Effect of carbon credits on economics of renewable energy sources

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Effect of Carbon Credits on Economics of Renewable Energy Sources



Centre for Energy studies


In fulfillment of the requirements of the degree of Doctor of Philosophy to the

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Indian Institute of Technology Delhi

April, 2011



This is to certify that the thesis entitled "Effect of carbon credits on economics of renewable energy sources" being submitted by Prabhakant to the 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.

(Dr. G.N. Tiwari) Professor

Centre for Energy studies

Indian Institute of Technology Delhi Hauz Khas, New Delhi - 110016

Date: April, 2011



It gives me immense pleasure to express my gratitude to my supervisor; Prof. G.N. Tiwari for his constant support and guidance. His utmost cooperation at every stage has been instrumental in the successful completion of this research work.

I am also very thankful to Prof. Avinash Chandra, Prof. T.S. Bhatti and Dr. Subodh Kumar of Centre for Energy Studies for their kind advice and support from time to time.

I am deeply indebted to Prof A.P. Singh, former Head of Deptt. Birla Institute of Technology, Mesra Ranchi. It was he who inspired me to explore the potentials of Renewable Energy Sources and explained the limitations of fossil fuel based systems. The early ideas given by him during my under graduate days has culminated into the present thesis.

My special thanks to my colleagues Dr. P Baranwal, Dr. Swapnil Dube, Dr. S.C. Solanki, Mr. Rahul Dev, Mr. Rajeev Mishra, Mr. Gaurav Kumar Singh, Basant Agrawal and others for their cooperation and moral support. My sincere thanks to Mr. Lakhmi Chand, Mr.

Shankar Lal Sharma and staff members of IIT, Delhi for their assistance during experimental work and help in completing this research work.

I have no befitting words to express my deep sentiments and reverence towards my parents;

Dr. Ayodhya Prasad and Mrs. S Prasad. I would like to specially thank my wife, Kavita for her unflinching support and patience during this period of study and last but not the least, a special thanks to my two little naughty sons, Ipsit and Alankrit who let their Daddy pursue his research partly at the cost of their share of time.

Date: April, 2011 (Prabhakant)



Energy consumption of a country is one of the indicators of its socio economic development. With decrease in conventional energy resources and growing environmental concerns it is expected that renewable energy systems are going to play a very significant role in future. Solar energy can be utilized in the form of either thermal energy or electrical energy (DC) by using photovoltaic (PV). It has been noticed that the PV modules do not maintain constant efficiency throughout their life span. The efficiency of the SAPV module depends on material of the PV cells, operating temperature, the dust content of the atmosphere, wind speed, maintenance (cleanliness) of the PV surface etc. Over a period of time the efficiency of the PV module decreases.

System utilizing more than one energy source to generate electricity/ heat is called a hybrid system. Common drawback with renewable energy systems is its unpredictable nature.

Stand alone photovoltaic (PV) or wind energy system, does not produce usable energy for considerable portion of time during the year. This is mainly due to dependence on sunshine hours, which are variable, in the former case and on relatively high cut-in wind speeds, which range from 3.5 to 4.5 m/s, in the latter case resulting in under utilization of capacity.

Similarly it has been observed that the biogas production is maximum when slurry temperature is in between 32 -37°C. The biogas production is also dependent on sunshine hours. It has been noticed that wind and PV systems complement each other as wind is generally available during night where as PV modules generate electricity during day.

The conversion efficiency of photovoltaic depends upon its operating temperature. The operating temperature of photovoltaic is maintained by withdrawing/utilizing the thermal


energy associated with it. The thermal energy available on the PV module can be carried away by flowing water below it. This type of system is known as hybrid photovoltaic- thermal (PVT) system. If the thermal energy withdrawn from the PVT collector is fed into the biogas digester to maintain optimum slurry temperature such systems are called active biogas PVT hybrid system.

In this thesis economic and thermal analysis of PVT collectors with different solar cell material have been carried out. It has been noticed that PV modules made of mono crystalline solar cell are most economical under Indian conditions. Energy matrices and return on capital analysis of various PVT systems installed in the solar energy park at IIT Delhi has been carried out. Carbon credit earned by such solar energy park has also been calculated. If such solar energy park is built at each district and at each village having population more than 1000, the cost of building such solar energy parks, total energy produced by them, carbon credits earned by all such SEPs have also been estimated.

