Solar Photovoltaics Engineering. A Power Quality Analysis Using Matlab Simulation Case Studies
©2016
Textbook
125 Pages
Summary
The solar Photovoltaic (PV) technology is gaining significant levels and is going to contribute a major share of total generated electricity in the coming years. PV technology is becoming a promising alternative source for fossil fuels. However, Power Quality (PQ) is the major concern that occurs between the grid and an end user. Any typical electrical distribution system exhibits a passive characteristic with respect to power flows when power flows from a substation to load. However, with inclusion of solar PV generators, this behaviour tends to be changed. The main characteristics related to PQ, such as voltage level, frequency, power factor and Total Harmonic Distortion (THD), may be affected.
This book presents the analysis of PQ with the integration of grid-connected PV systems as distributed generation. The role of Maximum Power Point Tracking (MPPT) technique is investigated through implementing few basic MPPT techniques. Using the Matlab-simulation platform, the analysis of PQ is demonstrated. This analysis is based on real measurements of THD, Voltage levels, Current levels, DC voltage levels, real power and reactive power flows.
This book presents the analysis of PQ with the integration of grid-connected PV systems as distributed generation. The role of Maximum Power Point Tracking (MPPT) technique is investigated through implementing few basic MPPT techniques. Using the Matlab-simulation platform, the analysis of PQ is demonstrated. This analysis is based on real measurements of THD, Voltage levels, Current levels, DC voltage levels, real power and reactive power flows.
Excerpt
Table Of Contents
Chapter 4 has highlighted the needs of PV installation components other than PV panels. These
components are jointly referred to as the Balance of System (BOS) and include the batteries, DC-
DC converters, DC-AC converters for AC loads and grid connected systems. Since P-V and V-I
curves of a solar panel are non-linear in nature, the need and importance of MPPT technique in
extracting variable solar power at maximum points is described in PCS systems.
In chapter 5, the introduction of PQ and its concerns has been presented. The various PQ issues
have been introduced and discussed according to IEEE and IEC standards. The effect of each of
PQ issue has been described for a distribution system according to IEC standard. It is discussed
that in electric power systems, hundreds of power generating stations and load centers are
interconnected and operated. There are various PQ problems likewise, voltage sag, voltage swell,
transients, voltage interruption, harmonics, noise and notching. Each PQ problem can be solved
by the proper coordination among all power system components.
Chapter 6 has presented that Matlab is a software package, which can be used to perform analysis
and solve mathematical and engineering problems. Introduction to various Matlab windows have
been given and described. Simulink contains a library editor of tools from which we can build
input/output devices and continuous and discrete time model simulations. Simulink has a
comprehensive block library which can be used to simulate linear, non-linear or discrete systems.
C codes can also be generated from Simulink models for embedded applications and rapid
prototyping of control systems. This chapter also highlights the procedure for the operation of
Simulink software with building blocks.
Chapter 7 has presented the modeling of solar PV single stage grid connected system at unity
power factor. No transformer is used in the proposed system as it increases the level of harmonics
in the overall system. The nature of real power generated by solar PV array through VSC has
been shown and proved that whenever the power from grid is un-available, the real power
requirement of the load is achieved by VSC. Data based MPPT is proposed through which
behavior of actual DC link voltage is discussed.
In chapter 8, the simulation of the proposed system is performed under two different cases. In
first case, the effect of changing power factor on active power, reactive power and THD values is
observed. It is observed that the THD of grid current increases with increase in the phase angle of
grid current VSC voltage. It affects the active power flow among VSC, load and utility grid. In
the second case, the effect of changing frequency on active power, reactive power and THD
values is noticed. It is observed that the THD of VSC current increases whereas, the THD of grid
current remains constant.
Chapter 9 has presented the analysis of two-stage solar PV grid connected system which is
evaluated at linear RLC load. In DC-DC boost converter, the IC-MPPT technique which is
capable to operate even under changing environmental conditions is implemented. Real and
reactive power exchange is exchanged among VSC, load and utility grid. Voltage and current
waveforms are presented. In order to evaluate the level of power quality, the THD analysis is
carried out using FFT. It has been found that although level of harmonics generation from VSC is
high, the control system is designed that level of harmonics is reduced for grid injected current.
Chapter 10 has discussed the system performance at P&O based MPPT technique for solar PV
two-stage grid connected system. It has been found that harmonic level is reduced for converter
current and grid injected current. However, this MPPT is not able to track the reference MPPT
voltage accurately. This validates that this MPPT is not able to operate under wide range of
changing environmental conditions. The behavior of voltage and current levels of VSC, load
connected and utility grid has also been discussed. Active and reactive power exchange among
VSC, load connected and utility grid has also been highlighted.
