Even though solar energy systems are dependent on good weather conditions, performance of such plants can greatly be extended with a back-up accumulation tank, that is capable of storing heat for several days.

On cloudy days when the sun is not shining, the accumulation tank allows the stored heat to be used to prolong energy production. At hours with lower solar collector performance (morning/evening) the stored heat can also be used to create a more balanced daily heat generation. In wintertime, the water in the tank can act as a frost protection for the solar collectors, thereby increasing efficiency in colder months.