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most efficient car on the planet

Discussion in 'Electric Vehicles' started by TEG, Aug 21, 2008.

  1. TEG

    TEG TMC Moderator

    Aug 20, 2006
    #1 TEG, Aug 21, 2008
    Last edited: Aug 21, 2008
    What is the most efficient car in the world?

    Here are some street legal ones:

    Here, they say:
    "Boasting NEDC consumption of just 12 kilowatt hours per 100 kilometres and zero carbon dioxide emissions, the smart fortwo electric drive is the most economical and climate-friendly alternative in urban traffic."

    Here, Tesla EPA sticker says "City: 32kW-hr/100 miles, Hwy: 33 kW-hr/100 miles".

    Here, Wrightspeed X1 says 200Whr/mile (20kW-hr/100 miles).

    Here, the 2000 EPA Fuel economy guide listed some EVs like this:
    NISSAN Altra EV ........... 29/26
    TOYOTA RAV4 EV .......... 29/37
    FORD Ranger Electric ... 40/45

    Here, they listed the EV1 as 30/25

    Then there are all the prototypes competing for Auto XPrize.
    Including the Aptera which supposedly does 120 miles out of 10kWh.
  2. vfx

    vfx Well-Known Member

    Aug 18, 2006
    CA CA
    This question needs the word "production" in it.
  3. graham

    graham Active Member

    Dec 2, 2007
    Aptos, California
    And may also depend on a definition of "car" :smile:
  4. TEG

    TEG TMC Moderator

    Aug 20, 2006
    Well, the latest Tesla newsletter said "...there’s still time to reserve your place in history as an owner of the most efficient car on the planet..."

    I think they should have qualified it... At least saying something like "one of the most efficient". The way it was written it sounds like a challenge to find a more efficient car anywhere on the planet (NEV?, used? prototype?) I think those SmartEVs on the road in the UK are probably more efficient. They didn't limit to the USA... They didn't say production cars only... They didn't say anything about fleet vehicles... They didn't even say "highway capable" so it leaves a rather large field of anything anywhere on the planet that would be considered a "car".

    Are they guaranteeing that when your Roadster is finally delivered (in 2009+) it will be the most efficient car on the planet at that time?

    I know it is nit-picky, but I think they should be careful with the superlatives.

  5. Joseph

    Joseph Member

    Nov 30, 2007
    South Florida
    In terms of efficiency, I'd guess the Roadster probably is the world's most efficient production car. The EV1 may have consumed less electricity than the Roadster, but after almost ten years I'd imagine that there have been improvements in inverter/controller technology and maybe even the motor has been improved.

    Of course, sacrafices were made for the EV1 to be so efficient. From what I can understand, it's very difficult to make a car with a lot of downforce and a low drag coefficient, so usually one of the two has to give way. For a sports car, you need downforce, so lowering its drag coefficient is usually very difficult. The EV1, not quite a performance car, probably had a big trade off here. Also, more noticably, are the huge fat tires on the Roadster and the skinny little LRR tires on the EV1. I think (well, hope) that if the Roadster was designed with only efficiency in mind, that it would be able to best the EV1.
  6. TEG

    TEG TMC Moderator

    Aug 20, 2006
    Yeah - I don't think the Roadster is likely the most efficient car ever, and possibly not even right now. The Roadster was designed for style, and performance with efficiency not being the primary design goal. If drag coefficient was top priority then it would look more egg shaped (like an Aptera or EV1) and not have such stylish lines. If performance wasn't a goal then it would have lower rolling resistance tires. If efficiency was the primary goal I would think they would have worked more on the brake blended regen idea and less on increasing PEM AMPs.
  7. GSP

    GSP Member

    Dec 28, 2007
    The Roadster powertrain likely is extremely efficient in the true sense of the word. That is max energy output for a given energy input.

    For say 100 kWh purchased from your utility company, the Tesla powertrain should apply about 70 kWh of work (force * distance) to the vehicle.

    Mechanical work - Wikipedia, the free encyclopedia

    This work is applied where the rubber meets the road. Lb-Ft or Hp-Hr are more common units in the US, but using kWh make efficiency calculations easier.

    This is likely better than the EV1 efficiency due to Conductive Charging, Lithium battery, more efficient IGBTs, and Copper Rotor.

    However, compared to the Roadster, the EV1 had narrow tires optimized for rolling resistance, a 0.19 Cd, and maybe less frontal area as well. So the EV1 required less work to perform to a given speed vs. time profile for a given distance (like the EPA city or highway cycles).

    TEG provided the bottom line from the EPA:

    Roadster: 32/33 kWh/100 mi
    EV1: 30/25 kWh/100 mi

    So the Roadster has a more efficient powertrain, but the EV1's more efficient chassis more than compensates. The 25 kWh/100 mi highway really shows how dramatic the 0.19 Cd can be. Congratulations to the aerodynamicists at AeroEnvironment, and the GM designers that worked with them.

    The EV1 also may have had a more efficient charger, despite the inductive connection to the vehicle. I think I saw a statement from Tesla somewhere that charger efficiency was not a priority for them (and rightly so, with a very small staff with more important problems to solve). Since the EPA measurements include the charger, this does make the "what is the most efficient car" question a bit fuzzy.

    There is another thing to consider beyond efficiency. The amount of energy used (your electric bill) will also depend on the speed vs. time profile and the distance traveled. Both of these can change if you have a car with more horsepower, but identical efficiency to a comparison car. Instead of driving the same speed vs. time profile, you likely will use the extra acceleration to get to your destination faster. You also may even alter your driving habits to drive more miles/day, since the faster car allows this to be done without investing more of your time. This requires more Force, and more Distance, respectively. This will result in more work being done on the vehicle, even though the cost of that work (per lb-ft) is identical to the lower power comparison car.

    Whew. I hope that make sense.


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