Table of Contents
Acknowledgement ... 5
Preface ... 7
List of Abbreviations ... 14
List of Tables ... 16
List of Figures ... 17
CHAPTER I: ELECTRIC POWER - A WORLD PERSPECTIVE ... 21
1.1. Introduction to Power Sector-A World Perspective ... 21
1.1.1 Coal ... 22
1.1.2 Natural gas ... 22
1.1.3 Petroleum and Other Liquid Fuels ... 22
1.1.4 Renewable Resources ... 22
1.2 Status of Indian Power Sector ... 23
1.3 Status of Global Renewable Energy ... 25
1.4 Conclusion ... 27
CHAPTER II: AN INTRODUCTION TO SOLAR PHOTOVOLTAIC CELL &
MODELING ... 28
2.1 Introduction ... 28
2.2 A Solar PV Cell-A p-n Junction Diode ... 28
2.3 Difference Between a Solar PV Cell and a p-n Junction Diode ... 30
2.4 Basic Parameters of Solar PV Cell ... 31
2.4.1 Voltage-Current (V-I) Characteristics ... 31
2.4.2 Short Circuit Current (I
SC
) ... 32
2.4.3 Open-Circuit Voltage (V
OC
) ... 32
2.4.4. Maximum Power Point (MPP) ... 33
2.4.5 Fill Factor (FF) ... 33
2.5 PV Module Arrangement ... 33
2.5.1 Typical Model of a Solar PV array ... 34
2.6 Conclusion ... 35
CHAPTER III: SOLAR CELL TECHNOLOGIES ... 36
3.1 Introduction ... 36
3.2 Classification of solar Photovoltaic Cells ... 36
3.2.1 Silicon Cells ... 37
3.2.2 Single-Crystal Silicon Cells ... 37
3.2.3 Multi-crystalline Silicon Cells ... 38
3.2.4 Thin Silicon (Buried Contact) Cells ... 38
3.2.5 Amorphous Silicon Cells ... 38
3.2.6 Gallium Arsenide Cells ... 39
3.2.7 Copper Indium (Gallium) Diselenide Cells ... 40
3.2.8 Cadmium Telluride Cells ... 40
3.3 Emerging Technologies ... 41
3.4 Conclusion ... 42
CHAPTER IV: MAXIMUM POWER POINT TRACKING IN POWER
CONDITIONING SYSTEM ... 43
4.1 Introduction ... 43
4.2 Need of MPPT Technique ... 43
4.2.1 DC-AC Converter Systems ... 44
4.2.2. DC-DC Converter Systems ... 45
4.3 Power Voltage and Voltage Current Characteristics of a Typical PV Module ... 46
4.4 Classification of MPPT Techniques ... 47
4.4.1 P&O-MPPT Technique ... 47
4.4.2 IC-MPPT Technique ... 50
4.5 Analysis of Other MPPT Techniques ... 51
4.5.1 Fractional Open-Circuit Voltage Technique ... 52
4.5.2. Fractional Short-Circuit Current Technique ... 52
4.6 Conclusion ... 52
CHAPTER V: INTRODUCTION TO POWER QUALITY ... 54
5.1 Introduction ... 54
5.2 Sources of Poor Power Quality ... 55
5.3 Need of Power Quality Concerns ... 55
5.4 Power Quality Problems ... 55
5.5 Solutions Adopted to Improve Power Quality ... 59
5.6 Power Quality Standards ... 59
5.7 Standards Related with Voltage Characteristics ... 59
5.7.1. IEEE Standards ... 59
5.7.2. IEC Electromagnetic Compatibility Standards ... 60
5.7.3. The European Voltage Characteristics Standards ... 60
5.8 Standards Related With Current Characteristics ... 61
5.8.1. IEEE Standards ... 61
5.8.2. The International Electro Technical Commission ... 62
5.9 Conclusion ... 62
CHAPTER VI: MATLAB & SIMULINK SOFTWARE ... 63
6.1 Introduction ... 63
6.2 Introduction to Matlab Software ... 63
6.3 Matlab Windows ... 64
6.4 Matlab File Types ... 65
6.5 Simulink Software ... 65
6.5.1 Controlling Execution of a Simulation ... 72
6.5.2 Starting a Simulation ... 72
6.5.3 Ending a Simulink Session ... 73
6.6 Conclusion ... 73
CHAPTER VII: SOLAR PV GRID CONNECTED SYSTEM WITH MPPT CONTROL.. 75
7.1 Introduction ... 75
7.2 System Computation Model ... 75
7.2.1. Rotating Reference Frame Transformation ... 76
7.2.2 Real & Reactive Power Control ... 77
7.2.3. Synchronization and Control of Three-Phase Grid Connected Inverter System ... 79
7.2.4. Generation of PWM Pulses ... 80
7.3 Controlling Scheme of Voltage Source Converter ... 82
7.4 Data MPPT Control for Maximum Power Point ... 84
7.6 Conclusion ... 89
CHAPTER VIII: EVALUATION AT DIFFERENT POWER FACTOR &
FREQUENCY ... 91
8.1 Introduction ... 91
8.2 Simulation Results and Discussion ... 91
8.2.1 Case I at different power factors and same frequency ... 91
8.2.2. Case II at different frequency and same power factors ... 100
8.3 Conclusion ... 104
CHAPTER IX: MODEL ANALYSIS WITH INCREMENTAL CONDUCTANCE
MPPT TECHNIQUE ... 106
9.1 Introduction ... 106
9.2 Voltage and Current Controllers ... 107
9.3 Solar PV Computation Model ... 108
9.4 Simulations Results and Discussion ... 110
9.5 Conclusion ... 115
CHAPTER X: MODEL ANALYSIS WITH PERTURB & OBSERVE MPPT
TECHNIQUE ... 116
10.1 Introduction ... 116
10.2 Proposed System Configuration ... 116
10.3 Simulation Results and Case Studies ... 117
10.4 Conclusion ... 122
References ... 123
14
List of Abbreviations
Air Mass
(AM)
Balance of System
(BOS)
Basic Linear Algebra Subprograms
(BLAS)
Bipolar Junction Transistor
(BJT)
Building Integrated PV
(BIPV)
Clean Power Plan
(CPP)
Copper Indium Gallium Diselenide
(CIGS)
Conference of Parties
(COP)
Electromagnetic Compatibility
(EMC)
Energy Information Administration
(EIA)
European Nation
(EN)
Fast Fourier Transform
(FFT)
Gallium arsenide
(GaAs)
Gigawatts-Thermal
(GW
th
)
