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DESIGN AND ECONOMIC ANALYSIS OF SOLAR PHOTOVOLTIAC
SYSTEM FOR URBAN AREA OF BANGLADESH
S. M. MOYNUL HAQUE
DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERINGBUET, DHAKA
NOVEMBER 2012
DESIGN AND ECONOMIC ANALYSIS OF SOLAR PHOTOVOLTIAC SYSTEM
FOR URBAN AREA OF BANGLADESH
By
S. M. Moynul Haque
(100706107P)
Supervised By
Dr. Shahidul Islam KhanProfessor, Department of Electrical and Electronic EngineeringBangladesh University of Engineering and Technology, Dhaka
This Thesis is submitted in Partial Fulfillment of the requirements for the Degree ofMaster of Science (M.Sc.) in Electrical and Electronic Engineering at Department ofElectrical and Electronic Engineering, Bangladesh University of Engineering and
Technology (BUET), Dhaka
November 2012
98
APPENDIX- E
Result obtained from PVSyst for 20 kWP system (On-grid)
99
100
101
102
103
104
APPENDIX- F
Cable Specification
105
106
APPENDIX- G
Result obtained from RETScreen for 3 kWP solar PV system(AC)( Off-Grid)
107
2.8 kWp Stand-Alone AC systemFor the 10 flat (Consider 2 fan of 80 W and 2 light of 23 W for each flat)
Project information (2.8 KWp Off-Grid)Project name 2.8 kWp Stad-alone(AC)Project location Dhaka, BangladeshPrepared for M.Sc.ThesisPrepared by S. M. Moynul HaqueProject type PowerTechnology PhotovoltaicGrid type Off-gridAnalysis type Method 2Heating value reference Lower heating value (LHV)Climate data location Dhāka
Load characteristics
Description AC/DC
Intermittentresource-loadcorrelation
Base caseload(kW)
Hours ofuse perday(h/d)
Days ofuse per
week (d/w)Fan 80 W 20 Piece DC Negative 1.60 4.00 7Light 23W 20 piece DC Negative 0.46 4.00 7
Proposed case power systemInverterCapacity kW 2.0Efficiency % 95%Miscellaneous losses % 5%BatteryDays of autonomy d 1.0Voltage V 48.0Efficiency % 90%Maximum depth of discharge % 60%Charge controller efficiency % 90%Temperature control method AmbientBattery temperature °CAverage battery temperature derating % 0.5%Capacity Ah 320Battery kWh 15
Resource assessmentSolar tracking mode FixedSlope ° 23.0Azimuth ° 0.0
108
Month Daily solar radiation -horizontal
Daily solar radiation -tilted
Electricityexported to grid
kWh/m²/d kWh/m²/d KWhJanuary 4.36 5.56 0.24February 4.92 5.78 0.22March 5.59 6.00 0.24April 5.76 5.69 0.24May 5.30 4.97 0.23June 4.53 4.19 0.19July 4.23 3.96 0.19August 4.29 4.15 0.20September 4.02 4.10 0.19October 4.32 4.82 0.23November 4.28 5.30 0.23December 4.21 5.52 0.24
Annual 4.65 5.00 2.65
Annual Solar RadiationAnnual solar radiation - horizontal KWh/m² 1700Annual solar radiation - tilted KWh/m² 1820
Energy ModelPhotovoltaicType poly-SiPower capacity kW 0.7Manufacturer BP SolarModel Poly-Si - BP 12 235WEfficiency % 14.1%Nominal operating cell temperature °C 45Temperature coefficient % / °C 0.40%Solar collector area m² 20Miscellaneous losses % 2.00%SummaryCapacity factor % 14.10%Electricity exported to grid KWh/yr 2650
Project CostInitial Cost AmountPhotovoltiac $ 3384Module Support Structure $ 600Other equipment $ 300Storage Battery $ 2000Transportation $ 300Training & commissioning $ 300Inverter & Charge controller $ 650
109
Contingencies $ 166Total Investment $ 7,700
Annual costs (credits) AmountOperation & maintenance cost $ 100Sub-total: $ 100
Periodic costs (credits) AmountInverter & controller 10 yr $ 650Battery Replacement 5 yr $ 1,600
RETScreen Financial Analysis - Power projectFinancial parametersFuel cost escalation rate % 5Inflation rate % 6Discount rate % 8Project life yr 20Incentives and grants $ 0Debt ratio % 0GHG Reduction SavingsNet GHG reduction tCO2/yr 2Net GHG reduction - 20 yrs tCO2 47GHG reduction credit rate $/tCO2 4GHG reduction income $ 9GHG reduction credit duration yr 20GHG reduction credit escalation rate % 5Annual savings and incomeFuel cost -base case $ 963GHG reduction income $ 9Total annual savings and income $ 972Financial viabilityPre-tax IRR - equity % 8.5Pre-tax IRR - assets % 8.5After-tax IRR - equity % 8.5After-tax IRR - assets % 8.5Simple payback yr 8.8Equity payback yr 8.9Net Present Value (NPV) $ 291Annual life cycle savings $/yr 30Benefit-Cost (B-C) ratio 1.04GHG reduction cost $/tCO2 33
110
Yearly cash flowsYear Pre-tax After-tax Cumulative
# $ $ $0 -7,700 -7,700 -7,7001 915 915 -6,7852 960 960 -5,8253 1,007 1,007 -4,8184 1,056 1,056 -3,7625 -1,034 -1,034 -4,7966 1,161 1,161 -3,6357 1,218 1,218 -2,4178 1,277 1,277 -1,1399 1,340 1,340 200
10 -2,624 -2,624 -2,42411 1,473 1,473 -95112 1,545 1,545 59413 1,620 1,620 2,21514 1,699 1,699 3,91415 -2,052 -2,052 1,86216 1,869 1,869 3,73017 1,960 1,960 5,69018 2,055 2,055 7,74519 2,155 2,155 9,900
From PVsyst program Energy production cost is US $ 0.32/kWh.
111
0
5000
10000
15000
20000
25000
30000
0 1 3 5 7 9 11 13 15 17 19
Year
Cum
mul
ativ
e In
vest
men
t ($)
Fig : Cumulative investment considering 6% inflation
For the 10 flat,Investment for IPS system=$ 400*10=$ 4000
Investment for Solar system=$ 7700Battery replaces 5 yrInverter/Ips controller replacement 10 yr.
From the above graph we see that cumulative investment for IPS system crosses that ofsolar system after 9 years as it has to pay for both energy and battery replacement
Comment : Solar system is better than IPS system considering more than 9 years.
Solar System
IPS System
I
DECLARATION
It is hereby declared that this thesis or any part of it has not been submitted elsewherefor the award of any degree or diploma.
Signature of the candidateS. M. Moynul HaqueRoll : 100706107 P
II
APPROVAL
The project entitled, “Design and economic analysis of solar Photovoltaic system forurban area of Bangladesh”, submitted by S. M. Moynul Haque, Roll No. 100706107P,Session October, 2007 has been accepted as satisfactory in partial fulfillment of therequirements for the degree of Master of Science in Electrical and ElectronicEngineering on November 14, 2012.
BOARD OF EXAMINERS
1. ……………………………………
Dr. Shahidul Islam Khan (Chairman)Professor (Supervisor)Department of Electrical & Electronic EngineeringBangladesh University of Engineering and Technology,Dhaka-1000, Bangladesh.
2. ……………………………………
Dr. Pran Kanai Saha (Member)Professor and Head of dept. (Ex-Officio)Department of Electrical & Electronic EngineeringBangladesh University of Engineering and Technology,Dhaka-1000, Bangladesh.
3. ……………………………………
Dr. Md. Shah Alam (Member)ProfessorDepartment of Electrical & Electronic EngineeringBangladesh University of Engineering and Technology,Dhaka-1000, Bangladesh.
4. ……………………………………
Dr. Abdur Rahim Mollah (Member)Professor and Head (External)Department of Electrical & Electronic EngineeringAhsanullah University of Science and Technology,Dhaka-1208, Bangladesh.
III
ACKNOWLEDGEMENT
To complete this work various persons help me in various ways. I wish to record
sincere thanks to all of them.
First of all I would like to take this opportunity to thank my supervisor Prof. Dr.
Shahidul Islam Khan, Professor, Electrical and Electronic Engineering Department,
Bangladesh University of Engineering and Technology, Dhaka for his valuable
guidance, inspirations, suggestions and support throughout my postgraduate program.
I would also like to express my special thanks to the concerned officials of Institute of
Renewable Energy (IRE), Dhaka University, Rahimafrooz Renewable Energy
Limited, Greenpower Renewable Energy Limited, Bangladesh Bank, Independent
University, Grameen Shakti, Banglalink Mobile Company for providing various PV
related information.
I also express thanks to the concerned officials of BPDB, REB, PGCB, Petrobangla
for various generation and Distribution related information.
Finally, I would like to thank my family and friends for their support throughout my
postgraduate school experience.
IV
DEDICATION
This thesis is dedicated for my parents and my wife.
V
ABSTRACT
Bangladesh, a developing country of south-east Asia with large population hasagricultural economy. It has severe shortage of electricity. The gas is the main fuel forelectricity generation which is depleting very quickly. In recent days government hasimplemented high cost imported liquid fuel based electricity generation plant as ashort time measure. Bangladesh has abundant sun shine to harness PV power. SolarHome System program with micro financing for rural electrification has gainedworldwide recognition. The government has adopted Renewable Energy Policy inDecember 2008. In this policy target has been set to generate 5% of total electricityfrom renewable sources by 2015 and 10% by 2020. Now this Stand Alone PV systemis becoming popular in urban areas due to acute load shedding. This thesis proposesthree different configurations of solar photovoltaic system for urban areas. Technicaland economic analysis has been done. It is proved that PV energy could be a costeffective solution to meet the electricity crisis in urban areas in Bangladesh. Feed-inTariff has also been calculated and found to be comparable to liquid fuel basedpower, if Government subsidy is provided.
VI
TABLE OF CONTENTS
ACKNOWLEDGEMENTS..................................................................................... III
DEDICATION ........................................................................................................ IV
ABSTRACT............................................................................................................. V
LIST OF TABLES ................................................................................................... X
LIST OF FIGURES................................................................................................. XI
Chapter 1: Introduction .......................................................................................... 11.1 Introduction 11.1 Sources of Energy: Renewable and Non-Renewable energy Resources 21.2 Renewable Energy Sources of Bangladesh 21.2.1 Wind Energy 21.2.2 Hydro Energy 21.2.3 Tidal power 31.2.4 Bio-gas 31.2.5 Solar Energy 31.3 Electricity statistics 51.4 Energy demand 61.5 Scenario of Solar power in Bangladesh 61.6 Scope of the thesis 7
Chapter 2: Basics of solar PV System..................................................................... 9
2.0 Introduction 92.1 Photovoltaic cell technology 92.2 Theory and Basics of solar cell 102.3 Solar radiation in atmosphere 132.4 Components of PV system 152.5 Balance of system equipment (BOS) 162.5.1 Charge controller 172.5.2 Battery storage 172.5.3 Inverter (DC-AC Converter) 192.5.4 Cables and Fuses or circuit breakers 212.6 Photovoltaic system types 212.6.1 Stand-Alone photovoltaic system 212.6.2 Grid-connected or utility-interactive photovoltaic system 222.6.3 'Hybrid Grid' - Solar Electric and Generator Combination systems 232.6 Conclusions 23
VII
Chapter 3: PV System design and financial analysis ........................................... 24
3.0 Introduction 243.1 System Design Procedure 243.2 Selection of Balance of system (BOS) components 283.3 System Installation 293.4 Investment Analysis 303.4.1 Simple payback period 303.4.2 Net Present Value (NPV) method 313.4.3 Internal Rate of Return (IRR) Method 323.4.4 Monthly energy expense 323.4.5 Year to positive cash flow 323.4.6 Profitability index - PI 333.5 Design and analysis of a PV system by PVsyst 5.56 software 333.6 Design and analysis of a PV system by RETScreen software 333.7 Conclusions 34
Chapter 4: Design and Analysis of a Stand-alone PV System ............................ 35
4.0 Introduction 354.1 Design parameter and important assumption for design and analysis 354.2 Design a stand-alone PV system by standard procedure 374.2.1 Base of solar home system design 384.2.2 Electric Load Calculation 384.2.3 Array Sizing Worksheet 384.2.4 Controller Sizing 394.2.5 Battery sizing 394.2.6 System wire sizing 394.3 Design PV system by PVsyst software 404.4 Economic analysis PV system by RETscreen software 414.5 Financial analysis for various conditions obtaine from RETScreen software 424.5.1 Effect of discount rate 424.5.2 Effect of Subsidy 424.5.3 Effect of autonomy 434.5.4 Load comparison with general AC system 444.6 Conclusions 44
Chapter 5: Grid-Interactive Solar PV System ..................................................... 45
5.0 Introduction 455.1 The Basic Principle 455.2 The Design Parameter 465.3 Design of a Typical Grid - Interactive SHS 475.3.1 Array Sizing 48
VIII
5.3.2 Choosing a Grid -Tied Inverter 485.3.3 Back up Controller device 485.3.4 Battery sizing 485.4 Design and analysis PV system by RETScreen software 495.4.1 Effect of discount rate 505.4.2 Effect of Subsidy 515.5 Conclusions 51
Chapter 6: Grid- Tied Solar PV System............................................................... 52
6.0 Introduction 526.1 The Basic Principle 526.2 The Design Parameter 536.3 Design of a Typical Grid - Tied SHS 596.3.1 Load Estimation 596.3.2 Array Sizing 596.3.3 Inverter sizing 596.4 Simulation Result 596.5 Economic analysis of the PV system by RETscreen 616.5.1 Effect of Subsidy 616.5.2 Effect of discount/depreciation rate 636.5.3 Effect on size of system 646.5.4 Effect on energy export rate 646.5.5 Effect on interest rate 656.6 Diesel generator verses solar system 666.7 GHG reduction effect 676.8 Conclusions 67
Chapter 7: Feed In tariff ....................................................................................... 68
7.0 Introduction 687.1 Key provisions for FIT 687.2 Types of FIT 687.3 Feed in tariff (FIT) in present world 697.4 Find a Feed in tariff perspective Bangladesh 707.5 Effect on interest rate 717.6 Conclusions 71
Chapter 8: Conclusion and Recommendations .................................................... 72
8.1 Findings from the study 728.2 Contribution/Achievement 738.3 Recommendation 73
REFERENCES 75
IX
APPENDICES
APPENDIX A ....................................................................................................... 77
APPENDIX B ....................................................................................................... 82
APPENDIX C ....................................................................................................... 88
APPENDIX D ....................................................................................................... 93
APPENDIX E ....................................................................................................... 98
APPENDIX F...................................................................................................... 104
APPENDIX G ..................................................................................................... 106
X
LIST OF TABLES
Table 1.1: Electricity statistics in Bangladesh ............................................................ 5
Table 2.1: Average horizontal solar radiation at different cities of Bangladesh ........ 15
Table 2.2: Cycling performance with respect to depth of discharge.......................... 18
Table 4.1: Table for Load Determination of Stand alone PV system for the house ... 38
Table 4.2: Load comparison of proposed PV system with general AC system.......... 44
Table 5.1: Energy consumption of the house............................................................ 47
Table 6.1: Changed of financial parameter with subsidy .......................................... 61
Table 7.1: FIT for different countries of the world ................................................... 69
XI
LIST OF FIGURES
Fig 1.1: Solar radiation data map of Bangladesh ........................................................ 4
Fig 2.1: The generation of electron-hole pairs by light ............................................. 11
Fig 2.2: Conversion of Light energy to Electrical Energy......................................... 12
Fig 2.3: Electrical equivalent circuit of a Solar Cell ................................................. 12
Fig 2.4: I/V and P/V characteristics curve of a Solar Cell......................................... 13
Fig 2.5: Solar radiation in atmosphere ..................................................................... 13
Fig 2.6: Effect of Air mass....................................................................................... 14
Fig 2.7: The Photovoltaic hierarchy ......................................................................... 16
Fig 2.8: Stand-alone system with battery storage powering DC and AC loads.......... 22
Fig 2.9: Block diagram of grid-connected photovoltaic system ................................ 23
Fig 4.1: Diagram of the PV system for the house ..................................................... 37
Fig 4.2: Energy usages for the whole year as obtained from PVsyst program.......... 40
Fig 4.3: Energy diagram over the whole year as obtained from PVsyst program ..... 41
Fig 4.4: Effect of discount on NPV and energy production cost ............................... 42
Fig 4.5: Effect of subsidy on Investment and energy production cost ....................... 43
Fig 4.6: Effect of autonomy on Investment and energy production cost ................... 43
Fig 5.1: Block diagram of the PV system for the house............................................ 48
Fig 5.2: Cumulative cash flow diagram of a 10 kW on-grid(battery backup) system 49
Fig 5.3: Effect of discount rate on energy production cost and NPV ........................ 50
Fig 5.4: Effect of discount rate on energy production cost and PI index ................... 50
Fig 5.5: Effect of subsidy on energy production cost, Investment and NPV ............. 51
XII
Fig 6.1: Block diagram of grid-connected photovoltaic system ................................ 53
Fig 6.2: Energy usages for the whole year from PVsyst ........................................... 60
Fig 6.3: Loss diagram over the whole year from PVsyst .......................................... 60
Fig 6.4: Cumulative cash flow graph from RETScreen ............................................ 61
Fig 6.5: Effect of subsidy on investment, energy production cost and NPV.............. 62
Fig 6.6: Effect of subsidy on NPV and profitable index(PI) ..................................... 62
Fig 6.7: Effect of discount rate on energy production cost and NPV ........................ 63
Fig 6.8: Effect of discount rate on energy production cost and PI............................. 63
Fig 6.9: Effect of system size on energy production cost and Investment ................. 64
Fig 6.10: Effect of energy export rate on NPV and IRR .......................................... 64
Fig 6.11: Effect of energy export rate on NPV and Payback period.......................... 65
Fig 6.12: Effect of energy export rate on NPV and PI .............................................. 65
Fig 6.13: Effect of Interest rate on energy cost, FIT and NPV................................. 66
Fig 6.14: Cumulative cost comparison of diesel generator and solar system............. 67
Fig 7.1: Effect of energy export rate on NPV and IRR ............................................. 70
Fig 7.2: Effect of system size on energy production cost and Investment ................. 70
Fig 7.3: Effect of Interest rate on FIT, energy production cost and NPV .................. 71
1
CHAPTER 1
Introduction
1.0 IntroductionEnergy crisis is the most important issue in today’s world. Adequate and affordableenergy is one of the most important factors for a country’s economic growth,eradicating poverty, improving human welfare and raising living standard. Bangladeshis an energy deficit and low-economy country with high population density in third-world. At present the peak power demand in Bangladesh is about 6400 MW and thegeneration is less than 5000 MW. As a result power shortage causes excessive loadshedding. Only 53 percent population [1] has access to electricity. Presently Per capitapower consumption is only 265 kWh.
