Bad vibrations: windfarms and seismic monitors

Sep 15 2011
VERTIC Blog >> Arms Control and Disarmament

Isadora Blachman-Biatch, London

The Guardian recently reported that the UK Ministry of Defence (MoD) blocked a planning application from REG Windpower to build a wind farm near Eskdalemuir. The MoD prevented construction because the vibrations from the wind farms would disturb seismic monitoring activities at Eskdalemuir. Although this frustrated REG Windpower, the Eskdalemuir monitor is part of the CTBT’s International Monitoring System (IMS). Preventing interference with this system is important, and the MoD has a strong reason to deny the application. The MoD would object to any new turbines within 50 km of the station to ensure monitoring is not disturbed. Wind power developers are free to build outside of the 50 km zone. The problem is that Eskdalemuir is an ideal space for wind farms because it is open and sparsely populated. Unfortunately, those are the same qualities that make it an excellent seismic monitoring site.

Wind farms’ seismic impact
In 1998, the UK has ratified the Comprehensive Nuclear Test-Ban Treaty (CTBT). This treaty bans all nuclear explosions in all environments. Treaty compliance is verified through an elaborate network comprising 337 monitoring stations worldwide. The stations employ four types of technology: seismic, hydroacoustic, infrasound and radionuclide. The seismic network consists of 50 primary and 120 auxiliary stations. Eskdalemuir is an auxiliary station in this network. The Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organization is charged with constructing and operating facilities. State parties to the treaty, on their part, have pledged not to interfere in their operation.

The problem is that wind turbines built too close to a monitoring station interfere with the station’s detection capabilities. Although wind turbines are designed to be balanced, imperfections in construction and uneven wind forces disrupt this balance. As the turbine blades rotate these imbalances cause the turbine itself to vibrate in tandem with the blades. These vibrations are translated into the ground, creating an interfering seismic signal. Large numbers of wind farms therefore raise the average signal noise within a particular area. If the average noise level is too high, the scientists cannot easily distinguish a distant nuclear explosion from background noise. REG Windpower’s proposed building wind farms within 50 km of Eskdalemuir. According to a 2004 study by the Applied & Environmental Geophysics Research Group (AEGRG), this is too close.

The need for a ‘noise budget’
It would unfortunate indeed if CTBT implementation would create an obstacle to the establishment of wind farms. Therefore, over the years, the MoD has made several decisions to enable greater wind power development.

Before 2004, the MoD objected to any wind farms within 80 km of Eskdalemuir. This objection removed 40 per cent of the UK’s potential wind energy capacity, or up to up to 1.6 gigawatts (GW) of wind energy.

As noted above, in 2004, the AEGRG released a study on the seismic impact of wind farms. This study establishes a set of guidelines that would allow the UK to develop more wind farms in Eskdalemuir. These guidelines also ensure that the wind farms would not damage the Eskdalemuir station’s monitoring capacity. As a part of the study, the AEGRG suggested the MoD revise its blanket ban. Instead, the MoD could enforce a ‘noise budget’ for the area 50 km from the station in all directions. And no one would be allowed to build wind farms in the area 10km from Eskdalemuir. Within the 50 km zone, the budget would be equal to the seismic noise of a windy day at Eskdalemuir, or 0.336 nanometres of uncertainty in vibration measurement.

This solution allowed businesses to construct wind farms ten to 50 km from Eskdalemuir, while ensuring that those farms would not interfere with seismic monitoring. These restrictions were relaxed after another AEGRG study to allow seismically-quiet ‘micro’ wind turbines. These turbines, which contribute an insignificant amount to the noise budget, can be built within 50 km of Eskdalemuir.

Building better wind farms
If wind power developers want to build wind farms near Eskdalemuir, they must integrate technology that diminishes the seismic impact of wind turbines. According to the AEGRG, technologies reduce the vibration of mechanical systems are available, though they are relatively new. For example, in April 2011, Reactrec Ltd, a UK company specialized in solving vibration problems, launched a ‘Seismically Quiet Tower’ (SQT) system that can significantly decrease turbine vibrations. Another possible solution may hang weights inside the turbines to deaden vibrations.

But proponents of wind power may not want to limit their scope to technology that decreases seismic activity. They could also potentially help their cause by funding or developing more accurate seismic monitors. Such monitors might allow a greater noise budget which could allow more wind farms near seismic monitors.

Wind farms in the Eskdalemuir area are an important part of the UK’s wind power program. However, seismic monitoring stations are also a key component of the CTBT’s monitoring regime. But it may not be necessary to choose between the two. Developers are now able to either build outside of the 50 km zone or use technology to decrease the turbines’ vibrations. And with the introduction of micro wind turbines, seismologists and developers may no longer have to fight over the same windy and barren patch of land.

Last changed: Sep 15 2011 at 7:06 PM




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