Wednesday, July 30, 2008

Safe setbacks: How far should wind turbines be from homes?

Let's start with what one manufacturer considers to be safe for its workers. The safety regulations for the Vestas V90, with a 300-ft rotor span and a total height of 410 feet, tell operators and technicians to stay 1,300 feet from an operating turbine -- over 3 times its total height -- unless absolutely necessary.

That already is a much greater distance than many regulations currently require as a minimum distance between wind turbines and homes, and it is concerned only with safety, not with noise, shadow flicker, or visual intrusion.

In February 2008, a 10-year-old Vestas turbine with a total height of less than 200 feet broke apart in a storm. Large pieces of the blades flew as far as 500 meters (1,640 feet) -- more than 8 times its total height.

The Fuhrländer turbine planned for Barrington, R.I., is 328 feet tall with a rotor diameter of 77 meters, or just over 250 feet (sweeping more than an acre of vertical air space). According to one news report, the manufacturer recommends a setback of 1,500 feet -- over 4.5 times the total height. In Wisconsin, where towns can regulate utility zoning for health and safety concerns, ordinances generally specify a setback of one-half mile (2,640 ft) to residences and workplaces.

But that may just be enough to protect the turbines from each other, not to adequately protect the peace and health of neighbors. When part of an array, turbines should be at least 10 rotor diameters apart to avoid turbulence from each other. In the case of the proposed 77-meter rotor span in Barrington, that would be 770 meters, or 2,525 feet. For the Gamesa G87, that's 2,850 feet; for the Vestas V90, 2,950 feet -- well over half a mile.

Since the human ear (not to mention the sensory systems of other animals or the internal organs of bats, which, it is now emerging, are crushed by the air pressure) is more sensitive than a giant industrial machine, doubling that would be a reasonable precaution (at least for the human neighbors -- it still doesn't help wildlife).

Jane and Julian Davis, whose home is 930 m (3,050 ft) from the Deeping St. Nicholas wind energy facility in England, were forced by the noise to rent another home in which to sleep. In July 2008 they were granted a 14% council tax reduction in recognition of their loss. It appears in this case that the combination of several turbines creates a manifold greater disturbance.

Sound experts Rick James and George Kamperman recommend a minimum 1 km (3,280 ft) distance in rural areas. James himself suggests that 2 km is better between turbines and homes, and Kamperman proposes 2-3 km as a minimum. German consultant Retexo-RISP also has suggested that "buildings, particulary housing, should not be nearer than 2 km to the windfarm"; and that was written when turbines were half the size of today's models.

Both the French Academy of Medicine and the U.K. Noise Association recommend a minimum of one mile (or 1.5 km, just under a mile) between giant wind turbines and homes. Trempealeau County in Wisconsin implemented such a setback. National Wind Watch likewise advocates a minimum one-mile setback.

Dr. Michael Nissenbaum and colleagues surveyed residents near wind turbines in Maine and found significantly worse sleep and mental health among those living 1.4 km or closer than those living farther from the machines.

Dr. Nina Pierpont, the preeminent expert on "wind turbine syndrome", recommends 1.25 miles (2 km). That is the minimum the Davises insist on as safe as well. In France, Marjolaine Villey-Migraine concluded that the minimum should be 5 km (3 miles). In June 2010, Ontario's environment ministry proposed requirements that offshore wind turbines be at least 5 km from the shoreline.

To protect human health, these distances are simply crude ways to minimize noise disturbance, especially at night, when atmospheric conditions often make wind turbine noise worse and carry it farther even as there is a greater expectation of (and need for) quiet. The World Health Organization says that the noise level inside a bedroom at night should be no greater than 30 dB(A) or 50 dB(C) (the latter measure includes more of the low-frequency spectrum of noise, which is felt as much as, or even more than, heard). A court case in Great Britain resulted in the “Den Brook” amplitude modulation conditions, which define and limit pulsating noise, which is especially intrusive, as any change, outside the dwelling, of >3 dB in the LAeq,125ms (125-millisecond averaged sound level) in any 2-second period at least 5 times in any minute with LAeq,1min (1-minute averaged sound level) ≥28 dB and such excess occurring within at least 6 minutes in any hour.

Updates: 

Since 2008, Queensland, Australia, has limited night-time noise indoors to 30 dB(A) (1-hour average), with limits of 35 dB(A) no more than 10% of the time and 40 db(A) 1%. Respective daytime limits are 5 dB(A) above the night-time limits. They also specify that existing continuous 90% sound levels should not be increased and that variable noise averages should not increase existing sound levels more than 5 dB(A) in the same time period.

Scottish Planning Policy “recommends” a distance of 2 km between wind energy developments and the edge of cities, towns, and villages to reduce visual impact. Since August 2011, Victoria, Australia, has allowed wind turbines within 2 km of a home only with the homeowner's written consent. In April 2013, the Québec, Canada, government approved a 2-km setback from homes in the municipalities of Haut-Saint-Laurent, Montérégie. Citizens groups in Germany suggest a minimum distance of 10 times the total turbine height to residential areas (see this story). Since July 2013, the state of Saxony has required 1 km between wind turbines and residential areas.

In February 2014, Newport, North Carolina, established a 5,000-ft (1.5-km) setback from property lines, a 35-dB limit for noise at the property lines, and a total height limit of 275 feet. The latter two conditions were also established by Carteret County, North Carolina, in February 2014, as well as a 1-mile setback from property lines.

Also see:  “Wind turbine setback and noise regulations since 2010”

wind power, wind energy, wind turbines, wind farms, human rights, animal rights