There will be some electrical issues that most likely render the idea impractical. A 26,000 volt generator that produces 1300MW would produce a current of 50,000 amps if my math is correct. And that would require an enormous amount of copper or aluminum to get that current down to earth at 26,000 volts. To reduce the amount of copper or aluminum wiring in terrestrial applications, the generator in question powers a step-up transformer to get the voltage up to transmission levels of say 250,000 volts. Since there are practical barriers (insulation) to building a generator that produces 250,000 volts, the considerable weight of the step-up transformer would have to be added to the flying apparatus. Insulating the conductors in equipment operating at 250,000 volts is not a trivial matter.
While the concept is intriguing and awesome if it works there are some questions that will probably only be resolved via testing, in particular testing to the point of failure. The math for flying and generating energy all looks good but my concern is with the cable tether. I saw the mass dampers in the PDF and if they are at the suspended end at 20,000' that is going to generate an oscillation that could effectively negate the wind lift and cause it to crash. Presumably there would be emergency parachutes on board to ensure a "soft" landing rather than a crash since we are talking about the weight of half that of a 747. I doubt that the FAA would approve something that size flying around unmanned unless there was a way to ensure that it won't crash. Getting back to the oscillations. We have all seen the video of the narrows bridge collapse caused by the wind induced oscillations that ultimately caused the failure. Now transpose that to something weighing half as much as a 747 at 20,000' in the air. Dampers and stabilizers can only do so much but anyone who has ever flown knows what it is like when the plane starts to hit air pockets. The plane can drop several hundred feet in an instant so the same thing must be expected to happen to the FEG's. Would that cause the cable tether to snap and what happens when it comes whip lashing back to ground level? I like the concept but I am just trying to imagine what happens when Murphy's Law comes into play. What reasonable measures can be used to prevent and/or mitigate any of the above points of failure?
It all has to be designed for high voltage. But that's something we do everyday. Nothing new. The very big transmission lines you see are often 500,000 volts.
You are asking me to write in detail about something you can look up. It comes out of the math. If you want to understand it, you have to put in the effort.
Which is why I said we need more like 1,000,000 volts - about 40 times less current. Using high voltage is key to the weight of the transmission lines as well as the weight of the generators. You can buy 500 KV generators off the shelf now.
Yes, yes, and yes, all are significant concerns. There are already parachutes for jet aircraft. So the technology for that exists. In a worst case it could auto-rotate down as well. It does require some tricky engineering. But compared to concepts like the space elevator, this is fairly easy. In many cases, if launched from the tops of mountains, or over the ocean, there might not be a lot of population to worry about if one comes down catastrophically. So flying over unpopulated areas is one easy way to help reduce risk.
Have you ever flown a kite? They don't stay up by themselves. You have to pull against them and redirect them. I am not saying that this can't be done; but if it can be done the engineering challenges are off the scale. I think that this is a good thing however, as even the attempt is bound to be a teachable event regarding engineering. It can't help but produce something interesting by way of progress. Very nice!
That sort of pull and pressure along the length of the cable and the cable connecting mechanism screams long term metal fatigue. Something is eventually going to violently part ways with devastating consequences. But still, I suppose that it could be tried in relatively uninhabited areas first; say for a decade or so as a precaution.
I'm not currently interested in understanding it. I would first have to find out whether it's true, or not. As I an unable to find any confirmation of your assertion online, I remain unconvinced.
Okay, I remember it is how you treat the system, and it is one reason why you don't see wind turbines with many blades. Cost and weight are factors but also, more blades don't add much to the yield. But I don't remember exactly how it falls out. But, shooting from the hip on the physics in play, I would guess that as a blade passes what we might treat as a horizontal column of air, as air hits the blade, a shock wave travels back at the speed of sound, away from the blade, due to the reduction in air speed at the front of the column. So now a slice of that column has less energy because it already gave up some energy to the blade. In the time it takes that slice of air to move past the line of the blade, the blade sweeps around just in time to interact with wind that has not lost energy.
https://interestingengineering.com/the-scientific-reason-why-wind-turbines-have-3-blades This is true for the reasons I was mentioning. Also, if you look at the graph in the op, it cites power per unit swept area. Don't you think they have maximized this with modern designs? Most use two blades.
