Pumped hydro doesn't require mountains, you can also dig an underground reservoir.

Pumped hydro requires a large volume of fluid and a height difference.

Valleys are useful as they provide a large volume that can be capped with relative ease.

An underground reservoir requires a large volume to be excavated (or a pre existing cave system) and a deeper chamber again for the turbines to powered by the fall .. to yet another deeper underground reservoir.

I'm not saying this is impossible, I stating that as an engineering venture (actual civil engineering not software "engineering") there are some real challenges and greater ones than using existing topography.

You're hand waving a lot away with your comment.

To be honest I'm pretty doubtful the economics of excavating a reservoir are going to work. It needs to be very big and very deep, which is going to be very expensive unless you're planning to go all Edward Teller (don't go all Edward Teller).

You're mixing it up with hydroelectric dams.

> That geography is very very common.

Could you provide some more info for this? My understanding was a lot of the sites that could do this, have done. If that's not the case it'd be good to see what the real picture is.

There's no point if you don't have energy to store. Only 1% of potential sites need to be developed

https://re100.eng.anu.edu.au/global/

Probably won't happen because batteries will be even cheaper by the time much of it is developed.

That link is what makes me concerned when talking on these topics. Far too much certainty and trust seem to be derived from and placed in such studies.

In this case, from the study:

> None of the PHES sites discussed in this study have been the subject of geological, hydrological, environmental, heritage and other studies, and it is not known whether any particular site would be suitable. The commercial feasibility of developing these sites is unknown.

> makes me concerned

There it is. Always so concerned" about whatever imaginary downside alternatives have, but completely credulous about nuclear which has failed over and over again.

You're claiming without any evidence whatsoever that at least 99% of geographically appropriate sites are unusable.

> Always so concerned" about whatever imaginary downside alternatives have

It's not a downside. It's a problem with the study.

> completely credulous about nuclear which has failed over and over again

Can you cite where I've done this?

> You're claiming without any evidence whatsoever that at least 99% of geographically appropriate sites are unusable.

And where I've done this?

yes and no. we've put dams in the obvious places, but we're mostly using them as generation rather than storage. switching them to be run as batteries will massively expand the amount of grid storage.

Pumped hydro is storage by definition, is it not?

A dam in a river can either be used as generation (if you always run it) or as storage if you vary the output. Most pumped hydro is already storage, but most hydro currently isn't pumped.

And it’s worth pointing out here that conventional hydro is being optimised in some places for a world with a lot of wind and solar in the grid.

In a nutshell, you put in more generators to maximise your peak generation capacity, and operate them only when required.

Ah, understood. But this isn't to do with renewable power storage at this point, just using artificial lakes as separate peak power storage?