Photovoltaic system with post-storage ovens

If it is a liquidity-based "either-or" question, you can certainly calculate it once. If not: the investment in a photovoltaic system on almost every house - regardless of the heating system.

100% agreement. And additionally: photovoltaics are of course also worthwhile with 100% external financing, so the "either-or" basically never exists in reality, because you usually always get an (additional) loan for photovoltaics.

Well, the bank does want some collateral for the loan for the photovoltaic system; the feed-in tariff is enough for the bank in very few cases. If it's all equity or a mortgage is already "used up," I would allow the either/or question.

Apart from that: I would definitely try to get rid of night storage heaters and install a new heating system, but:
- almost certainly no water-bearing heating surfaces available.
- Which energy carrier:
Oil... definitely not.
Gas... not available everywhere.
Pellets..... is there space for the bunker?
Air heat pump..... financial suicide if the house is not brought to a reasonably decent insulation standard beforehand.
Geothermal heat pump..... high initial investment or a lot of personal effort and experience required and only moderately ideal for poorly insulated houses.

Air heat pump.....financial suicide if the house is not brought to at least a somewhat reasonable insulation standard beforehand

Currently it is night storage heaters, so 1 kWh of electricity = 1 kWh of heat. Air-to-air heat pump with an assumed annual performance factor of 3: 1 kWh of electricity = 3 kWh of heat. The acquisition costs should be roughly as high as the cost of a newly constructed chimney flue - without any burner, piping, and heating coils. I don’t quite understand why this should be financial suicide. It will just be a bit drafty with the blown-in hot air, but that is also the case with night storage heaters. Of course, one should first minimize the heating load, i.e. possibly insulate the top floor ceiling, install new windows, seal the front door, etc. But retrofitting a gas heating system in an old house will cost at least 30K EUR. Not to mention an air-to-water heat pump with underfloor heating. Unless you’re renovating everything anyway and tearing up floors and walls, then I would do that at the same time. But that was not the topic here.

yes. a lot of that. and then charge the ovens during the day when the sun is shining.

So a typical heating load over the months looks like this (1000 shares = annual demand)

January	170 shares
February	150 shares
March	130 shares
April	80 shares
May	40 shares
June, July and August together	40 shares
September	30 shares
October	80 shares
November	120 shares
December	160 shares

So we see that the months of the summer half-year (April to September) account for only 19% of the annual heating amount. Unfortunately, the solar yield in this period, however, is 80% of the annual amount. So exactly opposite!

That also means that if you dimension for heating (= winter half-year October to March) you will produce more than 20 times the demand in the summer half-year. The 20-fold!

If the demand is 20,000 kWh heat p.a., you will need 16,000 of it in the winter half-year. For that, you need photovoltaics with roughly 80 kW peak, since this will produce 20% of 80,000 kWh in this period.

So now someone come along with 80 kW peak...

PS: With a heat pump and a good annual performance factor, you reduce the factor 20 by the corresponding value of the annual performance factor. So let's assume at the other end a KfW-55 house with 6000 kWh demand, that would still be 30 kW peak. Even with a heat pump with trench collector and an assumed annual performance factor of 5, we're talking about 6 kW peak to obtain around 1200 kWh electrical energy in the winter half-year. The remaining 4800 kWh of the 6 kW peak then occur in the summer half-year. Whether you need them then or not is irrelevant, right.

Currently, these are night storage heaters, so 1 kWh of electricity = 1 kWh of heat.

Air-to-air heat pump with an assumed annual performance factor of 3: 1 kWh of electricity = 3 kWh of heat.

The acquisition costs should be roughly as high as what it would cost to build a new chimney flue – still without burner, piping, and heating coils.

Why this should be financial suicide is not quite clear to me. ...

I don't think much of air-to-air heat pumps, unless the outside temperature does not fall below 5°C. The internet is full of reports from air-to-water heat pump owners in new houses who have massive electricity costs from 0°C onwards, because then heating is done electrically 1:1. You only get an averaged, real COP of 3:1 with air-to-water heat pumps.

In a passive house, such a thing might be fun, but in an old building? Never!