The document summarizes the principles and manufacturing process of photovoltaic solar cells. It discusses how sunlight is converted to electricity through the photovoltaic effect in solar cells made of semiconductor materials like silicon. The manufacturing process involves refining silicon from sand into ingots and wafers that are doped and assembled into solar modules. Different types of solar cells have varying conversion efficiencies from electricity generation. Key applications of photovoltaics include powering buildings, remote devices, vehicles, and lighting.
1. Unit -2 SOLAR ENERGY
Photovoltaic Solar Cells
BY
MR.K.STALIN
AP/MECH/AMET UNIV
2. Principle of Photovoltaic effect
Photovoltaic (PV)
effect is the
conversion of sunlight
energy into electricity.
3. When sunlight hit the cell, the photons in light excite some of the electrons in the
semiconductors to become electron-hole (negative-positive) pairs.
Since there is an internal electric field, these pairs are induced to separate. As a
consequence, the electrons move to the negative electrode while the holes move to the
positive electrode.
A conducting wire connects the negative electrode, the load, and the positive electrode in
series to form a circuit.
As a result, an electric current is generated to supply the external load. This is how PV effect
works in a solar cell.
Semi-conducting materials in the PV cell are doped to form P-N structure as an internal
electric field. The p-type (positive) silicon has the tendency to give up electrons and acquire
holes while the n-type (negative) silicon accepts electrons.
4. Manufacturing process
Raw material: silicon
Sand is mostly made up of silica. At the first step, silica goes through carbothermic reduction process and become
metallurgical grade silicon (MG-Si).The MG-Si then goes through refining and casting scratch process to become
poly-silicon.
5. Ingot growing or Brick Casting
The poly-silicon material goes into two different production process for mono-crystalline silicon and multi-
crystalline silicon production
For mono-crystalline silicon, the poly-silicon is used for ingot growing through the Float Zone (FZ) process.
For the multi-crystalline silicon, the poly-silicon material is melted and then cast into bricks.
Slicing
The mono-crystalline silicon ingot is then slice into wafers. As for the poly-crystalline silicon, the silicon brick is
first diced into bars and then sliced into wafers. Since mono crystalline silicon grows in a cylinder shape, their
wafers are not in perfect squares.
Doping
For both mono and multi-crystalline Silicon, a semiconductor junction is formed by diffusing n-type or p-type onto
the top surface of the silicon wafer to form the p-n junction in a solar cell. Depending on the process, it might start
out with an n-type waver, followed by a p-type layer.
6. Wiring
Solar cells are wired together to form a circuit.
Coating
Contacts are applied to the front and rear of the cell to protect the cells and increase efficiency in absorbing light.
Assembling
With the necessary functions to generate electricity, the solar cells are assembled to form solar modules. The
modules are the final solar products that can be arrange in arrays for larger output.
7. The different types of solar cells.
•Mono-crystalline silicon
•Polycrystalline silicon
•Flexible amorphous thin film
•Copper-indium-gallium-selenide (CIGS) thin film.
8. Conversion Efficiencies of Different PV Modules
The following are the conversion efficiencies of different PV modules:
•Mono-crystalline silicon - 12.5-15%
•Polycrystalline silicon - 11-14%
•Amorphous silicon (a-Si) - 5-7%
•Copper indium gallium selenide (CIGS) - 10-13%
•Cadmium telluride (CdTe) - 9-12%
9. The following are some of the key applications of photovoltaics:
•Building-integrated photovoltaics (BIPV) – Can be located on the building roofs.
•Cost-effective solar solutions for remote places
•Solar-powered LED lighting
•Auxiliary power for boats and cars
•As electric power for use in space
•To power calculators and novelty devices
•Solar-powered remote fixed devices - for products such as parking meters,
emergency telephones, water pumps, temporary traffic signs, trash compactors, and
remote guard posts and signals.
•Solar-powered lighting for roadways/highways
