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Photovoltaics (PV)

Solar electric (PV) panels contain silicon solar cells which produce electricity when exposed to solar light - the light not its heat. When the solar cell(s) are wired to an external circuit and exposed to light, electrons can flow through the circuit then return to the cell.

Sunlight can be described as a steam of tiny bullets of energy (photons) moving at incredibly high speed. PV cells are particularly responsive to that energy because they are made of light-sensitive materials. It works at any time as the sun is shining, but more electricity will be produced when the light is more intense (a sunny day) and is striking the PV arrays directly (when the rays of sunlight are perpendicular to the PV arrays).

Most photovoltaic panels are made of solar cells laminated in a plastic encapsulant between tempered glass and a plastic backskin. There are four types of the PV cells:

 

 

 

1. Single-Crystalline (Mono-Crystalline) Silicon:
The single crystal silicon is the widely available cell material. In the most common method of producing this material, the silicon raw material is first melted and purified in a crucible. A seed crystal is then placed in the liquid silicon and drawn at a slow constant rate. This results in a solid, single-crystal cylindrical ingot. The manufacturing process is slow and energy intensive, resulting in high raw material cost. The ingot is sliced using a diamond saw into thick wafers. The wafers are further cut into rectangular cells to maximize the number of cells that can be mounted together on a rectangular panel. Unfortunately, almost half of the expensive silicon ingot is wasted in slicing ingot and forming square cells.

2. Poly-Crystalline:
This is relatively a fast and low cost process to manufacture thick crystalline cells. Instead of drawing single crystals using seeds, the molten silicon is cast into ingots. In the process, it forms multiple crystals. The conversion efficiency is lower, but the cost is much lower, giving a net reduction in cost per watt of power.

3. Thin films:
These are new types of photovoltaics entering the market. Copper Indium diselenide, Cadmium Telluride, and Gallium Arsenide are all thin film materials, directly deposited on glass, stainless steel, ceramic or other compatible substrate materials. This technology uses much less material per square area of the cell, hence, is less expensive per watt of power generated.

4. Amorphous silicon:
In this technology, amorphous silicon vapor is deposited on a couple of amorphous (glassy) films on stainless steel rolls, typically 2000-feet long and 13-inches wide. Compared to the crystalline silicon, this technology uses only 1 percent of the material. Its efficiency is about one-half of the crystalline silicon at present, but the cost per watt generated is projected to be significantly lower.

These cells are very fragile and must be encapsulated in a plastic substrate to protect them from fracture and moisture penetration. Solar modules are manufactured to be strong enough to withstand the most extreme weather conditions, including extreme heat and cold, high humidity, and even hail storms.

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