Paduraru, C., Wenkert, R.: Cobalt(II) removal from aqueous solutions by natural hemp fibers: batch and fixed-bed column studies. Appl. Surf. Sci. 285P, 33–39 (2013). doi:10.1016/j.apsusc.2013.06.151 45. Paduraru, C., Tofan, L., Teodosiu, C., Bunia, I., Todorachi, N., Toma, O.: Biosorption of zinc(II) on rapeseed waste: equilibrium studies and thermogravimetric investigations. Process Saf. Environ. Prot. 94, 18–28 (2015). doi:10.1016/j.psep.2014.12.003 46. Yuvaraja, G., Krishnaiah, N., Subbaiah, M.V., Krishnaiah, A.: Biosorption of Pb(II) from aqueous solution by Solanum melongena leaf powder as a low-cost biosorbent prepared from agricultural waste. Colloids Surf. B Biointerfaces 114, 75–81 (2014). doi:10.1016/j. colsurfb.2013.09.039. Elsevier B.V. 47. Ifthikar, J., Wang, J., Wang, Q., Wang, T., Wang, H., Khan, A., Jawad, A., Sun, T., Jiao, X., Chen, Z.: Highly efficient lead distribution by magnetic sewage sludge biochar: sorption mechanisms and bench applications. Bioresour. Technol. 238, 399–406 (2017). http://dx.doi. org/10.1016/j.biortech.2017.03.133 48. Lucaci, D., Duta, A.: Adsorption of Cu2+ on white poplar and oak sawdust. Environ. Eng. Manag. J. 8, 871–876 (2009) 49. Lucaci, D., Visa, M., Duta, A.: Copper removal on wood-fly ash substrates - thermodynamic study. Revue Roumaine de Chimie 56, 1067–1074 (2011) 50. Rao, P.S., Reddy, K.V.N.S., Kalyar, S., Krishuciah, A.: Comparative sorption of copper and nickel from aqueous solutions by natural neem (Azadirachta indica) sawdust and acid treated sawdust. Wood Sci. Technol. 41, 427–442 (2007). doi:10.1007/s00226-006-0115-4 51. Shukla, S.S., Yu, L.J., Dorris, K.L., Shukla, A.: Removal of nickel from aqueous solutions by sawdust. J. Hazard. Mater. B121, 243–246 (2005). doi:10.1016/j.jhazmat.2004.11.025 52. Acar, F.N., Eren, Z.: Removal of Cu(II) ions by activated poplar sawdust (Samsun Clone) from aqueous solutions. J. Hazard. Mater. B137, 909–914 (2006). doi:10.1016/j.jhazmat. 2006.03.014 53. Ngah, W.S.W., Hanafiah, M.A.K.M.: Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: a review. Bioresour. Technol. 99, 3935– 3948 (2008). doi:10.1016/j.biortech.2007.06.011 54. Silvetti, M., Garau, G., Demurtas, D., Marceddu, S., Deiana, S., Castaldi, P.: Influence of lead in the sorption of arsenate by municipal solid waste composts: metal(loid) retention, desorption and phytotoxicity. Bioresour. Technol. 225, 90–98 (2017). http://dx.doi.org/10. 1016/j.biortech.2016.11.057 55. Redding, M.R., Lewis, R., Kearton, T., Smith, O.: Manure and sorbent fertilisers increase on-going nutrient availability relative to conventional fertilisers. Sci. Total Environ. 569– 570, 927–936 (2016). http://dx.doi.org/10.1016/j.scitotenv.2016.05.068 56. Al-Mashaqbeh, O., McLaughlan, R.G.: Non-equilibrium zinc uptake onto compost particles from synthetic stormwater. Bioresour. Technol. 123, 242–248 (2012). http://dx.doi.org/10. 1016/j.biortech.2012.07.034 57. Bouzid, J., Elouear, Z., Ksibi, M., Feki, A., Montiel, A.: A study on removal characteristics of copper from aqueous solution by sewage sludge and pomace ashes. J. Hazard. Mater. 152(2), 838–845 (2008). doi:10.1016/j.jhazmat.2007.07.092

Compost Based on Biomass Wastes Used as Biofertilizers or as Sorbents

585

58. Bozic, D., Stankovic, V., Gorgievski, M., Bogdanovic, G., Kovacevi, R.: Adsorption of heavy metal ions by sawdust of deciduous trees. J. Hazard. Mater. 171, 684–692 (2009). doi:10.1016/j.jhazmat.2009.06.055 59. Aksu, Z., Isoglu, I.A.: Removal of copper (II) ions from aqueous solution by biosorption onto agricultural waste sugar beet pulp. Process Biochem. 40, 3031–3044 (2005). doi:10. 1016/j.procbio.2005.02.004 60. Lu, S., Gibb, S.W.: Copper removal from wastewater using spent-grain as biosorbent. Bioresour. Technol. 99, 1509–1517 (2008). doi:10.1016/j.biortech.2007.04.024 61. Hasar, H.: Adsorption of Ni(II) from aqueous solution onto activated carbon prepared from almond husk. J. Hazard. Mater. 97, 49–57 (2003). https://doi-org.am.e-nformation.ro/10. 1016/S0304-3894(02)00237-6 62. Lu, D., Cao, Q., Li, X., Cao, X., Cao, F., Shao, W.: Kinetics and equilibrium of Cu(II) adsorption onto chemically modified orange peel cellulose biosorbents. Hydrometallurgy 95, 145–152 (2009). doi:10.1016/j.hydromet.2008.05.008 63. Fiol, N., Villaescusa, I., Martinez, M., Miralles, N., Poch, J., Serarols, J.: Sorption of Pb(II), Ni(II), Cu(II) and Cd(II) from aqueous solution by olive stone waste. Sep. Purif. Technol. 50, 132–140 (2006). doi:10.1016/j.seppur.2005.11.016 64. Bhatnagara, A., Sillanpaa, M.: Utilization of agro-industrial and municipal waste materials as potential adsorbents for water treatment - a review. Chem. Eng. J. 157, 277–296 (2010). doi:10.1016/j.cej.2010.01.007 65. Ho, Y.S., McKay, G.: The kinetics of sorption of divalent metal ions onto sphagnum moss peat. Water Res. 34, 735–742 (2000). https://doi-org.am.e-nformation.ro/10.1016/S00431354(99)00232-8 66. Ali, R.M., Hamad, H.A., Hussein, M.M., Malash, G.F.: Potential of using green adsorbent of heavy metal removal from aqueous solutions: Adsorption kinetics, isotherm, thermodynamic, mechanism and economic analysis. Ecol. Eng. 91, 317–332 (2016). http://dx.doi.org/ 10.1016/j.ecoleng.2016.03.015 67. Bhattacharya, A.K., Naiya, T.K., Mandal, S.N., Das, S.K.: Adsorption, kinetics and equilibrium studies on removal of Cr(VI) from aqueous solutions using different low-cost adsorbents. Chem. Eng. J. 137, 529–541 (2008). doi:10.1016/j.cej.2007.05.021 68. Bulgariu, L., Tudorache Fertu, D.I., Gavrilescu, M.: Sustainable use of biomass for cleaning-up aqueous effluents contaminated with heavy metals. Ann. Acad. Rom. Sci. 1, 5–18 (2014) 69. Febriana, N., Lesmana, S.O., Soetaredjo, F.E., Sunarso, J., Ismadji, S.: Neem leaf utilization for copper ions removal from aqueous solution. J. Taiwan Inst. Chem. Eng. 41, 111–114 (2010). doi:10.1016/j.jtice.2009.04.003 70. Mushtaq, M., Bhatti, H.N., Iqbal, M., Noreen, S.: Eriobotrya japonica seed biocomposite efficiency for copper, adsorption: isotherms, kinetics, thermodynamic and desorption studies. J. Environ. Manag. 176, 21–33 (2016). http://dx.doi.org/10.1016/j.jenvman.2016.03.013 71. Visa, M., Bogatu, C., Duta, A.: Simultaneous adsorption of dyes and heavy metals from multicomponent solutions using fly ash. Appl. Surf. Sci. 256, 5486–5491 (2010). doi:10. 1016/j.apsusc.2009.12.145

A Comparative Analysis of Pollutants Adsorption and Photocatalysis on Composite Materials Synthesized from Fly Ash Maria Visa(&), Nicoleta Popa, and Andreea Chelaru Renewable Energy Systems and Recycling Research Center, Transilvania University of Brasov, Brasov, Romania [email protected] Abstract. The composite materials were obtained from fly ash, collected from the electro filters of the Central Heat Power Plant from Brasov, Romania. This fly ash doesn’t aggregate in water and can form a new composite together with TiO2 and Al2Si2O7.2H2O. The raw ash combined with titanium oxide and silicate was modified by hydrothermal treatment under alkaline conditions. The new composites were characterized in terms of crystallinity (XRD), surface properties such as: morphology (SEM, AFM), wettability (contact angle measurements) and specific surface (BET). Simultaneous removal of heavy metals (Cd2+, Cu2+), dye (methylene blue - MB) and surfactant (sodium dodecylbenzene sulfonate - SDBS) pollutants was investigated by adsorption and photodegradation ontwo composites (FUS-DAl1 and FUS-DAl2). The adsorption parameters (contact time and amount of substrate) were optimized for obtaining a maximum efficiency and were further used in kinetic studies, comparatively discussed with the photocatalysis optimized operating parameters. The UV-photocatalytic properties of the obtained materials were evaluated in pollutant systems containing three (Cd2++MB+SDBS, Cu2++MB+SDBS) and four pollutants (Cd2++Cu2++MB+SDBS). Keywords: Fly ash


TiO2
Photocatalysis/adsorption
Heavy metals
Dye

1 Introduction Water quality and waste management represent two of the main problems that humanity faces nowadays. Population growth, increased urbanization and industrialization have led to the release of the hazardous inorganic and organic pollutants such as: heavy metals, dyes, surfactants, waxes, etc. into the environment [1]. Textile industry represents a potential major polluting sources because it uses large amounts of water during dyeing and rinsing processes. About 1–20% of the total world production of dyes is lost during the dyeing process and is released in the textile effluents [2]. Due to the large degree of aromatics existing in dye molecules and their stability, conventional biological treatment methods are ineffective for decolorization and degradation. Moreover, some dyes are reported to cause allergy, dermatitis, skin and eyes irritation, cancer and mutation in human body. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_41

A Comparative Analysis of Pollutants Adsorption

587

Other pollutants that result from the textile industry are heavy metals, contained in dyes and surfactants used as additives. Wastewaters with this complex load must be treated before discharge and this needs to be an important objective for all stakeholders involved in industrial wastewater treatment and management. The removal methods of pollutants (dyes, surfactants, heavy metals) from wastewater can be associated with chemical, physical, biological, electrochemical and radiation processes. Several methods can be used, such as: chemical precipitation [3], coagulation and flocculation [4], ion-exchange, membrane filtration [5], reverse osmosis [6], adsorption [7] and photodegradation [8]. Among these methods, adsorption and photocatalysis are often considered the most effective. Adsorption is one of the most effective and attractive strategies for the decontamination of wastewater loaded with non-biodegradable contaminants due to some reasons like: simple operation, simple equipment needed, the large variety of the adsorbent materials - some of which being low-cost since they are prepared from agricultural wastes, forest wastes, fly ash and natural zeolites - easy regeneration of the adsorbent, etc. Adsorption efficiency depends on both the adsorbent and pollutant properties. Zeolites are crystalline aluminosilicates with a three-dimensional framework structure that forms uniformly sized pores of molecular dimensions [9]. Zeolite structures which have been synthesised usually include, NaP1 [10–12], Na-A [13], and EPI-type [14]. In addition, there are reports on the use of nanorod zeolites in wastewater treatment for the removal of heavy metals and dyes [15, 16]. Activated carbon and resins are often used as common sorbent in the treatment of water contamination due to their high adsorption capacity. However, the high cost of these materials limits their large-scale application. During the last years, extensive research has been done to find low-cost, available, and high efficiency adsorbents for removal of organic and inorganic pollutants [17–20]. Organic pollutants such as dyes are very difficult to be removed due to their complex structure, with two or more aromatic rings, chromofore groups (azo -group (-N = N-) ketone group (-C = O), anthraquinone group), auxochrome groups (amino group (NH2), phenol hydroxyl group (-OH). For these pollutants the adsorption involves only phase transfer of pollutants without degradation, indicating that a subsequent waste treatment has to follow. Even if traditional techniques for wastewaters treatment are still in use, advanced oxidation processes (AOPs), based on the generation of reactive species (•OH radicals), are more and more recommended for the oxidative degradation of organic pollutants, targeting water reuse [21]. One of the semiconductors frequently used in the removal of organic pollutants by photocatalysis is TiO2 in spite of some disadvanteges like: TiO2 nanoparticles are subject to agglomeration when applied in wastewater treatment; low surface area, low thermal stability and poor mechanical resistance causing negative effects for long-term stability. Using suspensions of TiO2 powders in wastewater, the removal and separation process is difficult and could lead to the secondary pollution. Therefore, a photocatalytic configuration with such nanoparticles being incorporated in a durable biocompatible suport has the potential to both improve the stability of the photocatalytic nanoparticles and allow wastewater treatment without further contamination [22]. Researchers have explored multiple solid substrates to immobilize TiO2 or WO3 resulting in various composites of TiO2/glass fiber cloth [23], TiO2 on perlite granules, graphene-TiO2, zeolite/TiO2, fly ash/TiO2 [24, 25], fly ash/WO3 [26], etc.

588

M. Visa et al.

Incorporating TiO2/Al2O3 as support [27] would result in increased catalytic activity. Furthermore, it is reported that one kind of titanium dioxide photocatalyst was supported by glass fibers (GF), and more than 99% of the initial pollutant concentration of pollutants (benzamide, bisphenol A and its analogues) was degraded after 3.5 h of exposure to UV light [28]. The aim of the present study is to develop a composite substrate based on modified fly ash as support for TiO2 (Degussa P25) applied to the advanced treatment of wastewaters containing multiple pollutants through adsorption and photocatalysis.

2 Materials and Methods 2.1

Materials Synthesis

The new composites were synthesized from fly ash by the hydrothermal method using mild conditions. Oxides are the main compounds and the sum of the major oxides SiO2, Al2O3 and Fe2O3 is over 70% (Table 1), thus the FA is of type F and it does not aggregate in water when subjected to long agitation durations, according to the ASTM standard C-618-2a, [29]. Fe2O3 (8.97%) and MnO (0.08%) are important as possible participants in the organic pollutants photodegradation as photocatalyst and as Photo-Fenton co-reactants, respectively. The small amounts of the metals (Ba, Cu, Zr, Sn, Pb, As, Ni, Zn, Cr, V, Mn, Co, Ti) from raw fly ash (FA) collected from Central Heat Power Plant Brasov, Romania were identified by using emission spectrometry [15]. The grain size of the fly ash is between 20–200 µm. The fly ash washed with ultrapure water was filtered, dried in an oven at 105–120 °C, sieved (Sieve Analysette 3 Spartan) and the 20–40 µm fractions were selected for materials synthesis. Two new composites were prepared from the sieved fly ash by hydrothermal treatment under alkaline conditions [30]. One half of the washed sample was mixed with NaOH pellets, TiO2 powder (Degussa P25) and Al2Si2O7
2H2O; the second half was mixed only with NaOH pellets and Al2Si2O7
2H2O. Both samples were fused at 500 °C, followed by hydrothermal treatment. For the second sample the TiO2 powder was added during the hydrothermal treatment. The fly ash, the amorphous aluminosilicate (Al2Si2O7), both represents the support for TiO2 photocatalyst. The obtained substrates, noted FUSD-Al1 and FUSD-Al2 were further used in adsorption experiments and photocatalysis. Table 1. Fly ash composition Major oxides [%] SiO2 Al2O3 Fe2O3 CaO 53.32 22.05 8.97 5.24 L.O.I. - Loss of ignition Trace elements [ppm] Ba Cu Zr Sn Pb As 700 60 100 3 35 100

MgO K2O Na2O TiO2 MnO L.O.I. 2.44 2.66 0.63 1.07 0.08 1.58

Ni Zn Cr V Mn Co Ti 55 160 100 115 800 12 >3000

A Comparative Analysis of Pollutants Adsorption

2.2

589

Characterization of the New Composites

The composites were characterized in terms of crystallinity by X-ray diffraction (XRD, Bruker D8 Discover Diffractometer, Ka1 = 1.5406 Å, 40 kW, 20 mA, step size 0.002, scan-speed 2 s/step, 2h range from 10 to 80o). The size and morphology of the described synthesized particles were investigation by a scanning electron microscope (SEM, S-3400 N- Hitachi) at an accelerating voltage of 20 kV. The surface elemental composition was measured using energy dispersive X-ray spectroscopy (EDS Thermo Scientific Ultra Dry). The roughness and macro-pore size distribution were done using AFM (Ntegra Spectra, NT-MDT model BL222RNTE); images were taken in semi-contact mode with Golden silicon cantilever (NCSG10), with constant force 0.15 N/m, having the tip radius of 10 nm. Scanning was performed on at least three different points with a certain area of 5  5 lm each, chosen randomly at a scanning grate of 1 Hz. Surface characterization was completed by porosity analysis and BET surface (Autosorb-IQ-MP, Quantachrome Instruments).

3 Results and Discussion 3.1

Characterization of the Materials

The XRD analysis (Fig. 1) show a more complex composition for the new composites FUS-DAl1 and FUS-DAl2: the structure is composed of mostly alumino-silicates (Table 2). The crystallite sizes were calculated using the Scherrer Eq. (1) [31]: s¼

Kk b cos h

ð1Þ

where: s - is the size of crystallites, K - is the shape factor with a typical value 0.94, k is the X-ray wavelength (1.5406 Ẳ), b - is the line broadening at half the maximum intensity (of a peak), h - is diffraction angle. 2

3500

2

3000

3 Intensity [a.u.]

2500 2000

7 4

1500 1000

22

58

45 4 4 3

1 SiO2 quartz 2 Anatasse thetragonale (TiO2) 3 Rutile syn (TiO2) 4 Na6Al6Si10O32*12H2O 5 Albite low 6 Manganese (Mn2O3) 7 Chabasite-Na syn 8 Hematite (Fe2O3)

2

2

2 (C)

2

5 (B)

1

500

(A) 0 10

20

30

40

50

60

70

80

2Theta [degree]

Fig. 1. X-ray diffractogram of (A) FAw, (B) FUS-DAl1 and (C) FUS-DAl2

590

M. Visa et al.

Table 2. The composition of the crystalline phases, crystalline network, data of FAw, FUS-DAl1 and FUS-DAl2 Substrate

Compound

Cell parameters Crystallite size [Å]

26.865 Hexagonal a = 4.903 c = 5.393 a = b = 90° c = 120° Sodium Silicate (Na6Si8O19) (00-049-0162) 26.688 NA FUS-DAl1 Anatasesyn, TiO2 (01-086-1157) 25.321 Tetragonal 37.943 a = 3.73 48.111 c = 9.37 54.018 a = b = c = 90° 55.154 62.822 68.957 70.434 75.262 36.069 Tetragonal Rutile, syn, TiO2 (03-065-0190) 44.021 a = 4.592 56.688 c = 2.957 62.766 a = b = c = 90° 38.01 Orthorhombic Brookite, TiO2, (00-016-0617) 46.123 a = 5.455 54.245 c = 9.182 a = b = c = 90° Sodium Aluminum Silicate, Na2Al2Si5O14, 26.732 Hexagonal (00-048-0733) a = 20.69 c = 14.33 a = b = 90° c = 120° 25.313 Tetragonal Anatase, TiO2 (00-001-0562) 37.969 a = 3.73 62.828 c = 9.37 69.108 a = b = c = 90° 33.44 Monoclinic Manganese, Mn2O3 (00-001-1061) a = 6.795 b = 16.687 c = 9.54 a = 90° b = 100.2° 27.45 Triclinic Sodium Aluminum Silicate, NaAlSi2O6, (00-047-0288) a = 14.84 b = 9.18 c = 9.13 a = 90° b = 123.9° 28.039 Triclinic Sodium Aluminum Silicate, Na(AlSi3O8) (01-086-0099) a = 8.167 b = 12.856 c = 7.12 a = 93.34° b = 116.4° FAw

Quartz, SiO2, (00-001-0649)

2h theta

Net Area

Crystallinity

344.6

123.9 38.3%

144.0 149.1

123.9 584.0 78.2% 62.72 149.4 60.81 41.44 38.40 25.20 9.738 17.18 14.42 7.212 2.46 38.40 1.63 2.696 60.81

81.6

81.3

81.6

3.340

149.1

179.9

62.72 38.40 25.20 9.738 8.404

85.4

12.88

81.4

8.15

(continued)

A Comparative Analysis of Pollutants Adsorption

591

Table 2. (continued) Substrate

Compound

2h theta

Albite ordered (NaAlSi3O8) (00-019-1184)

41.32 Triclinic 48.074 a = 8.138 50.131 b = 12.79 c = 7.161 a = 94.27° b = 116.6°

81.5

5.78 126.2 32.73

Sodium Aluminum Silicate hydrate, Na6Al6Si10O32*12H2O (00-039-0219)

12.43 Tetragonal 17.713 a = b = 29 21.631 c = 18.77 a = b = 90° 28.095 Tetragonal 29.628 a = b = 10.01 37.120 c = 9.83 a = b = 90° 12.373 Orthorhombic 17.595 a = 9.868 26.733 b = 10.082 33.374 c = 10.098 44.101 a = b = 90° 46.144 62.775 12.494 Monoclinic 21.752 a = 7.256 33.394 b = 7.686 c = 8.683 a = 90.75° b = 99.75° 17.662 Orthorhombic 21.695 a = 9.965 27.601 b = 14.252 44.128 c = 14.252 a = b = 90° 54.237 Rhombo H axes a = b = 5.028 c = 13.73 a = b = 90° 25.264 Tetragonal 37.981 a = 37.3 2.790 c = 9.37 69.035 a = b = 90° 25.377 Tetragonal 37.016 a = 3.7852 37.810 c = 9.5139 48.086 a = b = 90° 55.183 70.341 75.110 27.421 Tetragonal 36.107 a = 4.594 56.659 c = 2.959 62.847 a = b = 90° 69.092

136.9

14.86 8.339 25.54

123.8

9.154 14.05 8.866

183.5

4.662 7.565 10.55 7.79 13.53 1.909 33.67 14.86 13.54 14.05

Sodium Aluminum Silicon Oxide Hydrate, Na2O*Al2O3*SiO2*H2O, (00-012-0221)

Sodium Aluminum Silicate Hydrate Na4(Al4Si12O32)(H2O)14, (01-080-0700)

Phillipsite-K (K,Na)2(Si,Al)8O16*4H2O (00-046-1427)

Phillipsite-Na Na4KAl5Si11O32(H2O)10 (01-073-1419)

Hematite, Fe2O3 (00-001-1053)

FUS-DAl2 Anatase, TiO2 (00-001-0562)

Anatasesyn, TiO2 (00-021-1272)

Rutile, TiO2 (01-072-1148)

Cell parameters Crystallite size [Å]

81.4

Net Area

207.3

0.309 13.54 30.85 1.909

129.6

56.42

150.7

721.8 59.43 23.49 7.26 721.8 7.306 59.43 153.5 38.61 7.26 20.62 30.00 11.9 2.112 23.49 7.26

192.5

106.5

Crystallinity

(continued)

592

M. Visa et al. Table 2. (continued)

Substrate

Compound Brookite, TiO2 (00-029-1360)

Hematite, Fe2O3 (00-001-1053)

2h theta

Cell parameters Crystallite size [Å] Orthorhombic a = 5.4558 b = 9.1819 c = 5.1429; a = b = 90°

33.269 Rhombo H axes a = 5.028 c = 13.73 a = b = 90° 54.274 Rhombo Hematite syn, Fe2O3 (00-002-0915) 62.790 H axes a = 5.028 c = 13.728 a = b = 90° 13.852 Triclinic Albite (low) NaAl0.91Si3O8, 25.434 a = 8.134 41.330 b = 12.785 48.20 c = 7.1582 b = 116.6° c = 87.685° 13.966 Monoclinic Sodium Aluminum Silicate, Na(AlSi3O8) (01-089-8574) 27.478 a = 8.126 36.221 b = 12.996 37.186 c = 7.164 37.810 a = 90° b = 116.65° 12.503 Tetragonal Sodium Aluminum Silicate Hydrate, 17.675 a = 10.043 Na6Al6Si10O32*12H2O (00-039-0219) 21.653 c = 12.043 28.075 a = b = 90° 33.417 38.02 17.731 Orthorhombic Phillipsitesyn, Na2O*Al2O3*SiO2*H2O (00-012-0195) 27.563 a = 14.10 l b = 14 c = 9.8 a = b = 90° Analcite, NaAl(SiO3)2*H2O (00-003-0391) 37.168 Cubic 69.050 a = 13.7 a = b = 90° 12.544 Orthorhombic Phillipsite-Na, Na4KAl5Si11O32(H2O)10 (01-073-1419) 13.963 a = 9.965 21.682 b = 14.252 33.317 c = 14.252 a = b = 90° 12.430 Orthorhombic Phillipsite-K, (K2.5Na) 13.906 a = 9.956 Al4.7Si11.3O32*13H2O (00-051-1497) 17.482 b = 14.253 27.414 c = 14.308 33.204 a = b = 90°

Net Area

81.7

110.3

8.481

81.7

9.307 52.65 23.49

81.4

5.965 721.8 4.117 153.5

81.8

30.00 11.9 7.306 59.43 23.49

174.8

4.786 2.145 5.478 30.00 9.307 59.43 2.154 30.00

81.3

81.5

59.43 7.26

256

4.786 5.759 5.478 9.307

380

4.786 5.759 2.154 30.00 9.307

Crystallinity

A Comparative Analysis of Pollutants Adsorption

593

As it can be seen from Fig. 1 and Table 2, new higher peaks are identified for FUS-DAl1 (anatase syn, TiO2 with 149.1 Å crystallite size and tetragonal cell; rutile, syn with 81.6 Å crystallite size and tetragonal cell; brookite with 81.3 Å crystallite size and orthorhombic cell; manganese, Mn2O3 with 179.9 Å crystallite size; sodium aluminium silicate hydrate (zeolite NaP1) Na6Al6Si10O32(H2O)12 with 136.9 Å crystallite size; Phillipsite-Na with 207.3 Å crystallite size) and for FUS-DAl2 (anatasesyn, TiO2 with 194.5 Å crystallite size; maghemite, syn, Fe2O3 with 183 Å crystallite size; Na6Al6Si10O32*12H2O with 174.8 Å crystallite size; manganese, Mn2O3 with181.8 Å crystallite size; Phillipsite-Na with 256 Å crystallite size; Phillipsite-K with 380 Å crystallite size) respectively. A new peak of albite with 81.4 Å crystallite size was due to the hydrothermal treatment, during which a chemical restructuring took place. Also the overall crystallinity increases from 38.3% to 78.2% for FUS-DAl1 and to 78.9% for FUS-DAl2. The composition of the FAw is confirmed by XRD spectra and is presented in Table 2. The predominant crystalline components of FAw are: SiO2 (quartz), Sodium Silicate c-Al2O3, hematite, ramsdellite (MnO2), titanium oxide (Ti5O9) all with crystallite size between 300–680.3 Å and 38.3% crystalline degree, the rest being represented by amorphous phases. The XRD data show that TiO2 phases with crystallite size 81.6–149.1 Å have been well embedded into the new composites (FUS-DAl1 and FUS-DAl2). Beside diffraction lines corresponding to the TiO2 tetragonal and orthorhombic phases, other lines with high peaks were identified in the FUS-DAl1 and FUS-DAl2, crystalline structures which prove the chemical restructuring of the FAw together with TiO2 during the hydrothermal treatment. The formation of new compounds, such as aluminosilicates, is the consequence of the dissolution/recrystallization processes followed by the partial transformation of the main components of FA in alkaline media. Information on the new substrates morphology/topography and surface characteristics respectively were obtained from the AFM and SEM micrographs (Figs. 2, 3 and 4). The AFM images and pore size distributions presented show different granular shapes. The highest roughness value (111.84 nm and 138.467 nm) corresponds to the new composites which have more aggregates with different, almost round and stable shapes (SEM image). Probably during the alkaline fusion (500 °C) followed by hydrothermal synthesis of the composites are involved in simultaneous dissolution/recrystallization processes, leading to an increase in the surface area up to 55.72 m2/g, the surface roughness and the pore volume diameter compared with FA and TiO2, Table 3. Table 3. The parameters of the FA-CET, TiO2, FUS-DAl1 and FUS-DAl2 obtained from adsorption-desorption isotherms Sample FAw FUS-DAl1 FUS-DAl2

Specific surface area (BET) [m2/g] 10.33 55.719 39.796

Micropores volume (t-plote) [cm3/g] 0.06 0.501 0.45

Micropores surface [m2/g] 2.25 5.71 2.69

Average pores Diameter [nm] 27.2 36.527 37.026

594

(a)

M. Visa et al.

( b)

3000

Counts/number of events

2500

2000

1500

1000

500

FUS DAl1 0 0

50

100

150

200

250

Pore diameters [mμ]

Fig. 2. (a) AFM image of FUS-DAl1 (average roughness: 111.84 nm) and (b) Pore histogram for FUS-DAl1

( b) Counts/number of events

(a)

2000

1500

1000

500

FUS DAl2 0 0

100

200

300

400

Pore diameters [mμ]

Fig. 3. (a) AFM image of FUS-DAl2 (average roughness: 138.46 nm) and (b) Pore histogram for FUS-DAl2

The surface properties are presented in Table 3 and confirm an increase in the BET surface area as a result of the increase in pores number with larger diameters, corresponding to a significant total pore volume of the two new materials, this indicating a new type of arrangement in the crystalline structure of the materials, FUS-DAl1, respectively, FUS-DAl2, that can be further used in processes like adsorption and photocatalysis. The grains’ dimension is also affected, varying from the large domain for FA (27.6…100 µm) to the narrower grains/agglomerates of 50…200 µm diameter, for the FUS-DAl1 and of 100–300 µm for FUS-DAl2, as shown in Figs. 2b and 3b respectively. After the hydrothermal process, the surface roughness increased from 91 nm to 111.84 nm and 138.46 nm, respectively. Increasing the populations of microspores is beneficial for improving the adsorption energy of substrates, thus the FUS-DAl1 has a higher adsorption rate constant that that of FUS-DAl2.

A Comparative Analysis of Pollutants Adsorption

(a)

595

(b)

Fig. 4. SEM image of (a) FUSD-Al1; (b) FUS-DAl2

Fig. 5. The elemental composition of surface, EDX images

The nanoparticles are well dispersed with uniform size distributions especially on FUS-Al1 surface. During the hydrothermal processing large agglomerates are formed, as confirmed by the SEM images (Fig. 4). The energy-dispersive X-ray spectroscopy (EDS) results of the composite are displayed in Fig. 5. Precise elemental mapping in Fig. 5 demonstrates the homogenous distributions of TiO2 quantum dots on the aluminosilicates. A few elements such as Si, Al, Ti, Fe, and O are present in the composites and demonstrate the homogenous distributions of Ti on Si from aluminosilicates, which is of essence in the photocatalytic processes. Results showed that the particles were irregular in shape and tended to agglomerate. The EDX results demonstrate that elements such as Si (1.36%), Al (1.99%), O (77.26%), and Ti (24.32%) are contained in the composite sample. The map images

596

M. Visa et al.

Fig. 6. The elemental composition of surface, EDX

(EDX) of the agglomerate with TiO2 (Fig. 6) show the distribution of the elements on its surface. The TiO2 particles are well dispersed on the surface in aluminosilicates agglomerates shape.

3.2

Adsorption and Photocatalytic Experiments

The pollutant systems tested in this work were prepared using bidistilled water and CdCl2
2.5H2O (ScharlauChemie S.A.), CuCl2
2H2O (ScharlauChemie S.A.,), methylene blue, MB (C16H18N3S) (Fluka AG, reagent grade) and sodium dodecylbenzenesulfonate, SDBS (CH3(CH2)11C6H4SO3Na) of technical grade, (Sigma-Aldrich, 98%). Adsorption experiments were done by mechanical stirring (100 rpm) at room temperature. Experiments were done on systems containing three pollutants (Cd2++MB +SDBS, Cu2++MB+SDBS) and respectively four pollutants (Cd2++Cu2++MB+SDBS). For all the experiments the initial concentration for heavy metals was 0.01 N, for MB (0.03125 mM) and 25 mg/L for the surfactant. The tests refer to 0.1 g substrates added to 100 mL of pollutant system. For the kinetic studies, aliquots were taken at fixed moments (10, 15, 30, 45, 60, 90, 120, 150 and 180 min) and the supernatant obtained after filtration was analyzed by AAS (Analytic Jena, ZEEnit 700) at: kCd = 228.8 nm, kCu = 324.75 nm and UV-VIS absorbance measurements (Perkin Elmer UV-VIS spectrophotometer, Lamda-950) were performed at the maximum absorption wavelength 664 nm for MB, respectively 224 nm for SDBS. The chemical structures of the dye and anionic surfactant are shown in Fig. 7. Ultrapure water with resistivity of 18.23 MX cm−1was used throughout the whole experiment. Photocatalytic experiments were also done on FUSDAl1 and FUSDAl2 using the same pollutant systems and the same overall concentration under UV irradiation and Fenton system (using Fenton reactive and hydrogen peroxide 30%), using quartz glasses. The home-made reactors are equipped with three F18W/T8 black light tubes (Philips), emitting a broad range of UV light, typically 340–400 nm, with kmax(emission) = 365 nm. The mean value of the radiation flux intensity, reaching the middle of the reacting suspension, measured with a digital Luxmeter (Mavolux5032C/BUSM) was 3Lx. As in the case of adsorption, after filtration the supernatant was analyzed by AAS and UV-Vis.

A Comparative Analysis of Pollutants Adsorption

597

(a)

(b)

Fig. 7. Chemical structure of the dye andanionic surfactant: (a) Methylene blue (C16H18ClN3S) and (b) Dodecylbenzenesulfonate (CH3(CH2)11C6H4SO3Na))

The removal efficiency was calculated using Eq. (2): g¼

ðciHM=MB=SDBS  ceHM=MB=SDBS Þ  100

ð2Þ

ciHM=MB=SDBS

where: ciHM=MB=SDBS = initial concentrations for heavy metals, dye and surfactant; ceHM=MB=SDBS = equilibrium momentary concentrations for heavy metals, dye and surfactant. During the experiments, the solutions were used at their natural pH, which varied between 5.19–7.21 for FUS-DAl1 and between 5.49–7.78 for FUS-DAl2. For simplicity, all the results obtained after adsorption were denoted with (A), the ones obtained after UV irradiation with (F). To investigate the removal efficiency of FUS-DAl1 and FUS-DAl2 on solutions containing three and four pollutants, the adsorption and photocatalytic experiments were carried out as described in Sect. 2.3. The results of the experiments are presented in Figs. 8, 9 and 10 for adsorption, in Figs. 11, 12 and 13 for photodegradation (under UV irradiation).

