CMU study suggests GM has wildly oversized the batteries in the Chevy Volt plug-in hybrid

Plug in hybrids vehicles are certainly the car of the very near future and a core climate solution. And electricity is the only alternative fuel that can lead to energy independence. But I have a long been concerned that General Motors has overdesigned its showcase plug-in hybrid electric vehicle (PHEV), the Chevy Volt (see “Is a 40-mile all electric range too much?“).

Now a major new study by a team of researchers from Carnegie Mellon University, “Impact of battery weight and charging patterns on the economic and environmental benefits of plug-in hybrid vehicles” (PDF here) confirms my basic analysis that plug-ins make sense, but a 40-mile all electric range (AER) does not:

We find that when charged frequently, every 20 miles or less, using average U.S. electricity, small-capacity PHEVs are less expensive and release fewer GHGs than hybrid-electric vehicles (HEVs) or conventional vehicles….

Large-capacity PHEVs sized for 40 or more miles of electric-only travel are not cost effective in any scenario, although they could minimize GHG emissions for some drivers.

Bloomberg quotes Jeremy Michalek, an engineering professor who led the study: “Forty miles might be a sweet spot for making sure a lot of people get to work without using gasoline, but you’re doing it at a cost that will never be repaid in fuel savings.”

Note that CMU considered a “high gas price” of $6.0 a gallon, which is the equivalent about $200 a barrel, a reasonable high price case for the next decade.

Perhaps the most significant finding for car companies who want to enter the plug-in hybrid business, minimize costs, and frankly crush GM, is something I have thought for a long time — a very short AER can make sense for a large fraction of drivers:

Our results suggest that for urban driving conditions and frequent charges every 10 miles or less, a low-capacity PHEV sized with an AER of about 7 miles would be a robust choice for minimizing gasoline consumption, cost, and greenhouse gas emissions.

Toyota seems to share the view that an AER far below 40 is optimum, as the Bloomberg piece notes:

Toyota also plans tests this year on a plug-in Prius able to go more than 10 miles on a charge.

The final range is likely to be less than half that of the Volt, said Bill Reinert, U.S. national manager for advanced technology for Toyota City, Japan-based Toyota….

“We believe that if you have a smaller battery charged more frequently, you can run on electricity more of the time, then your carbon emissions are going to be lower overall,” Reinert said.

I’m going to include this figure, even though it is a tad opaque, just to keep you off the streets for a few hours puzzling it out (click to enlarge):

Best vehicle choice for minimum fuel consumption, cost, or greenhouse gas emissions as a function of distance driven between charges across sensitivity scenarios.

Michalek is quoted in Green Car Congress piece explaining why smaller is better, at least when it comes to PHEV batteries:

Larger battery packs allow drivers to go longer distances on electric power. But batteries are heavy and expensive. Over a range of scenarios–including fluctuating gas prices, new battery technologies or high taxes on carbon dioxide emissions–plug-ins with small battery packs are economically competitive with ordinary hybrid and conventional vehicles for drivers who charge frequently.

The study, which was accepted this week for publication in a forthcoming issue of the journal Energy Policy, has public policy implications:

The dominance of the small-capacity PHEV over larger-capacity PHEVs across the wide range of scenarios examined in this study suggests that government incentives designed to increase adoption of PHEVs may be best targeted toward adoption of small capacity PHEVs by urban drivers who are able to charge frequently. Because nearly 50% of U.S. passenger vehicle miles are traveled by vehicles driving less than 20 miles per day (Samaras and Meisterling, 2008; US DOT, 2003), there remains significant potential in targeting this subset of drivers.

Once again, I strongly urge General Motors to revisit this issue of range. The company is on its last legs and simply can’t afford to have a major miscue on what will certainly be among its most important new products in the decade of the 20101.

Finally, I think this study is best looked at as describing the optimal plug-in the 2010s. In the 2020s and beyond, as peak oil and desperation about global warming starts to dominate, longer ranges will make more sense. The Volt may, fatally, be 15 years ahead of its time.

