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Weather service concerned over impact of Nebraska wind farm on radar  

Credit:  By Nancy Gaarder / World-Herald staff writer | November 10, 2014 | www.omaha.com ~~

A commercial wind farm proposed for south-central Nebraska would interfere with a National Weather Service radar station more than any other in the nation.

Dozens of turbines, each standing nearly 20 stories tall, would be built 2½ miles to 7 miles from the radar station at Blue Hill that serves south-central Nebraska and north-central Kansas.

Wind towers are mammoth pieces of industrial equipment: A turbine blade has a wingspan greater than that of a 747 airplane, and the tip can spin at speeds in excess of 140 mph.

For the most part, wind farms are a nuisance to forecasters, but this would be the first time in Tornado Alley that a wind farm would be built this close to weather a radar station.

The Cottonwood wind farm has been proposed by NextEra Energy Resources, the nation’s largest wind developer. It would have between 43 and 66 turbines and generate between 89 and 115 megawatts of electricity, depending on customer demand, said Steve Stengel, NextEra spokesman. That amount of electricity could power more than 25,000 homes, based on wind farms of similar size.

Stengel said NextEra is working with the weather service on options to lessen the impact of the wind farm during severe weather.

Weather radar takes readings based on movement. Thus, if a wind farm is turned off, it doesn’t affect weather radar.

Operating wind farms can affect weather radar from dozens of miles away. Within about 30 miles, their movement begins to consistently affect radar readings, and within 11 miles the effect increases exponentially, according to weather service analysis. Within 2 miles, the impacts are considered severe.

NextEra and a earlier developer agreed not to place any turbines within that 2-mile zone at this site.

The weather service has been monitoring the effects of wind farms on radar nationally for several years and expects the problem to become more widespread as wind farms become more common and the towers and turbines get larger.

Of most concern to the weather service is the potential for a wind farm to create false images when rain or a violent storm moves directly over the operating turbines. In rare instances that could cause meteorologists to miss an area of flooding rains or get a false tornado reading.

Otherwise, weather service officials say, they should be able to account for the ground clutter the wind farm adds to radar scans.

“In general, the impact should be fairly minimal,” said Mike Moritz, the warning coordination meteorologist for the weather service office in Hastings. “I’m not going to say there isn’t going to be any impact. … As meteorologists, we’re going to adapt through training and through experience, just like we always do.”

The Blue Hill radar station is operated by the Hastings office.

The project has been approved by the Nebraska Power Review Board. NextEra hopes to begin construction in 2015 or 2016 but still has some contracts to obtain before that’s possible, Stengel said.

The federal government doesn’t regulate wind turbines, so the weather service depends on voluntary cooperation from wind farm developers, said Ed Ciardi, a meteorologist at the NEXRAD Radar Operations Center, which is part of the weather service.

The most helpful thing a wind farm can do during violent weather is to shut down, Ciardi said. That’s because the radar is programmed to ignore stationary objects. If the wind turbines were silenced during a storm, it would be as if the farm wasn’t there.

In a handful of cases, wind farms have agreed to shut down when requested by the weather service.

“Those are tough to come by,” Ciardi said of the agreements.

The reason? Wind farms aren’t making money when they’re not operating.

Of the more than 900 wind farms in the nation, three have signed agreements with the weather service to shut down temporarily at the request of the local office, Ciardi said. Two of those are in Kansas and one is in New York. So far, none have had to shut down.

Stengel said NextEra is in discussions with the weather service about curtailing the Cottonwood wind farm during severe weather.

He noted that if wind gusts at Cottonwood were to reach 56 mph, the turbines would automatically shut down to avoid being damaged.

Ciardi said one other weather service station has a wind farm as close as the one proposed in Nebraska. But the terrain at that station, at Fort Drum, New York, slopes away, so the turbines don’t interfere in as many scans of the radar.

Moritz said the weather service has been talking with NextEra about providing the weather service with wind and rain data from the wind farm. This would offset some problems caused by the turbines.

“They’ve been a very good partner in working through this,” Moritz said, “and I think they’ll be a good partner going forward.”

Source:  By Nancy Gaarder / World-Herald staff writer | November 10, 2014 | www.omaha.com

This article is the work of the source indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

The copyright of this article resides with the author or publisher indicated. As part of its noncommercial effort to present the environmental, social, scientific, and economic issues of large-scale wind power development to a global audience seeking such information, National Wind Watch endeavors to observe “fair use” as provided for in section 107 of U.S. Copyright Law and similar “fair dealing” provisions of the copyright laws of other nations. Send requests to excerpt, general inquiries, and comments via e-mail.

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