Classification of solar collectors⦁ The classification is based on the way in which they collect solar radiation. The non-concentrating type absorbs the radiation as soon as it is received on the collector surface, while the concentrating type increases the concentration of the radiation per unit area before absorbing it.⦁ Furthermore, depending on the technique used for the concentration of the radiation, the concentrating type the type is further classified into focus and non-focus types. The focus type is further divided into linear and point focus depending on the focusing method.⦁ While unfocused type collectors consume both beam and diffuse radiation, focused type collectors use only beam radiation, since the scattered radiation cannot be concentrated.⦁ The important characteristics of a solar collector are:⦁ Collector efficiency: It is defined as the ratio between the energy actually absorbed by the collector and the energy incident on the collector.⦁ Concentration ratio ( CR): It is the ratio between the area of ​​the opening of the system to the area of ​​the receiver. The opening of the system is the projected area of ​​the collector facing the beam.⦁ Temperature range: is the temperature range at which the heat transfer fluid is heated by the collector.⦁ Non-concentrating collector or flat plate collector⦁ In it, l The area of ​​a collector intended to capture solar radiation is equal to the absorbing plate. Here no optical system is used to reduce solar radiation and therefore the concentration ratio is only 1.⦁ The flat plate collector is the most substantial component of any solar thermal energy system. It is basically a heat exchanger that transfers the radiant energy of incident sunlight to the sensible heat of a working fluid, liquid or air.⦁ Flat plate collectors are designed for operation in the low temperature range, from ambient to 60°C, or the average temperature range, from room to 100˚C.⦁ The construction details of a simple flat plate collector are shown in Fig. 1.2. Construction of the flat plate collectorBasic elements of a flat plate collector:⦁ Transparent cover (one or two sheets) of glass or plastic film that transmits radiation.⦁ Blackened absorbent plate usually of copper, aluminum or steel, typically 1-2 mm thick.⦁ Tubes (typically 1-2 cm in diameter), passages or channels, in thermal contact with the absorbent plate or connected to it.⦁ On the back and sides there is thermal insulation usually in glass fiber or expanded polystyrene, generally 5-10 cm thick, to minimize heat losses heat.⦁ Container or narrow enclosure to place the above ingredients. How the flat-plate collector works: ⦁ When solar radiation hits the specially treated absorbent metal plate, it is absorbed and increases its temperature.