(a)

(b)

2+

(Cd +MB+SDBS)/FUS-DAl1 (A) 2+ MB(MB+Cd +SDBS)/FUS-DAl1 (A) 2+ SDBS(SDBS+Cd +MB)/FUS-DAl1 (A)

90 80

2+

80 70

Efficiency [%]

Efficiency [%]

70

2+

Cd (Cd +MB+SDBS)/FUS-DAl2 (A) 2+ MB(MB+Cd +SDBS)/FUS-DAl2 (A) 2+ SDBS(SDBS+Cd +MB)/FUS-DAl2 (A)

90

60 50 40 30 20

60 50 40 30 20

10

10

0 0

20

40

60

80

100

120

Time [min]

140

160

180

0 0

20

40

60

80

100

120

140

160

180

Time [min]

Fig. 8. Removal efficiency vs. contact time of Cd2+, MB and SDBS by adsorption, from three-component system on (a) FUS-DAl1 and (b) FUS-DAl2

598

M. Visa et al.

(a)

(b)

(Cu2++MB+SDBS)/FUS-DAl1 (A) MB(MB+Cu 2++SDBS)/FUS-DAl1 (A) SDBS(SDBS+Cu2++MB)/FUS-DAl1 (A)

90 80

80 70

Efficiency[%]

70

Efficiency [%]

Cu2+(Cu2++MB+SDBS)/FUS-DAl2 (A) MB(MB+Cu 2++SDBS)/FUS-DAl2 (A) SDBS(SDBS+Cu2++MB)/FUS-DAl2 (A)

90

60 50 40

60 50 40

30

30

20

20

10

10 0

0 0

20

40

60

80

100

120

140

160

0

180

20

40

60

80

100

120

140

160

180

Time [min]

Time [min]

Fig. 9. Removal efficiency vs. contact time of Cu2+, MB and SDBS by adsorption, from three-component system on (a) FUS-DAl1 and (b) FUS-DAl2

(a)

2+

80 70

2+

(b)

2+

80 70

60 50 40 30 20

2+

2+

Cd (Cd +Cu MB+SDBS)/FUS-DAl2 (A) 2+ 2+ 2+ Cu (Cu +Cd MB+SDBS)/FUS-DAl2 (A) 2+ 2+ MB(MB+Cd +Cu +SDBS)/FUS-DAl2 (A) 2+ 2+ SDBS(SDBS+Cd +Cu MB)/FUS-DAl2 (A)

90

Efficiency [%]

Efficiency [%]

2+

Cd (Cd +Cu MB+SDBS)/FUS-DAl1 (A) 2+ 2+ 2+ Cu (Cu +Cd MB+SDBS)/FUS-DAl1 (A) 2+ 2+ MB(MB+Cd +Cu +SDBS)/FUS-DAl1 (A) 2+ 2+ SDBS(SDBS+Cd +Cu MB)/FUS-DAl1 (A)

90

60 50 40 30 20

10

10

0 0

20

40

60

80

100

120

140

160

0

180

0

20

40

60

Time [min]

80

100

120

140

160

180

Time [min]

Fig. 10. Removal efficiency vs. contact time of Cd2+, Cu2+, MB and SDBS by adsorption, from four-component system on (a) FUS-DAl1 and (b) FUS-DAl2

(a)

(b)

Cd 2+(Cd 2+ +MB+SDBS)/FUS-DAl1 (F) MB(MB+Cd 2++SDBS)/FUS-DAl1 (F) SDBS(SDBS+Cd 2++MB)/FUS-DAl1 (F)

90 80

90

70

Efficiency [%]

70

Efficiency [%]

Cd 2+(Cd 2++MB+SDBS)/FUS-DAl2 (F) MB(MB+Cd 2++SDBS)/FUS-DAl2 (F) SDBS(SDBS+Cd2++MB)/FUS-DAl2 (F)

80

60 50 40 30 20

60 50 40 30 20

10

10

0

0

50

100

150

200

Time [min]

250

300

350

0 0

50

100

150

200

250

300

350

Time [min]

Fig. 11. Removal efficiency vs. contact time of Cd2+, MB and SDBS by photodegradation, from three-component system on (a) FUS-DAl1 and (b) FUS-DAl2

The adsorption efficiency on the FUSD-Al1 substrate was better and especially for the copper cations compared to that of the cadmium cations. The BET surface influences the efficiency of the adsorption process. The adsorption of MB molecules on

A Comparative Analysis of Pollutants Adsorption

(a)

(b)

Cu2+(Cu2++MB+SDBS)/FUS-DAl1 (F) MB(MB+Cu 2++SDBS)/FUS-DAl1 (F) SDBS(SDBS+Cu2++MB)/FUS-DAl1 (F)

90 80

90

70

Efficiency [%]

60

Efficiency [%]

Cu2+(Cu 2++MB+SDBS)/FUS-DAl2 (F) MB(MB+Cu 2++SDBS)/FUS-DAl2 (F) SDBS(SDBS+Cu2++MB)/FUS-DAl2 (F)

80

70

50 40

599

60 50 40

30

30

20

20

10

10 0

0 0

50

100

150

200

250

300

0

350

50

100

150

200

250

300

350

Time [min]

Time [min]

Fig. 12. Removal efficiency vs. contact time of Cu2+, MB and SDBS by photodegradation, from three-component system on (a) FUS-DAl1 and (b) FUS-DAl2

(a)

Cd 2+(Cd 2++Cu 2++MB+SDBS)/FUS-DAl1 (F) Cu 2+(Cu2++Cd 2++MB+SDBS)/FUS-DAl1 (F) MB(MB+Cd 2++Cu 2++SDBS)/FUS-DAl1 (F) SDBS(SDBS+Cd 2++Cu 2++MB)/FUS-DAl1 (F)

90 80

(b)

90 80

Cd 2+(Cd 2++Cu2+ MB+SDBS)/FUS-DAl2 (F) Cu 2+(Cu 2++Cd2+MB+SDBS)/FUS-DAl2 (F) MB(MB+Cd 2++Cu2+ +SDBS)/FUS-DAl2 (F) SDBS(SDBS+Cd2++Cu2+ MB)/FUS-DAl2 (F)

70

Efficiency [%]

Efficiency [%]

70 60 50 40

60 50 40

30

30

20

20

10

10 0

0

0

50

100

150

200

Time [min]

250

300

350

0

50

100

150

200

250

300

350

Time [min]

Fig. 13. Removal efficiency vs. contact time of Cd2+, Cu2+, MB and SDBS by photodegradation, from four-component system on (a) FUS-DAl1 and (b) FUS-DAl2

composite FUSD-Al1 rapidly occurs during the first stage of the process, which may be due to the abundant active adsorption sites on the adsorbent surface available for MB. Cooper cations are adopted for the smaller pores. On the other hand, upon the UV light irradiation, TiO2 could form abundant photo-generated electron (e−) and hole (h+) pairs. The photo-generated electron (e−) could transfer to the conduction band of TiO2, and subsequently react with the adsorbed O2 molecules on the surface of substrates forming strong active superoxide ions (O2−). The photo-generated holes (h+) could react with H2O/HO− to form HO·. These ions are very active and decompose the dye and the surfactant. When it comes to adsorption and photocatalytic processes the surface charge of the substrate must be taken into consideration. In this case, both of the substrates used during the experiments are negatively charged. During the experiments, the solutions were used at their natural pH, which varied between 5.19–7.21 for FUS-DAl1 and between 5.49–7.78 for FUS-DAl2. These values were between the points of zero charge of the composites, respectively, for FUS-DAl1 the point of zero charge (4.97 and 8.63) and for FUS-DAl2 (5.06 and 8.17). Taking into consideration the working pH and based on the Pourbaix diagram [32], cadmium cations were not hydrolysed (the pH for hydrolysis for both of the cations is >9). The copper ion was the only one that slightly hydrolyzed (the working pH in case of removal of the ion from Cu2++MB

600

M. Visa et al.

+SDBS was 6.88 and according to the Pourbaix diagram at pH values above 6.8, the ion can be found as Cu(OH)+). During all experiments, in systems containing four pollutants, the order of removal of the heavy metals was Cu2+ > Cd2+, due to the higher mobility and lower hydration number for copper (4), comparative cadmium (6), Table 4.

Table 4. Ion beams (Anhydrous and Hydrated) used in experimental tests Heavy metals Radius of unhydrated ions [nm] Number of hydration molecules Radius of hydrated ions [nm]

Cadmium 0.097 6 0.426

Copper 0.072 4…6 0.295

As previous studies reported, the FA matrix preserves an overall negative surface charge. Under these conditions, cationic species (heavy metals and S+ from MB and heavy metals and Na+ from SDBS) are supposed to be adsorbed, in concurrent processes based on electrostatic attractive forces and the volume of the species. Under these conditions (0.1 g substrate for 50 mL), the composites are effective in adsorption and oxidative photodegradation processes with no significant differences.

3.3

The Adsorption Mechanism

In systems containing two or more pollutants and the substrate, several adsorption processes can develop/occur: (a) The Cd2+ and Cu2+ cations can be absorbed by the silanol group (Si-OH) of the layer, but with lower efficiency (Eqs. (3), (4)): Si-OH þ Cd2 þ ðH2 OÞn , Si-OCd þ ðH2 OÞnx þ 2H þ ðH2 OÞx

ð3Þ

Si-OH þ Cu2 þ ðH2 OÞ , ðSi-OÞ2 CuðH2 OÞnx þ 2H þ ðH2 OÞx

ð4Þ

(b) The adsorption of heavy metals onto aluminosilicates controlled by an ion-exchange mechanism. NaP1 zeolite has a cation exchange capacity over 2.7 meq/g while for analcine it is 0.6 meq/g. Three different stages are observed in the ion - exchange adsorption of the heavy metals: fast adsorption on the zeolite microcrystal surfaces during the first 30 min; then the inversion stage has a short-time prevalence of the desorption process connected with the diffusion flow from the zeolite microcrystals [33]. (c) In the multicomponent solutions, Cd2++MB or Cu2++SDBS interactions can be developed, further influencing the adsorption rate (Table 5) and its mechanisms. Many organic substances like aromatic compounds are attached to the FUS-DAl1 surface by hydrogen bonding, but stronger interactions with formation of new bonds can be observed for other molecules.

A Comparative Analysis of Pollutants Adsorption

601

Table 5. Surface energy data for the substrates [34] Substrate FA-w FUS-DAl1 FUS-DAl2

Surface energy [mN/m] 63.07 56.73 52.21

Disperse contribution [mN/m] 5.54 8.69 9.54

Polar contribution [mN/m] 58.43 48.04 42.67

(a) 2

+Cd2+2Cl-

(b)

Fig. 14. (a) The interaction of Cd2+ with Methylene blue molecules and (b) The interaction of Cu2+ with SDBS molecules

These surface complexes can adopt different topologies bidental bonds. The possible reactions are proposed in Fig. 14, involving the lone pair of electrons from the pyridine nitrogen atom or chlorine in MB and the -SO3− group of the SDBS molecules. Stereochemistry complexes with cadmium are determined only by the ionic volume strength of the strong electrostatic and covalent bonds. The volume effect makes the Cd2+ cation to be more apt to forms tetra- or hexa-coordinated complexes with distorted octahedral structure Fig. 14. These interactions/bonds can be correlated with FTIR spectra (Fig. 15). The peak at 578 cm−1 of MB disappears, but there are new peaks around 2345 and 2362 cm−1 which confirm the new bonds between cations and MB. The peak at 1630 cm−1 (C-Caromatic) confirms the aromatic ring from the molecules. The semiconductor substrates with heterogeneous surface, high roughness, larger BET surface tend to have better performance in the photodegradation of organic pollutants, if a balance between the number of active sites and their specific activity exists [35]. Once the electron-hole pair was formed, the most common mechanism involves the holes for hydroxyl radical production. In alkaline media several other reactions are possible [35, 36], involving the O2/HO−, O2/HOO−. Photocatalist + hv ! e þ h

ð5Þ

h þ H2 OðPhotocatÞ ! OHðPhotocatÞ þ H þ

ð6Þ

602

M. Visa et al.

0.10

0.08

(h) (g)

A [u.a.]

0.06

(f) (e)

0.04

(d) (c)

0.02

(b) (a)

0.00

0

1000

2000

3000

4000

ν [cm -1 ]

Fig. 15. FT-IR spectra of the (a) FUS-DAl1; (b) FUS-DAl2; (c) Cd2++MB+SDBS/FUSD-Al1 (A); (d) Cd2++MB+SDBS/FUSD-Al2(A); (e) Cd2++MB+SDBS/FUSD-Al1(F); (f) d2++MB +SDBS/FUSD-Al2(F); (g) Cd2++Cu2++MB+SDBS/FUS-DAl1; (h) MB+Cu2+, MB+Cd2++Cu2 + +SDBS

These are powerful oxidizing species, able to degrade the dye and surfactant molecules (adsorbed on the catalyst or in solution, near the photocatalyst surface) to smaller fragments less colored, (Eqs. (7), (8)), probably with similar dimensions/ charges which can further be adsorbed onto the active sites of the substrate or can be further degraded up to mineralization [37].

3.4

HO þ dye ! oxidation products

ð7Þ

HO þ oxidation products ! CO2 þ H2 O þ mineralization products

ð8Þ

Kinetic Studies

During adsorption and photocatalytic experiments, heavy metal, dye and surfactant uptake qe (mg/g) was evaluated for the kinetic studies by using the initial and current, t, concentrations (ci and ct) in a given solution volume (V = 50 mL) for a given amount of FUSD-Al1 and, respectively, FUSD-Al2 substrate (ms = 0.1 g) as given in Eq. (9): qe ¼

ðciHM=D=S  ctHM=D=S Þ
V ms

ð9Þ

A Comparative Analysis of Pollutants Adsorption

603

Table 6. Kinetic parameters of the processes (A) Substrate

2+

Pseudo first-order kinetics KL [min−1] R2

Pseudo second-order

Interparticle Difusion

k2 [g/mg.min] qe [mg/g] R2

Kid [mg/gmin1/2] C

R2

2+

Cd (Cd +MB+SDBS) A FUS- DAl1 0.25 0.24 FUS- DAl2 0.47 0.03 MB(MB+Cd2++SDBS) A FUS-DAl1 0.019 30.93 FUS-DAl2 0.634 33.69 SDBS(SDBS+Cd2++MB) A FUS-DAl1 0.07 0.852 114.62 FUS-DAl2 0.78 282.96 Cu2+(Cu2++MB+SDBS) A FUS-DAl1 0.509 0.016 FUS-DAl2 0.02 0.991 0.121 MB(MB+Cu2++SDBS) A FUS-DAl1 0.07 0.918 16.097 FUS-DAl2 0.559 88SDBS(SDBS+Cu2++MB) A FUS-DAl1 0.253 4.759 FUS-DAl2 0.577 1.994 Cd2+(Cd2++Cu2++MB+SDBS) A FUS-DAl1 0.01 0.207 FUS-DAl2 0.476 Cu2+(Cu2++Cd2++MB+SDBS) A FUS-DAl1 0.095 0.032 FUS-DAl2 0.752 0.129 MB((MB+Cd2++Cu2++SDBS) A FUS-DAl1 0.201 23.07 FUS-DAl2 0.483 SDBS(SDBS+Cd2++Cu2++MB) A FUS-DAl1 0.402 20.60 FUS-DAl2 0.665 29.25

96.15 89.28

0.998 0.997 11.28

0.618 13.85 0.882

0.199 0.143

0.986 0.996 -

-

0.099 0.095

0.981 0.005 0.971 0.007

0.040 0.869 0.008 0.948

64.516 63.694

0.998 0.995 3.567

0.718 26.54 0.993

0.490 -

0.995 0.021 0.646 0.007

0.231 0.803 0.037 0.995

0.873 0.547

0.998 0.021 0.996 0.049

0.603 0.862 0.279 0.924

15.624 -

0.985 0.313 2.935

0.728 39.14 0.849

35.461 45.455

0.979 0.990 -

-

0.351 -

0.977 0.036 0.675 0.011

0.043 0.933 0.132 0.930

0.532 0.586

0.964 0.987 0.061

0.764 0.021 0.910

0.666 0.782

0.102 0.754

By using the Eqs. (10) and (11) the kinetic studies were modeled based on: • the pseudo first-order equation [38]: logðqe  qt Þ ¼ log qe 

KL t 2:303

ð10Þ

where KL is the Lagergreen constant, qe is the equilibrium uptake value and qt the current metal uptake.

604

M. Visa et al. Table 7. Kinetic parameters of the processes (F)

Substrate

2+

Pseudo first-order kinetics KL [min−1] R2

Pseudo second-order

Interparticle Difusion

k2 [g/mg.min] qe [mg/g] R2

Kid [mg/gmin1/2] C

R2

2+

Cd (Cd +MB+SDBS) F FUS-DAl1 0.007 0.979 0.147 FUS-DAl2 0.728 0.231 MB(MB+Cd2++SDBS) F FUS-DAl1 0.780 FUS-DAl2 0.656 340.63 SDBS(SDBS+Cd2++MB) F FUS-DAl1 0.286 1466.40 FUS-DAl2 0.694 919.63 Cu2+(Cu2++MB+SDBS) F FUS-DAl1 0.755 0.429 FUS-DAl2 0.609 0.062 MB(MB+Cu2++SDBS) F FUS-DAl1 0.731 129.200 FUS-DAl2 0.638 36.88SDBS(SDBS+Cu2++MB) F FUS-DAl1 0.102 0.810 4.008 FUS-DAl2 0.514 37.023 Cd2+(Cd2++Cu2++MB+SDBS) F FUS-DAl1 0.244 0.119 FUS-DAl2 0.223 0.006 Cu2+(Cu2++Cd2++MB+SDBS) F FUS-DAl1 0.564 0.053 FUS-DAl2 0.017 0.978 0.653 MB((MB+Cd2++Cu2++SDBS) F FUS-DAl1 0.709 413.480 FUS-DAl2 0.622 SDBS(SDBS+Cd2++Cu2++MB) F FUS-DAl1 0.627 FUS-DAl2 0.637 414.55

67.114 104.167

0.975 5.381 0.971 7.237

6.78 0.892 9.782 0.928

0.171

0.479 0.994 0.009

0.566 0.011 0.946

0.134 0.056

0.971 0.005 0.956 0.003

0.007 0.955 0.002 0.921

30.120 51.546

0.980 1.218 0.982 5.206

11.38 0.919 4.088 0.856

0.407 -

0.936 0.022 0.852 0.010

0.010 0.967 0.119 0.927

0.419 0.824

0.992 0.038 0.995 0.025

0.049 0.889 0.382 0.876

35.971 20.040

0.978 4.036 0.976 -

2.188 0.929 0.740

41.152 49.261

0.979 3.901 0.997 3.553

3.547 0.887 2.567 0.951

0.628 -

0.834 0.123 0.007

0.746 0.051 0.985

0.701

0.332 0.894 -

-

0.707 0.278

• the pseudo-second order kinetic equation [39] t 1 t ¼ þ qt k2 q2e qe

ð11Þ

The interparticle diffusion is another possible kinetic model that can also be applied in the adsorption and photocatalytic processes. The amount of heavy metal ions, dye and surfactant adsorbed can be calculated with Eq. (12) [14]:

A Comparative Analysis of Pollutants Adsorption

q ¼ kid
t1=2 þ C

605

ð12Þ

where kid is the intraparticle diffusion rate constant (mg
g−1
min−0.5) and C is the thickness of the boundary layer [40]. For all pollutant systems, the kinetic parameters of the adsorption and photodegradation process are presented in Tables 6 and 7. As it can be seen from Tables 6 and 7 considering the correlation coefficient (R2) values, the adsorption and photocatalytic processes were best described by the pseudo-second order kinetics for all the pollutants from all four systems. Also it can be seen that in some cases, parallel mechanisms are developed, mostly for copper ion (pseudo-second order kinetic, pseudo-first order and interparticle diffusion). As it was mentioned before, this is due to the higher mobility of the copper ion (Table 4). Industrial wastewaters are usually loaded with mixed pollutants which can be involved in concurrent or parallel processes of adsorption and/or photocatalysis.

4 Conclusions In the present study the removal efficiency of two composites obtained from fly ash, TiO2, alumina and silica source was tested by different methods during adsorption and photocatalytic processes (under UV-irradiation). Considering both processes, a novel composites was developed in mild hydrothermal conditions, starting from fly ash and Degussa P25. The substrate analyses show that the composites have a regular surface aspect, high roughness, a large specific surface and high crystallinity. The results show that adsorption efficiency significantly depends on the surface properties, while process kinetics are mainly influenced by the type of cations, by the molecular structure (flexibility) of the surfactant and methylene blue. Kinetic studies showed that all the processes followed pseudo-second order kinetics. Considering the adsorption processes, the data indicate that the large volume of MB allows the rapid adsorption of the cations, leading to higher rate constants, as compared to cadmium. The pseudo-second order kinetic is the model that governs the entire process of removing pollutants from the complex systems and the parallel mechanisms (pseudo-first-order kinetics and inter-particle diffusion) affect the complex processes of simultaneous adsorption and photocatalytic to a negligible extent. The presence of more pollutants in aqueous solution may adversely affect the adsorption process of other pollutant. For example, qe of the cadmium removal from solution with three pollutants is 96.154 mg/g, while it is 15.625 mg/g in the case of removal from four pollutants solution. For strong adsorption of anionic surfactants (SDBS), the substrate should exhibit a positive charge, which can be achieved by lowering the pH below the PZC, but in our research the pH is close of neutral value. In this conditions the adsorption efficiency of Cu2+ ions and SDBS molecules, as well as the adsorption of Cd2+ ions and MB

606

M. Visa et al.

molecules increase in the same way and in accord with the interaction mechanism of Cu2+ with SDBS molecules and Cd2+ with MB molecules. These types of kinetic investigations are required in the design of the wastewater treatment processes (and equipment), particularly when advanced mineralization is targeted, for water re-use. Acknowledgments. This paper was supported by a grant of the Romanian National Authority for Scientific Research, ANCS - UEFISCDI, project number PNII-PT-PCCA-2013-4-0726.

References 1. Holkar, C.R., Jadhav, A.J., Pinjari, D.V., Mahamuni, N.M., Pandit, A.B.: A critical review on textile wastewater treatments: possible approaches. J. Environ. Manag. 182, 351–366 (2016) 2. Konstantinou, I.K., Albanis, T.A.: TiO2 – assisted photocatalytic degradation azo dyes in aqueous solution: kinetic and mechanistic investigations. Rev. Appl. Catal. B- Environ. 49, 1–14 (2004) 3. Shiau, B., Harwell, J.H., Scamehorn, J.F.: Precipitation of mixtures of anionic and cationic surfactants: III. Effect of added nonionic surfactant. J. Colloid Interface Sci. 167, 32–345 (1994) 4. Himanshu, P., Vashi, R.T.: Treatment of textile wastewater by adsorption and coagulation. J. Chem. 7, 1468–1476 (2010) 5. Bowen, R.W., Welfoot, J.S.: Modeling of membrane nanofiltration - pore size distribution effects. Chem. Eng. Sci. 57, 1393–1407 (2002) 6. Ujang, Z., Anderson, G.K.: Performance of low pressure reverses osmosis membrane (LPROM) for separating mono-and divalent Ions. J. Water Sci. Technol. 38, 521 (1998) 7. Visa, M., Bogatu, C., Duta, A.: Simultaneous adsorption of dyes and heavy metals from multicomponent solutions using fly ash. J. Appl. Surf. Sci. 256, 5486–5491 (2010) 8. Visa, M., Andronic, L., Duta, A.: Photocatalytic properties of titania - fly ash thin films. Environ. Engin. Manag. J. 8, 633–638 (2009) 9. Vongvoradit, P., Worathanakul, P.: Fast crystallization of SUZ-4 zeolite with hydrothermal synthesis: part I temperature and time effect. Procedia Eng. 32, 198–204 (2012) 10. Hernández-Montoya, V., Pérez-Cruz, M.A., Mendoza-Castillo, D.I., Moreno-Virgen, M.R., Bonilla-Petriciolet, A.: Competitive adsorption of dyes and heavy metals on zeolitic structures. J. Environ. Manag. 116, 213–221 (2013) 11. Yaping, Y., Xiaoqiang, Z., Weilan, Q., Mingwen, W.: Synthesis of pure zeolites from supersaturated silicon and aluminum alkali extracts from fused coal fly ash. Fuel 8, 188– 1886 (2008) 12. Juan, R., Hernandez, S., Andres, J.M.: Synthesis of granular zeolitic materials with high cation exchange capacity from agglomerated coal fly ash. Fuel 86, 1811–1821 (2007) 13. Tanaka, H., Eguchi, H., Fujimoto, S., Hino, R.: Two-step process for synthesis of a single phase Na-A zeolite from coal fly ash by dialysis. Fuel 85, 1329–1334 (2006) 14. Kantiranis, N., Filippidis, A., Mouhtaris, T., Paraskevopoulos, K.M., Zorba, T., Squires, C., Charistos, D.: EPI-type zeolite synthesis from Greek sulphocalcic fly ashes promoted by H2O2 solutions. Fuel 85, 360–366 (2006) 15. Visa, M., Chelaru, A.M.: Hydrothermally modified fly ash for heavy metals and dyes removal in advanced wastewater treatment. J. Appl. Surf. Sci. 303, 14–22 (2014)

A Comparative Analysis of Pollutants Adsorption

607

16. Dil, E.A., Ghaedi, M., Asfaram, A.: The performance of nanorods material as adsorbent for removal of azo dyes and heavy metal ions: application of ultrasound wave, optimization and modeling. Ultrason. Sonochem. 34, 792–802 (2017) 17. Crini, G., Badot, P.M.: Application of chitosan, a natural aminopolysaccharide, for dye removal from aqueous solutions by adsorption processes using batch studies: a review of recent literature. Prog. Polym. Sci. 33, 399–447 (2008) 18. Jiang, M.Q., Jin, X.Y., Lu, X.Q., Chen, Z.L.: Adsorption of Pb(II), Cd(II), Ni(II) and Cu(II) onto natural kaolinite clay. Desalination 252, 33–39 (2010) 19. Ho, Y.S., McKay, G.: Sorption of Cooper (II) from aqueous solution by peat. J. Water Air Soil Pollut. 158, 79–97 (2004) 20. Cheung, C.W.J., Porter, F., McKay, G.: Sorption kinetic analysis for the removal of cadmium ions from effluents using bone char. J. Water Res. 35, 605–612 (2001) 21. Tantak, N.P., Chaudhari, S.: Degradation of azo dyes sequential treatment. J. Hazard. Mater. B136, 698–705 (2006) 22. Chen, J., Qju, F., Xu, W., Cao, S., Zhu, H.: Recent progress in enhancing photocatalytic efficiency of TiO2-based materials. Appl. Catal. A: Gen. 495, 131–140 (2015) 23. Sun, P., Xue, R., Zhang, W., Zada, I., Liu, Q., Gu, J., Su, H., Zhang, Z., Zhang, J., Zhang, D.: Photocatalyst of organic pollutants decomposition. Catal. Today J. 274, 2–7 (2016) 24. Visa, M., Duta, A.: TiO2/fly ash novel substrate for simultaneous removal of heavy metals and surfactants. Chem. Eng. J. 223, 860–868 (2013) 25. Andronic, L., Andrasi, D., Enesca, A., Visa, M., Duta, A.: The influence of titanium dioxide phase composition on dyes photocatalysis. J. Sol-Gel Sci. Technol. 58, 201–208 (2011) 26. Visa, M., Bogatu, C., Duta, A.: Tungsten oxide - fly ash oxide composites in adsorption and photocatalysis. J. Hazard. Mater. 289, 244–256 (2015) 27. Rodseanglung, T., Ratana, T., Phongaksorn, M., Tunhkamania, S.: Effect of TiO2 incorporated with Al2O3 on the hydrodeoxygenation and hydrodenitrogenation CoMo, sulfide catalysts. Energy Procedia 79, 378–384 (2015) 28. Robert, D., Pricopo, A., Heintz, O., We, J.V.: Photocatalytic detoxification with TiO2 supported on glass-fibre by using artificial and natural light. Catal. Today J. 54, 291–296 (1999) 29. Ramme, B.W., Tharaniyil, M.P.: Coal Combustion Products Utilization Handbook, 2nd edn. Manufactured in the U.S. of America (2004) 30. Wałek, T.T., Saito, F., Zhang, Q.: The effect of low solid/liquid ratio on hydrothermal synthesis of zeolites from fly ash. Fuel 87, 3194–3208 (2008) 31. Zak, A.K., Majid, W.H.A., Abrishami, M.E., Yousefi, R., Parvizi, R.: Synthesis, magnetic properties and X-ray analysis of Zn0.97X0.03O nanoparticles (X = Mn, Ni, and Co) using Scherer and size-strain plot methods. Solid State Sci. 14, 488–494 (2012) 32. Takeno, N.: Atlas of Eh-pH diagrams, Intercomparison of thermodynamic, Databases of the National Institute of Advanced Industrial Science and Technology (2005) 33. Muruganandham, M., Swaminathan, M.: Solar driven decolourisation of Reactive Yellow 14 by advanced oxidation processes in heterogeneous and homogeneous media. Dyes Pigm. 72, 137–143 (2007) 34. Robert, O.J., Thomas, W.H.: Adsorption of hydrolyzable metal ions at the oxide water interface. I. Co(II) adsorption on SiO2 and TiO2 as model systems. J. Colloid Interface Sci. 40, 42–52 (1972) 35. Coronado, J.M., Fermando Fresno, M., Hermandez-Alonso, D., Portela, R.: Design of Advanced Photocatalytic Materials for Energy and Environmental Application, 12, 13 (2013). ISSN 1865-3537 (electronic) 36. Hsu, L.J., Lee, L.T., Lin, C.C.: Adsorption and photocatalytic degradation of polyvinyl alcohol in aqueous solutions using P-25 TiO2. Chem. Eng. J. 173, 698–705 (2011)

608

M. Visa et al.

37. Andronic, L., Duta, A.: Photodegradation processes in two- dyes systems - simultaneous analysis by first-order spectra derivative method. Chem. Eng. J. 198, 468–475 (2012) 38. Arami, M., Limaee, N.Y., Mahmoodi, N.M., Tabrizi, N.S.: Removal of dyes from colored textile wastewater by orange peel adsorbent: equilibrium and kinetic studies. J. Colloid Interface Sci. 288, 371–376 (2005) 39. Ho, Y.S., McKay, G.: The kinetic of sorption of basic dyes from aqueous solution by sphagnum Moss peat. Can. J. Chem. Eng. 76, 822–832 (1998) 40. Allen, S.J., Mc Kay, G., Khader, Z.H.: Interparticle diffusion of a basic dye during adsorption onto sphangum peat. J. Environ. Pollut. 56, 39–50 (1999)

Policies, Education and Training on Sustainability

Extending Production Waste Life Cycle and Energy Saving by Eco-Innovation and Eco-Design: The Case of Packaging Manufacturing Maria Gavrilescu1,2(&), Teofil Campean1,3, and Dan-Alexandru Gavrilescu1 1

Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, Gheorghe Asachi Technical University of Iasi, 73 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania {mgav,gda}@tuiasi.ro, [email protected] 2 Academy of Romanian Scientists, 54 Splaiul Independentei, 050094 Bucharest, Romania 3 Rondocarton SRL, Cluj-Napoca, 2 Aviatorilor Street, Sânnicoară-Apahida, 407042 Cluj-Napoca, Romania

Abstract. Resource efficiency is seen as a constituent of sustainable production and consumption, where yesterday’s waste is today’s raw material. In this context, our main goal is to track eco-innovative ways in the framework of circular economy to reuse production waste as eco-designed smart new products. The corrugated board and cardboard packaging manufacturing was found as one of the most available and proficient industries in applying the circular way to extend the life cycle of raw materials and save energy by combining economic and environmental targets in an eco-efficient manner. We have identified the need of a Romanian Manufacturer (RM), equipped with modern facilities and technologies to produce corrugated board and packaging, and also opened for knowledge transfer focused on the generation of economic benefits and environmental advantages by closing the production loop through reusing the production waste generated in the form of cardboard strips, edges and other production waste. Then, we developed and applied a challenging work-plan to create a new environmentally friendly and sustainable re-engineered product required by the market, by extending cardboard waste life cycle based on an eco-innovative approach, put in practice by following eco-design principles. In order to enable RM decision making process, we have performed Life Cycle Analysis (LCA) and Life Cycle Cost Analysis (LCCA) to identify and assess: (i) the environmental impacts induced by the reuse of waste production as raw materials for the product redesigned based on eco-innovation and eco-design concepts; (ii) the total cost performance in terms of materials and energy of the alternative proposed to be implemented in corrugated board and packaging manufacturing. These tools would enable the valorization of production waste so as to close the loop and extend the life cycle of cardboard in an eco-efficient way. In perspective, these production wastes are intended to be revalorized as subassemblies for building sectors. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_42

612

M. Gavrilescu et al. Keywords: Circular economy Manufacturing
Production waste




Eco-innovation




Eco-design




1 Introduction 1.1

Closing the Loop in Industrial Systems in the Context of Circular Economy

Industrial production is typically a waste generator, regardless of its claimed sustainability level. Today, synthetizing, designing and exploiting production systems means much more than choosing and conjoining conventional production elements with the purpose of generating high productivity and economic efficiency. So, it has become ever more imperative to consider all types of resources involved as inputs, as well as valuable products for distribution to consumers and also waste resulting from production processes, for that the most suitable actions should be taken to avoid, reduce, reuse or recycle it. It has become increasingly evident that the differences among the performance of various industrial systems appear in the manner they are able to exploit and manage waste, in particular that generated during manufacturing and production of goods, which is usually perceived as production losses. Applying various alternatives, some of them associated to waste management hierarchy, such as [1–3]: source reduction, reusing (in plant recycling), on site or off site recycling, recovery of valuable components from waste, simply avoiding dumping/landfilling, needs to produce a shift from a linear flowing economy (generating large quantities of waste) to a circular one, by closing the production loop. In this production pathway, products at the end of their life cycle, but also production waste as scraps, residual materials, and other waste materials are collected, conditioned, and reused or recycled to increase material efficiency, cost-effectiveness, and improve the environmental performance of industrial companies. Lots of adverse environmental impacts generated by emissions, waste, energy consumption, transport processes, packaging, can be avoided when the industrial entities are able to develop closed-loop production systems [4]. Therefore, the advantages of closed-loops consist in that they can meet their sustainability by synchronized improvements in economic and environmental performance [5]. All these issues are closely related to improvements in eco-efficiency, which would request any decreasing in resource consumption, reducing environmental impacts along the whole processes and products life cycle, extending producer responsibility. Life Cycle Assessment procedure, with its logical, scientific approach, offers a frame for the awareness of the environmental impact that a product may have on a case-by-case basis [6, 7]. Besides, finding innovative options for waste revaluation in the production process not only saves resources, but also supports air, soil, and water quality and human health protection.

Extending Production Waste Life Cycle and Energy Saving

1.2

613

Manufacturing Sector and Generation of Production Waste

Eurostat statistics for 2014 in EU-28 countries showed that manufacturing sectors generates 9.8% from the total waste, while construction generates 33.5% and mining and quarrying, 29.8% (Fig. 1) [8].

Fig. 1. Waste generation in EU-28 by various activities, in 2014 [8]

Waste, defined by Directive 2008/98/EC as “any substance or object which the holder discards or intends or is required to discard”, imposes a careful management, because it is a potential resource in the form of both materials and energy as well as a source of serious environmental threats [9]. Waste treatment in the EU-28 during 2004–2014 addresses essentially there categories of procedures (Fig. 2) [8]: • landfilling; • recycling and/or used for backfilling; • incineration (including energy recovery). Figure 2 reveals that waste recycling entailed only 42% from the whole quantity of waste in 2004, while it increased to almost 47% in 2006; 49% in 2008; 47% in 2010; 46% in 2012; 50% in 2014. Therefore, the share of this alternative in total managed waste grew from 42% in 2004, to almost 50% in 2014.

