I am sitting at an altitude of about 250m in NRW, so probably a somewhat different climate location. A few more square meters, not a bungalow, but with a basement, different construction method, but also a ventilation system. Construction method Energy Saving Ordinance 2009 KfW70. In the last 365 days, I have had approximately costs of €300 for heating and hot water (it is also a mild winter here). However, it is with a brine heat pump, gas would probably be a bit more expensive, but another system for heating/hot water support would not be worthwhile, even if I achieved 30% savings (which hot water support doesn't anyway, and heating support hardly does, because you heat the most when it is cold and dark), then that would be €100 per year. The costs would not be "recouped".
However, some users here, as far as I can assess, have at least a similar heating system, even if not necessarily a bungalow of that size. But they can certainly briefly post something about the costs. I also remember some threads from the past weeks in which some people mentioned their consumption and the share of solar support.