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What are the technical barriers to large battery-electric trucks?

Discussion in 'Electric Vehicles' started by douhgboy, Oct 20, 2014.

  1. douhgboy

    douhgboy Member

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    Large trucks (Articulated trucks, the things that Americans call 'semis' I think) account for maybe 20% of vehicles, but about 80% of road transport greenhouse gas emissions (or figures of that order). Some smaller rigid trucks have been successfully electrified (Smith Electric Newton for example), but as yet it seems that battery-electric Articulated trucks are not being developed. Why is this? Is there some basic law of physics (size v weight v power v battery size) that makes a Battery Electric Truck (BET?) impractical, or is it cost, or infrastructure ... or what?
    I'd have thought that a BET would be attractive to a haulage operator on commercial grounds - cheaper to run, cheaper to maintain, longer lasting. So why are none of the big truck companies developing one? Or have I just missed it?
    I've seen (Seimens I think) demonstrate trucks with pantographs much like a tram, that charge on the move. But that would require substantial infrastructure spend. Given the rigid organisation and route management haulage companies apply, I would have thought that chargers at a haulage base station would work well. Battery swapping would also be an easy task - most of those places have forklift trucks.
    Or are large trucks the one practical application of a hydrogen fuel cell?
     
  2. ggr

    ggr Roadster R80 537, SigS P85 29

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    I think the big problem is that (most of) the batteries would have to be in the trailer, not in the prime mover, and sometimes those trailers sit in lots for months at a time. The trailers are surprisingly cheap compared to the movers, and that would change if they contained large batteries. But this seems to be an engineering and design problem more than anything else; maybe a little "battery trailer" between the mover and the cargo trailer?
     
  3. gavine

    gavine Petrol Head turned EV Enthusiast

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    Maybe battery supply is too limited to make a dent. Those trucks would require many more batteries than a car so perhaps that will be another business for the gigafactory to supply.
     
  4. Saghost

    Saghost Active Member

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    I don't think there's a fundamental technical issue here - just a whole lot of money and some infrastructure questions.

    A typical semi used to get about 6 mpg on the highway, and might possibly be up to 8 mpg with the newer streamlined designs.

    A diesel car of similar size to the Model S is rated about 36 mpg on the highway. So figure a well designed electric semi will have five times the battery usage or thereabouts.

    There's plenty of room in the tractor during for such a pack, and the six or seven thousand pounds of battery isn't likely to be an issue - but that's at least a hundred thousand dollar battery pack, and it would last for about three hundred miles and then need either three hours at a supercharger or a charge station that puts out a bunch more power.

    It's absolutely within our technology to do, but for anything beyond local delivery you need seriously large DCFC installations at regular intervals along the route - at which point the extra hundred thousand dollars for the battery pack might begin to make sense and eventually pay itself off.
    Walter
     
  5. wraithnot

    wraithnot Model S VIN #5785

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    In the US the total gross weight of semi trucks is generally limited to 80,000 pounds. Thus every pound of battery comes at the expense of a pound of cargo. Charging at night to save money with off-peak electric rates also doesn't work as well for long-haul trucks, fork-lifts, taxi cabs, etc. that have to run pretty much constantly. So I don't think the economics of electric long-haul trucks looks nearly as attractive as the economics for electric cars used mainly for commuting.
     
  6. deonb

    deonb Active Member

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    A standard SuperCharger won't fit a truck anyway, so it will have to be a custom SuperCharger, which can put out more power.

    There's no technical reason that a larger battery should take any longer to charge at a supercharger than a smaller battery. A Tesla battery can charge up to 50% in 20 minutes - doesn't matter how big the battery is. (E.g. if you have 5 cars all pulling into a A,B,C,D,E SuperCharger configuration, they'll still all get their first 50% in 20 minutes).

    Might have to be 5 cables to connect instead of 1, but it's all doable.
     
  7. CalDreamin

    CalDreamin Member

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    80% of road transport GHG emissions don't come from large trucks. In the US, more than twice as much CO2 is produced from gasoline (almost entirely cars and light trucks) than from diesel (medium and large trucks, and diesel locomotives).

