From the Carnegie Institution , some lofty ideas. Would you imagine a steady energy supply coming from high altitude kites?
Enough wind to power global energy demand
Washington, D.C.— There is enough energy available in winds to meet all of the world’s demand. Atmospheric turbines that convert steadier and faster high-altitude winds into energy could generate even more power than ground- and ocean-based units. New research from Carnegie’s Ken Caldeira examines the limits of the amount of power that could be harvested from winds, as well as the effects high-altitude wind power could have on the climate as a whole. Their work is published September 9 by Nature Climate Change.
Led by Kate Marvel of Lawrence Livermore National Laboratory, who began this research at Carnegie, the team used models to quantify the amount of power that could be generated from both surface and atmospheric winds. Surface winds were defined as those that can be accessed by turbines supported by towers on land or rising out of the sea. High-altitude winds were defined as those that can be accessed by technology merging turbines and kites. The study looked only at the geophysical limitations of these techniques, not technical or economic factors.
Turbines create drag, or resistance, which removes momentum from the winds and tends to slow them. As the number of wind turbines increase, the amount of energy that is extracted increases. But at some point, the winds would be slowed so much that adding more turbines will not generate more electricity. This study focused on finding the point at which energy extraction is highest.
Using models, the team was able to determine that more than 400 terrawatts of power could be extracted from surface winds and more than 1,800 terrawatts could be generated by winds extracted throughout the atmosphere.
Today, civilization uses about 18 TW of power. Near-surface winds could provide more than 20 times today’s global power demand and wind turbines on kites could potentially capture 100 times the current global power demand.
At maximum levels of power extraction, there would be substantial climate effects to wind harvesting. But the study found that the climate effects of extracting wind energy at the level of current global demand would be small, as long as the turbines were spread out and not clustered in just a few regions. At the level of global energy demand, wind turbines might affect surface temperatures by about 0.1 degree Celsius and affect precipitation by about 1%. Overall, the environmental impacts would not be substantial.
“Looking at the big picture, it is more likely that economic, technological or political factors will determine the growth of wind power around the world, rather than geophysical limitations,” Caldeira said.
thallstd says:
This somewhat more “down to earth” approach seems to be promising.
http://www.makanipower.com/why-airborne-wind/
I never held out much hope for wind power before seeing this. But to this somewhat non-technical layman this looks like it holds promise. Or is it similarly plagued by needing too many in any one area to be practical?
I would think building one should be difficult enough for anyone. Remember that what is suggested is essentially to build an aircraft that is capable of flying essentially for ever, in storm, rain, hail and icing, guided by an autopilot that apparently never fails (the first one ever, by the way). This autopilot controls the aircraft and flies it in circles which means it must have ailerons and rudders, operated by (presumably) electrical actuators, which never wear or fail (also an all time first). Also this autopilot must have control laws that can cope with a wide variety of wind speeds, sudden gusts and changes in wind speed. It would realistically also have to be capable of bringing the aircraft in to a controlled dead-stick landing at a pre-determined spot either tethered or free-flying irrespective of weather when something goes wrong (which it will, most likely in bad weather).
But perhaps it is never calm where it is flying and the aircraft never needs any maintenance, and nothing ever goes wrong, since it has no visible landing gear (or it might have retractable gear, greatly adding to weight and complexity).
Having 40 years experience of aircraft and aircraft maintenance my opinion is that this is indeed a “down to earth” idea in the most literal sense.
tty… if you watch the video of their test flight (http://www.makanipower.com/category/flights/) it seems that a lot of what you indicate is needed either isn’t (maybe because it’s tethered and not free-flying?) or has already been accomplished (not to say it doesn’t need improvement) or the entire video is a fake. As for landing, once in operation it is housed on a small tower and never touches the ground so traditional landing gear and auto-logic is not needed. Not to say that there aren’t any number of things that can go wrong and long term maintenance is certainly to be factored in. But at some point we need to develop additional sources of energy and these folks are, as someone above pointed out, at least attempting it with private vs public funds. I wish them luck.
Paragliding stocks up this morning…
Obviously these things are sufficiently dangerous they will cross their own power lines which requires they have buried power lines anywhere in a circle defined by the length of the tether. Here is a logical feasibility test: Can these things be made to work unattended at sea? What is the recovery time for redeployment after a crash in a rain-soaked field? What is the compensation plan for when these systems crash across freeways or highways or railways, blocking traffic? What is the cost of unraveling the shrouds? What is a grant worth to study this trash?
