Comment by Tuna-Fish

> Do you have any links to those studies? Because the ones I've seen indicate the exact opposite. You only need 2-3 days of storage or so at most.

It depends very much on where you live. Famously, California can get to 100% renewable production with 3 hours of storage, because production is very stable, load peaks match production well and there is sufficient natural hydropower resources available.

In contrast, Finland would need about 3 months worth to hit 100% renewable. Because worst load peaks happen when production from both wind and solar can be zero for a prolonged period, and natural hydro output is limited at the same time. 3 months is absolutely not actually feasible, so there will always need to be some baseload from nuclear or fossil sources.

But 2-3 days of storage is still quite a lot. The recently started OL3 power plant had a total construction cost of ~11B€, making it one of the most expensive construction projects ever. It has a nameplate capacity of 1600MWe, assuming 95% capacity factor (it goes up when it's cold and down when it's warm), if you spent it's construction cost building grid-scale batteries, assuming the lowest cost of a completed battery project anywhere in the world, you'd get something like 27 hours of storage. So even if the primary production was free, if you need more than that, you'd be better off building the world's largest and most expensive nuclear power plant instead of batteries + renewables.