One might consider a design akin to the Osprey. Of course you don't need the fuselage, just a very large wing. It would be much wider than the wings on the osprey, and it might have four or more rotors, but the principle is the same. Take off as a remote-controlled helicopter [drone]. Then, when entering the jet stream at about 20,000 feet, start to power down the motors and switch them to generator mode. Begin to rotate the propeller and generator assembly to drag behind the wing. When the propellers reverse direction and reach the threshold velocity, begin generating power. It would all be controlled as a remotely flown aircraft. And it is always acting to keep the tethers in tension. I tend to think 3 tethers might be needed. In all seriousness, I really want to do this. I have a history that justifies giving me a shot. And I'm a good salesman when I'm dedicated to an idea. I think I will start sending my resume and a letter of explanation to key people. You never know. Sometimes lightning strikes.
It can be done IF the challenging requirement for instantaneous absorption is overcome, but, as stated in the link, it's not enough on a national scale compared to overall energy demand. From the link: "Sadly, it is completely, utterly unfeasible to use lightning for electricity. But cheer up, it is still beautiful to watch."
That is just a matter of using a very low ESR [effective series resistance] capacitor bank. The same problem comes up for rail guns and things like X-Ray LASERS, which require very large and very rapid current discharges at high voltage. If it was worth it, and you could control the strikes, it is certainly possible to design a capacitor that would handle it. But it wouldn't be cost effective. PS. To a certain extent we can direct lightning.
Just thinking... So assuming one FEG having enough area to produce an average of 1000 MW can be built for $200 million, with $20 million per year in operating and maintenance costs, and a 5 years until a major overhaul is required. Assume an average of $140 per MW-Hour https://www.eia.gov/electricity/monthly/update/wholesale_markets.php If we assume 80% up time, then we get 7000 hours per year at 1000 MW and $140/MW-hr = $981 million per year ??? Triple the cost to account for site construction, infrastructure, etc. By this estimate, it pays for itself in less than a year? Did I miss something...?
OTEC is where it's at if they can ever make it work commercially that is https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion
Flying generators don't necessarily have to have a cable https://en.wikipedia.org/wiki/Wireless_power_transfer#Microwaves fly them over desert areas, land is cheap to build a reciever and if they fall out the sky no one to get hurt.
I haven't been able to find anything published about the forces involved. What did you get for the cable tension? The only thing I found out was that a free-hanging kevlar cable would reach its rated strength at around 50 miles.
Wind load https://www.wikihow.com/Calculate-Wind-Load Basically the turbine acts like a solid wall against the wind. So the area A is the swept area of the turbines. Additionally there is lift, which is fighting the tether, and weight, which reduces the total force due to lift. For precise answers it requires a specific design and computer simulations.
Another way to estimate force is using the equation, Power = Force x Speed. We know the power. We know the wind speed. I will probably post some calculations later. But it has been a long week.
About 12 years ago, I started a company with the goal of making cost-competitive fuel from algae. It was too early, which we soon figured out [estimated 100s of $millions in research still needed], and it is coming, but I never really wanted to become an expert at algae. It was just the best path to a solution. FEGs are an exciting technology but we still need algae fuels. There really is no practical path to eliminating the need for liquid fuels; not anytime soon. So the most important energy source options are fuels derived from algae. But personally, I prefer FEGs to algae because they're fun! This is cool stuff!!! FEGs - More Fun than Algae
I'm not sure that I want to assume that the windmill part of the sysem (rotor) can be treated as a solid surface. With a properly designed "autopilot", lift can be made to equal weight within an envelope of wind speed variation. Through effective blade pitch control, total drag can be maintained at a relatively constant value. As the height is known, and the total drag can be calculated (but not by me in less than a month), I need the value of either one more angle or one more leg, in order to solve for cable tension. Here's what I have (sorry for the over-caffeinated printing:
I wasn't giving an opinion. That is key to the design of turbines. But you do have to factor in the efficiency of the energy transfer. 40% seems to be a common number for wind turbines. But it isn't that simple either because you have other factors, like turbulence. Note that I buried a 40% efficiency in my own estimates already. I multiplied assuming those losses. In the end there is a delta V for the wind velocity. That is the best measure of the force over the swept area. Yes. We know that Power = Force x Speed. That must always be true. So that is the down-and-dirty way to get an estimate. Then factor in some guess at efficiency. This is identical to the force required to pull the wing through the air at 50 meters per second. Same problem. How much power would be required to drag the wing and turbines at 50 meters per second. Assume the power is 1 GW Speed is about 50 meters per second....