UPDATE: Of course, if we build out a lot of charging stations in parking garages, malls, apartment buildings, residences, and so on over the next 15 years, than a considerably shorter range than 40 miles may still be optimal.

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35 Responses to CMU study suggests GM has wildly oversized the batteries in the Chevy Volt plug-in hybrid

  1. hapa says:

    maybe the volt’s battery size is related to the electric drive being primary, the need to keep acceleration available, and the speed that the range extender recharges it

  2. Anonymous says:

    The problem for me is that I commute 17 miles each way, but I don’t anticipate there being an outlet at my place of work in the near future anyway. So I need a 32 mile range. And even if I only went 10 miles – do I want to fill up every time I stop? That’s a non-starter.

    [JR: The trick isn’t designing the car for everyone, but for a large fraction of people, a large fraction of the time. Remember, you never have to charge, since you have the gasoline for longer range.]

  3. Robert says:

    I note the Michalek words quoted above, ‘drivers who charge frequently’. How many more charging stations would be needed if PHEVs have only 10-15 mile range, to make ‘frequently’ a possibility? Presumably the low-range approach shifts a portion of the costs of low-emission driving with EVs to employers, governments and others to allow people to charge at work or at other destinations, not only at home.

  4. Joe says:

    Part of the problem is designing the car to run purely on electricity all the time, rather than letting the gasoline do a little heavy lifting. That requires an overdesign of the battery, too.

  5. Hey Joe, just as an FYI, here’s how Bob Lutz justified the battery size during an interview I had with him last fall. He said there’s a misunderstanding out there that the Volt will be designed to use that entire 16 kilowatts to get maximum electric range. That would stretch the battery, he said.

    “Actually, in anticipation of that we designed the battery pack twice as big as it needs to be,” he said. “We have 16 kilowatts and use 8 kilowatts, charging to 80 per cent only and discharging to 30 per cent only. So we’re using this 50 per cent slice of the battery’s capability, and that is the slice where a high-tech battery like lithium-ion breaths very easily. We think that by not charging it above 80 per cent and not discharging it below 30 per cent, we can get that battery to cycle thousands and thousands of times and last 10 years. It’s the battery’s comfort zone.”

    Seemed at the time to make sense. Just throwing it out there. Curious to get your thoughts.


  6. Brewster says:

    I cannot imagine buying a car that only had 7 miles AER – that would get me very close to nowhere.

    The entire study sounds like it was produced by a few people with an agenda, stressing the negative aspects of a longer range PHEV as opposed to the best possible figures for the shorter range ones.

    “We believe that if you have a smaller battery charged more frequently, you can run on electricity more of the time, then your carbon emissions are going to be lower overall,” This statement is beyond me – I have run a dozen different (what I consider) real world scenarios, and in only one case was the short-range PHEV a better option.

    I have already heard that they based much of their cost-effectiveness on an assumption of $1000 per kWh for the batteries, and a much higher weight than GM is projecting for the Volt. GM claims these numbers are far too high even for the first models. And there is general agreement that Gen 2 batteries will be both cheaper (1/2 the price) and lighter.

    And even their graph shows the advantages of 40 Mi AER in terms of GHG over most realistic distances.

    Having said all that, perhaps GM would be wise to have a 20 Mi AER option – that would cut initial cost & weight for people who really don’t need the range (although I don’t consider saving 200 lbs on a vehicle of that size a big deal.)

    This might be an excellent option if GM offered a plan to move up to 40 Mi AER later if needed.

  7. Wonhyo says:

    The fundamental problem is not that 40 miles is too much range, but that the weight is too high and efficiency too low in the Volt. I’ll compare the Volt to the Aptera.

    The Volt’s 16 kWh battery is a result of a conventional approach to car design. With the Volt, Chevy applied a conventional (gasoline) car design approach to produce an extended range electric car. Predictably, this results in a car that requires a large battery.

