Efficient Gas or Coal-Derived Electric Vehicle?

Personal vehicles are on the “less desirable” end of the low-tech solution spectrum, to be sure, but even within the category, we see variation. Driving a large truck to get groceries is more wasteful than using it to haul building materials. Commuting long distances in a fuel-inefficient vehicle should be avoided. If you’re going to use a personal vehicle, it is a good idea to use the right tool for the right job. It might seem that electric vehicles are the best choice for commuting, but this isn’t always the case.

We’re going to do a head-to-head comparison of an efficient gasoline-powered vehicle and an all-electric vehicle. We won’t be going into questions of how much of a carbon impact the production of the vehicle has. Nor will we be discussing one of the biggest impacts: personal behavior, that is how far, how often, and how efficiently you drive. This is just a mile-for-mile comparison of two existing vehicles.

Traditional Gasoline-Powered Vehicle

First up, we have an efficient but traditional gasoline-powered vehicle, such as a Honda Fit or Civic (Full Disclosure: I own a 2012 Honda Fit but receive no incentives from Honda). These vehicles get about 33/41 mpg (city/highway) according to the manufacturer, which we’ll average to 37 mpg. For comparison purposes below, this vehicle weighs about 2550 lb.

The only real way to compare these vehicles’ efficiency is by pounds of carbon emitted to travel a mile under normal conditions. In this case, gasoline emits about 20 lb/gal. This means to travel a mile, about 0.54 lb of carbon are emitted. This can be improved or worsened by stop-and-go traffic, heavy acceleration, excessive idling, etc. If you’re interested in extreme mpgs, have a read of articles devoted to hypermiling (here and here).

Electric Vehicle

Second up, we’ll be looking at two different electric vehicles, the Ford Focus Electric and the Chevy Spark Electric Vehicle. Why two cars? Because we’ve got to compare a similarly weighted vehicle (the Spark weighs about 2,650 lb) and a similar passenger and cargo capacity to the Fit (the Focus is similarly sized but weighs almost 3,700 lb). The weight differential is due to the batteries and other equipment in the electric vehicles.

The Spark gets 128/109 MPGe (miles-per-gallon equivalents, that is 33.7 kWh is equal to 1 gal gasoline according to the EPA). Thus the Spark goes a mile on 0.28 kWh (that’s about what it takes to run a big-screen television for an hour).

The Focus isn’t as efficient, coming it at 118/96 MPGe, averaging out to to 107 MPGe, probably because it is a bit bigger and heavier than the Spark. This brings the Focus in at 0.31 kWh per mile.

Now, while gasoline is largely the same carbon footprint wherever it is burned, electricity is generated in different ways. If one had a dedicated solar or wind system to power his or her vehicle, one could get by without emitting carbon at all (at least not from the propulsion of the vehicle; remember we’re not talking about the creation and maintenance of the infrastructure here). But if one lives in a coal-powered state, for example, those emissions go up.

First, we have to calculate the local rate of pounds of carbon per kWh (these are lifecycle emissions, that is, how much carbon is emitted when the entire costs are considered, not just the combustion of the fuel at the time of generation). We can use IPCC numbers: coal, ca. 1.81 lb/kWh; natural gas, 1.08 lb/kWh; solar, 0.10 lb/kWh; hydro, 0.05 lb/kWh; nuclear, 0.03 lb/kWh; and wind, 0.02 lb/kWh.

About six percent of this energy is lost through transmission, so each of those numbers really represents 94 percent of a kWh, so they must all be multiplied by 1.064 to account for the lost energy.

In a coal-heavy state, such as West Virginia, which gets 96 percent of its energy from coal (let’s just calculate for 100 percent, shall we?), that would mean a Spark would emit 0.54 lb C/mi and the Focus would account for 0.60 lb C/mi. In this case, it is no better to drive an all-electric vehicle than an efficient gasoline-powered one, but this is really a best- to worst-case scenario.

In Vermont, one of the cleanest energy generators, two-fifths of the state’s power comes from hydro, wind, and solar, while the rest is largely from imported power generated from natural gas, thus an estimate might be about 0.71 lb/kWh. In Vermont, the spark would come in at 0.20 lb C/mi and the Focus at 0.22 lb C/mi.

The US average is about twice the value of Vermont, so you can count on emitting about 0.40-0.45 lb C/mi across the country. This is certainly better than the gas-powered vehicle, but not a quantum leap.

What About Hybrids?

Hybrids do pretty well in the direct output category: a Toyota Prius gets about 55 mpg on traditional gasoline, thus emitting 0.36 lb C/mi. Really, it comes down to where you live, how far you need to drive, and other factors in addition to just pounds of carbon per mile. In the end, this is an angel-on-the-head-of-a-pin argument, as we should really be looking for ways to get rid of personal vehicles instead of making them more efficient.


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