1. Solar PV Fundamentals Dr
Solar PV Fundamentals Dr. Sudhir Kumar Chief Executive Green Energy Solutions, Pune Mob:

2. Solar Photovoltaic Principles2

3. Solar cell material 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 3

4. Molecular orbital theory
Energy Levels
Molecular orbital theory
Atomic energy levels
Molecular energy levels
Single line representation
Lower level and higher level 4

5. Energy bands: Solid crystal
Many discrete energy levels together
Closely spaced in small region
Very close proximation forms band
Lower energy band, higher energy band
Valence band, conduction band, band gap 5

6. Insulator, Semiconductor, Conductor
Electricity conducts: conduction band, free electrons
Valence band holds bonding electrons
Bandgap and free electrons: deciding factors
Semiconductors:
Insulators when pure
Conduct when:
An impurity is added and
Excited by light, heat, voltage 6

7. Need for doping: p- and n- types
Pure semiconductor: perfect crystal lattice
Doping: adding impurities to these semiconductors
Impurity: extremely small; one atom in a million
N-type: electron rich, p-type: electron devoid
Ability of the crystal to conduct increased
Resistance of the semiconductor reduced 7

8. p-n Junction Layer of n- deposited on p- type base
Electrons move from n- to p- type
Junction stabilized: equillibrium attained
Potential gradient created
Doped semiconductors led to the invention of the transistor
The start of the ‘solid-state’ revolution
Photovoltaic application 8

9. Photovoltaic Effect Light energy strikes juction
Electrons flow: inside from p- to n-
Outer curcuit: from n- to p-
Suitable load attached for use

10. Photovoltaic cell Doped p- on n- base
Top metal grid (photolithography)
Bottom full metal cover
Positive and negative connections 10

11. I-V characteristics
Illumination: Additional power, Photo- votage, -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 11

12. Efficiency vs. Band gap Ideal material close to 1.54 e.V.
Corresponds to red wavelength 12

13. Band Gap Calculation Conversion between wavelength and energy
E = hc/λ, where hc = 1240 eV·nm
h is planks constant 6.626x10-34 j.s.
c is speed of light 3x108 m/s
λ is wavelength of light in nm
Green light for example:
E=1240 eV·nm/550 nm = 2.25 eV
Ideally best band gap should correspond to green light
But it corresponds to red due to inherent losses: Recombination
Higher the band gap greater the Voc
Lower the band gap greater the Isc 13

14. Semiconductor Band Gaps: Examples
S.N.
Material
Chemical formula
Band Gap (e.V.) at 300K 1
Silicon Si
1.11 2
Silicon dioxide
SiO2 9 3
Germanium Ge
0.67 4
Aluminium antimonide
AlSb
1.6 5
Diamond C
5.5 6
Gallium(III) phosphide
GaP
2.26 7
Gallium(III) arsenide
GaAs
1.43 8
Gallium(II) sulfide
GaS
2.5
Indium(III) phosphide
InP
1.35 10
Zinc selenide
ZnSe
2.7 11
Cadmium sulfide
CdS
2.42 12
Cadmium selenide
CdSe
1.73 13
Cadmium telluride
CdTe
1.49 14
Copper(II) oxide
Cu2O
2.17 14

15. 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
Amorphos Cells: % per degree over 25˚C
Power projects: 10-20% loss in summer, gain in winter 15

16. Radiation vs. Power Low radiation, low efficiency
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 (4.5 hrs/day) 16

17. Modules Common module: Opaque Solar Window: Transparent
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
Solar Window: Transparent
Window: energy generating asset
Block direct sunlight: no heating
Diffused light illuminates space
Shading and daylight combination
Energy savings:
Reduced lighting cost
Reduced cooling cost
Comfortable work environment
Winter: optimized solar heat gain 17

18. Cell, Module, Array Cells connected in series: Voltage added
Cells connected parallel: Current added
Parallel-series combination decides wattage, voltage
Same logic with modules to form array
Same logic with arrays to form solar field 18

19. Series – parallel combinations19

20. Effect of Mismatch in Series20

21. Effect of Mismatch in Parallel21

22. Central inverter or multiple inverters
(1) PV array, (1a/b) Part PV arrays, (2) PV Combiner Box, (3) Inverter 22

23. String inverters
(1) PV array, (2) DC-Isolator, (3) Inverter, (4) Grid 23

24. Inverters for individual modules
(1) PV array, (2) Inverter, (3) Grid 24

25. PV combiner box 25

26. Solar Photovoltaic Technologies26

27. Types of PV Cells Crystalline Thin film Emerging technologies
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" Section: "LATEST FROM WISE" 27

