Article about pumped hydro storage that does not involve dams or rivers.
I believe it would be best to cover the reservoirs with solar panels to minimize water evaporation and at the same time keep the solar panels cooler to maximize their efficiency. There are other advantages such as reducing the area used by solar panels. Since there is water accessible all around the panels, it will be simpler and easier to use some water to clean the panels.
https://wognews.net/news/2021/5/cheap-renewable-energy-storage