Solar Power

Photovoltaic simply means power (or "volts") from sunlight ("photo"). The photovoltaic process changes sunlight into electricity. Photovoltaic power is often confused with solar thermal technology, but the two types of power are very different.

Solar thermal technology uses the sun's heat to warm a fluid, which then is used to generate power via steam or other means. If water is the fluid, it is easily available for household hot water requirements. However, photovoltaic systems convert the sun's energy to electricity directly, without using an intermediary fluid.

At the heart of a photovoltaic cell is a material that is able to conduct electricity. The more efficiently the material can do this, the more energy you'll receive from your PV cell. Currently, silicon is the material of choice, although lots of solar research is underway, and it's very possible someone will come up with something better.

When sunlight hits the conductive material, some of it is absorbed. The light energy knocks some electrons loose, and they flow in a pre-determined direction dictated by the small electrical field that exists within the PV cell.

Since all the electrons are flowing the same direction, this creates an electrical current. When metal contacts are installed at either end of the PV cell, that current can be drawn off and used. As you can see, the more cells, the more current, and the more power.

Efficiency is an issue for PV-generated solar power. While we've come a long way from the first solar cells that had an efficiency of about 4.5%, we're still inching toward a 40% efficiency rate. Why so low?

Not all sunlight is absorbed by a solar cell. Remember, full-spectrum light coming from the sun arrives at Earth in a huge band of wavelengths. Not all wavelengths will pop those electrons free and make them run around. So a certain percentage is lost (and always will be) due to the nature of our sun.

Of course, we want our PV cells exposed to the sun, but that's only one element of being outside. Other elements in the Great Outdoors can damage expensive solar panels, so we want them protected, along with our investment. Protective glass, which lets in most of the sunlight, is the material of choice. But glass also reflects a certain amount of sunlight, so there's another loss of efficiency.

To get around the natural loss of efficiency, several ideas are under development. One of them involves using lenses or mirrors to concentrate and focus the sunlight directly onto the PV cell. Another uses a liquid layer sandwiched between two rigid but different layers, one above and one below.

In December 2006 the Boeing company announced that its wholly-owned subsidiary Spectrolab, Inc. created a solar cell that broke the 40% efficiency mark. While anxious to get this new development to market, we probably won't see it commercially available for several years yet.

However, as the cost of fossil fuels continues to rise and technological and production advances move forward, the cost of energy generated with solar photovoltaic cells is nearing that of standard energy. In a few years, your investment could pay off in benefits far beyond those of ecological conservation.