[ralphhughes]

If you're talking about seasonal storage I would have thought the natural fit would be power-to-gas or power-to-liquid syn-fuels? Absorb all those extra kWh from the sun in summer, store it for 4-8 months and then burn it during the cold, dark winter? Energy storage density higher than gravitational potential energy and less energy leakage than thermal-mass storage due to non-perfect thermal insulators etc?

[defrost]

FWiW I talk about storage liquid gas hydrogen byproducts a lot - I'm in Western Australia, we're putting up small country sized PV farms to power billion tonne per annum mining operations and with no actual "mountains" (although many mesa's) we look to ammonia | methanol and "infinity trains" rather than to hydro dams or gravity stacks, etc.

The GP comment mentioning "Scandanavia" seemed like a good excuse to spitball ideas with mountains - but as outlined they're no easy fix either - you can't just put a big dam anywhere without potential dangers and cold climates have issues with freezing, expansion, contraction, etc.

Where I'm at we're more concerned with overnight power for massive 24/7 continuous operation than with longer nights and less light in winter .. that's simply not a thing here.