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Engineers: Lowest Wh/mile possible for Gen3 at 55mph? Battery pack size

Discussion in 'Model 3' started by flyingpants, Sep 4, 2013.

  1. flyingpants

    flyingpants Member

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    This is a question for people with engineering knowledge. The current Model S consumes about 280Wh/mile at highway speeds (let's forget city driving for the moment). The future Gen3 car will be cheaper and smaller, with a smaller battery, but still needs to maintain the same range (200 miles). I think a 50kWh battery may be a good starting point:
    50,000Wh / 200 miles = 250Wh/mile

    Ways to extend range:
    -reducing size/weight by 20-25%
    -slowing the acceleration
    -using thinner tires
    -greatly reducing power used by the onboard computer systems etc.
    -eliminating side-mirrors
    -implementing rear wheel-covers as an option (I think they look REALLY cool, I don't understand what everyone's problem is)
    -using a more aerodynamic body shape (longer tail? like the VW XL1)

    So after doing all that, what is the absolute lowest Wh/mile figure possible at highway speeds (55mph) for a Tesla Gen3 BlueStar Model E? Or for ANY future 4-door car?

    Will it ever be possible to break 250Wh/mile (only about 10% less than 280Wh/mile)? If not, why not?

    Is aerodynamics the single most important factor? How much power do you save by (for example) cruising at 53mph instead of 55mph?
     
  2. mynameisjim

    mynameisjim Member

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    I'm not an engineer, but I can tell you that I routinely use 230Wh/mile or less in my Nissan Leaf (according to the onboard computer), if that helps.
     
  3. flyingpants

    flyingpants Member

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    At 55mph?
     
  4. essaunders

    essaunders Member

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    The LEAF is already at ~233wh/mile @ 55mph (idealized number - extracted from Tony's Chart)

    If Nissan could just figure out how to stick a heat-tolerant battery with 2x the density without an excessive cost upper, they'll beat Tesla at this game...
     
  5. mynameisjim

    mynameisjim Member

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    Yes, and Tony Williams (former Leaf and current Rav4 enthusiast) published some estimates that show similar values
     
  6. flyingpants

    flyingpants Member

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    Thanks for that info.

    That's great news, it means we can expect at least a reduction to 47-50kWh.
     
  7. rolosrevenge

    rolosrevenge Dr. EVS

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    0 kWh/mile, as long as you're going down a long steep hill :tongue:
     
  8. richkae

    richkae VIN587

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  9. flyingpants

    flyingpants Member

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  10. Tim

    Tim Member

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    I think the gen3 has a pretty easy roadmap. I assume top of the line car has 66Kwh pack. 10% efficiency improvements in drivetrain and CdA. 6% from wheels and tires. That gives a range roughly equivalent to the S85 using S60 efficiency as a baseline. Assuming battery improvements can yield a 3C charge rate and a 150KW charger gives about a 200 mile charge in 20 minutes. Nothing too earth shattering in those assumptions. Probably conservative. Sell the 50Kwh car for 35K stripped and the 66Kwh car for 45K stripped. I think wh/mile is a goal, but its not going to look like an Aptera nor does it have to. I think they're probably going to charge for supercharger access for the gen3 though which I wouldn't have a problem with. Just my guesses. If I was Tesla's competitors I'd assume this is coming and soon. If they don't have anything remotely comparable(including similar supercharging) then its going to be game over for them as far as EVs go. Assume cost per Kwh of $200 gives battery prices of $10K for the 50Kwh and $13K for the 66kwh. With a reasonable gross margin(20%), the manufacturing cost would be about $20K-25K a car ex battery. Totally doable imo.
     
  11. JPWhite

    JPWhite Member

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    That sounds about right.

    Over the last 3200 miles I have averaged 236 Wh/mile in my LEAF. My commute is 80% interstate, 65 mph cruise speed in the morning, but afternoon traffic cuts the average down.
     
  12. mkjayakumar

    mkjayakumar Active Member

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    #12 mkjayakumar, Feb 21, 2015
    Last edited: Feb 21, 2015
    But we have to remember that a 50kWh battery would perhaps only have a usable capacity of 45 kWh.

    Sometimes playing with these battery size numbers annoys me. Stating the full capacity of the battery is of no use, if the usable capacity is less than that and by an undisclosed amount. Only in KIA Soul EV I believe they state what is usable, and don't even bother to state what the extra buffer is.
     
  13. MartinAustin

    MartinAustin Active Member

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    I've actually done a 35-mile, level-ground trip in my P85 that was 241wh/mile... it was at night on a freeway, at 55mph w/ cruise control, headlights on, HVAC off. I was not very popular with the passing trucks. :frown: I routinely do a specific 50-mile trip around here for about 275wh/mile that is mostly freeway travel w/ some gentle hills involved... as long as I stay in the right-hand lane and don't really hold people up, there is plenty of opportunity to drive "slow enough". What's nice about the Model S is that I can hit the pedal and zoom off if I choose, but I can do 275wh/mile in this big car when I want to. I totally think 250wh/mile should be do-able in the Model 3. The question is, can it do 200wh/mile via the "economical" driving that allows the Model S to go 305 miles (as shown in Ideal Range mode)?


