This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
The weight of the cable is proportional to the current you need to transmit. The first time I did the calc using a 1" cable and 480 v generator, the cable didn't allow any current to actually get to the bottom.
Please understand, John, I am not disagreeing totally with you. I am just suggesting why the tether issue is overlooked.If you have, you pump it up to a Million Volts, then your losses in the tether are minimal.
The problem is that transforming 480v to 1,000,000 v requires a lot of windings. IIRC to step up voltage it is a ration of the windings on one side of the core to the other. Hysteresis now sticks in her ornery head and messes with you. The core is usually of some suitably heavy material, because it must be a magnetic material (I think) which I believe leaves aluminum out of the equation. To get the ration of windings needed, means a lot of wire, and suddenly it not the weight of the tether that is the issue, but the weight of the transformer.
So if we can't transform 480 v to 1,000,000 (although I think you can limit it to 144,000 if you are willing to accept 5% loss in transmission, which apparently the proponents are because it helps to keep the wire from freezing). Then we could try to make the generator output the high voltage directly without going through a transformer. I suspect that we will run into the exact same problem only more so in making such a generator, otherwise, GE et all would be making 144,000 V generators to be installed in Electric Plants so they could forgo the Big Ass transformer that they have to have. 10 years ago, Allegheny power had a spare transformer on site in West Virginia, $1M (IIRC) in capital sitting there stagnant just in case. The lead time on such a transformer was more than a year, which is why they always kept a couple handy in their system.
In the end though, you are screwed with flying generators. You have to have wire somewhere in the mix to get the current down to the ground. To just say that the tether is the problem flat foots you in an argument because they can immediately say transform it to a higher voltage and I sit there stuttering...
I am still stuck stuttering because I haven't found out how big the transformer would be (and more importantly how heavy).
The weight of the wire never exceeds its strength (although we don't have a lot of safety factor involved). The weight is significant but doesn't have to exceed the ability of a helicopter to lift (< 6000 lbs).
I think John is right though about the proof in the pudding. This is the type of project that if it were really viable would be in the sky already.
Power Transmission is the limiting factor, whether it be in the wire, transformer, or generator, weight bites you in the butt. The weight is 8 times more painful because you have to get it off the ground which means all those assumed calculations I just did about transmitting power to the ground are irrelevant, because you need to send 8 times the current back which means making the equipment significantly heavier...
The idea was worth an engineer playing with on paper, but someone should have kicked him in the ass after he got funding. .... Problem is that funding is the issue NOT reality. This goes for AGW and science in general these days. It doesn't matter so much that you have a viable project, just that it is politically correct and fundable.
And how much did you say the cable insulation weighed?
Not worried about the cable insulation. All we have to do is look at the weight of the FEG. 144,000 V generators aren't exactly light. Neither is a transformer big enough to up 480 v to 144000 V. Every pound you have to keep a loft represents an amount of electricity that cannot be generated because the energy needed to keep the beast aloft is used to keep it aloft NOT generate electricity.
TANSTAAFL rules no matter what you try to do.
What John is implying is that when you are up to the hundred thousands of volts, those volts have the nasty habit of throwing bolts of lightning around like the gods from Mt. Olympus. In other words, you need very thick insulating materials or large separation between conductors, or both. You might have noticed that on normal transmission lines no insulator is used; they just separate the lines a good 10 feet or more. On a tether, however, you don't have the luxury of widely spaced cables. They must be insulated from each other. Then even if you reduce the diameter of the conductor (less current) you have to increase the thickness of the insulator, so there goes your weight reduction. The size of the generators must increase, too, due to those high voltages: you have to keep certain parts farther apart to prevent arcing. Plus the tether must still hold the whole contraption firmly anchored to earth. Aluminum alone won't do. It has to be ACSR (Aluminum Conductor Steel Reinforced) cable, probably with an extra steel cable (non conducting) to provide the needed tensile strength.
I was suspicious of the high voltage solution potentially causing arcing issues. I will grant you that it is necessary.
As I tried it indicate at the end of my last post, no matter what you do to make the current feasible in the line the weight of the wires alone make it untenable. You never have to start to consider the weight of the insulator.
Make the cable thick enough to handle the current.
Make a transformer big enough to pump up the voltage.
Make a generator generate voltages that high.
All of these have a problem with LOTS of wire.
The heavier it is, the less of the jetstream will be converted to electricity and will be used to just keep the thing aloft. The heavier it is the more energy required to get it off the ground in the first place. This is where I think the real buggaboo is. You might be able to design a system that will get energy back to the ground.(a might iffy might) Using that same system to get a helicopter to lift off is the challenge.
30,000 ft runways might be an answer to that problem though.
Please observe, that I am not a proponent of this idea. I am just making sure that someone points out some of the items that will be brought up by real proponents and that we are able to address them.
Obviously, "It's the insulation, stupid!" hasn't managed to get them to wake up.
Of course "It's the weight, stupid" isn't gonna do it either.
Actually, adding "stupid" the end of any sentence is never a good idea. (And NO, John did not add it there, I added it).
I continually make the same wrong false assumption -- that you all can read my mind and will interpret my words accordingly.
Whenever someone says, "You don't have the luxury," the first question we should ask is "Why Not?"
One type of kite flown a lot these days has exactly that , two tethers. Logistics of unrolling two tethers simultaneously would be challenging, but not bad. You could easily keep them 10 ft or even more apart. Insulation problem solved.
Of course we are still stuck with the niggling problem of getting the buggers airborne. Sort of like Robinson Crusoes first Canoe. Big Bugger, only 80 ft from the stream to float it in. Nice boat, how ya gonna get it to the stream.
I raise my hat to a man who can easily keep a mile or more of bare high voltage cables apart, but pardon me if I absent myself from the demonstration.
I am not going to be anywhere near their test either. Not really worried about there ever being a test. As you pointed out, there are very good reasons why the demonstration model is in "planning" stages. This is akin to the oddballs out there pushing their PMMs and OUDs. If you could hook a generator up to one and start generating electricity, you could sell it.
AAAAH. What. Sell the electricity.. What the heck kind of business model is that.
You force me to consider other questions.
How much force would be required to keep the line straight?
How tall must the mast be to make the tether far enough from the ground?
How much will the line sag?
How far downstream of the mast must be cleared for the line sag?
How does aluminum wire fair with high voltage on it?
How does this affect its fatigue cycle.
Would I be offbase to guesstimate the length of the line as 1/4 of the circumference of a circle? 1/2*pi*r or 1.5 * height. So 15,000 ft of altitude is gonna require 22,500 ft of cable. and 30,000 ft is 45,000 ft of cable.
Which reminds me that there is a distinct possibility of those wires swinging together (if we were to use my duel kite string idea), so you would have to put spaces on the line (just as they do with power lines).
Once again, I wasn't supporting the idea, just exploring how many ways it was wrong. Mostly because I started repeating stuff I heard here other places and realized that some of the things I was saying were wrong. It was not that what was said here was incorrect, just that how I internalized it was incomplete. Now I can more informatively deride others who put forth the idea. I have to derided them without them knowing it though. The trick to changing someone's mind is to get them to think it was their idea.