Incremental Conductance
(IC)
Individual Harmonic Distortion
(IHD)
Independent Power Producers
(IPP)
Institution of Electrical and Electronic Engineering
(IEEE)
International Energy Outlook
(IEO)
Intended Nationally Determined Contributions
(INDCs)
Integrated Development Environment
(IDE)
International Electro-technical Commission
(IEC)
kilo-watt-hour
(KWH)
Linear Algebra PACKage
(LAPACK)
15
MATrix LABoratory
(MATLAB)
Maximum Power Point
(MPP)
Maximum Power Point Tracking
(MPPT)
Metal Insulator Semiconductor Inversion Layer
(MIS-IL)
Metal Oxide Semiconductor Field Effect Transistor
(MOSFET)
Million Tonnes of Oil Equivalent
(MTOE)
Molybdenum
(Mo)
Organization for Economic Cooperation and Development
(OECD)
Perturb & Observe
(P&O)
Phase Locked Loop
(PLL)
Photovoltaic
(PV)
Power Quality
(PQ)
Power-Voltage
(P-V)
Power Conditioning System
(PCS)
Pulse Width Modulation
(PWM)
Root Mean Square
(rms)
Sine Pulse Width Modulation
(SPWM)
Standard Test Condition
(STC)
Sustainable Development Goal
(SDG)
Total Demand Distortion
(TDD)
Total Harmonic Distortion
(THD)
Transparent Conducting Oxide
(TCO)
United Nations Framework Convention on Climate Changes
(UNFCCC)
Voltage-Current
(V-I)
Voltage Source Converter
(VSC)
Watt-Peak
(Wp)
16
List of Tables
Table 1.1: Plan wise capacity addition in grid connected renewable capacity ... 27
Table 4.1: Algorithm of P&O-MPPT Technique ... 50
Table 4.2: Efficiency Comparison of P&O and IC-MPPT technique ... 51
Table 7.1: Data used at solar radiation S
x
and temperatures T
x
values ... 85
Table 7.2: System configuration parameters ... 85
Table 9.1: Parameters of PV grid connected system ... 109
Table 9.2: Specifications adopted for single PV array (Sun Power SPR-305-WHT) ... 109
Table 9.3: Total harmonic distortion analysis using IC-MPPT ... 115
Table 10.1: Total harmonic distortion analysis using P&O MPPT ... 122
17
List of Figures
Figure 1.1: World net electricity generation from renewable power (2012-2040) ... 23
Figure 2.1: Electrical circuit of an ideal PV cell ... 29
Figure 2.2: Single-diode exponential model of a PV cell ... 30
Figure 2.3: Downward shifting of the dark V-I curve (a) when light shines on a p-n junction
diode and curve (b) is illuminated V-I curve ... 31
Figure 2.4: Voltage- Current and Power-Voltage solar cell characteristics ... 32
Figure 4.1: Block diagram of a solar PV grid connected application using MPPT ... 43
Figure 4.2: Typical connection scheme of a solar PV grid connected system ... 44
Figure 4.3: Changes in the V-I and P-V characteristics of the solar PV module due to
change in radiation level. ... 46
Figure 4.4: Changes in the V-I and P-V characteristics of the solar PV module due to change in
temperature. ... 47
Figure 4.5: Flowchart of Perturb & Observe MPPT technique ... 48
Figure 4.6 (a) Array P-V curve (b) Array V-I curve (c) Ramp up-down behavior of solar
radiation intensity ... 49
Figure 4.7: Flowchart of Incremental conductance MPPT technique ... 51
Figure 5.1: Waveform for voltage sag ... 56
Figure 5.2: Waveform for voltage swell ... 56
Figure 5.3: Waveform for voltage interruption ... 57
Figure 5.4: Waveform for notching ... 58
Figure 5.5: Waveform for noise ... 58
Figure 6.1: Matlab desktop main menu and Simulink icon ... 66
Figure 6.2: Simulink library browser ... 67
Figure 6.3: Blocks in Sources sub-node ... 68
Figure 6.4: Blocks in Sinks sub-node ... 69
Figure 6.5: Drag and drop blocks to workspace from library browser ... 70
Figure 6.6: Components for a Simulink model ... 70
Figure 6.7: Complete model of Simulink connected ... 71
Figure 6.8: To simulate a Simulink model ... 72
18
Figure 6.9: Options of Simulink simulation ... 73
Figure 7.1 Simulink model of solar PV grid connected system ... 76
Figure 7.2: Power flow between the two AC sources ... 77
Figure 7.3: Generation of PWM pulses ... 81
Figure 7.4: Simulink control model of voltage source converter ... 83
Figure 7.5: Simulink active and reactive power measurements ... 84
Figure 7.6: (a) Solar radiation in W/m2 (b) Solar array current (c) Solar array voltage
(d) Solar array power ... 87
Figure 7.7: actual DC link voltage and MPPT reference voltage ... 88
Figure 7.8: (a) Grid output power (b) Inverter output power ... 89
Figure 7.9: Modulation index ... 89
Figure 8.1: (a) Active power (b) Reactive power, variation of VSC, load and utility grid ... 92
Figure 8.2: FFT analysis of (a) VSC current and (b) grid current (Unity power factor, 50 Hz) ... 93
Figure 8.3: (a) Active power (b) Reactive power, variation of VSC, load and utility grid ... 94
Figure 8.4: FFT analysis of (a) VSC current and (b) grid current ... 95
Figure 8.5: (a) Active power (b) Reactive power, variation of VSC, load and utility grid
(Power factor=0.707, 50 Hz) ... 96
Figure 8.6: FFT analysis of (a) VSC current and (b) grid current (Power factor=0.707, 50 Hz) .. 97
