Biodiesel is a substitute fuel made from biomass, which means that it is inherently renewable and, in itself, it contributes nothing to carbon-dioxide loading of the atmosphere. Biodiesel commonly uses soybean or canola oil as its base, but animal fat or recycled cooking oil can also be used. To speed its market introduction, and dilute its additional cost over petroleum diesel fuel, the initial commercial product being studied is a blend of 20% biodiesel and 80% low-sulfur diesel fuel.
Low-level ethanol blends are sold in every state. Over 90% of U.S. gasoline contains up to 10% ethanol (E10) to boost octane, meet air quality requirements, or satisfy the Renewable Fuel Standard.
Ethanol, or grain alcohol, is produced by fermenting biomass, commonly corn. It is thus inherently a renewable resource, and contributes nothing in itself to greenhouse-gasloading of the atmosphere. As an alternative motor vehicle fuel, it is usually blended in a mixture of 85% ethanol, 15% unleaded gasoline.
Gaseous hydrogen (H2)
Hydrogen does not occur free in nature; it can be made by “re-forming” natural gas or another fossil fuel, or by using electricity to split (“electrolyze”) water into its components of oxygen and hydrogen. In this sense, hydrogen is like electricity: the energy to generate it can be obtained from sources ranging from the burning of high-sulfur coal to pollution-free photovoltaic cells (solar cells).
Electricity can be made by many means, from the burning of high-sulfur coal to pollution-free photovoltaic cells (or solar cells). Electric vehicles are generally divided into battery and hybrid classes, depending on whether the electricity is generated off-board and stored in a battery or generated by a small on-board powerplant. Hybrid electric vehicles can be designed to run on any fuel, including gasoline or diesel as well as alternative fuels, and can best be thought of as highly-efficient gasoline, diesel, or alternative-fueled vehicles.