You always combine solar power with wind power, that already solves more than 90% of the storage problem. In places like Europe the darker winter is usually quite windy.
For example, last Sunday Germany covered more than 100% of its own power load with renewables even though winter is approaching. Only a small part of that was solar power, most electricity was generated by wind turbines: https://www.energy-charts.info/charts/power/chart.htm?l=en&c...