Solar thermal collectors are devices capable of capturing solar radiation and transmit it to a fluid, for later use.
The solar collectors are divided into two groups:
Solar Collectors without concentration: And they do not exceed 70 ° C, so they are used in the applications of solar energy of low temperature heat. An application example would be the production of hot water.
Concentrating Solar Collectors: Which, using the methods of concentrating optics, are able to raise the temperature of fluid above 70 ° C. These are applied in solar thermal medium and high temperature. We can find examples of these in the thermal solar plant in Almeria (Spain), Grenoble (France) and in California.
Solar Collectors without concentration
These collectors are characterized by not having methods of concentrating solar energy, so that the relationship between the collector surface and solar collector absorbing surface is nearly unity.
Flat Plate Solar Collector:
Generally flat plate collector acts as a receptor that gathers energy from the sun and warms film. The energy stored in the plate is transferred to the fluid. Usually these collectors have a transparent cover of glass or plastic fail greenhouse, comprising a number of copper tubes, which exposed to sunlight absorb solar radiation and transmit the fluid passing through its interior.
Its application is the production of domestic hot water, pool heating and heating.
Collectors are flat type whose main characteristic is to have the air as heat transfer fluid. They have a maximum temperature limit (convective processes have a minor influence on the air) and work best in conditions of normal circulation, but in contrast have a low heat capacity and heat transfer process between plate and fluid is bad. Its main application is the heating.
Van equipped with a double deck envelope, sealed, insulated inside and outside, and which has been evacuated. Its purpose is to reduce convection losses. They are more expensive, besides losing the vacuum effect with the passage of time. Its main application is the production of sanitary water heating and pool heating.
They have a cylindrical symmetry, consisting of two concentric tubes; one outside and one inside glass painted black or selective paint. The fluid flows through the inner tube. Its main application is the heating.
Conical or spherical Collectors:
Its main feature is that constitute the unit simultaneously capture and storage. Its catchment area is conical or spherical with a cover glass in the same geometry. With these geometries it is achieved that the illuminated throughout the day, in the absence of shade surface is constant.
Installation is simple, but have problems of water stratification and service catchment area is small. Its main application is the production of hot water through solar energy .
2. Concentrating Solar Collectors:
use special systems in order to increase the intensity of radiation on the absorbent surface and thereby achieve high temperatures in the heat transfer fluid. The main complication is the need to have a monitoring system to ensure that the collector is permanently oriented toward the sun.
Cylindrical concentrators: Its reflecting surface is half a cylinder. Its main application is the production of steam in a power plant
Concentrators paraboloids: Its reflective surface has a geometry paraboloid of revolution. Its main application is the production of steam in a power plant.