How Is The Fuel Efficiency Different In A Plug In Hybrid Car Compared To A Regular Hybrid Car?

Discussion in 'In the News' started by xcel, Feb 24, 2017.

  1. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    [​IMG] Enjoy this one as it gets technical and "stuff". :)

    [​IMG]Wayne Gerdes – CleanMPG – Feb. 24, 2017

    2017 Hyundai Ioniq PHEV-27 - Pricing and availability TBA later this year. An estimated 27 miles of all-electric range is part of the bargain. MPG and MPGe results will be made available later this year as well.

    The 2017 Hyundai Ioniq Plug-in Hybrid incorporates a direct-injected, 104 hp and 109 lb-ft of torque, 1.6L Atkinson-cycle I4 with a thermodynamic efficiency of 40 percent. Along with a clutched 60 hp permanent magnet synchronous electric motor powered by a 8.9 kWh Li-Ion battery allowing an estimated 27 miles all-electric range (AER), the package is mated to a very quick-shifting six-speed dual clutch transmission.

    The Ioniq PHEV design selected the dual-clutch transmission not only for its superior energy transfer from input to output shaft but also to make it feel vastly different from the Continuously Variable Transmissions used in all other PHEVs.

    The Battery - Electric power storage for the PHEV is courtesy of a non-polymer lithium-ion battery that is 20 percent lighter than standard prismatic cell format Li-Ion batteries. This chemistry is said to provide lower memory sensitivity, excellent charge and discharge efficiency, outstanding maximum output, and better longevity.

    To go along with this intro, I received an interesting question regarding an upcoming event and I thought many here would be interested in the reply. I scrubbed some of the details as it is under an NDA but this may provide novices with more information about what a Plug-in Hybrid (PHEV) is and is not with regards to how its efficiency can and is calculated.

    2018 Hyundai Ioniq PHEV-27


    How is the fuel efficiency different in a plug in hybrid car compared to a regular hybrid car?

    Good question and a tough one at that. A Hybrid is relatively simple as you know. A driver covers a given distance on a given amount of gasoline or diesel providing the mpgUS, mpgIMP, L/100 km, or km/L end result. PHEV efficiency is not as clear cut.

    The Plug-In Hybrid (PHEV) is a very likely candidate to make up a very large percentage of our mobility future. The shorter range every day commute can be completed on renewable electric power while the long distance personal enjoyment or errand drive is covered with 5-minute refuels and very efficiently on gasoline.

    To your point directly, the PHEV is a mix of efficiencies and can be infinitely complicated.

    For example, some drivers try to drive their PHEV almost exclusively as an electric car with the car forcing almost a tank of fuel to be consumed once per year. Those drivers have an MPG rating in the hundreds or thousands of miles per gallon (mpg) not including the electricity consumption in that result. These type of people should have purchased a Battery electric instead.

    2017 Chevrolet Volt PHEV-53

    EPA rated at 43/42/42 mpgUS city/highway/combined and 53 miles on the plug.​

    Others rarely plug-in their PHEV cars and instead rely on the convenience of filling up at the gasoline pump while receiving the financial benefits of the PHEV purchase and efficiency benefits of a pure Hybrid car.

    Most PHEV owners however actually use a mix of the two efficient driving scenarios – gasoline hybrid and pure electric driving – with a single daily charge at home covering more than half of the daily commute estimated at 43 miles. Commuting accounts for ~ 10,500 miles/year of the approximately 13,500 miles/year that the typical American drives.

    PHEV Drivers Consumption and Efficiency Case Study

    I am going to use the 2017 Toyota Prius Prime because it has the easiest to calculate electric efficiency with a 25 kWh/100 rating while on the plug. Under the above scenario, a typical American’s mobility needs while driving a 2017 Toyota Prius Prime PHEV-25 could include a 43-mile avg. daily commute for 5-days a week and 49 weeks per year plus 60 miles of errand/vacation travel on average traveled after work and each weekend.

    2017 Toyota Prius Prime PHEV-25

    EPA rated at 55/53/54 mpgUS city/highway/combined and 25 miles on the plug.​

    The 2017 Toyota Prius Prime PHEV is rated for 25 miles of electric range from a full charge and has an 11.3 gallon fuel tank capacity.