A methodology to optimise a hybrid solar Photovoltaic-wind power system (HSWPS) for the villages situated in the remote areas, especially coastal regions of India has been developed. Analysis of return on capital for hybrid solar Photovoltaic—wind power system by incorporating the effect of embodied energy, life of the system, interest rates, energy payback time in a typical Indian condition has been carried out. The analytical analysis shows that the return on capital increases from 4.07% to 4.16% with increase in life cycle of the hybrid system from 20 years to 40 years. Cost of power produced declines from 0.176 to 0.147 €/kWh and cost of the HSWPS increases from € 3526.76 to € 3864.76 in the corresponding period. The energy payback time is 2.47 years and will lead to earn € 28.52 every year of carbon credits.


Analysis of return on capital for various types' biogas plants by incorporating the effect of embodied energy, life of the system, interest rates, energy payback time and size of the biogas plants in typical Indian condition has also been carried out. If 75% of the dung available in rural India is utilized for production of biogas by building 3 m3 floating dome type biogas plants, biogas produced, carbon dioxide mitigated and carbon credits earned by all such plants has also been estimated.

Energy balance equations for the different components of hybrid photovoltaic thermal -bio gas plant have been written for quasi-steady state conditions to develop a thermal model. An analytical expression for slurry temperature has been obtained as a function of design and climatic parameters (namely mass of the slurry, mass flow rate of fluid in collector, number of collectors, solar intensity and ambient temperature). Computations have been carried out for climatic conditions of Srinagar, India. Based on mathematical computations it has been observed that the optimum slurry temperature (— 37°C) is achieved for a given set of design parameters (Ms =2000 kg,

m f

= 0.05 kg/s, L = 25 m). Similarly the peak slurry temperature decreases with increase in mass of the slurry as expected. Equivalent CO2 credits earned by hybrid bio-gas plant for optimized parameters have also been evaluated.