Lot’s of kites blocking the free flow of wind could alter the climate in some modelably catastrophic way.
There, I’ve CAGW’d the proposal.
Will that not speed up the earth’s rotation? Just think, we could get twice as many days in a year.
@Rob L
I’m not an engineer (neither BE Mech nor ME Elec), so I still wait for you to tell me what the tether will weigh. Specify any cross sectional diameter, any material, any conductivity, and any dielectric constant for the insulation that you like (remember we’ll be talking around 25-30 miles long for a kite flying at 18 miles altitude. I’ll wait…
Won’t this daft idea speed up the earth’s rotation? Just think – twice as many days in a year…
tether weight is the limiting factor. this is a well known problem with anchoring boats in deep water. For example, a steel cable will break under its own weight if it exceeds 10 miles in length,
Rob L says:
September 10, 2012 at 6:19 am
While (as a mechanical engineer also) I don’t disagree with any of your technical points, what happens when a thunderstorm comes along? And what happens when one of these kites breaks loose and crashes into someone’s home or business? Seems like a lot of trouble to harvest energy which can be more easily be obtained and distributed (on a large scale) from other sources (e.g. coal, nuclear, and natural gas).
This is like debating the scientific accuracy of something from The Onion.
Being a free market capitalist, I encourage those who believe in this to invest their own money in R&D. But if you expect the government to fund this with taxpayer dollars….well, let’s just say “them’s fighin’ words.”
Fun fact: In gliding sports, the life-time of a glider is essentially directly related to the fabric’s sun exposure time. That’s why you don’t wanna mess around for hours when not flying — you pack it up immediately. And depending on how much hours you did, you might want to sell it off on Ebay after 2 seasons, because tehy lose air-tightness… With all day sun, every day up there, you can replace those kites every 3 months, hahaha (read: they not gonna be good for 3/5/10 years)
Having 40 years experience of aircraft and aircraft maintenance my opinion is that this is indeed a “down to earth” idea in the most literal sense.
How about looking at what Makani propose before you start criticising, I can assure you they are extremely talented engineers (having met a few of them).
They are rigid, durable, carbon fibre wings flying in loops, so very little control input required, and they actually achieve all the necessary control by simply modulating the drag from the multiple turbines distributed above and below the wing across its span.
With those same multiple turbines working as propellers have already demonstrated VTOL lift off and recovery back to their base station, as well as looping flight all under autopilot control.
They have power available to deal with loss of wind, they just stop generating and start using power to the props to stay aloft during a lull and can hover as they are pulled back to base if wind drops away too much to produce power.
They can slow the looping or even stop it if the wind gets too strong (but the kite flies at 70-100kt so winds are realistically never too strong).
They can ultimately have redundancy in the turbines to allow landing after one fails – like multicopters, There is also potential for autorotation with pitch control or even carrying some battery backup at ground and/or on the kite.
They can be landed when lightening threatens.
Their proposed 5MW wing can produce several $million in electricity per year, is about the same size as a single blade on a 5MW wind turbine, weighs probably 3-5 tonnes, and could probably be replaced every year and still be profitable (though I doubt it would need to be). $500/hour in electricity can pay for a lot of maintenance.
A.k.a turbulence
Why not? There are both economical and energy (great) issues to get this stuff into the air.
Also, there is an extra cost and loss of energy involved every time needed bringing them down before lightning/thunder storms and afterwards, when they are going back up again. (Reminds me of all the erroneous wind turbine calculations …) This also applies when the wind is not able to keep the kite in the air.
Rob L. and anyone else suggesting this idea. The problem is not technical. It is weather. You stick kites 5-10 miles up, by the thousands, you will alter weather patterns. You might only shift things a little where this power station is located, but thousand miles down wind, there is no modeling that can tell what will happen. If you disrupt weather for years, you create climate changes.
If you don’t agree, what does mountain ranges do? Look at the weather patterns down wind from these, and you will have the basics of what these kites will do.
Here is another example, take a wind tunnel, introduce a small obstacle, and watch the change through out the whole tunnel. Very little will do a whole lot.
Here on WUWT there were pictures of the “contrails” behind wind turbines. Not a big issue at ground level. Bad idea in the sky. I bet due to the wind slow down caused by a few thousand of these, you will trigger increased rainfail right behind/infront these farms. As the wind slows down, clouds pile up, just like waves crashing to shore. Place this in the wrong place, and you will have a desert 500 miles down wind.
