Hey Mr. Green,
Is an electric car really more efficient than a hybrid getting 50-plus miles per gallon running on gas? How efficient (and green) can it be to charge an electric car with natural gas or coal-based electricity, when we lose roughly 66 percent of the original energy in generation and transmission? -Keith in Boston
Hey Keith,
Once a gas-powered car gets around 45 to 50 miles per gallon, the energy it consumes decreases to about the same amount of energy needed to propel an electric vehicle, or EV, of the same size. But as you indicate, that's no reason to get all cheerful and start believing that EVs or super-efficient gas cars will save the world. They won't. Alas, they might even hasten our ruin by promoting the illusion that more-efficient cars are "good for the environment." I don't care how many times T. Boone Pickens comes on TV to peddle this fantasy--he's wrong. The best you can say about the most efficient car is that it is less of an environmental menace than a gas-guzzler.
Now if you must have a car, an EV is the best choice. But this does not absolve EVs from the terrible environmental damage that will continue as long as cars remain our primary mode of transportation, instead of what they should be: neat toys for special excursions, racing, and antique shows and sites for torrid romantic encounters. If you want to find out why, read on.
EVs are more efficient than most of today's gas-powered cars. An internal combustion engine loses a lot of its energy in gasoline to heat and friction. Since electric motors are highly efficient, up to 95 percent of the electrical energy put into them can be converted to torque. But as you note, making that electricity in the first place is a different proposition. You get much less energy out of an electric dynamo than you put into it: Only about 35 percent of the fossil-fuel energy burned to run a typical generator emerges as electrical energy. An additional 7 percent of the electrical energy itself can be lost in transmission , and another 10 to 20 percent is lost in charging an EV's batteries. (Some new "combined cycle" dynamos do recapture heat that is lost in a conventional generator, so their efficiency is as high as 50 to 60 percent. )
EVs would be an even better choice if their power came from clean renewable sources like wind or solar. But it will be a long time before we have cars running exclusively on renewables, and we don't yet understand the full environmental impact of building enough non-fossil-fuel sources of energy to power a few hundred million EVs.
There are several other advantages to EVs. First, it's easier for authorities to curb emissions at the smokestacks of a couple thousand power plants than at the tailpipes of a massive fleet of automobiles. Second, electric cars need a lot less lubrication than gasoline engines, which all living creatures should appreciate because more than 340 million gallons of used motor oil get dumped into the environment every year--a hellacious source of pollution and damage to wildlife. A lot of toxic oil simply seeps out of cars, creating the greasy pools and splotches seen in many parking lots.
Now to the specifics of your question: How efficient are EVs when you account for energy lost from power plant to motor? A 3,000-pound electric vehicle like Toyota's RAV4 uses about 0.2 kilowatt-hours per mile. That's equivalent to 682 British thermal units, or Btu, a common energy measurement that lets us compare different fuels. If you get that energy from a fossil-fuel-fired power plant, only 34 percent of the original input becomes electrical energy--the other 66 percent is lost in the generation process. So it takes about 2,000 Btu to get 0.2 kilowatt-hours. But because transmission and charging the battery can eat up 15 to 20 percent of the original electricity, you'll need at least another 300 Btu to generate enough electricity to make up for the loss. That means moving the RAV4 one mile requires a total fossil-fuel input of about 2,300 Btu.
How do gas-powered cars stack up? A gallon of gas is equivalent to 124,290 Btu--so a 25-mpg car uses 4,970 Btu per mile, nearly twice the energy required by its electric counterpart. However, as you imply, if we improve the mileage, the gas-powered car or hybrid comes closer and closer to the EV in terms of energy use. At 40 mpg, it's down to 3,110 Btu. Bump it up to a Prius-like 50 mpg, and, voila, it's about 2,490 Btu per mile--close to the RAV4.
Cost-wise, however, there's also no comparison. EVs win handily for the simple reason that energy sources used to make electricity are presently a lot cheaper than gasoline, which now costs about six times as much per unit of energy as coal. EV enthusiasts like to boast about how little it costs them to get around, and they've got good reason. At $4 a gallon for gas, even a 50-mpg car costs eight cents a mile for fuel. With electricity at 10 to 15 cents per kilowatt-hour, the EV can go that same distance for a piddling 2 to 3 cents a mile.
Sounds fabulous, almost magical, but I find it downright terrifying. We know from bitter, prairie-defiling, forest-ravaging, suburb-expanding, war-begetting experience that when fuel is cheap, people will drive more cars more miles, while developers create more residential enclaves farther from where people work, begetting even more driving.
We know because it has already happened. During the oil crisis of the mid-'70s, we responded by doubling the fuel economy of cars. It was a great technological achievement. However, because of this leap in efficiency, more petroleum was available, which helped keep gas prices down, which in turn pushed up the demand for fuel. This is one reason we now have nearly 115 million more cars and SUVs on the road than in 1975, we drive them 2,400 miles farther each year, and we burn 40 billion more gallons of fuel in them. If we continue in this direction, we will pave more land and sacrifice even more wildlife habitat and farmland to development and more precious urban space to the automobile. It doesn't matter what power the vehicles use, they are still going to create environmental and social havoc while remaining a public-health menace because of the millions of people injured in car wrecks and the 40,000-plus people killed in highway accidents each year.
Worse yet, if it comes to pass that EVs are propelled by cheap power produced by fossil fuels or nuclear fission or any material--from your discarded plastic furniture to your very own corpse--they could become the vehicle of choice for our continuing ride to oblivion. If new technology allows them to go farther between charges and gives us the accelerative kick we crave, the demand for EVs could skyrocket. And they would derive powerful moral torque from environmental spin: They would be touted as the green solution to pollution, the thinking person's car, earth-friendly transportation. You can see the ads already: leaf-fringed cars, vehicles driven by smiling endangered species, or illustrations of cars with feet advancing on ever smaller ecological footprints.
The point is that if EVs really boom, there will obviously be a tremendous need for new electric power sources. If this power comes from conventional systems, a lot of new power plants will have to be built, and a massive amount of fossil or nuclear fuel will have to be produced to run them. The environmental impacts that could result from building and supplying these power plants are staggering. Therefore, unless clean sources of alternative power can be developed cheaply and rapidly enough to power EVs, the so-called miracle car could be just another overhyped technological fix that failed to live up to our glorious expectations. (Like ethanol, or nuclear power that was going to be "too cheap to meter.")
But even if all these clean-power sources could be developed, we have to seriously consider their possible unintended consequences. How many windmills and in whose backyard? How many thousands of square miles of solar panels and in whose favorite retreats? In our blissful fantasies of technological utopia, we ignore such questions and conveniently forget basic laws of physics and economics.
I'm all for electric cars. Bring 'em on. But for godsake let's get real: Unless we also drive a whole lot less, and create a whole lot more efficient mass transit, EVs might very well compound the huge environmental and human damage we're already doing with our automobiles.