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?

,,,,,,,,,,,,

 

[joema]

If you mean why examine whether an alternative energy source can scale upward to supply a significant fraction of world demand, the answer is obvious: if it can't, it's mainly an interesting curiosity.

If you mean why doing so implies FEGs likely can't supply the world's energy needs (the thread title), as I stated before the math and implications are very simple. It would require 18 million 1.5 MW FEGs.

The website mentions using 20 MW FEGs without any analysis of whether that's actually possible. The largest terrestrial wind turbine ever made is the REPower 5M, a 5 megawatt unit with a rotor diameter of 126 meters. It weighs 120 tons. Each rotor blade weighs 18 tons. You'd need something maybe TWICE that size -- flying overhead -- for a single 20 MW FEG (accounting for higher rotor disc areal efficiency).

Then to supply the world's energy needs, you'd need 792,371 of those -- 1.18E17 watt hrs/yr / 149E9 watt hr/yr/FEG. It's should be obvious that's not realistically possible.

 

[Ivan Seeking]

If you mean why doing so implies FEGs likely can't supply the world's energy needs (the thread title), as I stated before the math and implications are very simple. It would require 18 million 1.5 MW FEGs.

The website mentions using 20 MW FEGs without any analysis of whether that's actually possible. The largest terrestrial wind turbine ever made is the REPower 5M, a 5 megawatt unit with a rotor diameter of 126 meters. It weighs 120 tons. Each rotor blade weighs 18 tons. You'd need something maybe TWICE that size -- flying overhead -- for a single 20 MW FEG (accounting for higher rotor disc areal efficiency).

You are assuming the same wind conditions as for the land based design, but that is a great deal of weight.

According the web site, for a given amount of power, it would use relatively smaller turbines due to the increased wind velocity as compared to land based turbines. And at least on the face of things, there is no reason why many turbines couldn't be used on a single platform. Why not make a large wing with ten or twenty of them onboard?

I keep thinking of an old design by NASA intended for overseas flights which involved a large flying wing to which 747's would dock at 30,000 feet. The wing was designed to remain in constant flight and could service four or five passenger planes at any time. The passengers would deplane and relax in the football field sized lounge. Again, the point being that we are really good at building fantastically large wings.

Then to supply the world's energy needs, you'd need 792,371 of those -- 1.18E17 watt hrs/yr / 149E9 watt hr/yr/FEG. It's should be obvious that's not realistically possible.

I'm not so quick to give up. How many cars, planes, and ships do we build? How many nuclear power plants would be required to produce the same amount of power, ~20,000? What is the cost of a nuclear plant compared to a platform like this? What is the liability? How long will it take to build 20,000 nuclear plants? And what are the chances that they could ever be built given the political climate and terror concerns.

After all we are talking about the entire planet. The idea of 800,000 generators isn't really so striking to me. In fact no matter what we do for energy, we have many of the same problems.

 

[Ivan Seeking]

One more thought for perspective: We are talking about replacing the entire world's energy infrastructure with one shot. We have to be able to imagine what already exists - all other sources of energy, their distribution systems, and all of the related political and environmental issues that go along with it.

 

[Ivan Seeking]

4. Airbus A380F 1,305,000 lb L: 239'3";S: 261'8"

That's 650 Tons

I didn't spot the maximum take off speed, but it wouldn't be more than 200 MPH, I would think. At that point I would think that most of the lift is generated by the body and wings?

 

[joema]

You are assuming the same wind conditions as for the land based design, but that is a great deal of weight.

Higher winds aloft mean higher stress. That in turn means more complexity and development and production expense for the same power output. It's much harder and more expensive to make light sophisticated things (e.g, airplanes) than heavy things (e.g, cars).

According the web site, for a given amount of power, it would use relatively smaller turbines due to the increased wind velocity as compared to land based turbines.

I already factored that in, by allowing a 2x reduction in size. However you lose some because you expend lift holding the huge contraption up. 2x the areal efficiency of a terrestrial turbine probably isn't far off, and that still equates to gigantic mass overhead, vastly beyond anything ever conceived thus far.

