yeah, maybe solar plus geothermal heat pump would be the most advantageous system right now. Although you can't store and there isn't much solar in December and January here.

Geothermal heat pumps "store"...

They pump heat into the ground in the summer for air conditioning and pump it back out in the winter for heating.

You don't need to be "much", you need to ideally match the TCO of other fuels (or come close, if you care more about reducing fossil fuel use and CO2, which is arguably more important than TCO. People obsess about heating costs but then run out and buy $60,000 luxury cars to do an hour+ commute each day in.)

Not all cold climates lack sun. Here at 6-10,000' in northern New Mexico, we still get lots of sun in the winter, but also very cold (overnight) temperatures. Air source heat pumps make more sense in almost every way, and will operate down to -13F/-25C.

Our 6.6kW array can provide roughly 1/3 the electricity we need to heat all of our 1875 adobe home, which is poorly insulated at best. If this was closer to passivhaus standards, I imagine it could get close to 100%.

Air source heat pumps are pretty cheap and work well to low temps now. You might still need the grid, but can net-out over the year.

Yeah, as I just mentioned adjacent to this, our 6.6kW array produces 1/3 of what we need during the winter, but 3x what we need in the summer. Last year (the first full year), we generated 93% of our electricity use over the full year. We heat solely with air source heat pumps.