Solar thermal energy

Solar radiation has its origin in the Sun which is mainly composed by hydrogen and has a temperature of 20 million Kelvin degrees. In these conditions, nuclear fusion reactions between hydrogen atoms take place, generating helium atoms and an energy of 64,070 Kw per square metre.

Not all this radiation reach the Earth due to the distance separating the Earth and the Sun, we only get about 1,367 W/square metre. Moreover, when radiation goes through the atmosphere, it gets weaker depending on the concentration of gases in the atmosphere, climate, latitude, etc.

Solar thermal systems make use of this part of the energy to raise the temperature of the solar collectors strategically placed to absorb as much as possible of this radiation. Then, this energy is transferred to the carrier fluid, which is normally water.

The basic functioning of this system is the heating of a fluid (water, air,...) making use of sun rays that get the surface under which this fluids runs.

Since the very beginning of our existence, the Sun has provided us with food and energy, but we have also made use of its qualities for other purposes. In the 15th century, Leonardo da Vinci developed a mechanism with a parabolic shape to use it as a weapon at war against the ships approaching the coast. At the end of the 19th century, during the industrial revolution, this energy was used as a cheap way to heat water for domestic use.

Solar thermal technology has developed a lot and its applications are plentiful. The classification of the different thermal systems depends on the temperature that the carrier fluid reaches, so we can find High, Medium and Low temperature systems.

Low temperature systems:

Those systems where water does not reach the boiling point. They can be used to Heat Sanitary Water, for domestic use, swimming pools heating, some industrial processes, etc. There are many types of technologies for these purposes: flat rubber collectors or metal grill collectors, coil collectors, selective layer collectors, etc.

Medium temperature systems:

Those systems use for applications that require water temperatures of over 80º C until 250ºC. They are normally used for industrial processes such as generating thermal fluids, desalination of sea water and refrigeration using solar energy.

High temperature systems:

A great number of mirrors are used to concentrate the Sun rays on the collector containig a fluid that reaches its boiling point, reaching a very high pressure that can be later used to move a turbine to produce electricity.

Other application of solar thermal systems without fluids is the solar drying (solar ovens and kitchens) very useful in developing countries.

Solar thermal energy gives us a great opportunity to take advantage of solar radiation. In some areas, it is the only possible way to obtain energy. Since it has a low cost, is easily installed and has a good performance it should be supported and promoted by governments.

Source: Ecological Research Institute.

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