On 08/02/2021 10:41, Andy Burns wrote:
S wrote:

I expect they say its because of PE =Â* m.g.h
where PE is Potential energy = massÂ* x value of gravity x hieght.
So by increasing the mass by 2.5x, you then get 2.5 x the PE.

but as well as getting 2.5x out, you have to put 2.5x in, plus you have
to deal with losses from pumping a more viscous fluid.

It's proposed as a battery; no batteries are 100% efficient.
Dinorwig is similar (albeit using water) and has been in use for many years.