More storage? or more capacity?-II

I was inspired to write my previous article by two things.   The first was a tweet by Simon Holmes à Court a few months ago, showing a chart of the combined output of South Australian wind farms, which was flat, rather than fluctuating in line with the winds, because output had been curtailed by the AEMO (Australia's grid manager).    He said that it looked like the output of a baseload power plant.  It did, and it made me start to think, I wonder if having extra renewable capacity across the grid would deliver the same effect.

The second was this article in CleanTechnica.   And this chart from that article is illuminating:

The grey band shows the costs of electricity from the grid.  Obviously, without a carbon price, or factoring in the cost to the environment of carbon emissions, new generating capacity must be cheaper than the average cost of the grid now to be taken up.  The red line A shows how, without storage, renewables are much cheaper than grid parity.  As we increase capacity in renewables, the costs rise steadily, because of curtailment.  By 60% curtailment, they start to increase above grid parity. 

The blue line shows the cost of battery storage.  With zero overcapacity in generation, we need a lot of storage, to cover those rare days when there is no wind and no sun and strong demand.  As we add more renewable overcapacity, it falls from 6 times grid parity at zero overcapacity/curtailment to below grid parity, because the extra capacity reduces the need for storage.

The black line shows the total cost, i.e., represents the sum of the blue and the red lines.  And the result is counter-intuitive: as we add surplus capacity, the average cost of capacity plus storage doesn't increase—it falls.   (Note that the authors call it dynamic curtailment because it changes as supply and demand positions change.)

Their costing are lower than mine.  But the conclusions are the same—we could run a grid on 100% wind and solar, by planning for overcapacity.  We don't need nuclear or other baseload power, which is not to say that legacy nuclear and hydro plants won't be useful.  The siren voices which insist we need nuclear to reach 100% renewables are wrong.