Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Energy Efficiency of EV's

  1. Aug 15, 2016 #1

    I'm looking for a good figure out there like this to describe electrical vehicles. I know EV's are on average 60% efficient but I'm looking to discuss the losses and percentage loss at the systems in an EV. Anyone have any insight?
  2. jcsd
  3. Aug 15, 2016 #2


    Staff: Mentor

    Are you considering only operating energy costs but not the production costs of the vehicles and the batteries or fuel?

    Typically, most PF threads start with a specific question.
  4. Aug 15, 2016 #3
    yes, only operating energy costs. I guess my question is what are the percentage losses at various systems within an EV like the picture displays above for a conventional vehicle.
  5. Aug 15, 2016 #4


    Staff: Mentor

    What does your own research show? I just googled "electric vehicle efficiency comparison" and got 1.6 million hits.
  6. Aug 15, 2016 #5


    User Avatar
    Gold Member

    One of the problems with numbers like this is their inconsistencies. In EVs especially the efficiencys vary based on a large number of factors. Those static efficiency numbers might be good for management or sales. It really depends what you need to use the numbers for. So my question for you, how do you plan on using these efficiencys?
  7. Aug 16, 2016 #6


    User Avatar

    Staff: Mentor

    I'm not sure what you mean by "60% efficient": all cars are exactly 0% efficient in that they produce zero output work. In other words, if you add up all the losses shown, they should equal 100%.

    So to alter those for an electric car, you should change the "engine loss" to what is appropriate (10-20% depending on what you include) and scale up the rest.
  8. Aug 17, 2016 #7
    Electric vehicles convert about 60% of the electrical energy from the battery to power the wheels—conventional gasoline vehicles only convert about 20% of the energy stored in gasoline to power the wheels

    I was curious about the losses in an EV relative to a conventional car
  9. Aug 17, 2016 #8
    Just as a comparison to conventional cars, not looking for very specific numbers as each EV is different as well
  10. Aug 17, 2016 #9

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    The heat engine for EV is whichever steam plant converted the fuel into the electric power that charged the vehicle battery.
    87% of US electricity comes from steam plants, coal & natural gas can approach 40% efficient , nukes 30%, combined cycle can approach 50%.
    So it might be proper accounting to assign that power plant loss to the EV when you tally up energy efficiency.

    old jim
  11. Aug 17, 2016 #10

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    If you have 62% in engine loss, you have 38% in non-engine loss. If an EV changes the engine loss to 20%, now you have 80% in non-engine loss. All those losses need to be scaled up by 80/38ths.
  12. Aug 17, 2016 #11


    User Avatar

    Staff: Mentor

    I thought I gave a useful answer, but your post implies you don't think so. Maybe you didn't get what I was trying to say (V50 just said the same thing). I'll run through a couple of examples from your first diagram (though not using the same numbers as V50):

    My interpretation of "standby" is that's idling, so that goes away completely and your "engine loss" drops to 40% using your 60% electrical efficiency (which seems very low to me, but I'll go with it). So instead of 21% useful power, you have 60%, of which 60/21*2=6% for accessories and 60/21*19=54% delivered to the drivetrain. From the drivetrain, 60/21*13=37% delivered to the axle. I'll let you take it from there.
  13. Aug 24, 2016 #12
    what you mean by 60% efficient. i don't understand it. clear me pls.
  14. Aug 31, 2016 #13


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    All motors waste some power as heat. So Power out ≠ Power in.

    The efficiency of a motor (%) = (Power Out/Power in)*100

    Say your motor delivers 156kW when consuming 213kW from the battery. The efficiency is then..

    (156/213)*100 = 73%

    The amount of power wasted as heat is...

    213kW - 156kW = 57kW
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted