One of my favorite theoretical energy storage methods is manmade island dams. The idea is to build a circular dyke in the ocean, and then use the encapsulated sea as pumped hydro storage. It would be paired with a windfarm, floating solar, and whatever other power generating methods would easily co-locate.
Unsurprisingly, the Dutch seem to have put a lot of thought into it: https://deingenieur.nl/artikelen/lievense-de-man-van-het-ops...
It sounds more like tidal energy: https://en.wikipedia.org/wiki/Tidal_power
Seems like storage potential would suffer from a lack of height and long dam length.