Official fuel economy testing for all vehicles is conducted on chassis dynamometers, which are basically treadmills for cars and trucks. One subtlety of chassis dynamometer testing is that vehicle fuel economy measurements using decades-old standard speed profiles may be overly optimistic compared to today’s average on-road fuel use. Official methods exist to adjust the test cycle fuel economy of conventional vehicles to better estimate expected real-world fuel use, but a similar adjustment method has yet to be finalized for PHEVs.
From a National Renewable Energy Lab paper on plug-in hybrid efficiency testing [via Green Car Congress].
The paper by scientists from the NREL and the Idaho National Lab (full PDF here) continues by explaining how even their newly proposed methodology has shortcomings:
The Blended Method…assumes that the increase in gasoline use during CD [charge depleting] mode is the same as the increase calculated for CS [charge sustaining] mode. This works well for blended PHEVs that have lower electric power capabilities for CD mode, and would thus require additional engine power (blended with the electrical power output) for more aggressive driving. The downside of this method is that PHEVs with high electric power capabilities may not need help from the engine and therefore would not use more gasoline in CD mode but would simply deplete their battery energy over a shorter distance. It is also possible that a blended PHEV would actually increase its depletion distance in the event that the vehicle controller commanded the added engine output in CD mode to be high power (to achieve high engine efficiency) and thus prolonged its battery depletion.
Even so, such tradeoffs between CD fuel consumption and depletion distance should somewhat balance out through UF [utility factor] application. For instance, though this Blended Method for applying adjustments may penalize the high electric power PHEV with some excess CD fuel use, the method assumes a longer CD distance than the vehicle actually achieves. This gives it an inflated UF weighting for CD fuel displacement (relative to its CS fuel use). These two factors may roughly balance each other out when calculating the total combined consumption. A similar balance (in the reverse direction) could work out for the longer depletion distance blended PHEV.
It’s worth a read as long as you’re comfortable with this kind of prose. Measuring plug-in efficiency is no picnic…
Here we go again.
Maybe the fuel economy numbers should be displayed in chart form, rather than simply city/highway, almost like a tax table. This way you could select the sort of driving you typically do and see what the annual fuel usage is. It would be nice if the EPA could break it down into several modes (and assume full overnight charging), such as:
100%/0% city/highway mode, 5k/15k/30k miles per year
75%/25% city/highway mode, 5k/15k/30k miles per year
50%/50% city/highway mode, 5k/15k/30k miles per year
25%/75% city/highway mode, 5k/15k/30k miles per year
0%/100% city/highway mode, 5k/15k/30k miles per year
This would give the consumer 15 different consumption rates to compare against other vehicles. The arguments will never end until some useable standards can be worked out.
I am sure there is a mode in which the Volt can get 230 mpg, but it won’t apply to the Volt driven all day on the highway 30k miles a year.
No shit!
GM just never got the hang of the “under promise, over deliver” thing.
It’s possible to drive a Volt in such a way as it never uses gasoline, actually. The problem is that that does not mean that the cost per mile to drive, in terms of fuel costs, is zero. Electricity costs.
Excellent gslippy.
This isn’t complicated. Put a sticker on the car that says how far it will go on electricity, city and highway, and how far on a gallon of gas after the battery is dead, city and highway.
We’ll take it from there. We’re not stupid.
Of course, the catch is, some of those numbers are going to look very mediocre and revealing mediocre numbers is not in GM’s game plan.
What about environmental factors? What’s the range when you’re commuting on a sub-zero day? What is the range on a 110 degree day when the AC and battery cooling systems are in overdrive?
Gslippy and Mcs:
You both forgot to ask about windage, stop/go driving, rush hour driving (lots of standing still with the AC running), and hill driving.
Having driven my Prius now for 5.5 years, I can tell you that these factors impact battery usage greatly. Yes, even the wind has an impact. Good if it’s behind me, bad if it’s hitting me from the front…even with a .26 coefficient of drag.
Yes, you can coast downhill, but if the car doesn’t recharge the batteries through braking, then those uphill climbs are gonna draw a lot of electricity from that battery.
That mustache creeps me out in a 1980’s “Leisure Suit Larry” sort of way. Fritz should make a date with a Gillette Mach 3 razor.
@ZoomZoom:
The only fair assessment of windage is to assume it is zero. Land speed records require the vehicle to travel in two opposite directions to “zero” out the wind factor.
