Solar energy is available in three forms: passive, active, and electric. Active and passive solar energy are generally used for space conditioning, such as heating and cooling. Active solar energy technologies are typically mechanical devices, such as solar hot water heaters, that are used to distribute solar energy. Passive solar heating integrates building design with environmental factors that enable the capture of solar energy, a simple example being south facing windows in a house. Solar electric devices such as photovoltaic cells convert sunlight into electricity.
Groups of photovoltaic cells can provide electricity in quantities ranging from a few milliwatts to several megawatts, and thus can power devices ranging from calculators to power plants. To get an idea of the scale, a large color TV requires approximately 1 kilowatt of power, while a power plant for a modern city requires approximately 3 gigawatts13.