Of course, it can be that something is added. But it will not be excessively much, because then no one can afford electricity anymore. If you consume an average to slightly below-average amount, you always know that you are not being excessively burdened. Especially electricity consumption for low-income earners is often just as high or even higher than in an average household due to old devices, poor insulation, old technology, etc. If this low-income household already spends, say, 120 EUR for electricity (5,000 kWh) and 100 EUR for heating (each as a monthly installment), then a 20 percent tax already amounts to 44 EUR per month there.
If you, as a home builder, earn rather well and use your highly efficient devices and LEDs in a two- instead of four-person household consuming 600 kWh for heating, 500 kWh for hot water, and 1,500 kWh for household electricity, you end up with an installment of 61 EUR for heating, hot water, and household electricity combined.
You talk about 20 kWh per m2 per year. The brine heat pump makes 20 kWh thermal from 4 kWh electric in the best case. For 150 sqm living space (for two?), that’s 600 kWh electricity per year. The savings costs due to the fireplace are therefore minimal.
And even if energy prices now rise by 20 percent, then you’re simply not at 61 EUR but at nearly 73 EUR including everything.
The problem with this is always that the less you consume, the less efficient savings become. That is why many passive houses also have air/water heat pumps.
If you only consume 15 kWh/m2/year in a passive house, that means 2,250 kWh thermal for a 150 sqm house, plus 900 kWh thermal hot water per person, so for 4 people 3,600 kWh thermal, resulting in nearly 6,000 kWh thermal. With a good air/water heat pump having an annual performance factor of 4 and a good brine/water heat pump having an annual performance factor of 5, this results in 1,500 or 1,200 kWh electric energy. These 300 kWh electricity savings never pay off in a passive house.
But if it really is just about model railways, fun, and what is technically feasible, then:
- Passive house with best insulation, best windows, summer shading with venetian blinds, best south orientation, etc. (of course controlled residential ventilation)
- Brine heat pump
- Photovoltaics with storage (if you take it really seriously, then three-phase)
- Huge, building-internal water storage, extremely insulated (see Timo Leukefeld)
- Plus lots and lots of solar thermal
- Fireplace with water jacket
- Exercise bike from Schwörerhaus feeding into photovoltaic storage (SchwörerTrainer)
- Something new are ice storages
- Of course also lowering the temperature a bit in midwinter and dressing thicker
- Planning through PHPP and a passive house planner
- Photovoltaics/solar thermal can of course also go on the garage or carport, if properly planned
- If you don’t already cycle year-round, then switch the car to electric (or pedelec)
- As far as I know, with a passive house it is also assessed how well it is connected in an area where local public supply is given and public transport can be used, allowing for largely no car usage
- etc....