Because wind farms can look like thunderstorms on weather radar, the NOAA National Weather Service Forecast Office in Hastings and the Cottonwood Wind Project, a special purpose entity of Next Era Energy Resources, recently signed a voluntary agreement to stop the wind turbines and eliminate interference during severe weather.
NextEra Energy Resource’s proposed project, consisting of up to 66 turbines, will be located south of Blue Hill, in Webster County, and the nearby Doppler weather radar operated by the NWS in Hastings. Wind turbines will be as close as 2 1/2 miles from the radar and cause some interference resulting in contaminated data.
Large utility-scale wind turbines, whose total height is typically up to 500 feet above the ground, can interfere with weather radars if they are in the radar’s line of sight. The rotating blades of the wind turbine defeat the radar’s clutter filtering mechanism, which is designed for stationary objects such as buildings and terrain. No known adequate wind turbine filtering technique is available at this time.
Returned signals from rotating wind turbines can look like rain showers or thunderstorms. The contaminated returned signal can also impact the radar’s algorithms, especially precipitation estimates above the wind farm area.
The voluntary agreement provides a strategy for mitigating the wind turbines’ effects. NextEra Energy Resources may cease or curtail operation of the wind turbines for 15 to 60 minutes at a time during an agreed upon curtailment season between March 21 and Sept. 21 by request of forecasters from the NWS office in Hastings. Reasons for curtailment include severe weather affecting the wind farm area and flash flooding caused by isolated, stationary thunderstorms.
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