fuel efficiency of electric vs. gas cars

I’ve been considering whether to buy an electric car as my next vehicle.  I found this detailed analysis at Do The Math really interesting and useful.  Key points:

On the surface, electric cars are a lot more efficient than gas-powered cars.

The MPG equivalent of [the Volt, Leaf, and Tesla energy consumption] is approximately 80, 110, and 170, respectively. All are much better deals than gasoline cars deliver, primarily because the electrical drive system is far more efficient than the typical 20% gasoline engine.

However, when charging a car like the Leaf, the source of the electricity is important.

Two-thirds of our electricity comes from fossil fuel plants, typically converting 35% of the fossil fuel thermal energy into electricity. Only 90% of this makes it through the transmission system, on average. If your electricity comes from a fossil fuel plant, the 30 kWh delivered to your house took about 95 kWh of fossil fuel energy. The 73 miles the Leaf travels on a full charge now puts it at an energy efficiency of 130 kWh/100-mi. The MPG equivalent number is 28 MPG. From a carbon-dioxide standpoint, you’d be better off burning the fossil fuel directly in your car.

On the other hand, this doesn’t automatically translate to “don’t buy electric”:

I’m not saying that transitioning to electric or hybrid cars is not a good idea. I think it’s animperative, if we want maintain a car culture, given that fossil fuel supplies are going to decline eventually, starting with oil. Obviously, if your power comes from hydroelectric, solar, wind, or even nuclear, you don’t have the same concerns. Also, emissions controls (for things other than CO2) are vastly better for fossil-fuel power plants than for automobiles, so electric cars are less polluting. But if your priority is either reduced resource consumption or climate change and CO2 reduction, let’s focus on getting electricity from carbon-free sources before transforming our fleet of cars to electric—or at least accomplish the two in tandem.

I’ll post more if I find more good resources comparing environmental impact of different car types.  And I suspect I’ll also be sharing more from Do The Math — it looks like my kind of blog.

1 Comment

  1. Brooks Moses Said,

    March 12, 2012 @ 4:11 pm

    Not only is that a useful analysis, but it’s an accurate and appropriately nuanced one (and with intelligent comments, even!), which is somewhat rare. Nice find!

    It does miss what I think is one of the current justifications for buying electric cars, which is to apply intentional market pressure to drive future development. Of course, that’s something that is very hard to evaluate (and more a matter of opinion than substantiable fact), so you can’t do much with it beyond mention it.

    Other things not mentioned are: On the resource-usage side, a lot of fossil-fuel electric power comes from coal, not oil, and so although it’s a finite fossil-fuel resource, it’s a different one that can’t easily be used for transportation fuel directly. It also means different pollution profiles; an old dirty coal plant is a horror compared to a modern car, but the best new ones are significantly cleaner than most cars.

    And, on the CO2 side, it is reasonably feasible to capture and sequester CO2 from a coal or oil plant (although economically a bit shy of viable — though not so far as one might think!), whereas that will never be possible in a car, so that affects the near-future tradeoffs in the two.

    This all gets back to the issue about intentionally applying market pressure. It seems very likely that electric cars will be overall a superior technology in the medium term, so there is an argument to be made for it being worthwhile to support their market and thus their technological development now by buying one.