ᐅ KfW 40 and QNG: The Role of Photovoltaics and Energy Storage

Hello dear community,

We are currently planning a new build, and one of my biggest questions is about sizing the photovoltaic system on the roof.
We want to build according to the KFW40 standard with QNG certification to receive the full subsidy.
My questions:
- Are photovoltaic panels plus storage mandatory for this?
- Are there specific requirements regarding the power output of the panels or the capacity of the storage system?

I would like to get a better understanding of the minimum requirements that need to be met in this area and what might be economically reasonable beyond that. Based on my current research, I tend to expect that I would keep the photovoltaic system to a minimum (roughly covering the base load).

I am very grateful for your opinions!

I don’t think a small balcony solar system with a mini battery is sufficient to qualify for funding.
I would plan a reasonable size considering the family, energy consumption, and roof area. There are specialists or forums for that.

All values are included in the overall analysis, so you do have some flexibility. For example, we don’t have any energy storage (but also no QNG). If something else is not performing optimally, you can compensate by adding more photovoltaic panels, for instance. So it’s not possible to make a general statement here; an energy consultant needs to enter all (!) parameters of your house into their calculations and see how things develop.

Schnubbihh schrieb:

Based on my current research, I tend to think that I would limit the photovoltaic system to a minimum (~ base load).

Keep in mind that costs do not scale linearly with size. A very small system will have correspondingly higher costs per kWp and will take longer to pay off. I know that with a 4% interest rate you want to save, but you might be cutting costs in the wrong place. Another question is which base load you mean. In summer, most would get by well with a larger balcony solar system, but in winter the heat pump runs and the yield per module is at its lowest.

Regarding what @WilderSueden said about winter yields, it is also worth considering optimizing the orientation and installation of a photovoltaic system for winter to achieve the highest possible self-sufficiency during that season. Of course, this depends on the house orientation, roof pitches, and so on.

It’s actually the other way around... the small photovoltaic system is more worthwhile because you need to borrow less capital at 4% interest and feed much less energy into the grid for a ridiculously low 10 cents/kWh.

It’s like at the supermarket. Sure, if you buy 20kg (44 pounds) of beef tenderloin, you get a better price. But if you only need 2kg (4.4 pounds), that doesn’t help at all. Because you either have to throw away or give away the rest...