# Fully Electric car with wind generators

1. Jul 15, 2009

I'm pretty sure someone somewhere has already built one, i've gone over the concepts involved and it does seem both practical and possible. The idea is this: electric-powered car that is recharged by several wind-generators(essentially fans on the roof) that recharge the batteries once the car is driven up to speed. Yes i do realize that any energy that is being used for recharging the batteries by the generators is how much extra the motor will have to work to overcome the drag(and consequently using battery power), but as long as the generators are generating enough power to equal what the motor is using to sustain constant speed, then the car could in theory run almost forever, right? The only situations where you would be draining the battery and not recovering the charge are: accelerating and going up hills, and of course, any power lost through heat given off through the wires(no electrical system is 100% efficient). Yes the batteries would eventually die, but you could always recharge them and you'd probably get at least hundreds of miles before you ran out. Any ideas why these kinds of cars aren't being marketed?

2. Jul 15, 2009

### mgb_phys

The 2nd law of thermodynamics?

(in before the lock!)

3. Jul 15, 2009

### negitron

Because it won't work, that's why. The only energy the generators will produce is entirely offset by the drag on the fan plus systemic losses, such as friction and generator electromagnetic losses. It's a net loss, overall.

4. Jul 15, 2009

yes i realize that it's a net loss, but you'd still probably get at least 40 miles or so on it before batteries died, right?

5. Jul 15, 2009

### negitron

You don't understand. You will ultimately get FEWER miles out of your batteries with your fan/generator than you would without it, all else being equal.

6. Jul 15, 2009

allright, thanks for clearing that up for me, another question: could a similiar system work in a hybrid? For example, let's say that you have a generator that produces 5hp at highway speeds to recharge the batteries. 5hp to a 100hp engine is not that much extra power for it to output and therefore doesn't consume too much more gas. Would this be practical or is it subject to the same impracticality?

7. Jul 15, 2009

### negitron

Same problem. Ultimately, all the vehicle's forward motion comes from it's engine/motor and anything you do to try to recover that energy, be it a fifth wheel driving a generator or a wind turbine, places an additional drag on the vehicle and results in a net loss due to conversion losses

8. Jul 15, 2009

### Danger

Given the malicious perversity of mechanical systems, I suspect that any actual losses would be even greater than those which would be calculated mathematically. Machines are out to screw us any way they can think of.

9. Jul 15, 2009

### Staff: Mentor

When I was about 11 years old, my dad found me cutting the bottom off of a coffee can for a project. He asked what I was doing, and I explained how I was going to mount two propellers on a shaft in the can, with the top propeller at one opening, and the bottom propeller at the bottom opening. I was going to put a harness on it so I could wear it like a backpack, and then when I spun up the propellers, the top one would provide the thrust, and the bottom one would recover the thrust and keep the top propeller spinning. I was looking forward to flying around like the jet-pack guy I'd seen on TV (dating myself here).

My dad sat me down and patiently explained why perpetual motion machines don't work, and how real jet engines do work, etc. I was disappointed, but it sure helped me understand the world better.

10. Jul 17, 2009

yeah, thanks. funny story.

11. Mar 7, 2010

### falinx

12. Mar 7, 2010

Interestingly enough, I saw an picture in Sci-Am of a proposed ship that had 2 giant wind turbines mounted where sails normally would be, and these would supposedly power a motor directly that turned a propeller, but once the math was worked out it turned out that just using sails would make a much faster ship.

13. Mar 7, 2010

### RonL

Until just a few years after 1492 it was a well known fact that the earth was flat.:rofl:

At some time in the near future, someone that doesn't know any better will likely have an idea that makes use of that mean old friction and law of motion. Behind some brick wall is a better idea.

I wonder what Columbus would think of the fancy sail boats moving around the ocean today.

14. Mar 7, 2010

### mgb_phys

Sails are very efficent - assuming the wind was in the right direction.
The wind turbine ship doesn't have to tack to maintain a course, tacking a 400m container ship through the English channel would be interesting.

There is an intermediate solution that has been tried - a giant parafoil kite deployed in front of the ship.

15. Mar 7, 2010

### mgb_phys

No it wasn't, nobody thought the earth was flat since they stopped hitting each other with rocks. The diameter of the spherical Earth was measured 2000 years before columbus.
The "they thought the Earth was flat" thing was made up by Washington Irvine to show how primitive and superstitious Europeans were compared to educated high tech scientific Americans (how times have changed).