And at least on the face of things, there is no reason why many turbines couldn't be used on a single platform. Why not make a large wing with ten or twenty of them onboard?

You could if you wanted 10 or 20 hundred foot diameter rotors spinning on the same structure. However that is vastly beyond any aerodynamic construction ever seriously considered.

...large flying wing to which 747's would dock at 30,000 feet. The wing was designed to remain in constant flight and could service four or five passenger planes at any time. The passengers would deplane and relax in the football field sized lounge. Again, the point being that we are really good at building fantastically large wings.

We are good at talking about it (and many other things) -- see Popular Science cover stories over the past 50 years. Most of those are never built and cannot ever be built.

I'm not so quick to give up. How many cars, planes, and ships do we build? How many nuclear power plants would be required to produce the same amount of power, ~20,000?

Using the Palos Verde nuclear plant mentioned on the SkyWindPower site, it would take 4,129 to supply the world's energy needs.

What is the cost of a nuclear plant compared to a platform like this? What is the liability? How long will it take to build 20,000 nuclear plants? And what are the chances that they could ever be built given the political climate and terror concerns.

I'm not saying a gigantic nuclear effort is clearly the answer, either. But just because there are problems with nuclear, or biofuel, etc, doesn't automatically mean some other alternative will work.

After all we are talking about the entire planet. The idea of 800,000 generators isn't really so striking to me. In fact no matter what we do for energy, we have many of the same problems.

That's exactly right -- there are problems with virtually all energy solutions, so picking one that's practically achievable is important.

 

[joema]

4. Airbus A380F 1,305,000 lb L: 239'3";S: 261'8"

That's 650 Tons

I didn't spot the maximum take off speed, but it wouldn't be more than 200 MPH, I would think. At that point I would think that most of the lift is generated by the body and wings?

You essentially need a gigantic helicopter, not a gigantic fixed-wing plane. As anybody familiar with aviation will corroborate, helicopters are much more expensive and complex than fixed-wing aircraft, and have much less lift capability.

E.g, the heaviest lift US plane, the C-5B Galaxy, can lift about 261,000 lbs. By contrast the heaviest lift US helicopter, the CH-53E, can lift about 30,000 lbs. Rotor-wing craft also also require far more maintenance than fixed wing. An FEG is much closer to a helicopter than a fixed-wing plane.

 

[Ivan Seeking]

Higher winds aloft mean higher stress. That in turn means more complexity and development and production expense for the same power output. It's much harder and more expensive to make light sophisticated things (e.g, airplanes) than heavy things (e.g, cars).

This may or may not be a significant issue. I don't think we can say at this point.

I already factored that in, by allowing a 2x reduction in size. However you lose some because you expend lift holding the huge contraption up. 2x the areal efficiency of a terrestrial turbine probably isn't far off, and that still equates to gigantic mass overhead, vastly beyond anything ever conceived thus far.

What I am saying is that we use a high-lift wing, not a gyro. The energy needed for lift then becomes a function of the wing size and not the turbine size. It becomes a tether and structure problem, and not an power problem.

You could if you wanted 10 or 20 hundred foot diameter rotors spinning on the same structure. However that is vastly beyond any aerodynamic construction ever seriously considered.

Well, at ten or twenty, I was talking about smaller turbines. But the point is that I have seen serious design concepts that were more radical. For now I'm thinking about something on the scale of the Airbus, and all we really need are the wings.

We are good at talking about it (and many other things) -- see Popular Science cover stories over the past 50 years. Most of those are never built and cannot ever be built.

same as above

Using the Palos Verde nuclear plant mentioned on the SkyWindPower site, it would take 4,129 to supply the world's energy needs.

Okay, I thought ~1 GW was the state of the art. But then we are still talking about plants that are five times larger.

I'm not saying a gigantic nuclear effort is clearly the answer, either. But just because there are problems with nuclear, or biofuel, etc, doesn't automatically mean some other alternative will work.

