Can this satisfy the world's energy needs? High-altitude wind power.

[Ivan Seeking]

This has come up a couple of times now, and if true then this needs greater exposure and is certainly worthy of discussion. At a glance, this or some variation on the idea seems most promising.

It was known to scientists before any of us were born, and not kept secret, that there is far more than enough energy in high altitude winds, miles above the Earth's surface, to supply all the world's power needs. And just average wind conditions high above the Earth in the temperate zones of the Northern and Southern Hemispheres are sufficient to supply all the world's energy needs. The jet stream does not have to be overhead.

...Please see pictures upper right of a FEG which he and his colleagues demonstrated at low altitude years ago, and lower right of an artist's view of the next planned FEG which Sky WindPower plans to demonstrate under Professor Roberts' direction at an altitude of 15,000 feet and above.

Our figures show now, that with the advent of very strong but light tether materials, through use of what is essentially existing rotorcraft technology, capture of high altitude wind energy should prove cheaper than as derived from any fossil fuel. [continued]

http://www.skywindpower.com/ww/index.htm

It seems to me that the energy available in the jet stream is of greater interest than this particular solution; though this may work... There must be at least several ways to approach this problem.

 

[Bystander]

Little disappointing that the "wind resources" section doesn't include any numbers for "solar power" requirements for driving the wind system. That is, have people looked at "environmental impacts" of extracting wind power vis a vis what fraction of the "available power" can be diverted without affecting weather patterns?

 

[russ_watters]

I'm sure you could make the calculation after 5 min of Googling for data, but if it isn't an issue for regular solar power, it won't be an issue for wind power either. IIRC, though, a solar array would need to be on the order of 300 miles square to satisfy the world's energy needs. That's half a percent of the cross sectional area of the earth.

Besides - one way or another, it all ends up as heat.

I think this is a good idea that should be pursued. It isn't without flaws (nothing is), but it is worth studying more.

 

[Cliff_J]

That is very interesting, especially how easily it could be established in a distributed manner. With the population center density a little higher in NE America it may be a little tougher to find locations, but with a better grid and the prospect of being able to generate and store hydrogen as an energy storage medium this could really be a promising technology for the rest of US. Might get tough again in parts of the EU because of space restrictions, but an offshore variant could maybe be made to work to keep saftey and asthetics in mind. If their charts are correct, most of the population lives at lattitudes that have plenty of power to extract.

 

[Bystander]

I'm sure you could make the calculation after 5 min of Googling for data,

Certainly. That's the point, no one peddling the idea includes such a calculation.

but if it isn't an issue for regular solar power, it won't be an issue for wind power either.

"If..." Still a big "if" when the calculation isn't done.

IIRC, though, a solar array would need to be on the order of 300 miles square to satisfy the world's energy needs. That's half a percent of the cross sectional area of the earth.

And, what's the percentage of absorbed sunlight?

Besides - one way or another, it all ends up as heat.

Correct: "one way" it goes through a cycle driving winds, lifting water, dropping it one golf courses, ski runs, and otherwise doing work in global circulation; "the other" is that less "weather" work is done and electrical work is done instead.

I think this is a good idea that should be pursued. It isn't without flaws (nothing is), but it is worth studying more.

"More study?" Yes. Do the calculation rather than wave hands. Russ, I've done it with my numbers, my assumptions, and my knowledge. I want to see someone else's numbers, assumptions, and knowledge, and I do not want to influence the approaches people might take before orders of magnitude results are compared.

So, is someone going to do the "five minutes googling?"

 

[Ivan Seeking]

I'm not sure about energy lost to space etc, but I come up with something like 10¹⁸ KWHrs per year energy influx due to sunlight, and a worldwide yearly energy demand of about 10¹⁴ KWHrs, as of 2003.

...need to double-check when I get back in my office though. I'm sitting here taking notes on a napkin.