Worse, set these offshore and a whole continent will see reduced rainfall.
The disruptions will be massive.
Interesting idea, but first you need to do some homework in fluid mechanics …
Flow through tubes requires optimal conditions, if it should be useful:
* Length and cross section area is of great importance for this. Since wind speed is a variable in the context, length and cross section area must be adjusted accordingly … (Ooops! Try that one in a simple construction, as the wind is constantly changing in speed …)
* All existing objects that are inside the tube reduces efficiency by turbulence, including turbine units. There are better and more controllable medium available than air! (ie. water, see below …)
* All bends reduce the flow. Reducing this problem requires a rotating device which can follow the wind. If the pipe is large enough, motors for rotating are required because of the mass … (requires power … a contradiction!)
* Turbulence also occurs in straight tubes, unless the flow is at the right speed. Control via ports does not help in this case, as it increases the flow resistance (compare with a silencer, which require adaptation to ammunition performance to be effective, but in this particular case the “flow” is regarded as a constant.)
* The density (mass) of what is flowing through the tube matters! The lower the density (mass), the easier it is to reduce flow. This is why water is more suitable than air for the purpose …
Your quick thinking reminds me of the young guys who think they can be easily and in a relatively inexpensive way to get more power out of a car engine. This by replacing the exhaust system with a larger one. If not pure luck, wrong! The consequence is rather higher noise and increased engine wear (piston rings, gaskets and expensive things like exhaust valves and valve seats …) and probably a disapproval at the annual national controlled vehicle inspection (noise and/or difficulties of measuring emissions). On most vehicles, the end pipe must be located at the rear of the vehicle. This limits (prevent) the possibility to shorten the total length of the exhaust pipe, to adapt to the enlarged cross section of the exhaust pipe. (Changing stuff like this on newer cars sold within EU, is not legal according to the WVTA (Whole Vehicle Type Approval), without a direct (ie. written) approval from the manufacturer …)
The trouble with carbon fibre is it has a shelf life and whilst very strong in certain design parameters is ultimately not very durable, I think some serious material design technology evoloution is required before these kites can become an every day reality, quite apart from the effect large numbers of them will have on the climate. If CO2 in its very small concentrations can have such an effect on climate, according to ‘the experts’ of funded climate science; logically the same thinking can be applied to perturbations in the upper atmosphere wind streams.
I bet the contrails of a thousand of these would be a sight. Not only from the kite, but also from the wires. Think of “Von Karman cloud vortices ” off of islands. I bet there will be a few environmental lawsuites.
More kids playing with toys, funded by my tax dollars.
“Led by Kate Marvel of Lawrence Livermore National Laboratory, who began this research at Carnegie, the team used models to quantify the amount of power that could be generated from both surface and atmospheric winds.”
Maybe Kate is a Marvel comic heir, carrying forward the family tradition.
Hello, I’m a kite minder. My job is to run and relaunch the kite. Unless the tree eats it.
“The study looked only at the geophysical limitations of these techniques, not technical or economic factors.”
This is not a study. This is a paper napkin calculation shoved across a table down at Morey’s for the amusement of a few academics, one of whom will promptly set a beer glass down on it.
“Looking at the big picture, it is more likely that economic, technological or political factors will determine the growth of wind power around the world, rather than geophysical limitations,” Caldeira said.
Duh.
Studies indicate that there’s enough energy in the squirrels of the world to power California—if only we could figure out how to get them all into those little, spinning cages and hook up all the tiny, squirrelly generators to the grid.
One problem not yet discussed is icing. I can envision the kites getting loaded up with ice. People will be very unhappy to have hail stones the size of aircraft crashing around or on them.
Rob L says:
September 10, 2012 at 6:19 am
How do the de-icing/anti-icing systems work on these high flying kites?
Here is a funny calculation. found a claim “http://www.ecomagination.com/the-power-above” claim up to 10kW per sq meter in the jetstream. Lets say they harvest half. so 5kW per sq meter. 200sqM for a MegaWatt. 200,000sqM for a GW. 200,000,000sqM for a TW. 2800 Sq Kilometers for all energy we need, 14 TeraWatts. So, a WALL, approximately 3000 feet tall and slightly short of 2000 miles wide, in the sky, slowing down the wind by half….
Did I do that calculation right??
If I did, that would constitute a massive impact on our climate. That is a brand new 2000 mile long mountain range, just to prevent a lousy estimated 0.1 Celsius temperature impact by CO2.