Solar Buffer Storage Tank
39.500-litres-buffer for a 100% solar heated house.
39.500-litres-buffer for a 100% solar heated house.

The sun is delivering heat in most abundance when the demand for heating energy is lowest, namely in summer. That's posing a problem to the application of Solar Heating Systems for Backup Heating: How to store (respectively: How to buffer) the thermal energy between generation and consumption. The simplest-to-use and most common storage medium is water, hold in very big tanks, the so-called buffer storage tanks.

The design of these tanks has to follow the same rules as the design of solar hot water tanks, in particular a tall and relatively slim shape (meaning a small diameter in relation to the height) to support the Thermal Stratification in the tank, and a thick insulation to minimise heat loss. Unlike hot water tanks, however, buffer tanks are integrated in a closed heating-circuit, containing not potable but heating-circuit water. Therefore most of them feature only one Heat Exchanger at the bottom of the tank to transfer the heat from the solar circuit to the heating-circuit.

Since the best insulation can only lower, but not forestall heat losses, any long-term heat storaging (for at least some weeks) requires a very high tank volumen in relation to the tank surface. Seasonal heat storage tanks of 100% solar heated one-family houses therefore have to be some floors tall.

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