Alternative Low / No Carbon Fuels
After many years of research and development, vehicles powered by fuels other than today’s dominant diesel and gasoline, are finally entering the marketplace. Primary examples are biofuels, advanced diesel, natural gas, hydrogen (for fuel cells), and electricity (for plug-ins and plug-in hybrids).
Plug-in hybrid cars and other electric drive vehicles are a promising option for reducing U.S. dependence on oil and reducing greenhouse gas emissions in the transportation sector. Electric motors benefit from superior efficiency in converting “fuel” (electricity) into mechanical power, giving them a significant advantage over gasoline combustion engines in reducing fuel costs and greenhouse gas emissions. At current U.S. retail electric rates—ranging from $0.08 to $0.18 per kilowatt-hour—fueling a passenger vehicle with electricity would cost the equivalent of one to two dollars per gallon of gasoline. Hybrid gasoline-electric vehicles that can be charged from the electric grid — aka “plug-in” hybrids — could lead the shift toward a new generation of partial and all-electric vehicles. The carbon footprint of electric vehicles would be significantly lower with the current mix of energy sources powering the U.S. electric grid, and it would continue shrinking as the electricity sector uses more renewable energy and decarbonizes. Plug-in hybrids could also be flexible fuel vehicles and run on biofuels when the vehicle is not operating in electric mode. Development of advanced batteries that can satisfy requirements for power, travel range, and durability is the subject of considerable public and private investment.
A number of transportation fuels can be produced from biomass, helping to alleviate demand for petroleum products and improve the greenhouse gas emissions profile of the transportation sector. Ethanol from corn and sugarcane, and biodiesel from soy, rapeseed, and oil palm, dominate the current market for biofuels, but a number of companies are moving forward aggressively to develop and market a number of advanced second-generation biofuels made from non-food feedstocks, such as municipal waste, algae, perennial grasses, and wood chips. These fuels include cellulosic ethanol, bio-butanol, methanol and a number of synthetic gasoline/diesel equivalents. The greenhouse gas and oil reduction potential of different biofuels can vary greatly depending on the specific process and feedstocks used. Biofuels can be used in blends with gasoline or diesel or can be used as standalone, drop-in fuels. Until we are able to produce a significant amount of electric vehicles that run on renewably-produced electricity, biofuels remain the only available widespread source of clean, renewable transportation energy.
A hydrogen fuel cell vehicle is a type of electric vehicle that uses a fuel cell instead of a battery to power the car. Hydrogen fuel cells can be a clean, reliable, quiet, and efficient source of high-quality electric power. They use hydrogen as a fuel to drive an electrochemical process that produces electricity, with water and heat as the only by-products. The two main applications for hydrogen fuel cells are in stationary power sources and hydrogen fuel cell vehicles (FCVs).
Hydrogen can be extracted from water using electrolysis, using power from renewable solar or wind, nuclear energy, or fossil energy. It can be extracted from renewable biomass or coal using high temperature gasification. Using chemical catalysts, it can also be derived from renewable biogas, renewable ethanol or methanol, or fossil natural gas. The environmental impact of hydrogen production depends on the sources and processes through which the hydrogen is derived. Today, most hydrogen is derived from fossil natural gas, emitting fossil carbon dioxide as a by-product.
FCVs have a driving range similar to a vehicle with an internal combustion engine – 250 to 400 miles per tank of fuel. FCVs are commercially available for lease, but a hydrogen refueling infrastructure does not exist yet in most parts of the country. California has a few stations in operation, and more under construction. The higher cost of hydrogen on an energy equivalent basis is outweighed by the greatly increased efficiency of the electric drive system relative to the internal combustion engine.
Natural gas, when used as a transportation fuel, can emit up to 25 percent less carbon per unit energy than conventional gasoline and can be sourced domestically. Natural gas is currently used in many transit buses, short-haul commercial trucks and some other vehicle fleets. Use in passenger vehicles is hindered by the added space needed for fuel storage and the limited availability of retail fueling stations, but has been explored by at least one major automaker.
A cleaner generation of diesel fuels and advanced diesel engines together are achieving emission levels that approach those of low-emission gasoline-powered engines, while diesel-powered vehicles can get more than 25 percent better fuel economy than comparable gasoline models. In the United States, diesel fuel is primarily used for trucks, buses, and trains. Half of all passenger vehicles in Europe, however, run on diesel and clean diesel technology may lead to expanded use in U.S. cars and light trucks.