Making Plug-in Hybrid Comparisons

Last year, General Motors officially launched the Chevy Volt, a range-extended electric vehicle (REEV) with an electric range of 35 miles and an EPA-rated electric-only equivalent fuel economy of 93 MPGe. This past summer, Fisker began deliveries of its REEV, the Fisker Karma luxury sports sedan, which will have an official range of 32 miles in all-electric mode—during which time it will get an equivalent efficiency of 52 MPGe. In a few months, Toyota will release its Prius Plug-in hybrid (PHEV,) which will be able to run gas free for its first 15 miles after charging, and is expected to receive an 87 MPGe rating.

All three cars run on both gas and battery power but there are key distinctions, stemming mostly from the differences between PHEVs and REEVs. Where the Volt and Karma run strictly on electricity until their battery range is depleted, the Prius optimizes use of its electric and gas power even when it’s battery is at or close to full charge. In other words, you can floor the accelerator while merging onto a freeway in a Volt or Karma and still operate on electricity alone, but a Prius Plug-in will likely use its gas engine to assist in that process.

What does this mean for drivers in terms of their emissions footprint and daily fuel costs? As Pike Research’s John Gartner pointed out this week, that all depends on how far you drive between charges. In comparing the Prius Plug-in to the Chevy Volt, Gartner calculated fuel costs for both vehicles as they relate to trip distance. (The Fisker Karma wasn’t included on the study, but it has the same electric range as the Volt and follows the same principals even though its gas-only fuel economy is lower.)

Gartner’s results, seen in the graph below, indicate that drivers who travel within their REEV’s electric-only range can expect significant fuel savings compared to a Prius Plug-in. Beyond that point the cost comparison begins to narrow:

“Assuming a gas price of $3.50 and electricity at 11 cents per kilowatt-hour, the Volt’s bigger battery makes it cheaper to operate as long as you drive 70 miles or less between charges.  At distances of greater than 70 miles, the Prius PHEVs’ greater fuel economy as a hybrid makes it cheaper to operate.”

It should be noted that a PHEV’s occasional use of its gas engine before its battery runs out contributes very little to total fuel use. A commuter driving less than 15 miles between charges won’t spend much on gas or contribute a significant emissions toll whether she’s in a Fisker Karma, a Chevy Volt, or a Prius Plug-in. Still, for some drivers who rarely travel more than 35 miles at a time, the allure of going totally gas free could prove to be a very attractive selling point for REEVs.

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  • Achilles

    Take a plug-in Prius. Now imagine adding an extra battery pack, lifting the engine-off range from ‘only’ 12 miles to over 30. Run the numbers again. The MPGe will now be similar to the Volt, but the battery-depleted MPG will be better at any speed, particularly at a steady 65 mph. The extra battery pack should be good value.

    An ‘extended range plug-in hybrid’ seems a better proposition than an extended range electric vehicle. Or are they almost the same, under the hood? No, having the engine drive the wheels via a generator makes no sense if the engine rarely needs to run at less than 50 mph. Direct connection when cruising, please. EREVs are ill-conceived and will fade away. Plug-in hybrids are the way forward, with BEVs as city runabouts.

  • ecodelta

    Actually the volt has direct connection between gas engine and wheels under certain conditions. Theoretically it could implement the driving behaviour you describe.

  • James Davis

    Chris, no matter how you slice these two cars, they are still just overpriced pieces of garbage that will keep you chained to the fossil fuel pumps. To get to one side of Chicago to the other, I have to enter the Interstate at 80 MPH to get ahead of or out of the way of oncoming traffic, and I have to maintain that speed until I can blend in with the rest of the traffic. Either of these two cars could leave me stranded in a very dangerous situation. There is nothing practical about either of these two cars or any other hybrid. Go with and stay with either an all ICE or an all EV. Hybrids – extended range, or whatever else you want to call them are just caskets on wheels.