    Aptera correctly recognized that the much smaller energy density of a battery (1/10 that of gasoline) makes efficiency of paramount importance. That’s why Aptera came up with a car design that gets double the all-electric range of the Volt with a 35% smaller battery (the extended range electric version is projected to get 50% more all electric range with a 70% smaller battery). Consequently, the projected base price of the Aptera has remained steady at “mid $20k”.

    The Volt’s design represents a fundamental failure to recognize the different design paradigm needed when dealing with the high cost and low energy density of batteries (when compared to gasoline).

    Having said that, a simple solution would be to cut the battery capacity and range in half (which would actually improve acceleration, and cut the range to a little more than half, since weight is being reduced). There may be a perceived marketing issue, as competing manufacturers (like Aptera) will offer longer range, but the simple solution to that is to offer a lower-priced half-range version, along with the higher-priced full-range version. Let the buyer decide how much (s)he is willing to pay for the extra range. Actually, I hope Aptera will also offer a lower-priced reduced-range version of their all-electric and extended-range electric vehicles.

    One problem is the electric car incentive in the stimulus bill does not reward efficiency, since the incentive is proportional to battery capacity, and not directly tied to efficiency. Thus, the Volt gets a 50% larger incentive rebate than the much more efficient Aptera.

    Both Tesla and Chevy have failed to recognize the fundamental difference in design drivers between gasoline and electric cars (Tesla perhaps intentionally so). I hope Chevy realizes the simple and practical solution of offering a lower-priced reduced range version of the Volt. Even if Aptera offers a more efficient solution, the simple production limits of the Aptera (20k/year) should leave much of the market open to a less efficient Volt, if the price is right. Volt also has seating for four (possibly five) compared to Aptera’s two adults plus one child seating.

    Actually, there’s potential for all three vehicles. At $109k Tesla’s target market is obvious. Chevy gets the $45k market for 4-5 seat vehicles (and widens the market if it offers a lower priced, half-range version). Aptera gets the $25k 2+1 seat market. Chevy is given an assist by the battery capacity proportional federal incentive.

    However, Chevy will have to follow up with a much more efficient design to remain competitive, as I expect Aptera will follow up their two seater with a four seater. I expect a four-seat car designed with Aptera’s design principles will be far more efficient (and capable of offering greater range with a smaller battery and price tag) than the Volt.

    Good luck to all three manufacturers!

  8. Wonhyo says:

    On another matter, the decision to use lithium ion batteries, instead of the more robust (and more expensive) lithium chemistries, is not necessarily a great decision. Lithium ion cells have higher energy density than the other lithium chemistries, but their finicky operating limits require reduced cycle depth and more careful environmental control. When you put together a lithium ion battery with the necessary monitoring and environmental controls, the weight and cost advantages at the battery cell level disappear. Another failure of systems engineering.

    Having said that, has anybody assessed the lifecycle environmental impact of all these car batteries? I know they’re great while they’re being used, but will we be able to dispose of them safely and efficiently? I hope this issue is not being ignored.

  9. John Hartman says:

    Very interesting, but I’m confused about one thing.

    How is that 20 miles/day average calculated? If a person drives 40 miles every other day, that is still a 20/day average, in which case these lower range vehicles wouldn’t be as practical.

    Is it a daily average or is it that on days when a car is used it is driven 20 miles or less?

  10. Wonhyo says:

    Having taken a more careful look at the graph, it seems pretty convincing, that the Volt is not only inefficient, but the range is too large. The plot presents a 7 mile battery capacity as being the best solution in all but one case, but this assumes charging every 7 miles. For most people, this will mean charging at the office, and I don’t think most offices will be able to ramp up their vehicle charging infrastructure very fast (although I hope they do).

    For the near term, I suspect the 20 mile battery range may be more cost effective, until at-work charging stations become widely available.

