Ba-Wü photovoltaic requirement for old buildings - renewing roof tiles

Good insulation is better everywhere than no insulation. But I recently read somewhere that there are [Es so Truhen Split-Klimas], which are installed exactly in the same position as the old night storage heaters, and so rows of houses have been at least somewhat modernized. So the split air conditioners are definitely better than night storage heaters.

When we bought the house, there was no talk yet of a photovoltaic obligation. And anyone who has bought a house in the Stuttgart metropolitan area in recent years knows what price level we are talking about here.

You contradict yourself a bit. The photovoltaic obligation has been decided for almost 4 years now and something like that doesn't just appear out of nowhere in a democracy. So either you didn't buy in recent years or you weren't paying attention. And if you bought before the photovoltaic obligation, your chance of additional financing back then would have been less than 1%.

I don't have any specific experience, but I quickly googled a bit. With night storage heaters, only about 30-40% of the electrical energy can apparently be converted into heat energy. With electric direct heaters (which include infrared and electric surface heaters), it's probably almost 100%.

I also quickly googled and found an article that at least claims the low efficiency of night storage heaters. Physically, that is not understandable to me. Heat from electricity is always virtually 100%, but with the night storage heater, it just doesn't come at the time when you need it. What actually has 30-40% efficiency is electricity generation from fossil fuels. But all electric heaters are affected by that.

The lower efficiency of storage heaters is due to their design. They are highly insulated, so the actual heat storage is inside and gets several hundred degrees hot. The transfer of heat through convection is strictly speaking a loss of heat; the heat is actually supposed to be distributed by a fan. The fan consumes additional electricity. So, in principle, it is a storage heater with an integrated fan heater. Whether this only accounts for 30-40% efficiency I don't know, but it is definitely less efficient than IR panels -> direct radiant heat or even air/air heat pump (climate split).

They are highly insulated, so the actual heat storage is inside and gets several hundred degrees hot.

Although I still somehow don’t quite understand what’s happening there. At first, it sounds to me as if you consume significantly more energy to heat something up to such a high temperature. But the energy shouldn’t just be "gone." A few comments also suggest that they always emit heat, even if you don’t want that, but when I think about more modern heating concepts – they aren’t designed to only heat during the day anymore (but rather to maintain a constant temperature) – so then that would almost be irrelevant again?

No, the high heat is not the problem, since you also want it warm. But if you want to heat effectively with it, then you have to use the blower and that consumes additional electricity. As I said, I can't imagine it consuming about 50% extra, but that's at least the explanation for why IR panels can be more efficient. And yes, the inertia is rather a problem, so at times like now when you have -2 at night but +10 degrees during the day, you have to decide at night whether to charge the storage for the next day or not. The operation used to be crazy too. You had one controller for heating up, that is how hot the storage should be, and then a thermostat that controls the blower. We didn’t understand that back then and nobody explained it to us, so we just had the blower running all the time (because the thermostat was set to 21°C, but the heat wasn’t charged. So cold air came out. Or vice versa. The heating electricity bill was almost going bankrupt. Unfortunately, I was still an 11-year-old kid back then and my interest in heating technology was really limited.

Such a blower needs almost nothing and I would be surprised if it draws more than 10 watts. Even if it is double that, compared to the heating function that is nothing. In the [Nachtspeicher-Wohnung] system, a [Nachtspeicherofen] also has about 100% efficiency.