Alternatives to gas, how are they calculated?

20 years is too long. Considering 10 still makes sense, beyond that you might unfortunately already be dealing with hardware failure.

I feel differently because I am assuming a 20-year lifespan of the heat generator.

But honestly, the forecast of the price development is a pure gamble. Nothing more, nothing less.

How is it actually if we install a gas heating system and then put photovoltaics on the roof for household electricity? Can you do it like that or is it not possible and you would have to take solar thermal? So from the point of view of the Energy Saving Ordinance...

How is it actually if we install a gas heating system and then put photovoltaic panels on the roof for household electricity? Can you do it that way or is that not possible and you have to use solar thermal energy? So from the perspective of the energy saving regulation...

If you heat with gas, you have to install solar thermal energy as well. It requires a certain percentage from renewable energies.

That is not entirely correct. The required renewable shares could also be covered via PVI if one were to opt, for example, for a gas boiler without hot water, and hot water through electricity/instantaneous water heater. But it will not be economical. PVI is much too expensive compared to solar thermal energy. I think you pay a 200% surcharge.

OK, so solar thermal with the gas heating after all... It’s a bit unfortunate, since with the electricity from the photovoltaic system one would be more flexible. That way, in a few years one could also charge a possible electric vehicle right away...

Or we start with gas and thermal and already lay the cables for photovoltaic on the roof!?