    Still improving efficiency (by reducing weight and drag) is a universally effective way to reduce both cost and GHGs, regardless of fuel type.

  11. Wonhyo says:

    John – The plot is labeled “distance between charges”.

  12. John Hartman says:

    Thanks Wonhyo, but I’m curious about the statement in the 2nd quote after the chart that says 50% of U.S. passenger miles are traveled by vehicles driven less than 20 miles/day.

    The chart is showing what PHEV would map to an individual’s charge frequency for the particular factors shown.

  13. EV1 fan says:

    40 miles of all-electric is too little, not too much. Why? Because it isn’t hard at all to make cars go around a hundred miles per charge. GM did it with the EV1 a few years ago, and Toyota also did it with the Rav4. Just bring those vehicles back. No new research is needed.

    The Tesla, on the other hand, goes 220+ miles on a charge and costs around $100K. Now that is what would be a vehicle with too much range per charge.

  14. There’s a big difference between what people need, and what they will buy, particularly when it comes to cars. If people bought the car they needed, most people in the United States would either be driving a minivan or a Ford Focus (or even a Ford Festiva, which I’m not even sure you can buy in the US).

    So, even if the PHEV-10 is the most cost-efficient vehicle, it’s possible that a PHEV-40 like the Volt appeals to more buyers.

  15. jorleh says:

    Why not take electricity like trains, a mast in the car top and grid above? No batteries, or small ones. All big roads with the grid, small roads with small own car engine.

  16. Bob Wallace says:

    jorleh –

    Think of the infrastructure required to string wires above roads.

    Think of the practical problems of changing lanes, moving from one road to another.

    My only experience with “electric buses” is in SF. There, when the driver wishes to move from one route to another, he/she has to get out and manually move to a different line.

    Buses can stick to constant routes. That would be way too constraining for individual vehicles.

  17. jorleh says:

    Bob: I disagree. Think of the long distance autobahns and heavily trafficked large urban streets. The point is that your connection to the above grid can be discontinuous, and when you don´t have connection with the grid with your “mast” your car batteries manage. Or hybrid. Another point is that when driving with the grid the grid loads all the time your small car battery as well as gives electric power for your going forwards. And so your battery is small and light, even the combustion engine small and light if hybrid. The more covering the grid, the more efficient the system. Of course there is driving which demands more independence, but only a minor fraction of all daily routine.

  18. jorleh says:

    Joe: sorry not to read your whole article in this hurry. Your car is a car with only electricity. But in that case the road grid and plug-in in home yard and in parking is an ideal small battery combination.

    [JR: Your comment is too cryptic to parse or reply to.]

  19. Marc Roberts says:

    Maybe this has already been covered. Sorry if it has, but does anyone have any projected figures for the increase in electricity generating capacity necessary for the large scale uptake of this technology and the impact this will have on prices/affordability. Where will all this additional green electricity capacity come from, globally, in the absence of massive nuclear investment? Even an electric car habit still looks un-viable, globally, over any significant period.

  20. Albert says:

    GM responds, faulting the study’s assumptions about battery cost:

  21. Sasparilla says:

    Boy did this topic key off a discussion. Something to keep in mind on the study – it assumed a static battery cost…this is actually the one thing whose price is expected to fall radically over the coming years (GM’s current battery cost for the Volt is already much lower than the Study assumed).

    I personally want the 40 mile range, I don’t want to need to charge (and hit our current electrical distribution infrastructure) throughout the day while its under peak load – cause I don’t want to burn gasoline at all. Besides I don’t think there will be much charging infrastructure out there for quite a while (gotta have enough cars to make it worthwhile first). But to keep things in perspective, the Volt is GM’s technology down payment for the next 50 years and initially is only set to produce 65,000 of them a year – this isn’t something they plan to sell like a Civic or even a Prius, until they get through the 1st generation and get costs down. Next generation vehicles will gradually target larger market areas as costs come down.

