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A solar or photovoltaic cell converts solar energy into electrical energy. It is a semiconductor device made from silicon. Solar cells are used in remote areas which are not connected to the electrical grid , in satellites , space stations . They are also used for consumer applications with low electric power requirements like calculators and watches. 

Most solar cells are made from silicon wafers. There are different types of silicon wafers which are classified according to the manufacturing process. 

Mono crystalline silicon has the highest efficiency in converting solar energy to electrical energy. Thin single crystal wafers are cut from cylindrical ingots and are expensive. Very high purity silicon is required.

Poly or multi crystalline silicon is made from square ingots of silicon. Since crystals of different sizes are formed during solidification of silicon, there are defects at the borders of the crystal.  These wafers are less efficient compared to mono crystalline silicon.

Amorphous silicon is formed when silicon is deposited on some other substrate material. The thickness of  silicon is less than 1 micron and production costs are lower. This silicon is used primarily for low cost consumer products like watches and calculators.

The cost of electricity generation per kwH using solar cells is currently higher than other conventional means of  power generation using fossil fuels. However, the cost of manufacturing solar cells is decreasing significantly every year and soon solar power may replace electricity in many applications.