|
Date | Comment |
George Fleming 10.12.04 |
Glad to see such a favorable article on wind power. Fine arguments and documentation. A Korean company called Wintec built some wind turbines with two rotors, a larger one upstream and a smaller one downstream. Prototypes were about 0.5 MW as I recall. However, I am not sure this company is still in business. I wasn't able to access their website today, www.wintec4nature.com, but printed several pages from it earlier this year. |
Steve Sturgill 10.13.04 |
Murray, I need some help locating the UW EROEI study you mentioned. I very much want to believe that wind energy's infrastructural EROEI is high, but I need to see how the conclusion was reached. Please post a link or some additional information so that I can find the study. Thanks. |
Tom Gray 10.13.04 |
Steve, I think http://fti.neep.wisc.edu/FTI/pdf/fdm1063.pdf is probably what you are looking for. Tom Gray American Wind Energy Association |
Len Gould 10.13.04 |
Murray: A commendable article, and I must say somewhat reluctantly that I essentially agree with all your points except the feasibility of young Dayna Walker's proposal for multiple turbines. If you notice, she's not proposing counter-rotating turbines, but co-rotating turbines. It has long been well known, as even her own discussion points out, that increasing the blade coverage percent can increase power out, but it also severely restricts the upper range of wind speed which can be used before needing to shut down, witness the old prairie water pumps. Much science has already gone into sorting out the optimal figures for this and I don't see that her efforts, commendable as they are for her age, contribute anything new. However, if you suggested multiple co-rotating turbines where individual blade groups could be feathered and halted as the wind speed increased, you might have something, though there would definitely be turbulence problems as the remaining working blades passed the halted blades. Probably not worth it. I'd always thought that wind generation was limited in reliability to a maximum of about 30% with many real-life installations not doing better than half that, but I've just come across a new contract just issued by Hydro Quebec for new wind farms (GE) on Canada's east coast. They've signed a solid contract with two developers for a total of 990 mW of wind turbines which will, by contract terms, generate 3,200 twhr per year of energy. That means they're going to generate at 36.87% on an annual basis including breakdowns, maintenance, and etc. It occurs to me that these guys have taken advantage of one of the complexities of wind power, which is that "it doesn't matter for reliability how fast the average wind speed is, what matters is how steady it is." !! Neat. If the wind speed is low but continuous, they simply need to install larger rotors, which costs very little extra. Find a location with steady, even, continuous wind speeds and you can do much better than even the places with the highest peak speeds and total power. The suppliers to Hydro Quebec state they can profitably sell wind power to the utility for Cdn$0.065 / kwhr with NO SUBSIDIES using GE turbines at an average cost of Cdn$1,800 / kw. Ov course hydro Quebec has the huge advantage of their enormous hydro generation facilities which can happily store the water whenever the wind is blowing, while releasing it for generation whenever needed. Looks like they're making an effort to become North America's greenpower supplier. |
Len Gould 10.13.04 |
Steve: Try also the ExternE study at http://externe.jrc.es/infosys.html or the WNA at http://www.greatchange.org/bb-thermochemical-WNA_energy_analysis_of_power_systems.html . Eg at the WNA site the differences between diffusion fuel processing and centrifuge processing are laid out for you. (The fact that the Wisconsin study cited by Tom used only the obsolete diffusion process figures makes me suspicious of their hidden agenda) Overall, nuclear's input/output ratio is closer to double the number stated in the Wisconsin so-called "study". |
Peter Bradford 10.15.04 |
An interesting
and thorough article. Thank you.