    Keep in mind the 2010 Prius will be touching $30,000.00 when loaded with some options and it won’t even have a plug – the Volt with its 40 mile range and tax break will be in that same price area. I’ll take the Volt and expect GM to roll out different capacities in future vehicles to suit customers needs. I don’t think GM will have any trouble selling every Volt they make.

    In reference to what Tyler mentioned about the capacity and GM only using part of it, this is a strategy all car companies use on their hybrid vehicles to allow their batteries to last a long time (on the prior generation NiMH cells they can essentially last longer than the vehicle if kept in this charge range), its good to know that LiIon cells GM is using respond in a similar manner, as it was one of the big questions on LithIons for cars.

  22. Bob Wallace says:

    Marc –

    Wind is cheap and often blows harder at night when grid demand is down. Wind is pretty perfect for overnight charging.

    And by sharing batteries with the grid a fleet of electric cars can do wonders for smoothing supply/demand problems.


    As was pointed out above in regards to 20 vs. 40 mile range PHEVs, the “best” solution is not necessarily the solution that looks best on paper, but the one that the market will accept. Can you imagine the problem convincing the general public to embrace a sky full of wires over our roads?

  23. Wonhyo says:

    Jorleh – The concept you describe, cars powered by overhead power, is taken one step further by hybrid dual-mode transit (DMT). DMT infrastructure would consist of elevated tracks that are electrified and automated. The DMT vehicle will be a privately owned electric vehicle (with small to modest battery) with normal wheels, along with an adapter to run on the dedicated track. The driver manually drives the DMT vehicle from garage to track, then enters the track. Once on the track, the vehicle is automatically routed from the entry station to the exit station. At the exit station, the driver again drives the vehicle manually to the office.

    The vehicle battery needs to be just large enough to get from garage to track and from track to office. The battery would charge while on the track (and at home, and at the office). As long as the on-track/off-track ratio is long enough, ALL of the charging could be done on the track (but augmented by home/office charging when necessary).

    The track is raised so that conventional surface roads are not sacrificed to accommodate DMT. The automated on-track routing allows very close “head-spacing”, allowing cars to be run 0.25 to 0.5 seconds apart, much closer than safe manual driving distance. The automation also allows relatively high speeds, without stopping, at close spacings.

    As a vehicle enters the track, a gap in traffic is created some distance back. By the time the vehicle merges with the main traffic, the gap has arrived at the merge point. Thus, the mainstream traffic does not slow down suddenly to accommodate oncoming vehicles.

    This concept was thoroughly considered in a systems engineering exercise in the mid-70’s, and proven to be feasible and provide a 2-5 times increase in vehicle throughput when applied to Los Angeles. At the time, the only missing piece of technology was the computing power required to efficiently route all the vehicles on the automated track. For more info, see “Fundamentals of Personal Rapid Transit”.

    While the 1970’s study proved this concept feasible and effective, actual implementations have fallen short. I suspect that’s due to a variety of cost and political compromises that were made.

  24. Maarten says:

    Marc Roberts: Just a rough, back-of-the-envelope calculation:
    100 million all-electric cars *
    15’000 to 20’000 km per year *
    .15 to .2 kWh per km
    => 2.25 to 4 MWh per car per year
    => 225 to 400 TWh per year for 100 million cars
    => about 20 to 40 large nuclear power plants, or a 3 kW PV array for every car, or 100 to 200 GW of wind power (100’000 to 200’000 1MW wind turbines), or a dedicated effort at electricity efficiency

  25. charlie says:

    Let’s be honest about why GM is building the Volt: To justify getting $25 billion in DOE loans. A little like the Dodge Omni in the 1980s: to show that an American company can build a working plug-in hybrid and get a government bailout.

    The Volt will be a failure. It is priced too high when it is introduced next year gas prices will still probably be in the $3 range (global demand). GM will cheap it out inside and make it look like a rental car when it is the high 30K price bracket.