In the the mix I proposed, “city” and “highway” would use the same protocols for city and highway used today, except pro-rated for the blend of driving that the consumer might have. Buyers today already know that if they sit forever in traffic, their efficiency is near zero.
@mcs:
The environmental factors have to be neutralized by testing to STP (standard temperature and pressure), with the assumption that – just like today – extremes will negatively impact efficiency. STP is usually 59 F and sea level.
@KixStart:
Your idea is attractive, except that with cars like the Volt the battery never really goes dead. It is maintained in some mid-range of charge so as to assist the ICE at times, and then recharge regeneratively at other times.
One problem with the Volt is that it is dual fuel – unlike the Prius or Leaf – which makes its annual cost of ownership very difficult to calculate.
gslippy : The environmental factors have to be neutralized by testing to STP
That would work for an ICE engine, but with these vehicles, temperature will be a bigger factor. With an ICE, you’re getting waste heat from the engine to keep the interior warm. With a Volt, the heat will be coming from the battery. What about the battery cooling system when it’s hot. How does that effect the range?
We kick this football around every week. If we could buy one we could post what really happens when it is driven. We cant because GM hasnt figured out how to finish the car and bring it to market. End of story.
couldn’t they just test the volt with the battery at the end of the test at the same charge level as in beginning, basically like a Prius that needs to deliver all it’s electricity from gasoline? that way we would not “green-wash” the mileage with electricity from the plug.
In the end the Volt never will drive on battery anyway. Toyota doesn’t even have an EV and if one company could build one it would be Toyota. In real life, with AC and heating and extreme temperatures the battery won’t perform as good as what they say. The battery will age. I’m not a skeptic and believe the challenges will be overcome. But will the company that can’t even built ICE cars be the one to resolve the problems? Heck, they built cars where the battery is in the crash zone of the car… do we really believe they can handle the all electric car? That Volt is only a pipedream to snow blind congress into giving them money. So far GM has shown us as much of an EV as I did. If they give me one for a road trip through the country I will manually calculate mileage (miles driven over gallons filled in). Maybe i even recharge the battery at every motel and include the kWh used in my calculation (1 kWh = X units CO2 = Y units gasoline). If i need less than 4.2 gallons for every 1000 miles (=230 mpg) I will give Fritz a kiss an apologize for everything I ever said.
Kaleun–
Ever lifted the battery from an old Mercedes Diesel? You’d be thankful if it were placed ahead of the front axle where it ought to be. Mine needed very frequent attention, and to pull that thing was nearly too much for my 140 pound frame.
GM isn’t the only company that puts the “mechanical” part that needs the most attention in the easiest spot to get to. At least they used to, until they started this battery-in-the-bumper nonsense. We have a 2006 Stratus, and it’s in the bumper too.
Nonsense.
@mcs:
There is no doubt that temperature extremes will adversely affect the batteries, both on the consumption side and the capacity side, and that the effect will be much worse for the batteries than for the ICE. I just don’t know how you express that to the average consumer. The wild deviations from average will drive people crazy.
All of this points to my assertion that the Volt will be doomed as much by its actual shortcomings as by the dreaded ‘perception gap’ that Bob Lutz embraces. It will be impossible to close the ‘perception gap’ with the Volt.
Most people paying $40k for the Volt will expect to be getting Windows, but instead they’ll get Linux – OK for a niche audience, but never mainstream.
Kaleun:
couldn’t they just test the volt with the battery at the end of the test at the same charge level as in beginning, basically like a Prius that needs to deliver all it’s electricity from gasoline? that way we would not “green-wash” the mileage with electricity from the plug.
The problem with that is part of the “advantage” to a PHEV is the ability to convert electric power from an outlet into motive power. The cost of per mile is much less than the cost per mile of the most fuel efficient ICE car out there. Why should this advantage not factor into the fuel economy figures?
I say “advantage” because there are several drawbacks to PHEVs that I think greatly outweigh the operational cost per mile.
