Module 2/7: Solar PV Module Technologies

Module 1 : Solar Technology Basics Module 2: Solar Photo Voltaic Module Technologies Module 3: Designing Solar PV Systems (Rooftops) Module 4: Designing Solar PV Systems ( Utility Scale) Module 5: Financial Analysis Module 6: DPR (Detailed Project Report) & EPC Module 7: The present Solar industry scenario and the future

Semiconductors used for solar cells IIIIIIVVVI BC (6) AlSi (14)PS ZnGaGe (32)AsSe CdInSbTe Semiconductors: Elementary – Si, Ge. Compound – GaAs, InP, CdTe. Ternary – AlGaAs, HgCdTe, CIS. Quaternary – CIGS, InGaAsP, InGaAIP.

Cell Technologies Crystalline silicon Mono- crystalline Pure and efficient 15-19% efficiency Multi- crystalline 12-15% efficiency Thin film Non Silicon based CdTe 8.5% efficiency CIGS 9-11% efficiency Silicon based Amorphous 5-7% efficiency

Technology Differences Optical Properties Band gap (direct, indirect) Absorption Coefficient Absorption length Electrical Properties Carrier Lifetime Mobility Diffusion length Manufacturing Absorber material Cells Modules Performance Efficiency Current, Voltage and FF Effect of temperature and radiation

Optical Properties: Band Gaps Fixed band gap of c-Si material (mono, multi). Tunable gaps of thin film compound semiconductors. Once a module is fixed, there can be no modification.

Optical Properties: Direct and Indirect band gap semiconductor High absorption probability. Thinner material only. Low absorption probability. Thicker material only.

Optical Properties: Material absorption lengths Absorption Length in Microns (for approx. 73% incoming light absorption) Wavelength (nm)c-Sia-SiCIGSGaAs 400 nm (3.1eV) nm (2eV) nm (1.55eV)9.3Not absorbed nm(1.24eV)180.9Not absorbed0.25Not absorbed Absorption length is much higher for Si because of lower absorption coefficient. Longer wavelength photons require more materials to get absorbed.

Electrical Properties: Mobility: Ease with which carriers move in semiconductor. Lifetime: Average time carriers spend in excited state. Diffusion Length: Average length travelled by carrier before recombining due to concentration difference.

Electrical Properties: Drift and Diffusion lengths Diffusion: Carrier movement due to concentration difference. Diffusion length: Average length travelled by carrier before recombination due to concentration difference. Drift: Carrier movement due to electric field. Drift length: Average length travelled by carrier before recombination under electric field.

Electrical Properties: Drift and Diffusion lengths High quality material scenario Low quality material scenario Carrier are transported by diffusion to the junction. Large diffusion length. Junction is very thin. Diffusion length are small. Drift length is about 10 times greater than diffusion length. Intrinsic layer is thicker.

Manufacturing: The difference Crystalline Technology Thin Film Mono-crystalline and Poly-crystalline Si substrates are grown. The substrate act as a light absorber material. The absorber layer is deposited in the thin film cells. A supporting substrate is required since the films are thin.

Performances Average module efficiencies are increasing for all technologies. PV module efficiencies lag behind as compared to laboratory cell efficiencies.

Temperature Coefficient Thin Film modules perform better due to smaller temperature coefficient. Temperature Coefficient could result in higher electricity generation.

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