In Bangladesh most of the power plant runs by conventional energy resources likenatural gas, coal and other fuel. These Conventional energy resources are not onlylimited but also the prime severe for environmental pollution. Their uses results globalwarming due to emission of greenhouse gases like carbon dioxide (CO2) into theatmosphere. Emissions of CO2 can be greatly reduced through the application ofrenewable energy technologies, which are already cost competitive with fossil fuels.
About 68% of the nation’s total energy comes from traditional fuels, such as fuelwood, crop residuals and animal biomass, while 32% is supplied by commercialenergy (including hydro power). Except natural gas, all commercial fuels are imported.Although coal is available in big amount, the production is economically not feasiblebecause of its deep position.
To reduce the dependency on imported fuel and the pressure on natural gas, the presentpower generation system must be diversified and at the same time indigenous energyresources have to be explored and developed. Gradual increase of electricity demandwith the growth of population always needs more conventional fuel and depletes itsreserves, but renewable energy sources save the conventional fuels and give a pollutionfree environment. Better exploitation and efficient utilization of the renewable energyresources require research, motivation and public awareness throughout the country.
Bangladesh is very successful in rural electrification in off grid areas with Solar HomeSystem (SHS). Under the umbrella of Infrastructure Development Company Limited(IDCOL), solar home system has popularized in rural areas. After the inception ofGrameen Shakti in 1996, the program has got impetus. Now Bangladesh has over 1.4million SHS [2] with a total capacity of 65 MW. But in urban area it is still neglected.Again load shedding is a common issue in our country but we cannot overcome thisproblem. Government is trying to solve this problem but still failed with convenient
2
resources. Renewable energy (mainly solar power) is most appropriate solution forBangladesh in this point of view. Study shows that On-grid [3], grid-tied [4] and Off-grid [5] solar systems are feasible in Bangladesh.
1.1 Sources of Energy: Renewable and Non-Renewable energy ResourcesRenewable: Energy sources, which are regenerated after a regular time cycle, arecommonly known as renewable sources of energy e.g. hydropower, wind, solarenergy, tidal energy, biomass fuels, etc.
Non-renewable: Energy resources formed within earth’s crust over a period ofmillions of years are called non-renewable energy sources; as for example coal, oil,natural gas. They are considered non-renewable because once they’ are removed fromthe ground and used they are not immediately replaced.
1.2 Renewable Energy sources of BangladeshBangladesh is blessed with a number of potential renewable and alternative resourcesare solar, wind, water, biomass and biogas.
1.2.1 Wind EnergyWind energy has been utilized since ancient times as windmills for milling and waterlifting in countries like Denmark, Norway and USA. In Bangladesh wind energy hasfound very limited applications, simply because of non-availability of reliable wind.Some costal locations of Bangladesh have fair wind speed between 4.0 and 4.5 m/s at25m above sea level. Between 4.5 and 6 m/s at 50m above ground level which is goodfor wind turbine.
In Bangladesh Small Wind Turbines can be installed in the coastal region andoffshore islands. Several organizations have installed low capacity wind turbines,mainly for battery charging in the coastal region (Chittagong, St.Martin’s island). Thepilot project (4×225 kW) at Muhuri Dam site under Feni district by BPDB is amilestone of Bangladesh for wind power. Later 20×50 kW system has been installedin Kutubdia Island. However, progress in the wind energy sector of Bangladesh is notimpressive.
1.2.2 Hydro EnergyBeing a flat country, Bangladesh is not in a favorable position for large-scalehydropower. There are small potential of mini and micro-hydropower in CHT regionand greater Sylhet region. The total hydropower potential of the country in threelocations (Kaptai, Sangu and Matamuhuri) is 1500 GWh/year (755 MW) of whichabout 1000 GWh/year (230 MW) has been harnessed at Kaptai through 5 units ofhydropower plants [6]. Future development of hydropower at Sangu and Matamuhurishould be considered with due attention to their negative impacts on environment andon local population.
3
1.2.3 Tidal powerA mean head of at least five meters is usually considered to be the minimum forviable tidal power generation. Therefore, there is very less potential prospect of tidalresource in Bangladesh. There may be scope of integrated tidal power plants in thecoastal regions[7].
1.2.4 Bio-gasAgriculture based country Bangladesh has huge potential for utilizing biogastechnology. Biogas is a fuel gas obtained from anaerobic (i.e. in the absence ofoxygen) digestion of cattle dung, poultry droppings, human excreta, and agriculturalresidues. Bangladesh is in a favorable position in respect of availability of rawmaterials and the climatic conditions for biogas production. Cost is the most dominantfactor limiting the wide application of biogas.
1.2.5 Solar EnergyThe energy received by the earth from the sun in the form of radiation is known assolar energy. The sun is a never-ending supply of free energy. Every day, the sunpours unimaginable amounts of energy into space. Some of it is in the form ofinfrared and ultraviolet light, but most of it is in the form of visible light. Some of thisenergy falls on the Earth, where it warms our planets surface, drives ocean currents,wind flow, used by plants to make food etc. Life on Earth depends totally on the sun.
Compared to any other renewable resources, solar has brighter prospect fromapplication point of view. To a good approximation, the earth acts as a perfect emitterof radiation (black body). At the outer limit of the atmosphere the total solarirradiation when the earth is at its mean distance from the sun is known as the solarconstant.
S = 1367 W/m2
Solar radiation intensity is strongly dependent on atmospheric conditions, time of theyear, and the angle of incidence for the sun’s rays on the surface of the earth. Solarradiation received at earth’s surface is quite different from extra terrestrial radiation isimportant for utilization point of view. In general, the total power from a radiantsource falling on a unit area is called irradiance.
Bangladesh is situated between 20.30 - 26.38o north latitude and 88.04 - 92.44o east,which is an ideal location for solar energy utilization. However, the use of solarenergy, as a commercial energy source has not yet received any popular acceptance inthe country. The availability of reliable and well-organized data on solar isolation inthe region is also limited. At present, solar isolation data (Fig. 1.1) can be found fromInstitute of Renewable Energy (IRE), Dhaka University (DU). Apart from the above
4
mentioned sources, few other organizations or institutes have also measured timeseries of global radiation, direct or beam radiation, diffuse radiation, sunshine hoursand temperatures of different parts of the country. But for meticulous estimation andsimulation of different solar energy applications several other parameters are requiredwhich are not available at the moment.
Fig. 1.1 Solar radiation data map of Bangladesh
5
1.3 Electricity statistics
In Jan 2010 the total capacity of the installed power plants of the country was about5800 MW from which the maximum attainable capacity amounted to 5100 MW [6],Most of the installed electric generating capacity (>90 %) was thermal (mainlynatural-gas fired) and the remainder hydroelectric and coal fired. Timely maintenanceand replacement of old units have not been possible due to non-availability of funds.As a result, till today it is difficult to maintain a reliable supply due to shortage ofavailable generation Capacity. At present some quick rental oil based power plant isinstalled to meet peak hour demand, whose production cost is high.
Table 1.1 Electricity statistics in Bangladesh
Installed Capacity (MW) 5719
Attainable Capacity (MW) 5166
Maximum peak Demand (MW) 6000-6100
Average generation (MW) 3500-3800
Transmission Line(230KV+132 KV) (km) 1,321+3,191
Per capita generation (kWh) 183
Per capita consumption (kWh) 165
Access to electricity 57%
Average growth rate 8%
1.4 Energy demand
In the rural areas about 83% of households depend on biomass fuels for cooking,while biomass fuel accounts for 70 to 76% of the total fuel in rural industries such aspaddy parboiling, smithies and potteries. In Bangladesh, commercial energy resourcesare used to meet the demand for the following end-use sectors: fertilizer (35%),industry (19%), transport (19%) and domestic (17%) sectors consume more energythan other energy sectors [9]. All of these sectors use electricity and 90% of thiselectricity is generated from natural gas, while fertilizer production requires thesupply of natural gas. Considering the projected future demand and concern about thesecurity of supply, over use of natural gas resources therefore needs to be avoided asenergy demand is increasing day by day due to various reasons.
1.5 Scenario of Solar Power in Bangladesh
Energy issue has become a global concern. Like other countries, Bangladesh also maynot find immediate and easy solution to the energy problem. Moreover, with thepassage of time the demand for energy in Bangladesh will increase further. From thepast experience it appears that there is prevalence of huge gap between demand andsupply.
6
Bangladesh has started the application of photovoltaic for remote homes in a massscale. Over 1,40,000 families now have solar electricity in their homes to light themup. And the number is going to be doubled soon. The total installed capacity of solarphotovoltaic applications has reached 65MWp [8]. Solar home systems have alreadybeen installed in different locations of the country for lighting rural home, Touristresort, off grid community clinic electrification, union paraishad complex, tribalcommunity electrification etc. by a number of government, semi government andautonomous bodies and also by some NGOs. But micro or mini grid PV system hasnot explored yet in Bangladesh. For the first time in Bangladesh, LGED hassuccessfully completed solar market electrification in a rural market at Gangutiaunder Shoilkupa upazila in Jhenaidah district. The successful installation of solarmarket electrification has created great enthusiasm among the local villagers and itwill act as a milestone for green energy movement in the country. Recently a I0KWpmini grid system has been installed in Barkal under Ragamati district by PDB. Alsothere is a 5kW mini grid system in Ukhia under cox’s bazar district. Bangladesh Bankin it’s headquarter in Dhaka has set up a 20.3kWp PV system.
Solar Home Systems have mainly targeted the rural areas of Bangladesh so the rangeof products is limited. These can however be expanded to include the solar lantern,solar torch light, solar thermal heater, and solar mobile charger. Small shop owners atrural growth centers, mini poultry farm owners, country boat operators, and policeand ansar-VDP forces, Union Parishad Chowkidars could be potential users of solarsystems. In urban areas slum people may use ‘these solar products to improve theirliving condition. Rickshaw puller may have the opportunity to use products like solarlantern in their rickshaws and other .products for their households.
In Bangladesh, building and houses located in all metropolitan areas could at least usesome of the solar products in lightning their garden, boundary wall, gates and furnishsecurity lights and water heating systems. RAJUK, CDA, KDA, RUK, citycorporations, which have a role in approving architectural and structural plans mayhave a good opportunity to recommend solar energy systems and hence reduce loadshed.
As strong solar radiation (varies from 4 to 4.5 kW/m2/day which is a very favorablerange for solar energy extraction) is available in Bangladesh throughout the wholeyear, photovoltaic technology is a feasible option to provide an alternative source ofenergy to meet the present requirement.
PV technology was not well known even few years ago in this country. However, thepotentiality of RETs is recognized by all and the power cell of the ministry of energy
7
and mineral resources has produced a draft renewable energy policy which is yet to beaccepted by the government of its implementation. The target proposed is to generatepower utilizing new renewable technologies to share 5% of total electricity demandby 2010 and 20% by 2020.
Bangladesh government has taken initiative to disseminate the renewable energy inremote areas where electricity will hardly reach in near future. To encourage thedevelopment of RET the Govt. of Bangladesh lifted the duty and Value Added Taxfrom solar PV in 1998.The Govt. of Bangladesh are also providing subsidies tovarious projects adopted by BPDB, REB and BCSIR.
1.6 Scope of the thesis
Per capita energy consumption in Bangladesh is one of the lowest in the world. Againgeneration of power is always less than demand. As a result power shortage causesexcessive load shedding. As strong solar radiation is available in Bangladeshthroughout the year except monsoon and hence at the moment photovoltaictechnology is a feasible option to provide an alternative source of energy to meet thepower requirement. Bangladesh is very successful in rural electrification in off gridareas with Solar Home System (SHS).Under the umbrella of InfrastructureDevelopment Company Limited (IDCOL), solar home system has popularized in ruralareas but the urban area is still neglected. Study shows that SHS [3] and grid-tied [4]systems are feasible in Bangladesh
The main objective of this thesis is to design and perform economic analysis of solarphotovoltaic system to overcome energy crisis in urban area hence reduce load shed.
The objectives are as follows:
i. Perform feasibility study of Solar Photovoltaic System for Urban areas ofBangladesh.
ii. Design of Solar Photovoltaic System for urban area with and without batterystorage.
iii. To perform economic analysis to find the cost effective solution of solarphotovoltaic system for different load and environmental condition in theurban areas of Bangladesh.
iv. To find a feed-in tariff for urban areas.
PVsyst 5.56 software [12] is used to design PV system and also RETscreensoftware[13] developed by Canada which is standard and integrated renewable energyproject analysis software has been used for the technical and economic analysis of theproposed system.
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In this thesis 3 types of PV system (Both Off and On grid) system will be designed forurban areas of Bangladesh. Its economic and technical evaluation and analysis hasbeen done.
Chapter 2 of this project describes the basic principle of solar conversion technologyand function of every components need for this system.
Chapter 3 describes the general standard procedure with necessary formula fordesigning a PV system such as load calculation, array sizing, charge controller sizing,battery sizing, inverter sizing, selection of cables etc. This chapter also brieflydescribes the various financial parameters such as year to pay back, net present value,internal rate of return, profitability index etc for financial analysis of the project andthe PVsyst software uses for technical and RETScreen software uses for technical andfinancial analysis.
In chapter 4, A 700WP stand-alone PV system is designed according to proceduredescribed in chapter 3 and technical and economic analysis is done.
In chapter 5, A 10kWP Grid-interactive (With battery back-up) PV system is designedfor medium size flat hose according to procedure described in chapter 3 and technicaland economic analysis is done.
In chapter 6, A 20kWP Grid-Tie (Without battery back-up) PV system is designed forcommercial or office building according to procedure described in chapter 3 andtechnical and economic analysis is done.
Chapter 7 describes about Feed In Tariff and find out a Feed In Tariff (FIT) for Grid-Tie system perspective Bangladesh.
In chapter 8, Specific conclusions are made on the basis of analysis. At the endrecommendations and future work has been suggested.
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CHAPTER 2
Basics of Solar PV System
2.0 Introduction
In today’s climate of growing energy needs and increasing environmental concern,alternatives to the use of non-renewable and polluting fossil fuels have to beinvestigated. One such alternative is solar energy.
Research into photovoltaic technology began over one hundred years ago. Scientistscontinued limited research on the selenium solar cell through the 1930’s, despite itslow efficiency and high production costs. The first conventional photovoltaic cellswere produced in the late 1950s and throughout the 1960s were principally used toprovide electrical power for earth-orbiting satellites. In the 1970s, improvements inmanufacturing, performance and quality of PV modules helped to reduce costs andopened up a number of opportunities for powering remote terrestrial applications,including battery charging for navigational aids, signals, telecommunicationsequipment and other critical, low power needs. In the 1980s, photovoltaic became apopular power source for consumer electronic devices, including calculators, watches,radios and other small battery charging applications. Today, a major internationalmarket for photovoltaic is providing power to the billions of people throughout theworld who live without electrical service, for application such as health care facilities,community centers, water delivery and purification systems and rural residences.
The worldwide demand for solar electric power systems has grown steadily over thelast 15 years. The need for reliable and low cost electric power in remote areas of theworld is the primary force driving the worldwide photovoltaic (PV) industry today.For a large number of applications, PV technology is simply the least-cost option.
2.1 Photovoltaic cell technology
To make modules, PV manufacturers utilize crystalline silicon wafers or advancedthin film technologies which vary from each other in terms of light absorptionefficiency, energy conversion efficiency, manufacturing technology and cost ofproduction. In the former, single crystal silicon (single-Si), polycrystalline silicon(poly-Si) or ribbon silicon (ribbon-Si) wafers are made into solar cells in productionlines utilizing processes and machinery typical of the silicon semiconductor industry.Solar cell manufacturers then assemble the cells into modules or sell them to modulemanufacturers for assembly. Because the first important applications of PV involvedbattery charging, most modules in the market are designed to deliver direct current
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(DC) at slightly over 12/24/48V. A typical crystalline silicon module consists of aseries and parallel circuit, encapsulated in a glass and plastic package for protectionfrom the environment. This package is framed and provided with an electricalconnection enclosure, or junction box.
In thin-film PV technologies, ultra-thin layers (a single amorphous cell can be as thinas 0.3 micrometers) of the PV material are deposited on glass or thin metal thatmechanically supports the cell or module. There are four advanced thin filmtechnologies. Their names derive from the active cell materials: cadmium telluride(CdTe), copper indium diselenide (CIS), amorphous silicon (a-Si) and thin filmsilicon (thin film-Si). However, thin film PV cells suffer from poor cell conversionefficiency.
The technology based on crystalline silicon is the most reliable and most developedtechnology at the present time. Crystalline silicon cells represent the largest part of themarket. To reduce the cost, these cells are now often made from multicrystallinematerial, rather than from the more expensive single crystals. Typical conversion(solar energy to electrical energy) efficiencies for common crystalline silicon modulesare in the 11 to 15 % range. Thin-film solar cells hold the promise of inexpensivetechnology with acceptable conversion efficiencies. Regardless of size, a typicalsilicon PV cell produces about 0.5-0.6 volt DC under open-circuit no-load conditions.The current (and power) output of a PV cell depends on its efficiency and size(surface area), and is proportional the intensity of sunlight striking the surface of thecell. A solar panel doesn’t store energy like a battery; it directly converts the Sun’sradiated electromagnetic energy to a flow of electrons (electricity). Without sunlight,the photoelectric effect stops.
2.2 Theory and Basics of Solar Cell
The most abundant and convenient source of renewable energy is solar energy, whichcan be harnessed by photovoltaic cells. The word photovoltaic comes from “photo”means light and “voltaic” means producing electricity. Therefore, the photovoltaicprocess is “producing electricity directly from sunlight”. The output power of aphotovoltaic cell depends on the amount of light projected on the cell. Time of theday, season, panel position and orientation are also the factors behind the outputpower. Sometimes photovoltaic cells are called PV cells or solar cells for short.
