How do you evaluate the performance of a solar thermal system? The criteria normally used are the operating temperature and efficiency, expressed in terms of thermal power extractable from solar radiation (the latter obviously depends on the geographical area in which the system is located).
Based on operating temperature and efficiency, the solar thermal systems more performing are those with 'vacuum collectors' (temperature range 0-220 ° C), a little less those with 'flat glazed collectors' (0-150 ° C) and finally those with uncovered collectors (0-30 ° C ).
Below in this article we give some info on the technologies of a solar thermal system as regards the price, the amounts per square meter reflect the performance. The most expensive are the vacuum collectors (450-600euro / sqm for DHW and 700-850 for DHW + heating), then the glazed flat collectors (350-450 for DHW - 600-700 for DHW + heating). The uncovered collectors are the cheapest (70-100 euros / sqm) and can only be used for the production of DHW, not for heating.
But what exactly is a solar thermal system? This definition refers to a plant for the production of domestic hot water that uses solar radiation (renewable energy) to produce heat, saving on the consumption of gas or electricity produced with fossil sources. For solar cooling, a newly developed technology, read our article Solar cooling fresh air from the sun.
From the point of view of manufacturing technology, a solar thermal system it can consist of: uncovered collectors (plastic pipes exposed to solar radiation for heating the internal liquid), glazed flat collectors (in which the radiation is absorbed by a flat metal collector and transferred to the liquid flowing in the lower part of the panel), vacuum collectors (pipes covered by an absorber material enclosed in vacuum glass ducts).
The manufacturing technology is a first distinction, but the solar thermal systems they can also be classified by the way they are connected to plumbing systems. There are two types of solar thermal systems: systems with natural circulation, in which the circulation of the fluid occurs with a convective / gravitational process; he solar thermal systems forced circulation, in which the circulation of the fluid is guaranteed by a system of pumps. The solar thermal systems of the forced circulation type today represent 90% or more of the installations.
Finally, there is a third classification with which a solar thermal system, and it is the one that concerns the final use of the heat generated by the system. On the basis of this distinction, one can find a solar thermal system for the production of domestic hot water or to a solar thermal system for the production of domestic hot water and at the same time for heating, in this case with the integration to a boiler defined as a storage system.