Frequently Asked Questions
1. What are the air emissions differences between CNG and fuel?
The latest diesel trucks, meeting EPA standards for engines manufactured on January 1, 2010 and later, also have very low emissions. In fact, the newest diesel engines can be as clean as natural gas engines in CNG and LNG applications. The difference, however, is that the newest diesel engines require very sophisticated emission control equipment including diesel particulate filters, selective catalytic reduction (SCR) systems and the continuous use of diesel exhaust fluid (DEF), while a comparable natural gas engine can meet the same NOx standards with a simple, maintenance free catalytic converter. Natural gas engines are also much quieter than even the newest diesel engines of a comparable size; it takes approximately 10 heavy duty natural gas vehicles to equal the sound of one comparable diesel vehicle.
The greenhouse gas emissions of CNG and LNG vehicles, however, are approximately 25% lower than diesel because, on average, natural gas releases less carbon dioxide per unit of energy than petroleum. Over an entire fuel lifecycle (production, refining, transportation and combustion) natural gas supplies in the U.S. have approximately 21 to 26% less greenhouse gas emissions than petroleum, but these numbers may vary depending on the source of the natural gas, the source of the petroleum and the specific engine application. For more information click here.
The sources of different fuels, including natural gas and petroleum, continue to change. Natural gas from shale deposits has been found in some studies to have higher greenhouse gas emissions than conventional natural gas deposits, but newer sources of petroleum, such as those from Alberta’s oil sands, may also have higher greenhouse gas emissions.
2. Fracking is bad, why is the state promoting CNG?
Modern shale gas is produced from deep wells that reach shale deposits thousands of feet below the surface, then turn and extend up to several miles horizontally to access more of the shale formation. These wells are then hydraulically fractured by injecting water, sand and a small amount of other chemicals into the shale formation to cause small fractures to form. When the pressure is reduced, the sand grains hold open the fractures and allow the natural gas to rise to the surface. Some of the sand used for hydraulic fracturing is mined and processed in Wisconsin. Two resources provide much more information on the basics of shale gas produced by hydraulic fracturing and a detailed examination of the environmental controversies with a broad stakeholder group convened by Secretary of Energy Steven Chu:
Two other resources can help put shale gas into perspective with other forms of energy, a symposium from the Wisconsin Public Utility Institute in 2011 that included presentation by industry and environmental representatives (including a member of DOE Secretary Chu’s advisory committee) and a publication of the University of Texas Energy Institute on the subject:
3. Won't using gas in vehicles compete with utility power plants for fuel and drive up electricity costs for consumers?
The WI State Energy Office provides detailed information on the supply and cost of energy to Wisconsin’s economy through the Energy Statistics annual reports that are found here.
The most recent data show that the single largest component of energy expenditures in Wisconsin is petroleum, at 48.7% of total 2009 energy expenditures in the state. Expenditures on electricity is 32.8% of the total 2009 energy expenditures, but natural gas was the source of only 6% of Wisconsin’s total energy used for electric generation (coal was the largest source, followed by nuclear). Thus, even if natural gas used for transportation caused an increase in the price of natural gas used for electricity, Wisconsin consumers would still likely have a very large net economic benefit by substituting natural gas for petroleum. A more detailed comparison between natural gas and petroleum was presented at the first Roundtable meeting on April 24th and can be found on the CNG Roundtable Meeting page.