Solar Collectors are used to heat water using only the radiant heat energy from the Sun. Water is run through a series of tubes sheltered from ambient air yet exposed to the Sun. There are several different methods of concentrating solar radiation to these tubes. One of the most common types of collectors is a flat plate collector, which can be easily mounted on a roof surface or in an open field. These collectors encase the series of tubes in a black-coated metal casing with a transparent glass or plastic covering that lets light and heat in and minimizes the heat escaping and air infiltration. Essentially acting as a greenhouse, these collectors are typically used to heat water from 80° to 160°F.

Another type runs the piping through clear vacuum tubes that only exchange radiant energy and have no air to absorb and exchange heat between pipe and glass surfaces. The water flowing through this type of collector is known to reach temperatures upwards of 300°F on a warm sunny day. These are much more efficient collectors in areas where a large temperature difference is required, such as process heating in cold mountainous climates.

Other types include different methods of concentrating sunlight through an array of mirrors focused on a single tank or by running a black water pipe along a mirrored trough.

Solar heated water has many applications, essentially anything where water needs to be heated. Pool heating with solar is a very common practice to keep the water at a comfortable temperature and extend the swimming season from spring to fall. They may be used for supplementing domestic water heating, reducing the fuel or power required to heat domestic hot water. They may also be used to supplement hot water for space conditioning such as in a radiant floor, concentrator systems are often used to produce steam for processes such as spinning a turbine for power generation.