That's exactly right -- there are problems with virtually all energy solutions, so picking one that's practically achievable is important.

Well, obviously there are alternative that are competitive in some areas now, but until now, no alternative to oil were viable globally except nuclear, using existing technology. In principle we could probably start building FEGs tomorrow. And if we can completely eliminate the risk of nuclear power and all of the related problems, what are the potential savings - a city, maybe much more?

The FEG idea also creates an implicitly robust grid with many generators distributed over the system, rather than having a highly centralized system. This even speaks to issues such as national security beyond the immediate concerns of a nuclear disaster.

Again, the rotor idea doesn't make sense to me either. A tethered wing with at least two counter rotating turbines could make much more sense. And again, the Airbus can take off with a max weight of 650 tons. This easily could lift two of your turbines, the generators etc, at least at ground level, and at something close to high altitude wind speeds. So we are already in the ball park with an existing, off-the-shelf wing. Of course a better design is easy to imagine but the point is that scale is there.

 

[Ivan Seeking]

Can we talk Iran into FEGs?

 

[joema]

This may or may not be a significant issue. I don't think we can say at this point.

A terrestrial 5MW wind turbine weighs 120 tons. Building a flying version with equivalent output would be vastly more expensive. Ask any engineer experienced in the area -- reducing weight while maintaining capability is almost always very expensive and complex.

What I am saying is that we use a high-lift wing, not a gyro. The energy needed for lift then becomes a function of the wing size and not the turbine size. It becomes a tether and structure problem, and not an power problem.

You're right if you could depend on approx 150 mph lateral winds, a tethered flying wing the size of a C-5B could lift about 118 metric tons. You can only count the payload weight, not the entire vehicle weight, as the wings must also lift the vehicle.

Considering a C-5B-size wing alone (no turbines) with a 10:1 lift/drag ratio, the drag would be 11.8 metric tons. To this you must add the drag force of the turbines and associated structure. A 20 MW turbine might have a turbine airfoil area of 1512 m^2 (roughly 2x the above-mentioned 5 MW terrestrial turbine). Assuming 10 degree angle of attack, the blade frontal area would be about 276 m^2, and drag coefficient (Cd) would be about 0.1. More info: http://www.risoe.dk/rispubl/VEA/veapdf/ris-r-1024.pdf Equation for drag force is:

Fd = cd 1/2 rho v^2 A, where

Fd = drag force (Newtons)
cd = drag coefficient (0.1 for C6 Corvette)
rho = density of fluid in kg/m^3, 0.56 kg/m^3 at sea at 20k ft
v = velocity in m/sec (150 mph, or 67 m/s)
A = frontal area in sq. meters (roughly 276 square meters)

Fd = 0.1 * 0.5 * 0.56 * 67^2 * 276
Fd = 34690 Newtons (7798 lbs force)

So at least the drag force from the turbine blades themselves seems low.

However you'd need a tether capable of carrying itself plus a 11.8 metric ton load, plus an approx 2x safety margin, so call it 25 metric tons. That appears no problem, even using conventional ropes: http://www.samsonrope.com/home/newcommfish/gp-2in1superstrongnylon.cfm?ProdNum=158

A 20,000 ft tether constructed of the above 1.5 inch line could restrain 34 metric tons (inc'l its own weight), and would itself weigh 5.4 metric tons.

obviously there are alternative that are competitive in some areas now, but until now, no alternative to oil were viable globally except nuclear, using existing technology.

The initial post asked about satisfying world energy need, not world petroleum consumption. Petroleum only accounts for very roughly 40% of world energy consumption, but is by far the most time-critical energy issue since at current rates conventional oil will be depleted in about 35 years, and peak oil will happen far sooner. By contrast there's enough coal for a 200 years at current consumption rates.

There is an existing alternative to oil using current technology, which is biodiesel from high yield algae. In theory that could supply world petroleum energy consumption within available acreage and construction/maintenance costs. Obviously remaining research is needed, but it could use existing production, transportation, and vehicle technology: http://www.unh.edu/p2/biodiesel/article_alge.html

In principle we could probably start building FEGs tomorrow. And if we can completely eliminate the risk of nuclear power and all of the related problems, what are the potential savings - a city, maybe much more?