This topic, and all Volt posts are entirely irrelevant unless GM stays in business long enough to actually produce a Volt.
iNeon: in a good car with good battery you replace the battery every 5-6 years or so. So that is not a big deal… as opposed to the battery being crashed in a crash and acid and DC and all that burning down the car :-) Of course, the Mercedes quality requires frequent repairs. that’s why i as a German drive a Japanese car :-)
Lumbergh21: I mean they could have a mielage for jsut driving on gasoline 9like a hybrid), and one for electric. the problem with the plug-in mileage is, that it will depend on what fraction is plug-in, what is gasoiline. Let’s say the Vold drives 20 miles on battery. If the EPA cycle is 20 miles, the gasoline consumption will be zerao, infinite mileage. If the cycle was 1000 miles, the plug-in would not really matter at all and we might have 30 mpg or so. So the numbers will be gibberish either way and unrealistic.
qslippy,
True, it’s never quite dead but there’s a state that GM calls “customer depletion point” or something similar, and they don’t let the charge go below that. They can use that for “dead.”
Full information allows a customer with 6th grad math skills to model his own use and see how well the car works for him. Or doesn’t.
How about mileage figures that take into account the Volt’s impact on the electric grid? Only about 1% of the electric grid comes from “gren” sources so it’s safe to say dead dinosaurs are going to be powering up the Volt somewhere. Or else the most evil of evil power sources: nuclear. The envirmaniacs rally hate splitting atoms to make energy, especially since it generates so much power, no green house gasses and waste that can actually be contained.
It is even more complex than that.
“City” can mean a million different conditions, short or long urban trips can be 50% different. I get 12 MPG on short trip cold starts but 18 MPG longer urban trips with warm engine.
“Highway” is equally vague, highway 55 MPH on cruise will give you almost TWICE the MPG of 85 MPH on cruise!
Instead of precisely defining the conditions above, like they do in EUROPE (90 kph country roads, 120 KPH highway are two very different numbers there!!!), the EPA does all kinds of VOO DOO so-called “adjustments” and extrapolates MPG from some silly lines that pass along widely dispersed points. I have seen its voluminous report which explains its lower 2008 MPG ratings, and so should you if interested, it is free and on the web, last time I checked.
OK…there’s no such thing as a gallon of electricity. Here’s how they should be measured.
kWh/mile city/hwy
electric range city/hwy
mpg city/hwy
What you’re paying for gas and electricty is your problem. They shouldn’t try to fix a ratio today, in 2009, of the price delta between gas and electricity and then convert that to mpg. This delta varies dramatically in time and location. What you really need to know is how far does your electricity take you, and what your electric range is and then you can make your OWN decisions from there. Of course, this assumes most people aren’t willfully ignorant, which they are. Estimated battery lifespan, degredation rate, temperature constraints, and replacement cost would also be useful in determining operation costs.
Also, we should switch from mpg to gallons/100 mi and, ideally, from miles to km like everywhere else. I traveled around the world for 9 months last year, and believe me- you can get used to metric VERY fast. I remember when I got back home I was even estimating temperature outside in C without even thinking about it. People would look at me crazy!
“carve :
October 1st, 2009 at 12:35 pm
OK…there’s no such thing as a gallon of electricity. Here’s how they should be measured.
kWh/mile city/hwy
electric range city/hwy
mpg city/hwy
What you’re paying for gas and electricty is your problem”
The advantage of the plug-in, that MAY justify its much higher price, is exsactly the VAST difference between gas and the dirt-cheap off-peak electricity you charge overnight.
The Fuel consumption figure should be useful only if it is in $/mile, or miles/$, either one. I am NOT spending stupid KWS or gallons, my wallet has $, and I am not buying the POS plug in with Kws or gallons, but with good old US $s.
The disadvantage of the above, of course, is that prices change every day. Too bad, but you need to estimate two average prices over the life of the vehicle and calc your various fuel costs in real $.
autosavant: That’s a terrible idea. For that to work, you’d have to update the fuel economy figures on a regular basis and provide different figures for every utility zone. You can’t have the volt getting 100 mpg in New York and 500 mpg in Washington state, and then a year later those numbers go to 120 and 575. The amount of energy they use use to go a certain distance will be the same next year as today. Do you complain that current mpg ratings are in mpg and not mp$? If you want them in mp$, should those be in 1979 dollars so you can compare the efficiency of your 5 year old car to the efficiency of a new one?