    Battery
    People talk about minimum battery capacities a lot on here, but I personally believe there is no “floor” below which Tesla won’t go… that enables the EPA staff to drive the car 200 miles during their test (probably 205 so that there is no doubt). I'll refer to that as the "EPA200." There will be larger battery options that allow the car to go further, but Tesla will charge extra for those.
    It’s been said in many presentations that improvements to battery density average about 7.5% per single year. (There is no guarantee of a year-on-year improvement, but the breakthroughs have averaged out to that amount since Li-Ion batteries were first rolled out by Sony in 1991.) By the time 2017 rolls around, energy density will have improved by 5 years’ worth over 2012, or 1.075*1.075*1.075*1.075*1.075 = 1.436. Batteries of equal capacity will also fall in physical volume by similar multiples. In 2017, an 85KWh battery will fit into a space that is 1/1.436th of the current Model S battery volume, which is approximately 2.13m x 1.22m x 0.15m or 0.38 cubic meters. Model 3 battery pack will take advantage of the latest improvements to density and anything else they can conjure up at the Gigafactory, to fit 85kWh into 0.27 cubic meters, and I believe this will actually be the volume of Tesla's Model 3 pack, since easier comparisons can be made about how far Model 3 can go on 85KWh vs. the Model S, which will have been on the road for 5 years.

    Just to show some math, here is that progression of capacity that fits into the Model S pack volume, with a 7.5% improvement each year:
    201285.0
    201391.4
    201498.2
    2015105.6
    2016113.5
    2017122.0
    2018131.2
    2019141.0
    2020151.6
    2021163.0
    2022175.2
    (If Tesla ends up accelerating this increase due to whatever chemistry research goes on inside the Gigafactory, things will be even better, but I won't assume that.)


    Power Electronics
    The 2017 Model 3 will use an all-new generation of power electronics, and basically convert energy back and forth more efficiently than the 2012-vintage Model S does now. Consider what JB Straubel had to say here JB Straubel | [email protected] SLAC 2013 - YouTube

    * Let’s assume the Model 3 invertor and motor provide a given torque using only 95% of the energy my car requires.
    * Let’s assume the Model 3 recharges the battery 5% better during regenerative braking.
    * Let’s assume that Vampire Drain will be smaller than it is today, and also that the touchscreen is smaller than 17" (and dashboard is also smaller), and the computer systems in the car use less juice.


    Car Size & Aerodynamics
    A major factor affecting the Model 3 car is its physically smaller size.
    Let’s assume it has the same mass as BMW’s 320i – about 3275lbs. (Putting it very unscientifically, the lightness of aluminium is offset by the weight of an EV battery.) This is vs. 4633lbs for the Model S-85, so the Modl 3 is only pushing 71% of the mass up to cruising speed.
    Also, being physically smaller means it will have a lower coefficient of drag. The Model S is the most aerodynamic production car on the road today, with Cd of 0.24 per manufacturer’s claim and independent measurement. Can they get the Model 3 down to 0.23? Aerodynamics will continue to play a crucial role for Model 3, especially for cruising speeds and range. Driving around town, you rarely move over 45mph and don’t benefit from aerodynamics too much; you’re also more likely to be able to charge here and there, and won't think about flat batteries. However, on longer trips, it's more likely to be over 50mph (on expressways, freeways etc.), and aerodynamics have a major impact on range. Assuming cameras are allowed in place of side mirrors by 2017, they'll be guaranteed on the Model 3 because they will allow for a lower-capacity battery to achieve EPA200. If for some reason you want to drive around with old style mirrors on your car, they will be sold along with the note that they shorten the range of your car.
    The cabin heater and AC compressor will require less power, since the interior volume of the car is smaller.


    Wheels & Tires
    The Model S is a big heavy performance car and starts out with 275/25ZR22 tires. The basic Model 3 will have perhaps the same as the base BMW 320i, which I believe is 225/50VR17 tires – so, a lot less rolling resistance, and somewhat improved aerodynamics, than Model S. Tesla will likely be lobbying Dunlop, Pirelli etc. to come up with a special tire for their needs – ultra-low rolling resistance – for the OEM parts.
    I totally agree with you that Tesla will create aerodynamic wheels and that these shall be the standard equipment on the base car. Great way to increase range by a few percent, and will pay for themselves (as far as Tesla's costs are concerned) by shrinking the size of battery required to achieve EPA200 by that same few percent. Other wheels will be available for extra money.


