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(JavaScript must be enabled to view this email address) April 8, 2009 8 Comments

Are the Benefits of Plug-In Hybrids Overstated?

Plug-in hybrids get better gas mileage than most other cars on the road, but the results vary all over the map. Google used professional drivers and designated routes to goose mileage. The DOE got about half that

When it comes to plug-in hybrids, your mileage will vary. All over the place.

Look at Google's highly touted, seven-week test of converted plug-in hybrid electric Priuses. The results showed that the cars were able to achieve an average of 93.5 miles per gallon. "The plug-ins did great, getting as much as 93 MPG average across all trips, and 115 MPG for city trips!" boasts Google.org on its Website.

That's good and fits in with the 100-mile-per-gallon standard often associated with the cars. But a close look at how Google did the tests, and it became apparent the tests don't reflect real-life.

Google hired five professional fleet drivers from a local shuttle service and had them drive on designated city and highway routes mostly located in flat Silicon Valley and under mild weather. Each trip was designed to allow the tester to complete it with power from a fully charged battery pack  (Google said some trips used up the entire battery before they ended).

Google also instructed drivers to accelerate moderately, tough it claimed it didn't otherwise teach the drivers tricks for getting the best mileage.

The Department of Energy conducted its own tests in a more hoi polloi fashion and got about half that.

As major carmakers get ready to launch mass-produced plug-in hybrids over the next few years, everyone from government agencies, private car fleet owners, utilities and researchers are carrying out more road tests to gauge just how good of a fuel economy could you expect from a plug-in hybrid. The plug-in hybrid passenger cars that can be seen on the road today are regular hybrids – mostly the Prius or Ford Escape – that have been outfitted with an extra battery pack and a cord for charging via a standard electrical outlet.

There are no national testing rules for determining a plug-in hybrid's fuel economy. The U.S. Environmental Protection Agency is still working on that. In the mean time, the U.S. Department of Energy's Advanced Vehicle Testing Activities program has been conducting a series of field tests in controlled and real-life settings with 12 models – mostly Prius and Escape – in 20 states and Canada.

The DOE started testing of plug-in hybrid cars in partnership with private and public fleet owners in 2006, and some of the recent results showed that drivers in real-world conditions were achieving an average of 51 miles per gallon when the same cars could yield more than 100 miles per gallon in controlled or lab settings (see baseline testing results and accelerated testing results of a Prius converted by Hymotion).

What happened? For one thing, those drivers were just going about their own business instead of traveling only on designated routes in more ideal weather conditions. The tests were done in different types of terrains, and the results included mileage data from when the cars' battery packs were in use and after they were depleted. And those battery packs were not necessary fully charged before each trip.

The tests involved not only fleet drivers but also consumers. The program partnered with UC Davis a year ago to launch a test involving about 70 members of the American Automobile Association in California, said James Francfort, a staff engineer for the DOE program at the Idaho National Laboratory. Most of the drivers didn't start taking their Hymotion Priuses on the road until last fall.

The DOE also has carried out controlled tests that use selected drivers who travel on designated roads. The Hymotion Prius has shown to achieve an average of 79.5 miles per gallon. 

Interestingly, Google – before it hired chauffeurs – was getting similar results in its plug-ins. Some got 66 miles per gallon.

Driving behavior, climate and road conditions all influenced the outcome, Francfort said. Electric cars are far more efficient at using its fuel than gasoline-powered cars. That means poor driving habits could have a greater impact on the fuel economy of an electric car, Francfort said (see page 18 of Francfort's presentation).

An electric motor can make use about 75 percent of the energy while an internal combustion engine can achieve about 20 percent efficiency, according to a DOE Website, Fueleconomy.gov.

Accelerating quickly is a major no-no for getting better fuel economy. When you speed up quickly, it requires a burst of energy that takes more battery juice. Cranking up the air conditioning also will lower the fuel economy. So will conquering steep hills. (Dave Hermance, the deceased Toyota exec who helped develop the second generation Prius, came up with some of the feathering techniques for increasing mileage.)

"But probably the single issue is: Have batteries been charged?" Francfort said. It isn't just about charging the battery in full before each day's use. "It may also be a lack of access to a place to charge, or of time due to job requirements."

