Batteries Proterra electric buses

Published on February 22nd, 2016 | by James Ayre


Electric Buses Efficient As He**, NREL Finds

February 22nd, 2016 by  

Originally published on EV Obsession.

Proterra electric buses

A new analysis of a recent 12-vehicle Proterra electric bus demonstration (put on by Foothill Transit in California) by the National Renewable Energy Laboratory has found that these buses possess an average fuel economy roughly 4 times higher than that of baseline CNG buses.

The exact comparison shows an overall average efficiency of 2.15 kilowatt-hours (kWh) per mile for the electric buses, which equates to 17.48 miles per diesel gallon equivalent, and an average fuel economy of 4.04 miles per gasoline gallon equivalent for the compressed natural gas (CNG) buses, which equates to 4.51 miles per diesel gallon equivalent.


The National Renewable Energy Laboratory (NREL) analysis found that reliability was also quite high — with the number of miles between road calls averaging more than 9000. Only 3 of these road calls during the data period (April 2014 through July 2015) were pertaining to battery system issues. This is apparently “exceptional for an advanced technology bus in the early stage of commercialization.”

Here are some of the other findings of the analysis (via Green Car Congress):

  • The average energy efficiency was 2.15 kWh per mile over 399,663 miles of use.
  • The average battery pack SOC is 75.4%, indicating a possibility for a usage window shift.
  • The average runtime per day is 13.2 hours with an average of 13 charges per day. Each charge averages 20 kWh energy delivered.
  • Accessory loads contribute to the overall range capability, as more than 50% of “system on” time is spent at a speed of 0 mph where lighting and HVAC loads are still required.


And an excerpt from the analysis:

Advanced technology demonstrations typically experience challenges and issues that need to be resolved. The challenges and lessons learned from the demonstration included bus-related problems as well as programmatic issues. One major challenge is addressing demand charges and time of use charges that affect electricity cost. This will be a major challenge for any fleet looking to deploy electric buses that charge during peak times.

The industry needs to work on a permanent solution for all BEB (battery electric bus) adopters to keep costs reasonable in the future. Another challenge is training operators and maintenance staff in the differences between BEBs and conventional buses. Foothill reports that there is still a lot of learning as the agency ramps up to a larger BEB fleet. The team needs to understand how service can transition to a higher number of buses.

A second report is expected to be released by NREL later this year, following the conclusion of another year of in-service performance evaluation

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About the Author

's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

  • neroden

    I doubt that NREL actually computed the efficiency of hell. All that fire and brimstone… seems pretty inefficient to me. 😉

  • philofthefuture

    So what happens to mass transit if Google comes out with a self driving UBER EV that costs maybe a buck to ride, picks you up at your door and delivers you right to your destination? That will be an interesting future.

  • sjc_1

    It is less than half the 17.48 miles per diesel gallon equivalent they quoted, they do not take into account the energy required to produce the electricity. Take that same gallon of diesel, put in in a generator then charge the batteries, see what you come up with.

    • Roger Lambert

      Did YOU include the costs of exploration, drilling, cracking, transportation, government subsidies, health costs, and environmental costs of diesel fuel? No? Didn’t think so.

      • sjc_1

        I am talking about a gallon of diesel or perhaps a therm of natural gas making electricity then charging a bus. Much of electricity in the west comes from natural gas at about 40% efficiency. Now transmit that power with losses, convert it with losses and charge/discharge batteries with losses.

    • That’s precisely what they did. If they were pretending the electricity came entirely from solar, what would the MPGe be?…

      • sjc_1

        It is still total energy per mile, since solar is 20% efficiency at best there you have it.

        • jeffhre

          Solar is 20% efficiency at best of what, sunbeams, that’s just plain hilarious!

        • Santeri Miettinen

          yes solar panels have roughly 20% efficiency but why would you care about that? light from the sun is free you know?

  • Freddy D

    $900,000 for a transit bus? There’s your problem. Has anyone on this thread ever had a laptop or mobile phone? What’s the best you can hope for regarding battery lifespan? I’m lucky to get 4 or 5 years when fully cycling these things daily.

