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Re: Pie in the Sky

A rough estimate is 35,000 cubic ft of helium balloon per (theoretical) ton lift. This includes about 100 lb of cable tension. Nowhere near enough for stability in practice. Ages back I used a barrage balloon as a skyhook but I can't recall what the cable tension was or where I've put the calculation references.

Clive

Re: Pie in the Sky

Clive,

Do you know if there is a limit to the size (volume) you can have for a helium filled balloon? Assuming the material the 'blimp' is made up from is light weight and 'non-tearing', how big a helium ballon could be built?

Now assuming you can use several of these to lift up the 'wind generator' and it's tethers (I'm assuming for stability you may need up to four tether wires) and power wire to the required height, and ignoring the ridiculous costs of this system, what fundamentally (ignoring all the practicalities of course) is there to stop this from happening?

Just how much more constant are wind speeds higher up in the atmospshere than at the surface?

KevinUK

Re: Pie in the Sky

Most airborne wind generator proposals mention aerofoils being used (impractically) for lift.

There is nothing to stop you in principle from building a very large balloon to carry up a wind generator. A further impracticality is that I'm not sure that a helium balloon constructed of lightweight and "non-tearing" material has indefinite durability, because the material is not actually an impermeable barrier to helium, and there is a high rate of gas depletion and a subsequent loss of lift. The balloon would have to descend every few days in order to be refilled. Stocks of helium are actually depleting very fast at the current rate of usage and the price is going up rapidly.

A hydrogen balloon might be a better idea because of the costs.

Re: Pie in the Sky

I think everyone so far has missed the real reason that these things keep coming back time after time - for the greenies, they're barrage balloons for passenger jets.

Re: Pie in the Sky

I am generally a huge skeptic when it comes to FREE energy from anywhere, but the company that I work for has just started contract work on the mechanical design of a high altitude (1000 ft) horizontal rotation wind generator demo (30 KW)unit.
They decided on 1000 ft as a compromise between the weight of the power cable and the higher wind speed at altitude.
In addition to the helium lift, additional lift is generated by the magnus effect (curve ball).
The really hard part is the weight restrictions. It makes it very difficult from an engineering point of view.
I suspect that this will not be economically viable but it should be an interesting engineering exercise.
BTW - The auto-gyro type wind generator has some severe control and safety issues.

Re: Pie in the Sky

William

Thanks for posting. Its always good when someone with first hand personally experience takes the time to engage in a discussion.

I'm intrigued to see that the airbourbe wind generator (AWG)you will be helping to design will be kept in the air via a helium balloon (which as I suspect would need to be the case). Although its only a 'demo' at this stage, 30KW doesn't sound like a significant generator. It is only 30kW at this stage largely because of the weight restrictions?

Although its most likely commercial information is there any chance you could for the purposes of discussion provide us with the approx. ratio of the weight of the power cable (which doubles as the thether cable?) to the weight of the payload. Although it'll only form one data point, it may help in assessing the likely weight of AWGs that are much larger.

KevinUK

Re: Pie in the Sky

Actually the helium balloon is the wind generator.
A horizontal cylinder about 50 feet in diameter has 3 large vanes, similar to an anemometer, that catch the wind. All this is inflated with helium. The overall diameter is about 80 feet.
The tether cable is NOT the conductor. Electrical conductors have a tendency to be relatively low in tensile strength. The conductor will be copper with a maximum of 12 amps. So for this test they are looking to use about 3000 volts. Clearly a 5 megawatt unit limited to 20 amps will need a voltage of 250,000. This is not all that outrageous considering that the newer transmission lines run over a million volts.
Again, from the engineering point of view the weight is the gorilla in the closet. Although, the bigger the generator the less this is a problem because the the helium lift increases with the cube of the volume, while the power goes up with the square of the size.
Actually one of the more difficult problems has to do with FAA flight regulations. This thing will be high enough to be a "hazard to navigation" and require lights and radar transponder.

Re: Pie in the Sky

"Although, the bigger the generator the less this is a problem because the the helium lift increases with the cube of the volume, while the power goes up with the square of the size."

As this is Number Watch, I hope it is not too pedantic to point out that helium (or any bouyant) lift increases in direct proportion to the displaced volume.