Solar thermal systems for heating water simply collect the sun's heat, but the high-tech way to harness the sun's power is with a photovoltaic (PV) system. When sunlight strikes the PV modules, it frees electrons. Semiconductors capture those electrons and turn them into electric current. The system will work anytime the sun is shining, but it works best when the sun is directly over the modules. As long as the sun keeps shining, you've got fuel -- with no noise, air pollution or additional cost. Still, the systems are expensive, and the amortized cost (what you'll pay over the life of the system) is as much as four times as high per kilowatt hour as the cost from a utility company. The newest PV technology uses thin film solar panels that manufacturers claim bring the cost per watt down to the level of utility companies.