Wind development in the promising borderlands region along the Scottish/English border has come to a standstill, due to very low intensity ground vibrations interfering with a key nuclear test ban monitoring station in Eskdalemur, Scotland.  The Ministry of Defence has been tracking the increasing seismic interference from wind farms in the region, and says that any more would push the wind turbine vibrations  to the point that their seismic monitoring array would no longer be able to reliably hear distant seismic anomalies.

According to an article in The Guardian, “the swishing blades of wind turbines cause vibrations in the ground that can be detected by the sophisticated monitoring equipment at Eskdalemuir. An expert study for the MoD concluded that although the station could cope with some seismic noise, increasing this beyond a certain level would be unacceptable. The limit has now been reached so the ministry is objecting to every new wind turbine within 50km of Eskdalemuir.”

An earlier 80km exclusion zone has been a flexible one, with a period during which the MoD only excluded wind development as close at 10km from the installation, with several wind farms built in the 50km zone (orange circle at right).  At this point, however, the MoD feels they have reached the limit of acceptable infrasonic interference.

One wind power company, REG, which recently had a planned development rejected due to MoD objections, reports that efforts are underway to find a technological fix that could reduce the subtle vibrations that are causing the issues. One idea is to hang weights like pendulums inside turbine towers to deaden the vibrations from the blades. The MoD promised it would reassess its opposition if there were a proven technological solution.

It must be stressed that the vibrations being discussed here are extremely small, far below what would be felt in a home.  We’re talking about a sensitivity that can pick up small seismic anomalies from around the world.  Nonetheless, even though the MoD’s concerns at 10-50km are about impacts far below thresholds that neighbors would notice, I do wonder whether dampening technology developed to address MoD concerns would also reduce some of the more localized vibrations.

We need to keep clear the distinction between pure vibration, transferred through the towers into the ground, and the infrasonic elements of the sound from wind off the blades; it’s unclear that the proposed pedulum-inside solution would affect the in-air infrasonics. For that matter, the press reports are fairly vague about the source of the troubling seismic interference, with that reference above to it being related to wind off the blades, which would, indeed, imply that the strong infrasonic component of wind turbine sound is the source of the problem.  Still, the MoD’s concerns about effects at 10km or 50km should not be taken to mean homes in these ranges are at risk.  However, this does make me wonder whether any other industrial developments (factories, especially) that produce strong infrasonic sound are an issue at distances as far as 50km; if not, it may offer an example of how wind turbines are a relatively unique acoustic presence in the landscape.