Consumer Reports Questions Plug-In Practicality

January 7, 2009

That Bible for smart shoppers, Consumer Reports—whose new-car reliability ratings are hugely influential—took a leap into the future in its February issue. It tested a Toyota Prius that had been converted to a plug-in hybrid, using the Hymotion L5 conversion kit sold by A123 Systems of Watertown, Massachusetts.

Did the no-nonsense, grimly methodical magazine give the plug-in a thumbs-up? As usual, the testers focused on the numbers. While Hymotion claims its kit can return up to 100 miles per gallon, CR’s Auto Test Center in East Haddam, Connecticut, logged just 67 mpg—against the 42 mpg they recorded in a stock Prius. “At almost $11,000,” the magazine noted, “the plug-in conversion clearly won’t save consumers money overall”—though they deigned to declare the plug-in technology “viable.”

The lengthy payback period is one of a handful of criticisms emerging against plug-ins, even as the 2010 production launches of the Chevrolet Volt and Toyota Prius Plug-In draw closer. While the lithium ion batteries used in that Hymotion kit hold the most energy for their size and weight, they’re also the most expensive.

Not all of the dozen or more plug-in converters use lithium cells. A conversion by 3Prong Power in Berkeley, California, for instance, uses old-fashioned lead-acid cells. They weigh more, and give an electric range of only 10 miles, but at a price of $6,700, that may be enough for local users who can recharge between short trips. As research now underway at Carnegie-Mellon University points out, correctly sizing a plug-in battery (which directly affects its cost) depends greatly on how the car will be used.

Environmental Payback

A second criticism is that in certain cases, converting a Prius to run on grid power may actually result in greater emissions of carbon dioxide (CO2) than running it exclusively on gasoline. The question was studied intensively for North America in a landmark study done by a partnership between the Electric Power Research Institute, a utility trade group, and the Natural Resources Defense Council. The study found that plug-ins emitted less CO2 on a “wells to wheels” basis than a conventional hybrid in most, but not all, cases.

Where the local power grid was fairly clean—in California, say, or hydro-heavy Washington—the plug-in clearly wins. But, in states with coal-fired grids—the two worst are North Dakota and Wyoming—the plug-in actually emits more CO2 per mile than a conventional hybrid.

A recent working paper from Duke University agrees that the local grid makeup determines whether hybrids or plug-ins have a lower carbon impact. But it also notes that plug-ins will likely cost far more than conventional hybrids for years to come—which will keep adoption rates low unless substantial tax incentives are maintained, or a carbon “price signal” is instituted. And it concludes that plug-ins become cost-effective only when gasoline hits $6 a gallon.

With credible and established conventional hybrid lines, Toyota and Honda have stressed these concerns in questioning the various benefits of plug-ins. General Motors, whose own hybrid efforts started later and sold far fewer units, has placed its green bets on the Volt, along with a Saturn Vue Plug-in Hybrid with a 10-mile electric range slated for 2011. As always, the market will be the ultimate arbiter.


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  • Paul Beerkens

    One of the points to take in account for the CO2 emission is that you move a lot of the pollution from the car to the power plant. So if you want to reduce co2 emission you now have to look at only a couple of hundred power plants compared to millions of cars.

  • Bryce

    It’s true, aftermarket conversions will never really be cost effective. Factory produced ones are much more economical for the consumer….plus, they come with atleast a $7500 tax credit. (and thats just federal….I would expect some more stuff from various states like New York, Washington, and California)

  • Rich

    For most plug-in and regular Hybrid owners, the break-even and Pay-Back comes on the first day they drive right by a long line of cars trying to buy gas that’s in short supply.

  • Ross Nicholson

    CO2 is not a pollutant, it is a recycled gas that plants turn back into oxygen and sugar. Less than 1/2 of 1% of the atmosphere is CO2. Higher CO2 levels increase rice yields.

  • GR

    True, the break-even point may be at $6 a gallon, but when gas shot up to $4 a gallon last summer hybrids were in short supply. We can’t wait again gas to shoot up to a point to where we NEED hybrids and plug-in hybrids. We have to start adopting them now. It won’t be long till gas prices go back up again.

  • RKRB

    The Consumer Reports test raises a question about GM’s decision to stake so much of its future on an expensive plug-in like the Volt. If the benefits of the plug-in are as controversial as the magazine’s test indicates it may not benefit GM’s image much, and if the batteries are expensive, GM may not make a profit, either.

  • Bryce

    Well given that the Volt will costs 25k-30k with tax credits and that it uses no fuel or gets 100+ mpg, and being similarly priced to sedans like the TOyota Camry and NIssan Altima that get about 35mpg, that sounds like a better buy to me. Even the Prius, though base priced at 23k, never sells for that ammount. People have to deal with dealer markups and options that they want making the vehicle 27k-30k itself. Volt wins mathematically. Better fuel economy, same price.

  • RKRB

    Yes, if GM can sell the tax-subsidized Volt at a price matching the Camry and Altima (or the marked-up Prius), there is little doubt the Volt would be the better buy, by far. But … at that price, if they can make a profit that brings the company out of the red, it will be a minor miracle.

