After a lot of public criticism, Gizmodo has changed the headline on a story by Andrew Liszewski from Wednesday. The criticism wasn't surprising. The old headline gave the impression Gizmodo thought perpetual motion machines were possible: "Strap this wind turbine to your electric car and you can drive forever."
The claim, repeated in a corresponding Tweet, provoked a cascade of eyerolling comments on the site and at least one link to a video containing a statement by a noted fictional expert in the physical sciences. It's understandable that Gizmodo changed the piece's head to "Strap This Wind Turbine To Your Electric Car To Stay Juiced in Park," claiming the original headline was intended tongue-in-cheek.
ReWire will take Gizmodo at its word on that. But there are still some problems with the claims that remain in the piece. Attaching a wind turbine to your vehicle and expecting to gain any energy at all, other than when it's parked facing the wind, still violates the laws of physics.
Let's briefly address the original, now-retracted headline. The First and Second Laws of Thermodynamics, involving conservation of energy and entropy, mean that every single interaction between energy and matter in a closed system involves losing some of the system's useful energy as waste heat, with no new energy magically appearing to take up the slack. Imagine you've fitted your electric car with a wind turbine sufficient to recharge the battery in realtime, given enough wind, and given it a push to get it started. You can postulate that the car starts out at the top of a long, steep hill to make your imaginary back hurt less.
At speed, the wind turbine will start turning and generating some power, which will charge the battery, which will feed power to the motor, which will turn the driveshaft, which will turn the axles, which will make the tires push the car forward against the pavement, which will make the car move relative to the air, which will turn the turbine blades.
With the First and Second Laws of Thermodynamics in play, though, every single step in the long list above sheds waste heat. It wouldn't be too long before the car ground to a stop. Add a bigger turbine to catch wind more efficiently and the greater weight means the car motor takes more juice to move the whole setup.
In point of fact, you're much likelier to make the car work if you design it according to the misspelled specs in this image from the "Troll Physics" meme that peaked a couple years ago ...
... because that car has fewer moving parts. And a sail that might just catch enough ambient wind to move the thing, making the car a non-closed system.
Gizmodo's original headline explicitly described a perpetual motion machine, in other words, and they were right to change it even if it was intended as a joke. (After more than 20 years online, I've come to the conclusion that there's no joke so obvious and broad that someone won't take it completely literally.)
But even with the amended, less funny headline, the laws of physics still mean the car-top turbine as pictured won't actually work.
"Aerodynamic styling" is one of those car sellers' buzzphrases that seems like it's repeated so often that it's lost all meaning. "Styling" might be the culprit there. It makes the "aerodynamic" part sound like a bit of fashion, discardable as soon as our aesthetic sensibilities nudge us away from our Corvettes and toward boxier things like PT Cruisers. In today's SUV-informed auto market, "sleek" seems a little 1970s.
But car engineers still spend a lot of time considering vehicle aerodynamics, for a very good reason: the more readily air flows along the surface of a vehicle without being slowed down, the less power a vehicle has to use to overcome resistance from the air (a.k.a. "drag") as it moves. A vehicle (or, in fact, any object) that offers less resistance to air flowing past it is said to have a lower "drag coefficient" than those that offer more resistance.
Cars like the GM EV1 or the Honda Insight, where designers put a premium on efficiency, can drag coefficients low enough that -- combined with their smaller size -- they experience less than half the wind resistance of a small pickup or SUV, and less than a fifth of something like a Hummer H2. That doesn't make much difference if either vehicle is toodling around city streets looking for a parking spot, because the average air speed across the car body is too low to make a difference.
But get up to highway speeds and a sleeker body makes a difference. Drive at 70 miles per hour into a 30 MPH headwind, and that wind hits any obstruction your vehicle offers at 100 miles per hour. That's why engineers interested in efficiency spend time minimizing drag as much as possible.
Plop a wind turbine atop that car, and the engineers' work goes out the window. The whole point of a wind turbine is to have the wind hit it and transfer as much energy to the turbine blades as possible. And that's just another way of describing wind resistance, or drag. In order to work efficiently a wind turbine has to maximize drag.
Unless the auto-mounted wind turbine somehow replaces a part of the vehicle that offered even more drag, the wind that hits the blades will make the car work harder than it would have without the turbine. Even if it's a small turbine producing just enough power to charge your smartphone, the inefficiencies of the design, and the long chain of steps from the car's engine or motors to the tires to the road to the wind to the turbine, pretty much guarantee that you'll use less energy just plugging your smartphone charger into the cigarette lighter.
In other words, Gizmodo did the right thing to re-title its post to make it suggest using the turbine in a windy parking place. Though if you're going to do that, you're better off finding a vertical axis wind turbine so that you don't have to drive all over finding a parking space that points upwind.