However can we figure out how to get the same result with twice the energy and the ability to store it indefinitely at 40% efficiency. Especially given that the costs of all these technologies are going down at two digit percent per year.
Coal plants in particular are dramatically unsuited for the rapid changes in output to respond to changing demands for power.
Gas plants on the other hand are. And gas plants are cheap!
Overbuilding renewables with combinations of solar, geothermal (where available) and wind gives pretty good availability on it's own and with gas plants as a backup it gives you plenty of grid stability.
Edit: A link you posted elsewhere (thanks!) points out how well this works:
> If other sources meet demand 5% of the time, electricity costs fall and the energy capacity cost target rises to $150/kWh.
Battery storage is already well below this $150/kWh price.
https://reneweconomy.com.au/solar-wind-and-battery-storage-n... gives "Utility-scale battery (four-hour storage duration) $145-167 per MWh" and references BloombergNEF
Better link for Bloomberg reference: https://www.energy-storage.news/behind-the-numbers-the-rapid...
As an example, for most of Aus, 5 hrs storage will only work for <80% renewables [0]. It's only practical on smaller scales which doesn't mean it isn't useful now but just means that the ~$100/MWh systems will not be practical everywhere, especially when renewables become more ubiquitous.
[0] https://reneweconomy.com.au/much-storage-back-high-renewable...
Edit: I had a deeper look at the NREL paper and most of their costs seem to be in the $100s/kWh rather than MWh. E.g ~$300/ kWh for 6 hour systems on Fig. 6.