  • Bryce

    Well, there is a difference between economic profits and normal profits. Normal profits, where cost = revenues is perfectly acceptable to a company. The only reason companies aim for economic profits is because they can pay shareholders and bonuses for emplyees…….and of course simply….a bit more money. However, speaking in a strictly sustainability point of view, normal profit is perfectly fine, especially for something experimental like this, and givn tax incentives provided by big bad government, it makes it economical to the consumer as well. A win-win for all. : )

  • RKRB

    I hope GM (and Ford) can pull it off. You’re right — everyone could benefit. As long as the shareholders and the UAW don’t get too greedy (although that seems like saying Mid East Peace is possible if we could just get the Israelis and Palestinians to start liking each other).

  • Bryce

    well, the shareholders oddly enough may represent the Palestinians becuase they kinda of don’t have control anymore. Their stocks are largely valueless and they have been thrown to the wayside and are recieving no dividends for the forseeable future whereas the UAW holds the cards to the next move. Let it not be forgotten that on the eve of compromise for the bailout, it was stubbroness on the part of the UAW that derailed it all, and they still are sticking to their guns…….or in this analogy…..their warplanes and tanks….I suppose….

    Not to deride Israel at all……if people had been shooting rockets at me for years……I would have killed them all in year one.

  • Zero X Owner

    Because the metric Consumer Reports (CR) used is hard bounded at the top at 99.9 mpg and when on all electric it really gets infinite mpg, mpg is a completely meaningless metric for either CS or EPA to use for any vehicle with electric drive capability. The mpg results are wrong no matter what you do. What Consumer Reports needs to do is to use the not so new correct EPA efficiency metric of number of kilowatt hours per 100 miles (# kWh / 100 miles), with the gasoline use portion simply translated by formula to that metric, using the energy content in the gasoline. EPA is in the middle of doing those translations for all old pure gasser vehicles back to 1991, keeping in mind that retail gasoline currently contains 10% ethanol, which has less energy and that diesel has more energy. Once done with all the math, they will publicly post the results. Consumer Reports can THEN compare their newly calculated findings on a plug in Prius on a # kWh / 100 miles basis to the posted EPA certified results for a regular non-plug-in Prius, on a # kWh / 100 miles basis. For comparison, a standard Tesla Roadster (not the Sport version) is EPA certified at 28 kWh / 100 miles and my Zero X (kitted) electric motorcycle uses 2 kWh / 100 miles, real world average. The lower that metric number is, the more efficient the vehicle. My motorcycle is thus 14 times more efficient than a standard Tesla Roadster (and cost less than $8,000).

    Remember, the official EPA metric is now # kWh / 100 miles, for pure gassers and hybrids too and that the lower the number, the more efficient the vehicle.

  • Zero X Owner

    Even if Consumer Reports does retest the PHEV, using the same method, but with the new (after 1995) efficiency metric, the results will tell us everything about the test driver’s driving and nothing about the difference between the plug in hybrid efficiency ( # kWh / 100 miles) versus the EPA certified and real world average (which requires many vehicles over thousands of miles for more than one year, to approach an unbiaased result). At the very least, Consumer Reports would have to put the PHEV modified Prius through an EPA test cycle with EPA certification at the end before publishing the results. When did Consumer Reports become so unscientific?

  • kengrubb

    We all breath the same air, so ultimately the overall net benefit from PHEVs will be enjoyed by all. California (#1) and Washington (#2) have the highest per capita sales of hybrids. It therefore stands to reason that PHEV sales will likely be highest in those two states.

    As emissions move from the tailpipe to the smokestack (or hopefully dam, PV farm, wind farm, et al.) it’s a whole lot easier to monitor and reduce emissions from hundreds of coal plants as opposed to millions of cars–many of which likely aren’t being maintained as well as they should be and thus probably aren’t as clean burning as they were the day they left the factory.

    A little basic deductive reasoning, and PHEVs only make sense–just as soon as the car makers can start producing them safely and reliably. Concluding PHEVs don’t work because the aftermarket conversions are expensive sounds like the kind of argument one would expect from the petroleum industry, not CU.

  • Dave ROhm

    I don’t get it. When they claim 100 mpg, are they claiming total miles driven on a full battery charge plus gas. And are they ignoring the kWh energy use of the batteries?

  • Zero X Owner

    @ Dave:

    Who knows? Any mpg claim for any vehicle that uses any amount of electric drive is pure gibberish. EPA needs to get off their lazy hind ends and report # kWh / 100 miles for ALL (inlcuding pure gassers) vehicles back to at least 1991. Once you have that information you can:

    1. Compare all vehicles’ efficiencies directly, apples to apples.
    2. Figure out some economics of vehicles based on efficiency (say, using a efficiency weighted car price of (# kWh / 100 miles) * (vehicle cost). where a smaller number is better. On this basis a Prius (1.875 M) beats a Jetta TDI (2.450 M) beats a Tesla Roadster (2.500 M). Note that Tesla is right in the cream of the crop, though, as they all crush a 2009 Yukon Denali XL (15.354 M), which costs as much as 2 Priuses and is 3 times less efficient.
    3. Compare energy sources by price. Currently, electric drive wins hugely as electricty is a cheaper price per kWh than gasoline and much, much more efficient.

  • Bryce

    That probably wouldn’t go over well with Joe Blow Car buyer. Remember we still use horsepower to determine the power of the car when Newtons would really be a better form….or maybe KJ….but we don’t. Things may stay in mpg form for a long time….if not indefinetly.

  • tapra1

    They weigh more, and give an electric range of only 10 miles, but at a price of $6,700, that may be enough for local users who can recharge between short trips. As research now underway at Carnegie-Mellon University points out,Best Cloud Hosting