Benefits & Considerations
Whether produced via conventional or renewable methods, the advantages of natural gas as an alternative fuel include its domestic availability, established distribution network, relatively low cost, and emissions benefits.
Natural gas produced via renewable methods offers additional benefits. Renewable natural gas (RNG) is essentially biogas—the gaseous product of the decomposition of organic matter—that has been processed to purity standards. Capturing biogas from landfills and livestock operations reduces emissions by preventing methane release into the atmosphere. Methane is 25 times stronger than carbon dioxide as a greenhouse gas. Additionally, producing biogas through anaerobic digestion reduces odors and produces nutrient-rich liquid fertilizer.
RNG and conventional natural gas, and must be compressed (CNG) or liquefied (LNG) for use in vehicles. Like any alternative fuel, there are some considerations to take into account when contemplating the use of natural gas.
In 2014, the United States imported about 27% of the petroleum it consumed, and transportation accounted for more than 70% of total U.S. petroleum consumption. With much of the world's petroleum reserves located in politically volatile countries, the United States is vulnerable to supply disruptions. However, because U.S. natural gas reserves are abundant, this alternative fuel can be domestically produced and used to offset the petroleum currently being imported for transportation use.
Natural gas vehicles (NGVs) are similar to gasoline or diesel vehicles with regard to power, acceleration, and cruising speed. The driving range of NGVs is generally less than that of comparable gasoline and diesel vehicles because, with natural gas, less overall energy content can be stored in the same size tank as the more energy dense gasoline or diesel fuels. Extra natural gas storage tanks or the use of LNG can help increase range for larger vehicles.
In heavy-duty vehicles, dual-fuel, compression-ignited engines are slightly more fuel-efficient than spark-ignited dedicated natural gas engines. However, a dual-fuel engine increases the complexity of the fuel-storage system by requiring storage of both types of fuel.
All new vehicles are equipped with effective emission control systems and must meet the same emissions standards, regardless of fuel type. Consequently, tailpipe emissions from natural gas vehicles are comparable to those of gasoline and diesel vehicles equipped with modern emissions controls. According to Argonne National Laboratory’s Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model, light-duty vehicles running on natural gas can reduce life cycle greenhouse gas emissions by 6% to 11%. In addition, because CNG fuel systems are completely sealed, the vehicles produce no evaporative emissions.
Infrastructure and Vehicle Availability
A wide variety of new, heavy-duty natural gas vehicles are available from U.S. original equipment manufacturers (OEMs). Although the number of available light-duty natural gas vehicles from OEMs is limited, the choices are steadily growing. For availability, see the Alternative Fuel and Advanced Vehicle Search or the Clean Cities 2015 Vehicle Buyers Guide (pdf).
Fleets and consumers also have the option of reliably converting existing gasoline or diesel vehicles for natural gas operation using qualified system retrofitters. It is critical that all vehicle and engine conversions meet the emissions and safety regulations and standards instituted by the U.S. Environmental Protection Agency, the National Highway Traffic Safety Administration, the National Fire Protection Agency's NFPA 52 Vehicular Gaseous Fuel Systems Code, and state agencies like the California Air Resources Board.
Although the United States has an extensive natural gas distribution system in place, vehicle fueling infrastructure is limited. Therefore, fleets may need to install their own natural gas fueling infrastructure, which can be costly. Finding partners who will commit to use the infrastructure can improve the payback period.