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New Jersey Turnpike As a Power Source?
New Jersites writes "New Jersey, home of the eponymous Jersey barrier, is considering wind turbines powered by the breeze generated from traffic on the Jersey Turnpike. The wind turbines won't be built on the side of the highway. They will be built inside — what else? — the Jersey barriers. By replacing sections of solid concrete with Darius turbines, they might be able to harvest enough energy to power a light-rail line."
I'm not a physicist, but won't the turbines cause a drag effect on the cars, resulting in the cars burning more fuel? Is so, aren't they just moving the problem from one place to another? There's no such thing as free energy, right?
Truly curious - I'd love an explanation if someone knows why this isn't the case.
Finally something I have to be proud about in NJ besides the Devils....
Oh wait, there's a traffic jam!
In other words, if the car drag is causing a wind of sorts, that wind would normally dissipate its energy as friction against the surfaces it blows along - causing the energy top be lost as heat. Now we're just providing an alternative energy soak that extracts the useful enrgy.
Engineering is the art of compromise.
Before everyone decides to start bashing good ole NJ. I would like to point out that the actual article says nothing about the NJ Turnpike. The current concrete barriers are called Jersey barriers, and all we have here is a new barrier with turbines...thus the name "NEW" Jersey Barrier.
But the cars are the wind generators, not the turbines. If a turbine generated any significant wind itself, then it wouldn't be a very effective generator, would it?
The stream of cars generates an air motion along their path. Like geese (though through a different mechanism) the leading cars reduce the amount of air drag experienced by following cars. This improves their fuel economy. (The phenomenon is even more pronounced with semi-trucks. "Drafting": following another truck closely to save even more fuel, is a common practice.
A smooth central barrier separating the two directions of traffic improves the situation by letting the two sides of the freeway have separate airstreams traveling in opposite directions. The barrier reduces energy lost to turbulence, improving the airflow.
Replacing the barrier with turbines will suck energy out of the air streams on both sides to generate electricity. The result will be to decelerate the airstreams that had been giving following vehicles an advantage.
While some of the power comes from captured crosswinds and some from capturing energy that would have been lost to turbulence anyhow, a large portion of it comes from increasing the drag on following vehicles by putting friction on the "following wind": Fuel economy for the trailing vehicles in a bunch is reduced to something near that of lone or leading vehicles.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
By the way:
There's PLENTY of power to be had WITHOUT disrupting the traffic airflow and canabalizing the fuel of the cars.
A freeway or toll road is a clear area and there will be plenty of winds ABOVE it that are essentially unrelated to the airflow near the ground. They're also faster - with energy going up with the CUBE of the airspeed.
By building a wind turbine that starts significantly above the ground the turbines can avoid disturbing the flow at traffic level while collecting plenty of energy.
Also: A Darrieus wants linear airflow THROUGH it. It would be great for salvaging power from crosswind, but rotten for snagging power from opposing winds on the two sides of its axes.
And they're a major hazard: Darrieus turbines fly at tip speeds of about 7 times the wind speed and their narrow blades experience drag loads about equivalent to a wind barrier with a cross-section the size of the swept area - reversing twice per rotation. This has tended to produce fatigue in their materials, sometimes ending with the mill coming apart in high winds some years after construction, with massive pieces flying around at a goodly fraction of the speed of sound.
A savonius-derived design (like the Sandia configuration) would be a better choice. Though it only collects about 2/3s as much power for a given swept area, it rotates at about an eighth the speed and has broad blades that can be much more solidly constructed.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
As has been pointed out already this is a stupid idea. It would make much more sense to put the turbine on the train so it's forward motion can generate electricity. That way the train is self powering. Much greener.