PERFORMANCE ANALYSIS OF HYBRID PHOTOVOLTAIC/ THERMAL (PV/T) ACTIVE
SOLAR DISTILLATION SYSTEM
By
SHIV KUMAR
Centre for Energy Studies
Submitted in fulfilment of the requirements of the degree of Doctor of Philosophy
to the
Indian Institute of Technology, Delhi
November, 2008
67_8.16!523.c)
SW1-P
CERTIFICATE
It is certified that the thesis entitled, "Performance Analysis of Hybrid Photovoltaic/ Thermal (PV/T) Active Solar Distillation System" submitted by Shiv Kumar to Indian Institute of Technology, Delhi is worthy of consideration for the award of the degree of 'Doctor of Philosophy' and is a record of the original bonafide research work carried out by him under my guidance and supervision. The results contained in the thesis have not been submitted in part or full to any other University or Institute for the award of any degree or diploma.
(D G N.Tiwari) Professor
Centre for Energy Studies Indian Institute of Technology Hauz Khas, New Delhi- 110016
(Dr. Subodh Kumar) S.S.0-I
Centre for Energy Studies Indian Institute of Technology Hauz Khas, New Delhi- 110016
Date: November, 2008
ACKNOWLEDGEMENTS
I have immense pleasure in expressing my heart felt gratitude to my supervisor, Prof. G.N. Tiwari and Dr. Subodh Kumar for their constant and consistent inspiring guidance and utmost co-operation at every stage which culminated in successful completion of my research work.
I am very much thankful to Prof. S.C. Kaushik, Head, Prof. A. Chandra and Prof. T. S. Bhatti of Centre for Energy Studies for their kind advice and assistance from time to time. My sincere thanks go to Prof. V. K. Srivastava, Ex-dean IRD and Prof. I.P. Singh of IDDC for academic discussion and encouragement.
I also express my thanks to Prof. S.K. Bhargava, Dean, M.B.M. Engg.
Colliege Jodhpur and Dr. Arvind Tiwari, Associate professor, K.I.E.T, Ghaziabad (UP) for providing me great moral support by taking keen interest in my work and helping me from time to time. My special thanks go to my colleagues and to my friends Dr. Bikash Sarkar, Dr. Vimal Dimri, Mr. V. K. Dwivedi, Mr. Swapnil Dubey, Mr. Rahul Dev, Mr. S.C. Solanki and Mr. M.K. Gaur for their cooperation.
I have no befitting words to express deep sentiments towards my Wife; Mrs Kalpana Dubey, Sons; Aseem and Ashmit Dubey for their whole hearted support and patience during the period of my study.
Last but not the least, I convey my sincere thanks to Mr. Lakhmi Chand, Mr.
Shankar Lal and staff members of IIT, Delhi for their kind support and help in completing this research work.
Date: November 5, 2008 (SHIV KUMAR)
ABSTRACT
Today in this changing world, some countries are striving to achieve excellence in every lifestyle whereas some others are still struggling to fulfill even basic need of food, clothing, shelter and pure water. Many people in the developing countries do not have access to even clean drinking water. Water is a primary need of the life, health and sanitation and is the most important issue on the international agenda. Water resources around the world are under pressure. The world's supply of fresh water is running out because of increasing demand due to increasing population and industrialization and draught at various locations, followed by desertification. The abailable freshwater resources, which are less than 1%, will not be able to meet all requirements because of its rapidly increasing demand and cannot expect an infinite supply of fresh water. The problem of non-availibilty of pure water is one of most serious health crisis and need more attention and resources than available today.
The present available fish water resources have not been found capable enough, inspite of large centrelized water purifying systems. The available water, after distillation, may be used for domestic and comercial use. However, these conventional methods of distillation are highly energy intensive and require sources of energy that deplets fast. In such circumstances, direct use of solar energy represents a promising option to obtain fresh water by the use of solar still, eliminating the major operating cost as well as global warming.
The solar still is a suitable solution of getting the pure water from the available brackish/saline water by powering it using the solar energy, which adds zero fuel cost.
The various impurties ranging from salt to microorganisms in the water can be removed effectively in the solar still.
iii
The aim of most of the research work done in the field of solar distillation is to increase the distillate output from the solar still. This can be achieved either by increasing the water temperature or by increasing the difference between water and glass cover temperature or by both. The higher water temperature can be achieved by feeding the additional thermal energy to the water after external heating in the collectors. Therefore, a new approach has been employed by designing the new hybrid photovoltaic/ thermal (PV/T) active solar still for a remote community, facing shortage of good quality of water for comercial use as well as scarcity of grid power supply. The thermal energy of PV module from its back surface can also been utilized for water heating beside generation of DC power to operate the system. Till now the study of hybrid (PV/T) active solar still has not been considered.