614

M. Gavrilescu et al.

Fig. 2. Waste treatment practices in EU-28 during 2004–2014 (million tons) [8]

2 Circular Economy by Closing-the-Loop for Production Waste in Manufacturing Sector European Commission adopted the Circular Economy Package [10], which aims at stimulating the transition towards a circular economy model in the Member States. This ambitious plan of action would cover the whole life cycle, including production, consumption and waste management, opening the market for secondary raw materials, by turning waste into resource. Therefore, by closing-the-loop of products life cycles, applying a serious recycling and reusing alternative in waste management for their revaluation in production process would bring benefits for both economy and environment [5]. In this context, research and industry started to put together their knowledge, skills, experience and efforts to increase the value of products, materials and resources for as long possible by: life cycle extending, source reduction and waste minimization, reusing waste - in plant recycling, or recycling it either on site or off site [1, 11]. The manufacturing sector has proven that it can behave as one of the most suitable and flexible systems, able to apply these alternatives in materials and energy sustainable management [12]. In particular, paper, cardboard and corrugated board packaging manufacturing is often considered as a circular economy (CE) model, since this sector offers a perfect opportunity to explore and apply the concept of circular economy, best practices in resource preservation, in tight connection with eco-innovation, eco-design, eco-efficiency principles. According to this approach, in cardboard and corrugated board packaging manufacturing sector, CE is more than just recycling, because it handles almost all steps of products life cycle: innovation, design, production distribution, use, recovery [13]. The European Federation of Corrugated Board Manufacturers (FEFCO) considered that “corrugated packaging already had formed a perfect circular economy” [14].

Extending Production Waste Life Cycle and Energy Saving

615

However, the sector hides other resources able to securely close the loop “in plant”, by revaluating the production waste at the place of generation. Consequently, we have identified a Romanian cardboard and corrugated packaging manufacturer (RM), equipped with modern facilities and technologies, having implemented ISO 9000, 14000, 18000 in an integrated management system, with a large availability for improving its eco-efficiency by closing production loops and extending materials life cycle, as well as its responsibility as producer. RM is very opened for knowledge transfer focused on the generation of economic benefits, environmental advantages (in particular by reducing carbon footprint), by reusing the production waste in the same process, therefore ensuring a sustainable manufacturing (Fig. 3). In this work, we propose to extend the life cycle of materials by using production waste generated during cardboard and corrugated board packaging manufacturing (with red circle, in Fig. 3), in order to develop an eco-product (Eco_P), which customarily is produced by RM from cardboard sheets and is already on the market, for packaging

Fig. 3. Closing-the-loop in pulp and paper manufacturing sector: (1) supplying wood pulp plants (usually is removed as part of forestry operations to ensure better growth or comes from specifically planned plantations for pulp plants); (2) supplying pulp industrial plants with wood waste (wood processing factories, plywood, furniture manufacturing); (3) pulp, paper and cardboard factories (integrated or non-integrated mills); (4) processing paper and board (paper webs, reams, corrugated board packaging, tissue etc.); (5) recovering and sorting paper and board products after their use, recycling by dispatching them to paper mills as recovered fibers; (6) processing recovered fibers as raw material for producing commercial pulp, paper and boards (7) managing the exhausted paper and board products, inappropriate for recycling due to various reasons (incorrect collecting and sorting, unsuitable for recycling etc.), (8) production waste (by-products from papermaking process (barks, non-recyclable fibers) reused for generating on-site energy for the process (9), with generation of CO2 (10), which is absorbed by trees, ensuing wood production (taken from Association of French Paper Industries at: http://www. copacel.fr/en/lindustrie-papetiere/procedes-de-fabrication.html)

616

M. Gavrilescu et al.

purposes, with an extending trend. A similar product is manufactured using wood as raw material, but by different other producers. Consequently, the manufacturer will be able to generate another loop (11) to close almost complete the production cycle (Fig. 4) in the same global circular outline as in Fig. 3. In this framework, we have applied eco-innovation and eco-design principles to improve the RM eco-efficiency, by re-thinking the existing products, manufacturing them from production waste, using the existing equipment. In this way, RM manufacturer will increase its economic and environmental performances. The eco-product (Eco_P) is the result of eco-innovation and eco-design, in the frame of a knowledge transfer shared between university and industry. This will enable thinking ahead, considering other possible ways for production waste (by-products) revaluation, adding value and extending materials life cycle.

Fig. 4. Closing the loop in the board and corrugated board packaging, by manufacturing an eco-innovated and eco-designed product from production waste (by-products) (adapted upon Association of French Paper Industries at: http://www.copacel.fr/en/lindustrie-papetiere/ procedes-de-fabrication.html)

3 The Context of Eco-Innovation and Eco-Design The awareness on the importance of innovative and design activities focused on decreasing the environmental impact of processes and products has become prevalent in the last years and has emerged in new activities directed toward specific objectives of integrating environmental requirements into conventional design techniques [15, 16].

Extending Production Waste Life Cycle and Energy Saving

617

Therefore, we have put in practice the concepts of eco-innovation and eco-design associated to sustainable development in industry to close the loop and extend materials life cycle. 3.1

Eco-Innovation

Based on literature provisions, we addressed eco-innovation for our purposes considering targets, mechanisms of eco-innovation and impacts [17–19]. Eco-innovation is considered as a way for industry and policy makers to accomplish their plans in improving, in a systemic manner, corporate environmental practices and performances [17], in particular in manufacturing industry. This approach is justified since these industries use to process a significant part of world resources and generate a large quantities of waste. It was found that the ecological footprint of industrial system increased significantly its contribution to the global ecological footprint, industry being the support for the social system, government system, all supporting the human system (Fig. 5) so that the Earth needs today almost the equivalent of two planets for recovering its resource consumed in a year and metabolize the corresponding generated waste (Fig. 6). In the 9th decade of the last century, Fussler and Jannes [20] explained eco-innovation “as a new product, process or service, development (NPD) practice that provides significant environmental performances”, and this description has been further developed by OECD [17]. The target of our eco-innovative strategy is of technological nature and involves both product and process, with some insights concerning marketing. The mechanism of eco-innovation is related to re-thinking the product by considering the eco-design of an existing product, following an alternative which substitute the initial raw materials, the cardboard plate in our case (or wood in a general case), with production waste in the

Fig. 5. Representation of the pressure put by humanity on the environment and natural resources via the industrial system as a support [1]

618

M. Gavrilescu et al.

Fig. 6. Evolution of the global ecological footprint for the industrial system [1]

form of strips, bands, shreds. Our eco-innovated product resulted from a re-design (eco-design) mechanism, and will be able to fulfill the same functional needs and operate as a substitute and/or complement for an existing product. 3.2

Eco-Design

“Eco-design is a design approach that leads to a profitable balance between ecological and economical requirements when developing products” [21]. Eco-design is a concept addressed by ISO 14006 [22], which explains it as the “integration of environmental aspects into product design and development, with the aim of reducing adverse environmental impacts throughout a product’s life cycle”. According to this way of dealing eco-design, the environmental performance is on the same level of importance as technical, cost or quality benchmarks [23, 24]. Eco-design was applied subsequent of idea and conception phases - eco-innovation of the planned product by taking into account environmental issues, so as to reduce the negative impacts generated by similar products, made of corrugated board, wood or plastics, while maintaining the same quality level or increasing it. In our perspective, the eco-design strategy applied for the use of production waste for developing eco-products should lead to: (i) substantial decrease in environmental load of RM, feasible in short term, (ii) materials and energy savings, (iii) reduction in waste by reuse for eco-products, (iv) advanced product design, (v) significant costs saving. The eco-design strategy was developed by ensuing basically the process flow as described in Fig. 7. The key phases address: (i) planning, (ii) analysis and generation of the layouts, (iii) design and development, (iv) checking (verification and approval).

Extending Production Waste Life Cycle and Energy Saving

619

Fig. 7. Eco-design strategy process flow (adapted upon [25])

3.3

Closing-the-Loop Based on Eco-Innovation and Eco-Design Approaches

As mentioned above, the paper and cardboard packaging manufacturing industry was selected for our study because it is one of the most advanced industrial sectors in terms of “closing the loop” degree, being also a very good example of available and proficient industry in applying the circular economy model (Fig. 3). It was estimated that, from 10 packaging items, more than 8 are recycled, which is over the targets imposed by Directive 2004/12/EC [26]. In our work we have followed the eco-design and development pathways, as a “set of processes that transforms requirements into specified characteristics or into specifications of a product, process or system” [22]. RM is characterized by a high adaptability, which facilitate the implementation of sustainable industrial production concept and principles in ensuring its eco-efficiency, by closing the production cycle. Its adaptability concerns the products in relation with resources, production process/technology, importance/performance, solutions for improvements (eco-innovation/eco-design) (Figs. 3, 4 and 8).

620

M. Gavrilescu et al.

4 Extending Materials Life Cycle in Cardboard and Corrugated Board Manufacturing by Eco-Innovation and Eco-Design Methods and Tools 4.1

Product Re-Thinking: Eco-Innovation

Our practical methodology for eco-innovation addresses two main directions: – planning the most appropriate strategies for re-thinking the pre-defined, existing conventional architecture, manufactured from original raw materials (cardboard plate); – development of similar or new architectures according to the structure of production waste (dimensional and quantitative) applying the most operational strategies for the extension of cardboard life-cycle by waste reuse in plant; The developed working plan was structured into a number of sequential steps, consisting in (Figs. 7 and 9); – dimensional and quantitative screening and classification of production waste to ascertain the raw material basis for the eco-innovated product; These analyses were developed at the RM headquarters to deduce from the study of the dimensions the different dimensional classes, the waste quantity associated with each dimensional class, and frequency. A ternary diagram plot was drawn (not shown), considering dimensional class, quantitative class and frequency as parameters; – analysis of original product architecture, in order to identify the main characteristics and possible design constraints generated by the existing dimensional and quantitative structure of production waste; The analysis of the conventional architecture would make possible the following activities: (i) describing the key constituents of the conventional product and its basic structure; (ii) evaluating the potential modularization of the conventional product (correspondence between units and components); (iii) analyzing possible interactions among components;

Fig. 8. Adaptability and flexibility of RM in forms of its product performance in relation with resources, process and performance (adapted upon [27])

Extending Production Waste Life Cycle and Energy Saving

621

– re-thinking/re-innovate/eco-innovate the product architecture based on production waste as raw material (eco-product(s) or subassemblies), for the extension of cardboard life-cycle. 4.2

Eco-Product Architecture and Eco-Design Alternatives

In a first step of eco-product development, modules and subassemblies eco-design, we have considered the so-called architecture design phase, as part of conceptual design and the generator for succeeding phases comprising embodiment and detailed design (Fig. 9) [28]. In fact, the first phase of product eco-design involves the analysis of the opportunity of re-design based on the functionality and performance constraints imposed by the results of dimensional and quantitative analysis of waste.

Fig. 9. Working approaches and steps in the eco-product eco-innovation and eco-design

As acknowledged above, the planned design supported two different categories of analyses: (1) analysis of conventional architecture(s), for a correct definition of the most suitable interventions for pre-existing products and an evaluation of environmental criticality; (2) architecture re-design for the improvement of environmental performance and the development of environmentally acceptable products. The eco-product(s) design planning and building consisted in establishing the modularity and projected geometric pattern (design), and identification of the connections among the main units, subassemblies or modules. Two succeeding phases of design were considered: (1) designing modules and layout; (2) designing components arrangements. Hence, a sequential analysis was performed to design the functional components according to production waste dimensions, shape, material and connection systems so as to ensure eco-product identity and user-friendliness, performance in terms of robustness, reliability and other characteristics associated with envisioned costs and environmental performance [29].

622

M. Gavrilescu et al.

5 Tools for Performance Evaluation of the Eco-Designed and Eco-Innovated Eco-Product In this particular instance of product eco-design, the analysis entails the best product architecture (materials, geometry and arrangement, assembling parts of systems) so as to warrant an effective extended life-cycle, foreseeing superior use and recovery of the resources involved [30]. The specific eco-product characteristics (robustness, consistency, resistance), directly dependent on eco-innovation and eco-design strategy, made at the component level (materials, geometry) were generally quantified by evaluating physical-mechanical properties applying specific methods and instruments. They are determined using specific methods, but these properties are not discussed in this paper. We can mention only that they are in accord with RM norms. The assessment tools allowing the analysis of life cycle extension and waste reuse strategies by closing the loop in the production process (Fig. 4), related to the eco-product architecture, involved a group of methodologies seeking to evaluate eco-product eco-efficiency: Life Cycle Assessment (LCA), Cost Benefit Analysis (CBA), Multi-Criteria Decision Analysis (MCDA) [16, 31]. In a first step, the result of eco-innovation and eco-design were analyzed to evaluate the environmental impacts of the extending life cycle of production waste used as raw material in eco-product architecture and eco-costs. The possible alternatives of the eco-product were analyzed as possible eco-innovation/eco-design scenarios by applying LCA, so that the most suitable to be selected and proposed to be simulated first in real conditions to ascertain its performance in terms of operational, costs, and environmental indicators. The detailed results will be presented in the future, since Eco_P is the subject of a patenting tentative. Also, the application of CBA and MCDA will be the subject of other papers. 5.1

Life Cycle Analysis

“Life Cycle Assessment (LCA) is an environmental assessment tool for evaluation of impacts that a product (or service) has on the environment over the entire period of its life - from the extraction of the raw materials from which it is made, through the manufacturing, packaging and marketing processes, and the use, re-use and maintenance of the product, and on to its eventual recycling or disposal as waste at the end of its useful life” [21, 22, 32]. LCA approach can help the decision makers and specialists in [2, 11, 15]: – examining and selecting the most beneficial life cycles (with marginal negative impacts on the environment); – making and assuming decisions in industry for choosing strategic directions and priorities in production and products planning, design or change; – selecting the most relevant indicators as metrics for process/product assessment in terms of environmental performance; – marketing of products based on environmental declaration or ecolabelling.

Extending Production Waste Life Cycle and Energy Saving

623

By conducting the LCA on the eco-product and comparing the results with those achieved on the conventional architecture, we have evaluated the environmental benefits and, therefore, the eco-effectiveness of the eco-innovative and eco-design strategies and eco-products/subassemblies/modules. Therefore, a broader and extended vision on product development is entailed, beyond the common context associated with production and use, as provided by Life-cycle Design (LCD) approach. This means that our strategy has taken into account all life-cycle phases of our eco-product product, from idea and concept definition (eco-innovation) to the detailed project progress by eco-design, considering the statement that the most operative changes, novelties and interventions are those applied in the earliest design phases [29, 33]. Further we went toward development, production, distribution, use, maintenance, disposal and recovery in a comparative assessment of the conventional and eco-innovated/eco-designed architectures. We have performed a complete LCA study according to the ISO 14040:2006 [34], by following four major phases (Fig. 10) [2, 11]:

Fig. 10. Stages of LCA according to ISO 14040 [34]

– goal and scope definition, which describes the objectives and scope of study, system boundaries and the functional unit; – inventory analysis, with a full assembling of all environmental inputs (resource and energy flows) and outputs (emissions and waste); – impact assessment, which involves evaluation of environmental impacts from the inventory and establish environmental performance of the product; – interpretation, when the results of the inventory are understood. The analysis was performed for three scenarios: – the first (basic) scenario is represented by the conventional process, which uses cardboard sheets to produce cardboard boxes, packaging supports - our targeted product, as well as production waste (strips, edges or similar waste) (Fig. 11a); – the second scenario closes the loop by reusing “in plant” the production waste (loop 11 in Fig. 4) resulting in cardboard boxes, a higher quantity of packaging

624

M. Gavrilescu et al.

Fig. 11. Scenarios proposed for LCA: (a) basic scenario; (b) scenario involving eco-innovation and eco-design for closing the loop by reusing “in plant” the production waste for eco-product manufacturing

supports - part of them being the result of eco-innovation and eco-design: the eco-product Eco_P (the second box in Fig. 11b) and a significantly diminished quantity of production waste (Fig. 11b). Also, we considered a third scenario, which uses wood as raw material for a similar product, but it is not associated with the scheme illustrated in Fig. 4. The system boundaries for the first two scenarios are those illustrated in Fig. 11(a) and (b), respectively. The functional unit was selected as 10t cardboard manufactured. Since the process is a complex one, we have presented here the materials flow only in the two proposed scenarios (Fig. 11). The analysis addressed the material balances for the conventional process (Fig. 11, scenario a), with the main material inputs as illustrated in Fig. 12(a–c), as well as for the process flow sheet entailing the eco-innovated and eco-designed product (Fig. 11, scenario b), as illustrated in Fig. 12d. Data were taken from corrugated board manufacturing technologies [35–37], Best Available Techniques [38], data from the RM process manufacturing and other sources [13–15, 30, 32, 39–41]. As illustrated in the scheme d (Fig. 12) the RM is able to close almost complete the production loop and reuse “in plant” the production waste for manufacturing the eco-product as packaging support as well as subassemblies that can be used for Eco_P manufacturing and/or reinforcing (or as insulating material in construction and building).

Extending Production Waste Life Cycle and Energy Saving

625

Fig. 12. Material balance in conventional corrugated board and cardboard packaging process (a, b), carboard packaging and packaging support manufacturing using cardboard sheet (c), and carboard packaging and Eco_P manufacturing from production waste (d)

The potential environmental impact was approached in terms of saving wood/forest necessary to produce the unit of eco-innovated and eco-designed product, in terms of carbon balance. The comparison was made with a similar product usually made by wood (spruce, in our case) (Fig. 13). Our evaluations showed that, revaluating the production waste and substituting the woody packaging supports with Eco_P would reduce the carbon footprint with an equivalent of almost 0.55 kg CO2/product item/year by saving over 2500 spruce trees [35, 36] (Fig. 13). Also, in terms of economic efficiency it was evaluated, using LCCA and eco-costs analysis - based on the scheme proposed in Fig. 13, an increased eco-efficiency of almost 50% per product item/year. This means that RM can improve its economic and environmental performance by closing the production loop (as illustrated in Fig. 4), with a potential increase in the profit representing 2.5% from the annual turnover and an environmental saving equivalent with 55 t CO2/year.

626

M. Gavrilescu et al.

Fig. 13. Environmental efficiency in CO2 equivalent potentially achieved by RM when reusing the production waste for Eco_P and replacing the woody products with the eco-innovated and e- designed eco-product

This would be a pertinent step in ensuring the sustainable pathway in industrial development, to reduce the pressure on the planet biocapacity as illustrated in Fig. 6. 5.2

Discussion on Impacts of Eco-Innovation and Eco-Design for RM

• Technical-economic impact In terms of technical-economic impacts, the valorization of production waste to RM will allow the reintegration in the production process waste in a feasible and efficient production stage, by applying strategies and solutions specific to eco-innovation and eco-design. The process eco-innovation is performed by source reduction and waste minimization by its revalorization as raw material in an eco-innovated and eco-designed product, existent in the production assortment of RM, but manufactured from other source of raw materials. Also, this way it is confirmed the capacity and availability of RM in applying the sustainable production principles and practices, as well as for knowledge transfer from university to industry, by integrating the technical expertise of university with these of the specialists from the production system. Product subassemblies could be also used in other sectors, such as building. Eco-efficiency is connected with added value, while the technology could be extended to other manufactures, based on intellectual property license.

Extending Production Waste Life Cycle and Energy Saving

627

• Environmental impacts and performance Our project will lead to the revaluation of production waste, while the manufacturing process tends toward the ‘zero emission’ target, by applying of the cradle-to-cradle approach associated with extended life cycle at the level of RM, using the existing equipment and expertise. The resulted product is totally recyclable and biodegradable, which can be reintegrated in paper manufacturing process at the end of its life cycle, according to the circular economy concept (and cradle-to-gate approach). The environmental impact is abated by reducing carbon footprint (CO2 equivalent, associated to climate changes) as a result of saving forests trees. Therefore applying eco-innovation and eco-design will contribute to the reduction of ecological footprints (global, carbon etc.). • Impact of knowledge transfer The eco-innovated and eco-designed product is a model for addressing the sustainability in industrial development, aiming at diminishing the value of streams from the environment to the industrial system (natural resources) and toward the environment (emissions, waste). This will facilitate the mutual knowledge integration and transfer between university and industry to develop a sustainable strategy for ensuring extended producer responsibility, by promoting research and development on the entire chain supply-production-sale, favorable for the market and business potential of RM. • Measuring technical-economic and environmental performance as a result of extending production waste life cycle by eco-innovation and eco-design Life Cycle Assessment (LCA) was applied as a versatile tool in assessing environmental performance of product and process, along production chain. Starting with its definition given by ISO 13030 (2006), LCA can assist in: – “identifying opportunities to improve the environmental performance of products at various points in their life cycle; – informing decision-makers in industry, government or non-government organizations (e.g.) for the purpose of strategic planning, priority salting, product or process design or redesign; – the selection of relevant indicators of environmental performance, including measurement techniques”. These provisions are in line with eco-innovation and eco-design purposes addressing the process/product manufactured by RM, since LCA is applied for assessing their environmental impacts, and for identifying other eco-innovative aspects in product/process susceptible for eco-design. • Impacts for the RM Company These impacts is largely associated with “internal drivers” for eco-innovation and eco-design to close the loop by revaluation of production waste. Table 1 details the most relevant impacts, as they were argued by Brezet and van Hemel [42].

628

M. Gavrilescu et al.

Table 1. Impacts generated at the level of RM, as a result of production waste revaluation and closing the production loop by applying eco-innovation and eco-design (“internal drivers”) Impact Increased production efficiency and quality Reduced costs and market availability

Increased awareness for eco-innovative activities

Manager’s sense of responsibility and the need to improve the company image and prestige

Short description Functionality, durability and maintenance of product made from production waste will go hand in hand with environmental performance and quality The market is highly interested by product, and costs saving will be possible due to changing in raw material (from cardboard plates to production waste) Immediate financial benefits will be registered, but also on long term An efficient use of energy, water other materials will contribute to costs saving Knowledge transfer from University to RM will contribute to the increase in the awareness of specialists and workers relative to eco-innovation and eco-design importance applied in production improvement as well as in the “combination of product, market and technology” Achievement of sustainable production by eco-innovation and eco-design is a chief task of RM’s manager, in terms of industrial system performance and his responsibility, to ensure environmental protection A good marketing and communication with the market regarding product quality and production eco-efficiency would ensure good relations with consumers, and an improved company’s image

6 Conclusions Today, the industrial system continues to work in an unsustainable way, since it consumes resources form the natural capital and generates waste and emissions, putting a strong pressure on planet’s biocapacity. Therefore, industrial production needs to be eco-efficient by combining the economic efficiency with low environmental impacts and social benefits. Although there are some options applied to ensure sustainable waste management, only a few address the life cycle extension of production waste, by closing the loop based on in plant recycling/reuse of byproducts treated as waste, and re-thinking and re-design an existing product, with high market potential. New tools developed to improve the resource efficiency and extend materials life cycle include eco-innovation and eco-design. This approach would enable the enhancement of resource efficiency by combining the economic issues with environmental performance in “win-win” synergy. Acknowledgement. This work was supported by two grants of the Romanian National Authority for Scientific Research, CNCS - UEFISCDI: (i) project number PN-III-P2-2.1-BG2016-0130, Contract 64BG/2016; (ii) project number PN-III-P2-2.1-BG-2016-0016, Contract 1BG/2016.

Extending Production Waste Life Cycle and Energy Saving

629

References 1. Gavrilescu, M.: Sustainable Industrial Production (in Romanian). Polytechnium Press, Iasi (2011) 2. Ghinea, C., Petraru, M., Simion, I.M., Sobariu, D., Bressers, H.T.A., Gavrilescu, M.: Life cycle assessment of waste management and recycled paper systems. Environ. Eng. Manag. J. 13, 2073–2085 (2014) 3. Haas, W., Krausmann, F., Wiedenhofer, D., Heinz, M.: How circular is the global economy?: an assessment of material flows, waste production, and recycling in the European Union and the World in 2005. J. Ind. Ecol. 19, 765–777 (2015) 4. Petraru, M., Gavrilescu, M.: Pollution prevention, a key to economic and environmental sustainability. Environ. Eng. Manag. J. 9, 597–614 (2010) 5. Ghisellini, P., Cialani, C., Ulgiati, S.: A review on circular economy: the expected transition to a balanced interplay of environmental and economic systems. J. Cleaner Prod. 114, 11–32 (2015) 6. Murphy, R.J., Norton, A.: Life Cycle Assessments of Natural Fibre Insulation Materials. Final Report. Imperial College London (2008). http://eiha.org/media/attach/372/lca_fibre.pdf. Accessed May 2017 7. Wrisberg, N., Udo de Haes, H.A., Triebswetter, U., Eder, P., Clift, R.: Analytical Tools for Environmental Design and Management in a Systems Perspective: The Combined Use of Analytical Tools. Springer Science & Business Media, Amsterdam (2012) 8. Eurostat. Eurostat Statistics Explained. Waste Statistics (2016). http://ec.europa.en/eurostat/ statistics-explained/index,php/Waste-statistics. Accessed May 2017 9. EC Directive 98. Directive 2008/98/EC of the European Parliament and of the Council of 19 November 2008 on waste and repealing certain Directive. Off. J. Eur. Union, L312, 3–30 (2008) 10. COM. Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions, Closing the loop - An EU action plan for the Circular Economy, COM (2015) 514 final. European Commission, Brussels, Belgium (2015) 11. Petraru, M.: Integration of Economics and Pollution Prevention Practices for a Sustainable Industry. Ph.D. thesis. Gheorghe Asachi Technical University of Iasi, Romania (2012) 12. Golińska, P., Kawa, A. (eds.): Technology Management for Sustainable Production and Logistics. Springer, Berlin (2015) 13. CNE. Packaging and Circular Economy: A case study of the circular economy model, Conseil National de l’Embalage, Paris, France (2014). http://www.conseil-emballage.org. Accessed May 2017 14. FEFCO. FEFCO touts cardboard’s circular step. European organization says bard packaging is ahead of circular economy goals, Recycling Today, Global Edition (2017). www. recyclingtodayglobal.com/article/fefco-ds-smith-recycling-occ-conversation/. Accessed May 2017 15. Ghinea, C., Petraru, M., Bressers, H.Th.A., Gavrilescu, M.: Environmental evaluation of waste management scenarios - Significance of the boundaries. J. Environ. Eng. Landscape Manag. 20, 76–85 (2012) 16. Ghinea, C., Drăgoi, E.N., Comăniţă, E.C., Gavrilescu, M., Câmpean, T., Curteanu, S., Gavrilescu, M.: Forecasting municipal solid waste generation using prognostic tools and regression analysis. J. Environ. Manag. 182, 80–93 (2017) 17. OECD: Sustainable Manufacturing and Eco-Innovation, Framework, Practices and Management. Synthesis Report. OECD, Paris (2009)

630

M. Gavrilescu et al.

18. Charter, M., Clark, T.: Sustainable Innovation: Key Conclusions from Sustainable Innovation Conferences 2003–2006 organized by The Centre for Sustainable Design, Centre for Sustainable Design, Farnham, UK (2007). http://cfsd.org.uk/SustainableInno vation/Sustainable-Innovation-report.pdf. Accessed May 2017 19. Reid, A., Miwedzinski, M.: Eco-innovation: Final Report for Sectoral InnovationWatch, Technopolis Group, Grighton, UK (2008) 20. Fussler, C., James, P.: Driving Eco-Innovation - A Breakthrough Discipline for Innovation and Sustainable. Pitman Publishing, Pearson Professional Ltd, London (1996) 21. Madu, C.: Handbook of Environmentally Conscious Manufacturing. Springer Science & Business Media, Amsterdam (2012) 22. ISO 14006. Environmental Management Systems - Guideline for incorporating eco-design. International Organization for Standardization, Geneva, Switzerland (2011) 23. Kemp, R., Pearson, P.: Measuring eco-innovation. Final report MEI project about measuring ecoinnovation. Project No: 044513-FP6 (2007). https://www.oecd.org/env/consumptioninnovation/43960830.pdf. Accessed May 2017 24. Cluzel, F., Vallet, F., Tyl, B., Leroy, Y.: Eco-design vs. eco-innovation: an industrial survey. In: Proceedings of the 13th International Design Conference - DESIGN 2014, May 2014, Dubrovnik, Croatia, pp. 1501–1510 (2014). https://hal.inria.fr/hal-01144352/document. Accessed May 2017 25. Mungcharoen, T., Boonyawatana, S.: Application of LCA & EcoDesign in Eco-Products Development: Case Study for Eco-compressor. In: International Workshop on “Capacity Building on Life Cycle Assessment in APEC Economies”, Bangkok, Thailand, 15–16 December 2005. http://www2.mtec.or.th/th/course_seminar/detail/capec/lca-pdf/Thumrong rut-1.pdf. Accessed May 2017 26. EC Directive 12. Directive 2004/12/EC of the European Parliament and of the Council of 11 February 2004, amending Directive 94/62/EC on packaging and packaging waste. Off. J. Eur. Union, L47, 26–31 (2004) 27. Nielsen, A.S.: Mastering True Value Creation. ICIS, Copenhagen (2002) 28. van Vie, M.J., Rajan, P., Campbell, M.I., Stone, R.B., Wood, K.L.: Representing Product Architecture. In: Proceedings of DETC 2003 ASME 2003, Design Engineering Technical Conferences and Computers and Information in Engineering Conference, Chicago, Illinois, USA, 2–6 September (2003). https://www.sutd.edu.sg/cmsresource/idc/papers/2003-_Repr esenting_product_architecture.pdf. Accessed May 2017 29. Arundel, A., Kemp, R.: Measuring eco-innovation. United Nations University, Working Paper Series, Maastricht Economic and Social Research and Training Center on Innovation and Technology, The Netherlands (2009) 30. FEFCO. European Database for Corrugated Board Life Cycle Studies (2012). http://www. fefco.org/sites/default/files/lca-report-2015.pdf. Accessed May 2017 31. Ghinea, C., Gavrilescu, M.: Costs analysis of municipal solid waste management scenarios: Iasi - Romania case study. J. Environ. Eng. Landscape Manag. 24, 185–199 (2016) 32. UNEP. Guidelines for Social Life Cycle Assessment of Products, United Nations Environment Program (2009). http://www.unep.fr/shared/publications/pdf/DTIx1164xPA-guidelines_sL CA.pdf. Accessed May 2017 33. Giudice, F., La Rosa, G., Risitano, A.: An ecodesign method for product architecture definition based on optimal life-cycle strategies. International Design Conference - Design 2002, 14–17 May, Dubrovnik (2002). https://www.designsociety.org/publication/29735/an_ ecodesign_method_for_product_architecture_definition_based_on_optimal_life-cycle_strate gies. Accessed May 2017 34. ISO 14040. Environmental Management: Life Cycle Assessment-Principles and framework. International Organization for Standardization, Geneva, Switzerland (2006)

Extending Production Waste Life Cycle and Energy Saving

631

35. Gavrilescu, D., Toth, S.: Corrugated Board (in Romanian). Gloria Press, Cluj-Napoca (2001) 36. Twede, D., Selke, S.E.M., Kamdem, D.-P., Shires, D.: Cartons, Crates and Corrugated Board, Second Edition: Handbook of Paper and Wood Packaging Technology. DEStech Publications Inc., Lancaster (2014) 37. Laakso, O., Rintamäki, T.: Production and Converting of Corrugated Board. Finnish Corrugated Board Association, Lahti (2003) 38. EU. Best Available Techniques (BAT) Reference Document for the Production of Pulp, Paper and Board. European Commission, Joint Research Centre, Institute for Prospective Technological Studies (2015). http://eippcb.jrc.ec.europa.eu/reference/BREF/PP_revised_ BREF_2015.pdf. Accessed May 2017 39. AEA. Carbon & Tree Facts (2016). http://www.arborenvironmentalalliance.com/carbontree-facts.asp. Accessed May 2017 40. PE International. GaBi Handbook and GaBi Modelling Principles (2012). http://www.gabisoftware.com/international/support/gabi/gabi-modelling-principles/PE. Accessed May 2017 41. Van Duinen, M., Deisl, N.: Handbook to Explain LCA Using the GaBi EDU Software Package. PE Americas, Boston (2009). http://isites.harvard.edu/fs/docs/icb.topic636070. files/GaBi%20EDU%20handbook%20-%20v1.pdf. Accessed May 2017 42. Brezet, H., van Hemel, C.: Ecodesign - A Promising Approach to Sustainable Production and Consumption. United Nations Environment Programme, Industry and Environment, Cleaner Production (1997). www.ivt.ntnu.no/ipd/fag/e.codesign/theory/theory-frames.htm. Accessed May 2017

Sustainability - A Principle of Education in Architecture (and Not Only) Ana-Maria Dabija1,2(&) 1

Center for Architectural and Urban Studies CSAU, “Ion Mincu” University of Architecture and Urbanism, Bucharest, Romania [email protected] 2 The Commission for Renewable Energies, Romanian Academy, Bucharest, Romania

Abstract. Sustainability is a term that defines the ability of a system to function for an indefinite time. From the definition given in the Brundtland report in 1987 as the “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” - the approach received different nuances and new facets, as today the term refers not only to the environmental development - that includes the natural resources - but also to the economic, social, cultural, safety aspects. Sustainability cannot be accomplished by actions coming from only one direction, all aspects that were mentioned above having to be studied and matched in a sustainable approach. Why this introduction? Because the architectural approach needs to be a complex one, that deals not only with building materials and building principles but also with traditions, culture, history, economy, sociology. In a very large sense, the architect is an educator and a mediator in the contemporary society and not only a builder. This paper intends to put a light on the relation between architecture and sustainability and the role of the architect in the contemporary society. Keywords: Sustainability


Buildings
Education

1 Introduction. A (Very) Brief History of the Concept of Sustainability A general definition of “sustainability” is given by the Business Dictionary: “the ability to maintain or support an activity or process over the long term”. According to Merriam-Webster Dictionary sustainability is “a method of harvesting or using a resource so that the resource is not depleted or permanently damaged”. The Cambridge Dictionary gives, for the same adjective, more nuanced definitions: “able to continue over a period of time”, respectively “causing little or no damage to the environment and therefore able to continue for a long time”. Sustainability may define the relation between humans and the environment: throughout history humans, not other species endangered the environment. “Everything that we need for our survival and well-being depends, either directly or indirectly, on our natural environment. To pursue sustainability is to create and maintain the conditions under which humans and nature can exist in productive harmony to support present and future generations [1]”. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_43

Sustainability - A Principle of Education in Architecture (and Not Only)

633

During the seventeenth and eighteenth centuries ideas about forest management were developed in Europe, as a response to a growing awareness of the depletion of timber resources in England. Preoccupations for the study of the interdependence between the increase in a nation’s food production, the well-being of the specific population and the growth of population was studied by Thomas Robert Malthus in the 1798 Essay on the Principle of Population. In the mid-twentieth century the synthetic fertilizers, herbicides and pesticides lead scientists to pull the alarm signal regarding devastating consequences for wildlife and not only. The United States Environmental Protection Agency consider that one of the first written documents regarding sustainability is the 1969 National Environmental Policy Act (NEPA), that establishes a national framework for environment protection. NEPA’s basic policy is “to assure that all branches of government give proper consideration to the environment prior to undertaking any major federal action that significantly affects the environment” [2].