Photovoltaic energy conversion relies on the quantum nature of light whereby weperceive light as a flux of particles photons which carry the energy
Eph (λ) =hc/ λ (2.1)
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Where,
h = Planck constant
c = Speed of light
λ = Wavelength of light.On a clear day, about 4.4 x 1017 photons strike a square centimeter of the Earth’ssurface in every second.
Only some of these Photons with energy higher than the band-gap energy of PVmaterial can make electrons in the material break free from atoms that hold them andcreate hole-electron pairs, as shown in Fig. 2.1. These electrons, however, will soonfall back into holes causing charge carriers to disappear. If a nearby electric field isprovided, those in the conduction band can be continuously swept away from holestoward a metallic contact where they will emerge as an electric current. The electricfield within the semiconductor itself at the junction between two regions of crystals ofdifferent type, called a p-n junction.
Fig. 2.1: The generation of electron-hole pairs by light
The PV cell has electrical contacts on its top and bottom to capture the electrons, as
shown in Figure 2.2. When the PV cell delivers power to the load, the electrons flow
out of the n-side into the connecting wire, through the load, and back to the p-side
where they recombine with holes. Note that conventional current flows in the opposite
direction from electrons.
The electrical equivalent circuit of a solar cell is shown in Fig. 2.3. It has a current
source IPh, a diode and two resistors (RS and RSH). Upon incidence of light on the
solar cell, current IL is generated and part of the current can be delivered to load.
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Fig. 2.2: Conversion of Light energy to Electrical Energy
Fig. 2.3: Electrical equivalent circuit of a Solar Cell
The Current of the solar cell is given by the following equation:
RshIRsVnKTIRsVqIoIphI /)(}1]/)({exp[ ……..(2.2)
Where,
I = Output current (amperes)
Iph= photo-generated current (amperes)
Id = diode current (amperes)
V = voltage across the output terminals (volts)
RS = series resistance (Ω)Io = reverse saturation current of diode (amperes)
n = diode ideality factor (1 for ideal diode)
q = elementary charge
k = Boltzmann's constant
T = absolute temperature
RSh = shunt resistance (Ω)
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No power is generated under short or open circuit. The maximum power Pmax
produced by the device is reached at a point on the characteristic where the productIV is maximum. This is shown graphically in Fig. 2.4 where the position of themaximum power point represents the largest area of the rectangle shown. One usuallydefines the fill-factor FF by
Pmax = Vm Im =FF Voc Isc ……………………….(2.3)
Where, Vm and Im, are the voltage and current at the maximum power point.
The current-voltage and power-voltage characteristics of a photovoltaic cell are
shown in Fig. 2.4.
Fig. 2.4: I/V and P/V characteristics curve of a Solar Cell
2.3 Solar radiation in atmosphere
The solar radiation that is not reflected or scattered and reaches the surface directly inline from the solar disc is called direct or beam radiation. The sunlight receivedindirectly, as a result of scattering due to clouds, fog, dust, moisture vapor or othersubstances in the atmosphere is called diffuse radiation. Some of the radiation mayreach a receiver after reflection from the ground and is called the albedo. The totalradiation consisting of these three components is called global.
Fig. 2.5 Solar radiation in atmosphere
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amount of radiation that reaches the ground is, of course, extremely variable, inaddition to the regular daily and yearly variation due to the apparent of the sun,irregular variations are caused by the climatic condition (cloud cover), as well as bythe general composition of the atmosphere. For this reason, the design of a PV systemrelies on the input of measured data close to the site of the installation. A conceptwhich characterizes the effect of a clear atmosphere on sunlight is the air mass ‘m’(Fig 2.6) equal to the relative length of the direct beam path through the atmosphere(with no clouds, dust, air pollution). On a clear summer day at sea level, the radiationfrom the sun at zenith (i.e. directly over head) corresponds to air mass 1(AM1); atother times, the air mass is approximately equal to l/cosθz , where θz is the zenithangle.
Air mass, m = 1/cosθz……………………….(2.4)
Fig. 2.6 Effect of Air mass
AM 0 = radiation outside earth’s atmosphere important for satellite applicationsAM 1 = refers to sun directly overhead
AM2 = zenith angle is 60
AM1.5 = is used for the calibration of solar cells and modules
Although the global irradiance can be as high as 1kW/m2, the available irradiance isusually considerably less than this maximum value because of the rotation of the earthand adverse weather condition. Solar irradiance integrated over a period of time iscalled solar irradiation.
The inclination close to the latitude angle of the site will maximize the radiation on aninclined panel over the whole year. In stand-alone systems, it is usual to choose asomewhat steeper angle to minimize storage requirement
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Table 2.1: Average horizontal solar radiation at different cities of Bangladesh
Month
Average solar radiation - horizontal
(kWh/m²/d)Average
temp.(°C)
Dhaka Rajshahi Sylhet Bogra Barishal Jessore Dhaka
January 4.36 4.32 4.37 4.34 4.35 4.28 18.8
February 4.92 5.25 5.04 5.07 4.95 4.91 22.5
March 5.59 5.95 5.60 5.87 5.57 5.60 26.5
April 5.76 6.33 5.62 6.05 5.65 5.90 27.1
May 5.3 5.74 4.84 5.51 5.25 5.53 27.9
June 4.53 5.04 4.22 4.74 4.05 4.62 27.8
July 4.23 4.41 4.18 4.26 3.89 4.24 27.3
August 4.29 4.36 4.30 4.30 3.91 4.24 27.3
September 4.02 4.03 3.94 3.91 3.83 4.02 26.5
October 4.32 4.42 4.36 4.36 4.29 4.33 24.6
November 4.28 4.46 4.29 4.39 4.23 4.27 21.3
December 4.21 4.21 4.17 4.17 4.24 4.18 18.7
Average 4.65 4.87 4.57 4.74 4.51 4.67 24.7
2.4 Components of PV Systems
PV modules are integrated into systems designed for specific applications.
PV cells, Modules, Panels and Arrays
PV cells are semiconductor devices that convert sunlight into direct-current. A typicalsilicon PV cell is a thin wafer consisting of an ultra-thin layer of phosphorus-doped(N-type) silicon on top of a thicker layer of boron-doped (P-type) silicon.
PV modules consist of PV cell circuits sealed in an environmentally protectivelaminate and are the fundamental building block of the complete photovoltaicgenerating unit. PV modules are rated on the basis of the power delivered underStandard Testing Conditions (STC). Their output measured under STC is expressed interms of “peak Watt” or Wp nominal capacity. A module is an assembly ofphotovoltaic cells wired in series or series/parallel to produce a desired voltage andcurrent.
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Fig 2.7 The photovoltaic hierarchy
The three most important electrical characteristics of a module are short-circuitcurrent, open-circuit voltage and the maximum power point as functions of thetemperature and irradiance. These characteristics resemble the I-V characteristic of asolar cell. Modules are available in a variety of sizes and shapes.
PV panels include more than one PV module assembled as a pre-wired, fieldinstallable unit. A panel is a group of modules wired together to achieve a desiredvoltage.
A PV array is the complete power-generating unit, consisting of any number of PVmodules and panels. The modules are connected in series strings to provide therequired operating voltage (in multiples of the module nominal voltage of 12V). Abypass diode is connected across each module to minimize the hot-spot effect. Stringsof modules are connected in parallel to increase the current and hence the powergenerated (in multiples of string current). A blocking diode is connected in series witheach string to prevent battery discharge at night and also to prevent reverse currentsflowing between imperfectly matched strings.
2.5 Balance of System Equipment (BOS)
A complete PV system consists not only of PV modules, but also the “balance ofsystem’ or BOS - the support structures, wiring (cables, fuses, grounding circuit etc.),charge controller, battery storage, inverters for converting from DC (from battery orPV array) to AC (for AC appliances or grid connection) etc. i.e. everything else in aPV system except the PV modules. These components are required in any PV systemto conduct, control, convert, distribute, and store the energy produced by the array.
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2.5.1 Charge Controller
The main job of the charge controller [20] is to feed electricity from the solar panel tothe battery in the most efficient manner. A charge controller will prevent the batteryfrom overcharging by automatically disconnecting the module from the battery bankthen it is fully loaded. Most charge controllers also prevent batteries from reachingdangerously low charge levels by stopping the supply of power to the DC load. Theinverter LVD needs to be programmed to disconnect the AC loads.
If high currents are required, two or more charge controllers can be used. When usingmore than one controller, it is necessary to divide the array into sub-arrays. Each sub-array will be wired into its own controller and then they will all be wired into thesame battery bank.
Shunt controllers are designed for very small systems. They prevent overcharging by“shunting” or bypassing the batteries when they are fully charged. These controllersmay also incorporate a blocking diode to prevent current from draining back from thebatteries through the solar array at night. In large applications, it is advisable todisconnect the battery from the PV array by means of series regulator. This can be anelectromechanical switch (for example, a relay) or a solid-state device (bipolartransistor, MOSFET, etc). The former devices have the advantage that they do notdissipate energy but their reliability can be a problem in location with high dust andsand occurrence. Modern charge controllers often come equipped with their ownbuilt-in power inverters.
2.5.2 Battery Storage
When a PV module is connected to a suitable load, it will deliver electrical power thatis proportional to the strength of the light falling on its surface, in darkness or cloudythe module produces no power). In most off-grid PV systems, the variable powerfrom the PV module (or modules) is fed into a storage battery [20-21] and the loadtakes whatever power it requires from this battery. The most important function ofbatteries in PV power system is to store energy during the daytime and to deliver theenergy to electrical loads as needed (during the night or cloudy weather). Otherreasons batteries are used in PV systems are to operate the array near its maximumpower point, to operate electrical loads at suitable voltages. Batteries can also providethe necessary amounts of surge power (current higher than the PV array) required tostart some motors.
The size and configuration of the battery bank depends on the operating voltage of thesystem and the amount of nighttime usage (autonomy). In addition, local weatherconditions must be considered in sizing a battery bank. The number of modules mustbe chosen to adequately recharge the batteries during the day.
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In Photovoltaic applications charging process takes place during the whole day andthe discharging takes place during the night. Therefore, the batteries must have theability to provide adequate current during discharge up to the pre-specified depth ofdischarge and regain its full capacity through charging. In typical photovoltaicapplications the batteries should have a minimum life expectancy of 08-10 years. Thiswill reduce the maintenance cost of the system. The cycling performance with respectto depth of discharge is shown in table shown in table 2.2.
Table 2.2: Cycling performance with respect to depth of discharge
Depth of Discharge No of discharge cycle Estimated life time
Up to 10 % 7000 20
Up to 50 % 3600 10
Up to 75 % 1600 5
Loss of voltage during self-discharge should be minimal. High rate of self-dischargereduces its nominal capacity significantly. Self-discharge would increase due to thenatural aging of the storage cell, poor maintenance, uncontrolled usage, adding ofnon-distilled or non-mineralized water, high operating temperature etc.
The most common used battery types in photovoltaic systems are lead- acid (Nominalopen circuit voltage: 2.0 V/cell, Typical end voltage: 1.8 V/cell) and nickel- cadmium(Nominal open circuit voltage: 1.2 V/cell, Typical end voltage: 0.9-1.0 V/cell). Eachof these is made in a wide variety of constructions for different uses. Both areavailable in a wide range of capacities. Per unit of electrical energy stored(kWh),nickel-cadmium batteries are normally 3-4 times the price of lead-acid batteries. Thisthe main reason why lead-acid batteries are by far the most common type used in thePV system.
Battery is the heart of the PV system. For economic viability of the Solar System righttype battery needs to be selected. If the battery life can be optimized, the leastmaintenance can be achieved. During the selection of battery, the following factorsshould he considered:
Plate type of the battery- Tubular Plate battery is usually recommended forPhotovoltaic application, as it is capable of delivering current longer period, which isone of the essential requirements for Solar PV System. Depth of Discharge (DOD)should be up to 80%, which helps, in smaller battery bank resulting low initial cost ofthe system.
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Gel type battery- A gel battery is also known as a "gel cell" and gets its name fromthe gellified electrolyte employed to reduce electrolyte evaporation and spillage whichoften leads to corrosion problems. Gel batteries are known for better resistance toextreme temperatures, shock, and vibration and do not even need to be kept upright.Chemically they are the same as wet-cell batteries except that the antimony in the leadplates is replaced by calcium. In addition, gel battery technology is very similar toAGM batteries but uses this gelled electrolyte to recycle the gassing instead of theAbsorbent Glass Material that AGM batteries utilize.
The gel battery is also considered a VRLA battery, or Valve Regulated Lead Acidbattery, and is designated a low-maintenance lead-acid rechargeable battery. The gelbattery is also referred to as a sealed lead-acid battery, but will always include a safetypressure relief valve. Because the gel battery uses much less electrolyte or battery acidthan traditional batteries, they are also considered an "acid starved" design.
Discharge characteristic curves - should not fall below 1.8 volt per cell at 10 hourrate.
Proper vent plugs - there should be free exit of internally produced gas but restrictsexternal dust to enter the battery.
2.5.3 Inverter (DC-AC Converter)
Alternating current is easier to transport over long distance and has become theconventional modern electrical standard. Consequently, most common appliances orloads are designed to operate on alternating current. We know photovoltaic modulesgenerate only direct current power. In addition, batteries can store only direct currentpower. Alternating current and direct current are, by nature, fundamentallyincompatible. Therefore, a “bridge”-an inverter is needed between the two.
The fundamental purpose of a photovoltaic system inverter is to converts the DCinput voltage from the battery or PV array to a symmetrical AC output voltage ofdesired magnitude and frequency to power conventional appliances or to couple to themain grid.
There are two categories of inverters. The first category is synchronous or line-tiedinverter, which are used with utility-connected photovoltaic systems. The secondcategory is stand-alone or static inverters, which are designed for independent, utility-free power systems and appropriate for remote photovoltaic installations. Someinverters may have features from both types to facilitate future utility-connectedoptions.
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Another classification for inverters is the type of waveform they produce. The threemost common waveforms including the flowing:
- Square wave
- Modified square wave
- Sine wave
Square wave inverters -These units switch the direct current input into a stepfunction or square alternating current output. They provide line output voltagecontrol, limited surge capability, and considerable harmonic distortion. Consequently,square wave inverters are only appropriate for small resistive heating loads, somesmall appliance and incandescent lights. These types of inverter are inexpensive.
Modified square wave inverters- These type of inverter uses field effect transistorsor silicon controlled rectifiers to switch direct current output. These complex circuitscan handle large surges and produce output with much less harmonic distortion. Thisstyle of inverter is more appropriate for operating a wide variety of loads, includingmotors, lights, and standard electronic equipment likes TV and stereos etc.
Sine wave inverters - Sine wave inverters are used to operate sensitive electronichardware that requires a high quality waveform. They have many advantages overmodified square wave inverters. The pure sine wave inverter produces minimalharmonic distortion as required by sensitive electronic equipment and at higherefficiency than the stepped sine wave inverter but is more expensive. They have highsurge capabilities and can start many types of motors easily. Sine wave inverters canalso feed electricity back into the grid.
Specifying an inverter
Watts output: This indicates how many watts of power the inverter can supplyduring standard operation. It is important to choose an inverter that will satisfy asystem peak load requirements. However, system designers should remember thatover-sizing the inverter could result in reduced system efficiency and increasedsystem cost.
Voltage Input or Battery Voltage: The DC input voltage that the inverter requires torun, usually 12, 24, 48 or 120. The inverter voltage must match the nominal,photovoltaic system voltage.
Frequency: High quality equipment requires precise frequency regulation; variationcan slowly damage equipment.
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Surge capacity: Most inverters are able to exceed their rated wattage for limitedperiods of time. This is necessary to power motors that can draw up to seven timestheir rated wattage during startup. As a rough “rule of thumb” minimum, surgerequirements of a load can be calculated by multiplying the required watts by three.
Voltage regulation: This indicates how much variability will occur in the outputvoltage. Better units will produce a near constant voltage.
Efficiency: The efficiency of the inverters usually depends on the load current being amaximum at the nominal output power. It can be as high as 95% but will be lower(75-80%) if the inverter runs under part load. An inverter is often used to power loadsat less than its rated capacity. Therefore, it is usually wise to choose a unit rated at ahigh efficiency over a broad range of loads.
2.5.4 Cables and Fuses or circuit breakers
Obviously the PV system should use weatherproof cable, especially cable withresistance to degradation from ultra-violet radiation and wide variation intemperature. The cable should also be robust in teams of the voltage and currenthandling capability. The cable should be sized adequately to continuously pass theexpected peak (short-circuit) current safely. The resistance of the cable used should helow enough that a significant voltage drop along the cable is avoided i.e. if there arelong cables then thicker cable is used. Voltage drop reduces the terminal voltage forcharging batteries and directly results in energy loss as heat in the cables. Larger PVsystems operating at high voltages and energy loss due to voltage drop is less of anissue. Fuses or circuit breakers are generally used for the purpose of protection.
2.6 Photovoltaic System Types
Photovoltaic powers Systems are generally classified according to their functional andoperational requirements, their component configurations, and how the equipment isconnected to other power sources and/or electrical loads. PV systems fall into twobasic categories: stand-alone and grid connected.
2.6.1 Stand-Alone Photovoltaic Systems
Stand-alone PV systems are designed to operate independent of the electric utilitygrid, and are generally designed and sized to supply certain DC and/or AC electricalloads. These types of systems may be powered by a PV array only, or may use wind,an engine-generator or utility power as an auxiliary power source in what is called aPV-hybrid system. In this type of PV system batteries are used for energy storage.
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Fig 2.8 Stand-alone system with battery storage powering DC and AC loads.
A Complete Standalone solar system is useful for complete independence from fossilfuels and electric utility companies. The advantage to this type of system is its abilityto provide power away from the utility grid, and to create a measure of self-independence. A complete Standalone home solar system will typically have twoinverters to supply the AC house current necessary to power large loads such as airconditioners. Having a second inverter helps to insure that power is available whenone of the inverters eventually requires servicing. These self-contained systems need asizable battery storage capacity to provide electricity when solar power is unavailabledue to prolonged adverse weather conditions. Typically this type of system is mostcost effective when the system is located away from the utility grid
2.6.2 Grid-connected or utility-interactive systems
Photovoltaic systems that are connected to the utility grid (utility-connected, grid-tieor line-tie systems) do not need battery storage in their design because the utility gridacts as a power reserve. Instead of storing surplus energy that is not used during theday, the homeowner sells the excess energy to a local utility through a speciallydesigned inverter. At night and during other periods when the electrical loads aregreater than the PV system output, the balance of power required by the loads isreceived from the electric utility. If the utility grid goes down, the inverterautomatically shuts off and will not feed solar generated electricity back into the grid.This safety feature is required in all grid-connected PV systems, and ensures that thePV system will not continue to operate and feed back onto the utility grid when thegrid is down for service or repair, Because utility-connected systems use the grid forstorage these systems will not have power if the utility grid goes down. For thatreason, some of these systems are also equipped with battery storage to provide powerin the event of power loss from the utility.
