Construction costs are currently skyrocketing

If the purchase price of the photovoltaic system increases, but at the same time the electricity prices, which will continue to rise over the next 25 years, I believe that even at today's prices, photovoltaic is worthwhile...

With electricity prices of 40 cents, every system should actually be able to pay off very well - even if the systems become more expensive. With a 10 kW system and conservatively 8,000 kWh production as well as 20% self-consumption, that is already over €500 in electricity savings per year. Over the 20-year lifetime of the system, you would therefore save around €20,000 (very roughly), plus the feed-in tariff or increased self-consumption through an electric car, etc.

The topic has already been discussed. The first question would be how long you get a warranty if you also use the EV battery for the household. The second very important question would be the durability of the battery. Constant charging and discharging will affect the lifespan, and then the question is whether it still pays off?

Unfortunately, I cannot answer that technically for you. From my rudimentary technical understanding, I have the following opinion:

My old phone still had about 80% battery capacity after around 1,500 full charge cycles (completely full and then discharged down to 10% remaining). VW states that their new batteries are supposed to survive around 3,000 charge cycles. As already mentioned, with our hybrid we could supply our household with electricity for about three days. So if I only used the battery for that purpose, it would fulfill its purpose for about 9,000 days. That would be about 25 years. From my point of view, that would definitely be worth it, although I am not sure if I want to keep the car that long ;-) Since we have two cars anyway, one could be used as storage and alternate driving with the other.

But financially worth it? No way. PS: Especially not at the prices currently being asked.

Does it have to be financially worthwhile to contribute to saving the climate and the Earth? What will the feed-in tariff look like in 5 years if the kWh costs 1€? Exactly because of your attitude, we are driving everything into the ground. Are schools financially worthwhile? Are hospitals? Is waste separation financially worthwhile or not pouring used oil into the forest?

This is our household consumption in the "coldest" month of the last heating season. NRW, 6.82 kWp photovoltaic system facing south, brine-water heat pump. No storage available. Note the energy generated by photovoltaics and the amount fed into the grid.

My need for photovoltaic storage remains very low.

As far as I know, for Li-ion batteries it is no longer the pure number of charging processes that matters, but full cycles. So it doesn't count (assuming 25 kWh capacity) that you charged 5 times 5 kWh, but 5 times 25 kWh as 5 charging cycles. Or in other words, 5 times 5 kWh is only one charging cycle. But I am no expert, someone please intervene if I am talking complete nonsense.

This is our household consumption in the "coldest" month of the last heating period. NRW, 6.82 kWp photovoltaic system facing south, brine-water heat pump. No storage available. Note the energy generated by photovoltaics and the amount fed into the grid.

My need for photovoltaic storage remains very low.

Clarification question: Do you heat with electricity or why do you emphasize the heating period so much? Could you also post the graphic for July for comparison?