Turning water into a high density slurry ?

Not sure how the powder get to the top of the hill as pumping it back up must obey the First Law.

BBC News

The 'secret sauce' helping to store renewable energy in D...

A 100-year-old idea for hydro electricity generation is being refashioned to help the energy crisis.

Edited 6 hours ago6 hr by studiot

It’s offered as energy storage, so it’s pumped storage with a higher density than water. No 1st law issues.

not sure what advantage us gained by increasing the density of the water to a slurry.
Sure, you can use a lower height for storage, but the pumping load increases proportionately with the increase in density.
I haven't done, or seen, calculations so I'm not sure of any benefits other than convenience of using existing geological formations.