After a fire apparently caused by ahitting 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 .
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 atin 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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