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Fig 2.9 Block diagram of grid-connected photovoltaic system.
2.6.3 ‘Hybrid Grid’ - Solar Electric and Generator Combination Systems
The ‘Hybrid’ - Solar Electric and Generator Combination provides a reliable powersource, and produces electricity even when the sun is not providing solar power.These ‘hybrid’ systems have the ability to charge the battery bank and provideelectricity when weather conditions are unfavorable for solar power production. Anadvantage to this type of system is the reduction of solar panels (PV array) necessaryto supply power, which makes this system an economical alternative to a largerStandalone system. When more power is needed than the solar panels are producing, agasoline, propane or diesel generator is activated. The generator will provide enoughpower to overcome the difference between solar power available and the electricityyou require. This type of system is used for cabins, remote homes and is a commonsystem used to provide power for small medical facilities in third world countries.Hybrid systems are most often found on islands. Pell worm islands in Germany andKynthos islands are notable examples (both are combined with wind). The Kynthosplant has reduced diesel consumption by 11.2%.
2.7 Conclusions
The photovoltaic system consists of a number of parts or subsystems such as PV arraywith mechanical support, batteries, inverter and control equipments. In this chapterthe physical principles of photovoltaic energy conversion have been discussed. Basiccomponents and types of solar PV system are also described. Distinction has beenmade between grid-connected and stand-alone systems.
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CHAPTER 3
PV System Design and Financial Analysis
3.0 Introduction
In order to design a PV system [12-21] to meet a particular need in the most costeffective way information is required on the expected resource, the expected dailyload and the array and BOS characteristics. This data is used to size the PV array andBOS components in several systems configurations to determine the optimum design.First the annual and monthly mean daily horizontal irradiance in kWh/m2/day isdetermined for the site. Stand-alone and grid connected system are then sized, indifferent ways due to the need for storage in the former. The purpose of this chapter isto examine all the necessary steps and key components needed to design and build aphotovoltaic power plant and then discuss the various methods for financial analysisof the project.
3.1 System Design Procedures
PV system is designed according to the following steps:
Step 1 : Site Selection
The factors, which influence the selection of a particular site to build a photovoltaicpower plant, include the following:
I) Insolation: It is the most important factor used in selecting a site to build aphotovoltaic power plant. The energy output of a photovoltaic system is directlyproportional to the insolation input. Other climatic and environmental factors such atemperature extremes, precipitation, wind and land topography, will limit andconstrain a PV plant but these factors are all secondary when compared with theavailability of insolation.
II) Land Area Requirements: Photovoltaic plants generally require large areas forsolar arrays. Larger areas are required in order to space the arrays for minimum inter-array shadow effects. Simpler arrays such as fixed, south tilting, east-west arraysrequire smaller areas compared to the two-degree-of-freedom tracking arrays. Thesurface area requirements for PV array installations are on the order of 8 to l2 m2 perkW of installed peak DC rated PV array capacity.
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III) Economic Factors: Economic consideration in site selection must account forthe cost of land required, the cost of site preparation and the cost of access to the site.While all these costs are important, it should be noted that land and site preparationcosts are generally a minor part of the overall cost of a photovoltaic power plant. Theaccess cost, however, has an additional significance since remote access willcontribute to the operation and maintenance cost over the years.
IV) Institutional Factors: Institutional criteria involve considerations of land userequirements and social activities. Population density is a prime determinant inchoosing sites.
Step 2 : Electric Load Estimation
The first task in designing a photovoltaic system is to estimate the system load. Todesign a PV system, one must know energy needs which can be estimated by listingall the daily loads. Total energy required by consumers in watt-hrs /day can be foundby the following equation-
ET(Wh) = P1 × N1 × H1 + P2 × N2 × H2 + --------- +Pn × Nn × Hn ……..(3.1)
Where,
P is power consumed by load in Watts
N is quantity of load used
H is the number of hours the load is used
For AC systems,
Total DC watt-hrs/day = E T (Wh) /Inverter efficiency…………………………. (3.2)
The required total energy consumed in Ampere hour (Ah) should be calculated using
the following formula-
ET (Ah) = ET (Wh) / Nominal system voltage……………………………………(3.3)
Step 3 : Battery Sizing
Battery sizing is the capability of a battery system to meet the load demand with nocontribution from the photovoltaic system. For a stand-alone photovoltaic system, theprincipal goal of battery storage is to ensure that the annual maximum photovoltaicsystem energy output equals the annual maximum load energy input. The amount ofbattery storage needed will depend on the load energy demand on weather patterns atthe site. Having too much energy and storage capacity will increase cost; thereforethere must be a trade-off between keeping the costing and meeting the energy demandduring low-solar-energy periods.
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The following is a list of battery characteristics that should understood beforeselecting battery to use for the PV system-
I) Depth of Discharge: When a battery is discharged, we measure how deeply it hasbeen discharged by the depth of discharge (DOD). This is the percentage of the ratedbattery capacity that is withdrawn from the battery.
II) State of Charge (SOC): The capacity of a battery at a particular time expressed ata percentage of its rated capacity. As a general rule SOC below 50% should not beexperienced for long period for any type of lead-acid battery. Ni-Cd batteries may bestored at very low SOC for long periods of time without harm.
III) Temperature Correction: The performance of a battery decreases withtemperature. Temperature correction is needed to correct the lowest temperature thatthe battery will be subjected to during its operation and the discharge rate expressed.
IV) Rated Battery Capacity: This is the maximum amount of energy that a batterycan produce. The same discharge rate must he used when comparing battery capacity.
V) Autonomy: The amount of time (normally in days) that a PV system can continueto operate with no energy available from the PV array.
The battery capacity required should be calculated using the following formula:
C10 (Ah) = Daily load (Ah) × NA / (DOD x Efficiency of the battery system) ….(3.4)
where,
NA is No of autonomy days = 3
DOD is depth of discharge = 35% for flat plate battery and 60% for tubularplate battery
Efficiency of the battery = 90%
Divide the total required battery capacity by the battery Amp-hour capacity suppliedby the manufacturer to determine the number of batteries in parallel needed. If thebattery bank includes batteries connected in a series configuration, the requirednumber of batteries in series is determined by dividing the DC system voltage by thebattery voltage.
Total batteries required= No. of batteries in series × No. of batteries in parallel. ..(3.5)
27
Step 4 : Photovoltaic Array Sizing
Three items need to be addressed when sizing a photovoltaic array and they are:
I)Module Selection: Specifications such as performance, physical size and cost mustbe compared between different modules before the decision on which module(s) touse is made.
II) Number of Modules: The number of modules to be connected in parallel in orderto produce the design current must be determined. Since this number is rarely a wholenumber a decision has to be made whether to round up or round down. In making thisdecision, system availability requirements must be considered. The number of seriesconnected modules needed to produce the design voltage must be calculated. Thiscalculation involves dividing the system voltage by the nominal module voltage. Forstand-alone PV systems, 12-V modules are commonly used.
The total solar array current requited is determined by dividing the total loading pluslosses and safety factor (calculated STEP 1) by the equivalent sun hours (ESH).
Imp=(A) ET (Ah) / Peak sun………………………………………………..(3.6)
where,
ET (Ah) is total daily energy demand by consumer per day
Peak Sun = 4.5 hours for Bangladesh
At this point, a particular PV module must be select for the system and use thespecifications for that module to complete further calculations.
Divide array peak Amps by peak Amps per module. The resulting number is therequired module in parallel.
To determine the required modules in Series, divide DC system voltage by thenominal module voltage. Next, multiply modules in series by modules in parallel todetermine the total modules required.
Step 5 : Controller Specification
To begin, multiply module short circuit current by modules in parallel from Step 3.Then multiply this by a safety factor of 1.25. The resulting figure is the array shortcircuit Amps that the controller must handle under a short circuit condition.
Divide the DC total connected watts front Step 1 to calculate the Maximum DC loadamp the controller will be required to handle [19].
28
Step 6 : The Power Conditioning Unit (Inverter)
Power Conditioning Units (PCU) is very important components in any stand-alonePV system that powers AC loads. The choice of PCU will impact the performanceand economics of the system. The PCU is the third largest cost component laggingonly behind the array and battery. The required capacity of the inverter should becalculated using the following formula:
Pinverter (VA) = PL/ (P.f × efficiency) ……………………………………..(3.7)
where,
PL is the energy consumed by the load
P.f. is the power factor = 0.8 and Efficiency of the inverter =0.95
For safety, inverter should be selected as the design value multiply by 1.2.
3.2 Selection of Balance of system (BOS) components
Many problems that confront a PV system can be traced to improper sizing orinstallation of the balance-of -system (BOS) components.
Type of Wire and Size
The performance and reliability of a PV system is increased if the correct size andtype of wire is chosen. Among the several types of wire available in the market today,only a few are recommended to be used in a stand-alone PV system. Copper wires aregenerally used in PV systems. Although aluminum wire is less expensive, it can causevery serious problems to the PV system if used incorrectly. When choosing the typeof wire to use, the total current carrying capability of the wire must be consideredalong with the fuses used to protect the conductors. This information is essentialbecause if the current level is exceeded, overheating, insulation breakdown and firesmay occur. Other factors that should be considered before selecting a wire, includethe voltage drop and power loss. Both of these factors are dependent on the resistanceof the wire, the amount of current and the length of the wire.
For the wire run from the PV panels to the controller or battery, use the short circuitcurrent multiplied by the number of panels in parallel. For the Wire from the batteryto the DC service panel, use the total load amps. After calculating the current,multiply it by 125%, so that the conductor never carries more than 80% of its ratedcapacity. This safety precaution must be done on all wire runs in a PV system toprotect all the components. NEC 690-8 requires an additional safety factor to beincluded in the wire that connects the PV array to batteries. This is to handle any extracurrent produced by the panels caused by reflection or exceptionally sunny days. Theshort circuit current must be multiplied by an additional 125% to ensure the propersize conductor and to code. Another way to size wires for a PV system uses anequation to calculate the voltage drop index (VDI).
VDI= (Amps x feet)/ (% voltage drop x nominal system voltage) ……….(3.8)
29
Switches, circuit breakers and Fuses
Fuses are used in PV systems to provide over current protection when ground faults orshort-circuit occur and switches are used to manually interrupt power in case ofemergency or maintenance. Since the battery is the major current source of concern ina stand-alone PV system, a fuse has to be connected between the array and thecontroller. This fuse will ensure the protection of the modules from batten currentshould a ground fault occur when the controller is engaged. The array short-circuitcurrent multiplied by a factor of 1.25 is generally used to size the fuse between thearray and the controller. In a stand-alone PV system, safety switches are installed toisolate the array, battery, controller and load.
Connections
Poor connections are responsible for most problems in a stand-alone PV system. Poorconnections may result to losses in system efficiency, system failure, and costlytroubleshooting and repairs. System connections must be secure and able to withstandextreme weather and temperature. Connections must also be protected from vibration.animal damage and corrosion. To prevent against corrosion, copper conductors shouldbe used for system connections.
3.3 System Installation
Mounting Scheme
A photovoltaic array can be mounted at a fixed angle from the horizontal or on a suntracking mechanism in order to increase energy production. The greatest concern formost arrays that are ground mounted is the uplifting force of wind on the array. Forthis reason, most ground arrays usually employ some kind of sturdy base such asconcrete. Fixed mounting is the more usual for economic reasons associated withmaintenance of tracking mechanisms. A tilt angle near the location’s latitude will givethe most energy annually. Tilt angles of Latitude ±15° will increase energy productiontoward winter or summer respectively.
Grounding Scheme
Grounding of a PV system provides a well-defined low-resistance path from selectedpoints of the system to the ground. If the system malfunctions, the fault current isexpected to travel through this path. For stand-alone PV systems, two types ofgrounding are essential and they are; systems ground and equipment ground. Systemgrounding consists of one of the current carrying conductors, usually the negativeconductor that is grounded at a single point. This configuration establishes themaximum voltage with respect to ground and also serves to discharge surge currentsinduced by lightning. Equipment grounding is done primarily for safety reasons [19].
30
3.4 Investment Analysis
This section illustrates the methods of analyzing photovoltaic applications fromcustomers/investors point of view, especially for urban areas. The financial appraisalshould take into account the social, environmental and technological aspects as well.Governments of various countries provide subsides for photovoltaic programs wherethe financial return is not the only consideration, subsidies are provided for social andenvironmental considerations.
The first step of financial appraisal is to determine all benefits and costs in monetaryterms. Benefits like environmental impacts, social benefits are excluded but it will bereflected when a whole program of an organization is evaluated. The costs forphotovoltaic systems are obviously the initial investment to purchase the system,repair and maintenance expenses, replacement of components like battery, chargeregulators, lamps etc. in future within the life time of the modules. On the other hand,the financial benefit is the revenue from the photovoltaic system.
The fundamental principle of appraisal methods [5] is to compare costs againstbenefits. Although the principle sounds simple but the analysis may becomesomewhat difficult because of the fact that costs and benefits are spread over a verylong period of time for photovoltaic system, over a period of 20 years. The morecontroversial issue is to estimate benefit/revenue/cost savings over a period of 20 to30 years. Because scenarios may radically change over the long period of time. Thepoint is that the appraisal methods are based on some implicit and explicitassumptions about income and expenditure stream, which may change dramaticallyover the life of the system or a project.
3.4.1 Simple payback period
It is the amount of time that takes for a project to recover its initial cost. Paybackperiod decision rule specifies that all independent projects with a payback period lessthan a specified number of years should be accepted.
If the initial investment for the system is Taka I, projected annual revenue fromenergy bill is Taka R and projected annual expense (annual maintenance cost) for thesystem is Taka E over the lifetime of the system (say N years), then the simplepayback period PP, expressed in years, is
PP = I/(R-E) ……………………………………………………….(3.9)
The rule for accepting investment would be at least PP < N
The basic premise of the payback method is that the more quickly the cost of aninvestment can be recovered, the more desirable is the investment.
31
Payback period method has serious limitations. First, the initial investment is not theonly investment that should be considered. To have power over a 20 years period theowner has to replace battery at least 4 times and other components as well. So thepayback period does not depict the full picture and may not be the right indicator forinvestment decision. A further criticism of the simple payback method is that it doesnot consider the time value of money, or the impact of inflation on the costs.
3.4.2 Net Present Value (NPV) method
NPV is the summation of the net cash flows discounted back to the present time. Thismethod is the most logical and the most widely used method for investment decision,especially in case of long-term investment decisions. NPV is calculated as the presentvalue of the project’s cash inflows minus the present value of the project’s cashoutflows.
Positive NPV values are an indicator of a potentially feasible project. The basicprinciple of present value method is the fact that a Taka today is worth more than aTaka tomorrow, because the Taka today can be invested to start earning interestimmediately. Thus, the present value of a delayed payoff may be found bymultiplying the payoff by a discount factor, which is less than one. If C1 denotes theexpected payoff after one year, then
Present Value (PV) = discount factor × C1……………………………...(3.10)
The discount factor is expressed as the reciprocal of 1 plus a rate of return, r
Discount factor = 1/(1 + r) …….. ……………………………………….(3.11)
The rate of return r is the reward that investors demand for accepting a delayedpayment. To calculate present value, we discount expected future payoffs by the rateof return offered by comparable investment alternatives. This rate is often referred toas the discount rate, hurdle rate or opportunity cost of capital. The net present value(NPV) is found by subtracting the required investment:
NPV = PV - required investment = C0 + C1/ (1+ r) ……………………..(3.12)
where, C0 is the initial investment at period 0 (that is today) which is a negative figureand the above formula is valid for an investment of one year duration.
Similarly, for an investment of two years duration
PV = C1/(1+ r1) + C2/(1+ r2)2 …. …………………..(3.13)
where, C1 and C2 are respective cash flow and r1 and r2 are respective discount rates.Then,
NPV = C0 + C1/(1+ r1) + C2/(1+ r2)2 ……………………………(3.14)
Now extending the formula for an investment of n years we have
PV = C0+C1/ (1+ r1)+ C2/ (1+ r2)2+ C3/ (1+ r3)
3+ -------- + Cn/ (1+ rn)n
= Σ Cn/ (1+ rn)n, n = 1,2,3,..........................n……………………….(3.15)
32
where, we have assumed that the discount rate is equal during the life of the project,i.e. r1 = r2 = r3 = ---------- = rn = r.
Then,
NPV = C0 + PV………………………………………………………….(3.16)
where, C0 is the initial investment and a negative figure.
For simplicity NPV is obtained by using MS Excel software.
3.4.3 Internal Rate of Return (IRR) method
IRR of a project is the discount rate at which the NPV is equal to zero. The IRRdecision rule specifies that all independent projects with an IRR greater than the costof capital should be accepted. On the other hand when selecting among mutuallyexclusive projects, the project with the highest IRR should be selected. IRR can becalculated from the following equation by trial and error method.
IRR= Σ = CF0 + + + --------- --- +
……………………………………………………………………………………(3.17)
Entrepreneurs would always prefer photovoltaic projects with higher IRR. A projectwith IRRs less than the commercial rate of interest does not make good investmentsense. But households may find photovoltaic systems beneficial considering socialfactors although the IRR is less than bank interest rate. If the internal rate of return ofthe project is equal to or greater than the required rate of return of the organization,then the project will likely be considered acceptable (assuming equal risk).
3.4.4 Monthly energy expense
The most common use for lighting in urban areas of Bangladesh is IPS during loadshed. One very simple way of justifying switching to photovoltaic technology is tocompare the monthly expenses for energy for both options: existing technology andphotovoltaic technology. Investment in photovoltaic system will be more and moreattractive once monthly cost of energy bill becomes closer to current monthlyexpenditure, notwithstanding the willing of customers to pay a premium price forgood quality of light and convenience of battery charging using solar modules.