    The capital on the bus must be cheap enough to budget full battery replacement once or twice per decade IMHO. If I’m a decision maker for a transit agency, I’m going to buy tried and true if the NPVs and all financial calculations are even close. When BEV or BEB is half the cost to operate per decade including a full battery refresh, now we’re talking.

    Don’t get me wrong, if I have a chance to ride a battery bus I’ll do it in a second. Just financial realities.

    • Steve Grinwis

      The decreased operating costs pay for the batteries in about 19 months.

    • Dragon

      I’ve had third-party phone and laptop batteries fail in under a year. However, comparing consumer electronics batteries to car batteries (generally with 8 year warranties and expected to last much longer – Prius cells are still going at 15-20 years) or bus batteries is kind of silly. Vehicle batteries have better chemistry and much better temperature and charge speed management. On the other hand, consumer electronics makers have every incentive to let you stress and degrade the battery so you can buy a new device in a few years or pay the device maker to install a new battery.

    • I met with the head of Barcelona’s transit agency a few years ago. They were trialling BYD’s electric bus. Based on lifetime estimates and how it was performing, he said it was cost-competitive with a conventional diesel bus on a lifetime basis. I’ve seen similar statements over and over since then regarding electric buses.

      Apparently, this study didn’t take it as far as to compare lifetime costs.

      • Freddy D

        It appears that something is very wrong with Jorrit’s calculations. At best these are close to equal on a lifetime basis, not paying back in 19 months. Let alone the risk of early battery failure. As battery prices fall, then there’s a value proposition.

        Reply to Jorrit above with numbers:
        Something is wrong with your calculations. A diesel bus burns 500 gallons/month to go 2000 miles/month. That’s maybe $1,000 or $1,500 per month total cost. Buses don’t cost $17k/month in fuel to operate. Maybe 19 Years or more.

    • Uncle B

      Batteries on that scale have large recycle value for the Li they contain?

  • hybridbear

    What about the maintenance issues? The BEBs had many less miles between service calls according to the data. Why? What went wrong with the BEBs?

  • Philip W

    Is the US really so uptight, that you need to censor ‘hell’?
    I already knew they were uptight about a lot of stuff and words (like shit), but that is really funny to me.
    You guys should come to Bavaria, you would not survive a single day here haha.

    • vensonata

      I think the U.S. is the most obscene and profanity laced country these days in the rankings. They have gone so far that they have come out the other side of the looking glass and it is now a hip irony to use asterisks on the word “he**”

    • Ha. I live in Breslau 😀 But we typically get backlash if I use a cuss word, so I try to respect some people’s sensitivity.

  • Ronald Brakels

    From the title I expected electric buses to be as efficient as helium fusion, which I though was a bit of an unusual thing to compare it to.

    • lol 😀

    • juxx0r

      Me too, kept looking for the annotation corresponding to the two asterisks.

  • Ian

    I think BYD buses are a bit cheaper ($550,000 on one web site) and they don’t have the added trouble of 13 charges a day- just one charge at night. I wonder if the high price of these buses is because it includes high-speed charging stations located out on the route?

    • Philip W

      I’m usually not a big fan about those inbetween-charge buses, but I imagine they can make sense on some bus lines. If there is only a bus driving by every 60 minutes (or even less frequent) then it might not make sense, but if there are buses coming by every 5 minutes, it could be very cost effective.

      Ofcourse it also means less flexibility since you’re constrained to bus lines with enough chargers on their way. Rail replacement service is most likely not possible with those buses.

      I’d really like an in-depth comparison between buses with big batteries and buses with small batteries + fast charging. Any of the cleantechnica authors willing to do that?

  • Kraylin

    Only 9,331 miles compared to 45,547 between road calls doesn’t seem very good. They did note most road calls were not for battery related issues so maybe this speaks more poorly above Proterra than Battery electric buses in general.

    • GCO

      On the flip side, the CNG buses stayed in the shop longer, and did cost more to maintain, despite being a much more mature technology…

    • JamesWimberley

      The non-propulsion maintenance costs per mile were also higher. So it is a question of the general standards of manufacturing.

