By on October 10, 2007

plug-in-hybrid-car-phev.jpgHow the Hell do you calculate the official Environmental Protection Agency (EPA) mileage figures for plug-in or serial hybrids, vehicles that can/will operate in electric-only, charge-sustaining, gas-only and/or blended modes? In a phone interview with TTAC [below], EPA Senior Project Engineer Carl Paulina reveals that the Feds have been working on the problem with the Society of Automotive Engineers (SAE) for the last year-and-a-half. And… they're still working on it. In fact, Paulina reckons it'll be another year, easy, before the SAE committee figures out how to modify SAE standard J1711 to deal with the new technology (the equivalent fuel cell committee met for five years). Meanwhile, I asked Paulina how the EPA measures current [parallel] hybrid MPG stats. The result is a rivet counter's wet dream. Bottom line: your mileage may vary. 

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29 Comments on “EPA Strugges to Devise Plug-In Hybrid MPG Rating...”

  • avatar
    Alex Dykes

    I sure hope they figure out some way of demonstrating the increase in your utility bill. The problem I foresee is people buying one thinking they get 100MPG and being dumb enough to not realize their electric bill will skyrocket. Oh, and don’t forget that 95% of the power delivered in the USA comes from non-renewable resources. At least this whole package makes more sense than the hydrogen cars being touted at the moment.

  • avatar

    Let’s see… They could actually drive one around in a varied, but set manner, and report actual mileage instead of just trying to approximate it.

    No, that would just make too much sense.

  • avatar
    Carl Paulina


    The present goal is to publish both a mile/gallon (MPG) and Mile/power (miles per kilowatt or kilowatts per mile) values, where these quantities are relevent. This should allow the vehicle users to calculate their costs based on their driving habits and energy costs.

  • avatar

    MPKw values sound sensible, as they will vary under different engine stresses like MPG, but such a change would have to be accompanied by a significant public information campaign; I imagine that for the vast majority of the population MPKw numbers would be basically meaningless as battery capacity, voltage v. amperage v. wattage, etc. is more or less outside the realm of most consumers’ understanding.

    Such a campaign would doubtless help improve consumer understanding of other devices, cell phones, laptops, etc. and be a good thing as society becomes increasingly dependent on the battery.

  • avatar
    Carl Paulina


    I believe that this is exactly what the premise for dynamometer testing is.

    However the test trace (speed verses time cycle), vehicle state [warm, cold, electrical operational cycle (pure electric operation, charge sustaining operation and charge depleting operation) , Reserve Energy Storage System State of Charge (%SOC), etc.] all impact the test results, as do a number of other factors.

    Because no test will duplicate ALL operating conditions, any test will result in being an approximation of people’s use (i.e. driving habits)

  • avatar

    The one eyed leading the blind. Another chance for hybrid owners to boast of fuel economy they never really got.

  • avatar

    no one sees the obvious reason there doing this–there going to put a road tax on top of the tax for your electric bill since they cant get you at the pump….and to Alex Dykes,why is hydrogen any worse than plugins? the electricity for both come from a power plant, and you wont have a battery in a landfill on a hydrogen powered car.

  • avatar

    The present goal is to publish both a mile/gallon (MPG) and Mile/power (miles per kilowatt or kilowatts per mile) values, where these quantities are relevent.
    O-O. Mile/power? WTF? What is that supposed to mean? Mile/hp, anyone?

    The relevant metric is mile/kWh (or inversely kWh/mile), in other words Distance traveled per unit of energy, as opposed to power. Hint: a gallon of gas presents a unit of energy. Power just tells you how fast you are using the available energy.

    No wonder this is taking so long…

  • avatar

    Why is hydrogen any worse than plugins?

    Here you go:

    Basically, the inefficiencies in creating, compressing, transporting, and then using hydrogen (in combustion engine or fuel cell) are huge. According to the above link, you get to use only 23% of the original energy with hydrogen instead of 69% if you go with battery.

