1. Training on Dr. Sudhir Kumar Grid Connected Rooftop PV Systems
Technical & Economic Fundamentals
2018-Ahmadabad, Jammu, Shimla, Dehradun
In cooperation with:
In cooperation with: 4
Dr. Sudhir Kumar

2. Solar PV Fundamentals
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3. P-N Junction Layer of n- deposited on p- type base
Electrons move from n- to p- type
Junction stabilized: equilibrium attained
Potential difference created
Photovoltaic application:
Photo-activation occurs
Light energy excites electrons to move from high to low potential
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4. Photovoltaic Effect Light energy strikes junction
Electrons flow: inside from p- to n-
Outer circuit: from n- to p-
Suitable load attached for use
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5. Ideal solar cell material:
Must be a solid semiconductor
Must have suitable band gap
Responsive to visible range
Stable under outdoor use
Should have affordable cost
Abundant availability in nature
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Network Centre of Steinbeis GmbH & Co. (KGfur Technologietransfer, Germany). | |

6. Efficiency Vs Band Gap
Band gap: Energy gap between highest and next lower energy level of molecule
Ideal material close to 1.54 eV
Corresponds to red wavelength (E=1240 eV·nm/1.54 eV= 805 nm)
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7. Semiconductor Band Gaps: Examples
S. No.
Material
Chemical formula
Band Gap (e.V.) at 300 K 1.
Silicon Si
1.11 2.
Silicon Dioxide
SiO2 9 3.
Aluminium Antimonide
AlSb
1.6 4.
Gallium(III) Phosphide
GaP
2.26 5.
Gallium(III) Arsenide
GaAs
1.43 6.
Gallium(II) Sulfide
GaS
2.5 7.
Indium(III) Phosphide
InP
1.35 8.
Zinc Selenide
ZnSe
2.7 9.
Cadmium Sulfide
CdS
2.42
10.
Cadmium Selenide
CdSe
1.73
11.
Cadmium Telluride
CdTe
1.49
12.
Copper(II) Oxide
Cu2O
2.17
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8. I-V Characteristics
Illumination: Additional power, Photo- voltage, -current
Pmax = Imp X Vmp
Fill factor: (Imp X Vmp) / (Isc X Voc)
Efficiency: (power output  Pmax)/(Solar power input  Pin)
STC: AM 1.5, 1000 W/m2 , 25 0C
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9. STC, AM1.5 and NOCT Standard Test Condition: AM 1.5, 1000 W/m2 , 25 0C
AM (Air Mass Coefficient): Ratio of the distance that solar radiation travels through the earth’s atmosphere (path length), to the distance (path length) it would travel if the sun were directly overhead.
AM 0 - Outside atmosphere
AM 1 - At the zenith
AM At 48°
AM 2 - At 60°
NOCT: Normal Operating Cell Temperature at AM 1.5, 800 W/m2 , 20 0C, Wind Speed 1m/s (Normally: 45±2 0C)
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10. Temperature Effect on I-V Curve
UMPP voltage range
Module voltage (V)
Module current (A)
Temp coefficient:
Isc increases slightly, Voc decreases more significantly
Pmax effectively decreases
Mono- and Poly- crystalline: (-) % per degree over 25˚C
Amorphous Cells: (-) % per degree over 25˚C
Power projects: 10-20% loss in summer, gain in winter
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11. Radiation vs. Power
UMPP voltage range
Module voltage (V)
Module current (A)
Low radiation, low efficiency, Actual field condition:
Low power output: morning, evening, Highest output: noon
Major variation in current output
Overall output: whole day average
Design radiation value: ~ 600 W/m2 (8hrs/day) or 1000 W/m2 (4.5hrs/day)
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12. Types of PV Cells Crystalline Mono-crystalline silicon solar cells
Polycrystalline silicon solar cells
Thin film
Amorphous silicon
Cadmium telluride
Copper indium di-selenide
Emerging technologies
Gallium arsenide
Organic semiconductors
Dye-sensitized cells
Nanotechnology solar cells
Suggested reading:
"Comparative assessment of Crystalline and Thin-film PV technologies in India"
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13. Appearance of PV Cells and Modules
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14. Modules Common module: Opaque Hermetically sealed
Two layers of ethylene vinyl acetate (EVA) encapsulant
Support:
Top toughened glass
Bottom DuPont™ Tedlar® (PVF) polyvinyl fluoride sheet
Sturdy, suitable for outdoor use
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15. Cell, Module, Array
Cells Connected: Series - Voltage added, Parallel: Current added
Parallel-Series combination decides wattage, voltage
Same logic with modules to form array and solar field
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16. Series, Parallel Combinations
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17. Effect of Mismatch in Series on Power Output
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18. Effect of Mismatch in Parallel on Power Output
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19. Central Inverter or Multiple Inverters
(1) PV array, (1a/b) Part PV arrays, (2) PV Combiner Box, (3) Inverter
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20. String Inverters (1) PV array, (2) DC-Isolator, (3) Inverter, (4) Grid
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21. Inverters for Individual Modules
(1) PV array, (2) Inverter, (3) Grid
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22. PV Combiner Box
Excess Voltage Suppressor:  Protects electronics from voltage spikes
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Network Centre of Steinbeis GmbH & Co. (KGfur Technologietransfer, Germany). | |

