Confirmed: Chevy Volt 230 mpg claim is bs

I came out very strongly against the bogus claim that the plug-in hybrid vehicle the Chevy Volt gets up to 230 mpg. At the time, I opined that it's high time that people that write such tripe get a basic short course in principles of thermodynamics, especially the conservation of energy principle (energy cannot be created nor destroyed, only transported and converted). I called the claim Enron energy accounting.

I've mentioned this ad infinitum in this blog especially in cases when claims are made that plug-in hybrid vehicles get 100 mpg by methods that would make accountants at Enron proud, like not counting the energy it took to fully charge those battery packs that mostly came from coal. (Another Plug-In Hybrid False Mileage/Energy Savings Claim) In that prior recent post (there are many more) here's how the numbers scam works: let's say you have a car that gets 25 miles to a gallon. You convert it into a hybrid vehicle by installing some electric motors in the wheel hub that are tied to batteries. Let's say those batteries are big enough to get you 25 miles worth of juice. Once it's gone, the engine kicks in. So your 50 mile trip used only 1 gallon of gasoline, and the claim is that you now have a 50 mile per gallon car! Viola! Except that you still only have a 25 mpg car, and that first 25 miles came from electricity derived from mostly likely coal! The efficiency of that process is even worse than if you had just burned gasoline.

What is basically happening with these ratings is that it is being gamed within the confines of the rule book. The energy it took to charge the battery in the first place is either not taken into account, or not accounted for correctly. I wrote about this before with the claim of a doubling of fuel mileage by going plug-in hybrid, but it's worth repeating here. It won't really double the cars mileage. It will just offset some gasoline with coal. Not the best trade-off in my opinion but there it is. Converting a car to hybrid may in fact save 120 million gallons of fuel per day, but that will come at the cost of using a whole lot of coal. Let's do a bit of math. Gasoline weighs 8 lb per gallon and has an energy content of 47 MJ/kg. Coal is at 30 MJ/kg. To get the same amount of electrical energy as that in 120 million gallons of gasoline, it would take about 1,840 million pounds of coal assuming a power plant efficiency of 33%! That is nearly 1 million tons of coal! Extra! That is, beyond what we are using now!

In any case, onto recent news along the above lines. From the Autoblog via Instapundit: Auto X Prize throws water on GM's 230 mpg claim, offers mpge calculator.

With all of the attention being paid to the 230 mpg number that the Chevy Volt will apparently be granted by the EPA, the Automotive X Prize thought it was time to weigh in on the subject of calculating fuel efficiency for vehicles that use energy sources other than gasoline. They don't like it. Instead, the AXP prefers MPGe, a "rigorous and more neutral measure" of fuel efficiency. The AXP's John Shore walked us through how the long-running competition thinks about MPGe. They've been at it for a while.

First, let's define MPGe. MPGe stands for miles per gallon equivalent, and measures fuel economy based on the energy content of a gallon of petroleum-based gasoline. For those who like formulas, the AXP defines MPGe as (miles driven) / [(total energy of all fuels consumed)/(energy of one gallon of gasoline)]). Understanding and using MPGe is important, now more than ever, Shore said, because MPG is no longer particularly useful from the consumer's point of view. "It is obsolete," he said. Shore gave three reasons for moving away from MPG:

1. The growing popularity of gasoline alternatives. When everyone was using gas (or diesel), MPG offered a decent way to compare the efficiency of different vehicles, especially if one drove prudently and understood how the ratings were calculated. But putting, for example, E85 into the tank changes the whole equation.
2. We are now seeing vehicles that can use two power sources, most obviously plug-in hybrids that use electricity and a liquid fuel. MPG really loses its meaning when there is more than one fuel and only looking at the liquid fuel allows PHEV advocates to claim they get 100 or 150 mpg, which is kind of true but also deceptive, Shore said.
3. Lastly, as soon as we introduce plug-in vehicles, the efficiency of the vehicle – no matter how you measure it – becomes a very strong function of how far you drive. This issue is not addressed by MPGe, but should be considered by people who want to understand fuel efficiency better. MPG is MPG no matter how long you drive it for. But a plug in hybrid changes depending how long it's been since the last charge.

I don't quite agree with 1. Miles per gallon gasoline will yield a different number than miles per gallon on E85. But it's still miles per actual gallon. Same with diesel and biodiesel. Furthermore, different blends of gasoline will vary in energy content, if only slightly. There was also this one tidbit that even surprised me:

a vehicle plugged into a 110 V circuit for eight hours gets about the same energy as what is in a third of a gallon of gasoline. Shore was surprised by this, and said that, "This shows why gasoline has remained king. in five minutes, you can put a sh*tload of energy into a car."

I would have thought it would be higher than that by at least a factor of 3. I wonder what they'll do to address this. A 220 V connection? 440 V in paces? A cable as thick as your thigh?

Previously:
Side-splitting headline of the day: GM touts Volt with 230 mpg city rating (by using Enron accounting methods)
Another Plug-In Hybrid False Mileage/Energy Savings Claim
Government report: electric cars won’t reduce carbon emissions and likely create more
UNTRUE! - Enron Accounting on the 100 mpg Hummer H3