ᐅ Solar System for Water Heating and Other Measures for KFW70 Standard

Hello everyone,

I have a question about solar water heating systems. I have heard several times that they are not very cost-effective when considering the initial investment, 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 affordable alternatives are there to achieve a KfW 70 house standard if you do not want to use the solar system usually offered as standard?

Thanks for your answers

Projekt_2014 schrieb:
.... I have heard several times that these are not very cost-effective considering investment costs, additional electricity costs, actual yield, and real cost savings?...

Verification methods on paper are based on standards that usually do not reflect actual, real-life conditions.
Example: Domestic hot water:
In the verification method, the demand is calculated as 12.5 x An. An is a hypothetical area that has little to do with the actual heated living area.
A 130 m² (1400 sq ft) house can be occupied by 2 or 6 people. It seems obvious that the actual, real energy demand for domestic hot water varies greatly! ;-)
Since the Energy Saving Ordinance 2009, the reference building has been used for verifications. This is inherently "loaded" with a solar thermal system for domestic hot water!
Theoretical coverage rates according to the verification method are 45–55% based on An!
These are rarely achieved in reality because actual user behavior and comfort preferences are largely ignored.

Projekt_2014 schrieb:
....What useful and affordable alternatives are there to achieve a KFW70 house if you do not want to use the solar system offered as standard?

Authorized alternative measures according to the Renewable Energy Sources Act (EEWG) or Energy Saving Ordinance.

Best regards. [/]

Forget about the standards when defining your own comfort behavior and trying to make the most of the sun. For the energy balance "KFW70," it’s quite nice.
All house builders (B), whether solid or prefabricated, offer you a "homeopathic" solar domestic hot water system. This is because there are no subsidies for new builds. But for the energy balance, it is definitely not insignificant. If you are a "calculator," you will say: no, too expensive!
However, calculate yourself assuming a 5% annual increase in energy prices – it might turn out surprisingly different.
I took a different approach. I invented my own heating system (utility model) and built it: works well. In short: solar thermal (66 vacuum tubes) + heat pump + ice ground collector + 1000-liter (264-gallon) buffer storage with domestic hot water in flow-through mode, plus an H2O chimney – so 3 heat sources!
No deep drilling, space requirement 30m² (320 sq ft)
Cost of collectors about €800...1200
Cost of heat pump (mine €2500, normally around 5000)
Cost of solar thermal system €2700 (self-installation)
Cost of hydraulics €1200, storage tank €1500 (2 heat sources: domestic hot water + solar)
Separate control system €700 (which is why I could use the “dumbest” heat pump (7kW))
Advantages: In summer, the solar thermal cannot overheat; with a large storage tank, I can switch off the heat pump from May on, last year even in April.
Small area, no reports, drilling, or permits required, as depth is less than 1.5m (5 feet) and no contact with groundwater.
For me, the energy performance certificate reached 15 kWh/m² (built in 2012), 170m² (1830 sq ft).