 

[Ivan Seeking]

okay, I was being too generous with the absorption. It is known that 1368 Watts/meter² enters the upper atmosphere, but we only absorb about a fourth of that:

Averaged over an entire year and the entire Earth, the Sun deposits 342 Watts of energy into every square meter of the Earth. This is a very large amount of heat—1.7 x 10¹⁷ watts of power that the Sun sends to the Earth/atmosphere system

http://earthobservatory.nasa.gov/Library/Oven/

Does this ignore atmospheric abosorption of solar energy before it reaches earth? Still, multiply by the hours in a year and we come out about right - 1.5 X 10¹⁸ KWHRS per year. So I guess it was about right

Here, the world energy demand is cited as being 421 X 10¹⁵ BTU per year, or 1.2 X 10¹⁴ KWHrs per year, for 2003.
http://www.eia.doe.gov/pub/international/iealf/tablee1.xls

Anyway, 0.01% is a promising number.

 

[Bystander]

(snip)Anyway, 0.01% is a promising number.

"0.01%?" Agreed.

Next question: "How much of the absorbed solar infall is available for conversion to mechanical energy (air circulation)? Numbers get a lot fuzzier here, and if we agree w'in an order of magnitude, I'll be surprised.

 

[Ivan Seeking]

It seems that I get to cheat.

As long as there is sunlight, there will be wind. The wind is a by-product of solar energy. Approximately 2% of the sun's energy reaching the Earth is converted into wind energy. The surface of the Earth heats and cools unevenly, creating atmospheric pressure zones that make air flow from high- to low-pressure areas.

http://www.energy.iastate.edu/renewable/wind/wem/wem-01_print.html

So we have about 3 X 10¹⁶ KWHRS per year in wind energy. We need about 0.4% of this; or say 1-2% in practice, were we to use only wind energy for all the worlds needs.

 

[Ivan Seeking]

...and this is a bit deceiving since it ignores that all of the converted wind energy will eventually make it back into the atmosphere as heat. I have no idea is this translates into another 2% wind energy or not, but I would tend to assume that more than 2% of this heat energy will be converted back into wind energy again.

 

[Bystander]

... 0.4% of this; or say 1-2% in practice...

Tenths of percent to percent --- again, agreed.

...and this is a bit deceiving since it ignores that all of the converted wind energy will eventually make it back into the atmosphere as heat.

Check.

I have no idea is this translates into another 2% wind energy or not, but I would tend to assume that more than 2% of this heat energy will be converted back into wind energy again.

Thermodynamic efficiency is going to be 20-30%. Depends on what you want to use for temperature limits on the "engine."

Given that tenths of percent in temperature are worrisome, are tenths of percent in atmospheric circulation energy throughput worrisome?

 

[Ivan Seeking]

This then has to be weighed against the benefits of the the complete cessation of energy related CO2 emissions, pollution and oil spills etc, river silting and fish habitat loss due to large dams... It seems to me that the positive impacts would be enormous. In fact, this and the ocean tide based generating systems are the first options that I have ever seen that combined, seem to offer a true solution to the energy problem.

 

[Andre]

I wonder about practical problems. You need to tether such a kite type of device at some 30,000 feet or so to get into the jetstream area to pick up the real signifiant winds. Probably with a couple of teflon cables or so. That might weight in the order of magnitude of ten metric tons per cable. Then you have to lift a power converter and metal cables weighting some order of
magnitude more to get the power on the ground

Interesting engineering problems.

What with wind direction changes? How large would that make the restricted area for aviation when that giant kite is swarving around?

But what if CO2 had nothing to do with climate?

 

[Ivan Seeking]

How do you come up with ten metric tons? You don't even know how strong the cables would have to be, hence you can't know the size needed or the weight. Also, obviously the conductors would be used as the tether.

Also, I would tend to expect that a metalized fiber would be used.

Its funny that most people seem concerned about air traffic. This seems a mere formality to me, esp given the pay-off.

 

[Ivan Seeking]

Six miles doesn't really seem like such a huge challenge. The fiber needed for the space elevator has to be something like 8Kg per Km.

