Solar Thermal Collectors and Systems
The basic principle of solar thermal collection is that when solar radiation strikes a surface, part of it is absorbed, thereby increasing the temperature of the surface. The efficiency of that surface as a solar collector depends not only on the absorption efficiency, but also on how the thermal and radiation losses to the surroundings are minimized and how the energy from the collector is removed for useful purposes. Various solar thermal collectors range from unglazed flat-plate-type solar collectors operating at about 5-10°C above the ambient, to central receivers collectors operating at above 1000°C. Table 12.1 lists various types of solar thermal collectors and their typical temperature and concentration ranges.