The BIGGEST problem with clean energy

is talking about limitations of lithium ion batteries, while showing a picture of a lead acid battery, which looks to have been either grossly overcharged with a welder or something, or frozen.

Imo the main limitation of pumped hydro is the specific geology you need for it be to practical.  you don't just need space, you need a space with a large elevation drop over a comparatively short distance.  Not only that, but if you don't want to have to blast your own reservoir's (massively expensive), you need a natural body of water\valley to dam at both the upper, and lower locations.

Should take a look (if you haven't already) into liquid metal batteries, seems VERY promising.  Cheap and abundant materials needed to build them and a long lifespan.  It's major downside is it's not really portable, but that doesn't matter for grid storage.

And i have to put in the obligatory nuclear statement, if only we could get over the fearmongering about it and educate people.