    On the typical 43-mile RT commute, 25 miles would be covered by the electric drivetrain and 18 miles would be covered from the gasoline drivetrain as a hybrid car for the daily commute.

    An additional 60 miles per week to meet the 13,750 mile yearly driver miles total would cover after work and weekend errands plus longer distance vacation travel. I would estimate a single 25 mile electric charge on the weekend and the other 35 miles on gasoline covering these after work errands, weekend errands, and vacation travel.

    Together, this typical American driver would drive and consume the following in his 2017 Toyota Prius Prime PHEV-25:

    150 miles on electricity at its EPA rated 25 kWh/100 miles or 37.5 kW
    125 miles on gasoline at its EPA rated 54 mpgUS or 2.31 gallons

    MPG - If efficiency was solely based on the gasoline consumed over the distance traveled, the Prius Prime PHEV-25 would have achieved 275 miles on 2.31 gallons or 119.0 mpgUS. This is a very unrealistic way to calculate the cumulative mpg. There is a problem with this direct calculation not apparent in the discussion. A gallon of gasoline can be equated to 120 MJ of energy but it takes approximately 60 additional MJ of energy to extract, pump, and refine the raw oil to gasoline and transport it to the fuel station. I used the fact that 19.6 lbs of CO2 is emitted when consuming a gallon of gasoline through an internal combustion engine (downstream) vs. the upstream emissions of approximately 10 lbs off CO2 emitted to get create a gallon of gasoline and move it to the pump when calculating the well to wheel efficiency.

    MPG and kWh/mi - If the gasoline and electric driving efficiency were separated, the efficiency would be based on their respective fuels. In this case the efficiency would be 54 mpgUS on gasoline AND 25 kWh/100 miles. I believe this is the best way to calculate efficiency because it keeps the two vastly different fuel sources and their vastly different efficiency (upstream to downstream) measurements separate.

    MPGe - If efficiency was instead based on a combination of both “fuel sources” as an MPGe result, 120 MJ or 33.7 kWh of electricity = 1 gallon of gasoline. In the case of the Prius Prime driving 275 miles/week, 150 miles on electricity and 125 miles on gasoline similar to what the average American would/could/should drive, we would have the following:

    37.5 kW * (1 gallon/33.7 kWh) = 1.11 “gallons of gasoline energy” consumed allowing 150 miles of driving in the case above.

    2.31 gallons of gasoline was consumed allowing 125 miles of driving in the case above.

    Cumulatively, the Prius Prime traveled 275 miles/(1.11 gallons equivalent + 2.31 gallons) equating to 80.41 MPGe.

    The problem with the MPGe calculation imho is this. A gallon of non-ethanol laced gasoline contains just over 120 MJ or 33.3 kWh of energy within. However, to generate a kWh of energy via a coal, NG, or Nuclear plant, the input heat source to kWh output is only 30 to 40 percent efficient. Meaning the energy content calculation is even further off than that of gasolines energy consumed to produce a gallon of gasoline discussed above. In the creation of a kW of energy, a majority amount of low quality waste heat is generated and discarded. Between 60 and 70 percent actually.

    This is why I believe the separation of the two "fuel" sources is the most accurate way to calculate the efficiency of a given PHEV. The upstream to downstream inefficiencies of each "fuel" are contained within their respective efficiency calculations.

    2017 Ford Fusion Energi PHEV-22

    EPA rated at 43/41/42 mpgUS city/highway/combined and 22 miles on the plug.​

    There are additional variables in the above calculations that in this single case, look at the average of the average. For one, most Hybrid and Plug-In Hybrid drivers have much longer commutes than the average American. Well over 15,000 miles per year on average. In this case, gasoline consumption would increase significantly while electric consumption would drop in concert. A 70 mile daily RT commute would be covered by 25 miles on electric and 45 miles on electric. I could describe an infinite number of scenarios but hopefully this write-up provides some insight as to the typical American PHEV owner.
  2. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    Yup. My commute is about 70 miles a day , usually times 6 days. About 25,000 miles a year. I still really like the idea of a PHEV. I'm not totally sure when I would drive on the battery and when I'd drive on gasoline. About 25 miles city/suburban and 45 miles highway each work day.
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  3. Carcus

    Carcus Well-Known Member

    Interesting piece.