    In terms of the 40 vs 20 mile range, I’m pretty neutral. I don’t know PHEV will fit into CAFE requirements, but I suspect that a lot of the higher range ones will be built as a unintended consequence of the regulations. If you are looking at people with 20 mile commutes, no electric car in the near future is going to in your plans. I suggest you move closer to where you work.

    IF the Volt really does have a 40 mile electric range (and Tyler’s comment about battery capacity make sense) the air quality improvements it would bring to major cities (LA, Washington, and Atlanta) would be worth the investment.

  26. Ric Merritt says:

    Valuable post, thanks. Studies like this make me curious whether variations in outside temps, and thus use of heat and AC, are taken into account. Prius experience tells me that heat and AC have some effect, but not drastic. Cold weather has an enormous effect for the first 5 or 10 minutes (exactly the important case for short commutes), but maybe that’s different when you’re not running the gas engine.

  27. Bob Wallace says:

    “The concept you describe, cars powered by overhead power, is taken one step further by hybrid dual-mode transit (DMT). DMT infrastructure would consist of elevated tracks that are electrified and automated. ”

    The overhead wire/track concepts remind me of the story of the beneficent king who wanted to do something to help his people.

    He noticed that many had injured feet from walking on rough roads, so he called for his ministers to cover the roads with leather to make walking more comfortable.

    A wise minister suggested that a better approach would be to cover the soles of each citizens feet with leather rather than cover the entire road.

    Thus were sandals born….

    Overhead wires, tracks, whatever create the need for huge amounts of infrastructure which would be both very costly to build, take large amounts of time to install, and cause a huge problem for those who wish to travel off the crowded path.

    Seems to me to make more sense to give each individual vehicle the ability to carry its own power.

    We can do that right now with existing battery technology and cut our use of petroleum by more than 75%.

    A cut of that magnitude would stretch the supply of petroleum far into the future and provide a huge decrease in transportation produced CO2.

  28. Wonhyo says:

    Bob – DMT does not exclude conventional road-bound battery vehicles. It solves the traffic congestion problem, as well as the charging infrastructure problem. The elevated track concept is designed to retain the existing surface level roads for road-bound cars, thus DMT will add to existing vehicle throughput, not compete with it. DMT will cut transit times for all, since it will take many vehicles off the surface roads and onto the track.

    A DMT vehicle would be essentially a battery powered vehicle with a track adapter, in additional to conventional wheels and tires. It will take surface roads from garage to track and from track to office. The transit through the most crowded areas will take place on the efficient, automated track.

    As for infrastructure, DMT will obviate the need for numerous individual car chargers. With conventional charging, each parking lot will have to install enough chargers for all the battery vehicles that park there. This would be a tremendous cost to employers, and an inefficient usage of charging infrastructure, as most charging stations would be utilized less than a third of the time (for an 8 hour workday). With DMT, the track IS the charging infrastructure.

    DMT will also reduce the required vehicle battery dramatically because the car will actually be charging while moving on the track, rather than discharging.

    I realize DMT is a huge infrastructure investment, but if you consider the alternatives, DMT is superior in providing faster transit times, greater throughput, reduced vehicle battery capacity requirements, dramatically reduced investment in individual charging stations, and the privacy of your own vehicle. Actually, taxi and public transit can also operate on DMT tracks, so DMT tracks can take taxis and buses off the road too. This will reduce the vehicle traffic on the surface roads, perhaps allowing wider lanes dedicated to bicycles (while retaining one or more lanes for conventional road-bound vehicles).

    It is a false choice to assume we make a DMT infrastructure investment or none at all. Whether we choose DMT or not, some major infrastructure investment will have to be made to provide charging stations, and to accommodate increase vehicle traffic. DMT solves both.

  29. Bob Wallace says:

    We can solve the traffic flow/spacing problems without building a track system.

    Right now we could “link” individual cars via inexpensive radar and turn speed/braking over to a CPU. A bit more easy to implement technology would break up the “car train” as needed at traffic lights.