Figure 8.7: (a) Active power (b) Reactive power, variation of VSC, load and utility grid
(Power factor=0.50, 50 Hz) ... 98
Figure 8.8: FFT analysis of (a) VSC current and (b) grid current (Power factor=0.50, 50 Hz) ... 99
Figure 8.9: (a) Active power (b) Reactive power, variation of VSC, load and utility grid
(Unity power factor, 49 Hz) ... 101
Figure 8.10: FFT analysis of (a) VSC current and (b) grid current (Unity power factor, 49 Hz) .. 102
Figure 8.11: (a) Active power (b) Reactive power, variation of VSC, load and utility grid
(Unity power factor, 51 Hz) ... 103
Figure 8.12: FFT analysis of (a) VSC current and (b) grid current (Unity power factor, 51 Hz) .. 104
Figure 9.1: Simulink diagram of incremental conductance MPPT technique ... 106
Figure 9.2: Simulink diagram of boost converter control ... 107
Figure 9.3: Simulink diagram of DC voltage PI controller ... 107
Figure 9.4: Simulink diagram of DC current PI controller ... 107
19
Figure 9.5: Simulink diagram of solar PV with connected load ... 108
Figure 9.6: Different signal measurement blocks ... 110
Figure 9.7: Waveform of a) VSC Voltage b) VSC Current c) Load Voltage d) Load Current
e) Utility grid Voltage f) Utility grid Current ... 111
Figure 9.8: Change in actual DC link voltage with MPPT reference voltage ... 112
Figure 9.9: Modulation index ... 112
Figure 9.10: Waveform of a) Real power and b) Reactive power, with IC MPPT technique ... 113
Figure 9.11: THD analysis of a) load current and b) grid current ... 114
Figure 10.1: Simulink diagram of photovoltaic grid connected system ... 117
Figure 10.2: Waveform of a) VSC Voltage b) VSC Current c) Load Voltage
d) Load Current e) Utility grid Voltage f) Utility grid Current ... 118
Figure 10.3: Waveform of a) Real power and b) Reactive power, with P&O MPPT technique ... 119
Figure 10.4: Change in actual DC link voltage with MPPT reference voltage ... 120
Figure 10.5: Modulation index ... 120
Figure 10.6: THD analysis of a) load current and b) grid current ... 121
21
CHAPTER I: ELECTRIC POWER - A WORLD PERSPECTIVE
1.1. Introduction to Power Sector-A World Perspective
The worldwide mix of primary fuels used to generate electricity has changed a great deal over the
past several decades. Coal continues to be the fuel most widely used in electricity generation [1],
but there have been significant shifts to other generation fuels. Generation from nuclear power
increased rapidly from the 1970s through the 1980s, and natural gas-fired generation increased
considerably after the 1980s. The use of oil for generation declined after the late 1970s, when
sharp increases in oil prices encouraged power generators to substitute other energy sources for
oil.
Beginning in the early 2000s, concerns about the environmental consequences of greenhouse gas
emissions heightened interest in the development of renewable energy sources, as well as natural
gas-a fossil fuel that emits significantly less CO
2
than either oil or coal per Kilo-Watt-Hour
(KWH) generated. In the International Energy Outlook (IEO) 2016, long-term global prospects
continue to improve for generation from natural gas, nuclear, and renewable energy sources.
Renewables are the fastest-growing source of energy for electricity generation, with annual
increases averaging 2.9% from 2012 to 2040. In particular, non hydropower renewable resources
are the fastest-growing energy sources for new generation capacity in both the Organization for
Economic Cooperation and Development (OECD) and non-OECD regions. Non hydropower
renewables accounted for 5% of total world electricity generation in 2012; their share in 2040 is
14% in the IEO-2016, with much of the growth coming from wind power.
After renewable energy sources, natural gas and nuclear power are the next fastest-growing
sources of electricity generation. From 2012 to 2040, natural gas-fired electricity generation
increases by 2.7%/year and nuclear power generation increases by 2.4%/year. With coal-fired
generation growing by only 0.8%/year, renewable generation (including both hydropower and
non hydropower resources) overtakes coal to become the world's largest source of energy for
electricity generation by 2040. The outlook for coal-fired electricity generation could be further
altered in the future by additional national policies or international agreements aimed at reducing
or limiting its use. It should be noted that the IEO-2016 does not include implementation of the
U.S. Clean Power Plan (CPP), which would reduce the use of coal in the United States
substantially. Finally, if other nations with shale gas resources (notably, China) are able to
22
replicate the U.S. success in exploiting shale gas production, the outlook for world natural gas-
fired electricity generation could be much different from that represented in the IEO-2016.