The sun's position changes with the seasons and as a results, the incident angle of the solar radiation on the cover varies throut the year. Therefore, in the present work, the annual performance of hybrid (PV/T) solar still has been investigated for comprative assesment with passive solar still. The fabricated passive and hybrid (PV/T) active solar stills kept oriented due south at 30° glass cover inclination to allow maximum solar radiation to enter inside throughout the year. The outdoor experiments conducted through out the year for different water depths, namely 0.05, 0.10 and 0.15m at solar energy park, I.I.T New Delhi, India. Results of experimental investigation revels that annual yield from hybrid (PV/T) active solar still is 3.5 times than that obtained from passive solar still.
The numerical models of internal heat transfer coefficent proposed by various researchers have been used to estimate the convective and evaporative heat transfer coefficients. The models have been cheacked for validity in outdoor experimental condition after caluculating the theoretical yield for experimental values of water, glass cover temperature and estimated evaporative heat transfer coefficient.
Comparision between the theoretical and experimental yield indicates that Kumar and Tiwari (1996) model found to be best fit than others model under consideration. This is also noticed that convective heat transfer coefficent has been improved almost by 3.5 times than the passive solar still.
A thermal model has been developed for hybrid (PV/T) active solar still to predict the water temperature, inner glass cover temperature and finally yield as predicted by other researchers for their own designs. This model has been validated after comparing the experimental and predicted results in summer and winter seasons and found in fair agreement.
Exergy efficiency of the system is true measure of the actual performance of any thermal system. Therefore, to campare the both solar still meaningfully, the exergy analysis has been carried out. The exergy efficiency of hybrid (PV/T) active solar still obtained higher than the passive solar still. In addition, the relative dominance of exergy fractions of internal exergy transfer within the solar stills has also been studied for different seasons. The interdependance of all the exergy fractions on water temperature and their behavior to the water temperature has also been investigated.
On the basis of annual yield to find the technoeconomic and social viability of passive and hybrid (PV/T) active solar still, the life cycle cost analysis has also been carried out to optimize the cost of distillate and payback period of solar still. Further, energy payback time (EPBT) has also been obtained for both the solar stills. The effect of running period of pump on annual energy saving has also been discussed with view point of reduced initial investment and payback time of hybrid (PV/T) active solar still.
TABLE OF CONTENTS
Page
List of Figures List of Tables Nomenclature
Chapter -I General introduction 1-26
1.1 Introduction 1
1.2 Favourable conditions for solar distillation 5 1.3 Major benefits to developing countries 5
1.4 Historical review 6
1.5 Material requirements of basin type solar stills 11
1.6 Principle of solar distillation 13
1.6.1 Understanding the evaporation rate of water 13 1.6.2 Energy requirement for water distillation 14
1.7 Heat transfer in the solar still 15
1.7.1 Internal heat transfer 15
1.7.2 External heat transfer 16
1.7.2.1 Top heat loss from glass cover 17
1.7.2.2 Bottom heat loss 18
1.7.2.3 Side heat loss 18
1.8 Factors affecting the performance of solar still 19 1.9 Classification of solar distillation systems 19
1.9.1 Passive solar still 19
1.9.2 Active solar still 20
1.10 Hybrid photovoltaic thermal (PV/T) system 21
1.10.1 Short circuit current 22
1.10.2 Open circuit voltage 22
1.10.3 Fill factor 22
1.10.4 Photovoltaic (PV) module 22
1.10.5 Packing factor 23
1.11 Identification of the research problem 23
1.12 Objectives of the present work 24
1.13 Outline of present study 25
Chapter — II Design, fabrication, instrumentation and experimental
