Optics and Heat Transfer for Asymmetric Compound Parabolic Photovoltaic Concentrators for Building Integrated Photovoltaics
Tapas K. Mallick
Thesis submitted for the degree of
Ph.D
Faculty of Engineering
July 2003
Abstract
Concentration of solar energy onto photovoltaic materials reduces overall system cost when concentrator cost is less than the displaced photovoltaic (PV) material. Concentration provides higher solar radiation intensity at the PV material increasing electrical power generation per unit PV area. Systems of asymmetric compound parabolic photovoltaic concentrators (ACPPVC) have been designed, fabricated and experimentally characterised for building façade integration in the UK. The ACPPVC system has an acceptance half-angle of 50° and 0° leading to a geometrical concentration ratio of 2.01. In house built Finite Element codes were used for Optics and heat transfer (CFD analysis) of the line-axis solar energy systems. Systems of air filled ACPPVC have been modelled for;
Convective behaviour inside a single trough and between consecutive troughs together with the effect of solar cell operating temperature is presented. Predicted optical efficiency was 85% for a wide range of solar incidence angles. A 95°C solar cell surface temperature was predicted for incident radiation of 1000 Wm-2. Forced convection at the rear aluminium plate and at the glass aperture cover reduced the solar cell surface temperature by 35°C.
The three trough ACPPVC-50 system was studied experimentally using a continuous solar simulator. The three trough ACPPVC-50 achieved a fill factor of 65% for a range of solar radiation intensities incident at the aperture cover. Two five-trough ACPPVC-50s incorporating modified reflector troughs were characterised experimentally under outdoor environmental conditions. Electrical output and temperature effects were investigated for;
The maximum power available from the ACPPVC-50 increased by 65% (i.e. a power ratio of 1.65) compared to the theoretical power ratio of 2.01. A power loss analysis indicated that the ACPPVC-50 can achieve a power ratio of up to 1.94 when solar cell spacing is reduced from 52 mm to 2 mm.
Notes on Access to Contents
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Acknowledgement
This thesis is the result of three and half years of hard work whereby I have been accompanied and supported by many people in various ways. It is a great pleasure that I have now the opportunity to express my gratitude to all of them.
First and foremost, I am deeply indebted to my supervisors Prof. P. C. Eames and Prof. B. Norton without whom this thesis would have read like Edward Lear’s “Complete Nonsense”. Prof. Eames and Prof. Norton have devoted so much time and effort in teaching me; from the basics of CFD to writing a research work that my labour would never be able to match. I owe them a lot of gratitude. I just aspire to be like them if I ever become a teacher. I never will forget the days when I did simulations, every single day whenever I had any problem I went to meet Prof. Eames and received valuable comments, a special thanks to you! I have no words to express my sincere gratitude to my supervisors for their invaluable corrections. Prof. Eames and Prof. Norton have been outstanding supervisors, whom I would not have traded for anyone else.
It is my great pleasure to get an opportunity to undertake my PhD work at CST for which I am deeply grateful to Prof H P Garg, who insisted me to work in Photovoltaics.
In general the CST, Centre for Sustainable Technologies is full of nice people providing the important social environment needed to do a good job, far away from home, thank you all!! I would specially like to thank Dr. T. J. Hyde for helping me to design and fabricate my experimental system. I am also thankful to Frank Stewart for supporting me throughout construction and monitoring of my experimental system. Thanks to Dr. P. Griffiths for helping me with the UNIX system which I required for my simulations. Special thanks to Dr. N. Hewitt, Dr. M. Smyth, Dr. S. Lo, Dr. Ming and Dr. Fang for their encouragement and support throughout my whole research period. Good luck to all research students specially Sarah, Jayanta, Chris and Harjit without their company life would have been much more difficult, thank you all!
Dr. Adhikari is acknowledged for encouraging me to undertake PhD at UUJ while I was at IIT, Delhi. My special thanks to all my friends living at India and abroad for communicating and supporting me whenever I needed. Many more people participated in various ways to ensure my research succeeded and I am thankful to all of them.
This research was supported and funded by the Engineering and Physical Sciences Research Council, Swindon, UK. I would like to thank BP Solar, Madrid, Spain for supply the Photovoltaic cells and the EVA used in this work.
I cannot say enough about my father Satkari and mother Bharati for making me who I am today and for being supportive all the time in all that I have done and that I ever wanted to do, a sincere gratitude to them! My brother, Dr. Tapan, inspired me since I was a child. His guidance, care and direction to all my siblings never can be forgotten. A big thanks to my sister Priti, sister-in-law Prativa and brother-in-law Swapan without their love, care and support this work never could have been finished. My brother, Sudipta has been a driver of every sector of life. I used to have good fun whenever I am with Chinu, Papan and Tulu, love you all!!
CONTENTS
Page No.
Abstract
Note on access to contents
Acknowledgements
Contents i
List of Figures vii
List of Tables xxv
Nomenclature xxvii
Abbreviations xxxii