Add a wind turbine to a car?

  • #76
3,042
16
To think I just read 5 pages of this...

To put it in complete layman's terms. Hold your hand out the window of a moving car. Then hold your hand out the window while holding a fan. The drag caused by the fan pushes your hand back harder now. If you have a 100% efficient wind turbine and a 100% efficient car engine you get all the drag added back as energy, but why? It would be easier to just directly couple the car engine to a generator, and that assumes everything is 100% efficient which is impossible. There is no way you can win.

If you decide to reduce drag and place a turbine in it's place then it's the same result. 10Kw required to keep the car at highway speeds, you reduce the drag to save 3kw then add a turbine that generates 1kw at 30% efficiency. Yup you win it now takes 10 kw to drive the car minus the 1kw you now generate, so 9kw. But, if you can reduce power required by 3kw then why add the generator? You can now drive at highway speeds on 7kw vice 10.

Somebody lock this thread please.

I have no idea where or what these "made up" power values come from.
 
  • #77
2,027
85
It was clearly a hypothetical example.
 
  • #78
3,042
16
It was clearly a hypothetical example.

The example doesn't even make any sense, and neither do the numbers. A wind turbine at the back of the car will promote flow separation. You cannot reduce the drag and then add a wind turbine. This is a fallacious line of argument.
 
  • #79
157
0
I have no idea where or what these "made up" power values come from.

Just hypothetical. It really doesn't matter because any numbers you put in will give you the same result. I was just illustrating a point.

Also I don't see where my point gets confusing. Anything you do to generate electricity adds drag. If you reduce drag to add drag then you lose from the inefficiencies of your generator. Why not just reduce the drag in the first place if you already have this ability.
 
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  • #80
2,027
85
The example doesn't even make any sense, and neither do the numbers. A wind turbine at the back of the car will promote flow separation. You cannot reduce the drag and then add a wind turbine. This is a fallacious line of argument.

It doesn't matter.

It illustrated the point that it adds another layer on efficiency to factor in (the numbers used not being mega accurate is irrelevent). It also demonstrated the extra steps the energy takes from engine to motion.

In the case above even though you think you are winning as you are recovering 1kw from the original 10. You still lose as you could only be using 7.


It's a case of spending a pound to save a penny.
 
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  • #81
3,042
16
Precisely.
 
  • #82
Ranger Mike
Science Advisor
Gold Member
2,189
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If supposing we were to add a wind turbine connected to a generator to a moving car, would we be able to get the air flowing around the car to turn the turbine and therefore gain some energy? If it is possible, is it economical? if it is, is it practical? would there be a loss? would there be any gain in overall efficiency??

A friend of mine wants to do this project for collage and wants to implement this idea... I just want to know if it is practical or not...

So... what do you guys think?
Of course it is possible to add a wind turbine. and this would produce energy in the form of electricity. Not practical or economic....It would take MORE gasoline to do this. anytime you add drag you need at add gas to overcome the drag. you can not get something for nothing. the fact you are adding drag is proven by wind tunnel drag tests. period..case closed.
now what you can do is to recover waste HEAT produced by the internal COMBUSTION engine. combustion being the key here.
 
  • #83
FredGarvin
Science Advisor
5,067
10
Perhaps if we build a large, wooden Badger...
 
  • #84
russ_watters
Mentor
21,175
7,982
This thread has run its course.

[Hey Fred, congrats, you've invented a new counterpart to Goodwin's law...we'll call it the Monty Python law. It states: "As an online engineering discussion grows longer, the probability of a reference to Monty Python approaches 1."]
 

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