To accurately understand and compare the gasoline alternatives for the transportation sector, it is helpful to first consider the underlying science of how two competing technologies convert a fossil-fuel source chemical energy to rotational work being performed by the vehicle – in short a well-to-wheel analysis. In order to most accurately address the claims put forth by Dr. Knittel in his piece
Leveling the Playing Field for Natural Gas in Transportation, this study will compare the same two models of electric vehicle (EV) and compressed natural gas fueled combustion engine vehicles (CNG) as did Dr. Knittel. The two models being examined are the all-electric Nissan Leaf and the CNG fueled Honda Civic GX
[1].
First examining the Leaf, the EPA rates the Leaf as having 99 miles per gallon of gasoline equivalent of energy stored in the battery. Layering in an ambitious 93% charging efficiency of the Leaf’s battery and 50.8% thermal efficiency of a NGCC plant
[2], 1GGE of NG fed into a combined cycle plant can only propel the Leaf 47 miles. Equivalently, 1000 cubic feet of natural gas can propel a Leaf 368 miles, assuming combined cycle power generation. With gas frequently on the margin of the power supply curve, this NGCC assumption is justified.
Moving on, despite its lighter curb weight the Honda Civic GX has an EPA rated 31 MPGge of range on natural gas. Even if we generously assume a perfectly efficient compressor stepping the gas up from interstate distribution pressures of 1100 psi to 3600 psi storage tanks, resulting in ~2% energy loss on a per unit of gas basis, the Civic is still only able to achieve 240 miles range per 1000 cubic feet of gas taken off the pipeline.
Simply put, electric vehicles offer over 53% more range per unit of pipeline gas.
[1] For a more complete table comparing the two vehicles refer to Appendix B – Table 2 on page 21 of Knittel’s piece
[2] National Energy Technology Laboratory (NETL)
http://www.netl.doe.gov/energy-analyses/pubs/deskreference/B_NGCC_FClass_051607.pdf
