While natural gas is a naturally occurring mixture of methane (approximately 90 percent or higher) and other gases, propane is a byproduct of both petroleum refining and natural gas processing. Natural gas must be cleaned before being used, and the byproducts of this process include hydrocarbons such as propane in addition to butane, ethane, hexane and pentane.
The following data compares and contrasts two alternative transportation fuels, CNG and Propane, by examining energy density and other physical properties, fuel safety, infrastructure economics, vehicle costs and availability, fuel costs, tailpipe emission information, fueling station counts, tank safety and long-term pricing stability.
A Comparison of CNG and Propane
Compressed Natural Gas (CNG) | Propane (LPG) |
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Fuel Safety | |
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Economics | |
Station Construction:
Example: A station can fill one truck at 8 GGE/minute on fast-fill or 100 trucks at 480 GGE/hour on time-fill. If a fleet’s vehicles sit in a parking lot overnight, every night, this is the most cost and time effective method of fueling. Time-fill stations are considerably less expensive than fast-fill stations, which reduces costs and increases convenience where applicable. |
Station Construction:
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Automobile Purchase/Conversion Light & Medium Duty Vehicles:
Heavy Duty Vehicles:
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Automobile Purchase/Conversion Light & Medium Duty Vehicles:
Heavy Duty Vehicles:
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Fuel Costs
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Fuel Costs
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Tailpipe Emissions/Environmental | |
Natural gas is the cleanest burning fossil fuel and consequently has the emissions advantage over diesel and gasoline. It can be argued that because of this inherent environmental quality, the EPA has been able to set stricter emission mandates (particularly with NOx and PM reductions) that forced expensive diesel emission technology to be created to be as environmental as natural gas. Natural gas was compliant with 2010 EPA emission requirements in 2007. Both natural gas and propane provide environmental advantages as these vehicles all must be certified to new demanding emission limits that require today’s motor vehicles to be 90% cleaner for most pollutants than was the case just a few years ago. The biggest benefit in both cases—natural gas and propane—is to introduce them to replace older, dirtier diesel vehicles. For emission benefits of particular vehicles, potential purchasers should obtain copies of actual certification data and consider the emission certification levels (e.g., Tier 2, 4, or ULEV, SULEV). | |
Infrastructure: Public vs. Private | |
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Safety | |
National Fire Protection Agency (NFPA) guidelines for both CNG and propane conversions are strictly enforced. CNG and propane systems are tested to meet or exceed all safety requirements for gasoline and diesel equivalents. (Question: If gasoline and diesel transportation fuels were introduced today, would they hold up under the same scrutiny as CNG?) | |
Long-Term Price Stability | |
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Pricing and Market Share Trends Any effort to compare the price of natural gas and propane with the price of gasoline should start by ensuring that the consumer is making an apples-to-apples comparison. CNG sold at retail is already converted to GGE units so consumers can easily determine if they are getting a good deal. For propane, it is generally sold in liquid gallons and must be converted to GGE units in order to put it on a level playing field for comparison sake (i.e., paying more or less for the same amount of energy). A gallon of propane compared to a GGE of propane nets a conversion factor of 1.38 gallons of propane to 1.00 GGE. Therefore, the cost of a GGE of propane is 1.38 times greater than the cost of a gallon of propane. ![]()
Additional Propane-to-Gasoline AnalysisIt is important to ensure that the GGE conversion is used when making comparisons because:
The aforementioned data is derived from the Transportation Energy Data Book (TEDB). The key point to this exercise is to calculate how much one is truly paying for the same amount of energy. That is why the Clean Cities Alternative Fuel Price Report (October 2015) provides exactly that type of analysis with charts that show the comparative price per GGE. . Looking at the Clean Cities’ report, the price of CNG offers a much better economic value than gasoline or propane. Btu values vary slightly from U.S. regions and it is important to check with local fuel suppliers to provide these numbers whenever possible. Also note that CNG and propane, have two different Btu numbers: an HHV (Higher Heating Value = Gross) and an LHV (Lower Heating Value = Net), both calculated based on heat of combustion, a term that measures the energy released as heat when a compound undergoes complete combustion with oxygen under standard conditions. HHV can have a significantly higher Btu value when compared to LHV due to the additional heat (transferred to energy) gained through the vaporization of residual water during the combustion process. The HHV Btu measurement can be employed when evaluating products like natural gas or propane home heating furnaces or hot water tanks because these technologies leverage additional heat (energy) gained through water vaporization. The internal combustion engine, however, cannot capture these efficiencies and so the LHV value must be used due to its inability to recover and utilize the net benefits of water vapor during the combustion process. The following graphs and charts are taken from various government entities responsible for tracking transportation fuels. They serve to visually show historical, current and forecasted industry trends. Source: US DOE AFDC Clean Cities Alternative Fuel Price Report (October 2015). The pie chart below shows that in 2011 (the most current analysis), natural gas accounted for 48% of the alternative fuels consumed; propane’s contribution was 24%. The next release date for the report of this market share data is not available but is estimated that natural gas will capture close to 60% of the market. Source: US Energy Information Agency Annual Energy Outlook 2013.
Source: US DOE Alternative Fuel Data Center Trend of Petroleum Savings 2004-2013 |
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Future: Scalability of Fuels and Infrastructure One of the important factors to consider when evaluating all transportation fuels, particularly for those responsible in fleet management, is scalability. A key question is whether natural gas and propane production and infrastructure can be scaled up to serve a large part of the U.S. transportation market. The U.S. market for natural gas at 24.9 quadrillion Btu per year (consumption) is equivalent to roughly 200 billion GGEs. Thus, the natural gas market today is now actually 14% larger than the on-road transportation fuels market. The propane market (US production) at 2.3 trillion Btu per year is equivalent of about 18.6 billion GGEs or 11% of the size of the on-road transportation fuels market. The amount of propane consumed is actually quite a bit smaller since much of propane is exported. Propane consumption in the U.S. represents only about 6% of the amount of natural gas consumed. To offset 5% to 10% of the total transportation fuel consumption (8.7 to 17.5 billion GGE), natural gas production would have to increase by about 4.4% to 8.8%, respectively. Propane production would have to increase by a staggering 46% to 93%, respectively. The actual impact on the US consumption would be even more significant since a large share of propane is now exported. For propane, it is doubtful that domestic supply or infrastructure could adjust to this level of demand without having a major impact on prices. Furthermore, there does not appear to be any effort in the propane industry to develop and expand the necessary infrastructure that would be required to service such an increase in demand. The natural gas industry on the other hand is investing hundreds of millions of dollars to expand its infrastructure to serve the transportation market. Thus, propane is most likely a niche market fuel at best that can help offset future transportation demand, but it will not have a substantial impact on the transportation fuels market or on petroleum imports. Propane proponents’ talking points critique the lack of and cost of infrastructure in the NGV market and choose to ignore the fact—that since 2009 there has been a 111% increase in U.S. CNG infrastructure. Additionally, recent natural gas infrastructure investments have totaled up to $750 million ($3/4 billion) with multiple stakeholders actively engaged in its development:
Very simply put, both the capital and operating expenses of natural gas infrastructure, no matter how high or low, should be considered and weighed against projected revenue (or fuel savings) to determine investment worthiness (i.e., will the investor, whether it be a fleet or fuel provider, net a desirable return on their investment). Given the sheer volume of investments occurring in natural gas fueling infrastructure today, it appears that the answer is a resounding “yes”. Last reviewed: January 29, 2016 |