2 From the Brundtland Report to the Present The term “sustainable development” is commonly accepted as being launched in the famous Brundtland Report - Our Common Future [3], a year after the explosion of the nuclear reactor in Cernobil, in 1986: “Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs”. It contains within it two key concepts: • The concept of ‘needs’, in particular, the essential needs of the world’s poor, to which overriding priority should be given; • The idea of limitations imposed by the state of technology and social organization on the environment’s ability to meet present and future needs [3]. This definition broadens the field of application of the term, from environmental sciences to economic and social sciences. As can be observed, the social and economic decisions intertwine with the environmental issues, sciences and actions. Thus, the “construction” supported by the three pillars has begun. Five years later, the United Nations Conference on Environment and Development (UNCED) - also known as the Rio de Janeiro Earth Summit - establishes new aims for humanity actions, where cooperation and partnership of the states should improve the quality of the Earth’s ecosystem [4], of the quality of life of the people [5], while finding ways and means of compensation for the victims of environmental damage [6]. Another document that emerged from the Earth Summit is the “Agenda 21”, where four sections of interventions are defined: 1. Social and Economic Dimensions: that aims to fight against poverty, especially in developing countries, by promoting health, changing consumption patterns.

634

A.-M. Dabija

2. Conservation and Management of Resources for Development: that includes control of pollution (including waste management), protection of fragile environments, of the atmosphere, combating deforestation, protecting fragile environments, conservation of the biodiversity. 3. Providing an important and solid role of the groups of people and communities: indigenous peoples, farmers children and youth, women, NGOs, local authorities, industry or business, and workers. 4. Means of Implementation: implementation includes science, technology transfer, education, international institutions and financial mechanisms. Further World assemblies that nuanced the Rio Agenda were carried out in 1997 (Rio+5), in 2002 (Rio+10) where the focus was moved towards culture and the implementation of measures at local level, in 2012 (Rio+20). The four sections of the Agenda 21 emphasize even more the “pillars of sustainability” as they were defined more than a decade later, in the 2005 World Summit: the societal pillar, the environmental pillar the economy pillar obviously in a different arrangement. They are often also referred to as people, planet and profits. In time, the number of criteria for the analysis grew from three to four - including the cultural pillar - or five, recently - the safety pillar. The representation (Fig. 1) aims to express the fact that any action on one pillar has implications on the other two (three or four, now) or, in other words, the development of one pillar unbalances the others. The intention is to ensure a balance of local and global efforts to meet basic human needs without destroying or degrading the natural environment. Therefore, all the pillars should be dealt with at the same time, equally. In this flowing stream of nuancing and developing the principles of sustainability, two other movements came to strengthen and color the theory: degrowth and resilience. Sustainable development versus degrowth, as developing something exhausts the resources; degrowth aims to decrease production and consumption, considering that overconsumption leads to environmental and social problems. The term as we know it

SUSTAINABILITY

Fig. 1. Common representations of the three pillars of sustainability

PLANET

PEOPLE

PROFIT

PLANET

PEOPLE

PROFIT

Sustainability - A Principle of Education in Architecture (and Not Only)

635

today was launched in the 1968–1972 reports of the Club of Rome, the main contributor being the Romanian American mathematician, statistician and economist Nicolae Georgescu-Roegen. The roots of the theory are much older, resulting as a response to the industrialist period of the 19-th century when philosophers and economists realized that the more we produce, the more resources we use. The selective use of materials or technologies lead to the “rebound effect”, defined by William Stanley Jevons as The Jevons paradox. In his 1865 book “The Coal Question” he observed that improvements in the way fuel is used increased the overall quantity of fuel used: “It is a confusion of ideas to suppose that the economical use of fuel is equivalent to diminished consumption. The very contrary is the truth” [7]. In other words, better efficiency in the use of a type of resource leads to more of that resource that is being used and to a change of human behavior that adapts to the specific use of the resource. The concerns that the Club of Rome dealt with are adopted by the theory of sustainable development: reduced availability of energy sources, declining quality of the environment, while principles of tackling degrowth can be identified in the principles of the sustainable development: preservation of the biodiversity and culture, minimize the waste production with education, reuse of resources - cradle to cradle theory - participation of local communities in the act of decision etc. Resilience is considered a nuanced sustainability; the roots of this concept lies in the definition of resilience, as the ability of a system to adapt after a shock (during hurricane Katrina many buildings designed and constructed according to sustainable principles fell apart, thus leading to the idea that the way structures adapt should also be taken into consideration). According to Reese in Sustainability vs Resilience, “Resilience then becomes a theoretical construct for sustainability that: (a) guides against breaching unknown systems boundaries; (b) suggests that continuous changes in certain driving variables is inherently dangerous (e.g., continuously increasing fishing pressure, escalating GHG emissions, or constant material growth) and; (c) warns that surviving the breach of a major tipping point, whether human induced or natural, will require unprecedented levels of investment, cooperation and other forms of institutional and societal adaptation. Human-induced climate change will almost certainly validate all these assertions” [8]. The Earth Charter, an international declaration of fundamental values and principles for building a just, sustainable, and peaceful global society in the 21st century “seeks to inspire in all peoples a sense of global interdependence and shared responsibility for the well-being of the human family, the greater community of life, and future generations” [9]. The Official Agenda for Sustainable Development [10] adopted on 25 September 2015 has 92 paragraphs that develop the main 17 goals (that can be grouped in the frame of the pillars of sustainability as well): • the societal pillar, cumulating ending poverty and ending hunger, ensuring health and well-being, providing education, providing gender equality, reduced inequalities, peace - justice and strong institutions; • the economic pillar with the targets of decent work and economic growth, industry innovation and infrastructure, responsible consumption and production;

636

A.-M. Dabija

• the environmental pillar, leading to sustainable cities and communities, clean water and sanitation, affordable and clean energy, climate action, life bellow water, life on land and a partnership for the goals.

3 Sustainability. A Principle of Education For UNESCO [11], education for sustainable development involves integrating sustainable development issues into the process of teaching and learning. It is, in a way, a measure from the societal pillar to influence the other two pillars: the environmental one, through knowledge regarding climate change, disaster risks, biodiversity, energy issues, life on the planet as well as poverty reduction and sustainable consumption. It also requires teaching and learning methods that motivate active participations in the life of the community as well as the ability to educate and change the behaviors to act for sustainable development. Some means that are emphasized are critical thinking, imagining future scenarios and making decisions in a collaborative way. The aim is to create a mentality that can keep a balance in the society between and within the pillars. Target 4.7 states that by 2030 education should develop ways to teach knowledge for sustainability in lifestyles, human rights, gender equality, culture of peace and non-violence, cultural diversity. In other words, education - an activity within the societal pillar - should be oriented to form mentalities and abilities to develop in harmony all the pillars. The Global Action Programme launched by UNESCO in 2014, benchmarked the aims of education in a sustainable society [12], with an even more oriented aim toward sustainable development.

4 Sustainability. A Principle of Education in Architecture Architecture is in itself a profession that deals with society, economy and environment. It is - as Mies van der Rohe stated - “the will of an epoch translated into space.” Maybe this is the reason why the profession always adapts to the requirements of the economy and societal challenges, whatever they are: in periods of economic development, architecture is also flourishing: after great catastrophes, architects have work to do; in periods of crisis it is time to re-evaluate principles, technologies, materials. Building technologies and materials are not scopes, but means for construction. A building is not sustainable if it is garnished with green roofs, green facades or building integrated photovoltaic systems. The building - the neighbourhood - the territory must be connected to one another, depending each on the other. Throughout history architecture changed, according to the “will of the epoch”; types of buildings disappeared, as different architecture programs disappeared or lost their importance, leaving place to other types of buildings, that accommodated other types of activities.

Sustainability - A Principle of Education in Architecture (and Not Only)

637

Fig. 2. Abbey Gateway, Chester, now under transformation into a two-bedroom residential property. Photo: John S Turner, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php? curid=3788155

The walls remained, thoroughly built to last for centuries and eventually accommodated new functions in old buildings, thus giving a fresh start - a new life - to otherwise deserted constructions. Examples can be churches or gateways that, in many western European countries, were transformed into dormitories, public libraries, markets, hotels (as seen in Fig. 2). The four Gasometers in Vienna, (Fig. 3) built in 1899, were used for supplying town gas to the city at the end of the nineteenth century; after 1984 they were no longer usefull, due to new technologies in gasometer construction and to the use of natural gas and were converted into multifunctional buildings, hosting retail, offices and residential functions. The conversion was designed by different architects for each building: Jean Nouvel, Coop Himmelblau, Manfred Wehdorn, Wilhelm Holzbauer. The assembly was finalized in 2001). In the contemporary world architects face new challenges: the massive migration of communities. The depopulation issue is a worldwide problem. Causes are different, geo-climatic, economic and political conditions are different but the fact remains: people are deserting places and move into other places. The deserted/remaining localities represent a built heritage that needs to be carefully considered: should it be preserved, with the original function, preserved but conversed to different architectural programmes, updated, retrofitted, integrated, demolished etc.

638

A.-M. Dabija

Fig. 3. The Vienna gasometers. Photo: Andreas Poeschek by CC-BY-SA-2.0-at

It is not only the physical buildings that are to be taken into consideration but also the entire world of links, connections to the culture, economy, sociology that the building/the environment, the territory was influenced by [13]. The issues of the role of education in architecture in the evolving society was studied in the frame of an Erasmus+ project: Confronting Wicked Problems; Adapting Architectural Education to the New Situation in Europe, coordinated by the Oslo School of Architecture and Design with the following partner institutions: the Delft Technical University, the Politecnico di Milano, the “Ion Mincu” University of Architecture and Urbanism, the European Association for Architectural Education and the Architect’s Council of Europe. It was a three-year project, with themes that dealt with important contemporary issues and was carried out through workshops with international teams of students and tutors. The themes that were studied focused on over-urbanisation and densifications produces by the inwards migrating working population in Rotterdam, Holland, on the rural depopulation in Dealu Frumos, Romania (Fig. 4), and on the contaminated industrial sites in Milano, Italy. Among the findings of the “wicked” themes the following conclusions were drawn [13, 14]: – the contemporary principles of sustainability and resilience imply the use of what we already have, focusing on how to evaluate the impact of our way of life on the built environment, what needs to be changed, how can we adapt what is already there and how to accommodate new functions in existing buildings/built sites, without destroying the balance of the network that connects the materiality to the immaterial spheres of the specific place (culture, religion, economy, tradition etc.); – depopulation as well as over-population greatly affects architecture - heritage and new build as well;

Sustainability - A Principle of Education in Architecture (and Not Only)

639

– peoples’ migration issues are phenomena that directly affect architectural heritage and people’s culture in general and as such they should be studied by architects and urban planners; – contaminated and polluted sites bring in the equation one more dimension: time. Time planning, schedules, interventions in and over time; – architectural education should take more into consideration the social aspects of the population benefiting from the envisioned planning. Furthermore, architects and planners should be educated to proper use a larger filed of instruments of social and (multi) ethnographical origin; – regional evaluation and strategy planning can lead to specific architectural solutions inside a certain place (village/town/area); – local strategies should take into consideration a broader regional spectrum of analysis and locality alliances; – local economy can be both autonomous and deeply affected by global economy. While the population can survive locally at a minimum level of existence, it cannot evolve/thrive past a certain point without external intervention or serious local collaboration efforts; – the future architect should be involved not only as a designer of material objects but as well as a manager, a communicator, a mediator between communities and authorities, not only a coordinator of multidisciplinary teams.

Fig. 4. Dealu Frumos village, seen from the tower of the fortified church (XIVth - XVth century). Photo: Ana-Maria Dabija

5 Conclusions As our world is confronted with environmental issues, social issues, multi-cultural issues, migration, violence, terrorism, hunger, economy crisis etc., the architect’s role is also to interact with the authorities as mediators in the attempt to “meet the needs of current generations without compromising the ability of future generations to meet their

640

A.-M. Dabija

own needs” (the Brundtland Report). In this context, education in architecture today should also include - beside principles of conception and design - elements of history, art, philosophy, sociology economy, engineering, geology, geography, botanics, physics, chemistry, IT, etc. The aim is to form professionals who understand societal, economical and environmental challenges, who lead inter and multi disciplinary teams, who act as mediators and influence the decision makers as well as groups of people, who, by their actions and work, educate and contribute to changing mentalities.

References 1. https://www.epa.gov/sustainability/learn-about-sustainability#what. Accessed May 2017 2. www.epa.gov/laws-regulations/summary-national-environmental-policy-act. Accessed May 2017 3. http://www.un-documents.net/our-common-future.pdf. Accessed May 2017 4. The Rio Declaration on Environment and Development, Preamble, Principle 7. http://www. unesco.org/education/pdf/RIO_E.PDF. Accessed May 2017 5. The Rio Declaration on Environment and Development, Preamble, Principle 8. http://www. unesco.org/education/pdf/RIO_E.PDF. Accessed May 2017 6. The Rio Declaration on Environment and Development, Preamble, Principle 13. http://www. unesco.org/education/pdf/RIO_E.PDF. Accessed May 2017 7. Jevons, W.S.: Chapter VII Of the Economy of Fuel. In: The Coal Question, VII.3. Macmillan and Co., London (1865). www.econlib.org/library/YPDBooks/Jevons/jvnCQ7. html. Accessed May 2017 8. Reese, W.: Sustainability vs Resilience (2014). http://www.resilience.org/stories/2014-0716/sustainability-vs-resilience/. Accessed May 2017 9. http://earthcharter.org/discover/what-is-the-earth-charter/. Accessed May 2017 10. www.un.org/sustainabledevelopment/sustainable-development-goals/. Accessed May 2017 11. http://www.unesco.org/new/en/education/themes/leading-the-international-agenda/educationfor-sustainable-development. Accessed May 2017 12. Education for Sustainable Development - The Global Action Programme after 2014. Accessed May 2017 13. Komosa, S., Sanaan-Bensi, N.: Ist Report of the workshop in Delft, in the frame of Erasmus+ Project Confronting Wicked Problems. Adapting Architectural Education to the New Situation in Europe (2015). http://www.eaae.be/activities/wicked-problems/. Accessed May 2017 14. Dabija, A.M., Bogdanescu, Z.: IInd Report of the workshop in Dealu Frumos, in the frame of Erasmus+ Project Confronting Wicked Problems. Adapting Architectural Education to the New Situation in Europe (2016). http://www.eaae.be/activities/wicked-problems/. Accessed May 2017

Sustainable Energy in Buildings: Academy Massive Open Online Courses Carlos Silva1 and Laura Aelenei2(&) 1

IN+, Center for Innovation, Technology and Policy Research, IST, Lisbon, Portugal 2 Laboratório Nacional de Energia e Geologia, Lisbon, Portugal [email protected]

Abstract. According with the Research and Markets [1] analysis, the growing demand of reliable online learning solutions and technologies is the driving force of Massive Open Online Course (MOOC) market. The industry forecast for MOOC market size is to grow from USD 1.83 Billion in 2015 to USD 8.50 Billion by 2020, at a compound annual growth rate (CAGR) of 36.0%. Adoption of device-based computing, increased connectivity of platform, and emergence of online and collaborative learning and personalization of technology are some of the prominent factors driving the adoption of MOOC platform and services. The authors of this paper intend to share some insights of a recent approved project financed within Kic Innoenergy framework, project EBA, Energy in Buildings Academy, with the main objective to offer a unique online educational offer on Energy Management in Buildings. Keywords: MOOC


Energy efficiency
Training

1 Introduction Energy consumption in buildings represents 40% of the primary energy consumption in Europe and is therefore one of the sectors that has a large potential to contribute to energy efficiency goals of Europe by 2020. However, and despite the numerous policy measures that stemmed from the different directives [2, 3], the building sectors still presents a lot of potential to improve that is not yet captured [4]. One of the latest directives 2012/27/EU [5] - which is currently being transposed to national laws - imposes the monitoring of energy consumption in buildings in order to contribute to the implementation and evaluation of energy efficiency measures. Further, organizations are increasingly aware of the importance of a specific training in energy in buildings (from monitoring, auditing and management), especially as the energy costs have been increasing in Europe and affects their competitiveness. However, most of the buildings do not have a qualified energy manager, as this “job” is often included in the facility manager job description. To obtain training in energy management for their employees, organizations may ask for dedicated courses from companies like internal training companies (e.g. SGS in energy management and ISO50001, EVO in IPMVP), national training organizations that present tailored solutions for local regulations and incentives. The type of offers varies, but in general is based in 3 to 5 days © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_44

642

C. Silva and L. Aelenei

theoretical training in a total of 20 to 40 h of classes, in some cases with field visits. There are some academic offers for the international market (Executive Summer Program - Energy Management Track, from Grenoble graduate school of business). The available online offer in this specific subject is very small, dispersed and recognized training institutions, like universities, do not provide it. The online distance education and training is not a new method and presents several educational delivery methods (Table 1) [6]. MOOCs are an online instructional delivery model. The MOOCs acronym, coined by David Cormier and Bryan Alexander in 2008, stands for Massive (i.e. hundreds of thousands, even 165 K, students in one section), Open (to anyone for free without prerequisites), Online (worldwide via the Internet), and Course (in a singular course) [6]. MOOCs can be classified in two types: cMOOC, Started in 2008 at University of Manitoba by Dave Cormier, Alec Couros, Stephen Downs, George Siemens & others and xMOOC, Established in 2012 - Udacity, Coursera, edX. Recently have MOOCs attracted widespread attention and become a powerful force in the higher education industry. In 2012, Coursera, edX, and Udacity were established and they are all affiliated with top-tier universities [6]. This paper will present an example of a project (EBA) for developing MOOC for sustainable energy in buildings. Table 1. Types of online delivery models [6] Primary models Ad Hoc

Description Online courses and programs not based on institutional policy and strategy Fully online No face-to-face organized around the concept known as master course (course is designed by instructional design team and faculty members, gets replicated and is taught by or facilitated by multiple instructors) School as a service Outsourcing/partnering with an external company for online content Educational External organizations provide parts of the online course and partnerships communities of practice, including a network of peer instructors worldwide working in similar programs Competency based Outcomes based education, which starts with desired outcomes and moves to the learning experiences that should lead students to those outcomes. These can be implemented in face-to-face, online and hybrid models. In Competency based education the outcomes are tied to job skills and employment needs and the methods are self-paced Blended/Hybrid/Flipped Combine face-to-face with online in a structured format. Objective is to make more effective use of the face-to-face time. Students prepare for the class using online tools. The instructor then uses class time to facilitate class participation and discussion MOOC Massive Open Online Courses - fully online courses scaled to enable an unlimited number of student registrants. Faculty members both design and lead the course. This replaces the master design concept and leverages the natural scaling power of online tools

Sustainable Energy in Buildings: Academy Massive Open Online Courses

643

2 Project EBA - Energy in Buildings Academy 2.1

Project Description

The Energy in Buildings Academy (EBA) will be the first massive open online learning activity for facility managers or energy managers in different sectors (public and private, hotels, office buildings, shopping centres); Energy Services Companies (ESCOs) and utilities providing energy efficiency services, including training to their customers; Higher education students in engineering and science that will provide training, evaluation and coaching for a large potential market (English, Spanish and Portuguese speakers). The project is based on the following factors: • The education market, namely the emergence of the use of digital tools to deliver contents; • The increase of broadband connection, so as the increase of digital literacy, so as it use, namely among younger generations; • The need to adapt workers and students to new skills (lifelong learning), the mobility of students and workers so as the higher costs of traditional training; • The latest changes on the market, namely the binding goals on Energy Efficiency for the Public Sector, Companies and Real Estate (buildings); • The increasing awareness of energy efficiency, namely in industries exposed to higher energy prices and the introduction of several products in the market to mitigate an inefficient energy use; • EU Policy so as its financial incentives to help public Sector, Companies and Consumers change achieved those goals. The Energy in Buildings Academy (EBA) is a unique online educational offer on Energy Management in Buildings that integrates 4 modules of online training materials, with online laboratorial exercises in real installations and also a coaching program for executive trainees to implement their training in their organization with successful results (Fig. 1). The activity will be offered in English for the international broad market, but also in Portuguese for the Portuguese speaking countries like Brazil and in Spanish for the Latin American market, targeting developing Mexico. The project partners are two universities (IST-Instituto Superior Técnico, U. Porto-Universidade do Porto), one research institution in Energy (LNEG-Laboratório Nacional de Energia e Geologia) and an engineering consultant and certification institution (ISQ- Instituto de Soldadura e Qualidade). In terms of value chain, MOOC supply chain can be decomposed in: the content providers and the distribution platforms. Figure 2 represents the value chain for the EBA MOOC. As it can be seen, the set of partners involved in the consortium cover all the value chain.

644

C. Silva and L. Aelenei

Fig. 1. EBA project contents

Fig. 2. EBA value chain

2.2

EBA MOOC Service Definition - Characteristics

The EBA MOOC proposed program is based on a following defined guidelines according with framework KIC-IE: • Each module (1, 5 ECTS) will be divided in 4 topics, where each topic will correspond to 1 week (up to 2 h of video); • Each topic is a collection of short videos (up to 10 min each), complemented with self-learning activities and quizzes and the virtual lab experiments;

Sustainable Energy in Buildings: Academy Massive Open Online Courses

645

• The student work, including watching the videos, reading the additional material and doing the assignments should be around 4–6 h per topic (per week); • The topics might be followed sequentially or in a flexible way. Table 2. Proposed EBA program Modules Models and tools (1, 5 ECTS)

Building systems (1, 5 ECTS)

Energy efficiency implementation (1, 5 ECTS)

Regulations & standards (1, 5 ECTS)

Topics Users comfort in buildings (thermal, lighting, air quality) Energy services modelling Building simulation Energy efficiency projects evaluation HVAC systems in buildings Lighting systems in buildings Renewable energy systems in buildings (solar, biomass) Energy management systems Energy audits in buildings with IPMVP Energy efficiency measures Energy tariffs and energy bills (with local context) Energy management plan development European regulations (directives) Other standards (ISO50001, IPMVP) Local regulations and certification Energy efficiency contracts

Hours 10 6 10 4 10 4 10 6 10 10 6 4 4 16 6 4

EBA Program is structured according with the following module, topics and duration (Table 2). Regarding the learning process, the main steps and the workflow are illustrated in the Fig. 3. The students do an initial evaluation exam to identify which are the modules they need to enroll (as the background, knowledge and experience will be very diverse). Individual training paths will be suggested to students, which may include all or part of sub modules (step 1). The modules will consist of a different set of material and activities developed in authoring tools for MOOC development, including videos, written material, assignments (for example develop a baseline from data, analyse of monitoring data, implementation of a control strategy for lighting control, demand response from renewable energies) and peer-review of colleagues assignments (step 2). Life remote experiments in specific location of university will be considered (step 3). Regarding the evaluation, the assignments will be reviewed automatically (step 4) and there will be a final evaluation that will grant the certification (step 5).

646

C. Silva and L. Aelenei

Fig. 3. EBA MOOC learning process

2.3

EBA MOOC Service Definition - Innovative Features

The Kic EBA MOOC will be available through some of the most used MOOC platforms, using state-of-art technologies and the best learning content quality. As a baseline, the course content will be available through the platforms capacities because this will ensure that all the students will access the same learning objects. On the other hand, the learning objects adaptation to each user will be activated through a proprietary a module that will expose an API that will be integrated as needed in the project integration steps. This API is independent of the base platform that each university or organization might use, so that it can the development, effort for integration of the content adaptation can be a medium light process. From the considered OpenSource platforms for integration as OpenedX, Moodle, WeMooc, only OpenedX provides conditional learning pathway, but it’s up to the user to define its path. None of them includes a dynamic content adaptation (adaptive learning). Despite the growing number of organizations having its own Learning Management Systems (LMS), updated reports state that the students conversion and conclusion rates are very poor, mainly due to the lack of poor adaptability, lack of the deep reporting capacities and other features that the modern businesses need. The Energy in Buildings Academy MOOC will include in its architecture an Adaptive e-learning module. The project and its adaptive features try to overcome some of the current LMS business limitations by contributing with top quality content delivered in a continuous and adaptive learning environment. It will enhances student retention in order for the companies or students effectively apply what they learn in real energy management situations. It is plan to be flexible, light, and reusable. Adaptive learning process can be described as a learning process which supports and integrates

Sustainable Energy in Buildings: Academy Massive Open Online Courses

647

the different characteristics of the learners as a decisive part of its process of content delivery. The orchestration of the available learning objects or resources - as texts, videos, quizzes or others - consists of displaying the correct content at the correct time from the student point of view. Opposed to the traditional fixed sequence learning, the sequential content delivery, the adaptive learning process can be seen as an approximately free zone of learning in which all, or most of the learning objects, are connected between themselves, and where each student learning path flows according to his or her specific profile (Fig. 4). The learning path of each student can then be drawn using his or her profile, and updated at each course new phase.

Fig. 4. Student flow in adaptive learning module

This module will be responsible for the adaptive capabilities of the delivered platform. Based on prior knowledge about student’s background profile, goals and preferences, the module will be capable of automatically define and monitor a specific sequence of learning objects for each particular student. The course content adaption will be fully automatic and need no assistance from teachers. Although the teacher will able to analyse and correct any automated feature or learning path of any student as a supervisor of the learning process. The main components of an adaptive learning system or module are the following: (a) Student model - The student model captures the specific profile of a user. It describes the knowledge and preferences of a learner and keeps track of the learning path applied. This model also gathers the information of the learner performance, as the accessing iterations on the learning objects (for example: number of times needed to accomplish a quiz). This approach is commonly referenced as automatic modelling, as an alternative for a more user centric collaborative student

648

C. Silva and L. Aelenei

modelling. Nonetheless, in the development phases of the project it will be evaluated the inclusion of some explicit user feedback mechanisms. (b) Expert model - The model that aggregates the information about the learning objects and modules of a course. The information kept will consist of the questions, quizzes, videos, texts, solutions and also structural and dependency information about the objects. (c) Instructional or Adaptation model - This model executes the adaptive delivery of learning objects. The core of this model analyses the student performance based to the predefined features and classifications shared by students and objects, and chooses the needed objects for the defined learning objective. Other important EBA MOOC feature is the E-Labs. E-Labs are virtual laboratories that enable students to perform experiences through internet (Fig. 5). They are not virtual laboratories, as the laboratorial facility exists and the user is able to make experiments by changing the parameters, collect the data of the experiment and see the experiment life. IST has already a set of laboratorial facilities that will allow developing online experiments in energy management: • Control of HVAC systems and lighting systems with the measuring of the impact in the energy consumption and users comfort; • Weather variables to make building simulation experiments and compare to real values; • Weather variables and generation data from solar systems (PV and thermal) for renewable energy systems integration; • Implementation of energy efficiency measures and evaluation of technical-economic impact. The Energy Lab (Room 1:58 - TagusPark) is a space dedicated to teaching and experimental work in energy management in buildings with particular emphasis on interactions between users and systems. It is equipped with a home automation system that lets you control all the lights, shading systems, air conditioning and taken in isolation through various interfaces, allowing the development of different jobs, from the intelligent lighting control, preventive control ambient conditions. Its versatility allows the development work for the residential sector and the service sector. The laboratory is powered by a micro-generation installation (1.4 kW and 0.4 kW PV wind),

Fig. 5. Web interface example at Tagus Park

Sustainable Energy in Buildings: Academy Massive Open Online Courses

649

with a storage capacity (720 Ah/24 V) without interruption since September 2012. This facility is dedicated to teaching and experimental work generation in isolated systems and microgrids.

3 Preliminary Results The first version of the EBA courses is already in development for each module proposed of the EBA contents. In Fig. 6 is presented an example of several sequence from one of the videos produced and published. The preliminary results in terms of comparison with other initiatives [7, 8] are illustrated in the Fig. 7.

Fig. 6. Example of several sequences videos

Fig. 7. EBA meta version (initial results)

650

C. Silva and L. Aelenei

It can be observed that in comparison to EdX and EPFL, EBA project presents a difference of approximatively 75% of explored activities and approximatively 15% in certified/statement of achievement. For the other hand EBA has a reduced % in terms of gender issue (female) and very closed to the other two reference in terms of % Bachelor’s.

4 Conclusions The authors of this paper intend to share some insights of a recent approved project financed within Kic Innoenergy framework, project EBA, Energy in Buildings Academy, with the main objective to offer a unique online educational offer on Energy Management in Buildings. The first preliminary results are presented and compared with other existing similar initiatives. Acknowledgments. We hereby acknowledge the KIC InnoEnergy SE Learning Module Project: EBA (Energy Buildings Academy), Ref. 10_2016_LM32_EBA.

References 1. http://www.researchandmarkets.com/research/tqrjls/massive_open. Accessed June 2017 2. Directive 2002/91/EC of the European Parliament and of the Council of 16 December 2002 on the energy performance of buildings. http://eur-lex.europa.eu/legal-content/EN/TXT/ PDF/?uri=CELEX:32002L0091&from=EN. Accessed June 2017 3. Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings (recast). http://eur-lex.europa.eu/legal-content/EN/TXT/ PDF/?uri=CELEX:32010L0031&from=en. Accessed June 2017 4. BPIE2011, Europe’s Buildings under the Microscope. http://bpie.eu/wp-content/uploads/ 2015/10/HR_EU_B_under_microscope_study.pdf. Accessed June 2017 5. Directive 2012/27/EU of the European Parliament and of the Council of 25 October 2012 on energy efficiency, amending Directives 2009/125/EC and 2010/30/EU and repealing Directives 2004/8/EC and 2006/32/EC. http://eur-lex.europa.eu/LexUriServ/LexUriServ.do? uri=OJ:L:2012:315:0001:0056:en:PDF. Accessed June 2017 6. Stepan, A.: Massive Open Online Courses (MOOC), Disruptive Impact on Higher Education, Master of Business Administration. http://summit.sfu.ca/item/13085. Accessed June 2017 7. EPFL: MOOC-Annual report 201-2014. https://documents.epfl.ch/groups/m/mo/moocs/www/ MOOCS_Report_2012-14_1006_HD.pdf. Accessed June 2017 8. Hansen, J., Reich, J.: Socioeconomic Status and MOOC Enrollment: Enriching Demographic Information with External Datasets. http://harvardx.harvard.edu/files/harvardx/files/ses_and_ mooc_enrollment_lak_colloquium_hx_working_paper_submission3.pdf. Accessed June 2017

Competences Development - Towards an Effective Implementation of nZEB in Romania Horia-Alexandru Petran(&), Marian-Ciprian Niculuta, and Cristian Petcu NIRD URBAN-INCERC, Bucharest, Romania [email protected]

Abstract. Although legal obligations are provided in the National legal framework by transposing the provisions of the 2010/31/EU Directive, the Nearly Zero Energy Building (nZEB) concept does not seem to be easily applicable yet in Romania. One of the main barriers for this consist in the skills gaps experienced by the building sector, the current qualification courses and training schemes being generally not satisfactory and underdeveloped to face the challenge of effective nZEB implementation. This paper presents the preliminary developments of the Train-to-nZEB project, namely the setting up of Building Knowledge Hubs (BKH) for practical trainings of construction workers and specialists for the design and construction of NZEBs. Building on the results of the BUILD UP Skills initiatives and Passive House principles, the BKHs will provide capacity for conducting practical trainings for on-site professionals, high level specialists and decision makers. To a large extent, the BKH training centres aim to satisfy the existing demand for practical training of trainers and teachers, to provide opportunities for organization of courses to certify builders of NZEBs and to update existing skills. As a major functional goal, BKHs will provide courses for continuing qualification and training for architects, engineers and building managers and other building professionals with the goal to improve the existing classroom-based training schemes with practical trainings using the new developed facilities. Keywords: Competences


nZEB
Passive House
Renewables

1 Introduction Following the adoption of the 20-20-20 package for energy and climate, the revision of the Energy Performance of Buildings Directive - EPBD (2010/31/EU Directive, Recasting 2003/91/EC) [1] provided explicit requirements on the energy performance of buildings and the need for design/construction of Nearly Zero Energy Buildings (nZEB). After 31 December 2018, all new buildings occupied and owned by public authorities should be nZEB, this requirement being applicable to all new buildings starting in 2021. Although legal obligations are provided in the National legal framework by transposing the provisions of the 2010/31/EU Directive, the Nearly Zero Energy © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_45

652

H.-A. Petran et al.

Building (nZEB) concept does not seem to be easily applicable yet in Romania. One of the main barriers for this consists in the skills gaps experienced by the building sector, the current qualification courses and training schemes being generally not satisfactory and underdeveloped to face the challenge of effective nZEB implementation. By definition, nZEBs are buildings with very high energy performance, with the very low energy demand being covered to a significant extent by energy from renewable sources (including energy produced on-site). Basically, nZEB is not only a high-efficiency building concept, but a building in which energy is intelligently used as much as possible from renewable sources available at the property level or in the neighbourhood, to provide a comfortable, friendly and healthy environment. For the purpose of implementing these buildings, particular attention should be paid to both the design and construction of envelope components, including the connection to the components of the building installations, the reduction of heat transfer through the thermal bridge elements and the air infiltration and the choice and use of intelligent technologies for producing and consuming energy to meet their own needs and, where appropriate, those of the community. These aspects, which generally have a significant impact on buildings built according to current practice, become critical and require particular attention in buildings where energy consumption is nearly zero. A good starting point for developing the nZEB concept, with regard to the very low energy demand, is to follow the principles which form the “Passive House” concept. This has been defined, applied and proven over the past 25 years, being grounded in the laws of building physics rather than through the EU or national legal framework. A “Passive House” is not only a building with a very low energy consumption, but one in which the comfort and health of the occupants are at the forefront. The “Passive House” principles are taken into account in the Train-to-NZEB project, which addresses the development of the competences of all specialists and workers involved in the building chain for the construction of nZEB buildings. This paper presents the steps taken in Romania in the direction of raising the competences level for the workforce in the construction sector, based on the actions implemented under the BUILD UP Skills initiative of the Intelligent Energy Europe and Construction Skills Topic of the HORIZON 2020 Programme. First the qualification roadmap and qualification schemes developed within the BUILD UP Skills actions are briefly described, then the preliminary developments of the Train-to-nZEB project are presented, namely the setting up of a network of training, information and consultation centres (Building Knowledge Hubs, BKH) for practical trainings of construction workers and specialists for the design and construction of NZEBs. Building on the results of the BUILD UP Skills initiatives and Passive House principles, the BKHs will provide capacity for conducting practical trainings for on-site professionals, high level specialists and decision makers. To a large extent, the BKH training centres aim to satisfy the existing demand for practical training of trainers and teachers, to provide opportunities for organization of courses to certify builders of NZEBs and to update existing skills. As a major functional goal, BKHs will provide courses for continuing qualification and training for architects, engineers and building managers and other building professionals with the goal to improve the existing

Competences Development - Towards an Effective Implementation

653

classroom-based training schemes with practical trainings using the new developed facilities. These facilities are also presented in the paper together with the key elements of necessary curricula for nZEB skills build up.

