Windmill on an electric car

Lets say an individual placed a windmill on the top of an electric hybrid car.

Could the harnessed energy increase the gas mileage by an appreciable amount?

Not if I understand you correctly. The drag and inefficiency of the windmill should require more energy than it generates. It sounds as if you’re talking about a perpetual motion machine here. That is, if I understood the question…

No I was not referring to a perpetual motion machine.

I was just wondering if you could get maybe another 10 mpg out of the car that way. You know charge the batteries up a bit when the car is using gas.

I do not know much about how these cars work and now that you have brought it to my attention. I suppose that the added drag would overcome any charging effect and would eliminate any gains.

Maybe if the windmill somehow only came out when breaking. I can’t imagine that it would make much difference. Run the car’s radio for a minute maybe.

Well maybe if you lived in hilly country and it only engaged while going downhill?

Granted I am envisioning something more like a small ducted wind turbine in the slipstream that would be covered when not producing downhill power to avoid drag.

That’s putting it mildly - there can be no such thing as a 100% efficient windmill, so it must consume more energy than it generates.

It is true that if you could pop the windmill out for braking, it could recover some of the energy otherwise lost as heat. But there are much better ways for cars to do this sort of regeneration.

I you live in windy country and have your car parked outdoors for much of the day, you could get some energy. (And if solar cells became cheap enough to have all over the car, you could get solar energy as long as you’re out in the sun.)

This is the key: If there’s genuine wind relative to the ground, and your car is anchored to the ground, then you can gain energy while it’s parked (but it’d probably be easier to leave the windmill permanently installed on your garage, instead of attaching it to the car). In fact, even if the car isn’t anchored, you could get some energy out of a true wind relative to the ground, though it’d probably be easier there to use sails (tacking if you want to go upwind). But if you’re talking about the “wind” from the car moving relative to the air, the windmill is guaranteed to cost you more in drag than it gives you, since the only place to get the energy from in the first place is the car’s own motion.

Replace the moon roof with photovoltaic cells.

Wouldn’t do much, but the batteries could be topped-up.

Don’t most or all hybrids use regenerative braking? Basically, the electric motors that power the wheels during acceleration act as generators during deceleration, putting some of the car’s kinetic energy back into the batteries.

I expect this, since it uses the strong coupling between the tires and the road, is phenomenally more efficient than trying to use the weaker coupling between the air and windmill blades.

That covers braking. Using a windmill during cruising or acceleration would just add friction, requiring the motors to apply more power to push the car along. Much more than could be gotten back from a windmill. It’s more profitable to do all you can to reduce wind resistance, to reduce the power needed to get a particular speed.

Is the car on a treadmill?

Somebody (and when I say “somebody”, I mean James L. Amick of Ann Arbor, MI) has apparently patented the wind-powered car idea:

Something like this?

A sailboat was made with a vertical mounted spinning sail like an elongated wind speed device. The wind spins the sail which is direct drive to an adjustable propeller. The boat can go in any direction, including straight up wind. Some small increase in power could be derived from such a device. The 3350 turbo compound aircraft engines like on the Super Connie’s had 3 turbines that the exhaust gases passed through that were direct drive connected to the crank shaft. About 150 HP was added from each device.
Any device that will spin from some imput, be it unused exhaust gas, absolute wind or relative wind and if it reduces drag in any amount, will increase power to some extent.
Ice boats go many times the speed of the wind due to the speed of the apparent wind on the sails. With the proper tech, sails could help with power to a greater or lesser degree depending on circumstance.

they could be used to great advantage along the whole west coast for example.


How can a car-mounted windmill do anything other than increase drag?

I was not clear. If there is a ball mounted on the top of the car, you have X drag. If you spin it, you have less than X drag. I am not implying less drag than without the wind turbine.

I thought the question was about an increase in power overall. I say yes but very small compared to an internal engine. But like the sail boat, if that is the only power plant, you can make the car go if there is wind.

That’s correct, but to me appears outside the scope of the OP, which seems to be asking whether the windmill can augment the car’s normal engine.

Based on this wording, you are still talking about a perpetual motion machine whether you know it or not. If this concept was possible, the gasoline engine part isn’t important. You could just put a car with a windmill and have it produce more energy than it is producing therefore keeping banks of batteries fully charged and they will never run out.

Here’s a piece in Time that shows an solar/turbine electric car.


I assume the OP is envisioning a windmill sticking up from the top of the car. In that case, the windmill is extracting power because of the force of the oncoming air on the windmill blades–that force turns the blades. However, that force is created because of the forward motion of the car. So the car needs to produce more power to push itself forward. Due to inefficiencies, there’s no way all that extra power required can be recovered.

Now, to be fair, there’s a complicating effect if the windmill is placed in front of (or within) the car. The interaction here changes the airflow over the car. In almost all cases, you’re still going to get additional drag, and have a net energy loss. However, I could imagine a scenario where rerouting the airflow might decrease the drag, or at least make it no greater. But those cases would require some heavy-duty design of flow profiles, and the power recovered from the “windmill” starts to be a minor portion of the pie (and I don’t even know if it’s possible).