Windpower at 35,000 feet

[davf]

Very interesting concept.<br /><br />In their notes they are talking of flying 600 of these things within a 10 by 20 mile rectangle. At 33,000ft given some slack / curvature of the cables due to gravity, let's just ballpark the cable distance as 8 miles. What if one of these cables fails... what are the odds it is going to fall and not strike one of the 599 others in that 10 x 20 mile rectangle. It just seems like a lot of other dominoes in the same area that could be hit.<br /><br />I'm not sure air traffic control would be an issue: there's a lot of waste-land you could put these in and there's already hundreds of restricted airspace blocks within the US... I wouldn't imagine another 50 or so of these 10 x 20 blocks really creating a big impact. <br /><br />You'd also need some de-icing system for the cables... how much of a loss would heating them electrically (the most practical that I can think of) bring to the generating efficiency?

 

[nexium]

Sorry, I do not yet have an opinion on your debate with spacester. Here is paste from another forum:<br /> <br /> />The tether can be tapered, perhaps halving the weight and thus the strain at the top end.<<br /><br />The *stress* at the bottom would be the concern, not at the top.<br /><br />Better fly these things a long way from civilization-wouldn't do to have falling pieces smash thru one's roof <br /> <br />Bottom is correct, (I think) for a typical kite because there is also wind loading for the string. With the tether as long as 50,000 feet, the kite = alternator assembly is lifting up to 100 tons of tether, so most of the strain is at the top. If there are multiple alternator assemblies distributed along the length of the tether, stain can be reduced and more or less equalized, I think. Some alternators need to operate as motors, briefly, when transients threaten to break the tether, but the lower assemblies will also produce power on the average. Is there any chance the tether can be shaped and oriented to behave as a lifting body?<br />If there are a total of 20 plus alternators on the tether, a series, parallel conection may illiminate the weight of the transformers. Electric power losses in the tether should produce enough heat to prevent ice from forming on the tether. Ice on the rotors and the rest of the alternator assemblies may however be a problem. <br /> <br />Pieces falling though the roof is a valid concern, even though the assemblies should land gently, like an autogyro in most failure scenarios. Suggestions, please, on reducing the hazards, as using the electricity near the bottom of the tether increases the usefulness and cost effectiveness. We should willingly accept extra cost and moderate risk, as continued dependance on Arab oil may be the death of all of us in world war three. Neil<br />

 

[igorsboss]

IMHO, I would consider other alternate technologies first:<br /><br />1) Ocean current turbines. The greater density of seawater allows the use of bouyant forces to lift the tether and turbine into position. Slow moving sea water can be far more powerful than fast moving air.<br /><br />2) Fly kites at low altitudes (up to 500 meters). The air is MUCH thicker, the cables don't have to be so long and strong, there is less falling danger when becalmed. How many more reasons would you like to hear?<br /><br />The kite generator concept should be proven at 500 meters before it is taken to 10,000 meters.

 

[askold]

Or, how about energy conservation?

 

[nexium]

1 Allowing the long tether to drag the water turbine just below the surface, would produce some additional (but not as much as you think) electricity, not subject to the line loss of the long tether. In this case the ocean current if any would produce little effect.<br />The tether is not needed if you have a five mile long anchor chain to the bottom in the Gulf Stream.<br />2 The air is 4 times thicker at 500 meters than at 35,000 feet; twice as thick as 19,000 feet.<br />3 Shorter tethers is likely the fall back position of skywindpower. Neil

 

[nexium]

