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Frictionless Windmills from China?
Jeremy Faludi, 23 Jul 06

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There's been a big splash about newly-invented maglev wind turbines in Worldwatch's blog and Treehugger (for those that read Chinese, the original article was in Xinhua News). No, they won't be levitating off the ground, and no, they won't be frictionless, but they may be significantly more efficient than existing windmills. Here's the scoop, with some technical introduction and details you won't find in the articles others have written about it.

The magnetic levitation that they use is between the rotating shaft and the fixed base of the machine, basically taking the place of ball bearings. Such magnetic bearings have been used for decades in smaller turbines and pumps by Ebara, Leybold, Seiko-Seiki, and others. (SKF has a nice FAQ on them.) However, they generally can't handle being bumped around much (the magnetic force isn't that strong), and they generally require actively controlled electromagnets (to keep the levitating magnets from crashing--play with some magnets for a minute or two and you'll see why). Making magnetic bearings beefy enough to handle the loads a wind turbine would put on them is hard, and would use prohibitive amounts of power just keeping the electromagnets running strongly enough. However, the Worldwatch article says the new Chinese device (invented by Guangzhou Energy Research Institute and Guangzhou Zhongke Hengyuan Energy Science & Technology Co.) uses "full-permanent" magnets, meaning there are no electromagnets, only cleverly placed permanent ones, so it should use no power. It sounds like they will be used on small turbines (perfect for home use), which would be similar in scale to the pumps and industrial turbines currently using magnetic bearings. But who knows, in a few years it might be possible to scale them up.

Unfortunately there's not a shred of additional technical information in the article, nor is there any to be found elsewhere online (if you have any, please leave a comment!), so we can only speculate what their solution was. A little research made me conclude (and this is also suggested by a couple highly knowledgeable Treehugger readers who left comments) that they're probably using Halbach arrays in a system like the Inductrack invented at Lawrence Livermore Labs several years ago. Any permanent magnet system would doubtless need lots of Neodymium ("rare earth") magnets, which may have questionable sustainability when mined in large amounts, but as it happens China is rich in that element--in fact, energy.buzz points out that China owns 90% of the world's market of rare earth magnets.

Whatever the specifics, magnetic bearings would indeed be a benefit, because they are well known to be much lower friction than physical bearings. Xinhua News / Worldwatch claims:


The Maglev generator is expected to boost wind energy generating capacity by as much as 20 percent over traditional wind turbines. This would effectively cut the operational expenses of wind farms by up to half, keeping the overall cost of wind power under 0.4 yuan ($US 5 cents), according to Guokun Li, the chief scientific developer of the new technology. Further, the Maglev is able to utilize winds with starting speeds as low as 1.5 meters per second (m/s), and cut-in speeds of 3 m/s...

I hope this is true, but it sounds optimistic. The inefficiency of a normal windmill's drive train (which includes the gears, shafts, and bearings, everything that moves except the motor and the turbine blades) is not so terribly big at moderate and high wind speeds. According to a paper by California Wind Energy Collaborative at UC Davis, the average wind turbine's drive train is 87-89% efficient from peak wind speeds down to less than half peak wind speed. However, below roughly a third of peak wind speed, things go rapidly downhill, and by about a quarter of peak wind speed, efficiencies are wallowing sadly in the 30-40% range. The Dutch windmill manufacturer Harakosan advertises a wind turbine that has 93 - 94% drive train efficiency all the way from peak wind speed down to a quarter of peak speed.

Granted, a study by NREL found the main losses in a wind turbine's drive train is lubrication oil churning, particularly at low speed. Using magnetic bearings (if they work at low speeds) would eliminate the need for such lubrication, and so would remove the drive train's biggest inefficiency. This is where it starts to matter what the specifics of the invention are. If the bearings do use Halback arrays, they will still not work at very low speeds--the arrays require a bit of motion in order to start levitating, and until it gets up to speed the rotor would sit on ordinary physical bearings. (However, it might be possible to optimize them for low-speed operation since they would no longer be used at high speeds.)

NREL's study also said that motor efficiency outweighed drive train efficiency, so fancy maglev bearings won't do you any good if you don't also have the best motor you can buy.

In any case, this is an exciting development in wind turbine technology, and if it makes even half as much difference as Guokun Li says it will to the economics of wind farms, it will be a huge boon to the industry, and to clean power.

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Comments

Some windmills work best at high speeds, so there's perhaps a market niche there.

I still see a problem with "storing wind energy", and that problem only gets worse if we place highly efficient windmills in high wind places. How do we do that? Several methods have been suggested and perhaps there's a good review somewhere?

I have been able to think of a few, without the devilish details: compressing air (there was a link to some natural caves that could be used for that purpose), moving water up-hill (I don't know if sea water would be usable), and even doing "timeless" work: work that can be done at any time of the day, so you store the products of that work. Maybe desalinating water and using that water as storage (currency?).

I even thought about something that I don't know if it's feasable or not: using windmills to pull cold water from deep oceans. Such "deep water" is very cold, so it can be used for air conditioning (think global warming) and also for condensing water vapour from huge solar stills. Any critique or developement of this idea would be appreciated!


Posted by: Lucas Gonzalez on 24 Jul 06

"using windmills to pull cold water from deep oceans."

The temperature differential between deep water and the surrounding air above is large enough to use it to power stirling motors. I once saw a documentation about an engineer who is working on that topic. The exiting cold (a little warmer than before) water can be used for cooling purposes just as you suggested.
I whish I'd remember the name of that guy or any other hook to fish the information out of the interweb.

