Solar Thermal Energy

In the past, solar collectors have mainly been used to produce warm water, although the last few years have seen an extension to include the support of space heating systems in the spring and autumn.
If solar energy is also to be used during the heating period, which is generally low in sun hours, it needs to be collected during the summer in long-term thermal energy storage units. The stored solar heat can then be used during the heating period to supplement the supply of heat to buildings.
In a long-term thermal energy storage unit the heat itself can be stored with the help of a storage medium such as water or gravel. More recent developments have opened up a new possibility - sorption storage. Here the adsorption of steam into silica gel is used to store heat, achieving an energy density in the storage unit which is four to five times greater than that provided by a conventional water storage tank. This cutting-edge technology, which was developed in Germany and is already available on the market, will make it possible in future to supply buildings with heat which was generated purely from solar energy, even in countries with temperate climates.
Solar thermal plants are already well established in Germany, and are born in mind in the planning phase for detached and semi-detached houses, where they can be integrated into the conventional roof, thus reducing the costs of solar thermal energy even further. 100,000 plants with a total collector surface of around 1,000,000 m² were installed in Germany in 2001 alone.