"I wasn't giving an opinion. " Sorry, my brain doesn't think that way. I would have to see some proof that a fan behaves as a wall. Otherwise, the way I see it, no propellor or fan could generate any thrust. The air must move through the system in order for it to function. Air does not move through a wall. --------------------------------------------------- Is that 40% efficiency for the total system? It seems reasonable.
Study turbine design. That's where the efficiency comes in. As I said, its a Delta V that finally determines the force. If you really want to understand this, read up on turbine design. But the Power = Force x Velocity is a far easier way to get at least the proper order of magnitude for the force. I gave you the numbers. You just needed to calculate and convert to whatever units you want. The beauty of physics is that basic laws always work if applied correctly. --------------------------------------------------- That is based on the graph in the op. At peak power, typical turbines are 40% efficient. So my numbers for 6400 meters squared for over 6 GW included the 0.4 multiplier.
Look at it this way, if you had the tether attached to an electric train on a long straight track, and the air was perfectly still, and you towed the wing to keep it in flight, Power = Force x Velocity represents P = power required by the electric train motor Force is the tether force Velocity is the velocity of the train. Same problem. How much work it would take to pull it, is the same as the work done on the system if held in place. Whether the wing is moving in still air, or the air is moving against a fixed wing is relative. Its the same problem.
Another basic law we can use Over some period of time, a mass M of air moves through the turbines and produces E-total Joules of energy. This energy was transferred from the moving air, to the turbine, and finally the generator. So the energy in the wind goes as: 1) E-wind = M/2 (Vinitial squared) where Vinitial is the initial velocity of the wind 2) The loss of energy in the wind is [Ewind initial - E wind final], ie M/2 (Vinitial squared) - M/2 (Vfinal Squared) = Change in wind energy = E-total that we get at the generator This has to be true by the conservation of energy law. How much energy we get is a direct measure of how much the wind velocity changes.
"Study turbine design." Hmm... not a convincing argument. "That is based on the graph in the op. At peak power, typical turbines are 40% efficient." OK then, I would need to know the weight of the complete turbine system in order to make a guess at the needed lift, thus the resultant drag of the wings.
What issues would arise with the use of 1 million volts? Might there be issues with the insulation required, both for the connecting circuitry and the generator itself?
As you see from the video, to contain the electrical "pressure" of voltage in that range is quite difficult. To harness that for practical use would require serious insulation and separation of the circuit conductors. And the weight of that insulation and supporting equipment may prove to be impractical for a large capacity flying generator. What are the practical limits of voltage in a rotating generator which uses electromagnetic induction? What is the voltage output of the *generator* in common steam driven utility stations?
So, I'm getting an 747, flown as a kite, could be rigged to lift 400tons of generators (without turbine blades) at a 250mph wind speed. That would require a horizontal cable at 67,000lbs of tension. Any increase in the angle of elevation would cause an increase in the component of cable tension to be added to the aircraft's weight. This would increase the drag, which would increase the cable tension. In the horizontal situation, you would probably want to use two cables of at least an inch and a half diameter. That would give you about a 200,000lbs breaking strength and weigh about 6,700lbs per mile. If my math is correct, and the 40° angle assumption is correct, the additional downforce created by the cable tension of around 90,000lbs would add around 4000lbs to the drag. At this point you would probably want two, two inch cables for a 400,000lbs rated breaking strength. That would weigh around 15,000lbs per mile.