However, your discussion of unsightliness did not mention a controversy that goes with the newer and larger towers, namely that they must be so tall that they are required to be topped by bright lights (in the U.S. at least) to warn off airplanes. This makes them especially controversial in mountainous areas with scenic ridgelines and tranquil night skies. Wind turbine sighting prospects in such areas would be much improved if the wind industry would work with the Federal Aviation Administration to develop alternative warning systems. After all, the ridges are often in clouds anyway, so the lights can't be the sole warning system. A warning system that worked by sound or that turned on its lights only when a plane was in the area would reduce the intensity of sighting controversies substantially. |
George Fleming 10.17.04 |
Mr. Gould's comment about blade coverage sent me looking for more information. The Wind Turbine Co. (www.windturbinecompany.com/technology/index.html), which has been developing two-blade downwind turbines, says: "It is well known that 2-blade turbines capture approximately 97% as much energy as 3-blade machines with the same rotor diameter." Several single-blade turbines have been built and tested, according to the book "Wind Power Plants" (Gasch and Twele: Solarpraxis AG, 2002). One of these was called MONOPTEROS (640 kW), and it looks something like a monster. These single-blade turbines worked, but the book does not say why they did not succeed in the market. I would like to see further comments on this subject by Mr. Gould and others. |
Murray Duffin 10.17.04 |
Len, - Clearly I am not an expert on wind turbines, but I have searched for info. on multi rotor experience and find a paucity of information. What struck me about Dayna Walkers results was the sheer magnitude of the improvement. Also my experience tells me that experts often end up unable to think outside the box. It may be that Dayna's work represents nothing new and her results are just an artifact of poor or limited experimental design. I hope not. Intuitively, it seems to me that her approach can lower the cut-in wind speed, increase the low wind speed output, and that feathering of the downwind rotor could raise the cut-out wind speed. The result could be to increase the percent of time that nominal power was reached quite considerably, thus further mitigating the intermittancy problem. There was a brief note in the Scientific American a couple of months ago about an experimenter who wondered why some whales have bumps on the leading edge of their flippers. He wind tunnel tested wing sections with and without bumps and found that the bumps increased lift, reduced drag, and lowered stall speed. This seems like another outside the box idea for wind turbine design. Peter, there are always peripheral issues to address, like tower lights. Most wind farms will not be located in scenic mountain areas, and if the choice is energy scarcity or lights we will take lights, or as you suggest find other solutions. Most of the negatives that have been raised about wind are much more serious and it was those issues that I wanted to address. Murray |
Len Gould 10.17.04 |
Murray: I agree,
many experts often lock themselves into boxes
with what they know and it often takes a non-expert
to break out. Check Doug Selsam's multi-rotor
designs at http://www.speakerfactory.net/wind.htm
. This concept is particularly an interesting
out-of-box development. The system eliminates
costly controls by simply installing the long
shaft on a spring-loaded tilt platform. In low
wind each rotor sees full wind. At higher wind
speeds wind pressure pushes the rearward rotors
down until they are shadowed by the ones in front.
I've been following this for a few years and he's
making excellent progress in development. Should
be cheap to mass produce.
A good discussion of blade fill percentage and count is at the Danish Wind Industry Org. site at http://www.windpower.org/en/tour/design/concepts.htm " Two- and one-bladed machines require a more complex design with a hinged (teetering hub) rotor as shown in the picture, i.e. the rotor has to be able to tilt in order to avoid too heavy shocks to the turbine when a rotor blades passes the tower. The rotor is therefore fitted onto a shaft which is perpendicular to the main shaft, and which rotates along with the main shaft" also at http://www.windpower.org/en/tour/design/optim.htm "The water pumping windmills to the left look very different from modern, large wind turbines. But they are quite sensibly designed for the purpose they serve: The very solid rotor with many blades means that they will be running even at very low wind speeds, and thus pumping a fair amount of water all year round. Clearly, they will be very inefficient at high wind speeds, and they will have to shut themselves down, and yaw out of the wind in order to avoid damage to the turbine, due to the very solid rotor. " |
Len Gould 10.17.04 |
FurtherWind turbines are built to catch the wind's kinetic (motion) energy. You may therefore wonder why modern wind turbines are not built with a lot of rotor blades, like the old "American" windmills you have seen in the Western movies. Turbines with many blades or very wide blades, i.e. turbines with a very solid rotor, however, will be subject to very large forces, when the wind blows at a hurricane speed. (Remember, that the energy content of the wind varies with the third power (the cube) of the wind speed). Wind turbine manufacturers have to certify that their turbines are built, so that they can withstand extreme winds which occur, say, during 10 minutes once every 50 years. To limit the influence of the extreme winds turbine manufacturers therefore generally prefer to build turbines with a few, long, narrow blades. see http://www.windpower.org/en/tour/design/index.htm One, two or three blades can capture as much power from a given wind as much more solid rotors simply by turning faster. Also, you can't get any energy from a wind if you slow it down too much. You wind up with static air behind your turbine and the wind just going around the whole thing. I've seen the math for this concept in a few places but can't find a reference right now. |
Scott White 10.18.04 |
In response to
Len Gould's comments about my study at the University
of Wisconsin: there was no hidden agenda. When
analyzing uranium enrichment, the diffusion process
was used only because it was the sole enrichment
process used in the U.S. at the time. While enrichment
using gas centrifuges or lasers are considerably
more energy efficient than gaseous diffusion,
neither were being used in as of 1998, when the
study was completed. At that time there were two
gaseous diffusion enrichment plants in operation
- one at Portsmouth, Ohio, the other at Paducah,
Kentucky. As I understand it, only the Paducah
plant is still operating. When enrichment plants
using the gas centrifuge or lasers become built
in the U.S., then this study should be updated.
