Comment by pfdietz

The amount of long term storage (and the duration) depends on the balance between wind and PV.

If wind and PV have similar levelized cost of energy (LCoE), then the solution will use the lack of correlation between the two to avoid much storage. In this case, long term storage is over period of the variability of wind, which might be weeks.

But if PV is significantly cheaper than wind -- and this is where trends are going -- then long term storage becomes more for seasonal leveling, at least at high latitudes.

There's still a large place for short term storage, and economics is still strongly affected by the cost of that storage. So it's great news batteries have become so cheap to produce.