The problem with calculating an “effective” MPG figure for the electric consumption is worse than the EPA city cycle; you have an even bigger problem picking a yardstick to use and justifying your choice.  Coal, NG, nuclear, hydro and wind energy are fungible at the car but yield wildly different numbers in the calculation.  The solution is to create an appropriate metric.  Measurements of all-electric range are a sine qua non, and separate measures of city and highway fuel economy in charge-sustaining mode (perhaps with cycles at different speeds) would also help a great deal.

Thank you for your comments. A few quick responses:

According to this article by Martin LaMonica, the 25KWH/100 mile figure was in fact from GM and based on the new EPA draft methodology. However, GM has not offered any useful detailed information on their calculation, at least not that I was able to find. What were your sources for your alternative explanation?

1) The main point of my article was that MPG is a faulty metric for calculating the Volt’s fuel economy. I believe you agree with that.

2) California’s electricity prices are not “much more expensive than the rest of the country.” According to the latest EIA data, CA ranks 12th among the states for most expensive power; most of New England, Alaska and Hawaii pay higher prices.

3) Time of use pricing is not offered by all utilities. I would like to see the source on which you base your claim that it would cut the price to 5 cents/kWh.

4) I would like to know how you arrive at the conclusion that 20 cents/kWh is unrealistic. I have studied coal, natural gas, and nuclear power in depth, as well as their various peaking profiles, and I have based my estimates on that study. Depending on how you draw the boundaries for cost analysis, the cost of new nuclear power is already over 20 cents/kWh. One recent analysis that supports this statement is “Business Risks and Costs of New Nuclear Power” by Craig A. Severance (January 2, 2009), in which he concludes “Generation costs/kWh for new nuclear (including fuel & O&M but not distribution to customers) are likely to be from 25 – 30 cents/kWh.” (According to the paper, Severance is co-author of The Economics of Nuclear and Coal Power (Praeger 1976), and former Assistant to the Chairman and to Commerce Counsel, Iowa State Commerce Commission. His practice is in Grand Junction, CO.)

–C

ErEVs like the Volt will be cheaper over their whole lifecycle when they get up to large production volumes, and achieve the same kinds of economies of scale available to infernal engine vehicles. That might be somewhere around 5-7 years from now, as a wild guess. My blog provides further details.

The Volt does indeed use about 20% as much gasoline as the Prius, and 10% as much as the average US vehicle on the road.

The Tesla is badly represented by a 132MPGe figure – that’s way too low, when you consider how inefficiently gasoline is actually used. I can understand why Tesla would be frustrated: they were too conservative in their calculations, and now they kind’ve stuck with a figure that understates how good the Tesla is, especially in comparison with an ErEV like the Volt.

MPG in particular, and efficiency calculations in general, aren’t easy.

I don’t think this is the way GM is approaching it. The 25KWH/100 mile figure is just their figure for wall to wheels electricity consumption – it’s not really part of the MPG calculation.

Also, I don’t think they’re using the 51 mile approach – I believe that was someone’s guess.

Instead, they used a detailed model of how a large number of drivers use their vehicles: the number of short drives, the number of longer ones, etc. What they’re doing boils down to saying that over a full year of driving, a Volt driver will use 1 gallon for every 230 miles.

A good way of thinking of it is that they project that on average the average driver will use electricity for 180 of every 230 miles, and 1 gallon of gas for the other 50.

A few other thoughts:

1) This does not include electricity – it’s just miles per gallon of fuel, for better or worse. If you feel that we have plenty of electricity, but a shortage of oil, then you may be comfortable with that. If you feel that ErEVs like the Volt will actually support low-CO2 wind by providing night demand and load buffering, then that would also help you feel comfortable with that. Otherwise, perhaps not.

1) California’s electricity is much more expensive than the rest of the country. The 11.5 cents/KWH nationa average figure includes tiered rates like those of CA.

2) If electricity costs are significant to the driver, they can always go to time-of-day pricing: all utilities are required to offer smart meters now. This should cut the cost to roughly 5 cents/KWH.

3) Anything over 20 cents/KWH is probably unrealistic, any time soon. Even Stern’s $80/ton pricing for CO2 wouldn’t begin to do that, and wind is much cheaper than that. The US really does have enough coal for whatever we’ll need, for better or worse (coal will, I think, face peak demand far before peak supply). The same appears to be true for Natural Gas. Even nuclear won’t go over 20 cents.