KFW70 Calculation + Hot Water Storage

And in the other post you write something about the efficiency of the heat pump for hot water generation...

Surely you always have hot water in the summer without heating. But at what cost? What does your solar thermal system cost you (and please don’t forget the space consumption for a 750l tank!)

When you then calculate the hot water costs saved with it, THAT is inefficient

.... Upon inquiry, everyone in the circle of acquaintances who operate solar thermal systems for hot water reports that the heating is completely off during the warm season and they still have good hot water temperatures in the morning for showering......

That may well be true. How many kWh/a are actually harvested with it? In principle, every kWh of fossil energy substituted by a solar thermal system is valuable, there is no doubt about that. However, this does not necessarily have to be economical for the operator. Assuming a theoretical demand coverage of 50%, the following savings result from the above demand and investment approximately: Gas condensing boiler => €102/a => 59 years Air heat pump => €69/a => 89 years Brine heat pump => €54/a => 111 years I hardly believe that solar thermal systems achieve such normative useful lifetimes. Additionally considering interest costs, depreciation, inflation as well as electricity costs for control and circulation pump, profitability for the operator is hardly to be expected. Therefore, I would rather invest the necessary money for a solar thermal system in improved building envelope insulation. Best regards