Medium-Temperature Solar Thermal
Low-temperature solar thermal energy is used in applications that require temperatures between 100ºC and 250ºC. From 80ºC the flat collectors practically no longer have any performance and it is necessary to resort to other capture systems.
Low-temperature thermal energy systems are used mainly for applications that demand thermal energy, that is, heat between 125º C and 400º C. To reach higher temperatures it is necessary to concentrate the solar radiation.
- Solar vacuum collectors
- Concentration solar collectors
Vacuum solar collectors
Vacuum solar collectors is a set of vacuum tubes that uses solar thermal energy. This type of solar collector consists of linear collectors housed in vacuum glass tubes. The solar panel has a comb structure, with a mast that conducts the heat transfer fluid, and a series of barbed tubes where the solar radiation is captured.
It is an intermediate solution between flat collectors and medium-temperature collectors, there are vacuum collectors that allow temperatures of up to 120º C. They usually use a collection surface formed by a series of finned tubes, covered with a selective surface and Circulating the fluid-heat-carrier inside it (photovoltaic solar energy).
The main advantage of vacuum solar collectors compared to flat collectors is their better thermal insulation. In the flat collectors there are thermodynamic losses by convection, while in the tubes, being isolated in vacuum, these losses are reduced to values around 5%. Compared to flat solar panels, these losses represent up to 35% less. The reduction of the heat loss allows to increase the yield remarkably.
Concentration solar collectors
If we want to reach higher temperatures we need to concentrate the solar radiation. Optical procedures with lens devices are enormously expensive. The most developed concentrators at present are those of reflection by means of mirrors and that for this temperature range corresponds to linear concentrators with a cylinder-parabolic reflective surface.
Basically, the concentration solar collector consists of a parabolic trough mirror that reflects all the solar radiation received on a glass tube located along the focal line of the mirror. Inside this tube is the absorbent surface in contact with the fluid-heat-carrier. This arrangement of the absorber and the fluid-heat-carrier is aimed at reducing convective losses.
Last review: April 18, 2018