Computing MPGe for Electric Hybrids

As Dan Reicher (Director, Climate Change and Energy Initiatives, Google.org) summarized in testimony early this year to the Senate Finance Committee, many people see energy efficiency as the 

“fastest, cheapest and cleanest opportunity to address our energy challenges….Duke Energy CEO James Rogers has termed energy efficiency our ‘fifth fuel’ and energy efficiency guru Amory Lovins measures it in ‘Negawatts’.”

In a nutshell, that’s why a main AXP figure of merit is miles-per-gallon equivalent (MPGe), a measure that expresses fuel economy in terms of the energy content of a gallon of petroleum-based gasoline. 

Basically we ask: how much energy was delivered to the vehicle, and how far did it go? We convert the energy to the number of gallons of gasoline containing equivalent energy, and we express the result as miles per gallon. 

Different fuels have different pros-and-cons, but in all cases it’s valuable to increase efficiency (increase MPGe), which conserves energy. This is even true, for example, if the fuel is electricity generated from alternative energy sources. Alternative energy is not infinite energy. Increasing electric vehicle efficiency will result in more energy available for other purposes. 

MPGe is an attractive figure of merit because it’s a direct measure of overall “pump-to-wheels” efficiency, because it’s technology-neutral, and because it relates nicely to consumer intuition – i.e., it reduces to the familiar MPG if the fuel is in fact gasoline. 

MPGe is also attractive because it applies if a vehicle is powered by more than one fuel, such as plug-in hybrid electric vehicles (PHEVs), which typically use electricity plus a liquid fuel (often, but not necessarily, gasoline). Here’s how to compute MPGe for this important case: 

MPGe = EG / (g*EF + e*EW)

where 

m = miles per gallon of liquid fuel used (MPG)

g = 1/m = gallons of liquid fuel used per mile (GPM)

e = plug-to-wheels electrical energy used per mile (Wh/mi)

EF = BTU per gallon of liquid fuel used (not necessarily gasoline)

EG = BTU per gallon of gasoline = 116,090

EW = BTU per Watt-hour (Wh) of electricity = 3.412

The formula above can also be used for pure battery electric vehicles (BEVs) and for pure liquid fuel vehicle – for BEVs, set g =0, and for pure liquid fuel vehicles, set e = 0. 

Informal published values for BEV and PHEV fuel economy abound, but they can be inadvertently misleading. For example, some results report gasoline usage but not electricity usage (electricity usage is harder to measure). Also, not all results are well-documented, so accurate comparisons can be difficult. 

One problem in applying the MPGe conversion formula above is that by definition MPGe is “pump/plug to wheels”, whereas the electricity usage (Wh/mi) data reported may be battery-to-wheels, which ignores the conversion loss that results from charging the battery via an AC (grid-connected) outlet. It’s not always obvious from test results whether or not the Wh/mi are measured from the plug or from the battery. 

Bearing these issues in mind, I have computed MPGe for some real examples based on published data. I include example results below. You can see the details and other examples in the spreadsheet available here, which can also be used to explore additional examples. To account for cases where the Wh/mi measurement is battery-to-wheels, the spreadsheet includes an option for applying a plug-to-battery conversion factor. 

Of the PHEV results, the main thing that stands out is that the Google.org data yield a significantly lower MPGe than other test data. This likely reflects the fact that the Google.org data are collected from actual daily driving by multiple drivers, whereas the other data are from fixed test cycles. Also noteworthy is the significant variation in the MPGe results from fixed test cycles, even for the same PHEV conversion tested over a similar range. 

Overall, the results reflect a basic underlying problem – the difficulty of establishing test procedures that are not only well-documented and repeatable, but that reliably predict the fuel economy that consumers would experience. Indeed, that’s why DOE and EPA are intensively developing next-generation test procedures. 