Battery technologies matter, of course. The cars used in the program are converted plug-in hybrids, and the lithium-ion batteries are more experimental, said Tim Murphy, manager of the DOE program.

"You can educate people about how to get the best performance out of the car," Murphy said. "As batteries become better over time, they are going to handle more harsh driving, and we are going to start seeing better average performances."

A regular Prius can achieve a combined city/highway mileage of 46 miles per gallon, Toyota said. Companies that offer covert kits, such as Hymotion (owned by battery maker A123 Systems) and Hybrid Plus, often tout their plug-in hybrids as being able to achieve more than 100 miles per gallon.

Those companies, as with automakers, also are quick to note that the actual mileage could vary based on the driving style, the weather and other factors.

That said, it doesn't hurt to create a tip sheet to train consumers to get the most of fuel savings from their plug-in hybrids, especially when companies such as General Motors plan to start selling them within two years.

That's what the folks at the DOE program are doing as part of its public outreach effort, Francfort said. He expects to complete the tip sheet in about two months.

Comments [8]

  • mike shurlteff 04/8/09 7:02 AM

    Ms. Wang,

    It is EXTREMELY important to differential between the two main types of Plug-Ins:

    1. Plug-in Parallel/Series HEVs, like the modified Prius.
    The Prius parallel/series technology is now over 10 years old.  Batteries did not support the deep-depth-of-discharge cycle life and electric motors were not small, light weight enough to build a series HEV.  The design is a compromise that’s no longer necessary.

    2. Plug-in SERIES ONLY HEVs (also called Extended-Range Electric Vehicles, E-REVs or Range-Extended Electric Vehicles, REEVs)
    Examples are the Aptera Type 1h (2010), GM Volt (2010), Fisker Karma (2009) & Karma S (2010), and Trinity XH-150 (two prototype SUVs).
    These are essentially Battery Electric Vehicles (BEVs) with a small Range Extending Generator, the best of both worlds.  They can operate at freeway speeds and under hard acceleration without using any fuel during their all-electric range: 120 miles, 40 miles, 50 miles, 50 miles, and 40 miles respectively for the E-REVs mentioned above.  E-REVs have two additional advantages: 
    (a) The generator is run at a single speed so it can be better optimized for efficiency (a turbine or fuel-cell can be used).
    (b) The superior battery (mostly next generation Li Ion) can be charged faster allowing for greatly improved regenerative braking.
    Some numbers on mileage:
    Aptera Typ-2 :  120 miles all-electric, 130 mpg in hybrid mode after that.  (Kicks ass.)
    120 miles no gas used all-electric
    250 miles 1 gallon gas used 250 mpg total
    380 miles 2 gallons gas used 190 mpg total
    510 miles 3 gallons gas used 170 mpg total
    GM Volt :  40 miles all-electric, 50 mpg in hybrid mode after that.
    40 miles no gas used all-electric
    90 miles 1 gallon gas used 90 mpg total
    140 miles 2 gallons gas used 70 mpg total
    190 miles 3 gallons gas used 63 mpg total
    Trinity XH-150 :  40 miles all-electric, 50 mpg? in hybrid mode after that.  (Same as Volt?)
    40 miles no gas used all-electric
    90 miles 1 gallon gas used 90 mpg total
    140 miles 2 gallons gas used 70 mpg total
    190 miles 3 gallons gas used 63 mpg total
    This does not even begin to show the efficiency most USA drivers will see from E-REVs, since 78% of USA drivers travel less than 40 miles per day.  I drive 18 miles to work, 36 miles per day.  I won?t need any gasoline to do this in any of the E-REVs mentioned above and it won?t be long before I?m charging at work.  I?ll purchase my own electrical meter and reimburse my employer.  (This is why I haven?t modified my Prius, but will be purchasing an E-REV in the future!) 
    Here is another example of actual fuel savings with :
    http://www.evworld.com/news.cfm?newsid=18280  AFS Trinity ? XH-150 Plug-in Hybrid (E-REV) - May 2008
    ?AFS Trinity Demonstrates XH-150 Plug-in Hybrid to California Official?
    ?SYNOPSIS: In a typical 340 mile week of driving, barely two gallons of fuel will be consumed, resulting in 170 miles per gallon.?
    This 170 mpg total is the week average mileage achieved by an average family!
    ?in an SUV E-REV!!!

