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427Union of Concerned Scientists engineer tries our PHEV

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  • Felix Kramer
    Jun 4 11:29 PM
      We've been watching the evolution of the Union of Concerned
      Scientists' attitudes toward PHEVs. Their excellent Hybrid Center
      resource, <http://www.hybridcenter.org> is positive: in their
      "matrix" of different kinds of hybrids at
      PHEVs come out looking best on all counts. Yet at the same time,
      their February '06 feature with popular science media personality
      Bill Nye mystifyingly perpetuated the attitude that plugging in is
      somehow bad and inconvenient, and implied that his hybrid's "own
      electrical system" somehow generates power from somewhere

      Progress since then: when we were in Washington DC, we gave one of
      UCS's engineers took a test drive, and following is his report at the
      Hybrid Center's blog, as well as several responses.

      mirrored at <http://www.workingforchange.com/article.cfm?ItemID=20900>
      Test spin in a plugin Prius

      Last Tuesday I got the chance to briefly drive the California Cars
      Initiative's Prius plug-in hybrid, converted by EnergyCS/EDrive.
      Unfortunately, I only had about three minutes behind the wheel, and
      about another three minutes riding in the back, but I did get a basic
      feel for it.

      Overall, it drove more or less like a normal Prius. I felt that it
      was a bit slower off the line when I really stepped on the gas,
      though CalCars founder Felix Kramer assured me this was only because
      we were lugging the weight of four people. The car seemed much
      happier to stay in electric-only mode compared to the Prii I've
      driven in the past. In the past, I've been driving in hotter weather
      with the AC running, which may help explain this difference, though
      the larger battery probably helps. In this case, it seemed that the
      gasoline engine might not have come on at all if I hadn't stepped on
      the gas pretty hard a couple of times. On our admittedly short trip
      around downtown DC we averaged over 100 miles per gallon of gasoline,
      although this does not account for the energy or emissions associated
      with charging the battery.

      The car uses a lithium-ion battery pack stored underneath the rear
      floor. In the stock Prius, there is a storage area in this space, but
      it seems to hold the battery nicely. The biggest problem with the
      battery pack is that it makes it impossible to get to the spare tire,
      but Kramer told me that the next generation of conversions from
      EnergyCS/EDrive would have a more compact battery pack that would
      allow access to the spare. There is no word yet on battery life, but
      they are aware that it may be shorter than in the stock Prius, due to
      their charging and discharging the battery more severely. The
      electricity supply for the car comes from a standard 120V outlet,
      meaning it can be plugged in just about anywhere.

      The plug-in Prius uses a custom battery management computer with the
      stock engine management computer. It also has a nifty gauge installed
      on the dash that shows how close you are to engaging the gasoline
      engine (unlike the stock Prius, which tells you whether the engine is
      on, but does not give you any way of knowing when it is about to
      engage). This feature will help the truly dedicated driver to keep
      his car in electric-only mode as much as possible.

      In sum, the conversion seems to be done pretty well, requiring only
      the sacrifice of a little bit of storage space. We'll have to wait
      and see what reliability is like, especially with respect to the
      battery pack. And finally, although it delivered good MPG numbers
      with respect to gasoline, we do not know what the efficiency is like
      with respect to the charging and discharging of the battery.
      Hopefully, CalCars will publicize charge histories for their
      vehicles, so we can evaluate not only the gallons of gas, but also
      the number of kilowatt-hours that have gone into them.

      Posted by: Don

      You can make a guess at the amount of kWh needed for this plug-in
      hybrid (PHEV) from info on the EDrive FAQ page at

      They say that the conversion was designed for 50 miles of
      electrically boosted range; they also say that up to 6.4 kWh of the
      nominal 9kWh capacity of the battery pack may be used. Assuming that
      these two figures refer to the same set of driving conditions (which
      is probably conservative, since it takes no account of regenerative
      braking), in 50 miles of fully boosted driving with a nominal 100 MPG
      indicated, you'd use half a gallon of gasoline and 6.4 kWh of
      wall-plug electricity. With an ordinary Prius at 50 MPG, you'd use a
      whole gallon of gas and no utility electricity (since it can't be plugged in).