I welcome comments on these examples as well as pointers to other well-documented data. If appropriate, I will republish the spreadsheet and this blog post (note that the table below includes a publication date). Here are the examples:

 

Vehicle	Type of Test	Source	Range (miles)	Miles-per-gallon of Gasoline used (MPG)	Plug-to-Wheels electricity used (Wh/mi)	MPGe
Prius PHEV conversion	Real-world driving	Google.org Recharge-IT (1/11/2008)	N.A.	66.2	110.6	54.5
Prius PHEV Conversion (Energy CS)	UDDS Charge-Depleting	DOE ANL	50	212	160.3	106
Prius PHEV Conversion (Energy CS)	UDDS Charge-Depleting (California Mode)	DOE ANL	90	113.9	86	88.4
Prius PHEV Conversion (Hymotion)	UDDS	DOE INL	100	83.7	35.8	76.9
Prius PHEV Conversion (Hymotion)	HWVET	DOE INL	100	67.4	39.2	62.5
Prius PHEV Conversion (Energy CS)	UDDS	DOE INL	100	89.2	56.5	77.7
Prius PHEV Conversion (Energy CS)	HWVET	DOE INL	100	75.2	59.3	66.5
Tesla Roadster EV	EPA Recharge	Tesla	245	0	310	109.8
2000 Nissan Altra EV (Li-Ion)	EPA Recharge	DOE	129	0	276.5	123.1
2003 Toyota RAV-4 EV (NiMH)	EPA Recharge	DOE	136	0	301.5	112.8

 

[Table Date: 30 January, 2008]

Comments

[Zane Selvans]

It is interesting to note that that the additional fuel savings (in actual gallons) for increases in fuel efficiency beyond say, 50 MPGe, is close to negligible, when compared to the amount of fuel that can be saved by simply upgrading the most inefficient vehicles. For instance, one saves more fuel by going from 13 to 17 MPG, than by going from 50 to 500 MPG. For 1000 miles of driving, the transition from 13 to 17 MPG saves 21.368 gallons. For the same distance, the transition from 50 to 500 MPG saves only 18.1 gallons.

If the ultimate goal of high efficiency vehicles is to reduce global warming gas emissions, and our dependence on foreign fossil fuels, we would do better to focus on improving the efficiency of the worst vehicles, not the best.

Unfortunately, that's more a cultural and political problem than it is a technology problem, which means it's hard for a few people to really change things by themselves.

[John Shore]

For a graph and discussion about the diminishing returns of increasing fuel economy, see the FAQ "Why 100 MPGe, why not reward greater fuel economy?" on page 27 of the Automotive X PRIZE Draft Guidelines (http://auto.xprize.org/files/downloads/auto/AXP_Draft_Competition_Guidelines_20070402.pdf).

[Ken Fry]

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! (http://www.calcars.org/calcars-news/111.html)

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/SourcesCarriers.html
http://www.eia.doe.gov/kids/energyfacts/sources/IntermediateHydrogen.html)
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.

[E.Gonzalez]

If anyone thinks that squeezing utilizable electrical energy from the ambient air is at all possible,please review uspto publication number (20070089918),Titled "Power Sysyem for electric land vehicles" and let me know if you're interested.I'm looking for the right people to partner up with.

[Jim Bullis]

Electricity might better be thought of as a means of transferring energy than as a form of energy. It is a means of transferring kinetic energy from the rotating shaft of one machine into kinetic energy of a rotating shaft of another machine. It could be thought of as a complicated drive train from an engine to the wheels of the car. Like the drive shaft, electricity is not energy by itself. If the generators stop turning, the electricity no longer exists.

Using the MPGe comparison is valid if correctly done. However, by proceeding as if energy quantities can be compared simply because they can be stated in the same units is a serious error.

In a nutshell, the following line from the lead article here posted is not a correct statement:

"BTU per Watt-hour (Wh) of electricity = 3.412"

Rewriting for absolute clarity:

One BTU of heat energy per one Wh of electric energy = 3.412

By algebra, this is to say:
One BTU of heat energy = 3.412 Wh of electric energy.

For this to be true, it has to work both ways. It is true that 3.412 Wh of electric energy will easily produce one BTU of heat energy. It is absolutely not true that one BTU of heat energy will produce 3.412 Wh of electric energy.

The equation fails (big time) because of the Second Law of Thermodynamics. Please see Sears, Mechanics,Heat and Sound, Addison-Wesley, 1950 for the clearest explanation I know of for thermodynamic laws of physics.

It is a serious error because it leads to incorrect decisions that could lead to great harm to the environment.

Perhaps there is confusion with small energy losses in energy transfer and the far greater energy losses in heat engines that are our primary means of generating electricity. Yes, that includes nuclear.

The idea of the magnitude of the losses can be accurately calculated as shown at http://www.miastrada.com/analyses where EIA data for 2005 is the basis for actual efficiency results.

At http://www.miastrada.com/references, there is a link to a paper that might help to understand how the power generating capacity would be used to provide for the added load that electric vehicle operation would represent.

