Alpha turbines on the roadside

Here is a fascinating idea that is going into production.
roadside turbines

If passing cars are powering the turbines, doesn't that mean the cars will experience higher wind resistance and lower mpg?  Wind energy is created by some outside mystery force but car wind is caused by cars and their engines/motors.  I think?

Yup, the cost is borne by the cars increased consumption of fuel. I think solar would work better since it is more passive and gleans energy from the sun not from a parasitic load on passing cars.

I like the idea. I just wish there was more specific.

Mike Haasl wrote:If passing cars are powering the turbines, doesn't that mean the cars will experience higher wind resistance and lower mpg?  Wind energy is created by some outside mystery force but car wind is caused by cars and their engines/motors.  I think?

My first thought was "cool, a way for property owners to put a little tax on traffic."  But if this were true, it wouldn't be socially efficient, because it's not an mechanically-efficient way to use fuel/energy.  

However, upon reflection, I'm not sure it's true.  Anybody who's ever "had their doors blown off" by a high speed vehicle passing too close knows that cars spend a lot of energy shoving air around.  Huge wind tunnels exist (fewer than there used to be when computer modeling wasn't yet a thing) so automotive engineers can blow smoke and watch the air motion, trying to reduce the extent to which cars interact with air.  Long before anybody cared about fuel efficiency, they were clear on the benefits of aerodynamic study to make cars go faster and vibrate less as they force their way along.  

So, vehicles shove a lot of still air, setting it in motion.  I have no idea what the larger emergent airflow patterns from traffic are, but it's vaguely plausible a nearby vertical wind turbine could harvest some tiny fraction of that auto-induced air-motion energy.  But does it follow that the turbine would increase wind resistance to the passing vehicles?  It might; taken to absurd extremes, you could mount these turbines in a solid row like concrete traffic barriers and we could imagine the air resistance to passing traffic going up, the way it does in a narrow tunnel.  (Stand on a subway platform and feel the rush of wind as a high speed train passes through the station; those trains seem to be pushing against a plug of compressed air in the tunnels that escapes at the stations.)  

But in real world situations, imagine that a land-owner set six of these turbines along his right of way.  (In practice this is going to be mostly illegal, because of roadside setback rules and such, but for discussion.)  Most of the escaping vehicle-pushed wind is going to pass between them frictionlessly.  By some extremely complex and chaotic modeling, you could perhaps calculate the fraction of wind that bounces off the turbine and increases the air pressure slash wind resistance in the roadway. My gut tells me it's going to be a fairly small fraction.  Perhaps miniscule.  They've done studies on this with respect to insane cyclists who "drift" in the vacuum vortex behind heavy vehicles so they don't need to pedal on the interstate.  What I've seen suggests that the "drag" on the semi is immeasurably scant because the semi is moving that bubble of air anyway, and doesn't really have to work very much harder to move it with a coasting cyclist in it.  The amount of drag the cyclist adds is insignificant in the total drag equation.

I would speculate that the same will be true of any likely quantity of roadside wind turbines.  But this is my own wild-ass guess and I'm barely able to comprehend the modeling process that would be necessary to confirm it; I certainly shouldn't be trusted in my speculations as to what those models would tell us.

P.S. That "outside mystery force" that powers wind is the sun. Wind energy is solar energy.  The sun heats various things, including air and surfaces that air touches; this (plus thermodynamics) creates energy gradients that want to equalize, so the air helpfully rushes around trying to even everything out again. The process, like all fluid dynamics processes, is impossibly complex in practice, and a real bear to model usefully.

Dan is on the money!
There is no extra drag on passing vehicles because of the turbines.
I have followed the development of theses, and they work best on what I know as Freeways, where traffic runs past in both directions with a wall between them.
As a Civil Engineer I am aware a lot of inner city roads are built in that manner.

Perhaps read the whole site and the technical bits.
I know from personal experience riding motorbikes and a large truck comes the other way!! The airwall is massive, but if the truck is streamlined its possible to feel the difference.
The only tim the presence of another close vehicle occurs with slip stream.
I still race motorcycles and if somebody gets into my slipstream it can be felt on your shoulders, and it slows you down.
So I would flick sideways in an effort to break the slip.
Likewise if I run up to someone else, the front runner is slowed marginally and I can pickup a sling shot from them.

I don't think the passing cars are part of the equation.  Mounting the turbines on light poles is an opportunistic way of getting some elevation for the unit by using existing infrastructure.  As we all know, the higher the better when it comes to wind energy.

Thomas, in this case higher is not better.
Movement of the cars is the driving factor.
They are designed to use the wind created by passing cars.
All the details are on the site I gave the link too,

By that same logic the turbine would affect the vehicle slipstream and marginally slow it down causing increased fuel use. When you are going down the road and pass a parked car you feel it, pass a guardrail you feel it. Both marginal changes to the slip stream causing drag.

The facts are still being discovered.
Anything else may be speculation.

Has anybody read the details?

Here are some details from the FAQ page on that site;
Won’t your turbines impact cars as they drive past and slow them down?
No. Cars displace air when they move and have already expelled that energy. The turbine has no more impact on another vehicle than you do when you stand by the side of the road.

How much energy can they produce?
One of our turbines is comparable to 20 square metres (14.6ft) of solar panels.

How much wind do they need to turn?
Our turbines will start generating power in winds of just 4mph.

What’s the cut-out speed?
There is no cut-out speed. More wind = more power.

Ok.  I stand corrected.  They make the claim.  I'm skeptical.

I did a little browsing and found this video

It goes into a little bit more detail.  As far as I can tell the clever bit is the shaftless design, which means the turbines can be retrofitted to existing street furniture.
I also found other cute vertical axis turbines.
I'm quite interested in that they state there is no maximum speed of the wind for the turbine operation (in another video).  This is one of the things that puts us off having a turbine here, where winds of 80-90mph happen most years. Oh dear, another project to put in the to-do list!

skepticism is OK I think that is how the wheel was created!

The turbine has no more impact on another vehicle than you do when you stand by the side of the road.

I winced when I read that because it sounded like a very carefully worded way to dodge facts and figures. So I asked a friend of mine who was an aeronautical engineer who used to design super-sonic aircraft. I figured if anyone would know about this stuff, he would.

He said yes they would make a difference, but not a significant one. I asked him how insignificant.  He replied that if he punched the figures into a calculator, the amount of energy used by the calculator would be greater than the difference to the fuel consumption caused by the turbines standing on the roadside.

Burra, I love your mates analogy!
Very good.
Nancy, I am guessing the terminal speed for these axial turbines is a function of the design.
At a point that is safe for this design, the turbine simply cannot go any faster, it is self limiting by its inherent design and since its not large we dont have huge forces to deal with
that can be present with other equipment.
For example, a 3 bladed wind turbine can just go faster and faster until many things including vibration occurs
and the dynamic forces which are a function of the blade speed and the blade weight become
so great the thing breaks up.