1.1.1 Coal
Coal continues to be the largest single fuel used for electricity generation worldwide in the IEO-
2016 until the end of the projection period, with renewable generation beginning to surpass coal-
fired generation in 2040. Coal-fired generation, which accounted for 40% of total world
electricity generation in 2012, declines to 29% of the total in 2040, despite a continued increase
in total coal-fired electricity generation from 8.6 trillion kWh in 2012 to 9.7 trillion kWh in 2020
and 10.6 trillion kWh in 2040. Total electricity generation from coal in 2040 is 23% above the
2012 total.
1.1.2 Natural gas
Worldwide natural gas consumption for electricity generation grows in the IEO-2016 by an
average of 2.7%/year from 2012 to 2040. From 22% of total world electricity generation in 2012,
the natural gas share increases to 28% in 2040 in the IEO-2016. In the United States, natural gas-
fired generation is encouraged by low prices and favorable greenhouse gas emission
characteristics. Natural gas is the least carbon-intensive fossil fuel; like all fossil fuels, natural gas
combustion emits carbon dioxide, but at about half the rate of coal.
1.1.3 Petroleum and Other Liquid Fuels
The use of petroleum and other liquid fuels for electricity generation continues to decline steadily
in the IEO-2016. The share of total world generation from liquid fuels falls from 5% in 2012 to
2% in 2040, an average decline of 2.2%/year. Despite their recent decline, oil prices are expected
to be higher in the long-term projection. As a result, liquids remain a more expensive option
compared to other fuels used for generating electricity, and generators replace liquids-fired
generation with other fuels where possible.
1.1.4 Renewable Resources
Renewables account for a rising share of the world's total electricity supply, and they are the
fastest growing source of electricity generation in the IEO-2016 (Figure 1.1). Total generation
from renewable resources increases by 2.9%/year, as the renewable share of world electricity
generation grows from 22% in 2012 to 29% in 2040. Generation from non hydropower
renewab
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24
with 4.8% global share in electricity generation surpassing Japan and Russia. During the year
2014-15, the per capita electricity generation in India was 1,010 kWh with total electricity
consumption (utilities and non utilities) of 938.823 billion or 746 kWh per capita electricity
consumption. Electric energy consumption in agriculture was recorded highest (18.45%) in 2014-
15 among all countries. The per capita electricity consumption is lower compared to many
countries despite cheaper electricity tariff in India.
Power is one of the most critical components of infrastructure crucial for the economic growth
and welfare of nations. The existence and development of adequate infrastructure is essential for
sustained growth of the Indian economy [3]. India's power sector is one of the most diversified in
the world. Sources of power generation range from conventional sources such as coal, lignite,
natural gas, oil, hydro and nuclear power to viable non-conventional sources such as wind, solar,
and agricultural and domestic waste. Electricity demand in the country has increased rapidly and
is expected to rise further in the years to come. In order to meet the increasing demand for
electricity in the country, massive addition to the installed generating capacity is required. India
ranks third, just behind US and China, among 40 countries with renewable energy focus, on back
of strong focus by the government on promoting renewable energy and implementation of
projects in a time bound manner.
Indian power sector is undergoing a significant change that has redefined the industry outlook.
Sustained economic growth continues to drive electricity demand in India. The Government of
India's focus on attaining `Power for all' has accelerated capacity addition in the country. At the
same time, the competitive intensity is increasing at both the market and supply sides (fuel,
logistics, finances, and manpower). Total capacity of renewable energy plants in India stood at
42,850 MW as on April 30, 2016, thereby surpassing the 42,783 MW capacity of large
hydroelectricity projects in the country. Cumulative solar installations in India crossed the 7.5
GW mark in May 2016, about 2.2 GW more than all of the solar installations in 2015.
The Indian Planning Commission's 12
th
five-year plan estimates total domestic energy
production to reach 669.6 Million Tonnes of Oil Equivalent (MTOE) by 201617 and 844
MTOE by 2021-22. As of January 2016, total thermal installed capacity stood at 200.74 GW,
while hydro (renewable) energy installed capacity totaled 42.66 GW. At 5.78 GW, nuclear
energy capacity remained broadly constant compared with the previous year.India's rooftop solar
capacity addition grew 66 per cent from last year to reach 525 MW, and has the potential to grow
25
up to 6.5 GW. India's wind power capacity, installed in financial year-2016, is estimated to
increase 20% over last year to 2,800 MW, led by favorable policy support that has encouraged
both Independent Power Producers (IPP) and non-IPPs. India is expected to add nearly 4,000
MW of solar power in 2016, nearly twice the addition of 2,133 MW in 2015.
India's wind energy market is expected to attract investments totaling Rs 1,00,000 crore (US$
14.82 billion) by 2020, and wind power capacity is estimated to almost double by 2020 from over
23,000 MW in June 2015, with an addition of about 4,000 MW per annum in the next five years.
