# Traffic Turbines

I saw a video on FaceBook today that showed traffic turbines. They supposedly generate "free" energy from the traffic that passes by them causing them to spin. Just because I'm curious, I was wondering if this energy isn't really free, but is in exchange of a minuscule drag put on the passing vehicles thereby transferring the energy cost (as small as it might be) to the drivers that pass by.

berkeman
Mentor

berkeman
Mentor
After a Mentor discussion and a PM discussion with the OP, the thread is re-opened. The key here is energy recovery without placing an extra energy burden on the passing vehicles. It appears that this may be possible with some of the technologies that the OP @InquiringMind has been reading about.

anorlunda
Staff Emeritus

You can surf on the wake of a boat. So can you surf on the wake of a truck, or otherwise extract useful energy from it? The answer depends on scale. On a micro scale, this is ridiculous. On a mega scale it is simply weather and wind power.

You can model a vehicle on the highway as H<<L (High pressure at the front, Low at the back, < shows direction of motion). Some vehicles are short H<L, some long H<<<L. So a highway with 4 vehicles might look like this.

H<<L.......................................H<L................H<<L..............................H<<<L................

If we put a pressure sensor on the side of the road, it would record a transient like this for each passing vehicle, with the time between high and low peaks roughly one half second.

Can we extract useful energy from those H and L pressure fluctuations?
• Micro scale: Could we extract useful energy from the random fluctuations in pressure of the air in a room? Clearly no. That is a the kind of question we don't allow here on PF. If you try really hard to analyze why it won't work, you will eventually come to Maxwell's Demon.
• Mega scale: Think of those H and L symbols on the weather map of your continent. We can and do extract energy from those fluctuations; and we call it wind power. It does not change things that a highway is one dimensional while the surface of the Earth is two dimensional.
• Intermediate scales: So where do we draw the line between mega/micro practical/crazy? If we were talking about hot/cold temperature fluctuations, then we have firm theoretical foundation, The Carnot Engine.
https://en.wikipedia.org/wiki/Carnot_heat_engine said:
No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between the same reservoirs.

I don't know of an equivalent to Carnot for pressure fluctuations, so I can't define where to draw the boundary. Nevertheless a boundary exists. Maybe some other PF member can provide an equivalent to Carnot's Theorem for this case.

So where does a traffic turbine fall on the macro/micro scale. Imagine the blades of the turbine accelerating, then reversing direction in a half second. What do you think?

[Note: I originally rejected this thread because I was thinking of the micro, which made this idea ridiculous. But that was hasty, and the better answer is that "it depends on scale."]

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berkeman
sophiecentaur
Gold Member
2020 Award
I saw a video on FaceBook today that showed traffic turbines.
It would help if you could give us the link to that video.

berkeman
Mentor
It would help if you could give us the link to that video.
It looks like the OP is not online yet today, so here are his links from my PM conversation with him:
The video that I originally saw on FaceBook was this one: featuring the Enlil Vertical Axis Wind Turbine. The company also has this video which says that the turbine "captures the flow of traffic on the road":
Since seeing these videos, I Googled Traffic Turbine, and found other references to the concept:

Even this one from Shell Oil: https://www.shell.com/inside-energy/turbine-turns-traffic-into-energy.html

sophiecentaur