To get a really clear idea of how badly this could all turn out, see http://fastlane.gmblogs.com/PDF/presentation-sm.pdf
At least these people at GM understand that electricity is only a medium of transfer of energy. On page 12 the whole outcome is made clear, where GM just sees the electric vehicle as a means to transfer more energy to transportation. Under this plan, we would see continuation of massive vehicles having no particular concern for real efficiency.

[Hengning Wu]

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.

[Hengning Wu]

There are many misleading fuel efficiency numbers by companies and individuals. For example, just look at the numbers at Wikipedia for electric vehicles.

But if someone claims 500 miles per gallon, that does not mean it is not possible. It is certainly not a typical car. Another unit may be more useful, passenger-mile per gallon. As a rule of thumb, passsenger-mile per gallon numbers are:

25 (typical cars, bus, and subway);
~100 (cars at full capacity);
~200 (better cars at full capacity);
~500 (optimized train at full capacity and low speed; optimized electric bike, optimized motorcycle).

[Jim Bullis]

RE the post by Ken Fry,
In case I was not clear on this, I have no objection to the well to wheel approach. It is just harder to get good data that way. Whereas if you start at the point of combustion, then mileage can be per BTU of heat. Then there is some rational accounting for the heat engine effect at the power plant. While I make the argument that most of the electricity that will be produced in response to the added load of electric cars will be from coal, I would not be against using the national fossil fuel average mix (35% thermal efficiency in 2005). This can be fairly easily calculated from solid national data as shown at http://www.miastrada.com/analyses

The data basis references of these calculations is the actual CO2 emitted for respective fuels, so the emission data can also be immediately calculated.

It does not account for mining and railroad transportation for coal or for similar costs for well to combustion point for gasoline, but the really significant thermal losses of electric power production are at least represented.

[Rolf M. Landaas]

What amaze me, is the complexity of the global projects when it comes to alternative energy production.

We started up with a military project initiated by the loss of personnel transporting what-ever-needs to the front lines and came up with a solution that takes the fuel out of the vehicles.
After a few years we have a simple of-the-shelf solution that benefits with no need for fossil fuel and no pollution what so ever.

The the sideeffect became obvious, like producing 10 kW electricity while being parked, used for whatever need there is.

So what started with a project based on the HMMWW and M113 APC, ended up as a possible solution for the electricity need for San Francisco with a disaster contingency plan, presented to Google and their RE

So we initially developed a of-the-shelf system for cars that produced the power with no fuel and no pollution and ended up with a powerplant with no fuel or pollution - every 20 MW module being approx 12 by 6 by 3 meters - we can even use it for propulsion on ships that is one of the major providers of CO2 and all we did was window shopping.

As we see it the technology is available, we just need to find the solutions, and apparently we did.

Is the reason for lack of commercial progress the gap between the focus of the tech masterminds and the need of the public?

Reg.
Rolf M.

[Jason Jungreis]

I think X Prize should resolve the MPGe issue by requiring gasoline as the fuel and completely ignoring stored electrical energy; i.e., you may not start the test with any on-board electricity. Equivalences for non-gasoline fuels are readily calculable, and removing the variable of electrical storage means that designers will have to focus on the true variables of efficient architecture. I certainly believe that electrical propulsion is the most efficient drivetrain and so I trust that all vehicles will be hybrids. In the alternative, I would propose that the electrical storage must assume an efficiency of 10,000 WH/gallon, which is about 33% efficiency in conversion of gasoline energy to electrical energy and what you can expect from a really good electrical generator.

[Craig Henderson]

The current auto x-prze rules do tend to favor electric drive with the current calculations for energy used and the limited range 200 miles for mainstreem and 100 miles for alternate class. I understand the reason for this is that electric cars with the current technology do have limited range and the X-prize wants to include as many teams as possible and let the market decide.
As a contestant I would like to see diffrent catagories for all electric and cars that you can mesure liquid or gasseious fuels and calculate btu difrences between the fuels ( all we need is more $$ from our sponcer "Progressive" )

Having been in three fuel economy contest in the past and actualy winning one at 103.7 mpg on deisel I know it will be very difficult for the contest to explaine that one car gets over 100mpg on fossel fuel and one car get over 100mpge on battery.

No matter what the final rules are, the Auto X-Prize goals are still being acomplished. I just wish I had been on the rules advisery board, I could always use an extra 10 million.