    "However, to generate a kWh of energy via a coal, NG, or Nuclear plant, the input heat source to kWh output is only 30 to 40 percent efficient. Meaning the energy content calculation is even further off than that of gasolines energy consumed to produce a gallon of gasoline discussed above. In the creation of a kW of energy, a majority amount of low quality waste heat is generated and discarded. Between 60 and 70 percent actually."

    .... which makes me wonder,... 50 or 100 or 150 years from now.... what will be THE most efficient (and presumably, most utilized) transportation fuel?

    I suppose solar panel generated electricity to BEV would be the most common answer, but biogas (methane) put into a 60+mpg CNG hybrid still seems like it could be in the running... as the creation of biogas (a field still in its infancy) is an exothermic process, and we have (apparently) not yet reached the end of hybrid efficiency gains.
    Last edited: Feb 25, 2017
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  4. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    Where did this factoid come from? I would not have expected any correlation between the commute distance and what we drove, technology-wise.

    xcel likes this.
  5. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Bill:

    I have seen and heard this from meetings with Toyota, Hyundai, other OEMs, and online reports involving driving statistics.

    BillLin likes this.
  6. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    Thanks, Wayne. This must be like Nielsen TV ratings. It never matches me or anyone I know. :)

    Gotta watch out for those professional poll takers.
    xcel likes this.
  7. alster

    alster Well-Known Member

    We have both, a 2010 Prius with 152,000 miles on the clock and a 2016 Volt with 12,000 miles. Our Volt, of course a plug in, when going down a long grade can store all the electricity you can acquire, where as the Prius, with its small battery, will quickly be fully charged and you will bleed off the energy by the computer spinning the engine or having to use your brakes.

    Now the Volt, wife's car, she makes her 32 mile round trip to her business everyday without the engine starting up, temps are always over 15 F, even in the dead of the winter where current battery range is 44-49 miles where in the summer 55-60+ is the norm. On gas, according to, is 44.08 mpg, overall average for about 3,000-4,000 miles on just gas.

    Now in closing here is the deciding factor if the plug in hybrid is for you. If your electric rates are over .15/ KWH, and gasoline is $2.25 or so per gallon and you get 50 mpg you may be better off in cost per mile with just a hybrid, like the Ioniq blue with an EPA avg. of 58 mpg. Also to consider there is charging losses when charging your battery. With our 240 Volt we use 16 KWH to charge the battery fully with an output of 14.0-14.3 kwh of useful on the road electricity.

    One advantage with a plug in like our Volt, you have the choice of using just electricity or gasoline. For instance if we take a trip from Seaside to Portland Oregon I can just push the Volt into Hold Mode and run just on the gas engine. When I get to Portland, 80 miles later, in downtown traffic I can switch to battery power for more efficient use.

    Its nice to have choices, and right now and in the future is a great time for choices on your purchase of hybrid and electric vehicles....
  8. NeilBlanchard

    NeilBlanchard Well-Known Member

    The main advantage of plugin hybrids depends on the distance you usually drive relative to the number of times you can charge the battery per day. A secondary advantage is more capacity for regen, so if you have a lot of elevation change, for example, you can get higher average MPG because more regen can be captured.
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  9. joshdurston

    joshdurston Rogue Canadian

    I recently purchased a 2017 Volt but considered a 2014 Accord Hybrid a 2016 Civic 1.5T, 2017 Prius (not Prime since it's not in Canada yet), and a VW TSI Golf/Jetta. I've got a 150mile roundtrip commute 2 days a week. It's a tough call since in the Volt I can't go electric the whole way, I'm sure there's a break even point where a hybrid makes more sense. But, here in Canada our fuel is much more expensive and I can charge off peak at night for just over $0.10kw/hr including delivery charges.
    After 3 weeks with the Volt I'm happy with my choice, I'm a total convert for the Voltec drivetrain. I do feel like the car has some compromises that some people couldn't live with (like the small backseat), but that has more to do with the body style than the drivetrain. The driving experience on gas or electric is top notch.

