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!

Malte1910 schrieb:

But why is that?

In short: a solar thermal system is not cost-effective. Even though it has a lower initial cost, it does not pay back the investment. On the other hand, a photovoltaic system does pay off, meaning it generates more value than it costs.
Using the electricity produced by the photovoltaic system for heating and hot water is a nice side benefit, but not a decisive factor.

Thank you for the quick response! So, the focus is less on the combination of an air-to-water heat pump and photovoltaic system, and more on looking at each individually? A photovoltaic system pays off because we continuously generate our own electricity that we can use ourselves? Whereas the use of solar thermal is limited to hot water?

Malte1910 schrieb:

I often read that combining an air-to-water heat pump with photovoltaic panels is better. But why is that? In our considerations, solar thermal systems reduce the electricity demand of the air-to-water heat pump for domestic hot water production. Also, solar thermal systems are cheaper to install.

Here in the forum, I’ve also read that combining with photovoltaic is more sensible because then you generate part of the electricity yourself that the air-to-water heat pump consumes. Is that effect greater than the support provided by solar thermal systems?

It’s actually quite simple. First, please consider solar thermal and photovoltaic systems separately from the heating system.
When does solar thermal produce hot water? In summer – the same period when photovoltaic systems generate electricity (which can be used indirectly). But solar thermal produces so much hot water that it could supply an entire street – which isn’t possible, meaning that solar energy goes to waste.
Photovoltaic systems, however, generate electricity that you can either use yourself (for example, to power air conditioning, which you need in summer when the photovoltaic system produces electricity) or feed back into the grid for compensation.

In winter, neither option is very effective because there is simply less sunlight.

Malte1910 schrieb:

So, is this more about looking at the air-to-water heat pump and photovoltaics separately rather than in combination?

Exactly, you can of course analyze it in a complex and combined way, but that doesn’t change the basic principle.
The existence of solar thermal systems is largely due to the KfW concept if you want to use gas.

Otherwise, as @nordanney says.
Maybe some rough figures: with a photovoltaic system costing around 10,000€ you can save and sell electricity worth about 1,000€ per year. With a solar thermal system costing around 7,000€, you can save around 150€ per year on electricity for hot water.

Great, thank you very much! That was very helpful. I will now start looking into the topic of photovoltaic systems and will probably reach out to you with one question or another.