3.4.5 Year to positive cash flow
It represents the length of time that it takes for the owner of a project to recoup itsown initial investment out of the project cash flows generated. The year-to-positivecash flow considers project cash flows following the first year as well as the leverageof the project, which makes it a better time indicator of the project merits than thesimple payback.
CF0
(1+IRR)t
CF1
(1+IRR)1
CF2
(1+IRR)2
CFT
(1+IRR)T
T
t=0
33
3.4.6 Profitability Index - PI
The profitability index which is an expression of the relative profitability of theproject. It is calculated as the ratio of the net present value (NPV) over the projectequity. Positive ratios are indicative of profitable projects. The profitability index,similar to the benefit- cost ratio, leads to the same conclusions as the net present valueindicator.
PI = Net present value / Initial investment……………………………….(3.18)
3.5 Design and analysis of a PV system by PVsyst 5.56 software
PVsyst 5.56 [13] is PV system design software which allows us to study and designphotovoltaic systems, which use solar panels to convert sunlight into electricity. Theprogram offers three main design options.
The preliminary design option - allow to evaluate grid-connected, stand-alone andpumping systems, and use monthly values to perform a quick evaluation of systemyield. For each project we have to specify the location and the system to be used. Theprogram includes predefined values of locations of different parts of the world but wecan also enter the geographical coordinates, and the monthly meteorologicalinformation of new locations.
The project design option - allow creating full-featured study and analysis of grid-connected, stand-alone, pumping, and dc-grid systems with accurately system yieldscomputed using detailed hourly simulation data. It can be used for differentsimulation variants, horizon shadings, include detailed losses, and add realcomponents to make economic evaluations. After finishing project it can generatereports and export information to the clipboard.
Tools option - This includes databases of meteorological information, components,solar toolboxes, and the analysis of real measured data. In the preferences it ispossible to change the systems units and modify the values of some hiddenparameters to obtain more accurate results.
3.6 Design and Economic analysis of a PV system by RETSereen software
RETScreen[13] is standardized and integrated renewable energy project analysissoftware. This tool provides a common platform for both decision support andcapacity building purposes. The RETScreen model can be used to evaluate grid-connected or off-grid photovoltaic projects, from larger scale central generation plantsto smaller scale distributed generation applications, anywhere in the world. It can beused worldwide to evaluate the energy production and greenhouse gas emissions
34
reduction for various renewable energy technologies (RETs). This research modelconsists of several interlinked Microsoft Excel worksheets (Energy Model, CostAnalysis and Financial Summary).The ultimate outputs from the model are NominalPV array power, Nominal battery capacity, Inverter capacity, Renewable energydelivered, IRR, NPV, Payback period, Year to positive cash flow, Profitability index,Energy generation cost, Cumulative cash flow and the brief cost analysis. There isalso a provision of updating the model with the following variables, changing the unitrates of the construction materials, the interest rate, the subsidy amount etc.
3.7 Conclusions
Sizing is an important part of PV system design. This chapter illustrates a briefdescription of the standard formula commonly use for designing a stand alone PVsystem (load requirement, array, battery, inverter etc.), PVsyst and RETScreensoftware. Financial analysis methods such as Pay back period, Average Return onInvestment (AROI) method, Monthly energy expense ,Year-to-positive cash flow, Netpresent value (NPV) method , Internal rate of return (IRR) , Profitability Index ( P1)also discussed in this chapter.
35
CHAPTER 4
Design and Analysis of a Stand-alone PV system
4.0 Introduction
Sizing of a PV system, particularly a stand-alone one, is an important part of itsdesign. The sizing of a system requires knowledge of the solar radiation data for thesite, the load profile, and the importance of supply continuity. The sizing procedurethen recommends the size of the photovoltaic generator and battery capacity that willbe optimum for the application. Since the capital equipment cost is the majorcomponent of the price of solar electricity, over sizing the plant has a very detrimentaleffect on the price of the generated power. Under sizing a stand-alone system, on theother hand, reduce the supply reliability.
In this chapter first, designing of a SHS (PV) system has been done by normalstandard procedure and then technical and financial analysis are done by PVsyst andRETScreen software to see the viability of the project.
4.1 Design parameter and important assumptions for design and analysis
The site consider for this project, located in urban areas of Bangladesh where gridelectricity is available but not continuous, that means load shed exist. The array slopewill be selected to maximize annual energy generation. The high quality monocrystalline-Si PV array will feed their output onto the mini grid through a chargecontroller or an inverter.
Followings are the important assumptions for the technical and financial analysis byPVsyst and RETScreen software for feasibility study of Stand alone system (SHS orPV mini grid system): -
Location of the project
Type of load
Average daily insolation / Sunshine hour
System nominal voltage
Type of battery
Battery maximum depth of discharge (DOD)
Battery efficiency (ηc)
:
:
:
:
:
:
:
Roof of a Building of urban areas
Mainly light and Fan load duringload shed period
4.5kWh/day/m2
12/24V DC or 230V AC
Tubular plate, Gel type battery
60%
90%
36
Battery life
Inverter efficiency(ηi)
PV module type
PV array controller
Slope of the PV array
Azimuth of PV array
Typical financial figures for the analysis are
Energy cost escalation rate
Inflation rate
Discount rate
Project life
:
:
:
:
:
:
:
:
:
:
:
5 years
95 ~ 97%
Mono-Si
Fixed
23o (true south face)
0 degree
US $ 3000
5%
6%
8 %
20 years
The utility does not pay income tax and the system is expected to last for about 20years or more. Feasibility study, development and engineering costs are included inPV and also balance of equipment cost which is about 10% of the total project costs.Annual operation and maintenance cost, contingency and unforeseen expenditure areconsidered as 7.5% of physical investment cost.
Unit cost for the construction items is mostly obtained from the local market andInternet. They may not represent the actual amount at the proposed site, but there is aprovision to update the unit cost. NPV and IRR and corresponding figures will beupdated automatically in the model. The other factors which are considered whensizing PV panel are:
Wire loss, Wi :
To reduce the I2R loss, wire size should be as large as possible and length should beshort. Specific resistance of the metal is as low as possible. The cumulative loss forthe wire is no more than 5%.
Soiling factor, Sc :
Due to the presence of dust and dirt particle in the air, the output of solar paneldecreases substantially. Dust and dirt particle creates a resistance for the panel forreceiving solar insolation. To overcome this problem, the panel size should be overdesigned by a factor, which is equivalent to 0~10%.
Battery Columbic efficiency (ηc):
During the charging of Battery, gas formed inside the battery, which creates resistancefor further charging the battery. To overcome this problem extra current is necessaryand the panel size should be increased 5-10% for supplying this extra current.
37
Temperature factor (Tr):
Standard practice for designing the life of panel is 20-30 years. The panel supplies80% of its capacity for 20 years. When the panel absorbs solar radiation, thetemperature increased nearly double than the environmental temperature. As the celltemperature increases, molecular vibration increases, cell voltage increases but thepanel life decreases. To get the benefit from the system for the whole panel life, thepanel size should be increased by 5 %.
Climatic condition:
Climatic condition is one of the major factors for the skyness index, which leads theinsolation. It is absorbed that the insolation is lowest in July but sometimes, innorthern districts no sunshine day’s goes to 10-15 days in winter, which should not betaken wider consideration for designing solar system. In Bangladesh, normal practicefor counting no sunshine days is 3, which is use for designing the battery autonomy.
4.2 Design a stand-alone PV system by standard parameter
A small house in Dhaka city with boundary area of 2800 square feet (sft) and withtwo flats of 1000 sft in each floor is considered for this study. As a law the groundfloor has to be used for car parking. This six storied building has total 10 flats. Theconnected load of this building is 24kW (10x2kW plus 4kW, utility).
According to utility’s calculation this house needs about 700Wp (3% of light, fanload) PV panel. It is proposed that it will not be connected to grid (off-grid) and willwork as an independent (dc) SHS. There will be dc appliances of 20 CFLs, 6W eachand 10 fans of 30W each. There usages are shown in Table 4.1. The block diagram ofthe PV system for the house is shown in Fig. 4.1.
Fig. 4.1 Diagram of the PV system for the house
38
4.2.1 Base of Solar Home System Design
A solar system with the following characteristics will make the most power output.
I. Faces South with Well Ventilation
II. Tilted Up At An Angle
III. Roof Space & Condition
IV. No Shade
4.2.2 Electric load calculation
Table 4.1: Table for Load Determination of Stand alone PV system for the house
Load TypeDevice
watt (w)Hrs of Daily
UseNo ofUnits
Total(W)
TotalWh
Fan 30 4 10 300 1200
Light for flat use 6 4 10 60 240
Light for Security 6 12 10 60 720
Total 420 2160
4.2.2 Array Sizing Worksheet
Daily ET (Ah) requirement =Total watt-hrs per day/System nominal voltage
= 2160/24 =90 Amp
Daily load current required, Amps = ET (Ah)/ESH
= 90/4.5
= 20
Considering 20% losses,
Daily minimum array current, Amps = 1.2 × 20 = 24
Considering 175 Wp panel (Nominal Voltage 28V, Operating Current 6.5 A)
Module required in series, NS = System nominal voltage/Module nominal voltage
= 24/28 =0.85 say 1
Modules in parallel, NP = Daily minimum array current /Module
operating current
= 24/6.5 = 3.69 say 4
Total module required = No. of module in series × No. of module in parallel
= 4 ×1
= 4
39
4.2.4 Controller sizing
Array short circuit current, A = Module short circuit current × Modules in
parallel
So, Controller array, Amps = 7 × 4 ×1.25 =35
Maximum DC load in Amps = DC total connected load / DC system voltage
= 420/24 = 17.5
So minimum 18 Amp rated charge controller will be needed.
4.2.5 Battery Sizing
The battery capacity required at C10 should be calculated using the following formula
C10 (Ah) = Daily load (Ah) ×NA / (DOD × Efficiency of the battery system)
Where,
Daily amp-hrs requirement = ET (Ah)=90
No of autonomy days = NA = 3
DOD (depth of discharge) = 60 %
Efficiency of the battery = 0.9
Hence, C10 (Ah) = (90 × 3) /(0.60 ×0.9) =500 Ah
No. of battery required in parallel = C10 (Ah) /Battery(Ah)
= 500/160 = 3.12 say 3 Nos.
No. of battery required in series = Nominal system voltage /cell voltage
= 24/12 = 2 Nos.
Total no. of battery required = 2 x 3 = 6 Nos.
4.2.6 System wire sizing
a) PV combiner box to controller /Controller to battery
Total amps =ISC of module × Nos. of module in parallel =7 × 4 = 28
NEC required = Total amps × 1.25 × 1.25 =43.45
Wire size - 1 × 6 rm, NYY
b) Battery to DC distribution box / Charge controller
Charging current of battery Io
Starting = 60A, Finishing 22A
Wire size - 1×16rm, NYY
c) MCB Selection
For DC system, MCB ratting =1.8 × maximum array current = 1.8 × 28 =50.4
For AC system, MCB ratting = 1.8 x AC load /230/. 8 = 4.2
40
4.3 Design PV system by PVSyst software
Considering roof top, tilt angle of 23° south facing, no shading effect and othercondition described in article 4.1 for the requirement showing in table 4.1, PVSystsoftware were run and following result were found…
Operating voltage = 24V DC
Array requirement = 693 WP say 700 WP
Using, 175 WP Panel = 175 × 4
= 700 WP
Charge controller required = 20 Amp
Specific production = 1567 kWh/yr
Available energy = 1097 kWh/yr
Energy required = 788 kWh/yr
Used energy = 784 kWh/yr
LOLP = 3 %
Excess unused =224 kWh/yr
Performance ratio = 56.4 %
Total initial investment US$ 2880 with a running cost of US$ 100. Consideringbattery replacement after 5 yrs, charge controller replacement after 10 yrs, loaninterest 8% (total investment from bank loan) and project life 20 yrs, unit productioncost is US$ 0.63. Normalized production and loss diagram of the system obtainedfrom PVSyst is shown in Fig.4.2 and Fig. 4.3 respectively.
Fig. 4.2 Energy usages for the whole year as obtained from PVsyst program
41
Fig. 4.3 Energy diagram over the whole year as obtained from PVsyst program
4.4 Economic analysis PV system by RETScreen software
For load showing on table 4.1, autonomy days 3 and other condition mentioned inarticle 4.1, ETScreen was run and found
Module required 700 WP (4×175)
Battery required 480 Ah with 24V
To examine financial indicator following cost data were considered…
Initial Cost Amount in US $ Amount in Tk.
Photovoltiac (700Wp) 910 74620Module Support Structure 150 12300Other equipment 150 12300Storage Battery 1,200 98400Transportation 100 8200Training & commissioning 100 8200Chagge controller 120 9840Contingencies 150 12300Total Initial Investment 2,880 236160Operation & maintenance cost per yr 20 1640Periodic costs (credits)Controller replace 10 yr 120 9840Battery Replacement 5 yr 1,000 82000
With above data RETScreen shows production cost US $ 0.51/kWh or Tk. 41.0/kWh
42
4.5 Financial analysis for various conditions obtained from RETScreen software
To evaluate a project or investment, it is important to calculate the NPV, IRR,payback period, year to positive cash flow and PI index for the particular project. Theparameter is very sensitive to PV cost, days of autonomy, discount rate and monthlyenergy bill.
4.5.1 Effect of discount rate
If considered electricity price rate Tk. 8.0 per unit in general case and 6 x 8 = Tk. 48.0(US $ 0.6) per unit for the proposed DC system, from the Fig. 4.4 it is seen thatdiscount rate above 8.5% is not feasible for this project at the costing point of view asabove 8.5% discount rate NPV is negative.
Fig. 4.4. Effect of discount on NPV and energy production cost
4.5.2 Effect of subsidy
With no subsidy total investment for the project is $ 2880 and energy production costis $ 0.51/kWh. If some subsidy is introduce then both the investment and energyproduction cost is decrease (Fig. 4.5). With no subsidy total investment is US $ 2880and energy production cost is US $ 0.51/kWh but with 20% subsidy total investmentreduced to US $ 2304 and energy production cost reduced to US $ 0.45/kWh.
-200
0
200
400
600
800
1000
1200
1400
1600
0 1 2 3 4 5 6 7 8 9
Discount rate %
NPV
($)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
Ener
gy C
ost (
$/kW
h)
Energy Cost
NPV
43
Fig. 4.5. Effect of subsidy on Investment and energy production cost
4.5.3 Effect of autonomy
If 2 days of autonomy (Fig. 4.6) is considered then the total investment decreases to$2380 and energy production cost is reduced to 0.48$/kWh. This result is obtainedfrom RETScreen program. This is the actual unit energy cost of Solar Home System(SHS) used in rural electrification.
Fig. 4.6. Effect of autonomy on Investment and energy production cost
0
500
1000
1500
2000
2500
3000
3500
4000
1 2 3 4Autonomy Days
Inve
stm
ent($
)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
Ener
gy C
ost (
$/kW
h)
0
500
1000
1500
2000
2500
3000
3500
0 10 20 30 40 50
Subsidy %
Inve
stm
ent (
$)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
Ener
gy C
ost (
$/kW
h)Energy Cost
Investment
Energy Cost
Investment
44
4.5.4 Load Comparison with general AC system
Table 4.2: Load comparison of proposed PV system with general AC system
LoadType
DailyUse(hr)
No ofUnits
Proposed DC system General AC system
Devicewatt(w)
Total(W)
Total(Wh)
Devicewatt(w)
Total(W)
Total(Wh)
Fan 4 10 30 300 1200 100 1000 4000Light forflat use
4 10 6 60 240 40 400 1600
Light forSecurity
12 10 6 60 720 60 600 7200
Total 420 2160 2000 12800
From Table 4.2 it is seen that with respect to general AC system total connected DCload is reduced to 2000/420= 4.76 say 5 times and the power consumption is reducedto 12800/2160= 5.92 say 6 times.
4.6 Conclusions
In this chapter a PV system is designed and verified by PVsyst and RETScreensoftware for a small house containing 10 flats of urban area to reduce load shedingand financial analysis is done for various condition. It is seen from analysis that thistype of system is viable for the house. Instead of using IPS, flat owners can use thissystem as its cost is almost same as 10 nos. of IPS for 10 flats. Instant Power Supply(IPS) is a local innovation. It converts ac grid electricity to dc by rectifier and storesin battery. During load shed period it uses battery current (by inverting) to run limitedload depending on IPS capacity. So this is a better solution for urban area instead ofusing IPS.
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CHAPTER 5
Gird-Interactive Solar PV System
5.0 Introduction
In this chapter, a basic concept about how to design a complete grid interactive SolarHome System (SHS) is discussed. This type of system incorporates energy storage inthe form of a battery to keep ‘critical load’ circuits in the house operating during autility outage (Load shed period). When an outage occurs the unit disconnects fromthe utility and powers specific circuits in the home. These critical load circuits arewired from a subpanel that is separate from the rest of the electrical circuits. If theoutage occurs during daylight hours, the PV array is able to assist the battery insupplying the house loads, if the outage occurs at night, the battery supplies the load.The amount of time critical loads can operate depends on the amount of power theyconsume and the energy stored in the battery system.
5.1 The Basic Principle
A Grid-Interactive system uses battery power storage to provide back-up duringutility outages.
i) Power from a renewable energy source (typically a solar array) is run to aMaximum Power Point Tracking (MPPT) charge controller (solar only). A chargecontroller is a device that regulates the charging of the batteries. Its primary functionis to prevent overcharging or over use of batteries which can damage the battery bank.
ii) Power runs from the charge controller to the battery bank. In most Grid- Interactivesystems, AGM or gel batteries are typically used.
iii) Power runs from the battery to the GFX or GVFX Pure Sine WaveInverter/Charger where the DC power is converted to AC power. AC power goes toboth the main panel (where excess power can be sold back to the utility) and to a sub-panel or secure load panel which has loads to be backed-up during a utility outage.
iv)Sub-Panel: Circuits requiring back-up must be moved from the main panel to thesecure load panel.
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Typical System Components are described below:
PV Array
The PV panels convert the light reaching them into DC power. The amount of powerthey produce is roughly proportional to the intensity and the angle of the lightreaching them. They are, therefore, positioned to take maximum advantage ofavailable sunlight within sitting constraints.
Grid-Interactive Inverter
The Inverter takes the DC power produced by the panels, converts it to AC, which isthen fed through either back into the house or onto the main electricity grid withsynchronization.
