Excuse me if the question is poorly worded or there already is a similar question, I searched but as a physics layman I do not know the proper terminology.
I was watching a Nova story just now and they mentioned that the major problem about renewable energy (solar and wind) is that there is no place to store the energy. Ie on a sunny day what do you do with the extra power generated to compensate for a cloudy day.
They mentioned how batteries are used but this is not an ideal solution for various reasons. I thought in my head could the extra power that is generated be used to pump water to a higher elevation and stored. Once power is needed again the water can be released to power water turbines to create hydro-electric power. (this is what I meant by water differential, if there is a proper term for this please feel free to correct my question.)
Now obviously this is not some brilliant idea or else someone would be doing it, so my question is why is this not practical?