A Proton Exchange Membrane (PEM) fuel cell powers the GreenCar and all its systems. Compressed hydrogen gas reacts with oxygen to form water, generating electricity in the process. When the car is parked, it doubles as a generator. Electricity produced by the fuel cell and regenerative braking is shunted to ultracapacitors, which collect charge and, with their faster release capabilities, make high-demand activities such as starting the car much easier than with a standard battery. The energy is stored by building up an electrostatic charge between the two plates and then transferred to the vehicle system through conduits.