    Mileage claims may be overstated for Parallel/Series HEVs like the modified Prius,
    BUT this has caused actual mileage improvements from E-REVs (that are just around the corner) to be ignored or disbelieved.

    (I don?t think much of yellow journalism.  I expect you to be critical, but please make more of an effort to give equal play to the positive side of these new technologies.  We already have big oil and stick in the mud conservatives for the negative side.)

    Reply
  • mike shurlteff 04/8/09 7:03 AM

    Ms. Wang,

    It is EXTREMELY important to differential between the two main types of Plug-Ins:

    1. Plug-in Parallel/Series HEVs, like the modified Prius.
    The Prius parallel/series technology is now over 10 years old.  Batteries did not support the deep-depth-of-discharge cycle life and electric motors were not small, light weight enough to build a series HEV.  The design is a compromise that’s no longer necessary.

    2. Plug-in SERIES ONLY HEVs (also called Extended-Range Electric Vehicles, E-REVs or Range-Extended Electric Vehicles, REEVs)
    Examples are the Aptera Type 1h (2010), GM Volt (2010), Fisker Karma (2009) & Karma S (2010), and Trinity XH-150 (two prototype SUVs).
    These are essentially Battery Electric Vehicles (BEVs) with a small Range Extending Generator, the best of both worlds.  They can operate at freeway speeds and under hard acceleration without using any fuel during their all-electric range: 120 miles, 40 miles, 50 miles, 50 miles, and 40 miles respectively for the E-REVs mentioned above.  E-REVs have two additional advantages: 
    (a) The generator is run at a single speed so it can be better optimized for efficiency (a turbine or fuel-cell can be used).
    (b) The superior battery (mostly next generation Li Ion) can be charged faster allowing for greatly improved regenerative braking.
    Some numbers on mileage:
    Aptera Typ-2 :  120 miles all-electric, 130 mpg in hybrid mode after that.  (Kicks ass.)
    120 miles no gas used all-electric
    250 miles 1 gallon gas used 250 mpg total
    380 miles 2 gallons gas used 190 mpg total
    510 miles 3 gallons gas used 170 mpg total
    GM Volt :  40 miles all-electric, 50 mpg in hybrid mode after that.
    40 miles no gas used all-electric
    90 miles 1 gallon gas used 90 mpg total
    140 miles 2 gallons gas used 70 mpg total
    190 miles 3 gallons gas used 63 mpg total
    Trinity XH-150 :  40 miles all-electric, 50 mpg? in hybrid mode after that.  (Same as Volt?)
    40 miles no gas used all-electric
    90 miles 1 gallon gas used 90 mpg total
    140 miles 2 gallons gas used 70 mpg total
    190 miles 3 gallons gas used 63 mpg total
    This does not even begin to show the efficiency most USA drivers will see from E-REVs, since 78% of USA drivers travel less than 40 miles per day.  I drive 18 miles to work, 36 miles per day.  I won?t need any gasoline to do this in any of the E-REVs mentioned above and it won?t be long before I?m charging at work.  I?ll purchase my own electrical meter and reimburse my employer.  (This is why I haven?t modified my Prius, but will be purchasing an E-REV in the future!) 
    Here is another example of actual fuel savings with :
    http://www.evworld.com/news.cfm?newsid=18280  AFS Trinity ? XH-150 Plug-in Hybrid (E-REV) - May 2008
    ?AFS Trinity Demonstrates XH-150 Plug-in Hybrid to California Official?
    ?SYNOPSIS: In a typical 340 mile week of driving, barely two gallons of fuel will be consumed, resulting in 170 miles per gallon.?
    This 170 mpg total is the week average mileage achieved by an average family!
    ?in an SUV E-REV!!!

    Mileage claims may be overstated for Parallel/Series HEVs like the modified Prius,
    BUT this has caused actual mileage improvements from E-REVs (that are just around the corner) to be ignored or disbelieved.

    (I don?t think much of yellow journalism.  I expect you to be critical, but please make more of an effort to give equal play to the positive side of these new technologies.  We already have big oil and stick in the mud conservatives for the negative side.)

    Reply
  • mike shurlteff 04/8/09 7:06 AM

    Sorry for the double post.
    I had this formatted way better if you want me to email to you then let me know and give me a direct email.

