Generate Cheap Energy From The Wind

I myself would like to know if anyone makes mini-wind turbines.

But if they do, the energy to spin them while you drive would come from the motion of the van, which is derived from the operation of the engine under the hood. So in that case you might as well charge the battery off the alternator. The intriguing part would still be to see how much energy you could get from the wind once you are parked.
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You are right about the drag being a big factor. However, if you are just using it to charge batteries for later, the only thing you have to worry about is the extra gas you'll have to buy to make up for the lower mpgs you'll get. It would just be the equivalent of adding another alternator on to your engine.
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You see what you are talking about on sail-boats all the time.

But in the case of driving, you would increase the drag on your vehicle by more than the amount of power you would get from the turbine. It would work when you are parked however.
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It would be more efficient to add an additional alternator to the engine. The decrease in mileage caused by the drag of the turbine would offset any possible gain in power storage.
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All answers above are good ones. Another idea is to mount a solar panel on top of the camper and let it charge your batteries in the camper. I sailed for a year and had a panel that kept my batteries charged this way.
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The small aircraft from many years ago had just the same thing,and it worked well.
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Yes, I've seen portable wind generators at several exhibits. Great if you're camping in a windy area like the high desert. Combined with solar panels and a battery bank you can do quite well.
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