The most time critical energy issue is petroleum, not energy (nuclear, coal, etc) for utility generation. Even if FEGs worked, using them for transportation energy via hydrogen/fuel cells would take many decades and entirely new vehicle and distribution infrastructure. Oil would be depleted long before that transition could happen.

The FEG idea also creates an implicitly robust grid with many generators distributed over the system, rather than having a highly centralized system.

The current energy production and distribution system is already highly distributed, with many generators spread across the system.

 

[Ivan Seeking]

A terrestrial 5MW wind turbine weighs 120 tons. Building a flying version with equivalent output would be vastly more expensive. Ask any engineer experienced in the area -- reducing weight while maintaining capability is almost always very expensive and complex.

If you mean to say that this is proof that it can't work, no way. We can't possibly know. At most is a concern. But since we have been building wings with props for over a hundred years now, I tend to doubt that this is a serious issue. It obviously does represent a focal point of the design.

You're right if you could depend on approx 150 mph lateral winds, a tethered flying wing the size of a C-5B could lift about 118 metric tons. You can only count the payload weight, not the entire vehicle weight, as the wings must also lift the vehicle.

We wouldn't have to carry most the weight of the vehicle. We only need the wings void of fuel and engines. Also, we don't need the fuselage, wheels, AC, most flight controls, etc. And again, this was only for comparison with existing technology. We could easily come up with a more appropriate design for this application.

Considering a C-5B-size wing alone (no turbines) with a 10:1 lift/drag ratio, the drag would be 11.8 metric tons. To this you must add the drag force of the turbines and associated structure. A 20 MW turbine might have a turbine airfoil area of 1512 m^2 (roughly 2x the above-mentioned 5 MW terrestrial turbine).

Edit: Sorry, I guess I don't understand the point

... oh, okay, were you just working this through?

The initial post asked about satisfying world energy need, not world petroleum consumption. Petroleum only accounts for very roughly 40% of world energy consumption, but is by far the most time-critical energy issue since at current rates conventional oil will be depleted in about 35 years, and peak oil will happen far sooner. By contrast there's enough coal for a 200 years at current consumption rates.

We still don't have clean coal. Not really a viable solution as yet.

There is an existing alternative to oil using current technology, which is biodiesel from high yield algae. In theory that could supply world petroleum energy consumption within available acreage and construction/maintenance costs. Obviously remaining research is needed, but it could use existing production, transportation, and vehicle technology: http://www.unh.edu/p2/biodiesel/article_alge.html

Not yet viable. And we still have the problem of 100-200 watts per sq meter yield.

The most time critical energy issue is petroleum, not energy (nuclear, coal, etc) for utility generation. Even if FEGs worked, using them for transportation energy via hydrogen/fuel cells would take many decades and entirely new vehicle and distribution infrastructure. Oil would be depleted long before that transition could happen.

We have this problem no matter what we do.

 

[Ivan Seeking]

I want to stress that I have been and am a huge supporter of all sorts of energy alternatives, but something that is always frustrating is the fact that nothing is quite there yet. And even something like biodiesel is still dirty and problematic, but its definitely worth doing from all that I see.

As for Bio-Willy, a flukey thing: We once took his private bus for a 1000 mile joy ride, for a long weekend. Back then he had this cool King Tut theme going. Anyway, long story but it was pretty cool.

 

[joema]

If you mean to say that this is proof that it can't work, no way. We can't possibly know...we have been building wings with props for over a hundred years now...

Not saying it CAN'T work, but it's likely economically unfeasible. Howard Hughes built the largest ever prop plane, but you don't see prop planes of that size flying today. Just because it CAN be done doesn't mean it's economically and technically feasible to do on a vast industrial scale.

We still don't have clean coal. Not really a viable solution as yet.

