4. Solar Collectors

Solar-thermal collectors are devices that absorb solar energy. These are of either concentrating or non-concentrating type. The collector and absorber area are the same in a non-concentrating type such that the whole panel absorbs solar energy, whereas a concentrating solar collectors have a larger interceptor compared with an absorber. A flat-plate collector (FPC) is at the heart of solar thermal devices with various applications in medium temperature ranges (≅100 °C) from domestic to pre-heating to industrial sectors. For the highest operating temperature range (≥300 °C) of solar thermal energy applications used in the industrial sector, concentrating systems can be used for power generation by using high-temperature boiling fluid as medium. For greater plant capacity (≥1 MW), solar-power generation is economical with grid power in a dust-free region (minimum cleaning of reflecting sheet). In contrast, evacuated tubular solar collectors (ETSC) are also used for thermal applications in temperature ranges between 100 and 300 °C. The ETSC can be used for the pre-heating of working fluid for power generation; for lower-capacity indirect space heating; and for crop drying by way of a heat exchanger.