    Chevy is the only one doing PHEV justice these days IMHO. I was excited by the Ford Energi cars a couple years ago, but thought the industry would've moved past the 20mile PHEVs by now. The Volt's 53 miles is a pretty good balance, however I would've paid a couple thousand extra to get a 70 mile electric range with some higher power charging options.

    Back the original topic, I'm annoyed by the combined energy consumption stats, they are not really comparable as Wayne pointed out. Many factors for both sources. It's nice to have a car that offers a choice.
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  10. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    And 70-80 miles was where the entry level EV was just a few years ago, so I think the Volt's 50+ is a great compromise. The 20+ PHEV range works for me, too, but my needs are simple. I'm hoping the Niro/Ioniq PHEVs come in at the right price points. Regarding the latter, the Ioniq PHEV was just introduced in Korea per a news article I just read.
    xcel likes this.
  11. Goldenyears

    Goldenyears New Member

    I traded my 2010 Prius for a 2017 Prius Prime. I got a $4500 Federal Tax Credit so I figured the Prime was cheaper than the plain hybrid Prius. I like it a lot except that the bigger traction battery has cut a lot of storage/luggage space so maybe I'll trade for a plug in Camry when Toyota offers it.

    I'm not an electrician. I was told there's an inefficiency in the charging process. How many KWh should it take to charge a 1 KWh battery?

    Electricity rates here are $0.0735 per KWh all hours. I am seeing 19 miles EV range because I'm running the heater. Assume 75% of the 8.8 traction battery used for EV driving and the charging process is 75% efficient so they cancel each other. Then the cost to charge the traction battery should be 8.8 Kwh X $0.0735 / 19 miles = $0.034 per mile.

    I'd like to know if my math is correct.
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  12. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Goldenyears:

    The Prius Prime was indeed a great purchase based on the total price after the giveaways vs. the std. Prius.

    And the shallower floor to hatch lid is indeed one of the drawbacks allowing 19.8 cu. ft of cargo volume vs. the std. Prius at 27.4 cu. ft. in the Two Eco, Four, and Four Touring and 24.6 cu. ft. in the Two, Three, and Three Touring.

    2017 Toyota Prius Prime, Prius Three and Prius Four Touring Cargo Volume Comparison

    Prius Prime and its 19.8 cu.ft. of cargo volume - A flat load floor from the rear hatch all the way into the rear seat seat backs.

    Prius Three and its 24.6 cu.ft. of cargo volume - Notice the lower depth edge at the base of the rear seat fulcrum?

    Prius Four and its 27.4 cu.ft. of cargo volume - Notice the taller edge at the base of the rear seat fulcrum?​

    Regarding your electric bill, can you look at the total and divide by your kWs used if there is no tier. It will give a much better representation of what your actual $/kWh charge is including the line charge, taxes, fees and any other darn thing your local utility may legally tack on.

    The Prius Prime from flat to full can take on about 6.25 kWh for its 25 miles. The charging process is lossy but it is not 25 percent. Probably a 10 percent loss. Anyone else have that figure???

    I am picking up a Prius Prime in two weeks and will Kill-a-watt it on the 120V outlet during the charge process to get some more detail on that.

    In any case, from flat to full should come in very close to 6.25 kWh and you are driving 19 miles on that amount of energy. Find out what your exact cost per kWh is from your bill ($0.xx/kWh), multiple that by 6.25 kWh and divide both by 19 miles for a more accurate cost per mile.

    At $0.0735/kWh, you have one fantastic electric rate and driving on the plug ($0.0241/mi) beats the hell out of gasoline down to about $1.31/gallon!!!

    Your current calculation: ((0.0735 $/kWh)*(6.25 kWh))/19 miles = $0.0242/mi

    Prius Prime and its EPA 54 mpgUS combined with the nationwide average cost for a gallon of gasoline at $2.20/gallon: ($2.20/gal)/(54 mi/gal) = $0.0407/mi.

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  13. alster

    alster Well-Known Member

    As far as electric losses when charging; Our 2016 Volt when using a 240 Volt charging system takes 16 KWH of electricity to charge the battery to an actual use
    of 14.0-14.3 KWH when driving. We also pay .117 per KWH, with all taxes, fees, etc. included so it cost $1.87 for a full charge which will give us 42-50 miles winter, 55-60+ miles in summer.
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