Solar thermal energy refers to using solar energy (the renewable energy generated from the sun) for thermal uses. This energy is completely renewable, which could solve worldwide energy problems. It is important to keep in mind that solar thermal energy generates a different kind of energy than photovoltaics. Solar thermal energy is harnessed through low, medium, and high solar collectors. Each applies the concept of thermal energy generation in various ways.
Low temperature collectors are flat plates, which are generally used for heating, cooling, ventilation, and process heating. Solar process heating is used to for hot water or space heating for large or commercial buildings. In the United States heating, ventilation, and air conditioning accounts for 25 to 50 percent of energy use. This large amount can be offset by instead using solar thermal energy. Thermal masses can be used to store energy collected from the sun during the day and is then able to release the energy during cooler periods, such as the evening. These thermal mass materials most often include stone, concrete, and water. An important aspect of using solar thermal energy is to consider the climate, daylight, and shading conditions. Without adequate sunlight, thermal energy does not work as well.
Medium temperature collectors are also flat plates, but instead are used for commercial and residential hot water heating. They are most often used for cooking. Temperatures can reach up to 350 degrees Celsius, which is more than adequate for cooking. Drying and pasteurization is also possible through the use of this form of solar collecting. The simplest form of medium solar cookers reaches temperatures between 50 and 100 degrees Celsius and is a basic box design. The thermal box material is heated from the sun throughout the day, creating the cooking temperatures.
High temperature collectors differ immensely from low and medium collectors, as they don't use plates. Instead, high temperature collectors use mirrors and lenses to concentrate sunlight. High temperature collectors often use a heat engine for their space heating. The efficiency of the heat engine increase with the temperature of the heat source. This is called concentrated solar power. This technique helps to lower the environmental impacts of conventional power usage. It is possible to generate temperatures up to 600 degrees Celsius with this technique. For higher temperatures steam turbines and gas turbines can be used. This form of collecting is generally used for electric power production.
Thermal heating is still currently used in the Middle East. A solar thermal chimney collects energy during the day and then released it as the day cools. Updrafts through the chimney pull the air through the building, creating heat. This technology has been around since Roman times.