Not 3 month period, but looking at e.g. capacity factor over 5 day period can be under 3% and even 10 day period can be under 5%. Capacity factor for whole year is around 30% (22TWh produced with 9433MW in 2025, rounded it up since some capacity came online during 2025). That's a lot of extra power or storage.

We’re optimizing for cost here, nothing else matters. You can always turn off a wind turbine.

If you’re proposing seasonal storage as a viable option then cutting total storage needs by 90% (to handle a 10 day lull vs 90 day gap) is inherently cheaper.

Hell traditional hydro is well suited for such situations as annual output and storage is limited but nontrivial. Doubling output for 10 days isn’t nearly as problematic as trying to cover a 90 day shortfall.