  • avatar

    Refer to the Hydrogen Hoax by Robert Zubrin for a detailed explanation of why hydrogen is a pipe dream, just 30 years away, as it has been for the last 50 years…

  • avatar

    Isn’t battery capacity measured in Ampre Hours? So rather than kWh/mile it would be Ah/mile. Again your mileage may vary depending on how many accessories you run during that mile. (A/C, radio, lights, seat heaters, coffee cup heater, Ipod, etc. etc.)

  • avatar

    This really should be simple. Publish conventional MPG ratings that are calculated without running down the battery and then publish battery range and miles/kWh. If you know, say, that your electricity costs $0.11/kWh and the vehicle goes 0.5 miles per kWh then you know you need 2 kWh hours to go a mile, so $0.22/mile of running costs.

    Actually, come to think of it, all the ratings are reported upside down. They should be gallons per mile and kWh/mile; then you could also publish $$$/mile with some assumptions on gasoline and electricity costs. That would also round out the differences between diesel, premium, regular, and electricity. An example car rating could be: $0.17/mile on gasoline, $0.22/mile on electricity, 40 mile electric range.

  • avatar

    Did anyone else catch the error the EPA guy made? He said ALL current hybrids use electrically driven wheels and the engine only generates electricity.

    Uh… HONDA? How about that Accord? And don’t the Vue, Escape/Mariner, etc. have an “in-line” electric motor and the vechicle can run entirely off the engine if needed?

    Or am I confused? (again!)

  • avatar

    One tidbit of info in this podcast I find pretty interesting: the impressive old 2007 EPA 61 MPG rating of the Toyota Prius is actually FOR REAL (given the specific test) and NOT due to running down the battery.

  • avatar

    Isn’t battery capacity measured in Ampre Hours? So rather than kWh/mile it would be Ah/mile.
    No – for a given battery, the voltage would be defined. It is therefore possible to substitute Ah to Wh as Ah * V = Wh.

    For a meaningful comparison that covers all possible battery configurations (voltages), the correct metric is mile/kWh (or the inverse).

  • avatar
    Carl Paulina

    Discussions on test method have included references to amps, amp-hrs, volts, kilowatts and kilowatt-hours.

    We are, at present, quantifying electric hybrids performance using amp-hrs for the +/- 1% allowable %SOC change during.

    Different hybrid vehicle designs run on various volt and amperage values, so just amp-hrs, when testing on vehicle stored, electric energy may not be an adequate energy parameter.

    Electrical energy will come from the electric companies whom sell electrical energy in kilowatts.

    Fuel Cell operation and their hydrogen to electricity conversion equations (which may have to be used to correct to 0% delta through the test) are more dependent on power than than energy.

    All the above units have been used in discussions so far.

    Because of the many possible designs for hybrids: pure electric operation capable, charge depleting operation, charge sustaining operation and blended operation (simultaneous gas engine and electric motor operation) hybrids will require a flexible and comprehensive test procedure.

    Hence the on-going committee discussions and multiple varied references to energy and power units.

  • avatar

    One tidbit of info in this podcast I find pretty interesting: the impressive old 2007 EPA 61 MPG rating of the Toyota Prius is actually FOR REAL (given the specific test) and NOT due to running down the battery.

    Of course it got that in the test. They can’t just publish something they don’t record. Hybrids benefitted disproportionately from the EPA tests because of no A/C and low speed, slow acceleration testing (keeps the battery on longer).

    I remember in 2005 as part of its promotion, Ford took the Escape Hybrid and drove it through Manhattan until it ran out of gas. The thing averaged something like 55 mpg because it just sat there half the time with no engine running or crept along very slowly on battery power and then braked which regenerated the battery.

    And, sure, you can get 50 from your Escape or 60 (probably 70 or 80) from your Prius or whatever if you drive like a grandma with no A/C and rarely exceed 25 mph and do a lot of braking. But that doesn’t represent what people will actually see.