Not a viable solution? Today coal provides 24% of world energy. It has already happened. You have to prioritize. The highest priority is transportation energy, not utility energy. If you allocate most resources now to developing new utility energy (when existing sources will last over 100 years) and transportation energy runs out in 30 years, what is the benefit?

Not yet viable. And we still have the problem of 100-200 watts per sq meter yield.

It's far more viable and less expensive than building a million 747-size wind turbines, hundreds of million new fuel cell cars, tens of millions new hydrogen fuel stations, etc. I have no idea what you mean by 100-200 watts/m^2 yield. If you read the web site, you'll see the yield is over 100x other common biofuel feedstocks, and the total acreage easily fits within available real estate.

We have this problem no matter what we do.

No -- the problem varies based on implementation time for the chosen technology. For hydrogen/fuel cells, every car, every engine in every car, every tanker truck, every pipeline, every service station -- EVERYTHING must change. That takes decades, even given huge economic support. Others like biofuels use the existing distribution and vehicle infrastructure, which means they can be implemented much faster and cheaper.

I can't stress strongly enough -- the issue isn't whether an individual FEG or solar panel or fuel cell car or biofuel car will work. Whatever technology is chosen must be economically scaleable to titanic industrial levels to have meaningful impact. Those are often two different things.

 

[Ivan Seeking]

Not saying it CAN'T work, but it's likely economically unfeasible.

I don't think so. In fact the review here implies just the opposite to me.

Not a viable solution? Today coal provides 24% of world energy. It has already happened. You have to prioritize. The highest priority is transportation energy, not utility energy. If you allocate most resources now to developing new utility energy (when existing sources will last over 100 years) and transportation energy runs out in 30 years, what is the benefit?

What good is coal for transportation? This is less viable for transportation than electric cars are now.

It's far more viable and less expensive than building a million 747-size wind turbines, hundreds of million new fuel cell cars, tens of millions new hydrogen fuel stations, etc. I have no idea what you mean by 100-200 watts/m^2 yield. If you read the web site, you'll see the yield is over 100x other common biofuel feedstocks, and the total acreage easily fits within available real estate.

Simple math. The total energy going to each square meter is limited to the energy from the sun. This is a theoretical max of 1300 watts per square meter, and then we factor in the eff of the system. Simply put, it can't replace oil. Especially if we want to eat.

No -- the problem varies based on implementation time for the chosen technology. For hydrogen/fuel cells, every car, every engine in every car, every tanker truck, every pipeline, every service station -- EVERYTHING must change. That takes decades, even given huge economic support. Others like biofuels use the existing distribution and vehicle infrastructure, which means they can be implemented much faster and cheaper.

I can't stress strongly enough -- the issue isn't whether an individual FEG or solar panel or fuel cell car or biofuel car will work. Whatever technology is chosen must be economically scaleable to titanic industrial levels to have meaningful impact. Those are often two different things.

However, if we can't find a complete solution, we're screwed, and bio-fuels can't do it. When do you propose that we begin on a real solution?

And we don't have clean coal technology yet, which is a huge problem.

The point is not whether or not FEGs should be used to replace everything, the question is, should we start building them given the proper design. Do they make sense? And so far I think they do. I also think when we talk about 1,000,000 generators or so, its simply a problem of recognizing the scale of what would be replaced. One generator every 2000 sq miles is not so hard to imagine as compared to the entire energy infrastructure.

 

[Ivan Seeking]

Correction, in order to replace oil with bio-fuel, I come up with something like 10¹⁰ sq meters if we assume 200 watts per sq meter. So that's not nearly as bad as I was thinking. 200 watts is probably way too generous, but even at 50 watts we are talking about something plausible, it seems.

We still need to look at the total energy of the process though. We haven't considered processing which I know requires harvesting, energy for separation and extraction, heat energy, and methanol. And we don't really know how efficient the system is for solar. It could easily be 1%, or worse. I was actually using the best case for solar cells as a number.

 

[Ivan Seeking]

Again, I am a bio-fuel fan, but my understanding is that serious issues still exist.

