Solar cells are the basic building blocks for all solar panels, from the portable battery charger to the roof mounted installation for a house. When you look at a typical solar panel, you can see the individual solar cells arranged in a grid pattern. These are wired together inside the panel to make the rated voltage – each cell only produces about half a volt by itself, but the panel may make a nominal 12 or 24 volts for use in the system.

Solar cells are made from silicon, which you may know better in the form of sand. Sand has some impurities that have to be taken out, but then the manufacturers put in other impurities such as boron or phosphorus (known as “doping”) to make the cell work. Many solar cells are crystalline, that is, made up of crystals, although some are single crystals and some are multiple crystals. A few types use amorphous silicon, which really just means it doesn’t have the formal structure of a crystal, and this is used for “thin-film” solar cells, which comprise a thin layer on another material such as glass or a flexible material.

photovoltaic cells

Photo: freedigitalphotos.net by pakorn

It was over 50 years ago when researchers at Bell Laboratories, investigating the (then) new semiconductor materials noticed that silicon was sensitive to light. Although the possibilities were probably not fully realized at the time, this, with the help of the space program demanding more intensive investigation, resulted in the solar cells we have today. What actually happens is that when the light, which consists of minute particles called photons, hits the cell the photons knock electrons out of it. Electrons have a negative charge, so if they are captured by a conducting grid before going back to the silicon they produce usable electricity.

The sun’s power is about 100 watts (like a light bulb output) for each square foot of the earth’s surface. Solar cells used commonly are about 8-15% efficient, the efficiency being the amount of that energy that is converted into electricity. The amorphous type of silicon is the least efficient, the crystal is the most, and you will see some differences even with the same size panels from different manufacturers. Unless space for the panels is an issue, the efficiency really doesn’t matter much – the electricity they generate is free, so the more important statistic is how much you need to spend for each watt of output.

 

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