    These plug-in tests present a similar challenge, although a far more complex one. How do you tell people what its really going to cost and how do you regulate a car’s efficiency properly? For plug-ins, a kWh conversion along with miles/gallon would seem to be the best way – maybe along with a total C02 footprint so that you understand that the electricity is not CO2 free either. And some people will probably average 50 mpg in their plug-in while others will average 100 mpg or more. That’s just the nature of your driving conditions.

  • avatar

    why does bmw and mazda have working models then? are they fake? for the inefficiencies of hydrogen-whats efficient about digging up and transporting coal to power the power plant a lot of people are going to get there electricity from?

  • avatar
    Carl Paulina


    Your comments are absolutely germane to the city driving test and insightful, thanks. The frequent vehicle starts and stops allow the hybrids to regain vehicle braking energy.

    In the highway fuel economy (HWFET) tests (vehicle warm and average 50-60 MPH) you can see the hybrid HWFET results get much closer to gasoline only vehicle results because there is less re-generation opportunity.

    What milages a user gets will be dependent on his personal drive requirements and the vehicle modes of operation during these requirements. That is the reason the committees are considering both Miles/gallon, miles per kilowatt-hour or gallons/mi and kWh/mi possibilities for various operational modes. I live 4 miles from my work, so I may never have to burn gas if I had a hybrid and the vehicle had an electric only range of 10 or more miles.

  • avatar

    why does bmw and mazda have working models then? are they fake?
    Those car companies that can afford them, use hydrogen vehicles as a publicity stunt. Seems like the stunt is working…

    Here’s how you can tell if hydrogen is coming down the pike or not: Before hydrogen makes much impact on surface travel, it would penetrate air travel, where the weight of the fuel is a factor (unlike surface travel). Once you see Boeing and Airbus producing hydrogen planes, you’d know that hydrogen is getting somewhere.

    Until such time hydrogen will remain an exotic fuel for use in space travel and other limited applications.

  • avatar

    Electrical energy will come from the electric companies whom sell electrical energy in kilowatts.
    You are getting me seriously worried here:
    1. Energy is measured in units of kWh, Joule, BTU, calories, etc. Power is measured in units of kW, hp, etc.
    2. Take a look at your home bill from the electric company – you will note that they charge you per kWh. No mention of kW.
    3. Electrical companies do charge large customers for peak power (kW) in an attempt to encourage them to minimize peak demand (to save the electric company from installing more equipment for as long as possible). That’s a separate issue. Even the large customers have to pay for energy used (kWh).

    In an automotive context: you pay for power when you buy the car (hp). You pay for energy every time you fill it up, independent of whether you are filling her up with hydrogen, electricity or gasoline.

  • avatar

    “Here’s how you can tell if hydrogen is coming down the pike or not: Before hydrogen makes much impact on surface travel, it would penetrate air travel, where the weight of the fuel is a factor (unlike surface travel). Once you see Boeing and Airbus producing hydrogen planes, you’d know that hydrogen is getting somewhere.”——————————–so thats why there were planes before cars were invented?

  • avatar

    I wonder how the weight of H2 + high pressure tank compares to the weight of liquid fuel. Storing a gas at several hundred atmospheres or at 20k is no walk in the park.

  • avatar

    You could retro fit a turbine powered plane; but I don’t think you could store enough hydrogen to get any range out of it.

    Look at the somewhat small(all things considered) fuel tank(s) on a semi-truck and look at how far they can go on that amount. Something like 800 miles? You could never get that type of range if you had a hydrogen powered semi-truck. Hydrogen just doesn’t have the energy equivalency to replace fuel on a one to one basis. You couldn’t put a big enough tank on a semi truck to make it viable. Look at hydrogen powered fuel cell type cars. Somewhat smallish tanks, and not so impressive range. You can’t make hydrogen cheaply. Take some water and run some DC current through it and watch it bubble. Now if you could speed up the process…

    A “fuel cell” car is nothing more then an electric car. You can “refuel” the battery vs’s “recharging” it. The “fuel cell” is the battery pack.

