Wednesday, October 01, 2008

CNG Cars – Once again, it ain’t easy being green

This recent listing on Craigslist for a used Honda Civic GX, a rare model that only runs on Compressed Natural Gas (CNG), sparked Miss Motor Mouth to ask me for some more information. What’s with CNG cars? Are they clean? What are the advantages or disadvantages? Where does one purchase fuel for them?

Most of us are familiar with CNG vehicles primarily in mass-transit use, such as shuttle buses at airports or city buses. The low emissions of CNG vehicles (think about it, this is the same stuff many of us cook with inside our homes) allows them to meet the tough PZEV emissions levels make them good choices for mass-transit operations concerned with their fleet emissions. Fuel cost is also low… reportedly about half the cost of gasoline per mile. Natural gas is also plentiful here in the U.S. so CNG use potentially reduces reliance on imported fuel. There are definitely some exciting upsides to CNG. Fleet use also eliminates many of the challenges associated with the fuel that affects individual drivers.

Those CNG buses are often easily identifiable because of the large auxiliary gas tanks on their roofs. This is needed because CNG has a substantial disadvantage relative to gasoline in terms of energy density. It takes over 126 cubic feet of natural gas to provide the same energy equivalent (measured in BTUs) as one gallon of gasoline. So, while the fuel costs a lot less you simply cannot carry as much of it at a time so range is limited in a regular-sized vehicle. In the case of the new 2009 Civic GX, according to Honda one can carry the energy equivalent of 8 gallons of gasoline (compared to 13.2 gallons for a normal Civic sedan) but this is with an enlarged high-compression tank that reduces cargo capacity to 6 cubic feet (half of the regular Civic sedan’s 12 cu. Ft. trunk capacity). With a combined EPA fuel efficiency of 26 mpg, this provides a driving range of a bit over 200 miles.

Buses equipped with auxiliary tanks can make up for much of the range deficiency. Fleets also provide their own refueling stations since they can utilize a central location for maintenance every night. However, public refueling for CNG cars is limited. According to the U.S. Department of Energy, there are only 109 public CNG refueling stations in the state of California… the state with the most developed infrastructure. The state of New York offers 28 such stations, for comparison. To make matters worse, these aren’t exactly gas stations on convenient street corners or right off the freeway exit. They tend to be available because they also serve those aforementioned fleets, so drivers need to visit airports, municipal maintenance lots, or the local energy company’s headquarters.

Like electric cars, however, there is an alternative… home fueling. If you have gas coming into your home the cleverly-named Phill home CNG fueling station can be installed, allowing one to use this existing pipeline. However, again like electric cars this isn’t a fast process. Phill’s manufacturer says it takes about 4 hours to refill the gas used for about 50 miles of driving at an average of 30 mpg. That’s 2.4 hours per gallon equivalent, or in other words, that Honda GX will take 19.2 hours to fill from empty. This makes recharging a Tesla look like a NASCAR pit stop.

Phill also costs about $4,000 not including between $1,500 and $2,000 for installation… quickly wiping out the savings realized from the cheaper fuel and some available tax credits. Then again, in California you do get to drive in the HOV lane.