[lazide]

The challenge is with the remainder, which is actually a much bigger problem.

Thermal heating for example, even using heat pumps, will require more than 5x the existing electrical grids peak energy capacity - just on its own. I’ve done the math several times, it’s staggering.

And it will do it during typically minimal insolation times.

Germany has made good progress, don’t get me wrong, but it highlights just how hard of a problem this really is.

[RGamma]

W.r.t. heating did you also consider the effects of increasing local production as well as transferability and variability of load (e.g. requiring larger heat pumps and other "steuerbare Verbrauchseinrichtungen" to be "adjustable", which Germany does)

[lazide]

It’s a straightforward thermodynamic equation - x fuel burnt (and useful heat from that) vs maximum theoretical efficiency for heat pumps for equivalent heat.

The reality is likely worse for a number of reasons, but even if way better it doesn’t get around that you’d need many multiples of the entire electrical grids peak capacity to come close. And that is assuming there is zero other load on the grid, which isn’t going to happen.

If everyone completely redid all their structures and all their use of heating, and installed all the best heat pumps, AND doubled grid capacity, maaaaybe. But we’re talking massive amounts of Capital. Capital that used to be cheap, but isn’t anymore.

Far more Capital than likely has been spent so far on renewables too, but it’s hard to calculate it because of the sheer distortion that it would cause trying to do something of this scale.

It might be legitimately cheaper to buy Northern Africa and move all Germans there instead (in new construction). That seems pretty unlikely for sócio-political reasons though.

[quickthrowman]

You don’t need to consider any of that, it’s simple arithmetic. Take the amount natural gas burned for heat, convert to kWh (100,000 BTUs or 2.83 cubic feet is 29.3kW), and divide by 3 to approximate the heat pump size you’d need to replace the boiler or furnace.

A 3 million BTU boiler will consume 85 cubic meters of gas in one hour running at max, or about 300kWh of electricity for the same amount of heat from a heat pump over one hour, assuming a COP of 3. It’s 360 amps of current at 480V three-phase (300kW/480/1.732 = 360.8A), or ~400 horsepower. Divide the above units by 30 for a large 100,000 BTU furnace in a home.

Where I live, 85 cubic meters of gas costs about $9 and 300kWh of electricity costs about $45. Natural gas still wins in cost even if your NG heater is only 25% efficient. Even though the heat pump is 3 times more efficient, it costs 5x as much to run vs an HE condensing boiler (at maximum, variable speed compressors will make the COP of the heat pump in practice better than 3 but it will still cost more to operate.)

Anyways, the above is why virtually every building in Minnesota (and similar climates) uses natural gas for heat: cost.

[RGamma]

I realize this doesn't really say anything about grid-level/national requirements, but at least in my situation 100% electric heating seems feasible.

Last year we used 7000kWh of natural gas (at 0.14€/kWh). Assuming 90% efficiency of our condensing boiler that's 6300kWh for heating water and air. We heat from ~November to ~February and use hot water all year round (though the cold water will vary by ~6 degC).

We have PV: 7.5kWp, 6kWh storage, electricity 2024: 6.3MWh generation, 2.1MWh usage at 80% autarky (100% from April to August, 90% March, Oktober, avg 50% November to February). 435kWh drawn from grid at 0.36€/kWh, 4.2MWh sent to grid at 0.075€/kWh

We can replace the boiler with a hot water heatpump that would be ~fully powered by our PV from ~March to ~Oktober. And for space heating we can use an air-air heatpump(s). We also have decent insulation and decentral ventilation with enthalpy exchanger.

Now the mystery is how much gas we waste in the non-heating period for hot water, and how little space heating we can get by with (small 60m^2 flat, kitchen, bedroom don't need heating) as well as the actual COP. My guess would be 3-4kWh of heating would be quite adequate plus whatever hot water will use.

We're currently looking for offers for getting rid of gas (and maybe central heating) completely. Wonder what calculation they'll come up with. Note that it doesn't need to be profitable at current prices as gas prices will rise, renewables will get cheaper, and you can still get 30-55% of subsidy.

I also consider getting rid of fossils completely a worthy struggle in itself as it reduces geopolitical dependence and increases resilience. But yeah, it's a multigenerational problem at this scale and scope, esp. considering all the other areas of overuse that need fixing.

[quickthrowman]

In your situation, switching over to heat pumps makes sense, given that you’re sending 66% of the power you generate to the grid. These are the sorts of installations I would expect to go forward since you aren’t spending more money to operate a heat pump.

[lazide]

Note that right now society is subsidizing that - at some point the opposite flow needs to happen (from a basic arithmetic perspective), and that subsidy needs to be a tax or the math doesn’t work society wide.

California had to start killing grid infeed and solar subsidies for instance as it was starting to bankrupt utilities.