  • James Thurber

    If the car owner routinely drives less than 70 miles per charge, he would be better off with a pure electric vehicle, such as a Leaf or a Ford Focus EV, than with a Volt; and renting an ICE vehicle for the occasional longer trip. The difference in vehicle price would more than pay for the cost and inconvenience of the vehicle rental.

  • van

    Great article and great comments!

    Boy would I have like to see the Leaf cost graphed with those two.

    Next, we have to consider the cost of ownership. At 12K to 15K miles per year, both cars should need replacement in about 10 years.

    So the difference in cost ($35,000 for the Volt after rebate and $25,000 for the PHV after rebate, a guess) is $1000 per year.
    If you divide that by say 12,000 miles, then the added cost per mile is 8 cents. So if you adjust up the Volt cost at the 30 mile point by $2.40, you will see that the Volt is way higher and the differ just gets bigger the more you drive. Now think about plotting the cost of ownership of the Karma. Talk about bad karma.

  • van

    I think the 15 mile range comes from “burning” 4.4 Kwh of juice. So if a kit was available to provide an additional 4.4 kwh of juice, the PHV would have a very similar range to the Volt. Now if they could market the kit at $500 per Kwh, then the kit would cost about $2500. Perhaps this is a pipe dream, but I think it is within the range of the possible.

  • Charles

    Over on PlugInCars this same graph got hammered for being wrong and right at the same time. The cross point is correct (at least based on some good assumptions), but the left side is incorrect. There should no be an inflection point for the Prius at 30 or so miles. That point should come before the graph starts.

  • Max Reid

    Even at 15 mile range and driving 300 days / year, we can drive 4,500 miles on electricity. Thats 1/3 for a person who drives 12,000 miles / year. So Plugins extract lot of juice with a small battery.

  • Capt. Concernicus


    After you spend thousands of dollars modifying your car please let me know how cost effective it was to do so.


    Why are you so anti-hybrid? I don’t get it. Tell you what. You drive your EV Leaf on any highway of Chicago and you’ll not only have trouble getting up to speed, but you’ll get run over because the Leaf won’t be able to keep up with traffic.

    Your unverifiable claims and fear mongering are best suited for a Fox News blog.

  • Bonaire

    The difference is Volt has a 10.4 kWh use of 16 kWh battery. Out of 10.4 kWh, summertime drivers get nearly 45, sometimes more. PiP is stated to get 13-15. PiP must be using more of the capacity discharge range of the Lithium pack. The full charge cycle, touted by Tesla owners, is an issue with such small packs in that after 1000+ full cycle charges, which could happen in 2 years if you plug in 1.5 times per day, the Lithium pack on a car that allows the full capacity range to be used (per-cell voltage of 4.2v down to 3.0v) will have a lower life than one that is kept in a sweet-spot band of 3.3v to 3.9v. We have yet to see if the PiP will need battery replacement early if they do happen to use the full amount of the capacity of the battery set. The price of that replacement set should be less than the Volt, of course. With the commoditization of Lithium batteries, it should be less than $2K (guessing) when it’s time to replace the PiP batteries.

    I was speaking to an Enginer PIHV conversion system owner this past September and he thought the Volt may have issues with the full cycles it would go through to reach 100K miles – 2800 if you always drove in CD-mode and recharged every 35 miles. Could the PiP small pack, plugged in twice-daily, offer a long-life? If not, then the replacement pack prices have to be something acceptable. There were a lot of complaints regarding the NiMH pack replacement costs for regular Prius over the years.

    PIHV futures will require ongoing lowering of the replacement pack costs through cost-of scale. A local Chevy dealer was downplaying costs of the Volt battery (ie. to get a sale) to me a few weeks ago saying that by the time the pack needs replacement, it would be $3K. We have no idea what it will cost but don’t let salesmen convince you of future parts prices without feedback from their HQ directly.

