Yesterday, Gizmodo got very excited about an array of four turbines that attaches to the roof of an electric car, and promises to recharge the car as it drives. It's one of those ideas that sounds really good for about half a second, at which point the massive flaw becomes readily apparent.
Gizmodo said of the device, “Electricity generating windmills chum out free energy as long as the wind is blowing, so strapping one to the roof of your car where there’s always a breeze as long as you’re driving just seems obvious.”
At high speed, a car's motor is working primarily to overcome air resistance, which is why the words "drag coefficient" are so important. A turbine like the one in the Transport Turbine, works by turning air resistance into rotational energy. This means that the turbine will significantly add to drag. In a universe with no friction, this could theoretically get as good as a net zero, when it comes to energy generation. In the real universe, power coming from the car's battery goes into a drivetrain, where there are heat losses, and then it overcomes air resistance and tire friction, where there are more energy losses, and the stupid turbine spins, losing energy to friction, and transmits energy back to the battery, where there are more losses to resistance in the wires.
We all should have learned that perpetual motion machines are impossible in physics, but apparently not. The only thing this will do is reduce the efficiency of the car to which it is attached and waste money.
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[via Gizmodo]
