A UK-based startup has come up with a crazy idea for storing mass amounts of energy, but it might just work. The company plans to suspend a 3,000-tonne cylindrical weight in disused mine shafts from 150m to 1,5000m deep. The weight is attached to a series of winches that can lift it, and when electricity is needed, the weight is dropped to drive a turbine that creates electricity. When the weight reaches the bottom of the shaft, it is then hauled back to the top of the shaft using cheap, off-peak electricity.