Craig Henderson
Guiness world record fuel economy 1986 at 103.7

[m rushton]

I believe we are all here to get to a common goal! The most universal and easily explainable unit to the public would be something like CO2/km or CO2/mile. Co2 being in the form of ppm. Or even CO2(units ppm)/100km.
In the end we are trying to reduce CO2. and perhaps the we can use the amount of CO2 in a Litre(gallon) of gas or the CO2 in a KWh of electricity.
If we go with a "dirty"coal type plant for electricity generation , then that could be the standard.If we source our electricity from renewables , then we can obviously acheive an even better result whereby the biggest inefficiencies will be transmission losses from the grid and battery/motor losses.
This is where a carbon tax applied to energy would be also more universal, and that is how we can get to where we want to go. Of course we need a value for CO2 (world carbon market) to calculate the costs!

[Nick G]

I think the current rule is much better than the DOE standard, for two reasons:

First, most EV charging will be done at night, which will preferentially use wind and nuclear power, which are low carbon. In fact, EV's will create demand for night time power, which will solve a big problem for wind (which generates more at night than during the day).

2nd, oil BTU's are much scarcer and more expensive than thermal BTU's (nuclear, coal and gas), so the current rule reflects economics.

[Don]

A lot has been said about hybrids. Can I expand on this a little?

A hybrid electric vehicle is a vehicle which combines a conventional propulsion system with an on-board rechargeable energy storage system (RESS) to achieve better fuel economy than a conventional vehicle without being hampered by range from a charging unit like a battery electric vehicle (BEV), which uses vibratior batteries charged by an external source. The different propulsion power systems may have common subsystems or components.

Regular HEVs most commonly use an internal combustion engine (ICE) in tandem with electric motors to power their propulsion system. Modern mass-produced HEVs prolong the charge on their batteries by capturing kinetic energy via regenerative braking, and some HEVs can use the combustion engine to generate electricity by spinning an electrical generator (often a motor-generator) to either recharge the battery or directly feed power to an electric motor that drives the vehicle. Many HEVs reduce idle emissions by shutting down the ICE at idle and restarting it when needed. An HEV's engine is smaller and may be run at various speeds, providing more efficiency.

HEVs became widely available to the public in the late 1990s with the introduction of the Honda Insight and Toyota Prius. HEVs are viewed by some automakers as a core segment of the future automotive market.An article for the July-August 2007 issue of THE FUTURIST magazine titled "Energy Diversity as a Business Imperative" included plug-in hybrid vehicles. GM vice president for environment and energy Elizabeth Lowery is quoted as saying, "Today, we are embracing multiple energy sources because there is no single answer available for the mass market.

[Lloyd Weaver]

The rules correctly reflect the economics and needs of America today. Indeed, when it comes to cents a mile, the 103.9-mpg diesel would cost 490 cents/gal/103.9 mpg or 4.7 cents a mile. But considering the short life of a diesel car including high repair costs, recycling and landfill costs, depreciation etc., it costs over 50 cents a mile to own that vehicle.

Whereas, a maximally efficient EV at 110 Wh/M at the national average 10.3 cents/kWh cost 10.3x110/1000 = 1.133 cents per mile. Since they are long-range valuable technology, all-electric vehicles will be composite made with a million-mile life at a minimum. Thus, all things considered including periodic lead-acid battery replacement (also 100% recyclable, even the acid makes liquid fertilizer) and capital payoff and the fact they will always be maximally efficient vehicle aerodynamically, an EV has a total cost per mile of about 6 cents (battery replacement is under 2 cents/mile if lead-acid). My friend thinks his SUV is costing him well over 55 cents a mile, but that was with gas at $3.50/gallon.

Further, all-electric EV’s will be charged at night, and given the average commute is 32 miles round trip, charged over a 10 hour period and considering we have 1 million of MW installed, 100 million EV’s (142 million people commute somehow US) would utilize a mere 2.8% of the national grid at night.

For example, in Maine, where we have no oil and no extra biomass beyond paper manufacturing, it’s been proposed we install 5000 MW in offshore wind farms. To service our 300,000 commuters daily with that electricity, and charging at night when little is needed, we would need only 20% of this capacity over a 10-hour period to recharge the 300,000 if maximally efficient all-electric EV's (hybrids are only about 1/4 as efficient PTW as designed now).

Also, we must not be concerned about road repair funded with gas taxes. This will become a thing of the past soon enough. Congress will tap the general fund etc. to pay for road repairs or whatever they have to do. They are just as interested in how we wean ourselves off oil and save money in commuting as the rest of us. We have to change to domestic energy sources. For commuting to work and getting family transportation costs under control, EV’s win hands down and is the right thing to do, environmentally, best use of capital, and probably in every other way you can think of as well.