      Converting these two quantities of energy into equivalent units is a
      bit tricky. One way is to use a figure from the DOE's Energy
      Information Administration that says there are 33.7 kWh in a gallon
      of gasoline; using this figure, the EDrive Prius PHEV uses the
      equivalent of less than a fifth of a gallon of gasoline to replace
      the "other" half-gallon of gasoline that would be used by the
      ordinary Prius. With this conversion, at
      <http://www.wrightspeed.com/x1.html> the Wrightspeed X1, an insane
      electric supercar that can skin any production car (short of a
      million-dollar, 1000 HP Bugatti) in a drag race, is said to have a
      fuel economy equivalent to 170 MPG in city driving at 0.2 kWh per mile.

      However, this comparison is biased in favor of electricity. A
      gasoline drivetrain (including that in a non-plug-in hybrid) wastes
      an enormous amount of energy in the car itself, whereas an electric
      drivetrain doesn't; however, a significant amount of energy is lost
      "upstream" from the car in generating and transporting the
      electricity. To be fair to the gasoline car, you should include this
      as part of the energy use of the plug-in vehicle. At

      AC Propulsion (who made the electric motor of the Wrightspeed X1)
      compares their slightly less insane supercar, the tzero (which can
      still take out a Ferrari or a Porsche in a drag race, but by a less
      embarrassing margin than the X1) with a Ferrari Maranello and a Honda
      Insight. Accounting for the "upstream" losses in electrical
      generation, they arrive at a conversion factor of 10.2 kWh per gallon
      of gasoline and thus quote a fuel economy equivalent of 56 MPH (same
      as the Insight hybrid!) for 0.18 kWh per mile power use in mixed
      driving. Using this conversion factor, the electricity used by the
      EDrive Prius is equivalent to a little over half a gallon of
      gasoline; accounting for the "upstream" energy waste in gasoline
      refining (about 10%, if I'm not mistaken), I think it's fair to say
      that the EDrive Prius uses the equivalent of about half a gallon of
      gasoline in "primary energy" (say, natural gas) to displace half a
      gallon of gasoline in the ordinary Prius.

      So are PHEVs a wash? I would say certainly not, for two main reasons
      now and one more in the future. First, electrical generation at a
      powerplant is cleaner than gasoline use in a car, and it gets cleaner
      over time as utility generating plants are upgraded, while a gasoline
      car gets dirtier over time as calibrations drift, catalysts age, etc.
      The California Air Resources Board calculated that a battery EV would
      be 95% cleaner over its lifetime in terms of smog-forming emissions
      than even the cleanest 2002 cars, including PZEV hybrids like the
      Prius; a PHEV, which still uses some gasoline, would also be cleaner
      than a non-plug-in hybrid, though not twenty times as clean! Second,
      almost none of that "half gallon" of electricity comes from oil;
      shifting half our transportation fuel use from oil to resources for
      which we don't have as much import dependency would be a good thing
      in its own right, and over time more and more of it could be shifted
      to renewable energy sources without a hiccup. (Try putting ethanol or
      biomethane in a non-plug-in Prius and see how it reacts...)

      And finally, looking toward the hoped-for future, please remember
      that the EDrive Prius is a retrofit, done by a "garage" startup.
      EDrive was limited by design choices that Toyota made for its
      non-plug-in Prius; if the major automakers can be persuaded (or
      coerced--I'm _tired_ of waiting, dammit!) to stop bad-mouthing the
      plug long enough to design factory PHEVs, they can avoid those
      compromises, put in a larger electric motor to take more of the load
      off the gasoline engine, put in more batteries for a longer
      all-electric range and higher all-electric speed, and so on, and so
      on. The fact that the first prototype of a retrofit kit, like the
      EDrive, equals the energy efficiency of the highly refined, second
      generation Prius (even ignoring the advantages of the non-petroleum
      nature of half that energy) surely bodes well for factory PHEVs in
      the future. UCS should throw its weight behind PHEVs wholeheartedly!
      --Posted by: altfuels | May 25, 2006 at 12:16 PM

      Forgot to mention--that "half gallon" of electricity will cost you
      about a quarter if you charge up overnight with a time-of-use rate;
      it's free if you have solar panels on your roof. Compare that with a
      buck and half for the half-gallon of gas--and going up...
      -- Posted by: altfuels | May 25, 2006 at 12:58 PM

      [After a quick once-over, EnergyCS's Greg Hansen wrote me,, "6.4kWh
      is the DC energy used.. You'd probably want to tack on another 10%
      for the battery losses and another 10% for the charger losses... so
      maybe closer to 7.5kWh AC from the wall.. Your mileage may vary."]

      -- -- -- -- -- -- -- -- -- -- -- --
      Felix Kramer fkramer@...
      Founder California Cars Initiative
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