Pumped hydroelectric storage is an obvious choice for the countries that have the geography, in effect meaning that most of the infrastructure for doing it is a

Pumped hydroelectric storage is an obvious choice for the countries that have the geography, in effect meaning that most of the infrastructure for doing it is already in place. Hydroelectric reservoirs allow storing energy more or less indefinitely. Of course, the capacity will rarely have been dimensioned for keeping 6 months of usage on hand, but combining pumped storage with over-provisioned wind energy would allow for living through months of unfavorable sun, rain or wind conditions.