Solar thermal energy is a technology for harnessing solar energy for heat. Solar thermal collectors are characterized 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.
Solar thermal energy of low and medium temperature can be used for solar water heating, solar pool heating and solar space heating in buildings. There are different types of low and high temperature collectors, such as flat-plate collectors, evacuated-tube collectors, direct collector-storage systems (open-circle systems) where the water is being heated at the collectors and is being used directly as domestic heat water, and thermodynamic collectors.
For applications in houses and offices where temperatures less than 200 oF are required, it is possible to use flat-plate collectors, while in applications where temperatures higher than 200 0F are required it is possible to use evacuated-tube collectors.