Backup controller
It is a device that enables the PV panel to produce electricity during utility outage. Itis needed because, PV plant disconnects from the grid in case of blackout. Duringload shed period at night utility will run by battery backup.
Battery
A small battery can be fitted, as it is usually only needed to bridge the night hours or acloudy day during load shed.
Metering
This device indicates how much electricity produced by the PV plant is being fed tothe grid. It also shows the amount of electricity that is used from the grid.
5.2 The Design Parameters
Site Screening
The conditions that have to be maintained during site screening are as same as theprevious chapters.
Load Determination
One should have the clear concept about load before designing a grid-interactive SHS.So the complete system design depends on the amount of the load.
Array Sizing
Array sizing should be done considering how much electricity one wants to use in hishousehold and also the electricity he wants to feed to the grid.
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Selection of Grid - Interactive Inverter
As this inverter is directly connected to the PV array, it should be chosen according tothe Watt - peak size of the array.
Backup controller device
The controller will allow the batteries to be charged from solar panel during day time.If the batteries are charged fully, then it will export the excess energy to grid. Duringload shed period battery will supply the light, fan and TV loads.
Selection of Battery
The battery size should be according to the amount of load run on load shed period bysolar electricity.
5.3 Design of a Typical Grid - Interactive SHS
In this case study 10 flats with a contracted load of 24 kW and peak load of 12 kW isconsidered. Usually light, fan, television (except air conditioner and high powerconsumed refrigerator) consumes approximately 40% of the total load. A solar systemis designed to meet this demand (40%) with a backup of 4 hours (during load shedperiod). The estimated monthly consumption of such a house is shown in Table 5.1and the block diagram of the PV system for the house is shown in Fig. 5.1.
Table 5.1: Energy consumption of the house
MonthEnergy consumed
(kWh/month)40% of load
(kWh/month)
Jan 1909 763.6
Feb 2075 830.0
Mar 2324 929.6
Apr 3154 1261.6
May 3030 1212.0
Jun 2905 1162.0
Jul 2988 1195.2
Aug 2739 1095.6
Sep 2490 996.0
Oct 2490 996.0
Nov 2241 896.4
Dec 2158 863.2
Total 30,503 12,201.2
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Fig. 5.1 Block diagram of the PV system for the house
5.3.1 Array Sizing
Suppose the system efficiency is 80%. Also it has been discussed earlier thatconsidering all losses the insolation should be 3.5 kWh/m2 . With this condition themodule size should be of :
12201/(365x3.5)=9.55 say 10 kWP
5.3.2 Choosing a Grid - Tied Inverter
Considering all the conditions stated earlier for a grid - interactive system, 2 no of5kW inverter has been chosen. Here it is recommended to use Sunny Boy by SMASolar which has the recommended maximum PV power of 5 kW.
5.3.3 Backup controller device
Considering the watt-demand which is 4.8 kW (12 × 40%) a backup device of SunnyBackup System by SMA is chosen which can supply the minimum watt requirementof 4.8 kW.
5.3.4 Battery Sizing
The battery capacity required at C should be calculated using the following formula
C (Ah) = PL (Ah) × Backup time / (DOD × Efficiency of the battery system × InverterEfficiency)
49
Where,
PL(Ah) = PL(W)/System DC voltage = (4.5 ×1000)/240 = 18.75
Backup time = 4 hr
DOD (depth of discharge) = 60% for tubular plate battery
Efficiency of the battery = 0.9
Efficiency of the Inverter = 0.95
Hence C(Ah) = (18.75 × 4) /(0.60 × 0.9 ×95) =146.2 Ah
Nearest available battery is 160 Ah. So it is better to select 1 set of 240 (12×20)V,160Ah battery for more safety.
No. of battery required in series = Nominal system voltage /cell voltage
= 240/12 = 20 Nos.
Total no. of battery required = 20 x 1 = 20
5.4 Design and analysis PV system by RETScreen software
Considering roof top, tilt angle of 23° south facing, no shading effect and othercondition described in article 4.1 for the requirement showing in Table 5.1,RETScreen software were run. Panel required is 10 kWp, 20 nos. of 160Ah batteriesare required. Approximate cost is US $ 30,000 with energy production cost of$0.20/kWh and the payback period is approximately 12 years (Fig. 5.2). The batterywill be replaced after 10 years as grid connection is available in urban area. Thissystem will be viable if feed-in tariff (over $0.20/kWh) or subsidy is provided.
Fig. 5.2 Cumulative cash flow diagram of a 10 kW on-grid (battery backup) system.
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5.4.1 Effect of discount rate
If discount rate is greater than 8%, NPV of the project becomes negative(fig. 5.3). So,higher than 8% discount rate is not feasible for this project. Again with higherdiscount rate energy production cost is higher and PI is lesser and with lesser discountrate energy production cost is also lesser and PI is higher (fig. 5.4).
Fig. 5.3 Effect of discount rate on energy production cost and NPV.
Fig. 5.4 Effect of discount rate on energy production cost and PI index.
0.000
0.050
0.100
0.150
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0 1 2 3 4 5 6 7 8 9
Discount Rate %
Ener
gy C
ost (
$/Kw
h)
-5000
0
5000
10000
15000
20000
25000
30000
35000
40000
NPV(
$)
Energy cost
NPV
Energy cost
PI
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5.4.2 Effect of subsidy
If 10% subsidy is provide, total investment reduced to US$ 27000, energy productioncost is reduced to US$ 0.18, NPV is increased to US$ 3107 and payback period is alsoreduced to approximately 10 years. If more subsidy is provided then the financialindicator goes more positive.
Fig. 5.5 Effect of subsidy on energy production cost, Investment and NPV.
5.5 Conclusions
In this case a house with 10 flats is considered. Usually this type of buildings has itsown small diesel generator set for emergency supply during load shed period. Alsoindividual flat has his own Instant Power Supply (IPS). Cost of generation by dieselgenerator is very high. Again IPS cannot produce any electricity by itself. It reservesenergy when electricity is available. So, IPS is an extra burden on the grid and henceincreases load shed. An alternate solution could be an on-grid solar system withsufficient storage capacity to be used during load shed period. By using this systemdescribes above they lead a comfort life as well as reduce load pressure on the grid.
0
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15000
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0 10 20 30 40 50
Subsidy %
Inve
stm
ent a
nd N
PV
($)
0.00
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Ene
rgy
cost
($/k
Wh)
Energy cost
Investment
NPV
52
CHAPTER 6
Grid- Tied Solar PV System
6.0 Introduction
In this chapter a basic concept about how to design a complete grid-tied Solar HomeSystem (SHS) is discussed. Grid-connected or utility-interactive PV systems aredesigned to operate in parallel with and interconnected with the electric utility grid.The primary component in grid - connected PV systems is the inverter or powerconditioning unit (PCU). The PCU converts the DC power produced by the PV arrayinto AC power consistent with the voltage and power quality requirements of theutility grid and automatically stops supplying power to the grid when the utility grid isnot energized. A bi-directional interface is made between the PV system AC outputcircuits and the electric utility network, typically at an on-site distribution panel orservice entrance. This allows the AC power produced by the PV system to eithersupply on-site electrical loads or to back-feed the grid when the PV system output isgreater than the on-site load demand. At night and during other periods when theelectrical loads are greater than the PV system output, the balance of power requiredby the loads is received from the electric utility. This safety feature is required in allgrid- connected PV systems, and ensures that the PV system will not continue tooperate and feed back into the utility grid when the grid is down for service or repair.
6.1 The Basic Principle
A Grid Connected solar PV system is a type of electrical inverter that converts directcurrent (DC) from PV array into alternating current (AC). When this PV system isconnected to the grid, it can transfer the extra energy to the grid after fulfilling thelocal demand. But when the system generates less than what is required to support thelocal demand, then extra energy is extracted from the grid. Thus PV solar energy actsas an alternative resource of electricity. The basic block diagram of a grid connectedsolar PV system is shown in Fig. 6.1.
The PV system aims to transfer electrical power from PV panels to the grid throughgrid-tie inverter. In the inverter, first a DC-DC converter is used to boost up PVvoltage to a level higher than the peak of grid voltage. The converter also tracks themaximum power point of PV array. The block diagram below is the representation ofthe grid connected PV system.
53
Fig 6.1: Block diagram of grid-connected photovoltaic system
6.2 The Design Parameters
The designing process starts from site screening. Thereafter selection of the loads isneeded. Then the calculation of the size of the system, i.e. the size of the PV moduleis done. After that the selection of other components of the system such as grid - tiedinverter etc. comes in front. Thus the full design of the system is done.
Site Screening
The conditions that should be maintained during site screening are as same as theprevious chapter.
Load Determination
One should have the clear concept about load before designing a grid-tied SHS. If theexact information about the loads and how much electricity one likes to feed to theutility grid are unknown, then the primary cost could be increased or the size of thePV array could be inappropriate and hence the system would not work effectively. Fordetermining the daily average load some common calculations should be done. Thesteps for determining the daily average loads and the electricity to be fed to the utilitygrid are given below.
i) Determining which loads should be connected to the system.
ii) Determining the power of those loads from their operating voltage and ratedcurrent.
iii) Determining the daily work hour of the loads.
iv) Sometimes the working hour of the loads may vary in seasons or months. Inthis case it should be kept in mind while calculating the average working hourof the loads.
54
v) Determining the daily work hour requirement of the loads by multiplying dailyaverage work time of the loads with their rated power
vi) Determining the amount of electricity to be fed to the utility grid. In this caseFeed In Tariff (FIT) must be known for a particular area.
Array Sizing
Correctly sizing grid-tied solar arrays is critical in today’s solar market. Most utilityrebate programs only pay back for the total amount of energy used at the site, andmoney that could have been earned from over-producing is lost. Because of this, thepenalty for over-sizing a solar array is a less cost-effective system and a longerpayback.
In an industry where every penny per watt is important, it is very important that thesolar array be sized accurately to the site - specific electric usage, array orientationand the type of equipment used. There are three variables in a basic array sizingcalculation, the equation is:
System size (watts) = (watt hours) × η / (sun hours) --------------------- (6.1)
Where η is the DC to AC system efficiency, Watt hours are obtained from the utilitybill, and sun hours are found using an online calculator from the National RenewableEnergy Laboratory (NREL).Once values for all three are obtained, it’s a simple matterof plug and play to get the solar array size in watts.
Selection of Grid-Tied Inverter
The inverter is one of the most important and most complex components in a grid-tiedsystem. PV panel produce DC, whereas utility grid supplies AC with a constantfrequency. So, the inverter should have the capability to supply AC withsynchronization capacity with the grid. To choose an inverter, the needs should bedefined. Here is a list of the factors that should be considered to select a grid-tieinverter.
Electrical Standards : The DC input voltage must confirm to that of the PV system.A higher voltage system carries less current, which makes system wiring cheaper andeasier. The inverter’s AC output must confirm to the conventional power in the regionin order to run locally available appliances. The standard for service in North Americais 115 and 230 volts at a frequency of 60 Hertz (cycles per second). In Europe, SouthAmerica, and most other places, it’s 220 volts at 50 Hertz and in Bangladesh 230volts at a frequency of 50 Hertz.
55
Safety Certification: An inverter should be certified by an independent testinglaboratory such as UL, ETL, CSA, etc., and be stamped accordingly. This is theassurance that it will be safe, will meet the manufacturer’s specifications, and will beapproved in an electrical inspection. There are different design and rating standardsfor various application environments (buildings, vehicles, boats, etc.). These also varyfrom one country to another.
Power Capacity : How much load can an inverter handle? Its power output is rated inwatts (wafts = amps x volts). There are three levels of power rating - continuousrating, limited-time rating and surge rating. Continuous means the amount of powerthe inverter can handle for an indefinite period of hours. When an inverter is rated at acertain number of watts that number generally refers to its continuous rating.
The limited-time rating is a higher number of watts that it can handle for a definedperiod of time, typically 10 or 20 minutes. The inverter specifications should definethese ratings in relation to ambient temperature (the temperature of the surroundingatmosphere). When the inverter gets too hot, it will shut off. This will happen morequickly in a hot atmosphere. The third level of power rating, surge capacity, is criticalto its ability to start motors.
Some inverters are designed to be interconnected or expanded in a modular fashion, inorder to increase their capacity. The most common scheme is to “stack” two inverters.A cable connects the two inverters to synchronize them so they perform as one Unit.
Power Quality - Sine Wave vs. Modified Sine Wave : Some inverters produce
“cleaner” power than others. Simply stated, “sine wave” is clean; anything else is
dirty. A sine wave has a naturally smooth geometry, like the track of a swinging
pendulum. It is the ideal form of AC power. The utility grid produces sine wave
power in its generators and (normally) delivers it to the customer relatively free of
distortion. A sine wave inverter can deliver cleaner, more stable power than most grid
connections.
How clean is a “sine wave”? The manufacturer may use the terms “pure” or “true” to
imply a low degree of distortion. The facts are included in the inverter’s
specifications. Total harmonic distortion (THD) lower than 6 percent, should satisfy
normal home requirements. One should look for less than 3 percent if he has
unusually critical electronics, as in a recording studio for example.
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A “modified sine wave” inverter is less expensive, but it produces a distorted squarewaveform that resembles the track of a pendulum being slammed back and forth byhammers. In truth, it isn’t a sine wave at all. The misleading term “modified sinewave” was invented by advertising people. Engineers prefer to call it ‘modifiedsquare wave.”
The “modified sine wave’’ has detrimental effects on many electrical loads. It reducesthe energy efficiency of motors and transformers by 10 to 20 percent. The wastedenergy causes abnormal heat which reduces the reliability and longevity of motorsand transformers and other devices, including some appliances and computers. Thechoppy waveform confuses some digital timing devices.
About 5 percent of household appliances simply won’t work on modified sine wavepower at all. A buzz will be heard from the speakers of nearly every audio device. Anannoying buzz will also be emitted by some fluorescent lights, ceiling fans, andtransformers. Some microwave ovens buzz or produce less heat. TVs and computersoften show rolling lines on the screen. Surge protectors may overheat and should notbe used.
Modified sine wave inverters were tolerated in the 1980s, but since then, true sinewave inverters have become more efficient and more affordable. Some peoplecompromise by using a modified wave inverter to run their larger power tools or otheroccasional heavy loads, and a small sine wave inverter to run their smaller, morefrequent, and more sensitive loads. Modified wave inverters in renewable energysystems have started fading into history.
Efficiency : It is not possible to convert power without losing some of it (it’s likefriction). Power is lost in the form of heat. Efficiency is the ratio of power out topower in, expressed as a percentage. If the efficiency is 90 percent, 10 percent of thepower is lost in the inverter. The efficiency of an inverter varies with the load.Typically, it will be highest at about two thirds of the inverter’s capacity. This iscalled its “peak efficiency.” The inverter requires some power just to run itself, so theefficiency of a large inverter will be low when running very small loads.
Internal Protection : An inverter’s sensitive components must be well protectedagainst surges from nearby lightning and static, and from surges that bounce backfrom motors under overload conditions. It must also be protected from overloads.Overloads can be caused by a faulty appliance, a wiring fault, or simply too muchload running at one time.
57
An inverter must include several sensing circuits to shut itself off if it cannot properlyserve the load. It also needs to shut off if the DC supply voltage from the PV is toolow. This protects the inverter and the loads from damages. These protective measuresare all standard on inverters that are certified for use in buildings.
Inductive Loads and Surge Capacity : Some loads absorb the AC wave’s energywith a time delay (like towing a car with a rubber strap). These are called inductiveloads. Motors are the most severely inductive loads. They are found in well pumps,washing machines, refrigerators, power tools, etc. TVs and microwave ovens are alsoinductive loads. Like motors, they draw a surge of power when they start.
If an inverter cannot efficiently feed an inductive load, it may simply shut downinstead of starting the device. If the inverter’s surge capacity is marginal, its outputvoltage will dip during the surge. This can cause a dimming of the lights in the house,and will sometimes crash a computer.
Idle Power : Idle power is the consumption of the inverter when it is on, but no loadsare running. It is ‘wasted’ power, so if you expect the inverter to be on for many hourswith small amount of load (as in most residential situations), it should be as low aspossible. Typical idle power ranges from 15 watts to 50 watts for a home-sizeinverter. An inverter’s specification sheet may describe the inverter’s “idle current” inamps. To get watts, multiplying the amps times with the DC voltage of the system isrequired.
Low Switching Frequency vs. High Switching Frequency : A low switchingfrequency inverter is big and heavy (generally about 20 pounds per kilowatt) andmore expensive. It has the high surge capacity (four to eight times the continuouscapacity) needed to start large motors. One should be careful about the acousticalbuzz that low switching frequency inverters make. If it is installed near a living space,one may be unhappy with the noise.
A high switching frequency inverter is much smaller and lighter (generally about 5pounds per kilowatt) and also less expensive. It has less surge capacity, typicallyabout two times the continuous capacity. It produces little or no audible noise. Theidle power is generally higher. If the inverter is oversized for motor starting, its idlepower will be higher yet, and may be prohibitive.
Both types of inverter have their virtues. Some people “divide and conquer” bysplitting their loads and using two inverters. This adds a measure of redundancy. Ifone ever fails, the other one can serve as backup.
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Automatic On/Off : Inverter idling can be a substantial load on a small powersystem. Most inverters made for home power systems have automatic load-sensing.The inverter puts out a brief pulse of power about every second (more or less). Whenan AC load is switched on, it senses the current draw and turns itself on.Manufacturers have various names for this feature, including “load demand,”“sleepmode,”“power saver,”“auto start,” and “standby.”
Phantom Loads and Idling Loads : High tech consumers are stuck with gadgets thatdraw power whenever they are plugged in. Some of them use power to do nothing atall. An example is a TV with a remote control. Its electric eye system is on day andnight, watching for the signal to turn the screen on. Every appliance with an externalwall-plug transformer uses power even when the appliance is turned off. These littledemons are called ‘phantom loads” because their power draw is unexpected, unseen,and easily forgotten.
A similar concern is ‘idling loads’. These are devices that must be on all the time inorder to function when needed. These include smoke detectors, alarm systems, motiondetector lights, fax machines, and answering machines. Central heating systems havea transformer in their thermostat circuit that stays on all the time. Cordless(rechargeable) appliances draw power even after their batteries reach a full charge. Ifin doubt, the device should be felt. If it’s warm, that indicates wasted energy. Howmany phantom or idling loads one can have?
