A seasonal storage has been used in several existing SDH plants to exploit this opportunity.
It depends on several boundary conditions e.g. locality, designed solar heat share on the annual heat production, operating temperature (the lower, the better), accumulation capacity of storage and system etc. Systems with solar heat share up to 30 % have usually annual specific gains between 400 and 500 kWh/m².
Certified ST collectors undergo a standard test procedure for evaluating their yield as well as their durability, reliability and safety easures. The EN 12975-1 and 2 and the CEN/TS 12977-1 and 2 are the reference standards.