    Electric cars can be built today and be a reality today. The same can’t be said for so called fuel cell cars and hydrogen powered cars now or anytime in the near future. It’s not even on the drawing board. Ford/GM’s hydrogen stuff is PR/Government money.

    The Tesla roadster and GM Volt will change things. Mitsubishi, Nissian, and Subarue all have serious EV’s in the works. Hybrids are transistion type, stop gap type vehicles. Used to “get the publics feet wet”. Warm them up to the idea. Plugins are the next stage. It wouldn’t take much at all to take an existing hybrid and turn it into a full blown electric vehicle. Take a Volt and yank out that fuel burner and put a nice sized battery pack in it’s place. How many people only own one car these days? You drive the electric to work and around town. You have another car that you use for long trips. Purpose built vehicles. This one for around town and commuting because it’s more economical and makes environmental sense. That other one for long trips because it can. Keep your (current) old car for the long trips.

    If fuel was $10/gal, things would be different. As long as fuel is available and cheap; things will likely remain the same.

    Some guy at work used to own two semi trucks. Said they got about three, three and a half miles per gallon pulling a cattle trailer.

    Electricity can be made by using means that don’t pollute. It doesn’t much matter how big or heavy it is considering it’s stationary. Pollution controls could be installed on coal plants that are the size of a warehouse for example. Pollution solutions are more easily solvable on non mobile installations. And consider how their are fewer power plants then vehicles. Those plants can be dealt with. You burn gasoline or diesel and you make CO2. Bottom line. If that’s what you want though, then that’s fine. It would be nice to have an alternative though(battery powered). Hydrogen is just a dream and a distraction. Price some. Make some. Convert your vehicle to run on some. It will be all too clear.

  • avatar

    so thats why there were planes before cars were invented?
    LOL! Good one!

    No, that’s why hydrogen is used for space travel only so far. It does not mean that space travel was invented before the automobile!

    Hydrogen has only one advantage: weight. So far only space travellers are prepared to deal with all of hydrogen’s disadvantages…

  • avatar

    i copied this from mazda,is it fake?—-japanes authorities approve leases with two companies in the energy sector

    HIROSHIMA, Japan— Mazda Motor Corporation received permission from Japan’s Ministry of Land Infrastructure and Transport (MLIT) on February 10, 2006, to begin leasing the RX-8 Hydrogen RE to its first two corporate customers. These vehicles, equipped with a rotary engine, feature a dual-fuel system that allows the driver to select either hydrogen or gasoline with the flick of a switch. Mazda has started limited leasing of the vehicles and today concluded leases with two energy-related companies, marking the first lease contracts of a hydrogen-powered rotary engine equipped vehicle in the world. Delivery of the vehicles is scheduled to take place in late March 2006.

    Idemitsu Kosan Co. Ltd. and Iwatani International Corporation, both companies operating in the energy sector, have leased one vehicle each. By the end of 2006, Mazda plans to lease about 10 RX-8 Hydrogen RE cars to local government and energy companies. In 2003, Mazda exhibited a RX-8 hydrogen rotary vehicle at the Tokyo Motor Show and received permission from MLIT in October 2004 to conduct public road tests for ongoing development and practical application of this advanced technology. Mazda undertook 29 months of development from the time of announcing the concept model to achieving the breakthrough, real-world rotary hydrogen vehicle.

    Employing a dual-fuel system, the Mazda RX-8 Hydrogen RE can run on either high-pressure hydrogen gas or gasoline. This combination offers excellent convenience because it can be driven in remote areas where hydrogen fueling stations are not readily available, easing driver concerns about running out of fuel. In addition, this system boasts great environmental friendliness—zero emission of carbon dioxide (CO 2) gas and near zero nitrogen oxide (NOx) emission when fueled by hydrogen—together with the natural driving feel of an internal combustion engine. It uses engine parts and production facilities that already exist in Mazda’s inventory, so this innovative engine can be built with a high degree of reliability at a relatively low cost.

