Solar system for water heating and other measures for KFW70

Hello everyone,

I have a question about solar systems for water heating. I have heard several times that they are not very profitable with regard to investment costs, additional electricity costs, the actual yield, and the real cost savings. Can you confirm this or have you had completely different experiences? What useful and not too expensive alternatives are there to achieve a KFW70 house if you do not use the solar system sold as standard?

Thanks for your answers

.... I have heard multiple times that these are not very profitable in terms of investment costs, additional electricity costs, the actual yield, and the real cost savings?...

Verification methods on paper are based on standards that usually have nothing to do with actual, real-world conditions.
Example hot water:
In the verification method, the demand is specified as 12.5 x An. An is a fictitious area that has little to do with the actual heated living area.
A 130 m² house can be inhabited by 2 or by 6 people. That the actual, real energy demand for hot water is completely different seems logical! ;-)
Since the Energy Saving Ordinance 2009, a reference building has been introduced for verifications. This is "preloaded" with a solar thermal system for hot water!
The theoretical coverage ratios according to the verification method are between 45..55% based on An!
In reality, these are rarely reached because actual user and comfort behavior have been ignored in particular.

....What useful and not too expensive alternatives are there to get a KFW70 house if you do not take the solar system sold as standard? (/quote] Permissible substitute measures according to EEWG or Energy Saving Ordinance.

Best regards.

Forget the normatives if you want to define your own comfort behavior and make the most of the sun. For the energy balance "KFW70" it is quite nice. All house builders (B) solid or prefab offer you a "homeopathic" solar domestic hot water system. That is because nothing is subsidized in new buildings. But for the energy balance it is not insignificant. If you are a "calculator" you will say: no, too expensive! But calculate yourself with a 5% annual energy price increase - it could be surprisingly different. I went a different way. I invented my own heating system (utility model) and built it: works well. In short: solar thermal (66V-tubes) + heat pump + ice trench collector + 1000l buffer tank with DHW in flow principle, plus an H2O fireplace - so 3 heat sources! No deep drilling, space requirement 30m² Costs collector approx. 800...1200 € Costs heat pump (mine 2500, normal approx. 5000,-) Costs ST (2700,-€ self-installation) Costs hydraulics 1200,- tank 1500,- (2WT: DHW+solar) separate control 700,-€ (that's why I could use the "dumbest" heat pump (7kW). Advantages: in summer the ST cannot overheat, due to large tank I can switch off the heat pump from May, last year already in April. small area, no expert reports, drilling, permits, since <1.50m depth and without groundwater contact. For me it brought the energy certificate to 15kWh/m² (built 2012). 170m²