More generation tends to be vastly cheaper than storage in the absence of a carbon tax. If carbon emissions and other externalities were fully priced in then that would favor storage.
The daily min vs max power output variation for wind is huge, but the median daily power output over large areas vs the min daily power output is far less so. Even more so when combined with solar which again has a significant minimum output.
If you look at 20% over capacity as adding 20% to the cost of wind and solar it’s still cheaper than coal. But the minimum is now 20% larger reducing the gap very significantly especially over several days.
Hydro naturally provides long term storage, so you can generally over any remaining gaps before looking to multi day battery storage. Plus your dealing with that 20% over capacity so the next day is very likely to be a net gain.
