In practice you only need to store about a day's worth of electricity, a few hours really. Solar panels are so stupidly cheap now that you can solve seasonal variations in production by just spamming solar panels. You deploy enough panels to meet your demand on a cloudy day in winter. Then the rest of the year you have dirt cheap abundant electricity. Maybe shut down some of your most energy-intensive industries on the cloudiest winter days if you must. Give everyone at the steel mill a week off and instead ask them to work longer hours in the summer.

And what about people living in extreme latitudes? We can use excess solar power during the summer to capture atmospheric CO2, use that to make synthetic liquid fuels, and the handful of folks living north of the arctic circle can just keep burning carbon-neutral diesel fuel forever. You could use small fission plants for these remote locations, but there's unlikely to ever be enough demand just in the high latitudes to sustain an entire nuclear supply chain. Synthetic carbon-neutral liquid fuels would have many applications, so a supply chain could be developed.