1.3 Status of Global Renewable Energy
The year 2015 was an extraordinary one for renewable energy, with the largest global capacity
additions seen to date, although challenges remain, particularly beyond the power sector [4]. The
year saw several developments that all have a bearing on renewable energy, including a dramatic
decline in global fossil fuel prices; a series of announcements regarding the lowest-ever prices for
renewable power long-term contracts; a significant increase in attention to energy storage; and a
historic climate agreement in Paris that brought together the global community.
Renewables are now established around the world as main-stream sources of energy. Rapid
growth, particularly in the power sector, is driven by several factors, including the improving
cost-competiveness of renewable technologies, dedicated policy initiatives, better access to
financing, energy security and environmental concerns, growing demand for energy in
developing and emerging economies, and the need for access to modern energy. Consequently,
new markets for both centralized and distributed renewable energy are emerging in all regions.
2015 was a year of firsts and high-profile agreements and announcements related to renewable
energy. These include commitments by both the G7 and the G20 to accelerate access to
renewable energy and to advance energy efficiency, and the United Nations General Assembly's
adoption of a dedicated Sustainable Development Goal on Sustainable Energy for All (SDG 7).
The year's events culminated in December at the United Nations Framework Convention on
Climate Change's (UNFCCC) 21
st
Conference of the Parties (COP21) in Paris, where 195
countries agreed to limit global warming to well below 2 degrees Celsius. A majority of countries
committed to scaling up renewable energy and energy efficiency through their Intended
Nationally Determined Contributions (INDCs). Out of the 189 countries that submitted INDCs,
147 countries mentioned renewable energy, and 167 countries mentioned energy efficiency; in
26
addition, some countries committed to reforming their subsidies for fossil fuels. Precedent-setting
commitments to renewable energy also were made by regional, state and local governments as
well as by the private sector.
Although many of the initiatives announced in Paris and elsewhere did not start to affect
renewable markets in 2015, there already were signs that a global energy transition is under way.
Renewable energy provided an estimated 19.2% of global final energy consumption in 2014, and
growth in capacity and generation continued in 2015. An estimated 147 GW of renewable power
capacity was added in 2015, the largest annual increase ever, while renewable heat capacity
increased by around 38 Gigawatts-Thermal (GWth), and total biofuels production also rose. This
growth occurred despite tumbling global prices for all fossil fuels, ongoing fossil fuel subsidies
and other challenges facing renewables, including the integration of rising shares of renewable
generation, policy and political instability, regulatory barriers and fiscal constraints. Global
investment also climbed to a new record level, in spite of the plunge in fossil fuel prices, the
strength of the US dollar (which reduced the dollar value of non-dollar investments), the
continued weakness of the European economy and further declines in per unit costs of wind and
solar Photovoltaic (PV). For the sixth consecutive year, renewables outpaced fossil fuels for net
investment in power capacity additions.
Private investors stepped up their commitments to renewable energy significantly during 2015.
The year witnessed both an increase in the number of large banks active in the renewables sector
and an increase in loan size, with major new commitments from international investment firms to
renewables and energy efficiency. New investment vehicles-including green bonds, crowd
funding and yield cos-expanded during the year. Mainstream financing and securitization
structures also continued to move into developing country markets as companies (particularly
solar PV) and investors sought higher yield, even at the expense of higher risk. In parallel with
growth in markets and investments, 2015 saw continued advances in renewable energy
technologies, ongoing energy efficiency improvements, increased use of smart grid technologies
and significant progress in hardware and software to support the integration of renewable energy,
as well as progress in energy storage development and commercialization. The year also saw
expanded use of heat pumps, which can be an energy-efficient solution for heating and cooling.
Employment in the renewable energy sector (not including large-scale hydropower) increased in
2015 to an estimated 8.1 million jobs (direct and indirect). Solar PV and bio-fuels provided the
27
largest numbers of renewable energy jobs. Large-scale hydropower accounted for an additional
1.3 million direct jobs. Considering all renewable energy technologies, the leading employers in
2015 were China, Brazil, the United States and India. India has a vast supply of renewable energy
resources, and it has one of the largest programs in the world for developing renewable energy
based product and systems. India is a developing and fast growing large economy and faces a
great challenge to meet its energy needs in a responsible and sustainable manner. Grid-interactive
renewable power capacity in the country reached 44244.27 MW on 30
th
June 2016 (Table 1.1),
which is about 14.5% of the total grid installed capacity in the country. Its contribution is about
8% to total electric power generation.
Table 1.1: Plan wise capacity addition in grid connected renewable capacity [5]
Financial year 2016-2017
Cumulative
Achievements
Resource
Target
(MW)
Achievement
(MW)
(as on 30.06.2016)
(MW)
Wind
4000
373.95
27151.40
Small-hydro
250
30.30
4304.25
Biomass
400
29.50
4860.83
Waste
10
7.5
122.58
PV
12000
1042.35
7805.21
Total
16660
1483.60
44244.27
1.4 Conclusion
This chapter mainly presents the world perspective and growth of electric power through
conventional sources and its vis-à-vis comparative growth with various sources of renewable energy.
It has been discussed that electric power has been one of the most critical component among others
available required for infrastructure and crucial for economic growth and welfare of any nation.
The growth of any developing nation mainly depends on various resources critically required in
growth of infrastructure. This chapter also highlights the recent advancements recently taken
place in renewable energy. The measures being adopted for building and supporting in the further
renewable energy growth in developing and developed economies is also presented.
