End use application: The case of solar thermal systems

The contribution of solar thermal systems in meeting the global energy demand is, differently to what it is often perceived, among the highest compared to traditional renewable energies (such as biomass and hydropower). It is slightly lower in terms of capacity (282.6 GWel) and energy produced (581.1 TWhel/y) than wind. Moreover, it is about double of the contribution of PV and about one order of magnitude larger than geothermal and CSP (concentrated solar power). The simplest and most widespread application of solar thermal systems is the production of domestic hot water (DHW). The solar heat can also be used for active heating and cooling of buildings, although the portion of the covered load is limited by the fact that the availability of solar radiation during the heating season is in general the lowest on an annual basis. Solar combi systems (for the combined production of DHW and heating) are widespread in some local markets (mainly European). Other solar thermal technology uses, less diffuse, with a high future application potential are: production of industrial process heat, solar district heating plants, solar cooling. The descriptions given of solar collectors in this section are also valid for these cases of application. However, these uses are beyond the scope of this text. More information about technological peculiarities and sizing criteria of the aforementioned systems can be found in the literature [1-4]. © Springer International Publishing Switzerland 2013.