Solar thermal energy is a form of energy in which the sun is used to produce heat that can be used in a variety of ways. People have been using this energy for thousands of years for a variety of tasks, and modern technology has considerably expanded the applications for the sun's heat. This should not be confused with solar power, in which the sun's light is used to produce electrical energy.
Some of the applications for solar thermal energy are very ancient. For example, solar drying is a technique that uses heat from the sun in food preservation. In this application, food products are laid out on rocks, and the sun's warmth is used to dry them. Evaporation ponds such as those used to concentrate salt also use heat energy from the sun, as can desalination plants.
This form of energy can also be used for cooking, sometimes in very creative ways. Solar ovens use solar thermal energy, and it can be used to heat water to generate steam for cooking. Pasteurization can also be accomplished with the use of concentrated heat from the sun. Another use for it is in the distillation of fluids, and, of course, in hot water heating. Water heated this way can be used for bathing, cleaning, and cooking. It can also be used for home heating; heated water, for example, can be circulated underneath a floor to warm it.
Solar thermal energy can even be used for cooling, although it sounds paradoxical to harness heat to cool things down. In this application, it is used in a process known as evaporative cooling, in which liquid water is evaporated, cooling the air. All of these applications for the sun's heat can be basic to advanced, accessible to people in communities all over the world, including communities in developing nations.
Heat from the sun can be used in electricity generation. This requires some extensive support technology, but one advantage is that, since heat can be stored, a solar thermal energy plant can operate 24 hours a day to meet power needs. These facilities are typically located in areas that get a lot of sun, so that the maximum amount of heat energy can be harnessed. Towers and reflective arrays of various kinds can be used to collect the sun's heat and concentrate it for the purpose of producing electricity.