    "EIA estimates that U.S. gasoline and diesel fuel consumption for transportation in 2013 resulted in the emission of about 1,095 and 427 million metric tons of CO[SUB]2[/SUB] respectively, for a total of 1,522 million metric tons of CO[SUB]2[/SUB]. This total was equivalent to 83% of total CO[SUB]2[/SUB] emissions by the U.S. transportation sector and 28% of total U.S. energy-related CO[SUB]2 [/SUB]emissions."
    http://www.eia.gov/tools/faqs/faq.cfm?id=307&t=9

    In the EU, total diesel consumption is a little over twice gasoline consumption. This is a higher percentage than the U.S., but still less than 80% of road transport GHG emissions come from heavy trucks in the EU. A significant part of the difference from US consumption patterns is the popularity of diesel cars in the EU

    http://ec.europa.eu/transport/facts-fundings/statistics/doc/2012/pocketbook2012.pdf
     
  8. Saghost

    Saghost Active Member

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    You're right. If you come up with a system to deliver ~600 kW to the truck, it could be charged as quickly as today's Model S is at the current supercharger.

    I mentioned the superchargers mainly because you're back to the chicken and egg problem - No one can do over the road trucking with a BEV truck until the charging stations are available, and no one can afford to spend money on the charging station network until the trucks are promising to use them. If Tesla was involved in the project, the supercharger network might be part of the answer, especially if the truck can grab two supercharger plugs at the same time.

    Access would of course be an issue - some lots seem to have the superchargers at the end of a straight shot where a semi could pull straight in and plug on the left and right front corners (the ones that Model S's are backed in to.) If the lot shape is right, that might work with a trailer attached.

    Of course, someone like Tesla whose motive is to electrify transportation might front the capital to start something rolling and develop lanes and standards designed specifically to handle the higher power for the trucks. If they know what they're going to want for standards, they might be able to roll it into the existing supercharger program (and funding) and add truck suitable lanes that can be used by current cars as well early, before they get the trucks together.
    Walter
     
  9. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    As much as I would love to see vehicles as large as Class 8s (the ones that can haul up to 80k pounds) become electrified, I have been of the belief that Wraithnot has the most important pitfall:
    As a demonstration of this, you need look no further than the US light truck ("pickup") market: Ford has just bet its company on the new aluminum-bodied F-150 series. Their rationale is the 500 pounds of weight saved translates into that much more hauling capacity and fuel economy. It will be telling to learn how the pickup is received by its market - there are some significant challenges.
     
  10. Saghost

    Saghost Active Member

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    That's a valid point, but I'm not sure the BEV truck would come out much heavier overall. I did a quick search online, and I think that a current generation Class 8 Kenworth has a 2600 pound engine, a thousand pound transmission, and at least a thousand pounds of fuel onboard.

    That's 4600 pounds without getting into the auxiliaries that can come out (no need for an APU, exhaust pipes, air filters, need only a smaller radiator, etc.)

    A 425 kWh pack to Tesla standards would be ~6500 pounds, and you'd need either a P85 drivetrain or a pair of standard S85 ones plus some minor modifications to drive the existing rigid axles and differentials (200 pounds?)

    If you designed from scratch for electric drive, I think you could get 3-400 mile range in about the same weight at the same size, using mostly off the shelf Model S bits and parts from the current truck line. Cabover might make a comeback, too, giving a chance for more cargo space in length limited locales - certainly it won't be maintenance issues that would prevent it.
     
  11. gavine

    gavine Petrol Head turned EV Enthusiast

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    Too bad solar panels are so heavy. If not, I have to think there's enough space on the trailer surfaces to at least extend the range a little.
     
  12. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    Economics.
    Start with all the people moving and maybe some light delivery. Forget semis for now, except in special cases like the Port of LA with its catenary system. There are advances in density and cost required for the "easy" BEV. Solve those firs, and then you can take another look. Semis are very heavy and magnify the challenges.
     
  13. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    Those are excellent considerations, Saghost.
     
  14. wraithnot

    wraithnot Model S VIN #5785

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    That seems like a reasonable back-of-the-envelope calculation. From a previous post on a similar topic, it looks like several companies are already building electric semi-trucks, but they're targeting them at short range applications at the moment. I'm not sure if this is mainly due to the battery costs, battery weight, or charging infrastructure required for long-haul trucks: How hard would it be to make an electric semi truck - Page 5
     
  15. RDoc

    RDoc S85D

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    I'm very doubtful that truckers would accept the idea of stopping every 150-200 miles for half an hour to recharge.
     