    The standard monthly lease price is 420,000 yen with tax included (400,000 yen/month without tax) which is almost half the monthly lease price of a fuel cell vehicle already available in Japan.

    With the RX-8 Hydrogen RE, Mazda continues to advance the possibilities of the internal combustion engine and improve the performance of hydrogen-fueled rotary engine vehicles. It represents another Mazda contribution to a more environmentally friendly hydrogen energy society of the future.

    Specifications and lease price of Mazda RX-8 Hydrogen RE



    Mazda LA-SE3P ‘Kai’ (modified model)

    Overall length/width/height

    4.435mm / 1.770mm / 1.340mm



    Curb weight


    Seating capacity

    4 adults



    RENESIS hydrogen rotary engine

    (Dual fuel system)




    0.654L x 2

    Maximum output

    Hydrogen 80kW (109PS)
    Gasoline 154kW (210PS)

    Maximum torque

    Hydrogen 140Nm (14.3kgm)
    Gasoline 222Nm (22.6kgm)



    Hydrogen/gasoline switch

    Fuel tank

    Hydrogen 110L/35MPa ( 350 bar ) high pressure hydrogen tank
    Gasoline 61L


    Cruising distance

    (10-15 mode)

    Hydrogen 100km

    Gasoline 549km

    * Standard lease price
    (Price without tax indicated in brackets.)

    420,000 yen (400,000 yen) per month

    *Monthly lease payment for the 30-month lease period.

    Mazda’s hydrogen vehicle development milestones


    Developed the first hydrogen rotary engine vehicle, HR-X


    Test drive of golf cart equipped with fuel cell


    Developed second hydrogen rotary engine vehicle, HR-X2

    Developed test version of MX-5 equipped with hydrogen rotary engine


    Conducted Japan’s first public road test with Capella Cargo equipped with hydrogen rotary engine


    Developed Demio (Mazda2) FC-EV


    Developed Premacy FC-EV and conducted first public road test in Japan (with methanol reformer fuel cell system)


    Announced Mazda RX-8 Hydrogen Rotary Engine vehicle development model


    Conducted the world’s first public road tests of the RX-8 hydrogen rotary engine that can run on two types of fuel–hydrogen and gasoline

    heres a newer link says it gets 200 km on a tank now

  • avatar
    EPA Guy


    Thanks for the units explaination, sorry your worried (yes your correct).

    When I’m measuring power instantaneously, it’s kilowatts, if we integrate power with time, isn’t it energy? (i.e. kWh, Joules, BTUs, Ft-lbs, calories) I apologize for mixing the references in these short responses, I should be more careful.

    And of course nothing is free.

  • avatar

    Your rather lengthy post proves that one can burn hydrogen in an ICE. That was news to you?

    It also list some numbers relevant to hydrogen’s (in)ability to penetrate the market:
    Maximum output
    Hydrogen 80kW (109PS)
    Gasoline 154kW (210PS)
    Note: ~ a 50% power penalty for using hydrogen.

    Cruising distance (10-15 mode)
    Hydrogen 100km
    Gasoline 549km
    Note: Hydrogen does not even have one fifth the range of gasoline.

    The conclusion seems obvious…

  • avatar

    sorry it was long – its been updated to 200 km and the reason im sure that battery power is yesterdays news is because the largest refinery in the midwest (my dads been there over 30 years)just spent a lot of time and money adding hydrogen production to the plant .id rather be driving an rx8 over a prius any day —and no this isnt news to me ive been following this closely for about 15 years,and hydrogen is almost here ,still think gas is just as clean as any of these technologies and the gov can tax it easier.

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