There are several ways to cope with phantom and idling loads:
i) These may be avoidable (in a small cabin or simple-living situation).
ii) Their use can be minimized and disconnected when not needed, using externalswitches (such as switched plug-in strips or receptacles).
iii) By modifying certain equipment one can work around them to shut offcompletely (central heating thermostat circuits, for example).
iv) DC appliances may be used.
v) Additional cost may be paid for a large enough power system to handle theextra loads plus the inverter’s idle current.
Quality Pays : A good inverter is an industrial quality device that is proven reliable,certified for safety, and can last for decades. A cheap inverter may soon end up in thejunk pile and can even be a fire hazard. An inverter should be considered to be afoundation component. A good one should be bought that allows for future expansionof one’s needs.
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The Final Choice : Choosing an inverter is not a difficult task. It should be definedthat where it is to be used. Then type of loads (appliances) should be defined one willbe powering. The maximum power should be determined that the inverter will need tohandle. By this, one may be able to choose the perfect inverter for ones use.
6.3 Design of a Typical Grid-Tied PV system
A commercial or industrial or residential building with load above 500kW isconsidered for this exercise.
6.3.1 Load Estimation
As per government rule 10% of total light, fan load has to be covered by the PVsystem.
10 % of load, PT = 1000 ×10%=100 kW
Consider 15% Light fan Load, P = 100 ×15% = 15 kW
6.3.2 Array Sizing
System Efficiency = Array efficiency × Inverter efficiency × Cable efficiency
= 0.98 ×0.95
= 0.93
Array Output required = P/(System Efficiency × P.f.)
= 15/(0.8 × 0.93)
=20.12 say 20 kW
6.3.3 Inverter Sizing
Considering all the conditions stated earlier for a grid-tied system, 2(two) no of 10kWor 4(four) no of 5kW inverter can be chosen. Choosing 4 no of 5kW inverter is betteroption.
6.4 Simulation Results
With the condition described in article 4.1 both PVsyst and RETScreen softwarewere run. Total energy will be exported directly to the grid through 3-phase ac lines at415V. Using RETScreen software the initial cost for this 20kWp is approximately$46,000. With this data PVsyst results are; production from the system is about31,000kWh/yr (Fig. 6.2), loss diagram shown in Fig. 6.3 and the energy productioncost is $0.15 per unit. With the same data RETScreen calculates unit cost at $0.12.Considering energy export rate (Feed-in Tariff) $ 0.20 per unit, from RETScreen
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program the simple payback period is approximately 7 years and equity paybackperiod is 6 years (Fig. 6.4).
Fig. 6.2 Energy usages for the whole year from PVsyst
Fig. 6.3 Loss diagram over the whole year from PVsyst
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Fig. 6.4 Cumulative Cash Flow Graph from RETScreen
Fig. 6.4 Cumulative cash flow graph from RETScreen
6.5 Economic analysis by RETScreen
To evaluate a project or investment, it is important to calculate the NPV, IRR,payback period, year to positive cash flow and PI index for the particular project. Theparameter is very sensitive to PV cost, subsidy, discount rate and energy price rate.
Generally, financial parameters such as avoided cost of energy, avoided cost ofcapacity, discount rate and energy cost escalation rate can be important to the overallcost-effectiveness of a particular project and project’s financial viability can besensitive to variation in these parameters. In addition to these parameters, other inputparameters are, PV module cost, subsidy/incentives, slope and azimuth of solarcollector, nominal array efficiency and the efficiency of power conditioning unit andcontingency costs. Now we will analysis the project considering above mentionedsensitive parameters by RETScreen.
6.5.1 Effect of subsidy
Table 6.1: Changed of financial parameter with subsidy
Subsidy(%)
Investment($)
EnergyCost
($/kWh)
IRR(%) NPV ($) Simple
Payback (Yr)
EquityPayback
(Yr)0 45000 0.123 16.0 34495.75 7.45 6.24
10 40500 0.113 17.8 38995.75 6.71 5.6920 36000 0.103 20.1 43495.75 5.97 5.1330 31500 0.093 22.8 47995.75 5.22 4.5640 27000 0.083 26.4 52495.75 4.48 3.9750 22500 0.073 31.4 56995.75 3.73 3.35
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If some subsidy is provided then the investment, energy production cost and paybackperiod is reduced and at the same time NPV, IRR, PI is increased.
Fig. 6.5 Effect of subsidy on investment, energy production cost and NPV
Fig. 6.6 Effect of subsidy on NPV and Profitable index(PI)
0
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6.5.2 Effect of discount/depreciation rate
With increase of discount rate NPV and profitable Index(PI) decrease but energy costincrease (Fig. 6.7 and Fig. 6.8). If depreciation rate is greater than 17 this project isnot feasible with energy export rate US$ 0.20. Because NPV is negetive whendepreciation rate is greater than 17%.
Fig. 6.7 Effect of discount rate on energy production cost and NPV
Fig. 6.8 Effect of discount rate on energy production cost and PI
0.00
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64
6.5.3 Effect on size of system
With increase in system size energy production cost is decrease. In 20 kW systemtotal investment is approximately US $ 46000 and energy production costapproximately TK. 10.50 whereas. In 50 kW system total investment is approximatelyUS $ 107500 and energy production cost approximately TK. 10.00 Fig. 6.9.
Fig. 6.9 Effect of system size on energy production cost and Investment
6.5.4 Effect on energy export rate
With increase on energy export rate NPV, IRR, PI are increased and Payback period
decreased (Fig. 6.10, Fig. 6.11, Fig. 6.12). To be feasible of investment IRR should be
greater than 8% and NPV should be positive. With energy export rate more than US $
0.125/kWh (Fig. 6.11) both the condition satisfied. Considering 30% profit, if Feed in
tariff is greater than US $ 0.163/kWh (0.125 ×1.3), the project is feasible.
Fig. 6.10 Effect of energy export rate on NPV and IRR
0
50000
100000
150000
200000
250000
10 20 30 40 50 75 100
System size (kW)
Inve
stm
ent (
$)
0
0.02
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0.1
0.12
0.14
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Ener
gy c
ost (
$/kW
h)
-60000
-40000
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0
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0.06 0.1 0.14 0.18 0.22 0.26 0.3
Energy export rate ($/kW h)
NPV
($)
-10
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5
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15
20
25
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IRR
(%)
Energy cost
Investment
NPV
IRR
65
Fig. 6.11 Effect of energy export rate on NPV and Payback period
Fig. 6.12 Effect of energy export rate on NPV and PI
6.5.5 Effect on interest rate
With the increase of interest rate NPV decrease and energy production cost isincrease. Considering energy export rate US $ 0.20/kWh, NPV is negative aboveinterest rate 23 % . Again consider 30 % profit and others factor then the system isfeasible if interest rate is not more than 14% (Fig.6.13).
-60000
-40000
-20000
0
20000
40000
60000
80000
100000
0.06 0.1 0.14 0.18 0.22 0.26 0.3
Energy export rate ($/kWh)
NPV
($)
02468101214161820
Equi
ty p
ayba
ck p
erio
d (Y
r)-60000
-40000
-20000
0
20000
40000
60000
80000
100000
0.06 0.1 0.14 0.18 0.22 0.26 0.3
Energy export rate ($/kW h)
NPV
($)
0.00
0.50
1.00
1.50
2.00
2.50
3.00
PI (P
rofit
able
inde
x)
NPV
Equity payback period
NPV
PI
66
Fig. 6.13 Effect of Interest rate on energy cost, FIT and NPV
6.6 Diesel generator verses solar system
If compare solar system with diesel generator it found that diesel generator system iscost effective for a several years but for long term investment solar system is morebetter in both cost and environmental effect.
Considering the following setup and operation cost for a 20 kWp system, the costcomparison is shown in Fig. 6.14.
Solar system:
Initial cost = $ 46000
Operation cost = $ 200/yr
Inverter replacement = 10 yr
Diesel generator system:
Initial cost = $ 6000
Operation cost for production of energy $ 0.2/kWh.
NPV at 16tk/unit
Energy cost
FIT
67
Fig. 6.14 : Cumulative cost comparison of diesel generator and solar system.
Initial investment of solar system is approximately 6.5 times greater than that of DGsystem but operation cost of solar system is negligible with respect to DG system. Ifsimple calculation is done then it is found that after 7 years cumulative cost of dieselgenerator system cross the cumulative cost of solar system but if consider inflationrate 6% then cumulative cost of diesel generator system cross the cumulative cost ofsolar system after 6 years.
6.7 GHG reduction effect
From RETScreen analysis net GHF emission has been found for proposed 20 kWp
PV system is equivalent to 27 tco2/yr for CO2 . As there was no CO2 emission occur ithas a positive impact on the environment and at the same time can get a credit fornon-producing GHG.
6.8 Conclusions
To solve the present energy crisis and reduce pressure on conventional energy sourcelike oil, gas, coal etc. as well as national grid, this solution need to be implement as aurgent basis. In this case performance ratio is higher than previously describedsystems as there is no loss due to unused energy. Again initial investment per unitgeneration is low compared to other systems. Compare to DG set it is most costeffective for a long term period. Government should give some subsidy as like in fuelprice (Diesel, Petrol, Kerosene) or to create opportunity for the investor to get loaneasy and low (5 - 8%) interest rate. Then this type of system become a profitablebusiness for the investor and hence reduce load shed on national grid.
0
50000
100000
150000
200000
250000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Year
Cost
$
DG (inflation 6%)
DG (simple)
Solar System
68
CHAPTER 7
Feed In Tariff
7.0 Introduction
A feed in tariff is whereby a grid connects system, where owner is paid by a utility orgovernment agency for generation of electricity by their systems. A feed-in-tariff(FIT, standard offer contract, advanced renewable tariff or renewable energypayments) is a policy mechanism designed to accelerate investment in renewableenergy technologies [22]. It achieves this by offering long-term contracts to renewableenergy producers, typically based on the cost of generation of each technology.Technologies such as wind power, for instance, are awarded a lower per-kWh price,while technologies such as solar PV and tidal power are offered a higher price,reflecting higher costs.
7.1 Key provisions for FIT
FITs typically include three key provisions:
a. Guaranteed grid access.
b. Long-term contracts for the electricity produced.
c. Purchase prices based on the cost of generation.
Under a feed-in tariff, eligible renewable electricity generators (which can includehome owners, business Owners, farmers, as well as private investors) are paid a cost-based price for the renewable electricity they produce. This enables a diversity oftechnologies (wind, solar, biogas, etc.) to be developed, providing investors areasonable return on their investments.
7.2 Types of FIT
There are two different types of tariffs
a. Gross FIT
b. Net FIT
A gross feed in tariff pays a premium on all electricity produced by the ownerwhereas a net feed in tariff only pays on surplus energy created by the system. Theamount paid is usually above market rate, but this varies from place to place.
69
7.3 Feed in tariff (FIT) in present world
The principle of Feed in tariff (FIT) was first explained in Germany’s 2000 RES act:
“The compensation rates have been determined by means of scientific studies, subjectto the provision that the rates identified should make it possible for an installation -when managed efficiently to be operated cost-effectively, based on the use of state-of-the-art technology and depending on the renewable energy sources naturally availablein a given geographical environment” [22].
In 2008, a detailed analysis by the European Commission concluded that, “welladapted feed in tariff regimes are generally the most efficient and effective supportschemes for promoting renewable electricity”. This conclusion has been supported bya number of recent analysis, including by the International Energy Agency, theEuropean Federation for Renewable Energy as well as by Deutsche Bank.
Feed in tariff laws were in place in 46 jurisdictions across the world by 2007.Research for information on feed in tariffs is difficult to find and typically extensiveresearch is required to find it. Information about solar feed in tariffs may be found in aconsolidated form, however not the entire countries are listed in this source [23].
As of 2011, feed-in tariff’ policies have been enacted in over 50 countries, includingin Algeria, Australia, Austria, Belgium, Brazil, Canada, China, Cyprus, the CzechRepublic, Denmark, Estonia, France, Germany. Greece, Hungary, Iran, Republic ofIreland, Israel, Italy, Kenya, the Republic of Korea, Lithuania, Luxembourg, theNetherlands, Portugal, South Africa, Spain, Switzerland, Tanzania, Thailand, Turkey.A list of FIT implemented in various countries for up to 30 kW grid-tied SHSs whosePV panels are rooftop mounted is given below [22]:
Table 7.1: FIT for different countries of the world
Country FIT (US $)/kWh Country FIT (US $)/kWhAustralia 0.4127 Iran 0.1147Canada 0.5509 South Africa 0.2668
Czech Republic 0.6504 Spain 0.4462Germany 0.5643 Uganda 0.2587Greece 0.5906 Ukraine 0.3620India 0.3970 Thailand 0.6036
70
7.4 Find a Feed in tariff perspective Bangladesh
In chapter 6, for 20 kWp on-grid system NPV and IRR is shown in Fig. 7.1 and foundNPV is positive when IRR is greater than 8% . Again from the figure, IRR is greaterthan 8% if FIT is greater than BDT. 10.25 (consider US $ 1.0 = BDT. 82.00).
Considering profit and other factors (30%) FIT of the above system should be,
FIT = Tk. 10.25 x 1.3 = Tk. 13.33
From cumulative cash flow graph, payback period is approximately 6.5 say 7 yearsand there is a inflation so it is better to set a FIT approximately 15.00 tk./kWh for aperiod of 8 to 10 years.
Fig. 6.8 Effect of FIT on NPV and IRR
Fig. 7.1 Effect of energy export rate on NPV and IRR
Fig. 7.2 Effect of system size on energy production cost and Investment
a
-4000000
-2000000
0
2000000
4000000
6000000
8000000
5.0 8.3 11.6 14.9 18.3 21.6 24.9
Energy export rate (tk./kWh)
NPV
(tk.)
-10
-5
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5
10
15
20
25
30
IRR
(%)
IRR
NPV
0
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System size (kW)
Ener
gy c
ost(t
k./k
Wh
020000004000000600000080000001000000012000000140000001600000018000000
Inve
stm
ent (
tk.)
Energy cost
Investment
71
In case of DG system energy production cost is approximately 16.00 tk./kWh (US $0.22/kWh) which also same as energy production cost of quick rental oil based powerplant. This amount has to be paid by government to get the generation into thenational grid.
So, FIT for solar system should not be greater than 16.00 tk./kWh (US $ 0.22/kWh)comparing with diesel generator (DG) system. But if we consider other environmentaleffect and operation cost then FIT for solar system may increase.
7.5 Effect on interest rate
With the increase of interest rate NPV decrease and energy production cost isincrease. Considering energy export rate US $ 0.20/kWh, NPV is negative aboveinterest rate 23 %. Again consider 30 % profit and others factor then the system isfeasible if interest rate is not more than 14%.
Fig. 7.3 Effect of Interest rate on FIT, energy production cost and NPV
7.5 Conclusions
To make practically possible to invest in solar PV system (mainly in on-grid), themass people have to be informed about the benefits of it. For a long term basis itmight be a profitable business if government give some subsidy or fix a FIT closer tothe unit electricity generation cost by DG. Then investor will encourage investing inthis sector specially in grid-tie system, which is good for the investor as well as goodfor the welfare of the country people and development of the country.
NPV at 16tk/unit
Energy cost
FIT
72
CHAPTER 8
Conclusion and Recommendation
Due to the shortage of power, Load shedding is a common issue in urban areas. Butfor development and welfare of the people ensuring supply of electricity is essential.Again population density and population growth rate is so high in Bangladesh but theelectricity generation growth rate is very low as a result pressure increase day by dayon national grid and increase load shed. Recently Bangladesh government is trying tosolve this by installing some quick rental diesel based power plant, but still failed toreduce load shed. Hence we can say the increasing demand for power in Bangladeshcannot be meet with only conventional sources of electricity and need to findalternative solution. Renewable energy (Mainly Solar Power) is most appropriatesolution for Bangladesh in this point of view.
In urban areas most of the house owner (who is capable) use IPS or diesel generator.Cost of generation by diesel generator is very high and also pollute atmosphere. AgainIPS cannot produce any electricity by itself. It reserves energy when electricity isavailable. So, IPS is an extra burden on the grid and hence increases load shed.
So by converting the solar energy resources into useful forms of energy might be ableto substitute imported fuel and slow down the over exploitation of the country’snatural gas resources. Renewable energy like PV system is not subject to sharp pricechanges and it gives people greater certainty about the cost of energy, which is goodfor society and the economy.
PV systems are now available for easy installation with all necessary accessories in acompetitive market of Bangladesh. As the interest of the common consumers in SolarPV increased, along with the interest of the institutional consumers, several morecompanies joined in importing and selling solar PV systems.
PV system offer enormous benefits to countries with a good solar resource and couldbe deployed much faster than the current rate. Bangladesh is very successful in ruralelectrification in off grid areas with Solar Home System (SHS). Under the umbrella ofInfrastructure Development Company Limited (IDCOL), solar home system haspopularized in rural areas but in urban area it is still neglected and to reduce load shedin urban areas promotion of renewable energy technologies (mainly solar) are primeconsiderations.
73
. 8.1 Findings from the Study
This thesis is focused on installing solar system in urban area where utility grid isavailable. But as the utility grid is not sufficient enough to fulfill electricity demandproperly, an alternate solution is needed to be introduced to lessen the pressure on theutility grid and at the same time helping in fulfilling electricity demand. A SHS is avery good solution as it is providing green energy and helping to minimize thepollution of our environment. Also it reduces the pressure on fossil fuel.
In the previous chapters, the cost and performance of different types of SHSs wereanalyzed. From these analyses it is found that…
i. Stand-alone PV system is the worst in performance and cost but suitable forlower or middle class family in urban area.
ii. Grid-interactive system is the best in performance among the three systemsand suitable for middle or high class family of urban area. With installingthis type of system flat owner can lead a comfortable life as they don’t haveto face the hassle of load shed.
iii. Grid-tied system is the most cost effective system among the PV systems asthere is no system loss due to unused.
8.2 Contribution/Achievement
i. Find a FIT (Feed In tariff) perspective Bangladesh.
ii. Find out a better solution to reduce load shed in urban area.
