Most promising green technologies number four: ultracapacitors

While batteries make most of the headlines when it comes to the energy storage requirements of electric cars, the capacitor could be an exciting and viable alternative. Unlike batteries, which store chemical energy and make it available for use as electrical energy, capacitors store energy in the electric field between a pair of conductors. Supercapacitors, or ultracapacitors, are currently being developed which could rival batteries in the amount of energy that they can store. Whether capacitors see use as part of a hybrid drivetrain or as the sole source of electricity for a pure electric vehicle, we expect to see them make a dent in the automotive sector as the future unfolds. Then again, we've been expecting some news on this front for a while (EESTOR, anyone?), so we might have to keep waiting.

Check out Number 3.