2 The BUILD UP Skills Initiative for a Qualified Workforce in the Romanian Construction Sector In the on-going process of implementing concerted and effective measures to achieve the 2020 targets, a high need exists for ensuring appropriate training schemes for architects, engineers, energy auditors, craftsmen, technicians and installers, since the application of energy efficient techniques and renewable systems is often technically very demanding. This need was addressed by the European Commission through the BUILD UP Skills initiative [2], which was funded by the Intelligent Energy Europe Programme of the EU. The initiative was implemented starting from 2011, in two pillars. Within Pillar I of the BUILD UP Skills initiative, a qualification roadmap [3] was developed to achieve the sustainable energy policy objectives for 2020, by focusing on the blue-collar workers. The BUILD UP Skills QualiShell project [4] represented a natural continuation of BUILD UP Skills Romania (ROBUST) project [5] and supported the development and implementation of two large scale and long lasting national qualification schemes for the installers of external thermal insulation composite systems (ETICS) and high efficiency windows systems (occupations with the largest qualification gap identified within the analysis of the construction sector [6]). The aim of the proposed approach was to ensure not only a high-quality installation of very efficient building envelope components, but also the development of effective tools to combine the evolution in the national qualification scheme with the adequate knowledge and skills and move towards the actual implementation of nearly zero energy buildings in Romania. Thus, the two schemes which were developed together in the BUILD UP Skills QualiShell project could be seen as one large qualification scheme focused on the execution of building envelope, with two tailored components: opaque and glazed parts. The concept of ‘qualification scheme’ (Fig. 1) was defined and implemented for the first time in Romania within the QualiShell initiative, by putting together all necessary documents and tools to perform training courses with certification of competences in the framework of the national qualification system (including tools for the evaluation of competences acquired in non-formal or informal ways [7]). The analysis of the occupational framework and documentation for the inclusion of the two mentioned occupations in the Classification of Occupations in Romania (COR Nomenclature) and in the Romanian Nomenclature for Classification of Qualifications (operative starting August 2014) are included in the report [8]. As mentioned above, the structure and content of the ‘qualification scheme’ was available, but the generation of qualified workers by the effective application of the

654

H.-A. Petran et al.

Fig. 1. The concept of ‘Qualification scheme’ (M-SOT = Installer of opaque thermal insulation systems for buildings, M-STT = Installer of thermal insulation fenestration systems) [9]

scheme needed adequate tools and mechanisms, which were discussed and promoted within the intensive stakeholders’ consultation process performed in the National Qualification Platform and National Consultation Committee. One of the key mechanisms to support the implementation of the developed scheme was identified as ‘Local partnership for qualification’ (Fig. 2). The concept is well described in the reports published within the QualiShell initiative [9, 10] and consists in voluntary partnership between a training supplier, a

Fig. 2. Partnership for qualification of the workforce in the construction sector [9]

Competences Development - Towards an Effective Implementation

655

supplier of construction materials/technology/system and a construction company. The partnerships are based on matching different offers and needs of implied partners as ‘natural drivers’ and should be supported by local authorities [11]. While this kind of partnerships can be done at local and regional level, comprising one or more actors in the same category, similarities with the concept of CLUSTER are obvious, the latter aiming to the development of the market in one field (e.g. construction of energy efficient buildings) and a defined geographical focus. The implementation of such local partnerships between the education system and the construction sector could realistically reduce the costs paid by the trainees from around 1000 EUR [10] to approximately 500 EUR by partial sharing of resources. Part of the costs could be also supported by the employer or by dedicated funding (e.g. European Social Fund, national training funds etc.). On the other hand, the large number of trainings financed by ESF (2007–2013) produced a negative side-effect on the qualification market, by strengthening the link between the performance of training courses and external funding, while the funds for the organization of trainings should come (in a big extent) from the trainees themselves. Basically, a paradox can be identified on the market: the need for skills upgrading in the construction sector is well acknowledged, but the demand for trainings is not sufficient in order to have a healthy system for this. Part of the solution in creating the real training demand is the introduction of minimum qualification requirements for companies and their workers as prerequisite for any public or private funded construction projects (e.g. in the building rehabilitation programs with public funding, starting with the inclusion of specific scoring in the tender specifications so that additional points could be granted to bidders with higher qualified staff).

3 Qualification versus Specialization Qualification programs are usually long duration trainings, minimum length of the programme being 360 h, 720 h and 1080 h, for the theoretical and practical training for which the qualification certificate is issued depending on the qualification level. As an example, a qualification program targeted to level 2 of qualification (EQF 3 to 4 [12]) requires course duration of 720 h in order to issue a recognised certificate of qualification. The duration may be reduced up to 360 h depending on the level of participants’ skills checked at the beginning of the training program. The key benefits of a qualification programme are the recognition by the National Qualification System and certification of competences for the particular occupation. Usually the qualifications are related to EQF2 to EQF4. Qualification programmes usually include in some extent cross-craft information. On the other hand, due to the long duration of the programme and high training costs, there is a general reluctance from individual persons to participate, but also from construction companies to send their employees to qualification programmes. Specialization programmes can be more flexible in terms of duration, based on the defined learning targets or competences and basic occupation and/or expertise of trainees. They are based on the assumption that the potential trainees are already qualified in one occupation in the construction sector, i.e. possess the relevant skills

656

H.-A. Petran et al.

required for construction design or work from their basic training. Thus, the aim of the specialization courses is to offer essential additional knowledge and specific competences related to the nZEB concept and principles. Instead of ‘inventing’ a ‘nZEB specialist’ as a separate occupation (which needs inclusion of COR, elaboration of occupational standard etc.) specific programs are tailored for each occupation (or group of similar occupations) in the construction process, as to ensure that every piece of the (construction) chain is ready to contribute to the actual realisation of an nZEB. In this case, the cross-craft understanding is more important. Compared with qualification programs, specialisation trainings are related to a larger field of qualification levels, from EQF2 to EQF7 and are more flexible (duration from 1 day - e.g. for decision makers, to 2–3 days for workers/trades people and 7–10 days for architects/designers), might require lower costs (attractive prices for trainees or smaller number of trainees per course) and thus, the availability of engagement from individual persons or employers gets bigger. The recognition of the acquired competences (implicitly of the specialization course) could come from the National Qualification System or directly from the industry (market). In fact, the recognition comes in time based on the confidence of the industry in the job done by the training suppliers, rather than from some logos representing either governmental organisations or market players. Starting from the above-mentioned considerations, the implementation of the qualification schemes developed in BUS QualiShell (and other qualifications for relevant occupations) has to be continued and supported, while nZEB specialization modular courses need to be defined to facilitate the actual implementation of nearly zero-energy buildings concept in Romania. One important step in this direction is made through the H2020 ‘Train to nZEB’, which is further presented.

4 Train-to-NZEB: The Building Knowledge Hubs The Train-to-NZEB project is designed to establish a functioning network of training and consultation centres (Building Knowledge Hubs, BKHs), providing practical trainings, demonstrations and complex consulting services for the implementation of nearly-zero energy buildings (nZEB). This is a development of the BUILD UP Skills initiative and reflects nZEB criteria, with the latter, in turn, reflecting the Passive House Standard as one existing, supra-national, consistent, tried and tested implementation of the nZEB definitions that meets the manifold criteria, including from “nearly-zero energy demand”, to “cost-optimal levels in life cycle perspective”, to “significant energy supply from on-site or nearby renewable energy systems (RES)”. Using new or improved training facilities, the BKHs will provide enhanced capacity for conducting trainings on curricula developed on BUILD UP Skills II, thus reaching a significant number of workers not covered by the initiative. Additionally, BKHs will offer trainings for highly-qualified building professionals and demonstrations for non-specialists with decision-making authority, which, combined with administrative and financial consultancy services, will result in increased capacity for implementation

Competences Development - Towards an Effective Implementation

657

of nZEB projects in the involved countries. Five European countries will benefit directly from the establishing of BKHs, namely, Bulgaria, Czech Republic, Turkey, Romania and Ukraine. Starting from the accepted definition of nZEB (as formulated by the EPBD recast), the first (necessary) condition is to ensure a very high energy performance of the building, which requires nearly zero or very low amount of energy, while the second (sufficient) condition is to add Renewable Energy Systems (RES) to cover significant part of this low energy demand. Thus, the most effective to achieve the first condition of nZEB is to start by focusing on the performance of the building envelope (the ‘fabric first’ approach). This includes the high level of thermal insulation, but also significantly improved levels of airtightness which leads to the need of use of controlled (mechanical) ventilation with heat recovery. The BKHs are intended to offer two types of services regarding nZEB implementation: trainings and consultancy, so the first set of requirements are related to the facilities for theoretical training (the why) and those for practical trainings and demonstration (the how). The design of the training facilities is based on a set of guidelines (Terms of Reference [13]), which includes requirements for the training premises and specification of the necessary equipment with review of the available products and solutions, description of the building materials, products installations and tools required for the quality implementation of trainings. The guidelines are focused on providing opportunities for conducting specialized trainings for all (or most) crafts and professions related to building shell, building services and RES installation in buildings. The experience from similar training centres already developed and working in some of the most advanced countries in Europe was used in the development of the terms of reference. The key requirements set up in the Terms of Reference [13] are summarized below; however, they are available in detail at www.train-to-nzeb.com. Classroom Training – Theory. The training content should be developed starting from clear learning objectives, which include (but are not limited to): nZEB definitions and basic design principles (including long term experience, e.g. Passive House Standard), the importance of thermal bridging airtightness and wind-tightness, high performance windows (components and mounting systems), mechanical ventilation heat recovery systems, renewable energy systems (RES’s), their effectiveness and interface with other mechanical services, principles of the ‘intelligent building’, concerning smart technologies that minimise energy consumption through optimised operation and coordination of services. Classroom training could be complemented by Online training in order to facilitate distance learning and then some of the classroom sessions (which require the physical presence of trainees) can be used primarily for practical training. Airtight Room – Practical. The airtight room is a multiple-use practical facility, built as a single space structure which exposes installed materials directly associated with airtightness in buildings (e.g. membranes, tapes). The room is used to demonstrate pressurisation tests (blower door) and accommodates functional mechanical ventilation

658

H.-A. Petran et al.

Fig. 3. Airtight room (Left - external view & blower door test, including infrared image of a window corner during a test, Right - internal view: airtightness layer & MVHR unit)

heat recovery equipment (MVHR), where calibration exercises for the ventilation system can be performed. Figure 3 presents the Airtight Room developed within BKH Romania at NIRD URBAN-INCERC in Bucharest. Construction Models – Practical. Different construction types that are relevant to the national construction technologies are fabricated with adaptation to ensure significantly higher energy and comfort performances, and installed are included in the practical facility area. Figure 4 illustrates the Demonstration Models which are under development in within BKH-RO, at NIRD URBAN-INCERC Bucharest.

Fig. 4. Mock-ups/models for constructive solutions/thermal bridges (BKH-RO, Bucharest)

Competences Development - Towards an Effective Implementation

659

The mock-ups include floor, external wall with cut window section, ceiling/roof as well as different materials and construction methods, and offer sound basis for systematic presentation of alternative high performance construction (including trainer description, trainee drawings and description, as useful means or effective teaching/learning). Additional 4 Practice Models (accommodating 2–3 trainees at a time) are developed to focus on the achievement of insulation, thermal bridge elimination and airtightness. Several mock MVHR units can be fitted for airtightness and insulation exercises (duct connections). RES - Practical. The practical training area contains also several operational full-size examples of solar thermal and photovoltaic panels, which demonstrates the functioning of the object itself and its workings within the larger system. Figure 5 illustrates the arrangement of different systems in the regional training shop in Brașov. Starting from the defined terms of reference, the BKH-RO were developed in Bucharest and Braşov to accommodate training programs for nZEB with combined theory and practice. The first courses organised by the Romanian Train-to-nZEB partners were the Certified Passive House Tradespersons (Bucharest) and Installers of PV Systems (Braşov). The first program was implemented by NIRD URBAN-INCERC as PHI official supplier, while the second was organised by FPIP based on the programme developed within the Intelligent Energy Europe PVTRIN project.

Fig. 5. Mock-ups/models for solar systems (BKH-RO, Brașov)

The practical training facility of BKH-RO was developed in partnership with industry representatives, who showed high interest for cooperation with BKH RO and to support the implementation of training programs. This is closely related to the initiatives to support the development of a healthy nZEB market in Romania, based on the joined effort implemented in the organisation within the recently founded association Cluster Pro-nZEB (Fig. 6).

660

H.-A. Petran et al.

Fig. 6. Pictures from the implementation of the first PH course (BKH-RO, Bucharest)

5 Cluster Pro-nZEB The Association “Cluster for Promoting Nearly Zero Energy Buildings” - Pro-nZEB is a non-profit organisation aiming to bring together key players from the building materials market, research and development institutions, educational representative organizations, public authorities, professional associations and other organizations having a catalyst role, in order to create and improve collaborative relationships for developing and implementing in Romania the concept of nearly zero energy building (nZEB). The vision of the Cluster for promoting nearly zero energy buildings is represented by the reduction up to elimination of the greenhouse gas emissions generated by using buildings, aiming to develop the research regarding the market of energy efficient buildings in Romania [14]. The Pro-nZEB Cluster is the only professional cluster tacking the ‘nearly zero energy building’ concept in the Romanian buildings market, based on the vast experience of its members. Actually, Pro-nZEB brings together relevant experience of own members covering all relevant sectors: builders’ associations, construction technology companies, energy efficiency and RES, representatives of universities and nationally recognized Research institutes. Pro-nZEB Cluster represents the centre of the builders’ network in terms of knowledge, technology and research, acting to remove technical and non-technological barriers (legislation, financing, cooperation etc.) existing in the Romanian market. The Cluster currently comprises of thirteen committed members representing one national research institute, six umbrella organisations (professionals, producers and

Competences Development - Towards an Effective Implementation

661

builders), five individual companies (of which 3 SMEs) and one foundation by the representative social partners in the construction sector. Several intentions to join the Cluster were expressed also by other industry representatives, universities and public administration. The main scope of the cluster alliance is to develop and implement technological concepts and specific projects for promoting nearly zero energy buildings in Romania. The general objective of the cluster is represented by the initiation and execution of activities together to define and implement research and development projects for nearly zero energy buildings and creating the market conditions to ensure fulfilment of Romania’s commitments for sustainable development and implementation of strategies for energy efficiency in the built environment. Among the strategic objectives of the cluster the most relevant are the knowledge development and promoting the technical principles and management solutions to achieve nearly zero energy buildings in Romania, conducting the performance studies of buildings in Romania and adopting solutions to achieve the objectives of the assumed national strategy and progress reports, in perspective of year 2020. As one of the key means to develop the market, Pro-nZEB is involved in strategic projects, structured and implemented together with European partners, which are nationally focused but in the same time seeking to harmonise the approach in different EU countries in order to facilitate the compliance with the EU legal framework and policies. Thus, the results of Train-to-nZEB project will be further developed by the Cluster Pro-nZEB as partner in the project Fit-to-nZEB.

6 Fit-to-nZEB: Innovative Training Schemes for Retrofitting to nZEB-Levels The Fit-to-nZEB initiative is a 24-month project starting on the 15th of June 2017, funded under the European Union’s HORIZON 2020 research and innovation programme (Construction Skills topic) with the aim to respond to the needs to be ready to deliver high energy performing renovations and, in particular, nearly zero-energy buildings, in order to facilitate the achievement of the 2020 and 2030 energy and climate objectives (see Fig. 7). Representing a major challenge to the construction sector, this goal requires a major effort to increase the number of qualified construction specialists at all levels, which is directly related to the accessibility and quality of the training and educational programmes and the inclusion of training on intelligent energy efficiency and RES solutions in building renovation. Thus, the project is designed to respond to these needs by targeting the objectives illustrated in Fig. 8. The FIT-TO-NZEB project aims to increasing competence and skills of the building professionals in the field of retrofitting to NZEB-levels in the target countries through the unique educational programmes developed by the consortium, which will contribute to both the quality and the scale of the deep energy building renovations. It

662

H.-A. Petran et al.

Fig. 7. The Fit-to-nZEB concept [15]

Fig. 8. The objectives of Fit-to-nZEB [15]

is intended to use the developments of the Train-to-nZEB initiative (e.g. the developed BKHs), while it is expected that the Fit-to-NZEB project will support the introduction of nZEB renovation related educational content in the curricula at all levels (universities, professional high schools and colleges, vocational training centres).

Competences Development - Towards an Effective Implementation

663

7 Conclusions Previous research shows that the necessary investments and the optimal integration of technologies suitable for the construction and/or renovation of buildings at the nZEB level, as well as the training of specialists in the field, are among the most important barriers recognized on the market. Moreover, gaining confidence in the building industry and building owners in the real energy performance of the NZEB and reducing the real risks associated with new technologies seem to be the strategic points whose solution could facilitate the realization of the large investments required in the process of increasing the energy performance of the building stock. Construction companies in Romania should develop a long-term vision to increase productivity by qualifying their personnel and, implicitly, by increasing the company’s competitiveness. Instead of asking “What if I qualify my workers and then they leave?”, employers should ask “What if I do not qualify and they stay?”. It is likely that, in the near future, builders who will not be ready to deliver quality construction at the nZEB level will no longer be able to remain on the market. In this paper, the results of several initiatives which tackled the above-mentioned market barriers are presented. The BUILD UP Skills QualiShell project succeeded in developing two national qualification schemes for the training of the construction workers in the most important occupations related to building envelope, namely the installer of opaque insulation systems for buildings and the installer of insulated window systems. Full sets of guidelines and training tools are ready to be used in the training market to ensure the need for qualified workers for high performance building envelopes by 2020 [9], so that the relevant qualification gap recognised by the Status Quo Analysis Report [6] and Roadmap for National Qualification of Building Workforce [3] can be filled. Building on the results of the BUILD UP Skills initiatives and Passive House principles, the Train-to-nZEB initiative develops the Building Knowledge Hub concept. The BKH training centres provide capacity for conducting practical trainings for on-site professionals, high level specialists and decision makers, aiming to satisfy the existing demand for practical training of trainers and teachers, to provide opportunities for organization of courses to certify builders of NZEBs and to update existing skills. The practical training facilities are presented in the paper together with the key elements of necessary curricula for nZEB skills build up. Collaborative market development initiatives such as the Pro-nZEB Cluster (www. pro-nzeb.ro) and the European projects Train-to-nZEB (train-to-nzeb.com) and Fit-tonZEB (Innovative Training Schemes for Renovation of Buildings at nZEB Level) address the necessity of improving the construction and installation technologies to the requirements of realizing the buildings of the nZEB category and the development of the competences of all the specialists and workers involved in the nZEB building chain. A change of attitude/mentality is required at the system level, but also at the individual level. One cannot hope for nearly zero-energy buildings designed and built based on the “small compromise” between professionals and beneficiaries or between owners/investors and authorities. The design, execution and operation of a building at nZEB level cannot be achieved by applying the “working anyway” principle. In order

664

H.-A. Petran et al.

to be able to hope for the actual implementation of the NZEB in Romania, we must firstly change ourselves as construction professionals by understanding the physical and economic principles underlying the nZEB concept (and why not building on the experience of implementing passive houses?), by raising the level of competencies, by pursuing adequate and complete approach of the details and, last but not least, by assuming a responsible attitude, of the “work well done”, oriented towards the comfort and health of building’ occupants. For the construction industry, preparing for nZEB should be part of the solution and not one of the many problems faced by the sector. Acknowledgments. The projects “BUILD UP Skills Romania” and “BUILD UP Skills QualiShell” were co-funded by the Intelligent Energy Europe programme of the European Union. The project “Train-to-nZEB: The Building Knowledge Hubs” has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 649810. The project “Fit-to-nZEB: The Building Knowledge Hubs” is funded by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 754059.

References 1. Directive 2010/31/EU of the European Parliament and of the Council, Energy Performance of Buildings (recast). Official J. European Union, L153, 13–35 2. http://www.buildup.eu/en/skills. Accessed 2017 3. Roadmap for National Qualification of Building Workforce BUILD UP Skills - Romania (2013). http://www.buildup.eu/sites/default/files/bus_projects/build-up-skills_roadmap_final_en_0. pdf. Accessed 2017 4. http://www.iee-robust.ro/qualishell. Accessed 2017 5. http://www.iee-robust.ro. Accessed 2017 6. Analysis of the National Status Quo, BUILD UP Skills - Romania (2012). http://www.buil dup.eu/sites/default/files/bus_projects/build-up-skills_romania_status_quo_en_0.pdf. Accessed 2017 7. User Guide for Set of Tools for the Evaluation of Competences Acquired in Non-formal or Informal Context (2015). http://www.iee-robust.ro/qualishell/downloads/D5-4_QualiShell_ Ghid-utilizare-instrumente-evaluare-competente.pdf. Accessed 2017 8. Report Regarding the Occupational Analysis of the 2 Qualifications (2014). http://www. iee-robust.ro/qualishell/en/downloads/D2-1_QualiShell_Raport_AO-SO-calificari_EN.pdf. Accessed 2017 9. Final Publishable Report. BUILD UP Skills QualiShell: National Qualification Scheme for Construction Workers to Ensure High Performance Building Envelopes (2015). http:// www.iee-robust.ro/qualishell/en/downloads/BUILD-UP-Skills_QualiShell_Publishable-Rep ort.pdf. Accessed 2017 10. Oriented Guide to Develop and Implement Addressed Qualification Schemes (2015). http:// www.iee-robust.ro/qualishell/en/downloads/D2-3_QualiShell_National_QS_Implementing_ Guidelines_EN.pdf. Accessed 2017 11. QualiShell: Romanian Qualification Schemes for Installers of Opaque Building Elements and/or Window Systems, FACTSHEET #52 (2017). http://qualicheck-platform.eu. Accessed 2017

Competences Development - Towards an Effective Implementation

665

12. Recommendation of the European Parliament and of the Council of 23 April 2008 on the Establishment of the European Qualifications Framework (EQF) for Lifelong Learning (2008/C 111/01) 13. Terms of Reference for Local Teams for the Creation of Building Knowledge Hubs. Deliverable 2.1 of the TRAIN-TO-NZEB project, financed under grant agreement No 649810 of HORIZON 2020 Programme of the EU (2016). http://www.train-to-nzeb.com/uploads/9/8/ 8/4/9884716/d2.1_terms_of_reference_technical_equipment__final.pdf. Accessed 2017 14. http://www.pro-nzeb.ro. Accessed 2017 15. Fit-to-nZEB: Innovative Training Schemes for Retrofitting to nZEB-Levels, HORIZON 2020 project, http://cordis.europa.eu/project/rcn/210594_en.html. Accessed 2017

P.A.E.S. Project and Housing Policies for Sustainable Buildings Renato Olivito1(&), Mircea Neagoe2, Petru Mihai3, Nikolaos Karanasios4, Eva Krìdlova Burdovà5, and Marco Della Puppa6 1

Civil Engineering Department, University of Calabria, Rende, Italy [email protected] 2 Transilvania University of Brasov, Brasov, Romania 3 Technical University of Iasi, Iasi, Romania 4 Technological Educational Institute of Serres, Serres, Greece 5 Technical University of Kosice, Kosice, Slovakia 6 Greek Italian Chamber of Commerce, Thessaloniki, Greece

Abstract. The project’s priority is the creation of the knowledge triangle, based on education, research and innovation; which includes collaboration between universities and enterprises, supporting the entrepreneurship, thanks to the support of research. This first choice is motivated by the fact that research, innovation and education, can ensure competitiveness in a global context in which other competitors, such as the emerging countries, can count on cheap labor or primary resources. Moreover, through this project, the idea is to innovate the methodological approach of the sustainable design: innovation means “produce, assimilate and exploit innovations successfully in the socio-economic sector.” PAES Project is focused on the development of vocational training according to high-quality work by sharing experiences, knowledge, skills and international qualifications in a common virtual space, creating a replicable model of cooperation between Training Institutions and Operators of the construction sector. The project, aimed at spreading the Sustainable Building, is perfectly in line with the Europe 2020 strategy that prioritizes sustainable growth: for a more efficient economy in terms of resources, greener and more competitive economy. Keywords: Sustainability
E-learning businesses
Sustainable housing




Green materials




Environmentally

1 Introduction The PAES project focuses on the “intelligent and eco-sustainable building” in all its declinations. It encompasses a set of didactic modules, whose topics regard the structure of technological installations, the technical standards of architectural design, as well as innovative materials. All these themes are linked to the building via “Smart City”. Each teaching module consists of a number of lessons, mandatory for obtaining training credits and a number of ancillary activities, not mandatory. The latter are necessary to deepen, clarify and develop more specifically the main theme of the © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_46

P.A.E.S. Project and Housing Policies for Sustainable Buildings

667

didactic module. It is a university specialized platform, aimed primarily at university students and researchers, but also to graduates and professors. In addition to teaching modules, the idea is to develop topical issues in order to focus on the research and development of “Smart Building”. Crucial point between Smart City and Smart Building are the “Smart Meters”, their task is to measure the consumption and optimize the use, with consequent reduction of costs for the end user. Finally, the smart meter performs the function of home automation control unit capable of managing all the equipment of the building that can connect cable or WI-FI. In this perspective, it is possible to allow students to investigate on Smart Meter as a support to propose program users, in order to simplify and optimize home management.

2 Sustainability and Methodological Assessment Sustainability represents, nowadays, the key factor of various application fields. The most important thing is that this key factor can achieve with higher performance levels taking in consideration, at the same time, economic, social, environmental and institutional aspects. Housing Policies for Sustainable Construction project (P.A.E.S.) deals with developing practical innovations in the Green Building, designing sustainable buildings, in order to minimize the environmental impact, production costs associated at all stages of the life cycle of the construction project and guaranteeing human well-being (security, health) equally distributed. The main objectives of the project include: – the creation of strategic alliances between universities, training institutions, chambers of commerce working in construction field; – the promotion of relations that combine technical aspects of the construction with innovative requests related to the environmental impact; – the consolidation between university academic systems and entrepreneurial systems. The Green Building Challenge process was born as a research and development project in 1996, coordinated by iiSBE (international initiative for a Sustainable Built Environment) with the aim of developing an international methodology for assessing building sustainability. In order to evaluate the sustainability of buildings, it is necessary to measure sustainability, thus assigning a building’s score to its sustainability level by analyzing its performance to the respect of a set of criteria. Cricial point of this system is the evaluation methodology necessary to organize the system through a number of levels (checklists), calculate the score, combine the score at the various levels set, and finally assign labels by communicating the quantitative result of the sustainability value obtained. In Italy only in 2000 there was the formation of a working group within the Green Building Challenge project and in 2002 ITACA (Federal Association of Italian Regions and Autonomous Provinces) adopted the SBTool international system in order to produce a tool capable of measuring the sustainability of a building called the ITACA [1, 2]. In 2005, it founded iiSBE Italy, the only managing entity authorized by

668

R. Olivito et al.

SBMethod in Italy. Subsequently, the Institute for Construction Technologies (ITC), scientific facility of the National Research Council (CNR), which operates mainly in the civil engineering sector, obtained together with iisbe Italy, an agreement for certified assets based on the SBTool. Internationally, in 2009 ITC is founder of the SBA (Sustainable Building Alliance), an organization to promote harmonization between sustainability certification system of participating states; in 2009, ITC adheres to the Common European Sustainable Building Assessment (CESBA), a European platform whose goal is to make sustainability a standard building approach. CESBA is supported by the European Commission through the funding of research projects dedicated to it. Actually, “ITACA protocol” is the reference rating system of the regional authorities in Italy; a total of 14 Italian regions are equipped with specific ITACA protocols according to their intended use: residential buildings, shopping centers, schools, industrial buildings, and tertiary [3, 4].

2.1

ITACA Protocol, “Standards for Sustainable Building”

The ITACA Protocol, “Standards for Sustainable Building”, is an energyenvironmental certification tool including quality of the building and building components. It is used to assess the building at design stage (competitions, call for tenders for residential public building mainly). The ITACA certification allows benefits as incentives for renovation and urbanization burden reduction, volumetric bonuses, controlled loans (for new buildings mainly). The final certification of sustainability also internationally recognized: iiSBE (Italy) established a written agreement with ITACA in order to support the Italian Regions to define and apply the assessment and certification system. ITACA Protocol evaluate the construction project of a structure in compliance to a set of performance requirements (indicators), previously defined, regarding integration with the context, resources use efficiency, impact on environment, indoor environment quality, service quality. Each indicator is given a score, and by the weighted sum a final building assessment is determined (ranging from −1 to +5), which leads to the performance class: excellent, great, good, sufficient, poor. ITACA protocol certification service of buildings includes different steps: Performing a diagnosis, or a project verification, aimed at evaluating the building environmental sustainability level in accordance to the ITACA protocol criteria and at the end the achieving of the environmental sustainability certificate. Specifically, the protocol is based on a multicriteria analysis system: from a set of criteria, the method provides a synthetic score, which quantifies the overall performance of the building. The final score is defined through a three-step procedure: 1. characterization: building performance are quantified through specific indicators associated with the criteria; 2. normalization: the value of the indicator is a dimensioned and compared in a specific range; 3. aggregation: scores are combined to produce the final synthetic score.

P.A.E.S. Project and Housing Policies for Sustainable Buildings

669

The main elements of the assessment system of ITACA Protocol are therefore the criteria, indicators, which allow to quantify the performance of the building in relation to each criterion, a normalization and aggregation method. The ITACA protocol is hierarchically structured in three levels: – level 1: Issue areas; – level 2: Categories; – level 3: Criteria. Areas are organized for general topics, based on the assessment of building sustainability; each area includes a variable number of Categories and the latter describes a specific aspect of the area to which it belongs. Categories include different Criteria, each of which describes the topic of the corresponding category in more detail. The Criteria define, through a number of calculations, whether a particular property, of the topic (Area), is satisfied or not, namely it analyses a specific performance. In fact, the Criteria with physical quantities are associated: the indicators. They can be qualitative and quantitative; in the first case performance is defined based on reference scenarios. In the first step of characterization, the physical quantity is calculated or the scenario is defined; the output of the step consists of a set of numeric values (values of the indicator) and each of them represents the performance of the building in relation to each criterion. In the second step of normalization, as already mentioned, all values obtained must be a dimensioned. The normalization method is based on two requirements: – through a performance scale, at the value of each indicator is assigned a score in the range [−1, 5], so called normalization interval; – best performance is associated with more normalized scores. Two criteria for normalization can be considered for quantitative criteria: – H.I.B. (Higher is Better): a higher value of the indicator corresponds better performance; – L.I.B. (Lower is Better): a lower value of the indicator corresponds better performance. In the last aggregation phase, the normalization scores determined in the previous step, are aggregated in order to calculate the final score of the intervention; this phase uses the scores obtained for the criteria, categories, and areas. Finally, “ITACA protocol” achieves three final scores: one related the site quality, another regarding the construction quality and the total score. In conclusion this score measures the sustainable level, as shows the following figure (Fig. 1):

Sufficient 1

Moderate 1,5

Good 2

Very good 2,5

Optimum 3

Fig. 1. Representation of different sustainability levels

Excellent 3,5

670

R. Olivito et al.

Actually, in Calabria region is equipped of ITACA protocol for residential building and schools, in the first case it is composed by five issue Area, nineteen Categories and thirty-three Criteria, whereas for schools it is composed by five issue Area, twenty Categories and thirty-six Criteria.

3 Greener Materials for Sustainable Buildings Obtaining new environmental friendly materials to comply with a wide range of requests, imposed by the development of new fields and applications, are a permanent necessity. In the constructions area is aimed the production of high performance materials, the improvement of the traditional and composite materials and hybrid structures development to accomplish more daring works. Concrete is one of the most used materials and the concrete technology brought the knowledge on it so far. The trend nowadays is upon discussing concrete as a composite material. The basic microstructure of this material fits very well the composite profile. In the last years many cement based composite materials or so-called mineral matrix composites appeared. Their evolution was closely connected to the expansion in civil engineering applications, increase in the structure mass production, the appearance of new constituents and technologies and the development of testing methods, numerical modelling and analytical computation. In constructions the mineral matrix is also called a binder. The binder is defined as an active material which mixed with water hardens in time and forms a rigid body with the aspect of a stone. As any type of matrix this influences the properties, durability and geometrical shape of the composite material. One of the most utilized binders is the cement based binder. Obtaining Portland cement is a high energy and natural resources consumption process and releases in the atmosphere large quantities of gases. The greening process in the cement industry is proposed through: changes in the manufacture process, using alternative energy and/or adjusting the cement composition. The cement composition can be modified by partial replacement with different subproducts or industrial wastes. The process to obtain a green microconcrete assumes the partial replacement of Portland cement with products obtained entirely from industrial wastes. The experimental analyses were made at microstructural level, to observe the internal structure of the material and the possibility to embed disperse fibres, and at macrostructural level, to observe the possibility of the mineral matrices to infiltrate through the textile structures. The main characteristics of this new material are [5]: – The “ideal” structure of a mineral material is represented by a compact mixture consisting of a network made out of aggregate granules embedded in a thin layer of binder and the water strictly necessary for their hydration. – The fibre volume fraction in the mineral matrices must be below 50%. The constraint is due to the matrix workability, its possibility to infiltrate and embed the fibres, and to the chemical compatibility with the fibres. For the mineral matrices case the main role of the reinforcement is to control the microcracking of the

P.A.E.S. Project and Housing Policies for Sustainable Buildings

671

material by forming “bridge” type mechanisms or a bond where the fracture develops. – The benefits of using a gypsum based admixture in the mineral matrices are many: (a) Obtaining a “green” product conformed to the actual trends imposed by the European Union; an admixture in the standard cement mix improves the product by reducing the alkalinity and increasing the performances of the fibres vulnerable to these substances; (b) On long term is obtained: decrease of the carbon emissions which could be emanated when producing clinker; decrease of the energy consumption because this product is obtained at lower temperatures than the ones used to obtain clinker; protecting the environment by saving the natural resources and using industrial wastes. – The mechanical properties of the ecological samples with respect to the traditional ones at a 28 days interval present an increase of the tensile strength. – Not all types of matrix are compatible with the textile structures. Considering the experiments made on several types of textile structures the developed ecological matrix had a superior workability and thus a better infiltration and embedding of the reinforcing fibres. 3.1

Improving of the Durability for Buildings Located in Seismic Areas

Earthquakes are among the most destructive phenomena on earth. Annually human lives and material assets are lost, activities and services for maintaining social relations are disturbed due to these phenomena. Thereby, seismic protection is a very important aspect in structural design and is a subject studied worldwide. Seismic design of structures provides certain performance criteria relating to the capacity of buildings to dissipate the seismic energy in a steady state and for as many motion cycles as possible. Current design theory is based on the acceptance of plastic zones occurrence in structural elements, but the design should be oriented so as to avoid structural collapse. Plastic zones, which in the case of bars become plastic hinges, are designed to develop only in the main beams, avoiding their occurrence in columns which obviously would facilitate the creation of collapse mechanisms of the structure. There are types of buildings whose resistance structure eliminates the occurrence of plastic hinges in beams. Frame structures with Slimdek composite floors or with flat slabs are such cases. In the first part of the e-learning material, the current state of research on some types of energy dissipative devices is presented. A classification and description of nonlinear computational models for structural steel structures is also presented. On the second part, new devices developed at Technical University of Iasi are proposed. Numerical analyses are performed on new energy dissipation devices designed for the anti-seismic protection of before mentioned structures: columns with unidirectional dissipation (SDU), multidirectional dissipation columns (SDM), columns with multidirectional dissipation and gravitational loads takeover (SDMG), friction dissipation columns (SDF) and energy dissipative brace (CD).

