Operating principle

There is water in a slurry pit or other large underground tank.

In winter, heat is extracted from the water with a heat pump. It cools down to 0°C and freezes.

In summer, the ice is thawed via hybrid collectors (PVT) and heated up to 25°C, thus also helping to cool the house "from above", i.e. from the roof.

The ice storage tank covers a large part of the house's heating and hot water.

Thanks to this seasonal storage, the freely available summer heat can be used cheaply in winter and even cools surrounding houses in summer.

An overview of the test object "Sunnegg" in Guntmadingen SH can be found here.


The storage tank can store significantly more heat through freezing than would be the case with normal heating of water.

The 0°C ice storage practically automatically draws heat from the environment in summer and helps to cool the houses.

Cold solar cells produce more electricity than those heated by the sun. This benefits electricity generation via the hybrid collectors.

An extremely inexpensive battery storage system provides intermediate storage for the surplus electricity produced during the day.

Thanks to the controlled room air system and the ice storage, the house remains pleasantly cool even in summer.

There are various options, which are explained in the detailed explanations.

To the detailed explanations