Many of the innovations in green energy involve the recapture of otherwise wasted energy. Regenerative breaking systems on hybrid automobiles recapture the kinetic energy inherent in the motion of the vehicle. In a conventional automobile, as the brakes are applied, friction in the braking system converts this kinetic energy to waste heat. But in a hybrid, a portion of this energy is converted to electricity and stored in batteries for future use. Since this energy would otherwise be wasted, this is essentially free energy. Similarly waste heat recovery systems recover energy that would otherwise be wasted from power generation facilities. Most conventional power generation facilities covert approximately half of the energy in the fuel into electricity. The remainder is lost as waste thermal heat. Waste heat recovery systems recapture this heat so it can be put to good use, increasing the efficiency of power generation facility. These are but two examples of innovative methods of recapturing otherwise wasted energy. There is another unharnessed form of energy rushing through our cities and countryside every day: our natural gas distribution pipelines.