This is an excellent idea. However, others have long since beat you to it. Pumped-storage Hydroelectricity.

This idea would address the problem of solar energy. The problem being that the sun shines only during the day and in order to have energy at night it has to be stored from daytime, and kinetic storage of water would address this. They haven't adopted solar power yet for public energy because of not having a good storage medium, and also the high cost of solar panels. But to lessen the cost people instead use wind energy, which has lots of funding now, and has the same problem of not always creating constant energy reliably. But the storage of kinetic energy, until we invent other storage mediums, is a good idea, if it is cost effective.

Hydro storage is used. At night when use is idle, water is pumped to the top side of a reservoir, and released in the day when demand is needed, through a more or less traditional hydro station.

The current favored paradigm for solar electric is similar.In the daytime, (excess) solar electricity is fed into the grid to lighten the loads of traditional all-time plants, and at night the consumer draws their power from the plant, which is less loaded because some commerce and industry are off-line for the night.