ᐅ Photovoltaic system with supplementary storage heaters

hampshire schrieb:

When it comes to a liquidity-based "either-or" question, it can certainly be calculated once.
If not: Investing in a photovoltaic system on almost every house makes sense—regardless of the heating system.

I fully agree. Additionally, photovoltaic systems are obviously worthwhile even when 100% financed externally; the "either-or" scenario rarely exists in reality because you can usually get a (additional) loan for photovoltaic systems.

@Tego12 Well, the bank usually requires collateral for the loan related to the photovoltaic system; the feed-in tariff is rarely sufficient for the bank. If all the equity or a mortgage has already been "used up," I would consider allowing the either/or option.

Aside from that: I would definitely try to replace night storage heaters with a new heating system, but:
- it’s quite likely there are no hydronic heating surfaces available.
- Which energy source:
Oil... definitely not.
Gas... not available everywhere.
Pellets... is there enough space for the storage silo?
Air-source heat pump... financial suicide if the house hasn’t been upgraded to a reasonably good insulation standard beforehand.
Ground-source heat pump... high initial investment or significant DIY effort and experience required, and with a poorly insulated house, it’s only moderately suitable.

Domski schrieb:

Air-source heat pump... financial suicide if the house is not first brought up to at least a decent insulation standard

Currently, it’s a storage heater, so 1 kWh of electricity equals 1 kWh of heat.

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

The initial investment would probably be roughly the same as the cost of installing a new chimney flue—without even including the burner, piping, and heating coils.

I don’t quite see why this should be financial suicide. It might be a bit drafty with the blown hot air, but that’s also the case with storage heaters. Of course, one should first try to minimize the heating demand, for example by insulating the top floor ceiling, installing new windows, sealing the front door, etc. But retrofitting a gas heating system in an old house would cost at least 30,000. Setting aside the air-to-water heat pump with underfloor heating. Unless you are renovating everything anyway and ripping up floors and walls, then I would go for that as well. However, that was not the topic here.

Yes, a lot of it. Then charge the ovens during the day when the sun is shining.

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

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

So we see that the months of the warmer half of the year (April to September) account for only 19% of the annual heating demand. Unfortunately, solar yield during this period is about 80% of the annual total. So exactly the opposite!

This also means that if you size your system for heating (= winter half-year from October to March), you will produce more than 20 times the summer demand during the warmer months. Twenty times!

If, for example, the annual heat demand is 20,000 kWh, then about 16,000 kWh of it will be needed during the winter half-year. For this, you would need roughly an 80 kW peak photovoltaic system, since it produces around 20% of 80,000 kWh in this period.

And now, good luck getting someone to install an 80 kW peak system…

PS: Using a heat pump with a good seasonal performance factor reduces the factor 20 by that same figure. Let’s take, for instance, a KfW-55 standard house with a 6,000 kWh annual heat demand. That would still require a 30 kW peak system. Even with a heat pump using a ground loop collector and an assumed seasonal performance factor of 5, we are talking about 6 kW peak to cover roughly 1,200 kWh of electricity consumption during the winter half-year. The remaining 4,800 kWh from the 6 kW peak system will occur in the summer half-year. Whether you need it then or not is irrelevant, of course.

Scout schrieb:

Currently, there are night storage heaters, so 1 kWh of electricity equals 1 kWh of heat.

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

The initial investment cost is probably about the same as what it would cost to build a new chimney stack—without even including the burner, piping, and heating coils.

I don’t quite understand why this is considered financial suicide. ...

I don’t think much of air-to-air heat pumps unless the outside temperature doesn’t drop below 5°C (41°F). There are plenty of reports online from owners of air-to-water heat pumps in new houses who face very high electricity costs from 0°C (32°F) downward because at that point the heating switches to direct electric resistance. You can only achieve an average true COP of 3:1 with air-to-water heat pumps.

In a passive house, such a system might be enjoyable, but in an older building? Never!