[Patrick]

Originally Posted by NeilBlanchard

I think these results speak for themselves! The electric cars are in general, giving much better efficiency,

That's apparently true, however, electrics are given about a 3-to-1 advantage over gas cars in the MPGe formula because it's not a well-to-wheels calculation. Here's an explanation of it from this blog http://autoxprize.typepad.com/axp/20...ing-mpge.html:

I hope the X-prize team makes the correction to the MPGe calculation as soon as possible. The DOE approach is a reasonable choice, as already pointed out by others. The rationale:

1) The current calculation is fundamentally incorrect since it assumes electricity generation at 100% efficiency.

2) It does not reflect a fair comparison of technology or vehicle. Suppose you have an electric car with battery as power source. The electricity is generated by an efficient (say 35%)gas-powered generator sitting in the car. You can measure this car's mpg directly. And you can also measure the electricity generated in Kwh and calculate the MPGe. The correct calculation will give the same result.

Let put some numbers here. Suppose 1 gallon of gas generates enough electricity to run 50 miles. Direct mpg=50 mile/gallon.

1 gallon of gas =116,090 BTU. At 35% efficiency, the electricity generated would be 116,090 BTU*35%/3.412BTU/Wh =11908 Wh.
Therefore, e=11908 Wh/50 mile =238 Wh/mile
MPGe=EG/(e*EW)=116090/(238*3.412)=143 mile/gallon. Now you see the problem with this calculation. You boost the fuel efficiency by 2.87 times simply by a calculation mistake.

Posted by: Hengning Wu


and:

The plug-to-wheels (PTW) standard gives a misleading view of the energy used by competing cars, and can not provide a fair method for comparing efficiency. Is it better to burn 500 pounds of coal at the power plant to fuel your electric car, or 10 pounds of gasoline to fuel your gas-powered car?

Wait… those figures can’t be right can they? No, they are not, but the only way we can know that is by measuring from well-to-wheels. If we measure only from plug-to-wheels then we are saying it doesn’t matter whether electricity is created by burning whales or by using photovoltaic cells. We’re saying we don’t care.

About a decade ago, advocates for electric cars were calculating MPGe of 59 for the GM EV1 (http://www.radix.net/~futurev/pwrplnt.pdf). Now, the Tesla, a less efficient vehicle, is portrayed (in your chart) as being nearly twice as efficient as the EV1. (Even the relatively old tech Toyota RAV4 and Nissan Altra also get figures over 100 MPGe despite the fact that both consume more energy than the EV1.) The difference is that the Tesla is measured PTW (which does not account for the energy source) whereas the EV1 was measured well-to-wheels (WTW), which does account for the energy source. The WTW concept has long been used by environmentalists, engineers, scientists, and even enlightened automobile manufacturers interested in the full lifecycle costs of their products.

Given the goals of this competition, I think we should encourage people to think about where energy comes from. If all the cars in the competition flop in the marketplace but we at least get people to think about energy, the environment, and security, we will have accomplished something worthwhile. The PTW standard is counter to that principal, because it treats electricity and hydrogen (which are energy carriers, rather than energy sources) as simply showing up at the plug (or nozzle) with no resource, environmental, or security cost.

The MPGe concept is good (at least for the American market), but the PTW implementation, in which resource consumption is ignored, is not. If, instead, it is implemented in WTW fashion, then we can realistically look at the environmental and resource depletion costs of various vehicle approaches. Because old vehicles like the Nissan Altra and Toyota RAV4 ostensibly already get more than 100 MPGe, the PTW approach makes this competition seem largely irrelevant (we’re already over 100 MPGe) and gives support to the status quo. The PTW alternative (and similar thinking) also leads to the kind of confusion currently seen in the automotive world.

What confusion? Well, when the Automotive X Prize was first announced, claims of 100+ MPG fuel efficiency were rare (except from crackpots who think fuel needs to be treated magnetically or pre-vaporized). Now however, such claims are common. Plug-in Prius conversions have been advertised at 100 MPG, 200 MPG and 300 MPG. There’s a guy that claims to be able to get 100 MPG from a converted 5000 lb ‘59Lincoln! There’s a plug-in Saturn Vue conversion being advertised at 150 MPG. Even the Tesla is being advertised at 135 MPG equivalent, despite its being 600 lb heavier than the 23 MPG Lotus from which it was derived. Former CIA director Jim Woolsey claims that 500 MPG is possible in a mid-sized car! (NY Sun: The 500-MPG Car: : A Pipeline Dream, or Full of Hot Air?)

These high MPG and MPGe figures seem implausible, don’t they? Some are technically correct, if you read the fine print, or thoroughly quiz the promoter. For example, the 500 MPG car of Jim Woolsey’s dreams runs on e85, which is 15% gasoline and 85% ethanol. It is also a plug-in hybrid. So it is technically correct that very little gasoline is used, because the vast majority of energy gets to the car in the form of ethanol and electricity. But, while technically correct, the spin is extremely misleading. The energy required to move this midsized car down the road comes from three sources, and two of these sources do not show up in the accounting!

The proposed PTW standard is only slightly less misleading than Woolsey’s spin, because it fails to consider the energy source. Electricity and hydrogen are both energy carriers, not energy sources. This is explained in these links, one to an article aimed primarily at kids. (http://www.cecarf.org/Programs/Fuels...sCarriers.html
EIA Energy Kids - Hydrogen)
If kids can understand this, then there is probably no need to dumb things down for the American public.

Favoring the WTW concept is not unique to obsessive engineering and scientific types. As the DOE says, in the Federal Register: June 12, 2000 (Volume 65, Number 113):

"When comparing gasoline vehicles with electric vehicles, it is
essential to consider the efficiency of the respective ``upstream''
processes in the two fuel cycles. A full description of the differences
in the processes is beyond the scope of this rulemaking, but the
critical difference is that a gasoline vehicle burns its fuel on-board
the vehicle, and an electric vehicle burns its fuel (the majority of
electricity in the U.S. is generated at fossil fuel burning
powerplants) off-board the vehicle. In both cases, the burning of fuels
to produce work is the least efficient step of the respective energy
cycles."

"Therefore, the PEF includes a term for expressing the relative
energy efficiency of the full energy cycles of gasoline and
electricity. This term, the gasoline-equivalent energy content of
electricity factor, abbreviated as Eg, is defined as:

Eg = gasoline-equivalent energy content of electricity =
(Tg * Tt * C) Tp
where:
Tg = U.S. average fossil-fuel electricity generation
efficiency = 0.328
Tt = U.S. average electricity transmission efficiency =
0.924
Tp = Petroleum refining and distribution efficiency = 0.830
C = Watt-hours of energy per gallon of gasoline conversion factor =
33,705 Wh/gal
Eg = (0.328 * 0.924 * 33705)/0.830 = 12,307 Wh/gal"

Using the DOE approach, the Tesla, which uses 245 Wh per mile, (based on their new claim of 220 miles per 53.9 kWh charge) would get 50 MPGe. That is an impressive doubling in efficiency over the much lighter Lotus equivalent. It also falls in line with the 59 MPGe of the more efficient EV1.

The hard work of determining upstream efficiencies has already been done, and numbers are given in the GREET charts used for the CO2 threshold calculations. If WTW makes sense for CO2 calculations, how can it not make sense for MPGe calculations? If the GREET figures are trusted for CO2 emissions, then they must be trusted for MPGe calculations.

PTW is counter to the goals of the X Prize competition. WTW supports those goals.

Posted by: Ken Fry