  • Bonaire

    Cost is debatable based on extra rebates per-state. Example is PA has a state rebate of $3500 for the Volt and $1000 for the PiP (Under 10kWh battery cap.) I can be in a Volt for under $29K after 7500 + 3500 off the base price of $39995 and have been offered $500 under MSRP already from a local dealer. If I had a GM Card earnings, I could pull another 1K off that price. Some states like Colorado offer $6K rebates on top of the federal.

    Total price to the owner is based on a lot of factors, including the various incentives and those incentive amounts based on the battery size. I do think the usable battery capacity is key to those incentives and the Volt “eeked by” these 10K incentive points. Federal 7500 is based on the Volt’s 16K capacity which is not all usable.

  • Bonaire

    It’s definitely not fair to say this without knowing the technology fully.

  • MrEnergyCzar

    I’ve driven 1,200 miles with my Volt using 1 gallon by just charging at home. Yes, the Prius wins if you drive 75 miles between charges which most people don’t do… The instant torque on the Volt makes driving fun again.


  • Frank Falcone

    One thing I think should be noted is that the Prius EV range is not really EV range but charge depleting range. It has a limited EV speed and requires the engine to assist for anything over very mild acceleration. Here in SoCal the Prius would be running its engine on every hill and every mile on the highway where the volt would be in EV only mode.

    As a result, the real distance required for the Prius to catch up to the Volt’s fuel consumption is probably another 10-15 miles out.

    Good use of data though, it’s about time we start putting some math to these questions.

    One other thing needs to be mentioned when comparing the Prius to the Volt. The Prius has budget fit and finish. The Volt has fit and finish typical of other $30-$40k vehicles. If you are in the market for a 30-40K vehicle, you just aren’t going to look at a slow, poor handling, Echo like fit and finish Prius. On the flip side, if you can’t afford a $30-$40k car, you aren’t going to test drive the Volt any more than you would any other car out of your price range (unless just for fun). From this standpoint, the Volt and Prius are really an apples to oranges comparison.


  • Gary

    Good article.
    In the end it depends a lot on how your usage.

    For us,
    An into town and back is just over 15 miles round trip and we do that nearly daily. About 5K miles a year. All electric in both cars.

    The rest of our driving tends to be long highway drives (the grandkids are 1200 miles away). This is about 10K miles per year.

    So, the two important numbers for me are the all electric range, AND the mpg after you are fully on gasoline — for us, the 2nd number is really the most important since 2/3rd of our driving is on gasoline. I suspect a lot of people are in this postion.

    You gave the first number but not the 2nd.
    From what I’ve heard (but not fully confirmed), the Prius plugin hybrid takes only a small hit on the 50 mpg the regular version of the hybrid gets when in all gas mode — this is good. I’ve heard that the Volt mpg when fully on gas is not great — in the 30’s? Anyone know for sure? This (to me) is very bad.


  • testing12

    That’s an informative study! And I agree that it would be interesting to see more vehicles in this comparison.

  • BigDaddy

    I’ve driven my Volt for almost 6 weeks now. A total of ~1050 miles. ~5% in “gas mode”. I average between 45 and 48 miles per charge. I’m averaging ~34mpg in “gas mode” in the city and 49mpg in “gas mode” on the highway. As has been said before it does make driving fun again. The one thing that most people don’t take into account when talking about the price is that with the options you get on it and the quality of build it has more of a luxury feel than any other electric or hybrid that I’ve seen.

  • Capt. Concernicus

    The Volt is an expensive way to try and save some money at the pump. It’s quality is questionable and it’s fit and finish is typical of any other Chevy out there now. In other words…mediocre.

    Here’s the other thing. It ONLY seats FOUR people. That’s right FOUR people. And from past articles and posts from some people on here that seems to be a deal breaker. Yet only seating four people with the Chevy Volt it’s quite alright. I sense some hypocrisy or it might just be import hating.

  • John Kerr

    Great comments. Glad I found this site.

    @Van — Very helpful annalyis, thanks.

    “TOTAL transportation dollars spent per year” averaged over a ten year period is a great way of looking at things.