Re: How do solar panels work?

A solar cell converts sunlight into electricity. Photons from the sun strike the solar panel made of a semiconductor material. The most common material used for a solar cell is silicon. The incident photons are absorbed by the electrons in the silicon semiconductor. The big panels of a solar cell are sometimes referred to as a the collectors because they do just that -- collect sunlight.

If the photon give the electron enough energy the electron becomes a conduction electron and can be used to carry energy in the form of electricty. If the electron does not get more than enough energy to "break free" the energy is re-released as a photon and some heat (vibration).

The sun produces photons in a range of energies with and majority in the range of 1 to 2 electron volts. The typical energy needed to create a conduction electron in photo-active semiconductor solar cells is about 1.2 electron volts. It turns out that about 75% of the sun's photons have an energy greater than this minimum energy.

Let's do a quick and approximate calculation. The intensity of sunlight on the earth is about 1000 Watt/meter^2. So we would need a thousand one meter by one meter solar collectors to generate about 750,000 Watts. A typical coal burning power plant is capable of generating 1,000,000 Watts of power for several hundred tons of coal.

Solar cells are ideal for some uses like calculators where a lot of power is not consumed. Another ideal use is in satellites. Out in space, the intensity of sunlight is far greater than on earth because the photons do not have to travel through the atmosphere to hit the collectors.

Unfortunately, the photons with energy below the threshhold reduce the efficiency because of the heating of the sunlight collector makes it less efficient. Worst of all, the semiconductor material degrades with time. The constant absorption of energy makes the material less receptive. Sometimes this degradation can be reversed by reprocessing the material but that can be difficult and certainly is a nuisance.

Materials scientists and private companies are constantly trying to improve solar cells. A huge variety of material compositions has been tried with various advantages. Presently, France, Japan, and Germany are the countries spending the most on research for improved solar cells. Because of the research and manufacturing costs, solar generated electricty still costs more dollars per kilowatt-hour than coal burning power plant electricity but soon it should be competitive. And once the initial cost of installing solar collectors on a house has been absorbed the future cost is very low. Some government incentives have been put in place to help offset some of the initial cost faced by home builders and owners.

At some time in the future (50 years or more) fossil fuels will be depleted and humans will have to turn to other energy sources and solar cells will be a big part of generating electricity.

For more information try a web search of solar cells

-Tom Cull