    By taking the driver out of the process we could allow cars to drive with less distance between them and maintain more constant speeds.

    Charging will not be a significant problem for the typical suburban/urban commuter. With ~40 mile ranges a lot of people could make the daily trip with only an overnight charge.

    Others will need to plug in at work, but those outlets would not be particularly expensive to install. In fact, they could be profit points for businesses that want to get into that business. The cost of living more than 20 miles from your job might be an extra quarter/half dollar per day to use a plug point.

    Remember, a (non-rapid) charging point is nothing more than the sort of outlet that many have in their houses for their electric clothes dryer/ranges. Just add in some metering capabilities.

    Given sufficient scale we can produce automatic plug in systems for not much money.

    Drive into a parking space and push the “Please Charge 100%/50%” button on your dash. An outlet will extend from the “parking meter”, read the code from your car, charge to the desire that you have requested, and bill your account.

    Systems like this can be built gradually. Track systems would be large undertakings which would require massive planning and construction.

  30. Wonhyo says:

    A trackless smart car system with sensor based vehicle spacing can help, but DMT still has some significant advantages….

    The stopping distance on surface roads is much less consistent, predictable, and controllable than the stopping distance on a track. DMT vehicles on a track can be spaced more closely together than similar smart vehicles running on surface streets. The DMT track also ADDs to existing surface street capacity. Thus DMT will provide higher speeds and greater throughput than surface street based systems, even when equipped with automatic spacing.

    Taking the driver out the process of driving is easier on a DMT track than on an open surface street. The track has well-defined and physically separated on- and off-ramps, isolated from surrounding bicycle and pedestrian traffic. A surface based automatic driving system will have to contend with those additional, unpredictable obstacles.

    A DMT vehicle will also have a higher uptime ratio (in proportion to time spent on the track). A road-bound vehicle has to make up for all of its driven miles with a corresponding amount of parked charging time. A DMT vehicle is charging while moving on the track, so there is much less parked downtime for charging. Increasing battery size will increase the continuous operating time for a road-bound vehicle, but also increases the required charging time.

    Track systems are large undertakings, but they can start small and be built gradually (take a look at the L.A. Metro, which is heavily utilized, despite its gradual buildup). Planning, when done right, is a good idea.

    Take any urban-suburban corridor, where you have a daily gridlock of commuters who drive

  31. Wonhyo says:

    Looks like my last post got cut (not sure if this is a feature to limit comment size). Anyway, to keep this on-topic, DMT can reduce to required battery size, since the vehicle is charging its battery while on the track. This also increases the service time ratio. A non-track car will have to spend charging time in proportion to driving time. A DMT vehicle that spends most of its driving time on the track will need very little charging time off track.

  32. DH says:

    The charge/discharge limits for a battery are very important, Hybrids have the same limitation, in order to extend battery life, and furthermore some Hybrids always need a large percentage of charge in reserve in order to provide full acceleration when required.

    Maximizing cost benefit, as some have pointed out, is only one factor. Convenience is also however very important. So, why not provide the customer with a range of battery capacity options, 20, 40, 60 & 80 mile ? The customer pays for what they want, and can purchase more modules later if desired.

  33. pjkPA says:

    CMU doesn’t mention that it would be easy for GM to offer a smaller battery if demand was there… it could also offer a all electric version…unlike the Prius which depends on a overcomplicated hybrid system where both the ICE and electric drive have to propel the vehicle.
    And why is it that the CMU doesn’t consider the incentives and discounts that anyone can get ..into their research. CMU based their research on $6/gallon gasoline skewing the results…..I’ve saved over $11,000 with my GM card alone. The last two GM vehicles I’ve owned were bought with a $10,000 discount … while I still hear of most foreign car owners still paying sticker price or just a little under. This fact is not in research.
    Who’s side is CMU on anyway? Do they support foreign manufacturers over our own American manufacturers? Maybe they have been “bought” like the majority of our “media”.