 

[Bystander]

How do you come up with ten metric tons? You don't even know how strong the cables would have to be,

Huh? Sure you do, power divided by wind speed is your bare minimum, divided by sin(tether angle from vertical), multiplied by whatever safety factor the neighbors demand. 1.3 MN (60,000 lbs) ( Edit: Thousand pardons, 280,000 --- no excuse.) for his 20MW FEG at 5 km (15,000 feet), ~15 m/s. Safety factor? Depends upon how good a Doppler radar he can get to monitor the "feed stream" for "upset conditions."

hence you can't know the size needed or the weight. Also, obviously the conductors would be used as the tether.

Copper and aluminum won't carry themselves five km in the air, let alone loads. Whatcha got in mind?

Also, I would tend to expect that a metalized fiber would be used.(snip)

For 20 MW transmission?

 

[russ_watters]

Six miles doesn't really seem like such a huge challenge. The fiber needed for the space elevator has to be something like 8Kg per Km.

The space elevator is still very hypothetical too. Maybe after someone builds the first carbon nanotube suspension bridge we can start wondering if it is feasible to build a space elevator. Right now, it is a flat - no.

It makes my crackpot alarm go off when a website says something is possible (the tether technology) and then doesn't explain how.

Perhaps the energy could be beamed back with microwaves?

 

[Ivan Seeking]

Huh? Sure you do, power divided by wind speed is your bare minimum, divided by sin(tether angle from vertical), multiplied by whatever safety factor the neighbors demand. 1.3 MN (60,000 lbs) ( Edit: Thousand pardons, 280,000 --- no excuse.) for his 20MW FEG at 5 km (15,000 feet), ~15 m/s. Safety factor? Depends upon how good a Doppler radar he can get to monitor the "feed stream" for "upset conditions."



Copper and aluminum won't carry themselves five km in the air, let alone loads. Whatcha got in mind?



For 20 MW transmission?

You can't know the total strength needed unless you know the material being used and its linear density. Picking out the blue and citing that as the number to use is ludicrous. Also, I already said that we surely wouldn't use simple steel cables. The tether technology is the key, and I cited the space elevator as an example of a much greater challenge already being pursued. With the many miracles of material science that I see every day, I find it easy to believe that this problem can be managed. And I already suggested a metalized fiber as a possible solution. There are already many incredibly strong and light fiber materials commercially available.

As for any crackpot alarms, well, that could be, and right away I mentioned that this particular solution may not be the correct one, but the energy is there in concentrated form, and that's the key.

What doesn't make sense if to assume a combative stance without even knowing what he plans to use. And as for me, I have had all of an hour to solve the problem, so it might take a little more time if you want me to figure it out myself.

 

[Ivan Seeking]

Forget about nuclear power. This is the problem that we need to solve.

The only reason that nuclear power seemed acceptable is that we didn't see any other immediate options. If this FEG design is feasible, we could be flying these things before the first new nuclear plant could even be commissioned.

Edit: Okay, I emailed the company requesting more information on the tether. It will be interesting to see how they respond. This could easily be propietary information, for obvious reasons.

Edit II: As an off-the-shelf grab, maybe something like this can be treated or modified to act as a conductor.
http://www.unirope.com/fiberropes/fr_db_pobon.shtml

More edits: Sorry, it seemed better than adding new posts
Some interesting information on fibers
http://www.machinedesign.com/BDE/materials/bdemat3/bdemat3_6.html

 

[Integral]

Ivan and I had a pretty good talk about this over dinner and a cup of coffee the other night.

I now envision the tethers separate from the conductor. It would seem practical to to use the tethers to create a safety zone around your conductor. Perhaps you could further use the tethers to help support the power umbilical.

We had several interesting possibilities. Use ships at sea as the anchors, this would get away from the not in my back yard problems and allow maneuverability to chase the best winds. The ships would then have Hydrogen production plants using seawater and wind power as the raw materials. The power could then be shipped to anyplace in the world in the form of fuel cells.

 

[Ivan Seeking]

For 20 MW transmission?

Surface area is the primary factor. I suspect that this is a key issue in this sort of tether technology: How do we achieve the desired conductance with a mininum of weight? Also, obviously we want to run the voltage as high as possible. If we are running 115KV, which is standard for long distance transmission, we only need to carry about 170 amps, for 20MW of power. I ran a 200 amp service to my office. This is not a large number.

