Solar Cells Facts

TYPES OF SOLAR CELLS

    A solar cell is the basic photovoltaic device which generates electricity when exposed to sunlight. A solar cell is a photo-diode which conducts current in one direction only. It is formed by creating a p-n junction using p-type and n-type silicon.

 

Monocrystalline Solar Cells. Semiconductor grade silicon is melted and through a crystal seeding process, a large single silicon crystal is formed. Crystals with diameters around 12cm are not uncommon.

    Once the crystal has been formed, it is sliced into wafers about 0.2 to 0.4mm thick. A phosphorous impurity is introduced into the surface layers of the wafer and metal grids are attached to the front and back of the wafer to facilitate the collection of electrons. Monocrystalline cells tested in the laboratory have given efficiencies of over 20%. In this case, various inefficiencies such as reflection and grid coverage have been reduced.

    Monocrystalline panels like Suntech are reaching more into the industry as they cover the whole range from 2Watt to 140Watt and are very well designed and made. Currently, there are a few brands providing cheaper panels like SolarKing, Powertech and many others that are making there mark in the solar market.

 

Multicrystalline panels are made up of multiple grains of monocrystalline silicon casted into ingots and then cut into wafers with a high efficiency.

Kyocera makes a slim-framed panel with shadow tolerance built in. Not only do these panels fold neatly and have a suitcase-style carry handle, they also produce the most watts and amps for their size in the market. BP Solar makes a similar panel.

Multicrystalline panels made by Kyocera, BP Solar and Sharp are very well known among the RV and camper trailer communities around the world.

 

Polycrystalline Solar Cells. Polycrystalline silicon is a block of material which instead of being a single crystal, is made up of many tiny crystals pieced together. Manufacturers have pioneered processes for mass-producing inexpensive poly crystalline cells, taking advantage of the fact that it is inherently easier to grow little crystals than big ones.

    A disadvantage of poly crystalline cells is that the boundaries between the tiny crystals tend to impede the flow of holes and electrons through the material. The cell efficiency suffers, though several techniques for coping with this problem have proven successful enough for 12% efficient poly crystalline cells to be produced.

Polycrystalline panels like Solarex are no longer on the market due to the multiple small silicon crystal that was used as a conducting gate material is no longer being produced. However, the panels were in a league of their own in their day.

 

Amorphous Solar Cells. Techniques such as the condensation of gaseous silicon are used to make cells with a thickness that can be measured in the number of atomic layers. The atoms in such thin films of silicon are arranged in a completely random fashion and the cell is called an amorphous thin-film cell.

    Though these cells are inexpensive, abandoning the crystal structure wreaks havoc on their efficiency. About 12% is the best that has ever been achieved, with average efficiencies of around 5%. They are also very shadow tolerant and work very well in the heat, with an operating temperature -40 to 80oC.

    The panels are incredibly portable due to the fact that they can be folded neatly into a small pouch.