"Zero emission" refers to a motor or engine that, by virtue of being fueled by electricity or more exotic means, generates no byproducts other than water vapor. The EV1 automobile built by General Motors is often cited as an example of a zero-emissions vehicle, or ZEV. Technically, the EV1's motor, as well as other battery-powered electric propulsion units that rely on the power grid for charging, is a displaced-emission powerplant. True zero-emission power includes solar power, wind power, tidal power, or hydroelectric power. Nuclear fusion would, in theory, fall into this category as well.