Wind farms are rapidly expanding across the Midwest, and a growing number of residents who live near the wind turbines are complaining about noise.
In Minnesota, those complaints prompted the Public Utilities Commission to investigate.
When Dennis and Cathryn Stillings chose a place to retire, they were looking for solitude and quiet. So a couple of years ago, they bought a farmstead in the rolling hills of eastern North Dakota.
Soon after they moved in, dozens of wind turbines sprouted in a neighbor's nearby field.
Dennis Stillings said he wasn't bothered at first because he supported wind energy and he was told the turbines were quiet, no louder than 55 decibels.
"Which is about the same level as your refrigerator running, or the same level as my conversation right now," Stillings said. "Well, if I was holding a conversation with someone in my living room and someone in the corner was sitting there going bop, bop, bop at 55 decibels, it would drive me nuts and I'd kick him out."
The Stillings said what bothers them is the pulsating, low-frequency sound. They say it's like a giant dishwasher, or a helicopter in the distance. Cathryn Stillings said there's no escaping the sound and that she's having trouble sleeping.
"It's a duller sound in the house but it's still out there," she said. "You can hear it through the walls. It just kind of gets in your bones."
The Stillings' complaints are similar to cases popping up around the country in the past couple of years, as wind farm expansion moves closer to populated areas. Complaints include headaches, dizziness and trouble sleeping.
In Minnesota, a handful of groups have organized to demand tougher regulation. They want the state to require more distance between wind turbines and homes. A report by the Minnesota Department of Health concluded there are potential health concerns.
The Minnesota Department of Health issued a white paper earlier this year which reviewed available research and concluded noise might be underestimated when planning wind farms and that better evaluation of low frequency sounds is needed. MDH also concluded cumulative sound from multiple turbines should be considered.
The Public Utilities Commission is considering changing the rules for wind turbines.
Bob Cupit, a permit manager with the Public Utilities Commission, said concerns about turbine noise are increasingly coming up in public comments about wind projects.
"We thought we needed an answer to the questions and if we didn't have a science-based answer, then we get uncomfortable about that," Cupit said.
Minnesota now requires wind turbines to meet a 50 decibel sound limit. That means most turbines are sited 1,000 feet or more from homes.
Some contend the minimum setback should be increased to about 2,000 feet or more. The National Research Council of the National Academies found there are few noise complaints beyond a half mile from a wind turbine.
Cupit said the PUC will take public comment and expect the wind industry to fund additional research.
"We're going to see what we get and we're going to rely on the industry to be responsive," he said. "Then we're going to put the facts on the table and see if we have enough to adequately shape an adjustment to setbacks that are appropriate and in the public interest."
Changing those setbacks could make placing wind farms more complicated and more expensive.
Leon Steinberg is CEO of Minneapolis-based National Wind. He said most wind farm developers already use setbacks that exceed state regulations.
"I don't think the industry believes it's a significant problem," Steinberg said. "But I believe the industry is concerned with the perception that it may be a problem."
Steinberg said a negative public perception could stall wind projects in the future, or make wind energy development more expensive, so he supports the state review of regulations.
"I can tell you that as far as I'm aware we have never had a complaint on one of our wind farms," Steinberg said. "But as you start developing in more urban areas or areas that have hobby farms and higher population densities, I think a higher level of scrutiny is needed."
Steinberg said he is confident research will prove there are no negative health effects from wind farms.
Wind developers are moving closer to populated areas because that's where transmission lines are located. Many isolated rural areas don't have enough transmission capacity to carry the electricity generated by wind farms back to urban areas where it's needed.
That's happening in Clay County where plans to erect hundreds of wind turbines are on the drawing board. The county recently passed an ordinance to control small wind developments of less than 5 MW, but the state still regulates larger wind developments.
Clay County Planner Tim Magnusson said most of the wind development is planned in the fastest growing area of the county. People are building homes because of hills, trees and wildlife. Magnusson hopes the state will establish standards that eliminate any dispute about health effects.
"It would be nice if the state agencies got together and used that white paper as a stepping off point to do some of that research to ensure that what's going to be a big business in the future is a safe business in the future," Magnusson said.
The proposed wind farms in Clay County prompted some area residents to ask for a review of state regulations.
Moorhead resident Per Anderson is one of the Minnesotans who asked the PUC to evaluate wind turbine setbacks.
Anderson said he supports wind energy; in fact he pays extra on his electric bill each month to support the city of Moorhead wind energy program. He owns land near a proposed wind farm and says any health issues are very important to the small number of people who experience them.
"Do they matter? They do, and we have to find a way to protect their interests because the stories they tell about the disruption of their lives strike me as very significant and indefensible," Anderson said. "But they are very small numbers against an overwhelming demand to create a very robust renewable energy system for this country."
Anderson said he's pleased the public has a chance to weigh in on turbine noise. He said he'll accept whatever the utilities commission decides after a complete analysis.
The Public Utilities Commission will take comment through mid September.