 

[Bystander]

You can't know the total strength needed unless you know the material being used and its linear density.

I'm NOT talking about the self-loading of the tether, I'm talking about the bare bones load of the FEG on the tether, power equals force times velocity for the 20MW platform size discussed on the website. There is an assumption on my part that they aren't planning on skyhooking 150 tons into the air and having it glide at a 20-25 m/s terminal velocity in a 15 m/s airstream, but that the force serving to "move" the FEG through the airstream is to be furnished by the tether.

(snip)

 

[Ivan Seeking]

Yes, sorry, I later realized that we were talking about different loads.

I was objecting to Andre's statement: "That might weight in the order of magnitude of ten metric tons per cable."...and worse for the conductors.

No way. We can do much better than that.

 

[russ_watters]

Well, the weight of the conductors is an issue I see as well. Certainly, you wouldn't use the conductors as a tether because it would be longer than dropping the conductors straight down. But even still - what do we have that can conduct electricity and hold it's own weight for a height of 15,000 feet?

You can't know the total strength needed unless you know the material being used and its linear density. Picking out the blue and citing that as the number to use is ludicrous.

Bystander was guessing based on experience, but it isn't hard to throw some numbers in:

Aluminum is a good conductor and has a good strength-to-weight ratio. At 30,000 psi and 17 lb/ft^3 (with very little safety factor), that'll get you up to about 3500 ft.

I'd bet money that if this company emails you back, they will tell you that the tethers and the conductors will both be made from carbon nanotubes.

 

[Bystander]

(snip)Bystander was guessing based on experience, but it isn't hard to throw some numbers in: (snip)

No "guessing" to it. Let's see what we got so far: 1) skin effect for power transmission, that's if we kick frequency up to 100 kHz; 2) high voltage to cut down conductor weight, if we can "fly" a 20 MW transformer, or build 100 kV dynamos; 3) exotic materials for tethers, say one of the spider silks (3-3.5 GPa or 500,000 psi tensile) gets us down to 50 ton tether masses with a marginal safety factor (2 tethers per 20 MW platform). That about it?

 

[Ivan Seeking]

Well, first of all, Russ, you set the problem up to fail. No, we can't use conductors alone so they must be incorporated into a tether that can carry the load. But I guess the weight of the addition tether needed for the conductor would determine if it was more efficient to incorportate this into the main tether, or to keep it separate. Still, it seems that some kind of deposition or weave with the appropriate fiber might be one avenue to explore.

And Bystander, you say that we need 50 tons of spider silk to sustain a 280,000 Lb load? You lost me somewhere.

 

[Ivan Seeking]

I think the high voltage generator technology already exists. For example

Very High Voltage Generators
Output power 5 to 55 MVA at 50 Hz
Voltages 20 to 70 kV
Frequency 50,60 Hz or VSD
Protection IP54, IP55, IP56
Cooling Water cooled
Standards IEC, NEMA
Hazardous areas Non-sparking
http://www.abb.com/global/abbzh/abb...e=us&m=9F2&c=F4ACFD05097CEBBBC1256DFA0027E000

And one might imagine running some number of generators in series.

Also, I don't think we need to leap to the conclusion that we have to use 100 KHz in order to avoid using solid conductors. After all, even at 30,000 feet this is a short distance for power transmission. Also, I see that systems as high as 500,000 volts transmission are now used. This would bring us down to about 40 amps at 20MW.

 

[Bystander]

20,000 feet of 1" super-silk, nylon, whatever is 4-5 tons. That's what I get for reading the LCD on my calculator by firelight.

 

[joema]

High altitude wind power is an interesting concept with some advantages over terrestrial wind turbines. However I doubt it could supply the world's energy. If further developed and if no unforeseen problems materialize, it might supply a few percent. Why? See below.

The world uses over 400 quadrillion BTU (1.18E17 watt hours) of energy per year. Assuming 1.5 MW Flying Electric Generators (FEGs), how many FEGs would be required to supply world energy needs?

