House heating may be passive heating or active heating . Passive heating and cooling is achieved by designing the house to let in the solar radiation during the winter and keep out the solar radiation in summer. Active heating systems use fans and solar collectors to heat the air and move it around the house. A bed of rocks under the house may be used to store the heat. Such systems can also cool the house at night, and make the bed of rocks cool for later use during the day.
Agricultural crop drying is usually a good use for solar radiation.
Solar heated air is not so hot that it spoils the produce, and the drying system protects food crops from rain, dirt, and insects. The use of solar heat for timber seasoning can save large amounts of conventional energy. Central power towers into which a large field of movable mirrors concentrates solar radiation to produce very high temperatures. Large fields of photovoltaic cells. These systems cannot compete economically against conventional power generation methods at present, but some of them may become important in the future.