Which heat accumulators are suitable for a solar thermal system?

In a solar thermal system, storage units have the function of intermediate storage of useful energy (heat), because the energy supply of the sun cannot be influenced and does not always match the time and extent of the heating and cooling requirements.

In any case, storage tanks must be equipped in such a way that heat losses are kept to a minimum. For this purpose they are covered with a thermal insulation layer. Efficient heat storage tanks (incl. floor insulation and correct execution of the connections) should be able to store heat for several days. In addition to high heat storage capacity, they must also meet the following criteria: high density, no toxicity, no fire or explosion hazard, no corrosive properties and suitability for the temperature range in question. (Source: Austrian Research and Testing Centre Arsenal Ges.m.b.H. 2007)

Storage tanks can be monovalent, which means that they are only heated by a single energy source, or bivalent, which means that an additional heating system is used if the solar radiation is not sufficient. Depending on the application, one of the two types of storage tanks is preferable.

Heat storage tanks can be differentiated according to the type of charging and discharging as well as the storage duration (short or long-term storage tank).