A few hours in nowhere near enough.

In Finland solar produces no power three months of the year. The months before and after that are marginal. To add joy, there are windstill periods of days, sometimes more than a week, in winter.

To add insult to injury, there isn't enough transmission capability to import all the renewable energy we would need to solely rely on renewables. There isn't enough hydro either so rely on that to take up the slack.

So, grid storage really is the hidden cost of both solar and wind, and multiple weeks of total grid output storage is needed for energy security if relying on renewables.

To reinterate, I really want to learn more about real long term storage. Anybody know where I can find solid info on that?