What the volt does is even worse, converting from mpkwh to mp$ to mpg, and even then the mpg figure is totally dependent on the arbitrary distance of the epa test. It does the standard 11 mile test using gas, and tacks the electric range on top of that assuming the electricity is FREE. So the volt can’t even get the dollar equivelent of 230 mpg. It also doesn’t consdier that you’re paying road taxes with gas but not with electricity. It is a monumuntally flawed and misinformative number.
Just tell us how energy efficient the car is on different energy sources and leave it to the locality and the time to determine the value and cost efficiency.
Just how difficult is it to get a good average MPG if they’ve actually built the car? I mean working out MPG on a car that’s still a giant lump of clay and some sketches on a drawing board is admittedly quite difficult, but GM have actually built the Volt, and if they actually tested it in an everyday situation then surely they’d get the true MPG rating? Does that make sense? Or am I being too logical?
Why so complicated?
Just ask a car company to drive the said car from the Freedom tower to the White House. Back and forth until 100k miles are reached in one year.
Add up all fuel costs (gasoline, premium gasoline, electricity, diesel, ethanol). Divide the total cost by the price of 1 gallon of regular gasoline on the first day of that year. You would have a very reliable and comparable figure.
carve :
I am fully aware of all of your points, and even mentioned some in my original post.
My points are still 100% VALID.
The volt will have ZERO advantage if we only express its fuel consumption in units of ENERGY, this is 100% WORTHLESS, since otherwise the volt would NEVER have been built.
The ADVANTAGE of EVs and Plug-ins is pRECISELY that they use electricity, and in particular DIRT CHEAP electricity in the off-peak overnight hours, that can be, per unit of energy, four or more times LESS expensive than gas.
When you check the fuel ECONOMY (NOT just fuel EFFICIENCY!) of YOUR car, should you just look at yoru MPG? WHO CARES about gallons? I CARE about how many $ I wasted to buy X gallons! SO one SHould ALWAYS also look at MP$ in addition to MPG, and the MP$ is FAR MORE IMPORTANT to your budget.
That’s the whole reason mpg is listed on the sticker- so you can determine operating cost. 18 mpg 10 years ago means something totally different than today, and means somethind different in Japan than in the US, but it is still 18 mpg no matter when and where they are. This is because the context changed. Would you rather the number be fixed at 1979 dollars per $.85/gal 1979 gas? The same 18 mpg car in 1979 would rate at 21.2 miles per dollar, and today it would be 7.2 miles per dollar with NO CHANGES othe than the cost of gas and the value of the dollar. Furthermore, that car will get 18 mpg whether the gas is expensive gas in Japan or cheap gas in Saudi Arabia, but the miles per dollar would be dramatically different.
The dollar changes too much, and the price of electricity and fuel are too variable for this to be a useful, published measure. Remember when diesel was more than gas recently? Could you imagine having to go check the miles per dollar of your car every few days? Just tell us the efficiency, and the energy providers will tell you the price of the fuel.
Of course, the volt is even using miles per dollar since that is entirely dependent on the length of your trip. They’re making it even more confusing.
On top of all that, to truly be miles per dollar, you’d have to consider the insurance, operations, and maintenance cost of your car. What you really need to know to make comparissons is a car’s energy efficiency and the cost of that energy FOR YOU. A blanket label for this will be correct for almost NOBODY.
It’s really, really simple. Three rules:
————-
1. If You Have More Than One Distinct Drive Mode, You Get More Than One Sticker.
2. Everything That’s On One Sticker Goes On The Other(s).
3. All Units Of Fuel Consumption Should Be Presented In Terms Of The Fuel(s) Actually Used, With “Consumption” Relative To The Moment The User First Acquires The Fuel(s).
————-
So, if you normally would have a sticker that says “30mpg city/36 mpg hwy/500 miles per tank”, and you make that into a series-style plug-in hybrid, you now have two stickers: one that says “30mpg city/36 mpg hwy/500 miles per tank”, and one that says “200 Wh/mi city/260 Wh/mi hwy/40 miles per charge” (with the Wh/mi being wall to wheels, not pack to wheels)
I don’t see why anyone would possibly want any other kind of measurement. Why wouldn’t you want all the info from one sticker for each distinct drive modes your vehicle has? Why wouldn’t you want your units in terms of when you acquire the fuel (I.e., wall-to-wheel energy efficiency instead of pack-to-wheel energy efficiency)? How could you possibly make an informed decision with everything lumped together into a contrived “mpg” rating that has no reflection on how you’ll actually drive the car?