Solar Thermal vs. Photovoltaics

As of today, we have produced 368kWh in December so far despite numerous dull foggy days and not even a south-facing roof.

I would be interested to know to what extent this covers the monthly electricity costs? How many kWh do you approximately consume in one month?

Don't know if you can offset that like this. You usually also turn on the power on sunny days in winter. Sure, it can be cold then, but at least the heating runs. Otherwise, you need more electricity when it's dark and there's no sun, and photovoltaic usually doesn't generate much yield then...

Isn't it also the case that the heating system with a solar-heated intermediate storage tank is harder to control?

I am specifically concerned about the winter period, like the mentioned December, for example. I am also considering building with photovoltaic and always hear that it is not worthwhile, but I have never seen exact figures. And I am well aware that it varies from family to family and house to house....

Currently, we have practically no feed-in (0-1kWh per day), so we use the electricity completely ourselves through the battery. Our current electricity consumption is not really meaningful, as we only moved in 3 months ago and a lot is still in disarray, especially the heat pump running with provisional basic settings. December consumption is currently at 860kWh. To evaluate the "worth," you have to look at the whole year. The fluctuations due to the weather alone make weekly or monthly considerations quite pointless. In summer, we also had weeks with >1000kWh yield. Looking into December, the difference between the best and worst daily value (26 to 4.5) was only 1 calendar day.

I am specifically concerned about the winter period, for example the December mentioned.
I am also considering building with photovoltaic and always hear that it is not worth it, but I have never seen exact figures. And I am well aware that it varies from family to family and house to house....

Photovoltaics are considered something that pays off in about 10 years depending on costs, orientation, and electricity consumption. I think you can run the heat pump relatively little on it. Sure, there are sunny cold days, but they are not very common here, and especially in December you simply have quite short days with a low sun angle. If you have a mountain (which is rather rare in NRW) or a neighbor whose huge house shadows the photovoltaic system, not much electricity is generated.