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Described here and in the references (patent, patent), the idea is to use a large fence as a grid electrode. Spray water droplets near a high voltage to charge them, and then the wind blows them away, converting wind pressure into electric potential?, then they hit another electrode or the Earth to complete the circuit.

enter image description here

The scientific basis for this is shown in FIG. 9 which shows charged particles 16, 16' removed toward infinity from a single isolated conducting sphere 17 of radius r0 According to the principles of electrical physics, work W=QV is done in removing the charges to infinity.

Would such a device actually work? If so, why isn't it built or used? Can the energy output be estimated and compared to a traditional wind turbine?

Some simple calculations:

According to the patent, the pylons to support the fence in the image are 1 km apart and 150 m high, and a 100,000 m² section of this size would produce 45 MW. This would be 450 W/m². The largest turbine in the world is the German RePower turbine producing 5 MW while sweeping an area of 12,000 m² = 401 W/m², so not much of an improvement?

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The reverse process works: if you have two electrodes with a large potential difference between them, you can generate wind; but I am not 100% sure how that works (only did the experiment and not thought about the theory). –  Willie Wong Jul 13 '11 at 16:47
    
@Willie: It ionizes the air and then the ions are attracted to the other electrode. The ions traveling through the air collide with neutral air molecules and impart some momentum on them in the process so more air moves at lower speed. This is the principle behind en.wikipedia.org/wiki/Ionocraft –  endolith Jul 13 '11 at 19:11
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there's a Wikipedia entry for that now, eh? Actually the experiment I did was to build an Ionocraft. We never achieved lift-off (because the power supply we were allowed to borrow did not go above 25kV, and at over 20kV we almost always end up with discharges), and for safety the entire experiment was done in a Faraday cage, but we did make a nice pleasant breeze. –  Willie Wong Jul 13 '11 at 19:27
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@endolith: To be honest, I'm no expert on this. I was mostly just going by Wikipedia, which says that "because of their inefficiency and the difficulty of insulating machines producing very high voltages, electrostatic generators had low power ratings and were never used for generation of commercially significant quantities of electric power." I'd guess, though, that part of the reason would be the efficiency of electromagnetic induction as compared to the physical transport of charge carriers up a potential barrier. –  Ilmari Karonen Jul 26 '12 at 15:35
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... Also, electrostatic generators usually produce high-voltage low-current DC power, which is not very convenient for most applications; thus, it needs to be converted to a lower voltage, with attendant conversion losses. –  Ilmari Karonen Jul 26 '12 at 15:35
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2 Answers 2

I am extremely skeptical of this design, and I don't think that there is any chance that the practical problems can be surmounted. If a generator like this can work, it will probably only be a novelty device, like the Kelvin thuderstorm, and it will only work in very unlikely conditions (like already highly ionized air). The Kelvin machine only works because water is a conductor, while air is an insulator.

ionization can't work

There is a huge gap between the ionization energy of a molecule and its kinetic energy, even in the strongest wind. The ionization energy is measured in eV per molecule, while the kinetic energy in an insanely strong wind of 300m/s is .04 eV. This means that you need to extract the ionization energy you use to make the ions when the molecules de-ionize with an impossible efficiency of 96% to have any hope of getting any energy out. This is certainly practically impossible.

Charging small spheres is difficult.

The problem with using wind to move spheres (like droplets) up a potential well is not that the droplets have to be charged up and discharged--- this can be done relatively cheaply. The problem is that air is an insulator, so the droplets have to transfer their charge by contact. The Kelvin thunderstorm works only because water has enough ions to be a conductor.

In order to get the wind to push the droplets, they must be actively sprayed into the wind. You won't be able to charge them up efficiently by just applying a potential, because they would have to touch the wire to charge up, then blow off with the wind. But the mesh will disrupt the wind, most of the wind will not want to go through a mesh barrier. So you have to charge and spray, the spraying will cost energy.

If you charge up water, then spray it into a region with a field, then let the wind blow it towards higher potential, you still need to gather up the charge at the higher potential region in an efficient way. This has to be a physical contact mechanism too, like a wire mesh, but you might be able to get away with letting the droplets fall by gravity onto a plate. Behind the mesh, you need to make an electric field using a gigantic fine charged wire-mesh which doesn't disrupt the wind.

The issues in this are all of scale: this thing has to be enormous! You need a big wire mesh to set up the electric field so that it is approximately opposite the wind, you need a sprayer to throw droplets in the air, and you need a big plate to gather up the droplets. The bigger the droplets, the more effective the system, because you don't have self-capacitance costs, so you are best off using one giant droplet.

But one giant droplet might as well be a traditional turbine, because you are back in the moving-parts bird-killing regime.

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Yes, it's large. 1 km long sections, 150 m high. The droplets are rainwater being sprayed out of nozzles under pressure from gravity, according the patent. –  endolith Apr 9 '12 at 19:18
    
Uh, Ron, don't just stick with an original patent description of an idea. There is much better reference out there. Do a Google search on the following: "Conceptual Design of an Electrofluid Dynamic Wind Energy System", by J. E. Minardi and M. O. Lawson. Another 180 some pages of EFD device detail can be found on a Google search of: "The Electrostatic Wind Energy Converter" by Dhiradj Djairan He still promotes natural air flow extraction of energy. But at least his physics has been well checked out by a set of experiments. –  William C. McKee Jul 26 '12 at 4:52
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This particular wind energy fence will not work. However I have a different conception of it that will very likely work. Not merely hanging metal work in a natural air flow. That it could be made to work, while also being novel will actually attract investors more than repel them.

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I'm not telling people that I don't know more details, as I'm going for the patent. –  William C. McKee Jul 26 '12 at 3:38
    
I have another patent: System and Process of Light Chain Hydrocarbon Synthesis. that should work well with the EFD and something else that I'm not talking about. –  William C. McKee Jul 26 '12 at 3:49
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