  16. drees

    drees Active Member

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    Let's look at the current capabilities of your current semi and see what it'd take to get an EV equivalent using some back-of-the-envelope calculations:

    Typically twin 100 gal tanks - typically around 6 mpg. So up to 1200 miles between fill-ups, but probably typically around 1000 miles in real life.

    To give even more benefit to the EV, let's say you actually only need to go 500 miles per charge - this lets you drive 8 hours before recharging and resting.

    Diesel holds about 38 kWh of energy per gallon - 6 mpg over 500 miles would burn 83 gallons or 3170 kWh of energy. A diesel is about 40% efficient, let's say that the EV drivetrain is 90% efficient, so needs about 1400 kWh to drive 500 miles or some where close to 3 kWh / mile.

    Yeah, that's a big battery - the equivalent of 17 85 kWh Model S packs.

    The Model S pack weighs over 1300 lbs or over 15 lbs / kWh, so a semi-sized pack would probably weigh close to 20,000 lbs - perhaps slightly less depending on how much packaging you could save by building a big pack.


    As a quick comparison, BYD builds 40-60ft buses with 324 kWh of battery and claims 155 miles of range - or about 2 kWh / mile. A semi is going to be less efficient than this (more tires, heavier, more drag) so I think my back-of-the-envelope numbers are fairly accurate.

    Looking at the weight of current trucks, it appears that the rig itself can typically weigh between 12-20k lbs.

    So perhaps with today's battery tech a pack around 600 kWh or so might work without giving up too much load capacity and have a usable range around 150 miles or so - this would work for regional trucking, but certainly not for long-haul trucking.

    If you look at the efforts made in the area today, that's currently what's being targeted - or routes even shorter than that.
     
  17. Saghost

    Saghost Active Member

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    It's a paradigm shift, but one that's already on the way. The new (2011) rules limit a driver to 11 driving hours per day, and require a 30 minute break somewhere in the first 8 hours:

    Hours of Service | Federal Motor Carrier Safety Administration

    I think that if you got to the point where they could get four reliable hours of freeway driving with a half hour charging/lunch/dinner break, it'd fit into the newer driving paradigm with no issues.

    You'd need supercharger type stations with megawatts of power and room for trucks, of course. (superduperchargers? :) )

    I doubt we'll see it right away - ItNotAboutTheMoney has a point that the local end is where electrification will start because the business cases are easier, the trucks cheaper, and you don't need superduperchargers. - but the technology exist now, and after the gigafactory it will likely be economically practical. :)
    Walter
     
  18. ElSupreme

    ElSupreme Model S 03182

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    Just about every truck that leaves my plant weighs out. They maybe have 20 pallets on them. If the truck weighs another 6000 pounds that is 2 less pallets. Or a 10% increase in trucking costs.

    weight is a huge issue. These things we are talking about are slower, heavier, and more expensive. Sure some day it might happen but battery cost and energy density go down it might work. But until diesel goes to $12 a gallon this is a long shot.
     
  19. Saghost

    Saghost Active Member

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    There are a few places I would argue you're being too pessimistic - thinking 6 mpg is still typical of a modern truck, expecting get 40% efficiency through the full ICE drivetrain in normal operation - but the reality is likely somewhere between your back of envelope and mine.

    More importantly, I don't think you need to plan for 500 miles of range - federal law now requires the driver to stop for half an hour somewhere in the first 8 hours and drive no more than 11 hours in a day. I think if you can get four or five reliable hours from a half hour quick charge, that should be enough - which means you only need 300-350 miles per DCFC (but you need more capacity beyond that to allow the fast charge for the full range.)
    Walter

    - - - Updated - - -

    I guess it's a question of what's expensive in the trucking costs... At national average rates, electricity costs about the same as diesel on a per kWh basis - but you get 2-2.5x as much of the power to the road, so it's effectively half the price or less per mile. If fuel is the dominant cost in trucking as I suspect, it'd still be cheaper.

    Also, it wouldn't be 6,000 extra pounds - Class 8 trucks have 2600-3200 pound engines (PACCAR MX-13, Cummins ISX15) and massive thousand pound transmissions and over a thousand pounds of diesel fuel. OTR trucks have to carry an APU now (350-500 pounds,) and then there's turbos and exhaust stacks and huge radiators and so forth.
    Walter
     
  20. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    It's not the truckers that are the problem, it's the companies paying them.
     

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