ᐅ Air-to-water heat pump combined with solar thermal or photovoltaic systems?

Hello everyone,
after reading a lot here, I would like to ask you a question.
We are currently renovating a house and aim to achieve KfW55 standard. Since we have received different opinions from the contractors regarding our heating system, I would like to get your input as well.

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

Originally, we planned to combine the heat pump with a solar thermal system to support hot water production. Several heating installers also recommended this to us.

However, the last heating installer we spoke to advised against it. I have also read in this forum that combining an air-to-water heat pump with solar thermal is not very effective.

I have seen many posts here suggesting that combining an air-to-water heat pump with photovoltaic panels is better. But why is that? Our reasoning is that the solar thermal system reduces the electricity demand of the air-to-water heat pump for hot water production. In addition, the solar thermal system has a lower initial cost.

I have also read here that combining with photovoltaic panels is more sensible since you generate part of the electricity consumed by the air-to-water heat pump yourself. Is this effect greater than the support provided by solar thermal?

We are open to all options and just want to understand better. The contractors couldn’t clear up the confusion in our heads, so I hope for your help.

Thank you very much and best regards!