Each 1.5 MW Flying Electric Generator (FEG) would have FOUR 88 ft. dia. rotors, EACH larger than the main rotor of the huge CH-53 helicopter.

Assuming a 50% capacity factor (roughly double terrestrial turbines), each such FEG could produce about 6.6E9 watt hrs per year. Total number of FEGs required:

1.18E17 / 6.6E9 = 17,878,787 FEGs

I can't envision 18 million of those flying overhead, even if most are in less populated areas. Even if mass produced, I doubt they'd cost less than $250k each. It would cost $4.5 trillion to build them. Like terrestrial turbines, they'd have a finite lifespan, so you'd have to replace them in about 20 years. However -- since global energy consumption increases by about 2.5% per year, you'd need about 30 million FEGs at time of first replacement.

 

[russ_watters]

Well, first of all, Russ, you set the problem up to fail.

I set it up knowing it would fail, but I didn't set it up to fail. It failed on its own. I chose aluminum because aluminum exists. Spider silk...spider silk?? We can't mass-produce spider silk (or carbon nanotubes, for that matter). Once you start requiring technology that doesn't exist just to make the numbers work, you've moved over into science fiction.

 

[Orefa]

Maybe accessory "wings" can be added between the generator and the ground just to help hold the weight of the conductors and/or tethers.

 

[Astronuc]

I guess one issue will be airspace - it will have to blackout and avoided - which might not be a problem if the area is limited out west some where.

I'll have to look at the details, but how much work/power has to be done to keep the generating system airborn vs how much energy is transmitted.

And what to do about storms and wind shear?

 

[Ivan Seeking]

I set it up knowing it would fail, but I didn't set it up to fail. It failed on its own. I chose aluminum because aluminum exists. Spider silk...spider silk?? We can't mass-produce spider silk (or carbon nanotubes, for that matter). Once you start requiring technology that doesn't exist just to make the numbers work, you've moved over into science fiction.

Even the rope that I linked can carry 181,000 Lbs, while presenting a 13,000 pound load, at 30,000 feet. And we haven't even talked about carbon fibers, Kevlar, etc.

Wings on the tether is an interesting idea. That's basically what is done with power lines.

I keep thinking that a flying wing, perhaps with a gyro assist, makes sense. I too am curious about the lift that must be generated. The high voltage generators should help to minimize the load but I couldn't find a data sheet that showed the weight. Still, I know that we can build really big beautiful wings that can carry a great deal of weight. This could make the energy demand for lift a moot point, less the drag load.

No answer from the company. If they don't respond within a few days I'll call.

So how about it aerospace engineers: What are the basic equation needed here to calculate the efficiency of the system as a function of the power needed for lift?

 

[joema]

The problem isn't the tether. You can easily find conventional materials of sufficient strength-to-weight ratio. At 115 kilovolts you can pump 10 MW across a #1 gauge aluminum wire, which weighs 77 lbs per 1000 ft. Or you could beam it to the ground with microwaves.

However, like many alternative energy concepts the problem isn't getting a few demonstration examples to work. The problem is scaling it to the huge industrial levels needed to make a major contribution.

It makes no difference if hydrogen fuel cells or FEGs or anything else works on a small scale, if it can't be scaled to the gigantic level required for world energy consumption. As the thread title says, could it satisfy WORLD energy need, not a few megawatt hours in a demonstration facility.

We tend to think if it works on a small scale, someone will figure out how to scale it up. That's backward. If it can't be scaled up, there's no need to even consider it.

To investigate ultimate feasibility, don't work numbers for tethers. Rather work backward and calculate what's required to supply 1.18E17 watt hours per year.

Doing that indicates FEGs are probably not feasible as the primary world energy supply.

 

[Ivan Seeking]

To investigate ultimate feasibility, don't work numbers for tethers. Rather work backward and calculate what's required to supply 1.18E17 watt hours per year.

Doing that indicates FEGs are probably not feasible as the primary world energy supply.

Why?

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