6000 MPG!!

We’ve decided to call our vehicle the mc2. It is, after all, all about energy. It gets 6000 MPG.

Are we kidding?

Yes. And no.

The EPA does not yet have a realistic standard for measuring fuel efficiency in vehicles which get their energy from more than one source. There are the CAFE standards, which inflate the mileage of any flex-fuel vehicle by a factor of 3.33, so a lumbering 15 mpg SUV is rated as 45 mpg for CAFE purposes. This is intended to enable GM, for example, to sell the most egregious gas guzzlers without incurring fines: for CAFE purposes, a huge flex-fuel SUV gets the same mileage as a Prius. Vehicles that run exclusively on an “alternative fuel” (or electricity) are given an astonishing 6.67 multiplier. Therefore, electric vehicles (which run on coal in most places) are considered 6.67 times as “good” as a gasoline-powered vehicle for CAFE purposes. Even if you live somewhere where electricity is generated mainly with coal (generally, every state other than California) electric vehicles are slightly cleaner than gasoline-powered vehicles, and obviously use less petroleum. However, they are not even remotely close to being 6.67 times as efficient, or 6.67 times as environmentally sound.

The EPA MPG number that appears on car stickers is another matter entirely. Although there have been complaints that these figures are optimistic, buyers have come to trust these figures as a good relative guide, because the EPA is independent of the manufacturers. Because of this trust, unaware buyers, when seeing claims of 100, 200 or 300 mpg for Plug-in hybrid Prius conversions think that these claims can also be trusted. They cannot: any plug-in vehicle can be rated at virtually figures, because there is no standard for the test sequence. These figures are meaningless unless the precise test conditions are given – and even then, the claims for most prototype plug-in hybrids are deceptive, because they do not account for the electrical energy that is actually running the car much of the time, nor do they account for the source of that energy. To get electricity, you can burn coal in an outdated plant (widely used, filthy, and inefficient) or from solar (scarcely used at all, but very clean). Those are the extremes, but there are many alternatives of varying “goodness”.

Suppose you want to advertise your plug-in Prius conversion as a 150 MPG car. The battery range makes little difference, because you can rig the numbers to fit: let’s pick a 20 mile range. We’ll call our “typical commute” 30 miles. That would be 20 miles on “no gas” and 10 miles on “gas.” A Prius will use about 1/5 of a gallon to go 10 miles (at 50 mpg). So, on 1/5 gallon of gas our converted Prius goes 30 miles: 150 MPG!

Let’s say you think you could sell more conversion kits if you advertised 250 MPG. Then write your ad copy like this: in a typical round trip commute of 25 miles you will use 1/10 gallon (at 50 mpg) to go 5 miles. 1/10 gallon, 25 miles traveled: 250 MPG!

Both the 150 MPG figure and the 250 MPG figure are based on completely ignoring the energy input from electricity, and on arbitrary trip distances. A far better approach, which cannot be “gamed” so easily, is to quote a figure for running on gasoline (45 mpg for a Prius, plug-in or not) and another for running off the batteries (4 miles per kilowatt hour, for a Prius). If you are environmentally aware, then you’d consider where your electricity comes from. If it is from coal, then you are getting about 4 miles per pound of coal (with one pound yielding roughly 1 kWh).

To go 45 miles on electricity in your plug-in Prius, you’d use 11 pounds of coal. If you live in California, the situation is less dismal, and there you might burn about 5 pounds of natural gas to generate the electricity to go 45 miles. (If, instead, you ran the Prius directly on gasoline, you’d use one gallon, or six pounds.) In any case, you can see that a 45 MPG Prius does not suddenly become a wonder of efficiency when plugged in. Claims of 150 MPG or 250 MPG certainly imply an efficiency three times or five times better than a standard Prius – and that is simply not the case.

Perhaps MPGe is a bad concept: electric vehicles do not run on gallons of anything. Why pretend that they do? People interested in the Automotive X Prize have been unable to agree how to measure MPGe. A well-to-wheels approach makes sense for engineers and people who are environmentally aware. A pump-or-plug to wheels approach appears to make sense for those who are only interested in dollar cost, or who want to actively promote electric vehicles. (There is no question that electric vehicles are cheaper to run, and they certainly have the potential for being very clean.) Any discussions of well-to-wheels equivalent tend to be contentious, because we generate electricity in so many ways, ranging from very inefficient and dirty… to moderately efficient and moderately clean… to capital intensive (solar, for example) but sparkling clean. What “well” do we use? The DOE does not predict the energy mix to improve at all over the next 2 decades, but at least the potential is there. So a well-to-wheels approach would have to be constantly updated to reflect the “wells” in use, and even then, there is unlikely to be regional agreement. (California electric car promoters like to quote well-to-wheel efficiencies much higher than those for other parts of the country).

So… I favor ditching the MPGe concept altogether. The mc2 gets 11 miles per kilowatt hour. It gets 110 MPG when the batteries are depleted. That’s simple, straightforward, and enables direct comparisons with other vehicles.

Our closest competitor, the Aptera, is rated like the plug-in Priuses (pick a number that sounds good) so a direct comparison is tricky. However if you dig far enough on their website, you will find that they claim a figure of 130 MPG in the battery-depleted mode. That would correspond to about 13 miles per kilowatt hour. The Aptera is substantially heavier than our mc2, wider, and taller… so you may wonder if their figures are a little too high, or ours too conservative. But at least you have a means for comparison, which MPGe (they claim 300, we claim… let’s see… 6000) does not allow.

The math for our 6000 MPG bogus claim is explained on the Gaia Transport website