Solar collector fluid

Solar collector fluid is a carrier medium consisting of a water-propylene glycol mixture in the solar circuit of a solar thermal system. Only in solar thermal systems with air collectors is no solar fluid used.

Solar fluid is heated by solar energy and flows through the solar collectors to the heat storage tank, where heat exchangers transfer the energy to heating and service water. The cooled solar fluid flows back into the solar collectors and heats up all over again.

In order for the solar fluid to flow well, it must be able to withstand sub-zero temperatures and high temperatures. This is why a water-glycol mixture with a mixing ratio of around 50% has become established for use as solar collector fluid, sometimes supplemented by corrosion protection agents. A collecting tank absorbs solar fluid vapour to protect the solar thermal system if the pressure builds up too much due to extremely high temperatures. In some solar thermal systems, the solar fluid is also automatically drained off at extremely low temperatures. Annual checks of the solar fluid ensure proper function and protection. If the solar fluid becomes cloudy, it is time for a replacement, which is usually after about five years.

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