672

R. Olivito et al.

Fig. 2. Patented multidirectional dissipation and gravitational loads takeover (SDMG)

The patented TUIASI device (SDMG) [6] and a description of the experimental models is made (Fig. 2). The experimental tests are performed on a shaking table and the results are also presented in this part. The material makes many contributions by performing a parametric study regarding the factors that influence the dynamic behavior of composite floors and also a comparative study between two types of composite floors taking into consideration specifications from Eurocode 4 and from “Floor Vibrations Due to Human Activity” design guide.

4 Evaluation of Material Compositions of Sloping Roofs from Environmental and Energy Aspects The world in 21st century faces daunting energy and environmental challenges [7]. As study [8] states, climate change is now a major research priority. The environmental and energy challenges associated with turning society in a more sustainable direction are tremendous and urgent [9]. Climate change has often been considered the most significant current threat and thus most of global attention has been on climate change mitigation and resilience to warming [10]. Issues related to improvement in the quality of products and to environmental protection in the economic policy of many countries and in the strategies of institutions and international organizations (e.g. European Union) have increased in importance in recent years as a consequence of the increase in environmental awareness of consumers [11]. Buildings play significant role in energy consumption and emission production through all phases of life cycle [12]. The Energy Performance Buildings Directive (EPBD) was issued to provide a common strategy for all European countries and to implement several actions for improving energy efficiency of buildings, responsible for 40% of energy consumption [13]. A transparent and comparable understanding of the energy efficiency, carbon footprint, and environmental impacts of renewable resources are required in the decision making and planning process towards a more sustainable energy system [14]. When the CO2

P.A.E.S. Project and Housing Policies for Sustainable Buildings

673

equivalent emissions are considered, the CO2 emissions from embodied energy make up an important share of the total, indicating that the building materials have a high importance which is often ignored when only the energy efficiency of running the building is considered [15]. Both the construction and use of buildings cause significant environmental pressures. The greenhouse gas (GHG) emissions imposed by buildings have been studied rather extensively, but less is known about other impacts. Still, climate change is only one harmful impact driven by buildings [10]. Globally, buildings consume nearly half of the total energy produced, and consequently responsible for a large share of CO2 emissions. A building’s life cycle energy (LCE) comprises its embodied energy (EE) and operational energy (OE). The building design, prevalent climatic conditions and occupant behavior primarily determines its LCE. Thus, for the identification of appropriate emission-reduction strategies, studies into building LCE are crucial [16]. The aim of the many research works is improve the energy efficiency of buildings. Study [17] presents an important contribution to cleaner production and environmental policy. Environmental emissions at foundation construction stage of buildings were investigated and compared for two foundation types, i.e., pile foundation and raft foundation [18]. Other study [19] investigated façade system for existing office buildings in Copenhagen. Study [20] is focused on comparison of environmental and energy performance of exterior walls. Another study [21] is focused on design strategy for low embodied carbon and low embodied energy buildings. Study [22] is focused on evaluation of structures design concept of lower structure from embodied energy and emissions. Life cycle assessment of alveolar brick construction system incorporating phase change materials is analyzed in the study. Environmental performance of material solutions is calculated by using the LCA assessment method within boundaries “cradle to cradle” [23]. LCA is used to quantify environmental impact and refers to the major activities in the course of the product’s lifespan, including raw material extraction, material or product manufacturing, construction, operation and maintenance, to its final decommissioning and disposal [24]. LCA evaluation is widespread and is used for example, for quantitative analysis of the environmental performances for different Italian wines production [25]. Life cycle methodology is used for sustainability appraisal of infrastructures systems [26], for mapping the flow of pollutant in the urban environment [27] as well as for environmental quality evaluation of hard coal [28]. Also interesting study [29] is a review on three streams of life cycle studies that have been frequently applied to evaluate the environmental impacts of building construction with a major focus on whether they can be used for decision making. The three streams are Life Cycle Assessment (LCA), Life Cycle Energy Assessment and Life Cycle Carbon Emissions Assessment. For the aim of this paper five variants of material compositions of sloping roofs were analyzed from environmental aspects. They were designed to fulfil the requirement from thermal transmittance (U = 0.10 W/m K) for nearly zero-energy buildings. The environmental impacts were expressed by indicators such as embodied energy (EE) from non-renewable resources, CO2eq emissions (GWP, global warming potential) and SO2eq emissions (AP, acidification potential) as well environmental indicator DOI3. They represented the equivalent emissions within the LCA boundary - cradle to gate and input data were extracted from the LCA database - IBO. The final values were compared by using methods of multi-criteria decision analysis. The lowest value of embodied energy

674

R. Olivito et al.

of 745.52 MJ/m2 achieved variant with lower thickness of mineral wool thermal insulation. Highest values of embodied energy of 1408.455 MJ/m2 achieved variant with additional thickness of mineral wool thermal insulation. The best alternative from CO2 emissions (−106.1 kgCO2eq./m2) was variant defined as green roof but concurrently it achieved the highest value of SO2 emissions (0.617 kgSO2eq./m2). The worst variant from CO2 emissions (57.75 kgCO2eq./m2) consisted of mineral wool thermal insulation. 4.1

Materials and Methods

Three variants of sloping roof constructions are designed to investigate the role of different building material compositions in term of the embodied energy from non-renewable resources, equivalent emissions of CO2 and SO2. Concurrently they are designed to fulfill the requirement for thermal transmittance of U = 0.10 W/m K for nearly zero-energy buildings. The constructions of sloping roofs for the evaluated variants are depicted in Fig. 3. Variant 1 is designed to be a green vegetation roof (Fig. 3a). Variants 2 and 3 were consist of mineral thermal insulation and blown thermal insulation of mineral wool, respectively (Fig. 3b, c) [30, 31].

a) Variant 1

b) Variant 2

c) Variant 3

d) Variant 4

e) Variant 5

Fig. 3. Material composition of sloping roof

The cradle-to-gate life cycle analysis was used and focused on environmental indicators such as embodied energy and emissions of CO2eq and SO2eq. The selection and combination of materials influence the amount of energy consumption and associated production of emissions during the building operation phase. Methods of multicriteria decision analysis (CDA, IPA, WSA, TOPSIS) were used for the interpretation of results. The goal of this paper was to evaluate material compositions for roof structures. Sloping roof 5 appears to be the most suitable from environmentally and thermo-physical point of view. Determined values of environmental impacts for sloping roof 5 are 745.52 MJ/m2 −102.055 kgCO2eq/m2 and 0.31043 kgSO2eq/m2 for embodied energy, CO2 and SO2 emissions, respectively.

5 Evaluation Design for the E-learning Courses In the frame of the PAES project, the electronic course development follows the methodology within the ADDIE model: A - Analysis; D - Design; D - Develop; I Implement; E - Evaluate [32], an iterative process schematically presented in Fig. 4.

P.A.E.S. Project and Housing Policies for Sustainable Buildings

675

Fig. 4. The ADDIE model for courseware development

The partners’ roles are well established in different phases of the process, following the design, development, implementation and evaluation. In the e-learning course development process, the evaluation is seen as a specific process with two dimensions, considering the purpose: – learning evaluation, addressed to the learner, who has to be aware about the status of his/her knowledge according to the intended learning objectives of the electronic course; – electronic course validation, meant to check the entire electronic course, in order to provide to its developers, the opportunity to improve it. 5.1

Learning Evaluation

Learning, as active process of seeking, mastering, interpreting, organizing information, applying it in new context is exclusively controlled by the learner in the e-learning environment. It is known that the integration of assessment with instruction have unprecedented power to increase student engagement and to improve learning outcomes [33]. Assessment, subsumed to learning, is meant to provide a judgment on learner’s own learning in the process completing the electronic course. Generally, the assessment process is considered as comprising three stages [34]: eliciting evidence of learning, interpreting the evidence, taking action. Depending on its purpose and its place in the course, one can discriminate the assessment as formative and summative [34]. The result of the assessment may be represented by the “feedback” or in form of mark or grade, based on a well-established scale. If the assessment stops, judging a summation of achieved learning outcomes, it is called summative assessment. If the result of the judgment (feedback) is used to offer the opportunity for improvements in terms of learning, the assessment is called formative [35].

676

R. Olivito et al.

The assessment is driving force for the learning process, and the feedback plays the major role in encouraging or discouraging learners. Four types of feedback were identified in the real classroom [33], and they can be transferred also in the web-based environment (Fig. 5). Type A (focusing on reward or sanction) and B (based on reward or punishment, but indicating a level of approval) are called evaluative feedback. Feedback allocated to type C (focused on the adequacy of the work in terms of success criteria) and type D (emphasizing the process aspect of the work) are called as descriptive and it provides evidence for achievements or need for improvement.

Descriptive feedback

Evaluative feedback

A: (+) rewarding (-) punishing

C specifies: attainament improvement

B: (+) approving (-) disapproving

D offers construction of: achievement way foreward

Fig. 5. Typology of feedback

Another typology considers different kinds of formative feedback [33]: – Weaker feedback - learner is informed about the score of grade he/she obtained (information about the result); – Feedback only - learner is informed about the score/grade, but also on the correct answers (information about correct results); – Weak formative assessment - learner is informed about the correct answers and some supplementary explanations are provided; – Moderate formative assessment - learner is informed about the correct answers, supplementary explanations and also suggestions for improvements are done; – Strong formative assessment - learner is informed about the correct answers and some supplementary explanations and specific actions for improvements. In the PAES project, the assessment process is structured as presented in Fig. 6, offering an overview on types of assessments performed in the electronic courses. The evaluation methodology contains both theoretical and practical information for developing the tests/assessment items.

P.A.E.S. Project and Housing Policies for Sustainable Buildings

677

Fig. 6. The assessment in the PAES project

5.2

Course Validation

Before implementation, the electronic course must be validated, in order to get a big picture of it. The validation process follows four stages, and a series of reports are provided, to be used for improvements before final implementation and delivery. First stage, performed by e-learning and domain experts is devoted to educational aspects of the electronic course. The second stage is meant to provide the observations of individual learners (usually a pilot group is involved) after completion the electronic course. The third stage is focused on validation of the instructional units which contain activities, exercises and tests. The fourth stage consists of operational tests to highlight the logistical, technical or educational issues which may occur in module implementation within the electronic course [36]. In the frame of the PAES project, the evaluation methodology contains the basic information and also specific forms in the validation process, to be used by course coordinator, domain experts, students and representative of organizations working in the field.

6 The Business Perspective of Sustainable Housing Construction of houses and also their structural and operational improvement, is being usually seen as a project, already decided, either to comply with the regulations, or to exploit the subsidies offered by the governments in such cases, or in many other cases as the way of restricting the energy costs and the respective benefits of energy efficiency interventions. Ownership of a house and interventions on it, exceed economic assessment, while they represent the social status of the resident. Decisions about investing in houses - that represent a part of real estate market - are based on economic forecasts and the speculation on early forecasting of the demand increment in a specific housing area. These decisions are business once, while they are considered only as financial.

678

R. Olivito et al.

Considering that the theories about the evolution of our species are correct, the first act of civilization has been the construction of caverns (shelters) and the abandonment of the natural once. Such housing is supported by archaeological evidence and those entitle to interpret them. Those, our remote ancestors, were seeking for a shelter to provide them with a controllable protection of the nature and soon after from their fiercest threat; fellow humans. After millennia of evolution and especially after the consolidation of the European principals, economic stability, despite neglecting interpretations, house owners and potential buyers of houses (historical or newly constructed) are still devoting efforts to identify hat their choice is coherent and in what extend. Assuming the management of a building it becomes a business. As a business, it becomes a subject of several uncertainties (risks) against expectations. Accepting that expectations, it reflects «pro-forma» evaluations, similar to every other kind of business, only much more simple. Every private building has a market price. It varies over time, as affected by the demand for housing (people hosting or commercial or even industrial activities) in the specific area (city quarter, neighborhood, recreation area, holidays, market, transportation of goods and people, facilities etc.). Although buildings follow the general price trend of the area they have been constructed, each building (or apartment) has a different «price tag» which is influenced by its architectural characteristics, as well as by the «taste for beauty and/or social status marking». The «Real Estate Market» has always been an important competitor of the trade market (not just the Stock Exchange Equity but also partnership in Small or Very Small Enterprises). Real Estate represents an investment (or even speculation) alternative to the private savings and also the various funds. Involvement in Real Estate Investment is mainly driven by a triple prospective; profits, stability and expectations. Every money manager, either of his own or handling a «fund», makes a position choice within the bounders of such a triangle. Trading private buildings (short term speculation), investing in such (mid-term modernization of the interiors), or Legacy administration (exploit heredity), is also on the same rank of the investment, because heredity acceptance is similar to investment, assimilates commercial decisions, in what accepting the heredity of real estate corresponds to an investment on a scale of taxes over expected value of the heredity. Owning a building is bringing up options, like making it a residence of the (new) owner, let it to rent, sell it, or change its characteristics and then let it to rent or sell it. When no option is adopted, the building will be, sooner than later, occupied by both people and rodents. There seem to be many unanswered questions, within Academia, while in the political arena; is tolerable towards depriving ownership of real estate. Modifications of energy consumption has little not effect at all to the price offered by the potential buyers. Business connected to profits and orientated to Stock Exchange are using intermediaries, who are promoting and promising «big and fast profits». Loss is banned from their vocabulary. Almost all of the published literature, when examining the economic impact, is making calculations of the Net Present Value of the savings that result from the reduction of «oil» consumption. This is arbitrary assuming that (a) oil prices remain stable, and (b) climate becomes stable.

P.A.E.S. Project and Housing Policies for Sustainable Buildings

679

Furthermore, «environment friendly» investments on buildings oversee that the material used has a life expectancy. Any modification of existing buildings, as well as any changes on new construction plans, is proposed to take into account: the time-span in which the engineering work or engineering interventions remain «state of the Art». The time required to modify the energetic behavior of a building, especially when it is considered to demonstrate a «cultural inheritance», has not been taken into quantitative consideration, because it lacks any standard pattern response. The literature review has not shown any relation between the cost of interventions on existing buildings or additional cost to new buildings, representing the savings to energy consumption, under the assumption that any such cost has a «time to live TTL» of 20 or less years in which it has to pay back the investor (Return on Investment = ROI). Cash flow has not been an issue of examination, while payments and future NON payments make a cash flow, sometimes positive (cash-in is exceeding payments), other times negative. Either the acquisition of an energy saving building or the modification of one, so that it saves energy, need liquidity to be transferred to either a super value to the owner (seller) or to cover the expenses of the improvement. While the cost has been well evaluated, cash flow is not. The selling price of a building may be increased in proportion to the investment on the energy saving installments and devices. Buying a building or spending to improve its energy performance, is the acquisition of value which reflects cash payments, it has to be counter-balanced to the future savings for energy. Investing in a building is a business, and as such it has to exploit all the entrepreneurial techniques, mostly Marketing, because from Marketing depends the demand and from demand the market price. It is the net present value of the savings on energy (as am equivalent to cash collection) that has to be calculated and compared to the investment, incremented by the market price increase because of the energy efficiency of the building. A small scale survey, conducted in March 2016 (50 real estate brokers have been interviewed in Chalkidiki [mostly holiday resorts], Thessaloniki [a city of 1.000.000 inhabitants by the sea] and Serres [100.000 inhabitants, inland town with higher summer and lower winter temperature], has shown a great difference of the value of the buildings, either as selling price or rent, between the three locations; In Chalkidiki it did not make any difference, in Thessaloniki there was some premium for energy efficiency, while in Serres the premium was noticeable, yet much lower than hypothesized [29, 37–41]. 6.1

Recognition of “Environmentally Sustainable Businesses” Through a Specific Validation Procedure

One of the main activities of PAES project is the development of an evaluation scheme for the recognition of the “environmentally sustainable businesses” that are active in the constructions’ sector. This activity is being implemented by the Greek-Italian Chamber of Commerce of Thessaloniki with the Scientific Coordination and Support of the University of Calabria - Department of Civil Engineering.

680

R. Olivito et al.

The above mentioned scheme includes three main tools: (a) the initial communication kit, that includes information concerning the PAES project, the topic of “environmental sustainability”, the benefits for an enterprise to act and to be recognized as “environmentally sustainable business”, the evaluation process developed within the project, as well as a 1-page pre-application form template for the companies to apply, (b) the business sustainability form and (c) the guidelines for the completion of the business sustainability form. The Business Sustainability Evaluation Form is addressed to companies that operate in the fields of constructions and construction materials in order to willingly evaluate and measure their sustainability in terms of the economy, environment and society. The evaluation is based on a series of qualitative and quantitative indicators measuring the financial capacity of the business as well as its environmental and social responsibility, in order to evaluate its sustainability. Companies that fulfil specific criteria according to the evaluation will be included to the list of “sustainable” companies which is going to be published in the PAES Platform. It should be noted that the above “recognition” does not substitute, replace or prevail in any case any national or international certificate related to quality or corporate social responsibility, given the fact that it has been developed in pilot and testing level for the needs of PAES project, in particular. The completion of the Business Sustainability Evaluation Form is not obligatory but it is considered as very valuable both for the companies’ self-evaluation, as well as for the project success. Therefore, we would like to invite you all to participate in our initiative by completing the present form. Within their self-evaluation, each company will achieve a specific score depending on the indicators’ and criteria’s fulfilment level. This score is highly confidential and it will not be published in public for any purpose. It will be only used for the purposes of the classification of the companies that will have achieved scores over the threshold in two categories “highly sustainable” & “sustainable”. Data related to companies with scores under the threshold (= 51 points) will never be published. As a reward, the companies that will complete the Business Sustainability Evaluation Form (as long as they achieve a total score higher than the set threshold) will have the benefit of a wide international promotion through the project platform and partners’ networks including mostly academics, researchers, professionals, local and regional authorities and associations’ representatives, students etc. A list of companies fulfilling Business Sustainability Criteria will be frequently updated and will be visible and promoted through the international project platform. As a supportive tool, the “Business Sustainability Evaluation Guidelines”, aims to provide detailed guidelines to all partner organizations, as well as other involved or interested parties for the completion of the Business Sustainability Evaluation Form. It comprises four main chapters and more precisely: CHAPTER 1 - Selection and definition of Business Sustainability Indicators; CHAPTER 2 - Presentation of Business Sustainability Evaluation Form;

P.A.E.S. Project and Housing Policies for Sustainable Buildings

681

CHAPTER 3 - Guidelines for the validation of the data provided and the score rating of each section; 3:1 Company’s Economic, HR and Activity Data; 3:2 Company’s Environmental Strategies and Measures; 3:3 Company’s Social Strategies and Measures; CHAPTER 4- Targets set per country. The above mentioned documents (Business Sustainability Evaluation Form & Guidelines) have been developed based on specific aspects of international standards such as ISO 14001, social responsibility evaluation models and other labels of similar non obligatory character (e.g. Label “Ospitalita Italiana”). In addition, business sustainability indicators have been divided into three sub-groups: (a) Economic - The indicators selected include the growth rate of companies’ turnover, profit and labor units for the past three years, while staff’s gender (number of women employed) and staff’s educational level is also evaluated. The main companies’ activities & products, as well as their main sales channels form also part of the qualitative evaluation within this sub-group. (b) Environmental - This sub-group includes the compliance of the companies with environmental EU and national legislation as well as with international standards (if applicable), the adaption of an organizational structure within the companies in order environmental issues to be handled in a concrete and systematic way, the organization of topic-related training activities, the frequency and the extent of application of specific measures related to the environmental protection (e.g. use of eco-friendly, low-energy and low water consuming materials/techniques/ processes, implementation of monitoring & control processes concerning the CO2 emissions, use of RES, waste disposal and recycling etc., as well as the evaluation of companies’ transparency in environmental issues. (c) Social - The compliance of companies with EU and National legislation as well as national or international standards related to their social performance and the health and safety issues (ISO 26000, SA 8000, OHSAS 18001 etc.), the frequency and the extent of application of specific measures related to social responsibility (measures towards non-discrimination, equal opportunities, pregnancy and motherhood support etc.) and the evaluation of companies’ transparency in social issues form the main elements of evaluation within this last sub-group. Each sub-group has a different impact on the final evaluation, where the environmental aspect is the one that counts most given that this is the topic where PAES project focuses. However, there would have not be any discussion concerning sustainability, if economic and social aspects had been excluded. In this sense, the evaluation score has been designed in such way that the maximum score per category (up to 100) reaches: – Company’s Economic, HR and Activity Data - 36 points; – Company’s Environmental Strategies and Measures - 54 points; – Company’s Social Strategies and Measures - 10 points.

682

R. Olivito et al.

The Environmental Sustainability Evaluation will run in a pilot level within the PAES project targeting to the evaluation of 20 companies per territory (= the wider area where each partner is active), thus 100 companies in total. After the completion of the pilot application of the activity within the PAES project, the label of “environmentally sustainable businesses” will be widely promoted in and out of partners’ territories, inviting more and more companies to run a self-evaluation in order to check how sustainable they are. Random checks (including request of related documentation) will be applied in order to ensure the responsible participation of the companies in this initiative. Through this process, it is expected both to: (a) establish an informal model of award for the companies of the constructions sector that respect the environment and contribute to the environmental protection, being at the same time economic sustainable and social responsible; (b) motivate companies of the constructions sector to improve their policies and measures in environmental and social issues. 6.2

Results in the Business Community

Apart from its participation in specific project activities, the Greek-Italian Chamber of Commerce of Thessaloniki has a very important role in the communication and dissemination of the PAES project outputs and results using its well-developed networks including chambers of commerce, business organizations and associations, local and regional authorities, experts and enterprises all over Europe. The main message set is “the usefulness of PAES platform not only for students but also for companies, helping them to improve their environmental performance through the studying of updated and recent academic material in relative topics, no matter the time and the place - since it is a web-platform accessible to everyone authorized for this purpose. In order to ensure maximum awareness, information and participation of business community, a structured and targeted dissemination and exploitation strategy should be developed, drafted prior to the beginning of the project, aiming to maximize impact in three interconnected and overlapping concepts, involved throughout the whole duration of the project. More specifically, these concepts are: (a) Visibility of the project, its ideas, objectives, activities and ambitions, throughout the duration of the project; (b) Dissemination of the first outcomes, experiences and results, produced by specific activities or aiming to raise awareness, inform, educate and encourage the participation of the targeted groups; (c) Exploitation of the main outcomes and results of the project, which are to be made and sustained available for the wider public to use, re-use, adapt and further develop them, ensuring their sustainable and effective impact, with relevance to the objectives and priorities they were developed.

P.A.E.S. Project and Housing Policies for Sustainable Buildings

683

Main communication tools used for the dissemination of PAES project and activities with a particular focus on the web platform, as well as the “sustainability evaluation” initiative are: (a) (b) (c) (d) (e)

Printed and electronic material; Press-releases & newsletters; Project website; Social media campaign; Presentations within open events, scientific conferences etc.

Unique visits in the project website and number of users - as far as PAES platform is concerned - are the main indicators used in a continuous basis, in order the communication strategy to be evaluated. Low numbers concerning these two indicators result to the revision of the communication strategy. Acknowledgements. The authors acknowledge the Indire Agency for funding the project with in the Erasmus+ program, activity KA2, Strategic Partnerships for Higher Education, call 2015, reference n° 2015-1-IT02-KA203-014974 and Title of the proposal: Politiche Abitative per l’Edilizia Sostenibile. This project was kindly supported by UNIVERSITY OF CALABRIA: Luciano Ombres; Natale Arcuri; Patrizia Piro; Domenico Grimaldi; Roberta Lucente; Laura Greco; Maria Francesca Viapiana; “GHEORGHE ASACHI” TECHNICAL UNIVERSITY OF IASI: Vasile-Mircea Venghiac; Raluca Onofrei; TECHNOLOGICAL EDUCATION INSTITUTE OF SERRES: Eleni Vlahonasiou; Myrofora Theodoridou; GREEK ITALIAN CHAMBER OF COMMERCE: Ioanna Papaioannou; Alexandra Genni; TECHNICAL UNIVERSITY OF KOSICE: Zuzana Poórová; Zuzana Vranayová; Silvia Vilcekova; Marek Kusnir; TRANSILVANIA UNIVERSITY OF BRASOV: Dana Perniu; Liviu Perniu.

References 1. UNI/PdR 13.0:2015 - Prassi di Riferimento - Environmental sustainability of construction works - Operational tools for sustainability assessment General framework and methodological principles 2. UNI/PdR 13.1:2015 - Prassi di Riferimento - Environmental sustainability of construction works - Operational tools for sustainability assessment Residential buildings 3. Protocollo ITACA Sintetico Residenziale regione Calabria - Maggio (2017) 4. Protocollo ITACA Scolastico regione Calabria - Maggio (2017) 5. Lungu, I., Taranu, G., Hohan, R., Plesu, G.: Efficient use of green cements in structural elements for civil engineering applications. In: Proceedings of the 3rd International Conference on Advanced Materials and Systems, pp. 67–72 (2010). http://dx.doi.org/10. 1016/j.enbuild.2013.09.023 6. Venghiac, V.M., Budescu, M.: The experimental analysis of an innovative yielding metallic damper. Math. Model. Civil Eng. 11(2), 38–45 (2015). doi:10.1515/mmce-2015-0009 7. Chang, Y., Ries, R.J., Wang, Y.: The quantification of the embodied impacts of construction projects on energy, environment, and society based on I-O LCA. Energy Policy 39, 6321– 6330 (2011). doi:10.1016/j.enpol.2011.07.033

684

R. Olivito et al.

8. Rosselló-Batle, B., Ribas, C., Moià-Pol, R., Martínez-Moll, V.: An assessment of the relationship between embodied and thermal energy demands in dwellings in a Mediterranean climate. Energy Build. 109, 230–244 (2015). doi:10.1016/j.enbuild.2015.10.007 9. Chang, Y., Ries, R., Wang, Y.: The embodied energy and environmental emissions of construction projects in China: an economic input-output LCA model. Energy Policy 38, 6597–6603 (2010). doi:10.1016/j.enpol.2010.06.030 10. Heinonen, J., Säynäjoki, A., Junnonen, J., Poyry, A.: Pre-use phase LCA of a multi-story residential building: can greenhouse gas emissions be used as a more general environmental performance indicator? Build. Environ. 95, 119–125 (2016). doi:10.1016/j.buildenv.2015. 09.006 11. Kulczyck, J., Smol, M.: Environmentally friendly pathways for the evaluation of investment projects using life cycle assessment (LCA) and life cycle cost analysis (LCCA), Clean Technol. Environ. Policy, 24 (2015, in press). doi:10.1007/s10098-015-1059-x 12. Sedláková, A., Vilčeková, S., Krídlová Burdová, E.: Evaluation of structures design concept of lower structure from embodied energy and emissions. Chem. Eng. Trans. 39, 139–144 (2014). doi:10.3303/CET1439024 13. Bueatti, C., Barbenera, M., Palladino, D.: An original tool for checking energy performance and certification of buildings by means of artificial neural networks. Appl. Energy 120, 125– 132 (2014). doi:10.1016/j.apenergy.2014.01.053 14. Pierie, F., Bekkering, J., Benders, R.M.J., van Gemert, W.J.Th., Moll, H.C.: A new approach for measuring the environmental sustainability of renewable energy production systems: focused on the modelling of green gas production pathways. Appl. Energy 162, 131–138 (2016). https://doi.org/10.1016/j.apenergy.2015.10.037 15. Airaksinen, M., Matilainen, P.: A carbon footprint of an office building. Energies 4, 1197– 1210 (2011). doi:10.3390/en4081197 16. Praseeda, K.I., Venkaratama Reddy, B.V., Mani, M.: Embodied and operational energy of urban residential buildings in India. Energy Build. 110, 211–219 (2016). doi:10.1016/j. enbuild.2015.09.072 17. Kravanja, Z., Varbanov, P.S., Klemeš, J.J.: Recent advances in green energy and product productions, environmentally friendly, healthier and safer technologies and processes, CO2 capturing, storage and recycling, and sustainability assessment in decision-making. Clean Technol. Environ. Policy 17(5), 1119–1126 (2015). doi:10.1007/s10098-015-0995-9 18. Sandanayake, M., Zhang, G., Setunge, S.: Environmental emissions at foundation construction stage of buildings - Two case studies. Build. Environ. 95, 189–198 (2016). doi:10.1016/j.buildenv.2015.09.002 19. Hannoundi, L.A., Christensen, J.E., Lauring, M.: Façade system for existing office buildings in Copenhagen. Energy Procedia 78, 937–942 (2015). doi:10.1016/j.egypro.2015.11.023 20. Vilčeková, S., Sedláková, A., Krídlová Burdová, E., Vojtuš, J.: Comparison of environmental and energy performance of exterior walls. Energy Procedia 78, 231–236 (2015) 21. Lupíšek, A., Vaculíková, M., Mančík, Š., Hodková, J., Ružička, J.: Design strategies for low embodied carbon and low embodied energy buildings: principles and examples. Energy Procedia 83, 147–156 (2015). doi:10.1016/j.egypro.2015.11.617 22. Castell, A., et al.: Life cycle assessment of alveolar brick construction system incorporating phase change materials (PCMs). Appl. Energy 101, 600–608 (2013). doi:10.1016/j. apenergy.2012.06.066 23. Benedetto, D., Klemeš, J.: The environmental performance strategy map: an integrated LCA approach to support the strategic decision-making process. J. Clean. Prod. 17, 900–906 (2009). doi:10.1016/j.jclepro.2009.02.012 24. Adhikari, R.S., Aste, N., Del Pero, C., Manfren, M.: Net Zero energy buildings: expense or investment? Energy Procedia 14, 1331–1336 (2012)

P.A.E.S. Project and Housing Policies for Sustainable Buildings

685

25. Iannone, R., Miranda, S., Riemma, S., de Marko, I.: Life cycle assessment of red and white wines production in southern Italy. Chem. Eng. Trans. 39, 595–600 (2014). doi:10.3303/ CET1439100 26. Reza, B., Sadiq, R., Hewage, K.: Energy-based life cycle assessment (Em-LCA) for sustainability appraisal of infrastructure systems: a case study on paved roads. Clean Technol. Environ. Policy 2, 251–266 (2014). doi:10.1007/s10098-013-0615-5 27. Azapagic, A., Pettit, C., Sinclair, P.: A life cycle methodology for mapping the flows of pollutants in the urban environment. Clean Technol. Environ. Policy 9(3), 99–214 (2007). doi:10.1007/s10098-007-0092-9 28. Czarnowska, L., Stanek, W., Pikon, K., Nadziakiewicz, J.: Environmental quality evaluation of hard coal using LCA and exergo-ecological cost methodology. Chem. Eng. Trans. 42, 139–144 (2014). doi:10.3303/CET1442024 29. Chau, C.K., Leung, T.M., Ng, W.Y.: A review on life cycle assessment, life cycle energy assessment and life cycle carbon emissions assessment on buildings. Appl. Energy 143, 395–413 (2015). doi:10.1016/j.apenergy.2015.01.023 30. Standard STN EN 730540. Thermal performance of buildings and components, thermal protection of buildings, Brussels (2012) 31. Waltjen, T.: Passivhaus-Bauteilkatalog, Ökologisch Bewertete Konstruktionen. Springer, Wien (2009) 32. Morrison, G.R., Ross, S.M., Kemp, J.E.: Designing Effective Instruction, 6th edn. Wiley, USA (2010). ISBN-13: 978-0470074268 33. Taras, M.: Assessment for learning: assessing the theory and evidence. Procedia Soc. Behav. Sci. 2, 3015–3022 (2010) 34. Wiliam, D.: What is assessment for learning? Stud. Educ. Eval. 37, 3–14 (2011) 35. Piskurich, G.M.: Rapid Instructional Design: Learning ID Fast and Right. Wiley, USA (2006). ISBN-13: 978-0787980733 36. Orsingher, C. (ed.): Assessing Quality in European Higher Education Institutions: Dissemination, Methods and Procedures. Springer Science & Business Media, Germany (2006). ISBN 978-3-7908-1659-4 37. Papadopoulos, A., Theodosiou, T., Kiaratzas, K.: Feasibility of energy saving renovation measures in urban buildings; the impact of energy prices and the acceptable pay back criterion. Elsevier, Energy Build. 34, 455–466 (2002) 38. Bullen, P.: Adaptive reuse and sustainability of commercial buildings. Facilities 25(1/2), 20– 31 (2007). doi:10.1108/02632770710716911 39. Kumbaroglu, G., Madlener, R.: Evaluation of Economically Optimal Retrofit Investment Options for Energy Savings in Buildings, FNC working paper No. 14/2011 40. Banfi, S., Farsi, M., Filippini, M., Jakob, M.: Willingness to pay for energy saving measures in residential buildings. Energy Econ. 30(2), 503–516 (2008) 41. Weston, J., Brigham, E.: Finanza Aziendale. Il Mulino, Bologna (1971)

Maintenance of Renewable Energy Systems A Challenge in Academic Education Sanda Budea(&) and Carmen-Anca Safta Power Engineering Faculty, Hydraulic, Hydraulic Machineries and Environmental Engineering, University Politehnica of Bucharest, Bucharest, Romania [email protected]

Abstract. It is an undeniable reality that new energy sources and conversion technologies related are “stars” of any energy policy of the XXI-th century. Few people know, however, that the between the conversion technologies, the most lifetime long technology is hydro (estimated between 50–100 years). With the condition that power output should not be less than 80% of rated power, lifetime of a wind turbine is estimated at 20 years and for solar panels at 25 years while estimation for hydro technologies is between 50 and 100 years. Also, corroborating prices per MWh installed and lifetimes, maintenance programs that we propose to implement only proactive type of maintenance, and that means monitoring and optimization. In this article the authors highlight the fact that, in the context of sustainable development is necessary to pay more attention to education in the field of renewable energy. For more than a decade in Romania, in the energy engineering field, is studying Renewable Energy Sources, in particular by approach the systems and equipment to capture and converse to renewable energy, sustainable development and resource management, the environment and ensuring health ambient space with RES etc. The authors show that is required a new approach in academic education regarding RES, focusing on operation and maintenance of capture and conversion systems, with new technologies and future trends in the field. The new methods and schemes in terms of educational approach, to address the needs of 21st century sustainable energy are proposed. Keywords: Renewable energy


Maintenance
Failure
Education

1 Introduction “More maintenance than redundancy and more maintenance than production” is a remark of Toshio Nakagawa [1] and a truth of the recent decades in all branches of engineering. And all these because maintenance refers not only how to repair a industrial system fail, but how to extend the life time of the system at high technical parameters of operation. It is well known that maintenance policies (preventive maintenance, predictive maintenance, total productive maintenance-TPM, and reliability centered maintenance-RCM) for industrial systems and public infrastructure need to respond to customers’ demands and exigencies, [2]. The time of run-of-failure maintenance management is gone. New maintenance policies come to improve © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_47

Maintenance of Renewable Energy Systems - A Challenge in Academic Education

687

productivity, product quality, safety and operating reliability, and last but not least to reduce overall maintenance costs and improves overall profits. In the power generation sector, electric energy production requires - due to the nature of the activity, a prevention maintenance policy of electrical and mechanical infrastructure failures, at least. The extension of equipment normal life time, the downtime reduction and minimization of the unplanned repairs will improve the availability of the energy system so that the maintenance costs not increase the price of electricity to the final consumer, [3]. Another motivation in addressing this paper regards the investments and operation costs in renewable energy. So, a study of VGB Power Tech regarding the investments and operation costs on electricity market sector in Europe, estimates that energy investments in renewable sources (small hydropower, wind onshore, solar PV and biomass) will not suffer from unpredictable and volatile costs, [4]. In Fig. 1 are presented the estimated investment costs (CAPEX) and operating and maintenance costs (OPEX) for run of river, wind onshore, solar PV and biomass until 2030 and 2050 with the mid-2011 as reliable values of estimation.