That's why we have maintenance schedules. Aircraft are no different. Fatigue and the time to failure can be calculated. It is done every day. But this is certainly more complicated than flying a kite.
I can believe that. It sounds like somewhat less than a wall. I think that any potential sonic effects are unnecessary to understand that a rotating propellor, which is resisting rotation, would create some amount of drag. It seems obvious that, since the propellor is resisting the wind, there would be some compression upwind and sime spillover around the "disk". It also seems obvious, that some air must pass through the "disk". I can't see how it could possibly function, otherwise.
Kites don't have the advantage of being in the jet stream. It does move and change but over days, not minutes. We all know the constancy of the jet stream from long fights, where the trip out takes two hours longer than the trip back, or visa versa. In my own thinking, I tend to land on a scenario where a fleet of FEGs are spread out over the regions of best wind and access. As conditions change, FEGs in low wind conditions can be brought down for maintenance. Others in the fleet are sent up where conditions are better. Design for the conditions. These seem to calculate out fantastically compared to something like nuclear. And it is better than natural gas, coal, or diesel because the fuel is free. Back of the napkin estimates suggest they pay for themselves in less than a year! Knowing that is unlikely, it is reasonable to assume that there will be other significant cost drivers, one of which might be down time. Note again that 1000 MW is the typical size of a single nuclear reactor.
The jet stream today. Looks like all FEGs in Vancouver BC, Washington, parts of Oregon and California, Idaho, Montana, North Dakota, Maine, Nova Scotia, and New Brunswick, should be flying. The wind speed is given in knots; 1 knot is 1.15 mph.
Space Solar would be cheaper, more dependable, easier to accomplish and less dangerous....it would also produce more energy by scale.
Great idea. Talk to me in a century. That is just pie in the sky for now. This is real and doable. Easier and cheaper? LOL! Not a chance. You are just grasping at straws now. Show me the math.
I said that you have to factor in the efficiency. You are taking what I said out of context and ignoring the most important part. I stated a value of 40%. So it must extract at least 40% of the power from the wind to generate power. That means that the wind velocity over the swept area has to be reduced. The actual power produced forces a minimum force value for the tether through Power = Force x Velocity. But you do need pressure waves, which travel at the speed of sound, to understand why more blades don't yield more energy. All pressure waves resulting from the blade rotation travel at the speed of sound. I told you how we know this. In order to extract energy from the wind, we need to reduce its speed. That is conservation of energy and it MUST always be true. Since turbines have now gone to two blades, we know that two blades have been shown to extract the maximum amount of energy to the point of diminishing returns. Note that they also turn very fast. It is all timed to yield the maximum efficiency.
I already stated that 500,000 volt generators can be purchased off the shelf. And I know we can go to 1 million volts. This is just known electrical design stuff. It is highly specialized but we understand it and have the technology to manage it. You can also increase the frequency to get more power for less weight. But there is a limit, probably around 1000 Hz, where you start to radiate too much radio energy. Even 60 Hz power lines are tuned to minimize radiative [low frequency radio] losses. For very long transmission distances, they even go to DC sometimes. Consider too that you can run generators in series. So we could in principle run two 500 KV generators but transmit at 1 million volts.
You may want to research before commenting. https://earthsky.org/earth/space-based-solar-energy-power-getting-closer-to-reality This is further along than jet stream wind generation.
I was worried about such a large turbine being capable of handling the forces involved. I don't know how large a turbine design for up to 250 mph winds can be made. Just as a point of reference, these rotors are some of the largest ever made. They can handle the wind speed but we would need 16 to reach the one-nuclear-reactor size for an FEG. https://www.aerospace-technology.com/features/feature-the-worlds-biggest-helicopters/
Uh huh. This is what they really have. This is light-years away. We have been making wings and rotors for a century. I'm not saying it isn't a great idea, eventually, but this requires highly complex operations in space. This won't happen any time soon. And citing price is ridiculous. There is no basis for even a wild-ass-guess yet. At the moment, we don't even have a manned space program without hitching a ride with the Russians.