Certificate i

Acknowledgements ii

Abstract iii

Contents vi

Figure captions xiii

Table captions xvi

Nomenclature xix

Chapter - I General Introduction 1-28

1.1 Introduction ...1

1.2 Literature survey ...7

1.2.1 Photovoltaic (PV) system ... 7

1.2.2 Photovoltaic—thermal (PVT) system ...9

1.2.3 Biogas system ...11

1.2.4 Hybrid photovoltaic thermal (HPVT)-bio gas system ...11

1.2.5 CO2 mitigation ...14

1.2.6 Carbon credits ...14

1.3 Solar photovoltaic cell ...17

1.3.1 Short circuit current (Is~) ...17

1.3.2 Open circuit voltage (Vo,) ...17

1.3.3 Fill factor (FF) ...18

1.3.4 Efficiency of a solar cell () ...18


1.3.5 Temperature dependent electrical efficien ...18

1.4 Photovoltaic (PV) module ... 20

1.4.1 Packing factor (PF) ... 20

1.4.2 Electrical efficiency of PV module ... 21

1.4.3 Overall thermal and exergy efficiency ... 21

1.5 Weather conditions ... 22

1.6 Criteria for the classification of climates ... 23

1.7 Embodied energy ... 24

1.8 Annualized uniform cost (Unacost) ... 24

1.9 Energy matrices ... 25

1.9.1 Energy pay back time (EPBT) ... 25

1.9.2 Energy production factor (EPF) ... 26

1.9.3 Life cycle conversion efficiency (LCCE) ... 26

1.10 Organization of the chapters ... 27


2.2 Types of solar cell ... 29

2.2.1 Mono crystalline silicon ... 29

2.2.2 Polycrystalline silicon (p-Si) ... 29

2.2.3 Ribbon silicon (r-Si) ... 30

2.2.4 Amorphous or thin film silicon (a-Si) ... 30

2.2.5 Cadmium telluride solar cell (CdTe) ... 31

2.2.6 Copper-Indium gallium selenide (CIGS) ... 31


2.2.7 Gallium arsenide (GaAs) ... 31

2.3 Efficiencies, life cycle and embodied energies of different solar cell ...31

2.4 Photovoltaic thermal (PVT) water collector ...32

2.5 Thermal modelling of PVT water collector ...34

2.6 Effect of solar cell on photovoltaic thermal ( PVT) collector ...38

2.7 Overall thermal energy gain of PVT collectors ...41

2.8 Overall exergy gain of PVT collectors ...42

2.8.1 Exergy of solar radiation ...42

2.8.2 Overall exergy of PVT collector ...43

2.9 Embodied Energy of the hybrid PVT collector ...44

2.9.1 Methodology ...44

2.10 Energy matrices of PVT water collectors ...49

2.11 Energy matrices when PV modules replaced after end of their life cycle ...52

2.12 Summery ...54

Chapter-3 ENERGY ANALYSIS OF SOLAR ENERGY PARK 55-85 3.1 Introduction ... 55

3. 2 Description of solar energy park (SEP) ...56

3.2.1 Photovoltaic system ... 5 6 3.2.2 Mud house (MH) ...58

3.2.3 Green house ...59

3.2.4 Hybrid photovoltaic thermal air collector (HPVTAC) ...62

3.2.5 Solar still ... 63

3.2.6 Water pump (WP) ... 65

3.2.7 Hybrid PVT water collector (HP VTWC) ...65

3.3 Assumptions ... 66


3.4 Numerical Computations ... 67

3.4.1 Electrical load in solar energy park ( SEP) ...67

3.4.2 Production of electrical and thermal energy by various PVT systems in SEP ...67

3.5 Carbon credits earned by solar energy park (SEP) ... 70

3.6 Return on capital cost of SAPV systems of SEP ... 71

3.7 Effect of initial cost ... 74

3.8 Effect of solar intensity and number of clear days ... 75

3.9 Embodied energy ... 77

3.10 Energy payback time (EPBT) ... 77

3.10.1 Energy pay back time ( Thermal) ... 78

3.10.2 Energy pay back time ( Electrical) ... 78

3.10.3 Life cycle conversion efficiency ... 79

3.10.4 Energy Production Factor (EPF) ... 80

3.11 Effect of embodied energy on return on capital ... 81

3.13 Carbon credit on national level ... 82

3.13.1 Solar energy park at district level ... 83

3.14 Summary ... 84


4.2 Objectives of present analysis ... 91

4.3 Proposed assumptions ... 92

4.4 Hybrid solar—wind system ... 92


4.4.2 Output from wind turbine generator ...94

4.4.3 Output from PV arrays ...98

4.4.4 Hybrid solar PV -wind system ...100

4.4.5 Capacity of the battery bank ...101

4.5 Numerical calculations ...102

4.5.1 Energy output from wind turbine ...102

4.5.2 Energy output from PV modules ...103

4.5.3 Energy output from the hybrid solar PV — wind system :...103

4.6 Optimisation the hybrid solar PV - wind system ...104

4.7 Optimisation of battery bank ...105

4.8 Embodied energy of the hybrid solar PV — wind system ...108

4.8.1 Wind turbine ...109

4.8.2 PV module ...110

4.8.3 Steel structures ...111

4.8.4 Total embodied energy of the hybrid solar PV- wind system ...112

4.9 Economic analysis of hybrid solar PV — wind system ...113

4.9.1 Cost of the system ...113

4.9.2 Power produced by the hybrid solar PV — wind system ...114

4.9.3 Carbon credits ...115

4.9.4 Return on capital analysis ...116

4.10 Energy matrices of the hybrid solar PV — wind system ...118

4.10.1 Energy payback time (EPBT) ...118

4.10.2 Energy production factor (EPF) ...119

4.10.3 Life cycle conversion efficiency (LCCE) ...120


4.11 Summary ...121


5.2 Objectives of the present studies ...124

5.3 Process of biogas production ...124

5.4 Biogas plants ...125

5.4.1 Floating dome type biogas plant ...125

5.4.2 Fixed dome type biogas plant :...131

5.4.3 Advantages and disadvantages of both the bio gas plants ...137

5.5 Assumptions ...137

5.6 Numerical Calculations ...13 8 5.6.1 Return on capital ...140

5.7 Energy pay pack time ...152

5.8 Effect of embodied energy on return on capital ...154

5.9 Economic impact of providing biogas plants at national level ...154

5.10 Summary ...15 7 Chapter-VI THERMAL MODELLING OF HYBRID PHOTOVOLTAIC THERMAL INTEGRATED - BIOGAS PLANT 159-189 6.1 Introduction ...15 9 6.2 Objectives ...160

6.3 Thermal modelling of hybrid biogas — PVT system ...161

6.3.1 Assumptions ...161

6.4 Discription of hybrid biogas — PVT system ...162


6.5 Energy Balance Equations ...163

6.6 Methodology ...171

6.7 Carbon Credits earned by the hybrid biogas — PVT system ...176

6.7.1 Carbon credits earned by PV cells ...176

6.7.2 Carbon credits earned by Biogas plant ...177

6.8 Experimental Validation ...177

6.8.1 Experimental Set-up ...178

6.9 Summary ...189


7.2 Recommendations ...191


AppendixI ... 203

AppendixII ... 205

AppendixIII ... 211

AppendixIV ...259

AppendixV ...261

Listof publications ...268

Briefbio-data ...269




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