Photovoltaic system with post-storage ovens

Phew.... night storage heaters.

Basically: Photovoltaics always pay off if you generate a reasonably direct self-consumption. A storage system currently (commercially) does not pay off in most cases.

For night storage, the calculation might look a bit different, but that depends specifically on the lifetime of the storage, your nighttime electricity equity, and the size of the photovoltaics. Then there is the fact that your photovoltaics, in order to generate a reasonably large amount of electricity for the night, must be significantly larger than 10kW. This requires comparatively expensive feed-in management, which reduces your margin again.

Example: With my 15kW photovoltaic system, I generated a gross yield of almost 8kWh today, and the day was relatively sunny. In my (KFW 55-Haus with approx. 170sqm living space), I had a heating demand of 18kWh from 0:00 until about 20:30. That’s just for heating, measured with a non-calibrated heat meter on the heating circuit. Approximate outside temperature between 10°C during the day and 2°C at night. So even here it doesn’t pay off. The only sensible option for using solar power for heating is a heat pump that fills a heating buffer with an efficiency of 3 or more during the day when there is enough sun.

Putting all computational tricks aside, I have serious concerns that the usage profile of a storage system is not designed for the load profile of night storage heaters and that the lifetime of the storage will suffer massively.

When does the sun shine?
When do you need the heating?
Find the mistake.

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.