8.3 Recommendation
The following broad recommendations are made to accelerate the expansion of PVtechnology in urban areas as a complementary to grid power:
iii. Attention should be given for grid connected PV system forcommercial/office user. As grid connected configurations can utilize all theproduced PV energy and no storage device is required, unit cost of thegenerated energy is less compared to other system.
iv. Government should give financial incentives/subsidy to private and non-governmental organizations to come forward with innovative PV programsand at the same time discourage conventional fuel base power plant..
v. A Renewable Energy Fund may be created by the Government to mobilizeresources for this sector so that private and non-government organizations
74
may receive fund at a reasonable cost for expansion of renewable energyprograms.
vi. Bank loan should be reasonable (low interest rate) and easy for installing PVsystem.
vii. Government should make a better policy and strictly apply to deploy solarsystem in every house of urban areas.
viii. Government should introduce a feed in tariff (FIT) to encourage investor toset-up solar PV system.
ix. Quality must be assured during implementation.
75
REFERENCES
[1] Upto-date Information of Power Sector, A Report by Power Cell, Ministry of
Power, Energy and Mineral Resources, Government of Bangladesh, April, 2012.
[2] Energy and Power, Dhaka, Bangladesh, Vol. 9, issue 21, 16 April
2012.(http//www.ep-bd.com/).
[3] S. Moury and R. Ahshan, “A Feasibility Study of an On-grid Solar Home System
in Bangladesh”, Proceedings 2nd International Conference on the Developments
in Renewable Energy Technology (ICRET 2010), Dhaka, Bangladesh, December
2012, pp.92-95.
[4] Md. R. R. Mojumder, Arif Md. W. Bhuiyan, H. Kadir, Md. N. H. Shakil and
Ahmed-Ur-Rahman, “Design and Analysis of an Optimized Grid-tied PV System
Perspective Bangladesh”, IACSIT International Journal of Engineering and
Technology, Vol.3, No.4, August 2011, pp.435-439
[5] Md. Abul kashem, Design and Analysis of a Mini Grid PV system for off grid
rural areas of Bangladesh, EEE BUET, May 2007.
[6] Bangladesh Power Development Board Annual report, 2010, Directorate of
System Planning, Dhaka, Bangladesh.
[7] Shahidul I. Khan, Md. Upal Mahfuz, “Prospect of tidal energy in Bangladesh”,
World Renewable Energy Congress VII, 29 June - 5 July, 2002, Cologne,
Germany, pp.875-877.
[8] “Sustainable Rural Energy” web site maintained by Local Government
Engineering Department, Bangladesh, http://www.sre.lged.gov.bd
[9] World Bank Final Report, ‘Market Assessment Survey of Solar PV Application in
Bangladesh”, Dhaka, Bangladesh, July 1998.
[10] Final report of solar and wind energy resource assessment(SWERA)-
Bangladesh. Renewable Energy Research centre(RERC) University of Dhaka.
[11] O. Bingol, A. Altinta, and Y. Oner, “Microcontroller based solar- trackingsystem
and its implementation,” Journal of Engineering Sciences, vol. 12, pp.243–248,
2006.
76
[12] PVSyst 5.56, A simulation based Solar System Design Software,
http//www.pvsyst.com/.
[13] RETScreen International, Renewable Energy Project Analysis Software,
National Resources Canada, 2007. http//www.retscreen.ge.ca/.
[14] B Zeinab Abdallah M. Elhassan1, Muhammad Fauzi Mohd Zain, Kamaruzzaman
Sopian and A. A. Abass, “Building integrated photovoltaic (BIPV) module in
urban housing in Khartoum: Concept and design considerations”, International
Journal of the Physical Sciences Vol.7 (3), pp. 487 - 494, 16 Jan, 2012.
[15] Solar Energy Grid Integration system, Program Concept Paper, U.S. Department
of Energy, Energy Efficiency and Renewable Energy, October 2007.
[16] Solar Energy: Fundamental, Design, Modeling and Applications, G.N. Tiwari,
2004.
[17] Blue sky ENERGY, SOLAR BOOST-TM 2000E, 25 amp12v dc maximum
power point tracking photovoltaic charge controller, ”Installation and operational
manual”, www.blueskyenergyinc.com.
[18] Photovoltiacs : System Design and Installation, California Energy Commission,
Energy Technology Development Division ,1516 Ninth Street, Sacramento,
California, 2001.
[19] Photovoltiacs : Basic Design Principles and components, US department of
Energy, Energy Efficiency and Renewable Energy,2004.
[20] Tomas Marvart , editors, Solar Electricity, University of southampton UK,
February 1995.
[21] Photovoltaics: Design and Installation Manual, Solar Energy International. New
Society Publishers, British Columbia, Canada, 2004.
[22] http://en.wikipedia.org/wiki/Feed-in-tariff.
[23] http://en.wikipedia.org/wiki/PV_financial_incentives.
[24] Design and operational recommendations on gridconnection of PV hybrid mini-
grids, IEA PVPS Task 11, Subtask 20, Activity 25, Report IEA-PVPS T11-06:
2011,October 2011.
77
APPENDIX- A
Result obtained from RETScreen for 700 WP solar PV system
78
700 Wp Stand-alone DC system
Project information (700 Wp Off-Grid)Project name 700 Wp Stad-alone(DC)Project location Dhaka, BangladeshPrepared for M.Sc.ThesisPrepared by S. M. Moynul HaqueProject type PowerTechnology PhotovoltaicGrid type Off-gridAnalysis type Method 2Heating value reference Lower heating value (LHV)Climate data location Dhāka
Load characteristics
Description AC/DC
Intermittentresource-loadcorrelation
Base caseload(kW)
Hours ofuse perday(h/d)
Days ofuse per
week (d/w)Fan 30 W 10 Piece DC Negative 0.30 4.00 7Light 6W 10 piece DC Negative 0.06 4.00 7Light 6W 10 piece DC Negative 0.06 12.00 7
Proposed case power systemInverterCapacity kWEfficiency %Miscellaneous losses %BatteryDays of autonomy d 3.0Voltage V 24.0Efficiency % 90%Maximum depth of discharge % 60%Charge controller efficiency % 90%Temperature control method AmbientBattery temperature °CAverage battery temperature derating % 0.5%Battery/load/resource mismatch factor %Capacity Ah 480Battery kWh 12
Resource assessmentSolar tracking mode FixedSlope ° 23.0Azimuth ° 0.0
79
Month Daily solar radiation -horizontal
Daily solarradiation - tilted
Electricityexport rate
Electricityexported to
gridkWh/m²/d kWh/m²/d $/KWh KWh
January 4.36 5.56 600.0 0.073February 4.92 5.78 600.0 0.068March 5.59 6.00 600.0 0.077April 5.76 5.69 600.0 0.071May 5.30 4.97 600.0 0.064June 4.53 4.19 600.0 0.053July 4.23 3.96 600.0 0.052August 4.29 4.15 600.0 0.054September 4.02 4.10 600.0 0.052October 4.32 4.82 600.0 0.062November 4.28 5.30 600.0 0.067December 4.21 5.52 600.0 0.073
Annual 4.65 5.00 600.00 0.784
Annual Solar RadiationAnnual solar radiation - horizontal KWh/m² 1700Annual solar radiation - tilted KWh/m² 1820
Energy ModelPhotovoltaicType mono-SiPower capacity kW 0.7Manufacturer BP SolarModel mono-Si - BP 4 175WEfficiency % 13.9%Nominal operating cell temperature °C 45Temperature coefficient % / °C 0.40%Solar collector area m² 5Miscellaneous losses % 2.00%SummaryCapacity factor % 14.10%Electricity exported to grid KWh/yr 784
Project CostInitial Cost AmountPhotovoltiac $ 910Module Support Structure $ 150Other equipment $ 150Storage Battery $ 1,200Transportation $ 100Training & commissioning $ 100
80
Charge controller $ 120Contingencies $ 150Total Investment $ 2,880
Annual costs (credits) AmountOperation & maintenance cost $ 20Sub-total: $ 20
Periodic costs (credits) AmountCharge controller 10 yr $ 120Battery Replacement 5 yr $ 1,000
RETScreen Financial Analysis - Power projectFinancial parametersFuel cost escalation rate % 5Inflation rate % 6Discount rate % 8Project life yr 20Incentives and grants $ 0Debt ratio % 0GHG Reduction SavingsNet GHG reduction tCO2/yr 1Net GHG reduction - 20 yrs tCO2 14GHG reduction credit rate $/tCO2 4GHG reduction income $ 3GHG reduction credit duration yr 20GHG reduction credit escalation rate % 5Annual savings and incomeFuel cost -base case $ 497GHG reduction income $ 3Total annual savings and income $ 500Financial viabilityPre-tax IRR - equity % 12.6Pre-tax IRR - assets % 10.0After-tax IRR - equity % 10.0After-tax IRR - assets % 10.0Simple payback yr 6.0Equity payback yr 7.2Net Present Value (NPV) $ 954Annual life cycle savings $/yr 97Benefit-Cost (B-C) ratio 1.33
81
Yearly cash flowsYear Pre-tax After-tax Cumulative
# $ $ $0 -30,003 -30,003 -30,0031 2,738 2,738 -27,2652 2,873 2,873 -24,3923 3,014 3,014 -21,3794 3,162 3,162 -18,2175 3,317 3,317 -14,9006 3,480 3,480 -11,4207 3,651 3,651 -7,7698 3,830 3,830 -3,9399 4,018 4,018 79
10 -11,902 -11,902 -11,82211 4,423 4,423 -7,39912 4,641 4,641 -2,75813 4,869 4,869 2,11114 5,108 5,108 7,21915 5,360 5,360 12,57916 5,623 5,623 18,20217 5,900 5,900 24,10218 6,190 6,190 30,29219 6,495 6,495 36,787
82
APPENDIX- B
Result obtained from PVSyst for 700 WP solar PV system
83
84
85
86
87
88
APPENDIX- C
Result obtained from RETScreen for 10 kWP system (With battery)
89
10 kWp On-Grid Project (Battery back-up)
Project information (10 KWp On-Grid)
Project nameDesign and Analysis of a 10KWp On-grid
Project location Dhaka, BangladeshPrepared for M.Sc.ThesisPrepared by S. M. Moynul HaqueProject type PowerTechnology PhotovoltaicGrid type Central-gridAnalysis type Method 2Heating value reference Lower heating value (LHV)Climate data location Dhāka
Resource assessmentSolar tracking mode FixedSlope ° 23.0Azimuth ° 0.0
Month Daily solar radiation -horizontal
Daily solarradiation - tilted
Electricityexport rate
Electricityexported to
gridkWh/m²/d kWh/m²/d $/KWh KWh
January 4.36 5.56 0.20 1276February 4.92 5.78 0.20 1179March 5.59 6.00 0.20 1335April 5.76 5.69 0.20 1229May 5.3 4.97 0.20 1118June 4.53 4.19 0.20 919July 4.23 3.96 0.20 900August 4.29 4.15 0.20 940September 4.02 4.10 0.20 899October 4.32 4.82 0.20 1088November 4.28 5.30 0.20 1165December 4.21 5.52 0.20 1264Annual 4.65 5.00 0.20 13312
Annual Solar RadiationAnnual solar radiation - horizontal KWh/m² 1700Annual solar radiation - tilted KWh/m² 1820
90
Energy ModelPhotovoltaicType mono-SiPower capacity kW 9.99Manufacturer BP SolarModel mono-Si - BP 4 185WEfficiency % 14.80%Nominal operating cell temperature °C 45Temperature coefficient % / °C 0.40%Solar collector area m² 68Miscellaneous losses % 2.00%InverterEfficiency % 90.00%Capacity kW 10Miscellaneous losses % 10.00%SummaryCapacity factor % 15.20%Electricity exported to grid KWh/yr 13312
Project CostInitial Cost AmountPhotovoltiac $12,000Module Support Structure $2,000Other equipment $2,000Storage Battery $4,000Transportation $1,000Training & commissioning & Installation $2,000Inverter $6,000Contingencies $1,000Total Investment $30,000
Annual costs (credits) AmountOperation & maintenance cost $100Sub-total: $100
Periodic costs (credits) AmountInverter replace 10 yr $5,500Battery Replacement 10 yr $ 3,500
91
RETScreen Financial Analysis - Power projectFinancial parametersFuel cost escalation rate % 5Inflation rate % 6Discount rate % 8Project life yr 20Incentives and grants $ 0Debt ratio % 0Annual incomeElectricity exported to grid KWh 13312Electricity export rate $ /KWh 0.20Electricity export income $ 2662Electricity export escalation rate % 5GHG Reduction SavingsNet GHG reduction tCO2/yr 12Net GHG reduction - 20 yrs tCO2 239GHG reduction credit rate $/tCO2 4GHG reduction income $ 48GHG reduction credit duration yr 29GHG reduction credit escalation rate % 2Annual savings and incomeElectricity export income $ 2,662GHG reduction income $ 40Total annual savings and income $ 2710Debt payments per yrs 0Net annual savings and income $ 2710Financial viabilityPre-tax IRR - equity % 8.7Pre-tax IRR - assets % 8.7
After-tax IRR - equity % 8.7After-tax IRR - assets % 8.7
Simple payback yr 11.5Equity payback yr 9.0
Net Present Value (NPV) $ 1712Annual life cycle savings $/yr 174Benefit-Cost (B-C) ratio 1.06Debt service coverage 0Energy production cost $/KWh 0.192GHG reduction cost $/tCO2 (15)
92
Yearly cash flowsYear Pre-tax After-tax Cumulative
# $ $ $0 -29999.7 -29999.7 -29999.71 2738.273 2738.273 -27261.42 2872.666 2872.666 -24388.73 3013.687 3013.687 -21375.14 3161.661 3161.661 -18213.45 3316.932 3316.932 -14896.56 3479.861 3479.861 -11416.67 3650.823 3650.823 -7765.788 3830.216 3830.216 -3935.569 4018.456 4018.456 82.8946
10 4215.979 4215.979 4298.87411 -12661.4 -12661.4 -8362.5712 4640.727 4640.727 -3721.8413 4868.935 4868.935 1147.09114 5108.398 5108.398 6255.48915 5359.668 5359.668 11615.1616 5623.328 5623.328 17238.4817 5899.989 5899.989 23138.4718 6190.292 6190.292 29328.7719 6494.908 6494.908 35823.67
93
APPENDIX- D
Result obtained from RETScreen for 20 kWP system (On-grid)
94
20 KWp On-Grid Project
Project information (20 KWp On-Grid)Project name Design and Analysis of a 20KWp On-gridProject location Dhaka, BangladeshPrepared for M.Sc.ThesisPrepared by S. M. Moynul HaqueProject type PowerTechnology PhotovoltaicGrid type Central-gridAnalysis type Method 2Heating value reference Lower heating value (LHV)Climate data location Dhāka
Resource assessmentSolar tracking mode FixedSlope ° 23.0Azimuth ° 0.0
Month Daily solar radiation -horizontal
Daily solarradiation - tilted
Electricityexport rate
Electricityexported to
gridkWh/m²/d kWh/m²/d $/KWh KWh
January 4.36 5.56 0.18 2995February 4.92 5.78 0.18 2767March 5.59 6.00 0.18 3134April 5.76 5.69 0.18 2884May 5.3 4.97 0.18 2623June 4.53 4.19 0.18 2158July 4.23 3.96 0.18 2113August 4.29 4.15 0.18 2205September 4.02 4.10 0.18 2110October 4.32 4.82 0.18 2555November 4.28 5.30 0.18 2734December 4.21 5.52 0.18 2966Annual 4.65 5.00 0.18 31245
Annual Solar RadiationAnnual solar radiation - horizontal KWh/m² 1700Annual solar radiation - tilted KWh/m² 1820
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Energy ModelPhotovoltaicType mono-SiPower capacity kW 20.35Manufacturer BP SolarModel mono-Si - BP 4 185WEfficiency % 14.80%Nominal operating cell temperature °C 45Temperature coefficient % / °C 0.40%Solar collector area m² 138Miscellaneous losses % 2.00%InverterEfficiency % 95.00%Capacity kW 20Miscellaneous losses % 2.00%SummaryCapacity factor % 17.50%Electricity exported to grid KWh/yr 31245
Project CostInitial Cost AmountPhotovoltiac $ 22,440Module Support Structure $ 4,000Other equipment $ 4,000Transportation $ 1,000Training & commissioning & Installation $ 2,000Inverter $ 12,000Contingencies $ 1,000Total Investment $ 46,000
Annual costs (credits) AmountOperation & maintenance cost $ 240Sub-total: $ 200
Periodic costs (credits) AmountInverter replace 10 yr $ 12,000
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RETScreen Financial Analysis - Power projectFinancial parametersFuel cost escalation rate % 5Inflation rate % 6Discount rate % 8Project life yr 20Incentives and grants $ 0Debt ratio % 0Annual incomeElectricity exported to grid KWh 31245Electricity export rate $ /KWh 0.18Electricity export income $ 5624.00Electricity export escalation rate % 5GHG Reduction SavingsNet GHG reduction tCO2/yr 28Net GHG reduction - 20 yrs tCO2 560GHG reduction credit rate $/tCO2 4GHG reduction income $ 112GHG reduction credit duration yr 20GHG reduction credit escalation rate % 2Annual savings and incomeElectricity export income $ 5,624GHG reduction income $ 112Total annual savings and income $ 5,720Debt payments per yrs 0Net annual savings and income $ 5,736Financial viabilityPre-tax IRR - equity % 14.0Pre-tax IRR - assets % 14.0
After-tax IRR - equity % 14.0After-tax IRR - assets % 14.0
Simple payback yr 8.4Equity payback yr 6.9
Net Present Value (NPV) $ 26341Annual life cycle savings $/yr 2683Benefit-Cost (B-C) ratio 1.57Debt service coverage 0Energy production cost $/KWh 0.124GHG reduction cost $/tCO2 (96)
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Yearly cash flowsYear Pre-tax After-tax Cumulative
# $ $ $0 -46000 -46000 -460001 5765.204 -40242.8 -40242.82 6047.494 -34195.3 -34195.33 6343.677 -27851.6 -27851.64 6654.437 -21197.2 -21197.25 6980.492 -14216.7 -14216.76 7322.596 -6894.1 -6894.17 7681.538 787.4378 787.43788 8058.147 8845.585 8845.5859 8453.293 17298.88 17298.88
10 8867.888 26166.77 26166.7711 -13476.7 12690.07 12690.0712 9759.301 22449.37 22449.3713 10238.18 32687.55 32687.5514 10740.62 43428.17 43428.1715 11267.79 54695.96 54695.9616 11820.91 66516.87 66516.8717 12401.24 78918.11 78918.1118 13010.14 91928.25 91928.2519 13649 105577.3 105577.320 14319.29 119896.5 119896.5
