Thermal storage

Popular mechanics
Letter by a person describing how he takes a galvanised tank and raps it in fiber glass. Finally sheets of polystyrene is rapped around the fiber glass enabling a storage tank that keeps hot water at the same temperature for two weeks.

Underwater energy bags
https://www.youtube.com/watch?v=ktup6CAvfGo

Hydrolic storage
https://www.youtube.com/watch?v=m3p_daUDvI8 Cut a huge cylindrical rock and lift it out of the ground with water. As it sags back under gravity it converts potential into kinetic energy.

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Air Engine