the potential energy of water stored at elevation is one of those genius, elegant solutions that clever communities have been using for hundreds of years to my knowledge, but probably longer. of course, rather than using photovoltaics, those people have been using wind driven pumps to effectively store water at elevation so they can release it at pressure for irrigation, etc. i saw setups like that all over the navajo reservation when i worked out there. they pump water from the aquifer and keep it in a gravity tank on a mesa. at just 6' of relative elevation, one can totally meet the flow requirements of drip irrigation. but at like 100 feet, the pressure is incredible and can hit 40PSI.

water is kinda wild, because it doesn't compress. the pressure just builds with depth and the "shock" or "hammer effect" can be captured. if you want to see some crazy low tech shit to move water, check out ram pumps. you can make a little one with shit from a hardware store, but seeing a serious one in action is fucking crazy.

i mostly think about moving water around when it comes to energy costs, because i'm an ag guy and delivering the right amount of water to the right place at the right time (often when weather patterns are not doing so) is the name of the game. for a long time, affluent growers have relied on gas and diesel pumps because fuel was cheap and there was no downside! back in the day, was only the tightwads (me) and the lazy (me) who would start trying to find site specific solutions using topography/gravity and look into picohydroelectric systems to trickle charge batteries and shit. having a access to a janky little stream that is flowing opens up a lot of possibilities for capturing energy.

but yeah, this system is basically capturing the periodic availability of solar energy (or wind energy is totally possible to run a pump) and storing it as gravitational potential energy (from elevating water) so it can be released on demand. honestly, the earthworks necessary to initially build out something like this is one of the few uses of fossil fuel energy i think is justifiable.