     Reply
  • Gerrett S 04/8/09 10:43 AM

    MDS,  I’m a stick in the mud conservative and I was going to post essentially the same thing you did about Parallel vs. series.  IMHO series hybrids really are the next logical progression.  I own a prius and I get fine MPG, but you can put whatever size battery in there you want and it will still run on gas when you go higher in speed or accelerate somewhat swiftly. 

    With something like the Fisker or Volt, the gas engine WON’T turn on until you deplete the battery to a certain level.  To me, that makes the most sense.  I am happy to accept that I’ll need gas to go long distance but if I’ve got a short commute I don’t want my gas engine to turn on. 

    Ms. Wang, I’d be interested in finding out exactly how many miles “real world” can be traveled with series hybrids (once they are out for review) vs. what the manufacturers claim.  We have enough Liberal Hippy vaporware advocates out there spewing misinformation it’s good to get the facts.

     Reply
  • marisa blumenthal 04/8/09 11:31 AM

    We definitely need to create a positive halo effect around PHEVs with the appropriate govt incentives and individual interest. We cannot wait till their performance meets a bar such as 100 MPG. Otherwise we will be stuck with this chicken and egg problem where people will not buy electric cars since they can only be charged at home and cities and businesses will not invest in charging facilities since there are not enough people with electric cars

    Reply
  • Ucilia Wang 04/8/09 2:08 PM

    Knowing the difference between a parallel and series hybrid just means you know how your PHEV works. What mileage you’ll get still depends largely on how and where you drive. The issue here is how realistic are the mpg claims. Average consumers aren’t likely to spend the time diving into technical details under the hood. But they will note quickly the mpg on the sticker and believe that they should be able to get close to that fuel economy, even if carmakers caution that “actual mileage may vary.” The EPA hasn’t set the rules for determining PHEVs’ fuel economy yet, so who knows what the mpg claims will be when series hybrids appear in showrooms. 

    Reply
  • Carl Hage 04/8/09 11:36 AM

    In the article, “But a close look at how Google did the tests, and it became apparent the tests don’t reflect real-life.” I did a close look (I’m not with Google but have a plain Prius and live near Google.) Actually, there are really 2 parts to the Google experiment—statistics from real-use (Silicon Valley knurds probably with non-agressive driving), and also a controlled experiment. Professional drivers were used to make a controlled comparison on a course with a route based on the highway survey (that measures total distances but not speed/wait profiles). This experiment is vastly better than the DOEs test cycle (I read that too), which is extremely unrealistic, but is reasonable to compare non-hybrid cars. The EPA test cycles are pretty far off reality for any Prius owner who understands how the gas/electric switching occurs.

    One of the complicating factors for the parallel hybrid Prius is that the gas engine turns on to accelerate, then (sometimes) turns off to sustain the y tweaking the gas pedal. All Prius owners seemed to have figured out how to do it. Adding the electric/economy/sport selector to the Prius was a good idea. A better test would have been to train the drivers on the tweaking and standardize acceleration to be “typical”. The real-life measurements of the PHEV seem disappointing, however.

    Winter driving really lowers the mileage because turning on the heater causes the gas engine to turn on. Also, driving short trips really lowers mileage because the engine always turns on at the start of the trip and stays on to heat up the catalytic converter. These factors will lower the Ironically, I get >60mpg on highway 101 during stop and go traffic (which I try to avoid).

    The current Prius plug-ins also seem to be at a disadvantage compared to a new design from Toyota. My understanding is that the Li battery is hotwired into the NiMh battery signals, and the car operates the same as if it were on the original battery. The NiMh battery can only supply the electric motor at half power (the other half comes from the motor-generator), put a 2 battery plug-in could theoretically supply full power, and could also capture more braking energy. Also, with more electric-only acceleration the gas engine could stay off more often. Perhaps even short low speed trips to the grocery store, etc. could be done on all electric instead of all-gasoline (to heat the emission control).

     Reply
  • Michael E. Russell 04/9/09 9:48 AM

    So what you’re saying is that hybrids aren’t really going to get 100 mpg, only 66 mpg. Damn Liars! That’s not good fuel economy, my 1998 Caviler gets 25 mpg, and isn’t even electric.

    Reply

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