I really like this idea: http://www.heindl-energy.com/media-and-newsletter/videos.html http://www.heindl-energy.com/media-and-newsletter/videos.htm... A gravit

I really like this idea: http://www.heindl-energy.com/media-and-newsletter/videos.html http://www.heindl-energy.com/media-and-newsletter/videos.htm... A gravity storage in form of a piston carved from rock. It's lifted with water that's pumped underneath. The seal is a rolling "sleeve": http://www.heindl-energy.com/gravity-storage/idea-function/sealing-the-rock-piston.html http://www.heindl-energy.com/gravity-storage/idea-function/s...