23. Single Cell Voltage and Current
S. No.
Material
Typical Cell Voltage
at Open-Circuit
Typical Cell Current
at Short-Circuit 1
Crystalline and Polycrystalline
Silicon (x-Si)
~0.6 Volts
~35 mA/cm2 2
Gallium Arsenide
~1.0 Volts
~27 mA/cm2 3
Amorphous Si (a-Si)
~0.9 Volts
~15 mA/cm2 4
Tandem a-Si
~1.8 Volts
~10 mA/cm2 5
Copper-lndium- Diselenide (CIS)
~0.4 volts 6
Cadmium Sulfide, Cadmium Telluride
~0.7 volts
~25 mA/cm2
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24. Types of Solar PV Cell Technology
Single-crystal silicon (also known as Mono-crystalline):- Efficiency- 13% and 17%.
Multi-crystal silicon (also known as Poly-crystalline) :-Efficiency - 11% and 15%.
Amorphous silicon (also known as thin film silicon) :-Efficiency - 6% and 8%.
Concentrating SPV (Silicon, GaAs, CIS, CIGS, CdTe, etc.):- Efficiency %
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25. Suitability for Rooftop Solar
Use the poly-crystalline modules solely because
Slight cost advantage,
Relatively easier availability with vendors
Good efficiency
Least degradation
Local availability and
Better life of cell
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26. Understand Module Data Sheets
Tier 1, 2,3 modules or company?
Grade A, B, C, D modules? Appearance Class
(A: Without visible defects and the electrical data in spec)
(B: Visible but tiny defects and the electrical data in spec)
(C: Visible defects and the electrical data off-spec)
(D: Broken and can not be cut in smaller cells)
Fire/Application Class A, B, C modules? (UL 1703/IEC 61730) Prefer A→B→C
How to choose best module
First Solar CdTe Thin Film Module Data Sheet
SunPower Mono Si Res. Module Data Sheet
SunPower Mono Si Com. Module Data Sheet
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27. Solar Photovoltaic Appliances
SPV Off-Grid
Water pumping
Portable lantern/ domestic light
Street light
Power pack
Micro-grid/Distributed Solar Generation
Grid Connected
Grid-tied rooftop
Gross Metering
Net Metering
Commercial Power Project
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28. How Many Watts Module I Need?
Energy Requirement Calculations
Case 1
Case 2
Case 3
Load in Watts W
500
1000
Operation hours per Day H 3 8 2
Energy requirement (W x H) WH
1500
4000
2000
Module Wattage Calculations
Radiation hours per day H (1kW/sq.m.)
4.5
Module wattage required Wp
333
889
444
Module related Losses %
30%
Actual Module Wattage requirement Wp
433
1156
577
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29. Problems to be Solved by Participants
A module has Imp- 8.36A, Vmp –38.34V, Isc – 8.92A, Voc V
What is the wattage of module?
What is the Fill Factor (FF) of module?
Why FF is relevant when comparing modules?
What is the efficiency of module at STC with module area of 2mx1m?
With temp. coeff. of Pm-0.41%/0C, what would be the wattage of the above module at -10 0C and 50 0C ambient temperature ?
With temp. coeff. of Voc -0.33%/0C, what would be the Voc of the above module at -10 0C?
Why temp. coeff. is important to decide fuse and wire capacity particularly at lower ambient temperature?
2. What is the design value of radiation for solar power project designing?
3. Mr. Sharma has in his house 10x15W LED bulbs (8hrs), 4x50W fans (6hrs), geyser 1x1.5 kW (2hrs).
What capacity of SPV modules is needed on his roof?
What should be ideally Ah of 24 V battery with 2 days autonomy?
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30. Thank You
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