Air-water heat pump with solar thermal or photovoltaic?

Hello everyone,
after having read a lot here, I would also like to ask you a question.
We are currently renovating a house and want to achieve KfW55. Since we have heard different opinions from the craftsmen about our heating system, I would also like to get your opinion on it.

We want to remove the existing oil heating system and replace it with a heat pump (there is no gas connection).

Originally, we planned to combine the heat pump with solar thermal to support hot water preparation. Several heating contractors also advised us to do so.

However, the last heating contractor we spoke to advised against it. And I have also read some posts here in the forum stating that the combination of air-to-water heat pump and solar thermal is not sensible.

I read a lot here that a combination of air-to-water heat pump and photovoltaics is better. But why is that? In our thinking, solar thermal ensures that the air-to-water heat pump needs less electricity for hot water preparation. In addition, solar thermal is cheaper to purchase.

Here in the forum, I have also read that it would be more sensible to combine with photovoltaics because then we generate part of the electricity ourselves that the air-to-water heat pump consumes. Is the effect greater than the support from solar thermal?

We are open to all options, just want to understand this. The craftsmen could not solve the knot in our heads, so I hope for your support.

Thank you very much and best regards!

But why is that?

In short: A solar thermal system is not cost-effective. Even if it is cheaper to purchase, it does not pay back the investment. On the other hand, a photovoltaic system amortizes itself, meaning it generates more income than it costs. The fact that the electricity generated by the photovoltaic system can be used for heating and hot water production is a nice side effect, but not a decisive factor.

Thank you very much for the quick response! So it's less about the combination of air-water heat pump and photovoltaics and more about an individual consideration? A photovoltaic system is cost-effective because we continuously produce our own electricity that we can use? Whereas the use of solar thermal is limited to hot water?

I read a lot here that a combination of an air-to-water heat pump and photovoltaics is better. But why is that? In our consideration, solar thermal ensures that the air-to-water heat pump requires less electricity for hot water preparation. In addition, solar thermal is cheaper to purchase. Here in the forum, I also read that it would be more sensible to combine with photovoltaics because then we generate part of the electricity ourselves that the air-to-water heat pump consumes. Is the effect greater than the support from solar thermal?

Actually quite simple. First, please consider solar thermal and photovoltaics separately from the heating system. When does solar thermal produce hot water? In summer - at that time, the photovoltaic system can also do so (indirectly via the generated electricity). But solar thermal produces so much hot water that you could supply the whole street with it - which is not possible, and thus the solar energy disappears into nothingness. However, the photovoltaic system produces electricity that you can either use yourself (e.g., with an air conditioner - which you need in summer when the photovoltaic system produces electricity) or feed into the power grid for money. In winter, you cannot really use either variant because there is simply little sun available.

So it is less about the combination of air-water heat pump and photovoltaic but rather an individual consideration?

Exactly, of course you can also consider it complicated and combined, but it does not change the basic principle. The fact that solar thermal energy even exists is also more due to the kfw concept if you want to use gas. Otherwise, as says. Perhaps some rough figures: With a photovoltaic system costing 10k€ you can save and sell electricity worth about 1000€ per year. With a solar thermal system costing 7k€ you can save electricity for hot water of about 150€ per year.

Great, thank you very much! That helped me a lot. Now I will start diving into the topic of photovoltaics and will definitely reach out to you with one question or another.