A bad idea (one more) came back to me after a few years. It involves a hydrogenerator that falls to the bottom of the water while spinning, then is lifted by a kite, still spinning (but unfortunately in the opposite direction, which slows it down at each half cycle). We could call this a gravity hydrogenerator kite. This is a reeling kite with power reel-in and reel-out phases. Here are the two versions, which are identical. Naturally, this is for remote areas.
A gravity hydrogenerator could also be a storage method if the waters are deep enough. After gravity use, the hydrogenerator is lifted by the kite for a new potential cycle, being then fixed under the floating barge (like on the first sketch, but using a waterproof magnet instead of a rebound plate (7)), a bit like Pumped-storage hydroelectricity - Wikipedia.
Simplified recent version:
That said, storage with sandbags is far simpler, with or without kites:
See also the comment on Energy storage and the preprint Gravity storage in an aquatic environment (DOI: https://doi.org/10.13140/RG.2.2.33141.44006).