Batteries have had a lot of problems meeting capacity as a storage solution. Pumped Hydro is pretty good but highly location dependent, Gravity and compressed air I believe show a lot of promise. I don't know enough about Hydrogen or thermal storage to comment. But we are no where near actually solving the energy storage needs to use solar and wind exclusively. Unless we demonstrate real breakthroughs in production ready storage we'll always need a backup. Nuclear whether fission or fusion would have been a better route to clean energy but we basically stopped innovating there decades ago and now we are too far behind.
Gravity storage is an absolute joke. About the cheapest substance you can use is iron ore because it reduces the size and cost of the frame, and if you had everything else for free it would still cost you over $70/kWh for a box of it to store 1kWh in a 500m high tower.
Renewables with straight gas backup and no other storage are already lower carbon than any other option, and batteries and off river PHES have only just started getting cheap.
The breakthroughs we need to cover the final gap have already been made if you're paying any attention at all.
Pumped hydro is not, in fact, "highly location dependent". It needs a hill, but there are many millions of hills.
Storage does not need any "breakthroughs". It will be built out when there is renewable generating capacity to charge it from. In the meantime, NG plants fill shortfalls.
The best storage solution is to offset normal hydro generation to build up capacity to be released when you have unmet demand. That massively changes the need for storage because dams are already storing months worth of energy so shifting demand within the day is effectively free barring possibly adding some turbines.
Globally 16% of electricity is produced by traditional hydro annually that can cover the majority of the projected need for storage in a pure wind/solar grid.
Also, by the time we need significant batteries the costs will have fallen even further. If you want to eventually cover 10% of the grids daily demand from batteries using projected costs from 2030 to 2040+ it doesn’t look unreasonable.