I'll pick some numbers out of the air to help me think. Generators are rated 4,5,6,7,8,9 megawatts = 39 megawatts with the biggest pair at 25,000 feet; smallest at 5000 feet; middle pair at 15,000 feet. They are connected in series and produce 390,000 volts DC when all is well. The loop current is 100 amps. We use #10 aluminum wire = .00164 ohms per foot times 50,000 feet of wire in a double 25,000 foot tether = 82 ohms: 8200 volts drop in the tether = 820,000 watts power loss in the tether = 16.4 watts per foot, which may be enough to prevent ice from forming under worst conditions. The power loss is 2.1 % We can add 10 and 11 megawatt alternators at 35,000 foot altitude without excessive power loss, but corona will quickly get out of hand as the voltage increases. We need to think more current to get to 70 megawatts, but a bit more current is ok with #10 wire with air circulating. The diameter of #10 aluminum wire is 2.588 millimeters = 0.103 inches. 9.55 pounds per 1000 feet = 455.5 pounds for 50,000 feet. I don't think #10 aluminum wire is strong enough to support its own weight over 25,000 feet, so we need CNT = carbon nano tubes coating the aluminum for extra strength. CNT can be a good thermal conductor of heat, but that may be in conflict with it being a good electrical insulator. We do need either wide spacing between the positive wire and the negative wire or very good electrical insulation at 390,000 volts difference in the bottom 10,000 feet altitude.<br />We can use 400 hertz alternators, but 390,000 volts RMS is possibly too high from a corona standpoint. <br />Several more costly metals conduct electricity almost as well as aluminum by weight. I suspect alternatives to CNT do not conduct heat as well making the 16.4 watts per foot risky and less watts per foot making ice more likely. If CNT works as well as I hope, #8 alluminum wire carring 160 amps may make 40,000 feet at 100 megawatts practical. Neil

 

[nexium]

Paste from another forum:<br />I think CNT is an insulator or conductor depending on the direction the nano tubes point and the binder (often epoxy) used. There has been some recent success with no binder. In any case we will select the direction for maximizing the reliability of the tether, unless a small sacrifice will give us better heat conduction from the aluminum to the surface where ice is likely to form. My guess is 99% of the current will flow in the aluminum/1% in the CNT even if we optimize for electrical CNT conduction. Likely the wide spacing air gap will be the only choice for over 20,000 volts which is enough for puny prototypes. Early proto types likely will not use CNT.<br /><br /> DC in series has the advantage that every generator can run at a different RPM and change speed from second to second to help stabilize the tether, suppress transients and adjust the attitude of each generating assembly. 60 hertz has the advantage that it can be put on the electric grid, if the voltage, frequency and phase are correct. 400 hertz has the advantage that the weight of the alternators can be reduced by two or more times. 400 hertz is standard for military and commercial aircraft because of the weight savings. Also missiles. Homes and businesses near the base of the teyher could use 400 hertz instead of 60 hertz. Three phase produces a weight savings of perhaps 20%, but makes most everything more complicated.<br /><br />I think the tethers will typically lean toward the East, but occasionally the wind shifts, sometimes abruptly. Two, three or even four tethers, spaced five meters apart could become tangled, especially if there are several independent tether systems within a few kilometers. The wind speed and direction can be different at different altitudes<br /><br />Many well educated Americans do not know the metric system. I get confused about newtons, baryes = dynes per square centimeter, BTU, calories, lumens, ergs not all of which are metric, so I use a mixt

 

[nexium]

Another paste: Conversions of 100 megawatts at 1/2 million volts likely are not be available off the shelf, so the first few will be costly and perhaps loose 50%. I suspect an average loss of 25% is possible with a million advanced solid state components: Mass produced perhaps for less than one million dollars. Conversion from 400 hertz to 50 hertz is dividing by 8. Dividing by 6.6666666666 may be almost impossible except by making DC = direct current which powers 60 hertz inverters. 480 hertz would likely be easier to convert to 60 hertz. It may be practical to convert 1/2 million volts DC with 600 inverters with the inputs in series and the outputs in series parallel. Neil

 

[nexium]

I suppose rogers_buck was being humorous, but some research on harnassing lightning is in progress. One of the problems is too many electrons move up, so a down strike often follows an up strike, repeatedly, so we need two rectifiyers rated a million volts or more with a peak surge rating of 10,000 amps or more. Neil

 

[vogon13]

Sounds like a trip to Radio Shack. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[igorsboss]

<font color="yellow">Sounds like a trip to Radio Shack.</font><br /><br />Great idea! I'd just love to direct a few lightning strikes at my local Radio Shack!