There is an organisation called the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty (CTBTO Preparation Committee), which was set up in 1996 with the purpose of banning nuclear explosions of any kind, anywhere on earth.
They aim to achieve this by bringing into force the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which was prepared in 1996 [1]. This goes further than previous treaties and initiatives on the topic of nuclear explosions going back decades, including the Baruch Plan, the Partial Nuclear Test Ban Treaty, the Nuclear Non-Proliferation Treaty, the Threshold Test Ban Treaty and the Peaceful Nuclear Explosions Treaty.
The CTBT is not in force because not enough states have ratified it, however it has been ratified by several states, including the United Kingdom [2].
Eskdalemuir Seismic Array
The Eskdalemuir Seismic Array (sometimes referred as EKA), is a facility located in Scotland. It is an auxiliary seismic network for the International Monitoring System [3]. It was originally established in the 1960s by the UK Atomic Energy Authority as part of the efforts at that time to identify underground nuclear tests [4]. More recently, it has also been used to monitor compliance with the CBNT, as one of over 300 monitoring sites for this purpose [5].
Seismic arrays contain instruments that can detect extremely faint vibrations, including those caused by nuclear explosions, earthquakes and other seismic activity that take place internationally. Vibrations are characterised by an amplitude, which is a physical length, and a frequency, which is a rate of oscillation.
In order to detect the faintest vibrations possible, seismic arrays are typically located in very quiet environments with minimal local vibrational noise. This means that, ideally, arrays would be located far from densely populated areas, busy roads or other sources of seismic activity such as excavation.
Wind Farms
Wind turbines, due to their physical size and the fact that they have such significant rotating elements, are a source of seismic vibration.
In addition, due to the many constraints on wind farm locations due technical requirements and (un)popular opinion, remote locations that are sparsely populated.
Unsurprisingly then, wind farms have been built and proposed in the area of the Eskdalemuir seismic array, which has led to concerns and indeed safeguarding policy in order to protect the EKA against interference from wind farms.
Figure 1: Landscape of a wind farm [11]
Eskdalemuir Safeguarding
The EKA is safeguarded by the Ministry of Defence. Much of the work relating to safeguarding the EKA is led by the Eskdalemuir Working Group (EWG). The EWG was reformed earlier in 2023, the core members are [6] understood to be:
- The Scottish Government.
- The UK Government.
- Ministry of Defence.
- Heads of Planning Scotland.
- Renewable UK.
- The Onshore Wind Strategic Leadership Group.
The EWG was reconvened in 2012 and reformed in 2018, and refined further in 2023. Its purpose is to enable effective engagement between core group members, identify interactions between approaches and policies; and to reach a consensus on the best available science and evidence.
Timeline of Eskdalemuir Safeguarding for Wind Turbines
2005:
- The Scottish Ministers and the Ministry of Defence issued a direction to planning authorities advising any sites within 10km-50km of the array would require consultation with the Ministry of Defence before determination.
- Developments within 10km were be considered automatically unacceptable to the Ministry of Defence.
- A report by Styles et al established a ‘noise budget’ which said that the cumulative effects of wind farms within 50km must result in a combined seismic noise of 0.336 nm or less [7].
2014:
- Further work by Xi Engineering produced a spreadsheet that allowed Ministry of Defence to manage the threshold.
2020:
- Energykontor UK, a wind developer, challenged the Ministry of Defence safeguarding policy, which is first-come first-served until the noise budget was reached. A Judicial Review found the Ministry of Defence policy to be unlawful [8].
2023:
- Further research by Xi Engineering [9], commissioned by the EWG, was released. This is intended to inform further work to unlock as much capacity as possible around the EKA.
Status Quo
Currently, the Ministry of Defence position is that the noise budget has been reached and it therefore objects to any developments within 50km of the array. This has been the case since 2018, any further applications simply go onto a waiting list [10].
Next Steps
Further work is proposed in order to better understand effects from turbines and potential solutions with a view to unlocking further capacity.