-jsl


Posted by: jsilence on 24 Jul 06

There's the Toronto Deep Lake Water Cooling project that is similar:
http://www.toronto.ca/environment/initiatives/cooling.htm


Posted by: Daniel Haran on 24 Jul 06

As for storing wind energy, two further options are chemical storage in hydrogen (by electrolysis of water) and thermal storage in liquid nitrogen (by cooling ambient air down to 77 K). My personal favorites are water pumping and compressed air because they are simple, low-tech solutions.

When it comes to storing wind energy, capacity and rate of conversion are paradoxically more important than conversion efficiency. The thing is, energy contained in wind grows with the third power of its speed (i.e. a 3-fold increase in wind speed means a 27-fold increase in power output). That means you really don't want to miss out on high-speed winds - so you need to quickly store a huge amount of energy. On a site where storms are frequent enough, a liquid nitrogen system with 50% conversion efficiency but a high conversion rate may get you more energy than a 90%-efficient battery pack that blows a fuse before the wind ever gets a chance to kick in.


Posted by: jh on 24 Jul 06

Using the wind power to pump cold water up from the ocean floor is an interesting idea. Because the the mechanical power can be used directly, (possibly without a transmission with an appropriate pump) the efficiency is bound to be very good. Having the mechanism be simple could also make the costs quite low.
Google OTEC to see more about the ocean temperature difference powered stirling engines.


Posted by: macrumpton on 24 Jul 06

Great piece, Jer. Thanks for once again illuminating all that technical info.


Posted by: Dawn Danby on 24 Jul 06

this is so great i have being waiting for this for a longtime. well done team keep the good work up.


Posted by: gideon on 24 Jul 06

Another obvious rout to increase efficiency is to decrease the weight of the blades. What are they currently made out of? I saw a program that showed smaller ones being built out of lightweight woods, but have not seen one about the larger ones which look like some sort of composite. What would the efficiency gains be if we started adding in Carbon Composites into the equation?


Posted by: Chris on 24 Jul 06

Here's a Scientific American article that proposes a national power grid of superconducting cables cooled by liquid hydrogen. The cables carry electricity and the hydrogen both stores energy and transports it. I'm skeptical about wrapping critical infrastructure in highly flammable liquid, but the concept is interesting:

By transporting the [electricity and hydrogen] together, the grid would serve both as a pipeline and as an energy store. For example, every 70-kilometer section of Super-Cable containing 40-centimeter-diameter pipes filled with liquid hydrogen would store 32 gigawatt-hours of energy. That is equivalent to the capacity of the Raccoon Mountain reservoir, the largest pumped hydroelectric facility in the U.S.

By transforming electricity into a less ephemeral commodity similar to oil or natural gas, the new grid could allow electricity markets to tolerate rapid swings in demand more reliably than they do today. Super-Grid links crossing several time zones and weather boundaries would allow power plants to tap excess nighttime capacity to meet the peak electricity needs of distant cities. By smoothing out fluctuations in demand, the low-loss grid could help reduce the need for new generation construction.

The Super-Grid could go a long way, too, toward removing one of the fundamental limitations to the large-scale use of inconstant energy from wind, tides, waves and sunlight. Renewable power plants could pump hydrogen onto the grid, rather than selling electricity. Alternatively, baseline generators could monitor the rise and fall in electrical output from these plants and might be able to use electrolysis to shift their electricity/hydricity blend to compensate.

... No major scientific advances are needed to begin building the SuperGrid, and the electric utility industry has already shown its interest in the concept by funding a SuperGrid project at EPRI which will explore the numerous engineering challenges that integrating Super-Cables into the existing power grid will pose. The largest of these is what to do if a Super-Cable fails.

... Safely transporting large amounts of hydrogen within the Super-Cable poses another challenge. ...Probably the best way to secure Super-Cables is to run them through tunnels deep underground. Burial could significantly reduce public and political opposition to the construction of new lines.

I'm not in favor of the massive expansion of nuclear the authors propose, either. If superconducting cables make long-distance transmission feasible, how about putting microwave receiving facilities in distant, uninhabited desert areas? Then beam microwave power down from orbiting solar PV satellites. Is that any less feasible or costly than doubling the number of U.S. nuclear plants?


Posted by: Laurence Aurbach on 25 Jul 06

As to storing energy from the windmill that isn't immediatly needed... why not just make a weighted lift? Mere rock could be pilled on the lift to make it heavier, or a denser material could be used on the lift to make it more space effecient. Anyway, this seems like a very low tech easy solution to me.


Posted by: tommy b. on 28 Jul 06

Funny, I'd been thinking the same thing tommy. Is it an efficient way to just transfer the mechanical energy from the windmill to lifting a series of huge heavy weights like a weight powered cuckoo clock that could unwind themselves to generate power during needed peak periods? On that note, why couldn't such a system be implemented in the home to store mechanical energy, from work out machines, treadmills/bikes, solar arrays or windmills which would then generate power while they unwind? Also, I'm wondering if there's a way to harness the heat from decomposition to generate energy in some way. I'm picturing a waste collection tank which with the proper chemicals added can create significant heat from methane, ammonia, decomposition, etc. which I'm envisioning somehow being reclaimed to generate power, although I suspect heating and water heating would obviously be a more ideal transference of the heat energy. Thoughts?


Posted by: Big Daddy on 4 Aug 06



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