16. Mar 7, 2010

### RonL

Thanks, you might have saved my day, learned something not nascar related.

17. Mar 8, 2010

11 years old and you thought of that? Plus you could understand the concepts of energy that your dad was telling you?

I could barely tie my shoes at eleven years old!!!

18. Mar 8, 2010

### vanesch

Staff Emeritus
What a terrible experience ! Did you become a terrorist ?

19. Mar 8, 2010

### sophiecentaur

Nearly two thousand years before 1492, the Greeks measured the radius of the Earth to within something like 16km.
(http://en.wikipedia.org/wiki/Spherical_Earth)

There have been plenty of "idea"s that ignore friction but have there been any proper theories or working inventions?

20. Mar 8, 2010

The parafoil kite is a cool idea, especially since winds tend to be stronger at higher altitudes, but it seems one is limited to the direction of wind travel, or at least close to it. With sails, one can sail in any direction except for about 70 degrees into the wind. Yes, you have to tack to go in certain directions, but not all. A broad reach or a run don't require tacking. With the wind turbine, it doesn't seem likely one could move directly into the wind, as the wind resistance would be stronger than the propeller force so some kind of tacking even with a wind turbine would require tacking.

21. Mar 8, 2010

### sophiecentaur

"With the wind turbine, it doesn't seem likely one could move directly into the wind, as the wind resistance would be stronger than the propeller force"
That doesn't follow. It is true that you couldn't go forward faster than the wind is blowing towards you but there is no reason why you couldn't make forward progress to windward, albeit at a low speed. It's not a matter of force, it's a matter of power. As long as forward speed times water propeller / turbine thrust is designed to be less than wind speed times normal force on turbine you are ok. The design factors would be the areas and pitch of the two turbines (air and water).
There would, of course, be a component of drift backwards (as there is always leeway when a boat is close hauled) but the overall movement could be forwards.

"When the wind wouldn't blow and the wind wouldn't blow, we got carter the ****** to start 'er."

22. Mar 8, 2010

### RonL

Might not be a proper theory, but consider how a boat gets on plane in the lake, it glides on top of the water much easier than plowing through it.
Think of a vehicle that moves forward at some velocity and forces most air under it and with side fairings the air is pretty well encapsulated. You have forward velocity and gravity applying a force to the volume of air as the vehicle in essence slides over it and if directed through some conversion mechanism that uses both frictional and thermal properties the air mass (or volume?) is reduced and dumped into the low pressure backdraft area of the forward moving vehicle.

Lots of physics and mechanics in what is described, lots of potential energy to move back into the power supply.

Someone in thermal engineering should have a good time with all of it.

Ron

Last edited: Mar 8, 2010
23. Mar 8, 2010

### sophiecentaur

"Someone in thermal engineering" would know that certain 'Laws' Apply throughout our physical lives.
Your rather vague suggestions about "sliding over" a volume of air have been tried and used, successfully by hovercraft to reduce contact friction with the ground but there are still many losses from the fan and from turbulence. You may have noticed that hovercraft are no longer used as serious commercial carriers except over swamps and other odd surfaces. They are not used commercially (much: I may be proved wrong in some obscure example), even over the sea because boats and hydrofoils work better.
The "potential energy" to which you refer is only the equivalent of raising the vehicle by a meter or so and that, as well as being very hard to recover, is only the same as you'd get by rolling down a 1m high hill.
In all these issues of Energy, you have to do the actual SUMS before seriously proposing any novel system - which is why so few novel systems don't actually work. It's not a matter of ultra conservativism in the Scientific community.

24. Mar 8, 2010

### RonL

You might have helped make my point. The hovercraft is almost the exact reverse of what I mentioned, a total waste of energy to lift a vehicle and make it move.

We are talking "energy recovery" and with the proper engineering to maintain operator control, you can have a method of making a 6,000 pound vehicle (electric) feel to it's power system as if it only weighs 1,500 pounds.

Last edited: Mar 9, 2010
25. Mar 8, 2010

### mgb_phys

The makers (kiteship) claim that the winds work for a lot of trade routes.
The big advantage is that you don't need any changes to the ship, no masts and rigging to make loading difficult. And you don't need the crew to manage the sails
It's just a computer controlled winch at the pointy end where the current anchor winch is.