In summary, the contest is correctly designed as to measurement and should not be changed. We are trying to get off oil and reduce emissions and supply family commuting vehicles that are universal in the fuel it can use (available to all of us with a simple plug), plus save families money. We do them no favor arguing WTW or PTW, or indirectly or directly promoting oil for commuting. PTW in this instance is a best measure overall.

[Car Loans]

Interesting article. Any idea on where I can get more information on this?

[Jim Bullis]

Looking carefully at the Google Rechargeit web site that you reference in your table, it becomes clear that the 66.2 MPG result reported by Google is determined from the amount of gasoline needed to run the cars where electric power is also used. As far as understanding car efficiency is concerned, this number is gibberish since the electric energy provided is not represented in this calculation.

They demonstrate how nonsensical such numbers are on their FAQ page.

[Jim Bullis]

Supplementing my previous, here I paste the Google calculations:

Why does mileage vary so much between vehicles and between trips?
The Google fleet includes hundreds of drivers who take out the plug-ins under a variety of driving conditions. On some trips, drivers have recorded over 100 miles per gallon, while on other trips, drivers have recorded much lower mileage. Often, low mileage is due to driver error (i.e. plug-in hybrid system switched off or failure to recharge the night before).

Some examples:

124 mpg, 18.9 mile trip – High mileage on a combined City/Highway trip with significant EV-only driving
79.5 mpg, 11.0 mile trip – Good mileage on trip with some city, some freeway driving
42.2 mpg, 49.1 mile trip – Poor mileage due to failure to recharge the night before
32.7 mpg, 2.6 mile trip – Very low mileage due to plug-in hybrid system accidentally switched off (battery stays at 100% SOC)
(Note: mileages shown are estimates with accuracy of approximately +- 10%, based on fuel usage data reported by the vehicle computer)

Notice that they have dropped all pretense of MPGE, rather the E is dropped so that the mileage is truly miles per gallon. The fact that this is misleadingly incomplete is not quite in the same category as a knowingly made false statement.

[Ken Fry]

Perhaps I have misread the intent of the Progressive Automotive X Prize. If it is simply to promote electric cars and to pretend that electric cars are charged by clean sources, then the current rules are fine. Before taking money from competitors though, that should be made clear: it would be silly to enter a highly-efficient diesel in a electric car contest.

The current rules give electric cars an unfair advantage because the energy for electricity must come from somewhere (coal mainly, some natural gas, some oil, some nuclear, some hydro, and tiny amounts of everything else) but that "somewhere" is completely absent from the accounting.

By well-to-wheel measures, (the standard for many years among environmentalists and engineers) a Tesla gets about 50mpge. The Lotus equivalent of the Tesla gets slightly less than half that, 23 mpg. Cleary the Tesla is the better bet, on a well-to-wheels basis: it's environmentally more sound, even though it generates CO2 at the power plant. (Well-to-wheels can tell you that; PTW cannot.) Any rational buyer would buy the Tesla, based on operating cost, CO2 generation, or resource depletion (ignoring its staggering purchase cost, of course).

So why give electric vehicles an ADDITIONAL 2:1 advantage in the competition by going with plug-to-wheels? To squelch creativity? To ensure that a plug-in hybrid can't compete? To ensure that a highly efficient diesel can't compete? To ensure that a diesel-hydraulic hybrid can't compete? Plug-to-wheels is not a valid way to measure efficiency in engineering, environmental, security, or resource depletion terms.

Is an overweight, boxy RAV4 EV more efficient than a 200 pound motor scooter or Honda Insight? On what planet? Where does electricity fall from trees? US tax payers have paid millions for the GREET numbers - why not use them?

[HID Light]

What a nice car! Thanks for information.

[HID kit]

Before taking money from competitors though, that should be made clear: it would be silly to enter a highly-efficient diesel in a electric car contest.

[HID lights kit]

wow this is some great info! mpg as a measurement can be very misleading.

[Lead Acid Battery]

Yeah i'd love to find more information on this aswell. It's a very interesting subject.

[truck rental]

I guess it is ok to calculate only the efficiency of the electric car, disregarding the electricity source. I mean- there is only so much we can solve all at once! I am a strong believer in electric energy and in producing it by turbines and solar energy.