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How low will wH/mile fall?

Discussion in 'Electric Vehicles' started by WannabeOwner, Dec 5, 2016.

  1. WannabeOwner

    WannabeOwner Active Member

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    I'm curious as to what level of efficiency might be achieved in "near future"

    I wonder if it is a factor that:

    Range of MPG in Gas cars is significant. 15MPG and 60MPG [USA gallons] at the extremes; is it fair to say? that there are "plenty" of performance cars in the 20MPG range and "plenty" in the economy range of 40-50MPG? a spread of 2x - 2.5x, maybe even 3x.

    Whereas with BEVs it seems that, at present, 250 wH/mi is very frugal and 400 wH/mi is an MS being driven pretty hard, and unlikely to be the actual average of the fleet, perhaps 350 wH/mi would be a fairer top-end figure. Seems to me that is a much tighter range of 1.4x. I wonder how low the wH/mi could go with more dense, therefore lighter weight, batteries (although Leaf at 1,000 pounds lighter isn't hugely more efficient than MS); perhaps there are drive-train economies to come too (although the efficiency of those seems pretty impressive already); perhaps more/better Regen to come (capacitors maybe ...) which will make a small improvement. Maybe improvements to Rolling resistance & aerodynamics to come? Maybe cold weather improvements?

    Not sure what the relevance & significance is, if any?
     
  2. YBT

    YBT Member

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    Interesting that you've identified a narrower delta in EV energy consumption figures than in ICE. Intuitively this would seem to relate to the efficiency (or lack thereof) of ICE vs BEV in converting energy into movement. This lack of efficiency will become noticeable as demand for power soars for larger vehicles. I'm sure someone with more knowledge will happily prove me wrong here.

    With regard to how low can they go?

    Well, obviously BEV's are in a very early stage of development so there are plenty of areas where refinement will drive up total system efficiency.

    - Weight (Battery, Drivetrain, Chassis Materials & Design)
    - Drag Coefficient (Mirrors, Wheel Well Disturbance)
    - Rolling Resistance
    - Conversion Losses / Inefficiencies (Motors, Inverters)
    - Energy Recovery (Regenerative Braking, Heat Pumping)

    Replacing side mirrors with cameras is the low hanging fruit on this tree representing an easily achieved 5 - 10% reduction in drag.

    I won't speculate too much about just how much room for improvement is left in each of these other than to say weight will come down considerably as improvements in all other areas will feed back into shedding mass.
     
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  3. WannabeOwner

    WannabeOwner Active Member

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    Thanks

    Is it significant that Leaf is a lot lighter than MS but not significantly more efficient? or is that just that Tesla have done an outstanding job making the MS efficient [by comparison]?

    I'm always staggered that the MS is hauling 2.5 tonnes around yet has outrageous acceleration, and yet relatively frugal wH/mi when I am not in a hurry :D
     
  4. YBT

    YBT Member

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    The Nissan Leaf is using a different (less efficient) electric motor tech (DC Brushless vs AC Induction), has different aero properties, different regen capabilities, single motor, tyres, etc. The higher efficiency of the S reflects a lot of attention to detail accumulating into a whole.

    The M3 will no doubt be segment/class leading in terms of efficiency but could drop the mic on the whole game by having a lower per mile consumption than tiny little compliance EV's like Fiat 500-e or Renault Zoe.
     
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