Solar thermal energy is a technology for harnessing solar energy for heat. This is very different from solar photovoltaics, which convert solar energy directly into electricity. Solar thermal collectors are characterized by the US Energy Information Agency as low, medium, or high temperature collectors. Low temperature collectors are flat plates generally used to heat swimming pools. Medium-temperature collectors are also usually flat plates but are used for creating hot water for residential and commercial use. High temperature collectors concentrate sunlight using mirrors or lenses and are generally used for electric power production.

For billions of years, the sun has poured out huge amounts of energy in several forms, including light, heat, radio waves, and even x-rays. The Earth, in orbit around the sun, intercepts a very small part of the sun’s immense output. On Earth, direct sunlight is available from sunrise until sunset, except during solar eclipses. Solar collectors and modules are designed to capture some of the sun’s energy and change it from radiation into more usable forms such as heat or electricity. In fact, sunlight is an excellent source of heat and electricity, the two most important forms of energy we consume.

Solar power is used synonymously with solar energy or more specifically to refer to the conversion of sunlight into electricity. This can be done either through the photovoltaic effect or by heating a transfer fluid to produce steam to run a generator.

Solar technologies range from traditional methods related to food, heat and light to large-scale electrical generation systems. Applications include:

* Biomass (wood, biofuel)
* Electricity generation (photovoltaics, heat engines)
* Evaporation (clothes drying, desalination, food preservation)
* Heat (hot water, building heat, cooking)
* Lighting (daylighting, hybrid lighting, daylight saving time)
* Transportation (solar car, solar plane, solar boat)