results of passive and hybrid (PV/T) active solar stills 27-61
2.1 Introduction 27
2.2 Significances of newly designed hybrid photovoltaic/ thermal
(PV/T) active solar distillation 28
2.3 Experimental set-up 29
2.3.1 Single slope passive solar still 29 2.3.2 Single slope hybrid (PV/T) active solar still 33
2.4 Instrumentation 37
2.5 Methodology 38
2.6 Experimental results and discussion 39
2.7 Thermal stratification 41
2.8 Parametric studies 45
2.8.1 Effect of solar radiation 45
2.8.1.1 Water and glass cover temperatures 45
2.8.1.2 Distillate yield 46
2.8.2 Effect of water depth 47
2.8.2.1 Water temperature 47
2.8.2.2 Distillate yield 48
2.9 Performance of PV module 50
2.10 Seasonal performance 51
2.10.1 Ambient and water temperature 52
2.10.2 Distillate yield 53
2.10.2.1 Passive solar still 53
2.10.2.2 Hybrid (PV/T) active solar still 54 vii
2.10.2.3 Distillate yield ratio 55
2.10.3 PV module-DC pump 56
2.11 Annual performance 57
2.12 Conclusions 60
Chapter- III Internal Heat and mass transfer analysis of the passive
and hybrid (PV/T) active solar stills 62-109
3.1 Introduction 62
3.2 Heat transfer models 64
3.2.1 Dunlde's model (DM) 64
3.2.2 Chen et al. model (CM) 65
3.2.3 Adhikari et al. model (AM) 65
3.2.4 Zheng et al. model (ZM) 66
3.2.5 Kumar and Tiwari model (KTM) 66
3.3 Testing of models 69
3.4 Results and discussion 69
3.5 Seasonal effect 79
3.6 Conclusions 81
Chapter- IV Thermal modeling of hybrid (PV/T) active solar still:
an experimental validation 83
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1094.1 Introduction 83
4.2 Experimental set up and observations 84
4.3 Thermal modeling 85
4.3.1 Photovoltaic integrated flat plate collector (Is' collector) 86
4.3.1.1 PV module 86
4.3.1.2 Blackened absorber plate temperature (T p )
below the PV module 87
4.3.1.3 Water flowing through pipe below the PV module 88 4.3.1.4 Outlet water temperature from PV integrated
Is' collector 89
4.3.2 Heat absorbed by water in IInd collector 90 4.3.3 Total heat absorbed by water from the combination of
two collectors connected in series 90 4.3.4 Energy balance in the solar still 92
4.4 Statistical analysis 97
4.5 Validation of thermal modeling 97
4.5.1 Water temperature 99
4.5.2 Inner glass cover temperature 103
4.5.3 Distillate yield 105
4.6 Conclusions 108
Chapter- V Energetic and exergetic analysis of solar stills 110-135
5.1 Introduction 110
5.2 Analytical analysis 112
5.2.1 Energy analysis 113
5.2.1.1 Passive solar stil 113
5.2.1.2 Hybrid (PV/T) active solar still 113
5.2.1.3 PV module 114
5.2.2 Exergy analysis 114
5.2.2.1 Passive solar still 116
5.2.2.2 Hybrid (PV/T) active solar still 116 5.3 Availablity of energy and exergy from PV/T flat plate collectors 117 5.4 Comprative analysis of passive and hybrid (PV/T) active solar stills119
5.4.1 Accounting of module power for energy and exergy
efficiency 120
5.4.1 Effect of water depth on exergy efficiency 121 5 .4.3 Daily energy and exergy efficiency of solar stills 122
5.5 Seasonal performance 124
5.5.1 Efficiency of PV module 124
5.5.2 Energy and exergy efficiency of solar stills 125
5.5.2.1 Energy efficiency 125
5.5.2.2 Energy efficiency 126
5.6 Fractional exergy of solar stills 128
5.6.1 Passive solar still 129
5.6.2 Hybrid (PV/T) active solar still 132
5.7 Conclusions 134
ix
Chapter- VI Life cycle cost analysis of passive and hybrid (PV/T) active
solar stills 136-161
6.1 Introduction 136
6.2 Systems design and dimensions 138
6.3 Economic analysis 138
6.3.1 Capital cost of solar stills, P3 140
6.3.2 Interest rate, i% 143
6.3.3 Maintenance cost, M3% 143
6.3.4 Life of the solar stills, n 144
6.3.5 Selling price, Sp 144
6.3.6 Salvage value, Ss 144
6.3.7 Payback period, n, 144
6.4 Energy payback time (EPBT) 146
6.5 Experimental observations and distillate water quality 148
6.6 Results and discussion 149
6.7 Optimizing the pump running time 153 6.7.1 Effect on distillate yield 156 6.7.2 Effect on energy efficiency 158
6.7.3 Power saving 159
6.8 Conclusions and recommendations 160
Chapter-VII Conclusions and recommendations 162-164
7.1 Conclusions 162
7.2 Recommendations 164
References 165-176
Appendix 177-216
Reprints/ preprints 217-218
Brief bio-data of the author 219
