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Earth Power Technology

Wind Farms Can Interfere With Doppler Radar 179

T Murphy writes "Wind farms can appear like storms or tornadoes on Doppler radar when placed too close to the radar. Tornado alley is a good area for wind farms, and good terrain for the turbines is also ideal for Doppler radar. With many new farms being constructed, the problem is growing. A false tornado warning was issued in Kansas by a computer, although canceled by a meteorologist aware of the problem — there are fears that false positives will grow. Worse would be a tornado ignored as a wind turbine. While meteorologists are trying to work with wind farm owners to shut off the turbines during bad weather, they have no control over the placement or operation of the turbines. Efforts are being made to improve detection technology to avoid further problems."
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Wind Farms Can Interfere With Doppler Radar

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  • by Sique ( 173459 ) on Sunday August 30, 2009 @03:26PM (#29253761) Homepage

    You turn the wings of the wind wheel so the resulting force is zero.

  • by WGFCrafty ( 1062506 ) on Sunday August 30, 2009 @03:27PM (#29253773)
    Two types of control:

    Stall Controlled Wind Turbines (Passive) stall controlled wind turbines have the rotor blades bolted onto the hub at a fixed angle. The geometry of the rotor blade profile, however has been aerodynamically designed to ensure that the moment the wind speed becomes too high, it creates turbulence on the side of the rotor blade which is not facing the wind as shown in the picture on the previous page. This stall prevents the lifting force of the rotor blade from acting on the rotor.

    Pitch Controlled Wind Turbines On a pitch controlled wind turbine the turbine's electronic controller checks the power output of the turbine several times per second. When the power output becomes too high, it sends an order to the blade pitch mechanism which immediately pitches (turns) the rotor blades slightly out of the wind. Conversely, the blades are turned back into the wind whenever the wind drops again.
    Taken from:
  • by negRo_slim ( 636783 ) <> on Sunday August 30, 2009 @03:30PM (#29253795) Homepage

    cheap free energy vs pretty pictures of wind on

    Well tornado warnings can, in fact, save lives. []

  • Not such a big deal. (Score:4, Informative)

    by benjamindees ( 441808 ) on Sunday August 30, 2009 @03:39PM (#29253857) Homepage

    Tornado warnings are extremely vague. Anyone who has spent significant time living in tornado alley can tell you they are routinely ignored. And the new technologies that attempt to pinpoint tornadoes exactly (TVS, VIPIR) aren't as accurate as they're made out to be. False positives are nothing new.

  • by Anonymous Coward on Sunday August 30, 2009 @03:49PM (#29253913)

    IAMFWDWR (I am a meteorologist familiar with Doppler weather radar) and it doesn't worry me at all. There are lots of objects that cause the same types of problems, including rotating radar antennas and buildings.

    When a weather radar system is set up the technicians will do a radar survey of the area and then flag areas for the computer (called an RPG, Radar Product Generator) to ignore. For a wind farm they'd look for an area in low scan levels with a high spectrum width and low to zero velocity and tell the RPG to ignore them. If these areas are too far away from the radar, they won't even be noticed by the radar (all scans are pointed slightly "upwards" so even with the lowest scan level something 200 feet tall would not be sensed unless it was within about 4.5 miles of the radar, give or take) unless you have a problem with subrefraction where the radar beam is bent downwards due to atmospheric effects. This would probably be the only time that the situation would cause a false positive and a meteorologist with any amount of common sense is going to investigate the area as it wouldn't be moving at all and would only appear in one or two scan levels.

    The automatic warnings generated by a NEXRAD system are helpful, but are nowhere near foolproof. A competent meteorologist will be able to investigate the areas and determine if a weather warning or advisory is warranted within only a few minutes. (generally less than 30 seconds with a proper setup) Detection technology is already in place and easily enacted. Article is ignorance at best, and scaremongering at worst.

  • Re:Simple fix? (Score:5, Informative)

    by whathappenedtomonday ( 581634 ) on Sunday August 30, 2009 @04:10PM (#29254043) Journal
    Also, AFAIK the turbines shut down at wind speeds >25 m/s / ~55mph
    Ah, found it here: [] Wind turbines start operating at wind speeds of 4 to 5 metres per second (around 10 miles an hour) and reach maximum power output at around 15 metres/second (around 33 miles per hour). At very high wind speeds, i.e. gale force winds, (25 metres/second, 50+ miles/hour) wind turbines shut down.
  • Re:Maps? (Score:5, Informative)

    by Ungrounded Lightning ( 62228 ) on Sunday August 30, 2009 @04:18PM (#29254101) Journal

    If only the wind turbines were on stationary towers, then they might be able to map them, and use such a map to inform their interpretation of the radar data.

