SOLAR THERMAL SYSTEM - Photovoltaic System - Solar Power System
The solar thermal system is a facility which produces hot sanitary water using solar energy, as a consequence the hot-water heater will be turned on less frequently. Usually, a correctly dimensioned solar thermal system could satisfy the whole hot sanitary water requirement from May to September.
The solar thermal system is mainly installed in order to have hot sanitary water production and to supplement the heating plant.
In private housing it could be used for solar cooling, namely air conditioning using solar energy to cool air, and to heat the swimming pool. In industrial applications it could be used to produce steam and heat for processes.

The fundamental part of the system are:
Solar collectors: these devices absorb the solar energy and transfer it to the working fluid, which will exchange the heat with the sanitary water.
Thermal store (boiler): it is an insulate tank which stores hot sanitary water; in general there is a thermal exchanger inside it in order to allow the heat exchange from the working fluid to the sanitary water.
The system may be:
Active system: if there is a pump to assure the working fluid circulation.

Passive system: It relies on heat-driven convection, the circulation of working fluid is assured by variations of fluid density with temperature. There are not pumps and the thermal store is over the collector.
Unloading system: It is installed in active systems in order to drain the plant when the hot sanitary water reaches the required temperature or when the outdoor temperature is too low.
There are two types of solar collectors which could be an optimal solution for different requirements:
Flat-plate collectors: These collectors consist of a dark flat-plate absorber of solar energy containing the working fluid and a external glass that allows solar energy to pass through but that it is opaque to infrared light, creating a greenhouse effect which reduces heat losses.
Some flat-plate collectors are uncovered, they don’t have the external glass and they work well only if external temperature is above 20°C; they are very cheap.
Evacuated tube collectors: They are made of two tubes, the inner dark metal tube is the absorber surface, the external one is a glass tube and the space between them is evacuated so thermal losses are almost zero. Evacuated tube collectors are airtight sealed in order to always guarantee vacuum.
Some evacuated tube are what is called a U-Tube: inside the metal tube there is a copper U-tube in which the working fluid flows, then it is pumped to the thermal store where heat exchange with sanitary water occurs.
Another system is called heat-pipe, it is a airtight sealed copper tube, inside the dark metal one, which contains a small amount of liquid; the heat exchange occurs at the top of the tube.
These collectors could produce thermal energy even if the outdoor temperature is low because they use the energy coming from the sunlight. The working fluid temperature may reach 100°C.
Thermal solar collectors could be laid down on an horizontal or tilted area with a southern exposure (roof, terrace, etc) without surrounding environment shadings (building, tree, mountain…). Collectors have to be installed with a specific tilt using support structures if it is necessary; in general the tilt angle should be equal to the building latitude, in order to guarantee the best performance.
In passive system, solar collectors and thermal store are both installed outdoor. This easy, cheap and compact solution works well when the system is small and set in mild weather area or if it is used only in summer.
In active and unloaded system, the thermal store is installed inside the building. The plant is more complex and more expensive than a passive system, but it can works even in areas with worse weather conditions.
Solar thermal systems mean life is 20 years. The principal components of the system are guaranteed for 5 years.
The types of collectors and the plant configuration affect the prize of solar thermal plant. A focused analysis of customer’s needs, number of users, weather conditions and building insulation is fundamental to have the correct plant sizing and configuration. Only a high qualified technician can do it.
Approximately, the prize ranges from 300€/m2 to 1200€/m2.
Thermal solar plant installation allow to access tax deduction.
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