Delft University of Technology Design Features of Product-Integrated PV An Evaluation of Various Factors under Indoor Irradiance Conditions Apostolou, Georgia DOI 10.4233/uuid:869ccea8-f765-418c-881f-96689f49b19d Publication date 2016 Document Version Final published version Citation (APA) Apostolou, G. (2016). Design Features of Product-Integrated PV: An Evaluation of Various Factors under Indoor Irradiance Conditions. Delft University of Technology. https://doi.org/10.4233/uuid:869ccea8-f765- 418c-881f-96689f49b19d Important note To cite this publication, please use the final published version (if applicable). Please check the document version above. Copyright Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons. Takedown policy Please contact us and provide details if you believe this document breaches copyrights. We will remove access to the work immediately and investigate your claim. This work is downloaded from Delft University of Technology. For technical reasons the number of authors shown on this cover page is limited to a maximum of 10. GBeer Design Features of Product-Integrated PV e o Johnston r An Evaluation of Various Factors under g Coiarnwell Indoor Irradiance Conditions A Self p o s to lo u D e s i g n F e a t u r e s o f P r o d u c t - I n t e g r a t e d P V Georgia Apostolou Design Features of Product-Integrated PV: An Evaluation of Various Factors under Indoor Irradiance Conditions Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus prof.ir. K.C.A.M. Luyben; voorzitter van het College voor Promoties, in het openbaar te verdedigen op maandag 27 juni 2016 om 12:30 uur door Technische Universiteit Delft, June 2016 Georgia APOSTOLOU Mechanical Engineer National Technical University of Athens geboren te Athene, Griekenland II This dissertation has been approved by the promotor: Prof.dr. A.H.M.E. Reinders Composition of the doctoral committee: Rector Magnificus, Chairman Prof.dr. A.H.M.E. Reinders, Delft University of Technology Independent members: Prof.dr.ir. J.M.P. Geraedts, Delft University of Technology Prof.dr.ir. J.C. Brezet, Delft University of Technology Prof.dr. S.C. Pont, Delft University of Technology Prof.dr.ir. A.L.P. Rosemann, E indhoven University of Technology Dr. W.G.J.A.M. van Sark, Utrecht University Design Features of Product-Integrated PV: An Evaluation of Various Factors under Indoor Irradiance Conditions Thesis Delft University of Technology, Delft, The Netherlands Design for Sustainability Program ISBN : 978-94-6186-662-2 Book design by Panagiota Sampani Printed by Tziolas Copyright © 2016 by Georgia Apostolou. All rights reserved. No part of this publication may be repro- duced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording or otherwise without any written permission from the author. III To Yannis IV SUMMARY This thesis explores the field of product-integrated photovoltaics (PIPV), a term which is used for all types of products that contain solar cells in one or more of their surfaces, aiming at providing power during the product’s use. Product-integrated photovoltaics (PIPV) began to be widely introduced around 2000, although the use of PV systems in products dates back to the 70s. PIPV includes products such as PV-powered boats, aircrafts, cars, bicycles, camping tents, street lights, recycling bins, decorative lights, PV-powered watches, calculators, PV-powered lamps, sensors, chargers, toys, low-powered kitchen appliances, entertainment appliances or PV-powered art objects. The incorporation of PV systems in products could offer various benefits, such as enhanced functionality of the product as a result of energy autonomy, and independence and freedom of use due to the absence of a connection to the electricity grid, as well as the opportunity to reduce the capacity of batteries in portable products and therefore making them more sustainable. Furthermore, photovoltaic products represent a very reliable solution for the supply of electricity in areas, which lack access to an electricity grid. This thesis focuses on the development of scientific and technological knowledge concerning product-integrated PV (PIPV), as it focuses on the aspects that designers need to take into consideration when designing PV products. This research is interdisciplinary by nature due to its embedding in the field of industrial design engineering, regarding the technological aspects of PV technologies in products and user interaction with PV products. This research focuses on aspects related to design engineering of indoor PV products and to the design of products with an acceptable performance for users, issues that have not been completely addressed by other researchers. Its multi-disciplin- ary character is the point where this work significantly differentiates from previous studies. Based on the relevance of sustainable product design for product- integrated PV, this thesis combines the technical knowledge of PV technologies, indoor irradiance conditions and performance of PV cells and PV products in environments with low irradiance together with the typical behavior of users with these products and the way this behavior influences the performance of the products themselves. Besides being directed towards researchers, results of this study are useful for industrial designers who are developing PV products. Manufacturing of PIPV and the combination of PV with other renewable energy sources have not been addressed in this dissertation. V In order to clarify the two types of PV-powered products, it is necessary to explain here that there are products that have integrated PV cells in one or more of their surfaces (and these are the PIPV, as we refer to them in this thesis) and those that are powered by PV cells, which are not attached on the product’s surface, but constitute an accessory of the basic product. The study approached the aforementioned issues by investigating: • Why research on product- integrated PV is important? • What is product-integrated PV and what are PV products? For example: What are the design features and function materials that these products use? • Where are the PV products used? That is to say under which conditions and irradiance are they used? • How do users interact with the PV products? The sub-questions, which helped to approach the main research question in a systematic and logical way, were: • What are the design features that existing PV products have? • Which are the indoor irradiance conditions? • What is the efficiency of different PV technologies indoors? • How do users interact with PV products? How could users’ interaction with indoor PV products influence the performance of the products? Finally, this thesis intents to support designers by exploring the topic mentioned above which they should take into consideration if they want to design indoor PV products