PLUG OK license plate
Union of Concerned Scientists engineer tries our PHEV
Jun 5, 2006 (From the CalCars-News archive)
This posting originally appeared at CalCars-News, our newsletter of breaking CalCars and plug-in hybrid news. View the original posting here.
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We've been watching the evolution of the Union of Concerned Scientists' attitudes toward PHEVs. Their excellent Hybrid Center resource, is positive: in their "matrix" of different kinds of hybrids at­hybrid-center-how-hybrid-cars-work-under-the-hood.html, 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 somewhere­owners/­bill-nye-plugin.html.

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.­my_weblog/­2006/­05/­test_spin_in_a_.html mirrored at­article.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 at­faq.html

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, at­x1.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. At­ACP_Archive.htm#anchor6166689

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."]

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