28
CHAPTER II: AN INTRODUCTION TO SOLAR
PHOTOVOLTAIC CELL & MODELING
2.1 Introduction
This chapter mainly the fundamentals on solar PV cells with the help of mathematical analysis.
Basic output current and voltage for a single PV cell has been presented and its importance is
described. In addition, the dependence of a solar PV cell on variable solar radiation and ambient
temperature is also discussed. This discussion has been carried out using Power-Voltage (P-V)
and Voltage-Current (V-I) curves at Maximum Power Point (MPP). Also, few models on a solar
PV cell based on empirical equations have been elaborated.
2.2 A Solar PV Cell-A p-n Junction Diode
A solar PV cell is a semiconductor device, which behaves as a current source when driven by a
flux of solar radiation from the sun. This occurs, when radiation is incident upon absorbing
material and separates positive and negative charge carriers in the presence of an electric field.
The electric field exists permanently at junctions or in homogeneities in solar cells, which can be
described as silicon semiconductor junction device. A silicon semiconductor junction device
contains a p-n junction similar to that of a common diode; however in a solar cell, it exists over a
large surface area. When solar PV cell is not illuminated and connected to a forward bias, it
mimics the electrical characteristics of an ideal diode, modeled by Equation 2.1, where the
current produced is referred to as the dark current I
d
:
(
1)
a
c
qV
kT
d
rs
I
I e
=
-
(2.1)
where, I
rs
is reverse saturation current of the diode (A), q is electron charge (1.602 × 10
-19
C), V
a
is the PV cell output voltage (V), k is Boltzmann's constant (1.38 × 10
-23
J/
K) and T
c
is the solar
cell temperature (
°
C). The current in the cell that results from solar radiation is called the photo
current, which flows in the direction opposite of the forward dark current. Its value remains the
same regardless of external voltage and therefore, it can be measured by the short-circuit current.
This current varies linearly with the intensity of solar radiation as a large radiation is able to
29
separate more number of charge carriers. The overall current is then described as the difference
between the dark current and the photocurrent [6-7]. The current I
a
produced by an illuminated
cell can be written as shown in Equation 2.2,
(
1)
a
c
qV
kT
a
ph
rs
I
I
I e
=
-
-
(2.2)
This is the mathematical equation, which models the behavior of an ideal PV cell shown in
Figure 2.1. The production of photocurrent is modeled with an ideal current source and the dark
current is modeled with a diode referred to as the diffusion diode, which is represented by a
single-diode model. Some authors have proposed more sophisticated models, [8-9], in which an
extra diode is used to represent the effect of the recombination of carriers. However, for
simplicity, we have studied and used the single-diode model of solar PV cell. The single-diode
model offers good compromise between the accuracy and simplicity. The simplicity of this
model makes the model easy and effective when used for the simulation of PV devices with
power converters.
Figure 2.1: Electrical circuit of an ideal PV cell
Figure 2.2 depicts a well-known equivalent circuit of single solar cell composed of a light
generated current source, a single-diode representing the non-linear impedance of p-n junction
with series resistance R
s
and shunt resistance R
p
. The series resistance accounts for any resistance
in current path through semiconductor material, metal grid, contacts, and current collecting bus
[10]. The shunt resistance as mentioned in reference [11] is a loss associated with a slight leakage
current through a parallel resistive path to the device. It is not noticeable as series resistance,
30
because the effects are minimal unless a number of PV modules are connected in parallel for a
large system.
Figure 2.2: Single-diode exponential model of a PV cell
2.3 Difference Between a Solar PV Cell and a p-n Junction Diode
In a p-n junction diode, there are four current components, which are present in equilibrium
conditions, namely, electron drift, electron diffusion, hole drift and hole diffusion. In equilibrium
condition, the net current is zero which requires drift and diffusion current of the carriers to be
equal and opposite. When light shines on the solar PV cells, it results in a large drift current due
to minority electrons and holes. These carriers flow from n-side to p-side. Since this current flow
is caused by the incident light, it is known as light generated current or photocurrent I
ph
. Note that
the generated photo-voltage due to light biases the p-n junction in a forward biased mode i.e. the
generated photo-voltage reduces the junction potential energy barrier. As a result, there is a
diffusion current, which flows in the opposite direction of photocurrent. But the magnitude of
photocurrent is larger than the forward biased diffusion current and hence, the net current flows
from the n-side to p-side (opposite to that of forward biased diode current). Thus, when the light
shines on a PV cell, the current flows in the opposite direction to that of the generated voltage.
Overall, the effect of light shining is to shift the V-I curve of the diode downwards on the current
voltage axis, as depicted in the Figure 2.3. It is found that in the fourth quadrant of this curve, the
voltage is positive and current is negative resulting in negative power. The negative power
implies that the power can be extracted from the device. Therefore, a solar PV cell generates the
power, instead of consuming power like the other electronic devices, where the power is positive.
31
2.4 Basic Parameters of Solar PV Cell
Normally, the electrical characteristics of a PV cell are displayed as a relation between the cell
voltage and current, and a relation between the cell voltage and power. However, several electric
quantities are important to describe the operation of the PV cell. These electric quantities include:
the cell voltage under open-circuit conditions (V
OC
), the cell current under short-circuit conditions
(I
SC
), the cell voltage, current and power at MPP, V
MPP
, I
MPP
, and, P
MPP
, respectively.