    Efficiency & Range
    So with all those differences to take into account (none of which we really know the hard data on), let’s consider what they could mean for the range of the Model 3. Elon repeatedly says 200 miles, but they won’t be saying “a 200 mile range no matter what you do” or even “200 mile range if you drive economically” - it'll be "the EPA tested it and they got 205 miles." They will follow up with a specification for getting some other number which they believe is repeatable - for example, 55mph, level ground at sea level, zero wind, no HVAC and so on, will get you 220 miles. If the Model 3's efficiency increases allow it to achieve EPA200 at only 200wh/mile, at that efficiency, it'd use 40kWh. Allow 5KWh for buffers and you have a 45KWh battery in the base model.
    Its upper power limit will be lower than what I currently have (320KW) but I can impose my own upper limit if I want to, which allows me to achieve 275wh/mile whenever I want. Restricting the upper power limit is a pretty non-fun way to guarantee longer distances - since you can't get up steep hills very easily, or accelerate with super-speed. Tesla Motors could fake that in the base Model 3, to give the notion that it is a cut-down car, and allow buyers of higher-spec cars to feel better. I do not believe Elon would want to do that, however. I believe restraint with the accelerator pedal, and looking ahead to anticipate slow-downs (in order to exploit regen) will be two great ways drivers can achieve extra miles.
     
  14. Bangor Bob

    Bangor Bob Member

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    The non-tractive loads need work. Particularly in the cold extremes where pack and cabin heating consume considerable amounts of energy. It may be that integrating a non-combustible insulating layer into the battery pack, and improving cabin insulation (and glass coatings) will pay dividends. It would help in the heat too, keeping exterior heat from soaking back into the pack and cabin once it's been removed. There are probably efficiency gains available in the heatpump/ac units too.

    The biggest single bang-for-the-buck is probably the aero though, yeah.

    - - - Updated - - -

    Apparently I'm not allowed to edit yet.

    Note on the Aero post above. Aero drag is the Cd multiplied by the frontal area (and a few other things, air viscosity and the cube of velocity). Those first two terms multiplied together are called the CdA or the drag area. So having the same Cd as a Model S, at 80% of the frontal area means you automatically have a CdA which is 80% of the Model S's.

    Carry on...
     
  15. David99

    David99 Active Member

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    Let's take the BMW i3 as an example. EPA rating for the i3 is 124 MPGe combined, the Model S is 89. That's about a 1/3 difference. In other words, according to the EPA, if the Model S needs 300 Wh/mile the i3 would need 200 Wh/mile. The BMW i3 uses about 33% less energy than the Model S. The I3 is significantly lighter, has lower rolling resistance tires and probably a slightly more efficient drive train. In terms of aerodynamics, the i3 isn't ideal so there is room for improvement for highway speeds.
     
  16. CalDreamin

    CalDreamin Member

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    EPA ratings for the 2015 Tesla Model S
    60....... 95 MPGe
    85....... 89 MPGe
    85D... 100 MPGe
    P85D... 93 MPGe
     
  17. stopcrazypp

    stopcrazypp Well-Known Member

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    The i3 benefits heavily on the EPA cycle from its light weight and skinny tires. However, in the real world, maximizing range matters the most on the highway and there aerodynamics play a big part (so a shape like the i3 is not ideal).
     
  18. David_Cary

    David_Cary Member

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    Yeah - Model 3 will not have the i3's super skinny clown tires.

    Martin - base tires are 19 in, 245 wide. Not sure where you got 275 and 22 in. So sure you can go down to 225s easily but you are talking 10% size change, not "a lot less" rolling resistance. Tire manufacturers have been pushed by everyone for LRR tires. This matters to everyone given government regulations. I'm not sure where a sub .1% manufacturer is going have any special influence

    Of course the Model 3 will be more efficient. But doubtful it will be more efficient than an i3 because the car won't be compromised as much. At some point, bigger battery is cheaper than other efficiency gains. I mean, if we predict $200 a kwh, then 5 more kwh is only $1000. Cheaper than aluminum and carbon fiber as far as bang for your range buck. Sure there is a weight penalty with a bigger battery, but it isn't as big as people seem to think.

    Vampire losses are not measured with EPA so they are irrelevant.

    Heating and a/c are also pretty tiny. I forget the exact testing procedure that EPA uses but HVAC use is not a big part of the equation.
     
  19. WarpedOne

    WarpedOne Supreme Premier

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    When speculating on M3 specs one should start by comparing MS60 an MS85.
    By all efficiency-important metrics they only really differ in weight - by some 50kg or 150 pounds. They have same aerodynamics and tires (rolling resistance). MS60 has a bit lower max power so it has a bit lower internal losses under max acceleration.

    M3 will be even lower weight with a bit skinnier tires (225?)
    Because it will be narrower it will have a new battery pack format. I'd guess it will start with a 50kWh pack and achieve 20x EPA range.
    Weight will be over BMW 3, somewhere around 3800 pounds.
    There is not much Tesla can save by using lighter materials, they can only save on weight by using less of it.

    Maybe we will be offered full moon wheel covers? :p
     
  20. scaesare

    scaesare Active Member

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    Or a coupon to your local restaurant supply redeemable for a set of pizza pans, and a set of self-tapping screws.
     

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