First of all, the author assumes that we could convert to B100 [100% biodiesel as opposed to a mix with petro-diesel]. My understanding is that in no way can most vehicles do this. In fact around here they recommend B2 - 2% Bio to 98% petro. The stuff is untenable at low temperatures and many standard engines have had problems with injector systems, filters, seals, etc. The advocates say that most of these problems are resolved but in no way have I found a consensus on this point.

When I started checking into this, due to all of the problems experienced, no diesel engine manufacturer would warranty an engine for use with bio-diesel. And of course all ignition vehicles would have to be replaced with diesel engines, and, I don't think this can be used for aviation fuel, which is never mentioned.

Creating new farmland is energy intensive. And we already are seeing issues with water shortages in places like california, Nevada, etc. The solution to clean water shortages is desalination, which requires energy. So water supplies alone could be an issue - and irrigation requires energy. This is what seemed to kill biodiesel crops in many areas, but your link offers a different twist.

NREL's research focused on the development of algae farms in desert regions, using shallow saltwater pools for growing the algae. Using saltwater eliminates the need for desalination, but could lead to problems as far as salt build-up in bonds. Building the ponds in deserts also leads to problems of high evaporation rates. There are solutions to these problems, but for the purpose of this paper, we will focus instead on the potential such ponds can promise, ignoring for the moment the methods of addressing the solvable challenges remaining when the Aquatic Species Program at NREL ended.

So they could escape some concerns by using salt water algae. That is good!

I will say this, I know where I would have rather put our $300,000,000,000, besides Iraq.

III. Cost

In "The Controlled Eutrophication process: Using Microalgae for CO2 Utilization and Agircultural Fertilizer Recycling"3, the authors estimated a cost per hectare of $40,000 for algal ponds. In their model, the algal ponds would be built around the Salton Sea (in the Sonora desert) feeding off of the agircultural waste streams that normally pollute the Salton Sea with over 10,000 tons of nitrogen and phosphate fertilizers each year. The estimate is based on fairly large ponds, 8 hectares in size each. To be conservative (since their estimate is fairly optimistic), we'll arbitrarily increase the cost per hectare by 100% as a margin of safety. That brings the cost per hectare to $80,000. Ponds equivalent to their design could be built around the country, using wastewater streams (human, animal, and agricultural) as feed sources. We found that at NREL's yield rates, 15,000 square miles (3.85 million hectares) of algae ponds would be needed to replace all petroleum transportation fuels with biodiesel. At the cost of $80,000 per hectare, that would work out to roughly $308 billion to build the farms.

The operating costs (including power consumption, labor, chemicals, and fixed capital costs (taxes, maintenance, insurance, depreciation, and return on investment) worked out to $12,000 per hectare. That would equate to $46.2 billion per year for all the algae farms, to yield all the oil feedstock necessary for the entire country. Compare that to the $100-150 billion the US spends each year just on purchasing crude oil from foreign countries, with all of that money leaving the US economy.

So according to this, for about the price of the Iraq war we could in principle end our dependence on petroleum altogether.

The biggest problem that I see here is that this is the usual problem; it's not ready to go. There is always the qualifier, "more research is needed". So at least it sounds like no one has actually farmed salt-water algae and used it for the practical production of bio-diesel.

The Office of Fuels Development, a division of the Department of Energy, funded a program from 1978 through 1996 under the National Renewable Energy Laboratory known as the "Aquatic Species Program". The focus of this program was to investigate high-oil algaes that could be grown specifically for the purpose of wide scale biodiesel production1. The research began as a project looking into using quick-growing algae to sequester carbon in CO2 emissions from coal power plants. Noticing that some algae have very high oil content, the project shifted its focus to growing algae for another purpose - producing biodiesel. Some species of algae are ideally suited to biodiesel production due to their high oil content (some well over 50% oil), and extremely fast growth rates. From the results of the Aquatic Species Program2, algae farms would let us supply enough biodiesel to completely replace petroleum as a transportation fuel in the US (as well as its other main use - home heating oil) - but we first have to solve a few of the problems they encountered along the way.