The Natural Gas Alternative
Boone Pickens has recently been calling attention to the potential of natural gas (NG) as an alternative fuel for vehicles. There are two basic alternatives, compressed natural gas (CNG) and liquefied natural gas (LNG). Using NG to fuel vehicles is not new. Europe has been using NG vehicles for, at least, 50 years. Worldwide it is estimated that there are approximately 7 million NG vehicles. There are approximately one million in the U.S.

There are some distinct advantages to the use of CNG as a fuel instead of gasoline or diesel. The principal advantage is that CNG is much cleaner fuel. CNG engines produce less fine particulate matter (PM), smog producing NOX and VOC and CO₂ than either gasoline or diesel engines. The amount of emissions reduced varies based on the size and type of engine. But generally, the largest reductions come from replacing large diesel engines. For example, according to Cummins Westport their newest NG heavy-duty engine, primarily used for refuse and bus applications, emits 6X less NOx than the newest clean diesel applications. For some specific test comparison results click here. Additionally, CNG does not have to be refined or transported by truck and thus eliminates those associated emissions. For a non-attainment region ^[1], like Houston, NG vehicles could make a substantial contribution in the reduction of emissions.

Also, at today’s prices, there is a significant savings from CNG. CNG prices vary substantially, but generally the price per gallon equivalent (PGE) is just under $3. Some fleet operators with long-term NG supply contracts report even lower costs.

Finally, the U.S. has a very large supply of natural gas. The Energy Information Agency (EIA) projects that domestic production of natural gas will be near 20 trillon cubic annually through 2030.^[2] A significant conversion of vehicle fuel from imported oil to domestic natural gas could be a meaningful part of our energy independence. Also NG, which is primarily composed of methane (CH₄), is a renewable source that can be generated from landfills and wastewater treatment plants.

However, there are also some significant disadvantages to NG vehicles. First, NG vehicles are significantly more expensive. The only original equipment manufactured (OEM) vehicles are a Honda GX and heavy duty trucks. The only current alternative for light duty trucks or sedans is after-market conversions. These after-market conversions for light/medium-duty vehicles can run $10,000-$15,000. Heavy-duty OEM NG trucks will typically cost an extra $40,000 to $60,000. However, there are various government grants and tax credits that assist in the purchase of NG vehicles.

Also, the space required to store CNG is significantly greater than gasoline. As a result vehicles typically must give up some of their storage capacity to accommodate the larger tanks. As shown in the photograph below, the CNG tank takes up about 1/3 of a half-ton pick-up bed. On a refuse truck, the CNG tanks add about two feet to the chassis length.

NG tank in bed of pick-up NG tank on garbage truck

Another disadvantage is that light-duty NG vehicles have a considerably shorter range than gasoline or diesel vehicles. Generally, around 200 miles is the maximum range. This limited range is combined with the fact that there are only a handful of locations where NG is publicly available makes NG vehicles fairly impractical for personal use.

The place where NG vehicles make the most sense is in large fleet operations which return to the same location each day. Garbage trucks for example are an excellent application. San Antonio and Austin both fuel a portion of their garbage trucks with NG. Also, many transit agencies are using NG vehicles. DART, Dallas’ transit agency, now operates nearly 200 NG buses and the City Dallas has 1,200 NG vehicles. Airport shuttles are another common application.

Surprisingly, little has been done in the Houston region to develop NG vehicle applications. Neither Metro nor the City of Houston has any NG vehicles. Metro conducted a test of LNG buses in the 1990s. The tests were not successful and apparently left a bad taste in Metro’s mouth for NG buses. However, at a recent Metro Board meeting, Board member George DeMontrond requested that the staff take another look at NG as an alternative.

The City of Lake Jackson began a CNG program in 2000 and now operates 16 garbage trucks, about a dozen light duty trucks and six Honda NG sedans which are used by the public works department. Lake Jackson has a long-term supply contract giving it a current cost of $1.38 PGE! Lake Jackson has its own compressor station at its fleet barn where the vehicles are re-fueled overnight. Craig Nesbitt, the public works director there gave me a tour of their facilities. For anyone interested, he is very knowledgeable and generous with his time in sharing Lake Jackson’s experience.

NG refueling station Lake Jackson compressor station

There are a number of private companies in the region testing NG applications. Silver Eagle and HEB have converted several of their large delivery trucks.

NG vehicles are not a silver bullet solution to our energy or air quality problems. However, it does appear to be a piece of the puzzle. At a minimum we should be testing applications in our garbage trucks, transit buses and airport shuttles. Houston is after all the natural gas capitol of the world. It hardly seems right that Dallas, San Antonio and Austin would be ahead of us!!!

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[1] A non-attainment region is one that does not meet Federal ozone standards.

[2] http://www.eia.doe.gov/oiaf/aeo/pdf/trend_4.pdf