with a better performance than the existing ones. It is worth noting that since 2011, when this research study started, many aspects of photovoltaic powered products have changed. Firstly, more PV products of various product categories for both outdoor and indoor use were launched on the markets. The PV products that were used during the tests and the field trials of this research study are the products that were commercially available at the time of the beginning of this research. Over four years of research, it was observed that many aspects and design features improved in PV products, such as their technical features (e.g. materials, use, electrical and mechanical components, etc.) and their aesthetics. In this research the technical features of PV products have mainly been analysed, because this knowledge is essential for the improvement of the products, mainly regarding their performance and usability. This analysis is useful for designers and researchers, as other researchers in the field have not addressed all the information that it offers as yet. VI In Chapter 1 a short market analysis on PV-powered products for indoor use shows that most of the available products at present offer sub-standard and poorly designed solutions. While investigating commercially available PV lighting products, which is currently the largest area of PIPV, it can be concluded that apart from being PV-powered and portable, most products do not have any additional features. The majority of PV products that are commercially available at present are of low quality and perform insufficiently. However, there are a few PV products that have sufficient performance and that are of good quality. In Chapter 2 various PV technologies and the basic knowledge concerning the integration of PV cells in consumer products were briefly discussed, serving as an introduction to the most common PV technologies that are used for commercial PV product applications, which are mono-crystalline, multi-crystalline and amorphous silicon solar cells. It was found that several factors exist that greatly affect the performance of PV cells in products, such as indoor irradiance conditions, the efficiency of PV cells in an indoor environment, the area of the PV cell surface, shad(ow)ing of PV cells, as well as the combination of the PV cell and battery technologies. Subsequently, Chapter 3 focuses on identifying which product- integrated PV and PV products are and what their design features are. Various categories of product-integrated photovoltaics can be identified: consumer products with integrated PV, lighting products, business-to-business applications, recreational products, vehicles and transportation, and arts. Amongthese product categories outlined above, the majority of products are mainly high power PV products designed for outdoor use. Different product categories are modified for indoor use. The low power PV product categories for indoor use range from 1 mW up to a maximum of 10 W and they are defined as follows: consumer products (including mainly toys, calculators, watches, entertainment applications, PV chargers for indoor use), lighting products (including low power desk lamps) and art objects (Objets d’ art) (requiring low energy supplies). Moreover, an overview of PV product’s general design features is provided. The overview is based on a survey of preselected PV products PIPV’s power level ranges from several mWatts up to hundreds of kWatts. Four PV system categories were determined: (1) autonomous PV system including battery, (2) chargeable PV system including battery, (3) autonomous PV system excluding battery and (4) autonomous hybrid PV system including battery. The majority, namely 65 out of 90 PV products analysed consist of an autonomous PV system with batteries. 67 % of PV products are used outdoors, while around 14 % are used indoors and 19 % both indoors VII and outdoors. Approximately 30 % of the low power PV products in the range of 0 to 17 Wp use thin film solar cells (a-Si), whereas 55 % of high power PV products in the range of 17 Wp to 27 kWp use crystalline silicon solar cells (x-Si) or a-Si. 86 % of PIPV products use an energy storage device, while 14 % do not use any batteries. Chapter 4 explores the indoor environments in which PV products are used. In this chapter, results of measurements of irradiance under various conditions indoors are presented. First, the theoretical framework for indoor irradiance is given and next measurements under various conditions are presented. According to the above- presented measurements and results, it is concluded that indoor irradiance differentiates broadly according to the orientation of the room, as well as according to the type of light sources, either natural or artificial, and the distance between them. Results showed that typical indoor irradiance (total diffuse radiation) in an office in the Netherlands during June ranges between 1 and 25 W/m2 depending on the orientation of the room towards the sun. However, these values cannot be considered fixed, as they are strongly influenced by the latitude and longitude of the room, the season (winter, summer, etc.), weather conditions (sunny, cloudy, rainy, etc.), the use of artificial lighting (amount of lamps, type of luminaires, either LEDs, CFL or halogen lamps), objects and optical interactions (e.g. shadows, interreflections) at the indoor environment, distance between windows and artificial light sources, type of glazing etc. Indoor irradiance based on artificial lighting usually ranges between 1 and 7 W/m2, which is sufficient for low-powered PV products to function at this environment. Based on the above conclusions, it is inferred that very low power PV products with power consumption in the range of μW up to a few mW could be used indoors, such as clocks, calculators, excent lighting products, sensors, temperature indicators, toys, chargers or PV-powered remote controls for televisions. During the design process of an indoor PV product, designers should consider the typical indoor irradiance range as discussed above. Taking these values as a starting point, designers will make critical decisions regarding the products that can perform sufficiently under these conditions and make the right choices beforehand. Chapter 5 explores the efficiency of PIPV with the help of a simple model, which estimates the performance of PV cells in an indoor environment and under mixed indoor light that partially contains outdoor light. To start with, the efficiency of different PV technologies is discussed. These PV technologies, which were used indoors during the experiments and the results of the measurements are presented and analyzed. A mathematical model of the indoor performance of PV cells is proposed, which estimates the indoor efficiency of various PV materials.