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

II III IV V VI

B C (6)

Al Si (14) P S

Zn Ga Ge (32) As Se

Cd In Sb Te

Semiconductors: Elementary – Si, Ge. Compound – GaAs, InP, CdTe. Ternary – AlGaAs, HgCdTe, CIS. Quaternary – CIGS, InGaAsP, InGaAIP.

Cell TechnologiesCrystalline 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-Si a-Si CIGS GaAs

400 nm (3.1eV) 0.15 0.05 0.05 0.09

600 nm (2eV) 1.8 0.14 0.06 0.18

800 nm (1.55eV)

9.3 Not absorbed

0.14 1.1

1000nm(1.24eV)

180.9 Not absorbed

0.25 Not 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.

Shading Effects