Elon Musk Explains Electric Car Energy Density

And May Reveal More About the Hurdles EVs Face Than He Meant

Tesla model S-Elon Musk-energy density

Energy Density Limits EVs

After a fire apparently caused by a Tesla Model S hitting some debris on the road, Tesla CEO jumped into the media fray with a letter addressing the incident.  While Musk’s defense of the safety of the Model S, particularly in relation to a gas-fueled car, is well-taken, part of his letter responding to the fire (which was followed by two other fires soon after) also revealed one of the ongoing hurdles faced by electric vehicles. In spite of EVs’ great efficiency, their “fuel” doesn’t approach the density of gasoline. Here’s the key portion of Elon’s letter:

Had a conventional gasoline car encountered the same object on the highway, the result could have been far worse. A typical gasoline car only has a thin metal sheet protecting the underbody, leaving it vulnerable to destruction of the fuel supply lines or fuel tank, which causes a pool of gasoline to form and often burn the entire car to the ground. In contrast, the combustion energy of our battery pack is only about 10% of the energy contained in a gasoline tank and is divided into 16 modules with firewalls in between. As a consequence, the effective combustion potential is only about 1% that of the fuel in a comparable gasoline sedan. [As printed in AutoWeek magazine]

As Musk noted, the combustion energy of the Model S battery pack is only about 10 percent of the energy contained in a typical gasoline tank. But it is not only the combustion energy of a battery pack that is significantly lower than gasoline, but it’s energy density, particularly when looked at on an energy/kg basis. According to a good summary on Science 2.0, gasoline has an energy density of 44 MJ/kg while lithium-ion batteries are about 1/16th of that. In a nutshell, that helps explain why it takes only a few gallons of gasoline to take a car the same distance that would require several hundred pounds of batteries in an electric car.

The Science 2.0 author adds – and I would agree – that the energy density issue does not negate the value of EVs or their technology, it merely points out the challenges of the real world. Of course, Musk can counter that his $80,000+ Model S can take you more than 250 miles, but for those looking at electric cars in the price range of an average car, the real world limit on a charge is closer to 100 miles at best. The energy density issue remains the challenge that battery developers must overcome, along with cost issues, in order to offer an electric car that is a true alternative to today’s efficient gas and diesel cars.

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About Author: Michael Coates

is editor at Clean Fleet Report and an internationally recognized expert in the field of automotive environmental issues. He has been an automotive editor and writer for more than three decades. His media experience includes Petersen Publishing (now part of Source Interlink), Green Car Journal, trade magazines, newspaper and television news reporting. He currently serves on the Board of the Western Automotive Journalists.

3 thoughts on “Elon Musk Explains Electric Car Energy Density

  1. Rocky
    April 16, 2014 at 7:49 am

    While your description about energy density is true, in these discussions, you ALWAYS need to talk about both the energy density, and then the engine/motor’s efficiency to be able to use that energy for moving the vehicle. Gas engines’ efficiency is pathetic in that area, so each side has an advantage, which is why they come out in a pretty similar ballpark. So come on, don’t just give one-sided info.

    • April 16, 2014 at 8:17 am

      @Rocky,
      Your point is well-taken (and noted in my story), but engine/motor efficiency only gets you so far in the real world when you’re weighted down with batteries. Gas and diesel engines may be “pathetic” in terms of efficiency, but their fuel packs quite a punch. You have to admit that a relatively lightweight tank of gas/diesel can take the average car significantly further than a much heavier and more expensive pack of batteries. And then there’s the “refueling time” issue. -ed.

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