Taking the Prius Beyond 100 MPG

For Prius owners in California who want to take fuel economy to a new level, a Bay Area company called OEMtek may have the answer. The Milpitas-based company is one of the growing number of companies offering plug-in conversion services. OEMtek will outfit a Prius with a bigger battery pack and potentially double its mileage—to more than 100 miles per gallon—for a cost of $12,500. The company claims the enhancement will give the Prius up to 30 miles of all-electric driving,. “There are people who want this right now, no matter what,” said Cindi Choi, vice president of business development of the six-employee company.

OEMtek’s conversion process is dubbed “BREEZ” (or battery-range extender EZ). The change involves installing a 200-pound pack of lithium-phosphate batteries with six times greater energy storage than the Prius’s original battery pack. That original battery system remains intact and unaltered, along with the vehicle’s existing software system. The batteries come from Texas-based Valence Technology. After the conversion, Toyota will not honor the original buyer agreement and void its factory warranty.

With more than one million Priuses already on American roadways, and an additional million annual global sales expected in the next few years, the plug-in conversion market could grow from a cottage industry to substantial proportions. OEMtek is planning to do about 100 conversions per month by the end of 2008.

More Hybrid News...

  • vinayababu

    A positive news for the PHEV lovers, but the pertinent point is reliability of the battery pack. The Lithium-phoshate version and all modified Li variants under development need extensive tests that may reuire years. Even Toyota is hesitating to come first without making doubly sure about the safety factor with such a new battery pack. Any failure or a single accident will cause irreparable damage to the confidence of the people.

  • David

    Vinayababu, Do you think that Toyota is worried about the safety more than the factory ability to manufacture the packs in mass quantities? I was under the impression that Toyota is upscaling their operations to make the amount of lithium batteries needed for the prius.

  • PaulRivers

    I wish people would stop saying these ridiculous things about mpg.

    Over in the anti-hybrid camp, we have people claiming that driving a hummer is more environmentally friendly than driving a Prius, which is a load of BS.

    Over here in the hybrid camp, we have people claiming that because they plugged in their car, the electricity used doesn’t count towards mileage so they’re getting over 100 mpg, which is also a lot of BS.

    I love the direction the Prius is heading – by starting with hybrids, then going to partial plugin options we’ll (hopefully) fund more and more battery research to the point where eventually we’ll have a battery that charges in 5 miles and can propel the car 400 miles. And with the car giving off absolutely no emmisions. (I’ve always thought that even if the car only gives off water, an entire city of cars giving off water is going to effect the local environment.) One day (hopefully!).

    But this whole BS about how you’re getting 100mpg while failing to account for the electricity used, or the fact that you only got that kind of mileage as long as you went under 30 miles is about as accurate as me claiming that I got over 100 mpg last weekend in a rented Jeep Cherokee. It’s true! – I’m just failing to mention that it was on a 10 mile stretch heading down the side of a mountain in neutral.

  • CLD


    What you’ve noted is true. And if you’re looking at this purely in environmental terms, the trade-off of petroleum vs electricity must be taken into account. However, if you’re talking in terms of energy security, the significant difference between using electicity and using petroleum is that electricity in the United States is produced almost exclusively from domestic sources. Therefore, cutting the amount of petroleum–over 60% of which is imported in the United States–used by an automobile by 50% is a significant accomplishment. On top of that, there are studies that indicate that even accounting for the fact that about 50% of the electricity generated in the U.S. comes from coal-fired power plants, plug-in hybrids would still reduce greenhouse gas emissions relative to conventional hybrids (http://www.calcars.org/vehicles.html).

    Also, I believe the claim about 100 mpg–while somewhat arbitrary in that there isn’t a lot of real world data to date–implies per tankful, not just for the first 30 miles.

    I’m with you though. The sooner the better for PHEV’s.

  • ex-EV1 driver

    You’re right in that a lot of folks who are advertising equivalent MPG numbers for plug-in hybrids fail to neglect the upstream energy used to produce the electricity, however, NO ONE who advertises MPG numbers for gasoline or diesel vehicles EVER mentions the upstream energy costs to pump, deliver, and refine gasoline or diesel. This number is actually quite difficult to even find.
    Estimates I’ve seen indicate that an efficient EV could travel somewhere between about 10 and 30 miles using the electricity required to produce a gallon of gasoline (sorry, its going to take a while for me to dig out the documentation for this).
    For the well-to-wheels efficiency of pure EV’s and plug-ins, assuming gasoline is used to generate the electricity (not the way it is done but it allows apples-to-apples comparisons), all modern EV’s that I’ve seen under development get well over 100 mpg(equivalent).
    This means that, assuming a Plug-in converted Prius got perhaps 160 mpg(E) in EV mode for perhaps the first 40 miles of a trip, it would have consumed 1/4 equivalent gallon. If it then ran in hybrid mode (EV + ICE) for the remaining 400 miles during which time, it consumed 5 gallons of gasoline (80 mpg – enabled by the larger hybrid battery), it would have traveled 440 miles on 5.25 gallons of gas, or effectively 83.8 mpg.
    Of course, days when one didn’t drive 440 miles between charging would yield significantly better equivalent MPG. In fact, if one drives the normal usage of less than 30 miles per day, you would never use gasoline at all and your effective mpg would be closer to the 160 mpg(E) of the pure EV.
    This great mpg is all because of the excellent efficiency of an electric motor and battery system, coupled with the extreme efficiency of the electrical distribution grid as well as the improved efficiency of large, stationary power stations, when compared to the poor efficiency of the gasoline Internal Combustion Engine (ICE).
    So, in summary, I agree with you that the mpg numbers for Plug-In vehicles are a stretch for some situations, I can certainly come up with realistic conditions (perhaps even normal ones) where they are actually somewhat conservative.