As for the study you reference in the same response, I have yet to study it to see why it's results differ from my own. Also, relating to wind energy, the study results of wind are currently being reexamined and I plan to present the updated results at the 2005 American Wind Energy Association conference in Denver next May. At the time the original study was published, 2 of the 3 windfarms analyzed did not have a full years' worth of production data to figure into the analysis, which meant the production data was based on the operators projections. Since there are now at least 6 years of generation data to base these projections, the results have changed somewhat. For more information on the wind results, see the open-file report for the wind data at: http://fti.neep.wisc.edu/FTI/pdf/fdm1092.pdf, which has more details then the refereed article Tom Gray pointed out. |
Len Gould 10.18.04 |
Scott: Thanks
for the new data. I didn't realize that the centrifuge
system wasn't yet being use in the US. Perhaps
to present a fair picture of the potential of
nuclear power it might have been prudent to reference
other countries systems
"Some reactors, for example the Canadian-designed Candu and the British Magnox reactors, use natural uranium as their fuel. " "A number of enrichment processes have been demonstrated in the laboratory but only two, the gaseous diffusion process and the centrifuge process, are operating on a commercial scale." Surely this last bit of data wasn't unavailable to you only 5 years ago. "The gaseous diffusion process consumes about 2500 kWh (9000 MJ) per SWU, while modern gas centrifuge plants require only about 50 kWh (180 MJ) per SWU." |
Graham Cowan 10.18.04 |
Actually I see
White
and Kulcinski's paper says the basis
of its uranium enrichment energy estimates was
in fact gas centrifuge enrichment. In its table
5 it shows, for fuel preparation, 1203 thermal
TJ per electrical gigawatt-year. Supposing 33
percent heat-to-electricity conversion that's
1.26 percent of the yield of the fuel produced,
which is indeed less than the roughly two percent
that gaseous diffusion nowadays takes.
It's not as much less as I would have expected given the 50-fold reduction, mentioned here, in enrichment's electricity needs when centrifuges replace gaseous diffusion, but there are other parts to the fuel-preparation process besides enrichment, I suppose.
Windpower is favored in that paper, as it acknowledges, by its ignoring of the energy cost of storage, or as in current systems, of calling in other kinds of power plant that can pick up when the wind weakens.
If that would knock wind's lifetime EROEI from 27 down to 20, still beating the figure there computed for nuclear, that, in my opinion, would be just another illustration of the unimportance of EROEI (as long as it's above ~2).
This emerged in another discussion where solar-concentrating heat engines looked as if what I suppose is the dominant EI in making them, the mirrors, turned out to take only a few weeks' worth of their output to make. Labor was the scarce good they really wasted. Or, as a certain kind of advocate would say, job creation was one of their major benefits.
--- former hydrogen fan Graham Cowan |
Scott White 10.18.04 |
Graham is correct in that our study did use gas centrifuge and not gaseous diffusion - I should have actually gone back and looked at it before responding earlier. My apologies. And to Len, yes we did know about the gas centrifuge and did opt to use that data instead of diffusion. I'm still not sure why the discrepancy is so large, but will not be able to revisit this until later in the week due to some other business. And as Graham did note, we did clearly state that the wind energy results benefit from not considering energy storage. That is for another study. To compare apples to apples (and baseload to baseload) energy storage should be factored in when comparing intermittent technologies to baseload ones. However, in small enough doses, there is enough load-following capacity to both allow intermittent technologies (such as wind) onto the grid and to justify studying them as stand alone as we did. Denholm and Kulcinski did a study on energy storage in 2003. The results here showed that the EPR of wind dropped from 23 to 17 using pumped hydro storage and to 10 with compressed air storage. This report can be viewed at: http://www.ecw.org/prod/223-1.pdf |
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