  • Kyle Prell

    So at this rate it will only take 30 years for the bus to pay for the difference in initial cost.

    • Jorrit

      First: no. At about 2k miles/mth, fuel cost electric are: 2,15kwh/mile*0,12US/kwH*2000mile= 540US. For CNG its 4.04GGE*2,08US/GGE*2000=17,500US. That makes these things pay for themselves within 19 months. Secondly; although new tech may be expensive at first, it might develop into financially competitive alternatives once they are given an opportunity for real world learning and scale up a bit. Your question, then, is a very cynical vision, one which would never allow new technologies to develop beyond pilot project phase. Fortunately there are entrepreneurs who have a vision (and balance sheet) to look beyond next quarters earnings

      • Freddy D

        Something is wrong with your calculations. A diesel bus burns 500 gallons/month to go 2000 miles/month. That’s maybe $1,000 or $1,500 per month total cost. Buses don’t cost $17k/month in fuel to operate. Maybe 19 Years or more.

        • Uncle B

          CNG! Not carcinogenic benzene containing Diesel with the emissions?

  • Frank

    Curious how many of those 13 charges per day happen during solar hours. In 2016, California had as much as 6GW of solar come on line some days, and this year will be much more.

  • tibi stibi

    i find the diff in purchase cost enormous. 575k or 904k i know batteries are expensive but that much? or is it because these buses do not have volume jet?

    • Preston C.

      I’d say it’s a issue with volume, and maybe materials used in Proterra. I think they use extensive carbon fiber. I’m pretty sure an electric BYD bus only goes for $400k.

      • JamesWimberley

        Proterra’s main selling point is the Stars and Stripes. BYD battle all the time – not just in the USA – against protectionist sentiment and a prejudice against Chinese quality. If their buses came all in white with an Apple logo, no one would mind.

        • voracity

          There’s no protectionist sentiment in China?

      • neroden

        It’s mostly an issue with low volume — have to cover the fixed costs of the production line somehow, and it’s spread over a relatively small number of buses.

    • Sreehari Variar

      I’m wondering why a Diesel bus costs 575k? I know long haul multi axle volvo buses for a fact only cost in the vicinity of 150000 USD in India. And most of the time, comparable vehicles are costlier in India than USA.

      • Dragon

        The $575k bus shown on the chart is Compressed Natural Gas (CNG), not diesel.

        • Geoff Wood

          The CNG upcharge should be no more than 60K over diesel. It’s less than that for dedicated CNG large trucks, but buses have a different requirement for placement of CNG tanks and thus I assume higher balance of plant costs. Sreehari’s question is very valid.

        • Sreehari Variar

          But why still so big of a difference? If a multi axle diesel bus costs only 150k, why should a CNG city bus cost 575k?

  • So after two years of improved batteries what is the price of the Proterra BE35

    • Zooba

      It can’t be the battery that is the largest contributor to the difference in cost here. The table lists it as an 88kWh battery. A 90kWh battery in a model S costs Tesla about $20,000, maybe less by now. Even considering much worse $/kWh it still doesn’t come close to explaining the difference.

      My guess is that since these buses are some of the first of their kind you’re paying for the inefficiencies of low volume production, recouping R&D and maybe a healthy margin for the “green-cred”.

      • vensonata .

        Sounds about right. Notice Lithium Titanate battery, the most expensive with very high cycle life. Will they actually get to use all those cycles? Well, this is early days and these are prototypes. There are simply no inherent reasons why they need to be any more expensive than i.c.e. vehicles once scale production begins.

      • GCO

        Not at all the same battery tech. The Proterra Li-Ti can charge roughly 10× faster, going from 0 to 90% in 6 minutes, repeatedly (the buses in this study averaged 10 partial charges per day).

        • vensonata

          Right, that makes sense for high cycle life. At 10 cycles a day they have a chance of using the cycle life and justifying the cost. Also, I had forgotten about the extreme rapid charge capability of these batteries.

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