There is also Superconducting Magnetic Energy Storage(SMES), train energy storage, molecular spring energy storage. Train energy storage is driving a trainload

There is also Superconducting Magnetic Energy Storage(SMES), train energy storage, molecular spring energy storage. Train energy storage is driving a trainload of concrete blocks uphill when power is cheap and doing regenerative braking on the way down[1]. It's just like pumped hydro, but without the need for water. Molecular spring energy storage is essentially making a windup mechanism, except with advanced materials like carbon nanotubes. Unfortunately it is not very practical today.[2] [0] https://en.wikipedia.org/wiki/Superconducting_magnetic_energy_storage https://en.wikipedia.org/wiki/Superconducting_magnetic_energ... [1] http://www.gizmag.com/ares-rail-energy-storage/28395/ http://www.gizmag.com/ares-rail-energy-storage/28395/ [2] https://en.wikipedia.org/wiki/Carbon_nanotube_springs https://en.wikipedia.org/wiki/Carbon_nanotube_springs