Solar thermal or photovoltaic with a gas heating system

Hello everyone,

the construction of our single-family house has begun and it is currently planned to combine the gas heating with a solar thermal system (approx. 5 sqm collectors only for domestic hot water without heating support).
The solar thermal system is apparently mandatory as a renewable share and not my voluntary decision although a central controlled residential ventilation system with heat recovery will also be installed.

Now I have asked the construction company if I can have photovoltaics instead of solar thermal. Answer: yes, but then the hot water storage tank (300L) must be heated with electricity from the photovoltaic system via an electric heating element using a priority control.

Now I am wondering what I would gain from this exchange. For the solar thermal system including the hot water storage, I would receive a refund of about 3,700 euros. Then there would be the costs for a 5 kWp system (I think somewhere between 7,000 and 9,000 euros) and the costs for an alternative hot water storage tank.

Since solar thermal is uneconomical, I actually wanted to avoid it. I need your help to make a correct decision. Therefore, the following questions:

1. Can the priority control simply be removed technically later after moving in?
2. Would that be legal, in a grey area, or already illegal?
3. If the priority control must remain (see question 2), does the exchange of solar thermal for photovoltaics even make economic sense?

3. If the priority must remain (see question 2), does swapping solar thermal for photovoltaics make economic sense at all?

Photovoltaics always make sense. And be glad if the hot water tank is simply heated with cheap (own) electricity instead of buying it expensively. If photovoltaics, then preferably large. 10 kWp should be around €11-12k. With that, you will get a decent amount credited to your account every month.

1. Is it technically possible to simply remove the priority again after moving in? 2. Would that be legal, in a gray area, or already illegal?

Anything that can be turned on can also be turned off...

Photovoltaics always make sense. And be glad when the hot water tank is simply heated with the cheap (own) electricity instead of buying it expensively.
If photovoltaics, then preferably large. 10kWp should cost around €11-12k. With that, you get a decent amount credited to your account every month.


Anything you can turn on, you can also turn off...

I think 10 kWp will be quite difficult with our hip roof and the house dimensions of 11.30x8.30 m. Or am I mistaken? Making a good yield more difficult is that the neighboring house on the east side is only 6 m away and three stories high, so it will probably cast a shadow on the east side of the roof (see drawing). Or are my concerns unfounded?

One must have it calculated sometime.

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