2.4.1 Voltage-Current (V-I) Characteristics
V-I characteristics curve represents all possible current and voltage operating points for PV cell.
This curve can be generated by changing the electrical load value during lab experiment. As can
be seen in Figure 2.4, when voltage increases, the current start at its maximum value then
decreases gradually to reach the zero. The operating point at V-I curve is determined by the
electrical load. Certain points at the V-I curve are highlighted to rate the PV module performance
and are used for the design of PV systems. These measured values are taken at the Standard Test
Condition (STC), which are at solar radiation (G=1000 W/m
2
), Temperature (T= 25 C), and Air
Mass (AM=1.5). The knee points, in both V-I and P-V curves, represent the MPP. The optimum
electrical load is the load that operates the PV at its MPP, if the PV generator is able to deliver
maximum power.
V
a
I
a
I
ph
(a)
(b)
Figure 2.3: Downward shifting of the dark V-I curve (a) when light shines on a p-n junction diode and
curve (b) is illuminated V-I curve [12]
32
The ele
tempera
different
a strong
effect on
solar rad
while ne
2.4.2 Sh
Short-ci
Figure 2
by conn
proporti
2.4.3 Op
Open-ci
voltage
connecte
Fig
ectrical char
ature. There
t levels of th
g effect on t
n the open-
diation has
egligible eff
hort Circuit
ircuit curren
2.4. In other
necting the p
ional to the a
pen-Circuit
ircuit voltag
represents
ed to the cir
ure 2.4: Volta
racteristics
is a propor
he solar rad
the short-cir
circuit volta
a significan
fect on the s
t Current (I
nt is the ma
r words, wh
positive and
available su
t Voltage (V
ge is the m
the maxim
rcuit or in ca
age- Current
of a PV c
rtional relat
diation and c
rcuit curren
age. On the
nt effect on
short-circuit
I
SC
)
ximum pos
en there is n
d negative t
unlight.
V
OC
)
maximum v
mum possibl
ase of no loa
and Power-V
cell depend
tionship bet
constant tem
nt and the ou
e other hand
the open-c
t current.
sible curren
negligible e
terminals to
voltage, at
le voltage v
ad.
Voltage solar
d on the v
tween the c
mperature. A
utput power
d, any chang
circuit volta
nt in the circ
electrical loa
ogether. The
zero curren
value, whic
cell characte
ariable sola
current and
Any change
r of the sola
ge in the tem
ge and outp
cuit, at zero
ad in the cir
e short-circ
nt. In other
ch occurs w
ristics
ar radiation
the solar ra
in solar rad
ar cell, but
mperature a
put power o
o voltage as
rcuit. This c
uit current
r words, op
when a hug
n and cell
adiation at
diation has
negligible
at constant
of the cell,
s shown in
ase occurs
is directly
pen-circuit
ge load in
33
2.4.4. Maximum Power Point (MPP)
In case of short-circuit or open-circuit operating points, there is no power generated from a solar
PV cell. As a result, the operating point should fall into the range of the maximum power output
of PV cell. This operating point is determined by choosing the correct value of the connected
load. The maximum output power is defined as the multiplication of the voltage and the current
at the MPP. Where V
MPP
and I
MPP
are voltage and current the values that gives the maximum
operating power. MPP is the rate of the unit by W
p
(Watt-Peak).
2.4.5 Fill Factor (FF)
The fill factor is an indicator of the quality of the PV cell. The sharpness of the knee in an V-I
curve indicates how well a p-n junction is manufactured. The maximum value of the fill factor is
one, which is theoretical value only. The maximum practical value in silicon is 0.88. FF is
defined as the ratio between the maximum generated power at MPP and the maximum theoretical
power (I
sc
multiply by V
oc
).
For a good V-I curve profile with fill factor close to unity, the current should stay constant while
the voltage increases till the operating point reach the knee of the curve. After that point, the
current of a solar PV cell should also gradually decrease.
2.5 PV Module Arrangement
PV modules are composed of series and parallel connection of solar PV cells with blocking and
bypass diodes as additional components. While the manufacture and size of solar PV cells vary,
in general, a single PV cell has a relatively low voltage handling capability on the order of 0.6 V.
In order to package PV cells as a more practical device, most manufacturers produce solar
modules. In the modules, a group of solar PV cells are connected in series and parallel in order to
increase the voltage and current handling capability, respectively.
The major factors that affect the efficiency of a solar PV module are its ambient temperature and
solar radiation. The output voltage of a solar PV cell is a function of load current and depends on
the photocurrent that is determined by the incident solar radiation level during operation, [13].
The V-I equation of a module is similar to that of solar PV cell. The V-I curve of the module is
the combination of V-I curve of all solar cells connected in a module. Equation 2.3 gives output
current I
a
[13-14] for a PV array as:
Details
- Pages
- Type of Edition
- Erstausgabe
- Year
- 2016
- ISBN (PDF)
- 9783960675822
- ISBN (Softcover)
- 9783960670827
- File size
- 10.4 MB
- Language
- English
- Publication date
- 2016 (October)
- Keywords
- Maximum power point tracking Power quality Simulink Solar power Solar energy Solar photovoltaic grid connected system Solar Cell Technology Model analysis MPPT Control