Fig. 1. CAPEX of different RES technologies using VGB data, [4]

VGB’s estimations show a significant decrease of CAPEX on solar PV technology with the observation that investment costs on 2011 are between 2800 and 3200 EUR/kW. The operating and maintenance expenses (OPEX) are estimated as a percentage of CAPEX per year as follows: 1% for run of river; 3.3% for wind onshore; 1% for solar PV and 2.5% for biomass technology, [4]. Renewable electricity, RE, generation technologies are not chipper than fossil full power technology (with a CAPEX of 650 EUR/kW estimated in 2011 for gas open cycle technology, [4]). This is another important reason which must be considered and developed as an academic curricula in accordance with market demands and social expectations. Besides, the structure of electricity production indicates that the renewable electricity generation is about 12.51% from E-RES facilities other than hydropower, [5]. In Romania, the renewable energy facilities commissioned in the last ten years and dispatched into the grid are wind farms with a capacity of 3,129 MW, solar parks with

688

S. Budea and C.-A. Safta

photovoltaic panels having a total capacity of 1,312 MW, micro-hydro power plants of 583 MW and biomass-based projects with a combined power of 103 MW, [6]. According to the law, only those plants that were accredited by December 31, 2016 benefited from the green certificate support scheme [7]. In Romania, until last year, 962 photovoltaic power plants or photovoltaic parks were built, 212 of them produce less than 1 MW and 112 have a production below 2 MW. Most PV plants were built in Timiş - 64, Olt, Dâmboviţa and Prahova, each with 57 separate investments. The South-Muntenia region has most solar fields (302). As installed power, the largest parks are in Giurgiu (maximum 79.2 MW), Braşov (61 MW) and Călăraşi (60 MW). And because one of the eight pillars of total productive maintenance refers to training and education, [8], the purpose of the paper is the approach of the renewable energy maintenance as an academic curricula of a master program. The Maintenance of the Renewable Energy Equipment Master’s Program aims is to provide students with a basic understanding of maintenance knowledge applied in renewable energy technology. Working-life competencies and knowledge specific to the Maintenance of the RE Equipment Master’s Program are proposed taking into account that students acquire the skills they need for their future careers in agreement with the needs of stakeholders.

2 Assessment of Accidents in E-RES Facilities of Solar PV, Small Hydropower and Wind Turbines Systems In this paragraph, it is made a brief analysis of accidents in photovoltaic systems, hydropower systems and wind turbines, in an attempt to emphasize the need to develop a new master program aimed at the maintenance of equipment used to convert energy from renewable sources. The information included in this analysis refers to 2006–2017 wind turbine statistical data and from 2006–2012 for photovoltaic systems or hydroelectric installations. It is found that the accidents in the wind farms are dominant, and on the other hand, there is a tendency to decrease the incidents in all electric renewable energy systems (E-RES). Romanian authorities did not report failures and serious accidents at the renewable technology sites implemented in the country. The figures presented in the paper are analyzed globally.

2.1

Accidents in Photovoltaic Energy Systems

To reduce the costs of photovoltaic systems it must to increase the reliability and the service life time of the PV modules. Statistics show degradation rates of the rated power for crystalline silicon PV modules of 0.8%/year [9]. Typical failures of PV modules are divided in three categories: infant failures, midlife-failures and wear-out-failures. The rate is given relative to the total number of failures [10]. Failures of photovoltaic modules are consisting in mechanical failures (glass breakage, delamination,

Maintenance of Renewable Energy Systems - A Challenge in Academic Education

689

damage of PV’s panel frame, transport damage) and electrical failures (power loss, J-box and cables), like in Fig. 2. A lot of mechanical failures can appear in the photovoltaic tracked modules [11].

Fig. 2. Failures of photovoltaic modules [10]

The statistic is based on a total volume of approximately 2 million delivered PV modules. Failure rates of PV modules relative of IEC 61215 and IEC 61646 standards [12, 13] shows that in 2012 the rate of failed of PV systems had dropped to 10%, Fig. 3.

Fig. 3. Failure rate in PV modules relative to IEC standards [12, 13]

690

S. Budea and C.-A. Safta

PV modules failures are due to external cause: clamping, transport and installation, mechanical defects. Failure of the connectors can cause fire, and lightning are also damaging. 2.2

Accidents in Hydropower Energy Systems

In Romania hydropower is currently the most important renewable source of the electricity and there is still a considerable untapped potential in micro hydro areas. Turbines failures not only decrease the plant down-time but also pose a serious threat to the life of the maintenance personnel, if we consider the August 2009 accident from the Saiano-Sussenskaia hydroelectric plant, [14]. Cavitation and abrasive erosion can be one of the important failures affecting turbine useful life. In hydraulic turbine the main causes of cavitations appears due to the blade design of the turbine and to the frequent change in the operating condition. Parts that are most susceptible to cavitations and to the erosion are the blades with the leading edge. The material fatigue or material defects are another form of hydraulic turbine failure mode [15]. Also the water hammer phenomenon from the pipes plant can produce the damage of the system. Annual operations and maintenance (O&M) costs in hydropower system are often quoted as a percentage of the investment cost per kW and typical values range are varying from 1% to 4% for small hydropower plant. Small hydropower plant is considered, by the European Small Hydropower Association-ESHA, to be “any scheme with install capacity of 10 MW or less”, [16]. Annual O&M costs are average around 2% to 2.5% for large hydropower projects, [17]. Small hydropower projects don’t have the same economies of scale and can have these costs of between 1% and 6%, or in some cases even higher [17]. The study in [17] indicated that operation and maintenance costs averaged USD 45/kW/year for large-scale hydropower plants and around USD 52/kW/year for smallscale hydropower plants. In Fig. 4 are presented the level costs of electricity LCOE for small hydropower plants [17], assumed 10% cost of capital. O&M costs are different depending on the size of the micro-hydropower plant and the technical solution adopted. The average of LCOE cost for European countries ranges from USD 0.04 to USD 0.18/kWh.

2.3

Accidents in Wind Farms

In “Summary of Wind Turbine Accident data to 31 March 2017”, [18], can find information like: total number of accidents (2057), number of fatal accidents (130), accidents with human injury (149), as in Fig. 5. The biggest number of incidents was due to blade failure - whole blades or pieces of blade being thrown from the turbine. A total of 388 separate incidences were found (Fig. 6). Accidents with human vulnerability may have a direct or indirect impact. Feinstein in [19] gives an average fatality curve with the average probability of fatality from fragment impacts on the human body.

Maintenance of Renewable Energy Systems - A Challenge in Academic Education

691

Fig. 4. LCOE of small hydropower plants

Fig. 5. Total number of accidents E-RES facilities, [18]

In the case of small wind turbines which are mounted on the building’s roof the human accidents with indirect impact, generated by the wind turbine break, assume that the number of fatalities is in proportion with the percentage floor area of buildings that collapses; see HSE Reports [20, 21]. For a total collapse of roof, 60% of the building occupants are assumed to be fatalities; so, the building offers 40% protection, even in a collapse scenario, which is not wished (Fig. 7). Even though the first Romanian wind farm has been in operation for almost ten years, (see the Fantanele-Cogealac wind farm), there have been no fatal accidents that would pay the public attention, as it happens in countries like United Kingdom, United States of America, Canada, Germany and others. Also, there is currently no history of major incidents made available to the public. The history of the failures of technological equipment must exist to any power producer. Based on the equipment’s event

692

S. Budea and C.-A. Safta

Fig. 6. Wind turbine accidents due to blade failure, fire, structural failure and ice throw, [18]

Fig. 7. Accidents in wind turbine farms due to blade transport, environmental damage and miscellaneous accidents, [18]

history, estimates can be made about the reliability and lifetime of the equipment, or maintenance schedule planning.

3 Curriculum Planning in Maintenance of RE Equipment It is obviously that such a boom of the renewable energy developed in Romania over the last ten years causes the necessity to develop a training program of renewable energy engineering. And indeed, in 56 Romanian universities there are 7 universities (in Brasov, Bucuresti, Constanta, Cluj, Galati, Oradea) that have master’s programs in renewable energy technology. In Bucharest there are two master’s programs in “renewables” organized by Power Engineering Faculty within University Politehnica of Bucharest, and Faculty of Physics within University of Bucharest. University “Ovidius” of Constanta has organized the

Maintenance of Renewable Energy Systems - A Challenge in Academic Education

693

master program of “Engineering Systems with Renewable Energy Sources” within the Faculty of Applied Sciences and Engineering. Also, Technical University of Cluj (Faculty of Mechanics), University “Dunarea de Jos” of Galati (Faculty of Computer Science, Electrical and Electronics Engineering), and University of Oradea (Faculty of Energy Engineering and Industrial Management) organize and manage the master’s programs in renewable energy and predominantly having this name. Each type of master’s program in renewable energy has been developed taking account the industrial and economic conditions in the area. So, in the master curricula of “Renewable Energy” which has been organized by University of Oradea, solar energy and geothermal energy are developed as renewable technologies mostly. An example of sustainable development in Romanian higher education is given by “Transilvania” University of Brasov, which in the field of renewable energies had an integrated strategy for education and research. The research center for development and innovation RESREC (Renewable Energy Systems and Recycling) was born in 2005 as a response to current trends in industry: to obtain complex interdisciplinary solutions that will ensure energy efficiency, energy saving, and low greenhouse gases, known as “20-20-20” the European targets until 2020, [22]. For the first time, in Romania, it is proposed within “Transilvania” University the undergraduate program in renewable energy entitled “Engineering of renewable energy systems” which has started in 2007–2008, [23]. The postgraduate program named “Design Engineering and Management of the Renewable Energy System” has been proposed as a naturally continuation of academic studies in renewable energy and sustainable development sectors. At the “Transilvania” University, through RESREC research and innovation center, there is a strategy for training highly qualified human resources in the field of renewable energy systems, [23]. “Renewable Energy Sources” is the name of the master’s program organized by Power Engineering Faculty within University Politehnica of Bucharest, very popular and sought by graduates of technical faculties due to the development tendencies in the new energy technologies and the opportunities offered by the labor market. This master’s program “Renewable Energy Sources” is coherent, unitary and developed in accordance with the faculty of Power engineering strategy, which goal is to create high quality learning environments, capable of preparing professionals in proper implementation and operation of new energy converting technologies. The master’s degree program in renewable energy included four semesters during two year of full-time studying, and what curriculum includes is presented in Fig. 8. The program includes 120 ECTS (European Credit Transfer and Accumulation System), with 30 ECTS each semester. It is observed that the courses respond of the desired outcomes regarding the planning, designing, operation and economical issues of renewable energy technology but no implication of maintenance of these systems, too. In the process of learning the curriculum is a key factor and reflects the result of cooperation between university and the stakeholders so that to provide industry relevant competencies, [24]. In nowadays, the complexity of the converting electric energy technology at low prices and safety made that maintenance to be an important mission at high-quality standards to save money, time and resources. For this reason a master’s program in “Maintenance of the renewable energy equipment” must be as a complement

694

S. Budea and C.-A. Safta

SEMESTER I

SEMESTER II

Sustainable development

Geothermal energy and heat pumps Distributed generation impact on electrical network (E.N)

Renewable energy electric machineries Photovoltaic systems Energy recovery of surface fuels Renewable energy storage systems Research project, I

SEMESTER III

Hydrogen and fuel cells Passive solar systems Research project, II

SEMESTER IV

Financing energy projects Small hydropower and ocean energy

Internship

Wind energy Integration of microgeneration systems distributed on E.N.

Electric drives for renewable energy

Dissertation project

Research project, III

Fig. 8. Training of master’s program in “Renewable Energy Sources”, Power Engineering Faculty, University Politehnica of Bucharest, www.energ.pub.ro.

of existing ones. In Fig. 9 is presented the curriculum proposed for a master program in maintenance of renewable energy equipment. A master’s program in Maintenance Engineering seems to be unusual but it is a necessity, [25, 26]. And the assessment made in chapter two of this paper reveled that from the three types of renewable energy sources, wind energy conversion technology is mostly expose to failures and fatal accidents. So, a good maintenance planning and a critical assessment regarding the accidents causes and their circumstances can improve the design and reliability of the wind turbines. On the other hand, the reliability

Maintenance of Renewable Energy Systems - A Challenge in Academic Education

SEMESTER I

SEMESTER II

Maintenance Engineering

Operation and Management Hydropower Reliability and Statistical Analysis

Structural Integrity & Failure Material Mechanics Metheorolgical, Measurements, Forecasting & Data Aquisition

Risk Management

695

Data Base and Maintenance Monitoring & Control System

Research project, I

Research project, II

SEMESTER III

SEMESTER IV

Reliability Modeling Maintenance Cost Planning Wind Power Plant Maintenance and Operation Thermal process and Maintenance. Reliability Operational Analysis

Internship

Dissertation project

Research project, III

Fig. 9. Training of master’s program in “Maintenance of the renewable energy equipment”, proposal

modeling and simulation experiments can improve the wind turbine maintenance management and their design. Even photovoltaic panels are not maintenance free and their long time efficiency can be improved by optimizing the maintenance plan. For this reason the courses proposed in the curricula master program in “Maintenance of the Renewable Energy Equipment” included general information about maintenance and then how to apply a preventive maintenance to photovoltaic power plants, hydropower plants or wind plants. Mathematical models in maintenance planning and scheduling, reliability modeling and simulations or how to monitor the parameters for preventing maintenance using SCADA systems are consisting a minimum knowledge base for any curricula in Maintenance Engineering.

696

S. Budea and C.-A. Safta

Fig. 10. Scheme of knowledge-competencies-skills and learning methods

A good practice in the maintenance of RE equipment needs knowledge, competencies and skills related. In Fig. 10 are presented a specific scheme of knowledgecompetencies-skills and learning methods for a maintenance master’s program applied in electric renewable energy sources. Nowadays most students are visual and sensing learners and the teaching in engineering education is traditionally deductive [27]. An effective learning technique and active learning is efficient to promote problem-based learning [27, 28]. Group-design projects, computer simulations, experiments, virtual laboratory are parts of the active learning. Because “education can power renewable energy” and taking over from RECRES experience, some modules from the proposed curricula in “Maintenance of the renewable energy equipment” can be promoted as summer school courses in a lifelong learning program in Maintenance Engineering. Essentially, “our whole life is an Education - we are ever-learning, every moment of time, everywhere”, [29].

4 Conclusions Starting from a brief analysis of accidents in photovoltaic systems, hydropower systems and wind turbines, the paper attempt to emphasize the need to develop a new master program aimed at the maintenance of equipment used to convert energy from renewable sources.

Maintenance of Renewable Energy Systems - A Challenge in Academic Education

697

A curricula in “Maintenance of the renewable energy equipment” master program is proposed based on a critical analysis regarding the number of accidents caused by renewable energy technology, and the analysis regarding energy investments in renewable sources (small hydropower, wind onshore, solar PV and biomass) in EUR/kW. Faculties with postgraduate studies in renewable energy are named and is highlighted the experience of RESREC within “Transilvania” University of Brasov. The curricula of “Renewable Energy Sources” master program from Power Engineering Faculty within University Politehnica of Bucharest is presented, too. It is underline that a curriculum reflects the university’s rules and defines the program outcomes.

References 1. Nakagawa, T.: Maintenance Theory of Reliability. Springer Science & Business Media, Berlin (2006) 2. Mobley, R.K.: An introduction to predictive maintenance. Elsevier Science, SUA (2002) 3. Costinaş, S.: Ingineria mentenanţei. Concepte şi aplicaţii în instalaţiile electroenergetice. Proxima, Bucureşti (2007) 4. VGB Power Tech study. Investments and operation cost figures - Generation Portofolio (2012). www.vgb.org/en/. Accessed Apr 2017 5. Global Legal Insights. Energy 2017, 5th edn. (2017) 6. Transelectrica site. www.transelectrica.ro\7productie16.xls. Accessed Apr 2017 7. Asociatia Romana pentru Energie Eoliana site. http://rwea.ro/energia-eoliana/energiaeoliana-in-romania/. Accessed Apr 2017 8. Nakajima, S.: Introduction to TPM: Total Productive Maintenance. Preventive Maintenance Series (1988) 9. Jordan, D.C., Kurtz, S.R.: Photovoltaic degradation rates - an analytical review. Prog. Photovolt: Res. Appl. 21, 12–29 (2011). doi:10.1002/pip.1182 10. Richter, A.: Schadensbilder nach Wareneingang und im Reklamationsfall. In: Workshop “Photovoltaik-Modultechnik”, 24/25. November 2011, TÜV Rheinland, Köln (2011) 11. Visa, I., Comsit, M., Moldovan, M.D., Duta, A.: Outdoor simultaneous testing of four types of photovoltaic traked modules. J. Renew. Sustain. Energy 6, 033142 (2014) 12. International Electrotechnical Commission (IEC) 61215: 2nd edn. (2005). Crystalline silicon terrestrial photovoltaic (PV) modules - Design qualification and type approval. Edition 2, April 2005 13. International Electrotechnical Commission (IEC) 61646: 2nd edn. (2008). Thin-film terrestrial photovoltaic (PV) modules - Design qualification and type approval. Edition 2.0, May 2008 14. https://en.wikipedia.org/wiki/List_of_hydroelectric_power_station_failures. Accessed Apr 2017 15. Ugyen, D., Ghomashchi, R.: Hydro turbine failure mechanisms: an overview. Eng. Fail. Anal. 44, 136–147 (2014) 16. European Small Hydropower Association-ESHA. Guide on How to Develop a Small Hydropower Plant (2004) 17. International Renewable Energy Agency IRENA. Renewable Energy Technologies: Cost Analysis Series, 1 Power Sector, 3/5 Hydropower (2012)

698

S. Budea and C.-A. Safta

18. Summary of Wind Turbine Accident data to 31 March 2017. http://www. caithnesswindfarms.co.uk/AccidentStatistics.htm. Accessed Apr 2017 19. Feinstein, D.I., Haugel, W.F., Kardatzke, M.L., Weinstock, A.: Personnel Casualty Study, Illinois Institute of Technology Research Institute Project No. J6067 (1968) 20. Atkins, W.S.: Derivation of fatality probability functions for occupants of buildings subject to blast loads - Phases 1, 2 and 3, HSE Contract Research Report 147 (1997) 21. Atkins, W.S.: Derivation of fatality probability functions for occupants of buildings subject to blast loads - Phase 4, HSE Contract Research Report 151 (1997) 22. Ea Energy Agency. Energy Analysis, Overview of European Union Climate and Energy Policies, Copenhagen (2012). www.eaea.dk 23. Visa, I., Duta, A., Neagoe, M.: Cercetari si educatie in domeniul sistemelor de energii regenerabile in cadrul Universitatii “Transilvania” din Brasov, Romania. Lucrarile celei de-a VIII a editii a Conferintei anuale a ASTR, Sectiunea Educatie Inginereasca, pp. 424–433 (2013) 24. Malkki, H., Paatero, V.J.: Curriculum planning in energy engineering education. J. Cleaner Prod. 106, 292–299 (2015) 25. Syllabus Master Programme in Maintenance Engineering for study year 2016/2017. Lulea University of Technology. https://www.ltu.se/edu/program/TMUTA/programme-syllabus?l= en. Accessed Apr 2017 26. Dumitru, D.-C., Gligor, A.: Designing of a renewable energy training programme for engineering education. Procedia Technol. 12, 753–758 (2014) 27. Demirel, Y.: Teaching engineering courses with workbooks. Chem. Eng. Ed. 38, 74 (2004) 28. Felder, R.M., Silverman, L.K.: Learning and teaching styles in engineering education. Eng. Educ. 78(7), 674 (1988) 29. Hood, E.P.: Self-Formation: Twelve Chapters for Young Thinkers. Publisher Judd & Glass (1852)

Sustainable Buildings - Technological Innovation or a Different Way of Interpreting the Traditional House Teodora Raduca(&) University of Architecture and Urban Planning “Ion Mincu”, Bucharest, Romania [email protected]

Abstract. Considering that the impact of the irresponsible use of the planets’ natural resources became visible, combined with the effects of the pollution produced by the unreasonable exploitation of resources, the European Union decided through the Directives 2010/31 and EU 2012/27 of the European Parliament and the Council to issue documents of commitment of the Member States for assuming the overall program of meeting the requirements that, after December 2018, all buildings belonging or managed by public institutions to be nZEB, as well as all new buildings constructed later than December 2020. As a member of the European Union, Romania pledged to comply with nZEB building concepts by 2020 for all newly constructed buildings. Despite this, we find that in practice, throughout the country, the concepts of designing and building responsible according to sustainable principles are not yet widespread and respected. The sad reality on the field is that professionals (both designers and builders) are not even aware that it is mandatory to produce such buildings. Meanwhile, good quality architecture is awarded and promoted in Romania but somehow the sustainability of the design doesn’t usually make it to the criteria list. Since the theory behind the building of sustainable houses should be rapidly assimilated and that the change of this situation overnight is not possible, we consider that any form of communication and explanation of the European legal framework and of the possible approaches of meeting the Energy Performance of Buildings Directive’s requirements is necessary and also urgent. This paper presents principles of sustainable buildings and the state of the art in Romania. Keywords: Buildings


Sustainability
Architecture

1 The Awareness of the Necessity of Sustainable Design in Romanian Context Given the fact that the building industry is currently responsible for 40% out of the greenhouse gas emissions worldwide, environmental agencies all around the Globe have pointed out the necessity of a sustainable approach to future development starting with 1987 by the Brundtland report [1]. Beginning with 1987s SOS, the regulatory framework worldwide became more and more specific in its requests towards sustainable strategies implementation with special focus and efforts from the European © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_48

700

T. Raduca

Community and its Member States. A Swedish researcher - Bo Adamson from the Lund University together with German physicist Wolfgang Feist from The Institut für Wohnen und Umwelt are the first ones to lay down the principles of the passive house. The German financed research led to the overall concept and in September 1996 The Passivhaus-Institute in Dramstadt begun its activity. Measures like the Horizon 2020 programme and the Energy Performance of Buildings Directive have been adapted to Romanian regulations through the 159/2013 Law and the Ordinance no. 13/2016 for modifying and completion of the no. 372/2205 Law concerning the energy performance of buildings which introduced for the first time a definition of the nZEB building concept with its demand that 10% of the energy consumption should be covered through the use of renewable resources. In order to stimulate the interest of producing this kind of low energy consumption buildings, by the power of example, Romanian legislations states that after December 31st 2018 Building Permits will be issued for buildings of the public administration only if they comply with the nZEB requirements, while all new buildings in the private sector will have to follow the same principle starting December 31st 2020. 1.1

The Public Response to the nZEB Regulations

As the date of December 31st 2018 is one year away, it would be expected that by now, major part of the Romanian society (meaning both professionals in the building sector and stakeholders) should at least be aware, even though only superficially, of the fact that new buildings to come should comply with the nZEB building requirements. Opposed to this legit expectancy, the situation in Romania begs to differ. As a 2011 survey states, in Romania there are 5.3 million buildings out of which 5.1 are housing units and other 0.2 million cumulate non-residential buildings. As the bpie.eu platform informs trough the Implementing nearly zero-Energy Buildings (nZEB) in Romania report [2], approximately 53% out of the housing units have been built before 1970 and have an energy performance level between 150–400 kWh/m2/ year. The energy necessary for heating rises up from 55%, in flats located in collective housing units, to 80% in single family houses. In order to meet the fact that buildings built before 1990 have a low rate energy performance (180–400 kWh/m2/year), the local administrations lead this most popular national campaign, which aims at reducing energy demand for heating and cooling, known as the ‘thermal rehabilitation of existing collective housing’. In other words, this programme consists in insulating the existing collective housing buildings with expanded polystyrene (10 cm depth EPS, on 90% of the envelope) and mineral wool, remaking the waterproofing system on the rooftops, replacing the windows with uPVC ones with double pane low-e glazing and upgrading the monitoring system of measuring the heating consume in all rooms of the flats. No interventions or upgrade in the MEP system of the buildings, which even after this operation remains the original one; all the water used by all MEP systems is potable and the only ventilation available remains the natural one. There are, however, some examples of good practice among the young professionals who, by using sustainable concepts for single family houses like ‘Prispa’ [3] concept house capable of producing 9501 kWh/year from its own resources with a

Sustainable Buildings - Technological Innovation or a Different Way of Interpreting

701

yearly consumption of 7508.11 kWh/year or EFdeN [4] as solutions for their winning projects in international competitions (Solardecathlon [5]), gain a certain visibility for projects with energy consumption concern. Both projects are bioclimatic buildings and are available to visit and purchase. The National Chamber of Architects has also begun to host classes on sustainable design and building methods through its Continuous Development programme and this raises the awareness for energy economy and passive means among professionals in the first place and the wide public, as potential end-user concerned with a cheaper energy bill (Fig. 1).

Fig. 1. BREEAM/LEED - regional distribution of certifications in Romania [6]

According to data available on the Passive House international website [7], in Romania there are only three PH certified buildings and eleven registered in their database. These few examples are most welcome and generate a real enthusiasm among both professionals and public but, far from being a constant practice, they represent an insignificant number on the scale of new buildings during last 27 years. According to 2017 Colliers Report, across form single houses initiative, on the great scale of private investment in retail and offices buildings, there seems to be a rising interest for eco-certifications like LEED and BREEAM for buildings located in the biggest cities of the country (Fig. 2). Besides professionals who are in a certain contact with the principals of the sustainable design, the builders’ sector available in Romania is unfortunately unprepared and untrained in using new technologically improved construction materials with higher energy performance while the state institutions are mostly dedicated to harmonise a heavy and sometimes obsolete buildings’ legislation. According to a 2016 survey [8] on sustainable building design in general and nZEB ones in particular, distributed among the National Chamber of Architects - composed of 3763 active members - only 42 correspondents answered its simple 10 questions; fact that proves the degree of interest of the NCA members on such matters. Out of the ones who

702

T. Raduca

Fig. 2. A sorting by function of buildings BREEAM and LEED certification [6]

answered the survey, the most interested proved to be the ones with a 5–10 years practice experience (33%) while the oldest ones were the less attracted. The question concerning their actual experience in designing a nZEB building returned 40% negative answers which leads to a conclusion that only 18.8 architects out of the ones who answered the survey have had this experience. Concerning the obstacles met in the implementation of the nZEB concept, the answers for lack of request in the building market raised to 66.6% and ones claiming costs over an affordable level raised up to 68.9% along with lack of information available on both nZEB technology (44.4%) and qualified labour (46.7%). The concern regarding energy efficient buildings is still limited in Romania and this is partially due to the professional environment (architects, engineers, builders, construction material industry) who still hasn’t a proper education in sustainable design, limiting it as a mere option amongst others, not even bringing to light that instilling a friendly approach to environment through our design is not only mandatory by law, but also common sense, I dare say. On the other hand, the contemporary construction market doesn’t help much, as the main criteria of evaluating a building is the lowest price/built square meter and the shortest timespan in which an investor is able to recover its capital regardless of the quality of the building he produced. Hence, the vast majority of the buildings mirror the reality of the lowest price in both design fees and construction materials on site.

2 Methods, Tools and Adaptation Options “never divert from nature, but mold yourself onto its law and its example; this is the wisdom” (Lucius Annaeus Seneca, 4BC-65 AD, De Vita Beata - letter to Gallio) [9] “…because nature ought to be our guide; reason accounts on its behalf and asks it for advice; hence, living happy is the same thing as living according to nature’s principles” (Lucius Annaeus Seneca, 4BC-65 AD, De Vita Beata - letter to Gallio) [9]

Sustainable Buildings - Technological Innovation or a Different Way of Interpreting

703

Fig. 3. Climatic zoning of Romania during cold season [10]

Among the legal regulation which aims at harmonising the process of a sustainable approach focused on the energy demands needed to assure the comfort of the inhabitants from the earliest of design stages, the No. 386/201656 Order for modifying and completion of the technical legislative measure “Technical regulation concerning the thermo-technic calculation of the construction elements of the buildings”, named C 107-2005 approved by the Transportation, Buildings and Tourism Minister’s Order no. 2.055/2005 introduces a new climatic zone for Winter season, the 5th climatic zone, with an exterior calculation temperature of −24 °C, as shown in the map below from the Annex D of the technical regulation mentioned above. It can be seen that the nominal values of the primary energy and CO2 emissions for new buildings starting from 2015 are classified based on multiple criteria listed in the Annex L - as shown in Fig. 4. The newly introduced data bought by this legislative measure are: • Classification of buildings into five climatic zones during winter, in order to have a joint calculus temperature; • The buildings are divided into five categories based on their destination: single housing, collective housing, offices buildings, educational institutions and hospitality buildings; • For each of these categories, the limit values of both primary energy (kWh/m2year) and CO2 emissions (kWh/m2year) are fixed on to two deadlines, respectively 2015, 31.12.2018 and 31.21.2020. This completion of the law implies a standardised zoning of the country based on the geographical and environmental qualities of each region. In other words, before even starting to design, from a broader point of perspective, it is recommended to

704

T. Raduca

Fig. 4. The estimated decrease level of the energy demand and CO2 emissions for buildings as described in C107-2005 [10]

become familiar with the properties of the region where the new building is to be built and…this focus on identifying the qualities and the hazards of a plot located in a specific geographical environment is one of the first principles of bioclimatic and ecological design. At the same time, this also constitutes the universal principle followed worldwide from the first human shelter until today. Examples of the way mankind had to adapt its shelters to the geographical traits of the region can be found worldwide [11]. Meanwhile, deeply marked by the principles of the Modern Movement, the stylistic expression of the good quality Romanian projects of the recent years follows, sometimes obviously, some other times filtered by postmodern accents, the prototype of Corbusier’s “machine for living”. But as the form does not make sense without an ideological content, these buildings that represent the contemporary Romanian architecture, follow not only the stylistic principles of Modernism, but also emphasize the breaking of the tradition. The global context of natural resources that can be managed through more responsible sustainable design means (both active and passive) brings into the spotlight new technologies that, handled with precision by the designer and being produced by more developed (elaborated) technical processes, teach us (again) - after many years of modernity - how to use the sun, wind, water and soil so that buildings that are designed today can be as efficient in terms of energy used in order to produce the building materials as well as, during the usage period. To build as respectfully as possible towards nature in order to have low degree of polluting emissions that would affect the environment for the generations to come, many certified systems of sustainable designs start from principles like: the orientation of the building by the area which is more exposed to solar radiation, the design of ventilation considers the direction of the dominant winds, the use of locally available

Sustainable Buildings - Technological Innovation or a Different Way of Interpreting

705

building materials (the bioclimatic and ecological house design) and arrive at a more technical approach using new hi-tech performant materials (the Passive House standard) and systems (active house) in order to reach certain parameters. As stated on various occasions by PhD. Feist [12], The Passive House respects five crystal clear principles which, if followed can insure a minimum amount of energy demand and a good interior comfort. The principals (Fig. 5) of The Passive House can easily be adapted to environmental context worldwide, as they request: • Very good insulation of the envelope of the building (Uvalue < 0.15 W/m2K), thus limiting the loss of heat through the envelope caused by the differences in temperature between interior and exterior space, the envelope becoming the barrier which regulates the thermic transfer; • Thermal bridge-free design of the same envelope; • Climate-adapted windows; • An airtight envelope; • A ventilation system equipped with heat recovery. As passive measures of designing buildings with less energy consumption are becoming a EU trend, other professionals look back into the Roman past and into the use of active measures in order to reduce the energy consumption. Hence, active house measures like ground air collectors, labyrinth foundation designed in order to direct the air supply, the ancient Roman- inspired muro-causter and hypo-causter building wall and floor systems are means by which the building is thermally activated by natural pre-cooled air in the summertime and pre-heated air during winter [13].

Fig. 5. Illustration of the Passive House principles [14]

706

T. Raduca

But as the history of traditional architecture in the world is a huge encyclopedia of countless ways of adapting human shelters to the geographical environmental conditions, the perspective of the technical innovation is worth to be examined and discussed in comparative analysis of the systems of adapting to the geographical context, to the environmental conditions of “yesterday” and “today”. Following the principle of zoning the country trough sorting by average temperature during cold season as shown above (Fig. 3), I believe that a parallel view of both the new design methods with a friendly environmental approach and old-traditional configuration ones can be yet another source of inspiration and can generate a better integration of buildings into their context in order to reach a significant energy amount provided by renewable resources. For example, in the Romanian case, a map which displays the main traditional architectural icons of the big regions of the country (Fig. 6) leads to identifying many common points with bioclimatic architecture like some examples below. This map best displays the way in which the configuration of the traditional house has evolved trough history into meeting the specific environmental requirements of each geographical region of Romania. Each sketch displayed in the map below represents a traditional house prototype for a certain region of the country and its design features have evolved through history through their good response to environmental conditions. • The area to volume ratio which seems to be a typical trait of the traditional Romanian architecture, as it takes in to account the heat demand and heat loss influenced by the shape of the building. As houses located in mountain regions have to face both heavy rain and snow and also scarce winters and hot summers, their

Fig. 6. Map which displays the main architectural icons of the main regions of the country [15]

Sustainable Buildings - Technological Innovation or a Different Way of Interpreting

• • • •

707

special configuration tends to be a compact one. In a regular rectangular prism the average home comprises cellar on the ground floor (in order to take advantage of the thermal inertia of the earth and the household for all family members in the 1st floor. As we move South and towards the sea, houses tend to unfold only on the ground floor and all rooms are aligned to a buffer space, a porch, which helps with cooling all spaces during hot summers. Designing the shape of the roof as a response to the type and abundance of the local precipitation Fig. 7a, b; Using construction materials from local easily-available sources Fig. 8; Designing a buffer space between exterior and interior space like a porch, or a greenhouse Fig. 9; Green roofs used because of their great insulating properties Fig. 10.

Fig. 7. (a) Roof slope of  45% - mountain region of Maramures -house in abundant precipitation area and (b) roof slope of 35% - hill region house in average precipitation area

708

T. Raduca

Fig. 8. The roof is made out of straws in the Delta regions, where straw was abundant

Fig. 9. The porch (veranda) was widely used as a buffer zone South oriented, as an enclosure improving the solar radiation and heating during winter and providing shade through summer [17]

The sun generates an approximate of 5000 times more energy than the worldwide consumption. In this context the orientation of the predominant facades’ glazing in order to increase the heating during winter and decrease the strong sun radiation, trough well designed shading systems, during summer time, constitutes a means of reduction of energy demand by absorbing the solar energy available (an average of 255.9 kWh/m2) on a South-South-East orientation [16].

Sustainable Buildings - Technological Innovation or a Different Way of Interpreting

709

Fig. 10. Green roofs used in Roma homestead and workshops

3 Conclusions Contemporary buildings have to reach gradually exigent sustainable requirements and this is going to happen at low or high pace depending on various factors amongst which are the national strategical policies, the easy communication of the advantages of nZEB buildings for the end-user, and the friendly taxation systems in order to encourage stakeholders and investors. All this is yet to be done while applying the principles of integrated design in professional milieu and certification of the labor force. Bearing in mind the objectives set by Horizon 2020 and its implementation predictions by 2050 concerning the reduction of energy consumption and CO2 emissions, the study of implementing sustainable design and building systems constitutes a work in progress and a constant preoccupation during the years to come.