28. Types of PV Cells

29. Mono-crystalline Silicon Solar Cells
Majority solar cells manufacturers
Input material SiO2 (Sand)available abundantly
Principle of Czocharalski process (Crystal pulling method)
Practical efficiencies - 14 to 17% 29

30. Polycrystalline Silicon Solar Cells
Second most common natural substance
Manufacturing process - simpler and cheaper
Casting process, cutting: wafers
Practical efficiencies - 13 to 15% 30

31. Amorphous Silicon Solar Cell
Easy manufacturing:
process temperature: low
Large-area deposition
Low material requirements
Low energy consumption
Possibility of automation
Commercialized
Features:
Light soaking reduction
Low efficiency 6-9%
Faster degradation
Low temp coefficient

32. Cadmium Telluride Solar Cell
Highest theoretical conversion efficiency
Energy gap of 1.44 e.V.
Efficiency - 6 to 10%
Technically best among thin films
Degradation more than crystalline
Possibility of production hazards
Environmental pollution
Commercialized 32

33. Copper Indium Di-selenide Solar Cell
Number of alloy components: multiple processes complex
Theoretically ideal material
Band gap of 1.53 ev
Efficiency 11.4%
Expensive rare metals
Not commercialized 33

34. Gallium Arsenide Most efficient solar cell Band gap: 1.43 e.V.
Cell efficiencies - 30 to 34%
Used in space application
Very high cost
Too expensive for terrestrial applications 34

35. Organic Semiconductors
Advantage: reel-to-reel deposition
Possibilities for ultra thin, flexible devices
Solar power conversion efficiency of over 3%
Types: insoluble, soluble and liquid crystalline
Organic solar cells have a stability problem 35

36. Dye-sensitized Cells
Photosensitization of wide-band-gap semiconductors
Does not require high-purity semiconductors
Efficiencies of 7% on 30 cm x 30 cm areas reached
Considered as a potential and low-cost PV technology
Under research 36

37. Nanotechnology solar cells
Utilize tiny nano-rods
Objective:
Spectrum modification
Increase efficiency
Reduce manufacturing cost
Not made from silicon
Costly rare earth metals: Lanthenides
Praseodymium- Pr3+
Yttrium fluorides- YF3
Gadolinium- Gd3+
Under research 37

38. Palak (Spinach) Solar Cells
Massachusetts Institute of Technology, USA extracted PS1 poteines from Palak
Placed ~2 billion PS1 on a piece of glass in artificial cell membrane
Fixed a layer of proteins between layers of semiconductors
Exposed to sun light to produce electric current 38

39. Bio-Solar Cells: Challenges Ahead
ISSUES:
Less Power - Less current (1 mA/cm2) vs. Silicon (30 mA/cm2)
Short Lifespan– Few weeks to nine months vs. Silicon (25 yrs)
Dis-orientation:
PS1 proteines in mambrane of live plant: Same orienataion
Extracted PS1 is applied to a surface and dried: Disoriented
That’s bad for energy production
RESEARCH REQUIRED:
Make protein-based solar cell self-repairing by swapping out the old copies for new one: to improve life
Prepare synthetic PS1 protein dominant PALAK: to produce solar electricity
Synthesize light sensitive PS1 porteins which rearrange in single orientation when photo-exposed: to capture maximum sunlight
Improve transparency and coductivity of PALAK membrane: to use the leaf directly as semiconductor with well oriented PS1 39

40. Solar Photovoltaic Applications40

41. SPV off-grid Water pumping Home/ domestic light Street light
Portable lantern
Power pack
Micro-grid
Remote village electrification 41

42. 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
Energy requirement (W x H) WH
1500
4000
2000
Module Wattage Calculations
Radiation hours per day H (1kW/m)
4.5
Module wattage required Wp
333
889
444
Module related Losses %
30%
Actual Module Wattage requirement Wp
480
1270
635 42

43. 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 43

44. Grid-Connected Roof Top PV (GRTPV)
Indian Cities
Warehouse at India's Largest Foodpark, Tumkur, Karnataka
St. Joseph’s Old Age Home by Visakhapatnam Steel Plant   44

45. THANK YOU
Dr. Sudhir Kumar, Chief Executive, Green Energy Solutions, 8/15, Mazda Deluxe Homes, Porwal Park, Tank Road, Off: Alandi Road, Yerwada, Pune , India. Cell No , 45