[8bitsrule]

>there is a lot of R&D into large-scale energy storage, there aren't really any great solutions yet

Re#1: Storing water in a reservoir behind a set of generators is a pretty good solution.

R&D isn't needed. Energy storage is not rocket science or necessarily expensive. You just use excess energy to lift something high ... pump it or railroad it uphill, or stack it. Reverse to power generators. Of course that's just a boring, cheap, low-tech, well-proven solution.

Re#2: Of course if you try rewewables in the wrong place, you get unsatisfying results. With a big enough reservoir,'days or weeks' isn't hard ... and so you don't need backup plants. Even then, while costs of backup plant fuels are high. renewable fuel costs are nearly zero. At the right sites, the average costs are at least competitive.

[hn_throwaway_99]

FWIW, the proposed costs for doing what you recommend with Hoover Dam is $3 billion:

https://www.nytimes.com/interactive/2018/07/24/business/ener...

Couple this with water shortages exacerbated by global warming and hydrostatic storage is by no means a panacea.