[jerry292]

Yeah true. I heard of another Bill Gates backed startup that actually stored the energy in a form of potential energy which was way more cost effective. Keep in mind though dams are super catastrophic to the environment as far as water flow which can be detrimental to moisture and animals that depend on water in certain areas

[beatgammit]

I'm sure you could do it with a closed system, e.g. pump water up a cliff, and when you need power, bring it back down. I'm guessing using dams on existing rivers is just more convenient than building a closed system from scratch since it can double dip on hydro infrastructure.