  • vinayababu

    Yes David, honestly I believe that the hitch in PHEV becoming successful is the battery pack. Even GM is also not sure if and when they will get a reliable pack from their suppliers for their VOLT. It could be true that Toyota wishes to manufacture the battery pack themselves in their plant though they also have some arrangement with at least two battery manufacturers. Already similar PHEV conversion centers are there, but there is no appreciable willing customers who are prepared to go for this experimental installations. I wont say that OEMtek will not be a successful venture if their battery pack stands the test of time. Best wishes to them.

  • AP

    ex-EV1 driver, you said

    “This great mpg is all because of the excellent efficiency of an electric motor and battery system, coupled with the extreme efficiency of the electrical distribution grid as well as the improved efficiency of large, stationary power stations, when compared to the poor efficiency of the gasoline Internal Combustion Engine (ICE).”

    This is a common misinterpretation of efficiencies. An electric powerplant is only about 33% efficient at producing electrical energy from the heat of the fuel used. For every 1 kW-hr of electricity it sends out, 1 kW-hr of heat goes up the exhaust stack, and 1 kW-hr goes out the cooling tower. Add the inefficiencies of the transformers, lines, and battery charge/discharge, and the efficiency of an electric motor is about the same as that “hated” ICE (which produces ALL of a conventional hybrid’s power).

    The reason is that an electrical powerplant does the hard work of converting heat into mechanical energy (a turning turbine shaft), which is about 40% efficient. It then turns that into electrical energy in a generator (which is 90+% efficient). All your electric motor has to do is another easy part: turning electrical energy into mechanical energy (again, 90+% efficient).

    You’re right that including the energy consumption in refineries must be added for ICE’s.

    So why does using electric motors in hybrids improve fuel economy? They don’t use energy idling, and they can partially regain energy using regenerative braking.

    And why are electric cars cheaper to run? Natural gas is a cheaper fuel source than crude oil, for one, but another big one is that electric companies don’t charge road taxes. A shortage of refineries also creates an artificial limit on supply, driving prices higher for gasoline.

  • changetheworldnow

    I think the banter back and forth is interesting.

    PHEV are the way to go in my opinion.
    They give the option of driving off into the sunset anytime we like using the ice but the practicality of all electric mode for our mundane ‘real lives’.

    I would like to add another tidbit for consumption. Buy the Volt or the plug in prius or other PHEV that will be coming out soon ( we hope).

    Add a solar panel to your roof and you really would be having over 100 mpg, even a solar powered car for your routine shopping and commuting chores during the week.

    I think the guys at CalCar are doing that now are they not?


  • ex-EV1 driver

    The efficiency numbers you mention are probably about correct for old coal electrical plants. It isn’t fair to burden new, clean technology with the oldest, dirtiest, inefficient electrical generation sources though. Rather, we need to look toward the future.
    Modern, combined cycle electrical co-generation facilties that use natural gas are over 70% thermally efficient, depending, of course, on some assumptions. They don’t lose 50% to the combustion (stack) or 50% to the condensation (cooling tower) as you propose. Electrical power distribution averages over 90% efficient so we don’t lose too much there either.
    Additionally, when looking toward the future, our electricity won’t be coming from either coal or gas because of their detrimental affects and their finite supply. Electrical propulsion is the best way to use any alternative energy source we have to meet our future transportation needs. Fortunately, its pretty efficient as well.
    Today’s non-plug-in Hybrids save over pure ICE for the reasons you mention (idling and regen) but they actually gain the most by permitting small, efficient, lightly loaded ICE to be used. Serial Plug-in hybrids have the advantage that their primary energy can come from the efficient and (potentially) alternately powered electrical grid while using the mobile ICE only for occassional long trips.
    Oil costs compared with Natural gas (and coal, nuke, and hydro) prices addition to Road taxes certainly to add to the cost of oil, however, even adding 25% or 30% to the price of electricity for electric vehicles still makes them cheaper to operate than gasoline ICE – and it is a sustainable technology that can be here for the future, and doesn’t need foreign controlled oil today.

  • Anonymous

    Chevy already has a car that runs 40 miles on electricity. http://www.chevrolet.com/pop/electriccar/2007/60miles_en.jsp

  • MW

    Now, 100 mpg I might be interested in, allowing of course for the upstream energy used in the making of electricity that Paul mentions. However, I wouldn’t even consider buying a Prius as they currently stand. I hear 45 mpg advertised as though it were the most amazing thing in the world–well, guess what. I’m driving an ’88 Toyota Corolla that I got secondhand for 500 dollars, and I’m getting 42 miles per gallon.

    I will likely be dubbed a liar by many, but that’s too bad. Anyways, my car is fully manual: manual steering, transmission, manual (not power) brakes, manual windows, locks, everything. When I first started driving it, I only got about 34 mpg because I wasn’t used to driving a manual. Now I’m more used to it, I coast downhill or coast to stops with my foot on the clutch, riding in neutral, and my mileage keeps getting better.

  • hydro-one


    we need Bombproof battrEEZ

    Hydro POWER ROCKS!

    All you fossil fuelers watch out, were going phase out the