References 1. http://www.un-documents.net/our-common-future.pdf. Accessed May 2017 2. http://bpie.eu/wp-content/uploads/2015/10/nZEB-Full-Report-Romania.pdf. Accessed May 2017 3. http://prispa.org/sde2012/. Accessed May 2017

710

T. Raduca

4. http://efden.org/proiect/. Accessed May 2017 5. https://www.solardecathlon.gov/. Accessed May 2017 6. http://www.colliers.com/-/media/files/emea/romania/research/romania/reserch-and-forecastreport_2017web.pdf?la=en-GB. Accessed May 2017 7. http://www.passivhausprojekte.de/index.php?lang=en#s_2da7a82d7200dfdcf8d108a61f2ef456. Accessed May 2017 8. Raetchi, S-I.: Premise de proiectare a cladirlor aproape zero energie. In: Teza de doctorat, Bucuresti, Universitatea de Arhitectura si Urbanism Ion Mincu (2016) 9. Costa, I., Dumitru, V.-E., Ferchedau, S.: Seneca, Despre viata fericita. CD in lectura lui Victor Rebengiuc, Track 03, 08 (2014) 10. http://lege5.ro/Gratuit/geydknzugezq/ordinul-nr-386-2016-pentru-modificarea-si-completareareglementarii-tehnice-normativ-privind-calculul-termotehnic-al-elementelor-de-constructie-alecladirilor-indicativ-c-107-2005-aprobata-prin-ordinulnr.386/2016. Accessed May 2017 11. Dabija, A-M.: Architecture - Space - Technology a Possible Introduction. Milan (2015) 12. Feist, W.: Passive House - a convincing solution for NZEB. In: International passive house conference, Conference Proceedings, Vienna, Austria, pp. 65–76 (2017) 13. Zeiler, W.: Active house concept versus passive house (2014). https://www.researchgate.net/ publication/254844852_Active_house_concept_versus_passive_House. Accessed May 2017 14. https://upload.wikimedia.org/wikipedia/commons/b/bd/Passivhaus_section_en.jpg. Accessed May 2017 15. Institutul de proiectare Prahova: Studii de arhitectura traditionala in vederea conservarii si valorificarii prin tipizare. Locuinta Sateasca din Romania (1989) 16. Daniels, K.: The Technology of Ecological Building. Birkhauser Verlag, Basel/Boston/ Berlin (1997) 17. Photo Courtesy of Dusoiu, E-C.: Sustainability in Romanian Architecture. Tradition versus Experiment, Ion Mincu Univerisity of Architecture and Urban Planning (2016)

Multi-functional Products - A Way to Decrease the Products Environmental Impact Anca Barsan1(&), Lucian Barsan1, Aurelian Leu2, and Larisa Zafiu2 1

Renewable Energy Systems and Recycling Research Centre, Transilvania University of Brasov, Brasov, Romania [email protected] 2 Transilvania University of Brasov, Brasov, Romania

Abstract. A multi-functional product is covering more functions during its use stage. Usually, these functions are achieved by using several products. Starting with a short presentation of the ecodesign principles versus the traditional design, defining the lifecycle of a product, the paper demonstrates that the impact of the multi-functional products on the environment is lower than in case of using single function products to fulfil the same functions: less resources, less waste and emissions during the production and packaging, transport and distribution stages and at the product end-of life, less waste to be processed. During the multi-functional product use stage, the energy used is comparable with the sum of energy resources needed to act the corresponding single function products. The paper presents as a case study a new and fresh design for a coffee maker to take over the functions of three other devices: classic infusion coffee maker, syphon coffee maker and tea maker. The benefits of this new device, branded as “BRWR”, concerning its relation with the environment, is appreciated as a good example of a multi-functional product. Keywords: Ecodesign
Lifecycle Multi-functional
Optimization




Sustainable

development




1 Design and Ecodesign Even the history of industrial design is not a very long one, designers existed and created useful and good-looking artefacts long before the word “design” has been invented. A different approach permits seeing that innovation, functionality and delight were not features of industrial products, but are treasured in different ways and places on Earth: from the Inuit’s igloo to a robotized assembly line in Japan, from the stilt fishing villages in Philippines to the technologically high-risk environment of the International Space Station. The conclusion is that designer is “universally” accepted as an essential contributor to the society. The design process deals with the products development, including machines, tools, appliances and other objects, and therefore has a direct and profound influence on the environment, by using natural resources and generating pollution.

© Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_49

712

A. Barsan et al.

Starting with the early 70s, simultaneously with the Ecology development - science which studies the relationships between living organisms and their environment people begin being aware of problems related to the large amounts of waste, the decreasing of the natural resources, the ozone layer depletion, the greenhouse gases generating, the land and water acidification etc. The first action in order to solve these problems was recycling the materials from out-of-use products, which appeared as a necessary step in reducing the increasing amounts of waste, this solution being fortunately supported by the increasing of raw materials prices especially after the oil crisis [1–4]. Nevertheless, recycling several materials couldn’t solve all the environmental problems and therefore the design concerns were oriented towards other design activities connected to the environmental issues, such as: • • • •

Material selection considering the environment; Decreasing the use of natural resources; Using of production methods with lower impact on the environment; Avoiding the materials and processes potentially hazardous for the environment.

Considering the above goals, it was of great interest for the designers, when in the early 90s, the concept of sustainable development were stated by the United Nation’s Brundtland Commission, as that “development that meets the needs of the present without compromising the ability of future generations to meet their needs”. In design terms, sustainable development is about designing objects that use limited resources and effects the environment less; it is also about social responsibility and ethics. In order to fulfil the requirements imposed by the sustainable development concept, it was obviously that a product and its effects on the environment have to be evaluated on a longer period of time. This should begin with the product raw materials obtaining, the product manufacturing, its distribution, use, until its end of life. These interlinked stages are representing the “life of a product”. Considering also the possibilities of product reusing, material recycling or incineration, the concept of “life of a product” can be extended to the concept “life-cycle of a product” (see Fig. 1). In the design process, the designer has to have in mind the design principles that ensure a lower negative impact upon the environment during the entire lifecycle of the product [5]. Nowadays, a designer has to obey in his activity two categories of constrains, the classical designing constrains (resistance, reliability, financial) and environmental constrains (materials, embodied energy, recyclability, product reuse, materials availability etc.). By fulfilling all these criteria, the outcome of the designer’s work will be a (more) sustainable product, as a result of an ecodesign process. LCA (lifecycle assessment) represents a quantitative methodology design to assess the environmental impact of a product throughout its lifecycle. By using this tool, a designer can analyse how much environmental friendly a product is helping him to have a confirmation, and therefore to improve the results of his work. LCA is based on the ISO 14040/44 standards, the framework used by many international standards and sustainability initiatives [6]. Ecodesign was defined in 2006, by the European Environment Agency, as “the integration of environmental aspects into the product development process, by balancing ecological and economic requirements. Ecodesign considers environmental

Multi-functional Products

Incinerate or Disposal

713

Raw Materials Obtaining

Manufacturing

End of Life Recovery

Materials Recycling

Upgrade Reuse

Use/Consumption and Maintenance

Package, Distribution and Transportation

Fig. 1. A product lifecycle, containing the product lifecycle stages and end of life options

aspects at all stages of the product development process, striving for products which make the lowest possible environmental impact throughout the product life-cycle”. Ecodesign is to design for a safer future!

2 The Lifecycle of a Product As it was previously described, in order to evaluate its impact on the environment, a product is assessed during its entire life, through a number of consecutive and interlinked stages potentially ecologically dangerous and material and energy resources consumers. The “life of a product” starts from “raw material acquisition or generation of natural resources, over manufacture, transport, and use to the final disposal” (EN ISO 14040/1997). In case the product is recovered and somehow re-introduced into use (with or without re-processing), this whole process becomes the “lifecycle” of a product. The Fig. 1 presents the five stages of a product lifecycle, including the recovering and non-recovering options. • Raw materials obtaining consists in natural resources converting into the raw materials needed for the product;

714

A. Barsan et al.

• Manufacturing involves all the processes to obtain the product components from raw materials, but also assembling of the new product components. At the end of stage, the new product is ready to be packed and distributed; • Packaging, transport and distribution represents the stage corresponding to the transfer of the new product, after it was packed, from the manufacturer to the client/customer; • Product use (or consumption for foods or drinks) may include maintenance and repairs which extend its useful life; • The end of life stage is reached when the product cannot be used any longer because of various reasons (product failure, obsolescence, or even it is functional, the customer get rid of it). There are several options regarding the possible actions at the product end of life, as (see Fig. 2): (a) Product reuse. At its end of life, a product could be reintroduced in the life cycle, as it is (if it is any more useful), or after repairing, remanufacturing or upgrading it and, this way, the useful life of the product is extended. (b) Recycling. If a product cannot be reused, after collecting the product and its dismantling and sorting of the components materials, recycling would represent the next alternative. (c) Incineration. For energy recovery, the products and components that cannot be reused or recycled should be incinerated. (d) Land filling. If none of the previous options is suitable for the product and its materials, landfill sites can be used to store the wastes represented by the product or by some of its components. It should be the last option considered by the designer and avoided whenever one of the previous options is possible.

Fig. 2. End of life options for a product

Multi-functional Products

715

During the product lifecycle, in order that a stage to be fulfilled, it requires material and energy resources, delivering, besides the specific result of the stage, wastes and emissions which are released in the environment. The European legislation regarding the environment constrains more and more the manufacturers to limit their resources for a product and also the corresponding wastes and emissions. Usually, the manufacturers are acting towards manufacturing operations and the product end of life, considered that some curative measures as recycling, reclaiming, waste disposal, decreasing of emissions are sufficient for obtaining a more environmental friendly product. Better results could be achieved by the company with respect to the environment, but also on economical level, by developing a new design for the product they are manufacturing, in order to use less material and energy resources, this new design having also at its basis the design for reuse, design for recycling and the design for durability. Accordingly, the waste and emissions would be also reduced [7]. Designing a product to facilitate reusing, recycling or increasing its usage stage represents an important way to reduce the product impact on the environment, significant amounts of material and energy being saved and, in the same time, wastes and emissions being reduced [8–10].

3 Creating Multi-functional Products Multi-functionality represents a way of using more intensive a product during the usage stage of its lifecycle, in order to decrease its impact on the environment. A multi-functional product fulfils a variety of functions that would otherwise be carried out by separate products. As it was shown before, the impact of a product on the environment is assessed during its entire life, starting with the obtaining raw material stage, product manufacturing, product package, transport and distribution, product use and product end of life stages. This traditional, linear model is exemplified in Fig. 3, for a number of products fulfilling different separate functions. If a multi-functional product is created to take over the separate functions of all the previous products, then the traditional,

Fig. 3. Traditional linear life model for three different products

716

A. Barsan et al.

Fig. 4. The life model for a multi-functional product

linear model of the products life is replaced by a life model which is presented in Fig. 4. Considering that the multi-functional product should use comparable amounts and quality of materials as the separate products whose functions are taken over and the processes to obtain the components of the products, with separate functions and the multi-functional one, are similar, a cut down on the environmental impact during the raw material, production and distribution stages, as well as during the end of life stage should be expected. In the same time, the impact of the multi-functional product during the use stage should be comparable with the combined impact of the single-function products.

4 The “BRWR” - An Example of Multi-functional Product The “BRWR” is a 3 in 1 machine that gives the user the opportunity to select the perfect method for making coffee or infusing tea (see Fig. 5d). It consists of a borosilicate glass pot, insulating elements made of cork and several versatile aluminium connectors. The device assures two different ways for making coffee and one for making tea, as it follows: (a) Obtaining brewed coffee. The coffee is made by pouring hot water onto ground coffee beans, then allowing brewing; (b) Obtaining coffee by using the Syphon method. A vacuum coffee maker brews coffee using two chambers where vapour pressure and vacuum produce coffee; (c) Brewing tea. Additionally, the “BRWR” pot, due to its design, gives the possibility to be transported with the beverage in safe conditions. The “BRWR” device is inspired from the Chemex coffee maker (see Fig. 5a), invented in 1941, by Dr. Peter Schlumbohm, a chemist, who developed his product starting from the Erlenmeyer flask. Made simply from non-porous, borosilicate glass and fastened with a wood collar and a leather tie, it brews coffee without imparting any flavours of its own.

Multi-functional Products

717

Fig. 5. Different coffee and tea machines: (a) Chemex coffee maker [11], (b) Syphon coffee maker [12], (c) Tea brewer [13], (d) The virtual model of the “BRWR” multi-functional device

The most important characteristic of the “BRWR” is that it is replacing three other devices for coffee and tea brewing: the Chemex coffee maker (Fig. 5a), the Syphon coffee maker (Fig. 5b) and the tea brewer (Fig. 5c). The “BRWR” follows a similar pattern for materials and processes as the Chemex coffee maker. Glass is the main material used in the product of the product, but some components are made of aluminium and cork, replacing the leather and the wood from the initial Chemex coffee maker. Cork and aluminium are added for a better use, a longer life, an easier recycling process, a wider usage and, of course, for aesthetic purpose. Theoretically there is no end of life for these products if used as intended since they are especially designed to last. But when they do fail, in case of malfunction, abuse or accidental damage, they can easily be recycled or even up-cycled. The “BRWR” products are made of only three materials - glass, aluminium and cork- being 100% recyclable. The simple design of the product and its assemblies encourages the parts dismantling for a correct separation of the component materials for the recycling process.

718

A. Barsan et al.

Repurposing or up-cycling is a good alternative to recycling and it consists in re-using the product (entirely or only parts of it) in a whole other way. For example, one can turn the glass container into a vase or use it to contain other liquids. The “BRWR”, by its design, is also a product it might be considered “desirable” by the customers. A “desirable” product is that product which makes the customers being fond of it and therefore they, the customers, tend to keep it as long as they can and not to get rid of it as soon as another product from the same family appears or when a reparable failure occurs, without trying to repair it. This product has a minimalist style, with a simple shape, with aesthetic characteristics. It is simple to use it; it is replacing at least two devices, saving space from kitchens or offices where it could be used. The product considers also the present day habit of young people, especially, to carry away, with them, the beverage, on their way. The “BRWR” design permits to transport safely the beverage, even hot, by the product owner. All these factors recommend the “BRWR” as a versatile, desirable product. The product’s owners will tend to extend the lifespan of the product, another way of decreasing a product impact on the environment. The “BRWR” is an example of carrying into practice the ecodesign principles. It is a product designed with respect to the environment.

5 Conclusions Starting with the basics of the ecodesign principles versus the traditional design, enhancing the idea that the today designer has to fulfil the traditional requirement of the product design but, in the same time, he has to consider the new requirement regarding the environment and the resources, the paper demonstrates that the impact of the multi-functional products on the environment is lower than in case of using single function products to fulfil the same functions: less resources, less waste and emissions during the production and packaging, transport and distribution stages and at the product end-of life, less waste to be processed. During the multi-functional product use stage, the energy used is comparable with the sum of energy resources needed to act the corresponding single function products. To exemplify the idea and the benefits of multi-functionality and multi-functional product related to environment, a new and fresh design for a coffee maker to take over the function of at least two other devices is presenting. Considering some usual strategies specific to ecodesign, it can be demonstrated that “BRWR” is a multi-functional product designed with respect to the environment. • Due to its multi-functionality, the “BRWR” uses less material and energy resources, compared to the corresponding single function products. This decreasing of the used resources corresponds to the raw materials, manufacturing, packaging, transport, and distribution stages from the product lifecycle. Also, during the end of life stage, less waste has to be processed. • The product has a simple shape, few components and necessity simple technologies which are using not so many energy resources.

Multi-functional Products

719

• The selected materials are with low impact for the environment - glass, aluminium and cork. These materials can be obtained from natural resources with large distribution on Earth - sand, as recycled materials for aluminium and glass, or as renewable material - cork. All these materials can be recycled. • The “BRWR” lifetime is optimised, just a reduced maintenance needed. Parts of the product can be re-used or remanufactured at product end of life. • The “BRWR”, by its design - a minimalist one - fulfilled functions, saved space, ease of maintenance and disassembly, name is a product it might be considered “desirable” by the customers, who tend to keep it as long as they can increasing the lifespan of the product and its materials. • The components are assembled by using reversible joining systems by shape or friction, fact that is facilitating and encourage disassembling for an easy maintenance and, at the end of life, material separation. The previous discussed characteristics of the proposed multi-functional product the “BRWR” - shows that the ecodesign principles can be successfully carried out into practice, the result being functional products with a lower impact on the environment compared to other similar existing products.

References 1. Bârsan, A., Bârsan, L.: Ecodesign for Sustainable Development. Volume 1. Fundamentals. Transilvania University of Brasov Press, Brasov (2007). ISBN 978-973-598-104-4 2. Fuad-Luke, A.: Ecodesign. The Sourcebook. Thames & Hudson, London (2006). ISBN 978-0-8118-5532-7 3. Kutz, M.: Environmentally Conscious Mechanical Design, vol. 1. Wiley, Hoboken (2007). ISBN 978-0-471-72636-4 4. Vezzoli, C.A., Manzini, E.: Design for Environmental Sustainability. Springer, London (2008). ISBN 978-1-84800-162-6 5. European Commission: EUROPE 2020. A strategy for smart, sustainable and inclusive growth, Brussels (2010) 6. https://www.pre-sustainability.com/. Accessed Apr 2017 7. Reid, A., Miedzinski, M.: Eco-innovation. Final report for sectorial innovation watch (2014). www.technopolis-group.com. May 2008. Accessed Mar 2017 8. Barsan, A., Barsan, L.: The ecodesign education-a necessity towards sustainable products. In: Visa, I. (ed.) Sustainable Energy in the Built Environment - Steps Towards nZEB, Springer Proceedings in Energy, pp. 495–502 (2014). doi:10.1007/978-3-319-09707-7_37 9. Russell, D.A.M., Shiang, D.L.: Thinking about more sustainable products: using an efficient tool for sustainability education, innovation, and project management to encourage sustainability thinking in a multinational corporation. ACS Sustain. Chem. Eng. 1(1), 2–7 (2013). doi:10.1021/sc300131e 10. Gmelin, H., Seuring, S.: Determinants of a sustainable new product development. J. Clean. Prod. 69, 1–9 (2014) 11. https://commons.wikimedia.org/wiki/File:Chemex_Coffeemaker.jpg. Accessed June 2017 12. https://commons.wikimedia.org/wiki/File:Yama_Vac_Pot.JPG. Accessed June 2017 13. https://commons.wikimedia.org/wiki/File:Vanilla_Tisane.jpg. Accessed June 2017

Using “Serious Game” for Children and Youth Education in Sustainable Energy Field and Environment Protection Mihaela-Ioana Baritz(&) Advanced Mechatronics Systems Research Center, Transilvania University of Brasov, Brasov, Romania [email protected] Abstract. Lately, it has been demonstrated that the use of “serious game” in the education of children and youth can open new opportunities for transmission of information and development of technical skills. For this, increasingly more educational environments apply to the transmission of information, knowledge and technical systems development by making practical or virtual applications, like “serious game”, in which our children or students can dynamically participate. In this paper, in the first part, the principles of the concept of partnership development through mentoring by which wanted students involvement in educational effective and understanding practical activities, also application aspects of environmental protection and efficient use of sources of green energy are presented. In the second part of paper, the concept was materialized in the design, implementation and use of checkerboard constructed from recoverable materials and green energy sources. Youth participation, both in design and in finding practical solutions for construction and the propagation of information about the environment or energy sources, for young students having the same age with them were the main objectives of this approach. Chess, with all its qualities became the mean by which can realize the objective of the educational process. In the final part of paper, conclusions recorded from carrying out of this project are presented. Keywords: Education protection
Chess


Serious game
Sustainability energy
Environment

1 Introduction The concept of learning through the game has become an effective way of transmitting information and demonstrating physical, social, economic or financial principles. A lot of media work during this time to develop communication channels between different cultural levels, and the first choice was game - direct, interactive, or digital, or community. At this time, the “game industry” is a dynamic field, with a strong financial impact, and it is getting more and more in areas that seemed untouchable by such means. So for the energy field, serious play has become a means of communication, information, education and even social development for the population in general. © Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5_50

Using “Serious Game” for Children and Youth Education

721

As shown in [1] for example, US energy consumption in 2006 was structured in the economic sector in a balanced proportion, and in the residential sector there was a diverse range of consumption, the highest value being allocated to the heating of dwellings and of the workspace (Fig. 1).

Fig. 1. Values of energy consumed by economic and residential sector (United States 2006) [1]

From the point of view of informing and educating the population (of any age) in the field of energy saving, it has been found that information reaches faster and more efficiently on accessible, known routes and even from unused domains so far. As shown in various studies, authors like “Thomas Malone has identified games into three main ways to motivate players: fantasy challenge and curiosity. When a player is focused in a game, he is more likely to solve complex problem and interpret new knowledge. As Prensky’s interpretation, the challenges presented and your ability to solve them is almost perfectly matched, and you often accomplish things that you didn’t think you could, along with a great deal of pleasure. Play might enable a learner to solve problems that they might otherwise not be able to address in a different state of mind” [1]. The benefits of e-learning and digital versus the traditional knowledge transfer system can be seen at all levels of education (from primary school to university) and can be quantified through flexibility, minimal costs by reducing paper usage, accessibility and comfort by increasing the speed transfer of information.

2 Serious Games The virtual simulations used to build serious games (SG) are dynamic elements of playing complex and deep information in the field of energy consumption or environmental protection which makes the impact important and lasting. “There are some existing games intended to reduce energy consumption and change energy related beliefs of users” [2]. For example, in computer game EnerCities, “the player has to build his own metropolis with the goal to keep the city sustainable. Players have to balance the People Planet and Profit while maintaining electricity supplies, energy conservation and reducing CO2. 2020Energy is other online serious game about energy efficiency,

722

M.-I. Baritz

renewable energy and sustainable development. The name 2020Energy is due to the expected energy resource depletion and the possible deadlock in the year 2020. The player has to help people to make better energy choices” [2] (Fig. 2).

Fig. 2. Main windows of game 2020Energy [3]

Serious games contain multiple components and can be developed by simulations, modelling or just personalized interactivity. In addition to these forms, physical components can also be developed to mobilize young people to directly address environmental issues, reduce energy consumption, or develop green energy sources. A fundamental part of the learning process is driven by the feedback of educational activities based on serious games. Some of these feed-backs may even be “changing people’s energy consumption patterns in the home” [4] or changing behaviour in society relative to reusable materials or electricity consumption. From the point of view of the effectiveness of a serious game, researches has set a number of 21 criteria grouped into four categories real-life energy use/management, goals and feedback, social comparison and personal relevance. Energy serious games (ESG) have their own specific criteria to meet in terms of making energy use more visible, comprehensible and personally relevant and encouraging players to become more energy literate. While excellent frameworks exist to evaluate SGs generally, these were insufficient for the evaluation of the potential effectiveness of an energy SG. For that it is necessary to have a set of criteria for reviewing the effectiveness of energy SGs that can also identify options for further development of games that increase energy literacy and potentially help to reduce consumption [5]. From the analysis of the present information, in the current world and European context of development and adaptation of the educational processes to the evolution of science and culture, there is a systematic and complex orientation of approaching other ways of communication between the educator and the disciple. The role of empowerment in the development of thinking, learning, or communication between people is an essential skill that develops especially in the first period of life, when the ability of young people to assimilate knowledge is much more dynamic and the way of transmission must be much clearer and simpler - even in the form of a serious game…!! [6].

Using “Serious Game” for Children and Youth Education

723

Therefore, starting from these important aspects - responsibility, thinking, scientific and cultural knowledge, communication, game, we propose that the objectives of this research be developed in two directions, and in the future to diversify and refine in function of results.

3 Experimental Setup The main objectives set in the project are: Developing practical skills for design, design and construction of objects with aesthetic and functional load, made of reusable materials to protect the environment; Designing and implementing a procedure to stimulate the use and reuse of plastic materials through chess games. These main objectives have been applied with the volunteer student group to design, realize and use, through chess, those elements that open young people to the interest and desire to engage in environmental protection and the use of green energy (Fig. 3).

Initial space to develop serious game “Chess” Fig. 3. Collecting, selecting and identifying the location for chess board (inside) construction

For this action, some forms of PETs have been collected and selected to be used to create new forms of chess pieces. The action consisted of collecting as many shapes and sizes of PETs as possible in order to develop the customized chess pieces and to identify a suitable location for chess game. The collection of materials (plastic, cardboard, natural materials), PETs, metal parts, wood or any other reusable material was possible by involving all the students participating in the project. Thus, chess pieces from PETs and reusable materials (Fig. 3) were designed and made by the students in practical classes. Chess boards were placed in two different shapes and positions (Figs. 4, 5, 6 and 7) and chess series between students team’s, during break courses or in different activities are developed (Fig. 8). The motivation and development of this serious-game project lies in the fact that if students succeed in coagulating a group to assume and implement this new concept, then, this action can be extended over time to other categories of students, on the same coordinates of mentoring and communication. Involvement of pupils in joint actions with students (their ages, concepts and methods of interaction are very close), the possibility of knowing by the students from high school the professional activity of the university environment in all its coordinates, the creation of interactive competitions, the identification of common volunteer

724

M.-I. Baritz

Fig. 4. Chess pieces shape’s designed for chess table (inside position)

Fig. 5. Chess pieces shape’s built for chess table (inside and outside position of chess table)

Fig. 6. Plastic pieces on vertical magnetic table designed for chess and other similar games

Using “Serious Game” for Children and Youth Education

725

Fig. 7. Plastic chess pieces on horizontal table designed for chess and other similar games

Fig. 8. Running the chess game with students team on the University Days, on March 1, 2017

activities are part of the variants of partnership development through mentoring between students and students from high school. What can be more exciting and stimulating than to support and help to build teams of young people (students, pupil) who are responsible for the environment, involve each other, support themselves in different actions and improve, at the same time, the professional skills?

726

M.-I. Baritz

Fig. 9. Decorative items and chess pieces (support for flower pots and boxes of gifts) made of reusable materials (PET)

This is why the creation of a mentoring strategy, as widely as possible, between students and pupils through which the triad of educational values, empowerment and involvement is the focal point of professional activity, will benefit both structures involved. The materialization of this goal will be much broader, starting with identifying variants and designing them to create spaces for the same chess game accessible to students, protecting the environment, using green energy, continuing with active support for customized projects and not least, the coordination and guidance of support activities. These activities focus on developing communication skills among young people, creating and optimizing new methods of involving students in mentoring and tutorials and, last but not least, enhancing professional skills in finding practical solutions for materials reuse. An important part of the students’ activity in this serious game consisted also in the construction of a material for promoting, describing and explaining the concept of project “S.A.H.” (Fig. 10). This was materialized in a flyer and a poster with easy-to-identify design elements and assimilated to the game of chess. According to the established procedures, the chess game (board and pieces) is equipped with the help of teams of 4 pupils each having a well-defined role in the construction of the pieces (use of equipment, devices, consumables). The chess game is used in teams of 4 pupils, of which 2 pupils actually perform the chess game (principal) and the other two (second) help to position the pieces outside the boards and to ensure the correct way of playing the game stages. The stages of a complete chess game cycle must be ensured by the participation of a group of at least 10 pupils in mentoring with at least 4 students to train the groups of students (2 mentoring students and a group of 5 pupils - 4 active pupils and one student book).

Using “Serious Game” for Children and Youth Education

Fig. 10. Promotional flyer, diploma and poster of S.A.H. project

Fig. 11. Mentoring guide ver.01

727

728

M.-I. Baritz

Fig. 12. Promotional features for presenting the S.A.H. concept

These mentoring and tutoring actions are based on the principles outlined and developed in the Mentoring Guide (Fig. 11), conceived within the project. Student activities within this serious game project were also stimulated by the use of customized insignia or the use of general use items that created a sense of belonging to a dynamic and involved acting group (Fig. 12) [7].

4 Conclusions Through this project-concept, a series of activities of guidance, information, awareness and development to students and to high school student’s skills to engage in volunteer actions in terms of environmental protection, the use of green energy and elements/ components which a serious game can offer to them. In this respect, students used reusable materials for the construction of chess games, which they have modelled, assembled and built so that the result has an aesthetic effect, to fit into the ambient area and to become a stimulated for the creation of chess pieces or other decorative items (Fig. 9). The S.A.H. (Applied School with Talent) project, as an action and concept, allows multi-stage development like: concept and design, technique and technology, awareness and involvement in environmental protection, support for physiological sensory recovery processes, system development dedicated and not least of personal development, socialization, volunteering and mentoring of all “actors” involved in the educational process. Change in this area can be achieved through changes in the perception of evolution, mentality, education, design, and technological achievements that improve the environment and its relationships with human society. Thus, serious game chess is a game in which we discover a series of qualities, features and many behavioral spaces achieved by these features. Starting from the game’s elegance and durability feature, we can identify a number of modeling qualities that we can explore, define and apply in terms of human interaction, educational processes, and development possibilities. Youth education in the spirit of environmental protection and the development of renewable energy systems is a continuous, dynamic and generous activity that can lead to the change of mentalities and the improvement of life even through the use of serious game!!

Using “Serious Game” for Children and Youth Education

729

Acknowledgments. In these experiments we’ve developed the activities with equipment from optometric laboratory and “S.A.H.” project at University Transylvania of Brasov. We want to thank very much to the participants (students) at this project for their understanding, permanent implication and dedication.

References 1. Yang, L.: BIM GAME: A “Serious Game” to Educate Non‐experts about Energy‐related Design and Living, Degree of Master of Science in Architecture Studies. Massachusetts Institute of Technology (2009) 2. Kashif, A., Ploix, S., Dugdale, J., Reignier, P., Shahzad, M.K.: Virtual simulation with real occupants using serious games. In: Proceedings of BS2015: 14th Conference of International Building Performance Simulation Association, Hyderabad, India (2015) 3. http://www.2020energy.eu/game. Accessed May 2017 4. Bang, M., Svahn, M., Gustafsson, A.: Persuasive design of a mobile energy conservation game with direct feedback and social cues. In: Proceedings of DiGRA (2009) 5. Wood, G., et al.: Serious games for energy social science research. Technol. Anal. Strateg. Manag. 26(10), 1212–1227 (2014). http://dx.doi.org/10.1080/09537325.2014.978277 6. Baritz, M.: Serious games for serious vision problems of children. In: The 12th International Scientific Conference eLearning and Software for Education, eLSE Bucharest (2016) 7. Baritz, M.: Raport of SAH Project. University Transilvania Brasov (2016)

Author Index

A Aelenei, Laura, 25, 641 Agathokleous, Rafaela, 201 Andronic, Luminita, 550 B Badescu, Viorel, 434 Baiceanu, Mihai, 70 Bancuta, Iulian, 39 Baritz, Mihaela-Ioana, 720 Barjoveanu, George, 473 Barsan, Anca, 711 Barsan, Lucian, 711 Bartha, Sándor, 227 Blaga, Robert, 337 Bobei, Andreea, 317 Bogatu, Cristina, 263, 521, 566 Bostan, Ion, 490, 500 Bostan, Viorel, 490, 500 Budea, Sanda, 686 Burdovà, Eva Krìdlova, 168, 666 Burduhos, Bogdan, 3, 50 Butacu, Claudiu, 70 Buzatu, Doru, 348 C Cailean (Gavrilescu), Daniela, 473 Campean, Teofil, 611 Catalina, Tiberiu, 70 Cazan, Cristina, 375 Chelaru, Andreea, 586 Ciobanu, Daniela, 443 Ciobanu, Oleg, 490 Ciobanu, Radu, 490 Comsit, Mihai, 364 Cornea, Octavian, 460

Cosnita, Mihaela, 375 Covei, Maria, 521 Craciunescu, Dan, 317 Cretescu, Nadia, 283 D Dabija, Ana-Maria, 80, 632 Daguenet-Frick, Xavier, 239 Dinolov, Ognyan, 120, 395 Dobosi, Ioan Silviu, 421 Dragan, Florin, 317 Draghici, Camelia, 566 Dudita, Mihaela, 239 Dulgheru, Valeriu, 490, 500 Dumitrescu, Lucia, 566 Duta, Anca, 3, 50, 263, 283, 375, 513, 521, 550 E Enesca, Alexandru, 263, 550 Evstatiev, Boris, 120, 395 F Fara, Laurentiu, 317 Farkas, Istvan, 218 Fekete, Istvan, 218 Fried, Miklos, 513 G Gabrovska-Evstatieva, Katerina, 120, 395 Gantenbein, Paul, 239 Gartner, Mariuca, 513 Gavrilescu, Dan-Alexandru, 611 Gavrilescu, Maria, 611

© Springer International Publishing AG 2018 I. Visa and A. Duta (eds.), Nearly Zero Energy Communities, Springer Proceedings in Energy, DOI 10.1007/978-3-319-63215-5

731

732 Gheorghe, Marin, 513 Gladis, Vitalie, 490, 500 Gonçalves, Helder, 25 H Hulea, Dan, 460 I Ilie, Adrian Constantin, 247 Iordache, Florin, 102, 296 Iorga, Mirela, 405 Isac, Luminita, 263, 521 J Jaliu, Codruta, 443 K Kalogirou, Soteris, 201 Karanasios, Nikolaos, 666 Krozer, Yoram, 89 Kusnir, Marek, 168 L Leu, Aurelian, 711 Lucaci, Dora, 566 M Manciulea, Ileana, 566 Mandric, Eugen, 102, 296 Mihai, Petru, 666 Mihailov, Nicolay, 120, 395 Mirica, Marius, 348, 405 Miron-Alexe, Viorel, 39 Moldovan, Carmen, 513 Moldovan, Macedon, 3, 50, 129, 364 Muntean, Daniel, 148 Muntean, Nicolae, 460

Author Index P Panait, Ramona, 263 Panaite, Florin, 443 Pasti, Mihai Toader, 70 Paulescu, Marius, 337, 434 Pavel, Stefan, 421 Perniu, Dana, 263, 521 Petcu, Cristian, 159, 651 Petra, Sorina, 179 Petran, Horia-Alexandru, 159, 651 Popa, Nicoleta, 586 Puppa, Marco Della, 666 Putz, Mihai, 348, 405 R Raduca, Teodora, 699 Raducanu, Eduard-Daniel, 70 S Sabadus, Andreea, 434 Safta, Carmen-Anca, 686 Saulescu, Radu, 443 Silva, Carlos, 641 Sobor, Ion, 500 Stan, Daniel, 421 Sterian, Paul, 317 Szava, Gabriel Fischer, 421 T Talpiga, Mugurel-Florin, 102, 296 Teodosiu, Carmen, 473 Toderasc, Mihai-Constantin, 159 U Ungureanu, Viorel, 148

N Neagoe, Mircea, 283, 364, 666 Nicolae, Ileana, 179 Niculuta, Marian-Ciprian, 651

V Vajda, Boglárka, 227 Vasile, Nicolae, 39 Vasile, Vasilica, 159 Vilcekova, Silvia, 168 Visa, Ion, 3, 129, 247, 283, 375, 550 Visa, Maria, 586 Vonderviszt, Ferenc, 513

O Olivito, Renato, 666

Z Zafiu, Larisa, 711