Not Carnot, it's mechanical. https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...

It's not 100%, but it's not bad.

The comment you're replying to is discussing using heat for pressure, not electrical pumps.

Ah, you're absolutely right, that was my mistake. hp48fan seems correct that it would make a minuscule difference.

Are floating solar panels a thing? My naive assumption is that (most places) land is abundant enough that you can put solar panels everywhere. Dealing with the nature-hates-you-engineering of working with water seems like a method of last resort.

You get co-benefits of reducing water evaporation and plant growth (some places just use plastic balls for this same purpose) on the water side and on the solar side you get some cooling which increases efficiency.

For existing dams the ability to share the existing connections in an area that probably isn't flat except for the water is neat.