    If only the tip voitices stayed at the blades, rather than trailing for miles downwind.

    If only "downwind" was always the same direction, rather than moving around when the wind changes - especially when it changes rapidly during a storm.

    If only the vortices were reliably visible to the radar, rather than sending a variable strength return depending on how many raindrops are getting blown around by each section of it at any given moment.

    = = = =

    More interestingly: The conditions that form tornadoes are weather-driven but the exact location they form, path they take, and indeed whether the finally DO form, are dependent on local things that disturb the airflow. Like mountains. And buildings. And forests. And freeways full of moving cars. And big windmills...

    Tornadoes have been documented to prefer to form up a short distance downwind of expressways. Perhaps the twisting air behind the mills of a wind farm will trigger the tornadoes in that area.

    If so it might be good: Triggering them in particular, known, mostly uninhabited spaces. Triggering them when the storm is not fully formed so they can dissipate the energy as small vortices - maybe not even making it to the ground - rather than letting conditions build until you finally get a small number of big skyscraper-topplers.

  • by Ungrounded Lightning ( 62228 ) on Sunday August 30, 2009 @04:27PM (#29254163) Journal

    You missed yaw controlled wind turbines - the common system for homebrewed and also the old "patent windmill" designs like classic the water-pumpers. These pivot the tail which makes the mill turn sideways to the wind to reduce power input or even stop the mill.

    Many modern homebrew designs use an off-center and tilted tail pivot and a slightly offset turbine axis, plus a couple stops to limit the tail travel (mainly to avoid it hitting the blades). Combined with the weight of the tail this makes the mill automatically yaw-furl in high winds to prevent electrical overheating or overspeed mechanical stresses.

    Some homebrewed wind generators, once they're stopped, are sometimes KEPT stopped by shorting the output, whichmakes them act like an electric brake. The blades rotate very slowly and stay in aerodynamic stall. But trying to do that when they're under power in a storm is more likely to burn out the generator than stop the mill. Available power goes up with the CUBE of the windspeed, torque with the square, and heating from current in a permanent-magnet alternator with the FOURTH POWER.

  • Re:Simple fix? (Score:5, Informative)

    by polar red ( 215081 ) on Sunday August 30, 2009 @05:10PM (#29254433)

    but the blades still rotate in the wind when shutdown

    No they don't, otherwise they would start spinnig too fast. and this : [] would happen. (blade hits the pole)

  • by BlackThorne_DK ( 688564 ) on Sunday August 30, 2009 @05:42PM (#29254689)
    I think most of the towers already have sensors, since they need them to detect when to shut down. The collection of data is another matter, but it shouldn't be too hard to do, some guys over here already did it []
  • Re:Simple fix? (Score:4, Informative)

    by JesVestervang ( 872086 ) on Sunday August 30, 2009 @06:05PM (#29254847)
    Newer turbines don't lock the rotor if there is no emergency - they just pitch the blades so that they will not turn the rotor significantly. Therefore, the rotor may actually still rotate (slowly) even when the turbine is shut down.
  • Storage (Score:2, Informative)

    by zogger ( 617870 ) on Sunday August 30, 2009 @09:05PM (#29256077) Homepage Journal

    Recent advances in giant batteries for wind power load balancing: []

  • by pearl298 ( 1585049 ) <mikewatersaz&gmail,com> on Sunday August 30, 2009 @09:47PM (#29256321)

    For many years I lived on a sailboat with a wind generator which shorted the output to stop the blades as well as to KEEP them stopped.

    Worked fine even in gale force +++ winds.

    One VERY dark night headed for Fiji though a magnet came loose in the generator and THAT was spectacular!

    Think a 1/2 inch hardened steel rod with a 45 degree bend before it broke!

    I now understand that the bade was close to MACH 1 when it broke free!

    THANK CTHULU that the flying blade that flew off didn't hit anyone on board but went into the Pacific Ocean! My abject apologies to any fish ...

    The CUBE relationship is the biggest problem with wind power - 99% of the time you have to eke out every watt, but for that 1% you have SO much power that it destroys things.

    Especially at night when I am off watch :-(

    Captain Bligh was a NICE guy compared to me!

  • by KDR_11k ( 778916 ) on Monday August 31, 2009 @08:31AM (#29259137)

    Wind turbines have a safe operation range, outside of that the windmill's brakes are engaged to prevent it from being damaged or destroyed (there's a youtube video of a wind turbine with a broken brake spinning up and shattering in a storm, extremely dangerous since you get large high-velocity fragments flying around that could probably demolish a house). I think the upper limit is something like 50km/h wind speed, above that the mills shut down.

"To take a significant step forward, you must make a series of finite improvements." -- Donald J. Atwood, General Motors