Photovoltaic system air-water heat pump - profitability single-family house KFW55EE

I'm really doing well with my 51% for half of November and all of December :)
But there is always someone at home with us, so it's not that surprising.

My house has a heating load of about 9 kW at the current (~-4°) temperatures. [...] Dec around 30%. 28 kWp

I have lost track. 9 kW heating load at -4°C is quite a lot and explains a lot. Are there any more details about the (old?) building? Then it is actually within range, although I turn green with envy at 28% autonomy in December!

I still charged my car at noon in October with reduced power at the home office for higher self-consumption. But I switched that off afterwards and now charge with the full 7 kW. It didn't make sense. On the days when I produce more than the consumption of the heat pump, I turn on the washing machine or put a pizza in the oven.

I'm really doing quite well with my 51% for half of November and the whole of December :)
But someone is always home with us too, so not too surprising.

That's really decent. Do you heat up intentionally during the day? With or without battery?
Usually, someone is home here as well, but at these temperatures, I can hardly do anything against the heating load at night. At least not if we don't want to freeze...

Are there any detailed information about the (old?) building here?

I don't think so, at least not in the forum until now.
Built in '62, extension '88. Mostly 30 cm Poroton without insulation. About 260 sqm living space + 140 sqm basement. Roof has been done, windows from 2000, a bit of insulation still between screed and basement ceiling. In 2020 everything was converted to underfloor heating and heat pump. Calculated heating load approx. 13 kW at -10°. Roughly accurate after two winters of experience. If you want to know more, I suggest PM before we kill the whole thread here. ;-)

I also have the comparison to a 2016 new build with just under kfw55, 135 sqm and 22 kWp east/west system. Since the heat pump is an on-off heat pump that doesn’t really let itself be persuaded to mainly heat during the day, the house only achieves about 30% autonomy in Nov/Dec. Maybe there’s still potential if I take a look at this smart grid thing...

That's really decent. Do you deliberately heat up during the day? With or without battery?

Of course without battery ;)
Yes, I have a 1.5-degree night setback from 10 pm to 7 am. I counteract the cooling down overnight with our storage stove when it gets cold.
But it also works easily with ~150 sqm KfW55. Also a modulating heat pump. In December, I believe it was around ~330 kWh for heating and hot water, without control and ventilation (I think).

Oh yes, 23.25 kWp SSW and NNE in sunny Bavaria. I've been operational since 11/11 and today I cracked the MWh in generation.

Ouch, since I'm currently in the process of buying a photovoltaic system myself, the 14% feels like a slap in the face. Why so little? Why produce hot water instead of feeding in the electricity even if it’s only 7 or 8 cents?

I don’t know, it’s just what came out. You have to say that 4.55 kWp is not much photovoltaic power. But when it’s REALLY cold outside, the heat pump just needs the most electricity. The milder it is, the more efficient, and the colder it gets, the steeper the graph shows how much more the unit consumes. That’s just the nature of the matter, how the technology of these devices works. As limited as my understanding of it may be. And on precisely those freezing cold days, you basically get nothing from the photovoltaic system. We had summer months where consumption was at a 40% photovoltaic share. But in the summer months, the system also only draws a fraction of the electricity it does in January. And then the photovoltaic share is significantly lower, even if everything that the photovoltaic system generates flows into the air-water heat pump.

We heat the domestic water higher in summer because it is usually mixed with cold water when you shower or bathe, meaning you can use the hot water as a kind of energy storage. It’s cheaper to heat the water with the photovoltaic electricity (which I could only sell for 9 cents) than to keep the water at 40°C and then have to reheat more water in the evening and pay 25 cents per kWh for the process.

You have to look at it more positively, almost 100% of the photovoltaic yield in winter goes directly into heating ;)

In 2021, without much optimization, we had 29% self-consumption with a 9.2kWp system.