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Wind Farms Can Interfere With Doppler Radar
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."
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: www.windpower.org/en/tour/wtrb/powerreg.htm
cheap free energy vs pretty pictures of wind on weather.com
Well tornado warnings can, in fact, save lives.
On the Oregon Cost born and raised, On the beach is where I spent most of my days
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.
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.
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but the blades still rotate in the wind when shutdown
No they don't, otherwise they would start spinnig too fast. and this : http://www.youtube.com/watch?v=7nSB1SdVHqQ would happen. (blade hits the pole)
Yes, I'm left. You have a problem with that?