The 2023 study by Xi Engineering does offer some insights into how progress may be made. Some key points are:
- The wind turbines within the 50km consultation zone were audited and revised, the cumulative impact was re-calculated. This indicated all wind farms with allocated budget up to and including Scotston Bank have a cumulative impact significantly below the threshold value (0.21810 out of 0.336 has been used up based on the revised calculations).
- A Seismic Impact Limit value, which could become a stipulation for future turbines, was calculated, applying this limit would provide at least 1 GW of additional capacity within the 50 km zone.
There is no official deadline by which changes to the current safeguarding status will take place. Target dates are mentioned in some cases within the EWG meeting minutes, which are publicly available in some cases, however these same documents highlight the lack of available resources from the relevant parties. Subjectively, these meeting minutes could be interpreted as an indicator that EKA safeguarding changes are on the back burner, this is of course not an official position.
Prognosis
It is always difficult to predict with any meaningful level of certainty whether a problem will be solved in the future. The EKA is not the first technical constraint to wind farm development, nor is it the only one with which developers in today’s environment must contend.
The nature of problem is that wind turbines will always cause some level of vibration, and those vibrations appear likely to remain fundamentally problematic for the array. This is because they will likely remain indistinguishable from vibrations of interest or that they will mask other small vibrations that will subsequently remain undetected. Whilst the science and engineering that goes into making an array with the sensitivity of the EKA is extraordinarily impressive, the array itself is conceptually somewhat rudimentary because the only external stimulus from which it can draw conclusions is miniscule oscillations in the ground. The physical phenomenon caused by the turbines, vibrations within the ground, is and will remain the exact phenomenon that a seismic array is measuring.
This inherent limitation to likely solutions stands in contrast with some other technical constraints, such as radar impact. Wind turbines can adversely affect radar by, for example, showing up as a moving target on a radar screen. However, this is not because radar echoes from wind turbines are fundamentally indistinguishable from those that come from aircraft. Rather, it is that most radar systems (with some possible recent exceptions), were not designed to make any delineation between wind turbines and aircraft, because there was simply no requirement to do so at the time that they were designed. This potentially allows more flexibility in terms of mitigation options because there is room to manoeuvre. Indeed, one of the more successful and enduring mitigation solutions for radar impact has been the provision of local in-fill radar that can distinguish between wind turbines and aircraft. The potential for other, even more creative solutions seems fairly wide because a spinning turbine rotor is fundamentally different from an aircraft flying in the sky, and anything that can characterise that difference has the potential to provide a solution.
In the case of impacts on the seismic array, it seems as though the only viable solution from a mitigation perspective would be more effective damping of vibrations from the turbines themselves, because this is the only thing that would target the interference phenomenon at source. Whilst significant advances in this area should not be discounted, achieving this objective seems to be at odds with the more established trend of making wind turbines bigger in order to generate more energy. Furthermore, improved damping is unlikely to bring any other significant benefit outside of reducing impact on sensitive instruments in the immediate vicinity, such that the level of spend on development of such solutions may be restricted.
Ultimately, it may well be that a hard limit is established and reached when it comes to development within 50 km of EKA. Whether the current figures represent that hard limit or not remains to be seen.
Pager Power
Pager Power has been serving the wind energy with technical analysis, advice and representation for over 20 years. If your project is facing constraints, particularly with regard to aviation safety, telecommunications or shadow flicker, please contact us.
References
[1] CTBTO (link), last accessed September 2023
[2] United Nations Office for Disarmament Affairs (link), last accessed September 2023
[3] Gurlap (link), last accessed September 2023
[4] Scottish Places Info (link), last accessed September 2023
[5] CTBTO (link), embedded video last accessed September 2023
[6] Eskdalemuir Working Group – 18th April 2023 Meeting Minutes (link), last accessed September 2023
[7] Styles P. et al. 2005. Microseismic and infrasound monitoring of low frequency noise and vibrations from windfarms. Recommendations of the siting of windfarms in the vicinity of Eskdalemuir, Scotland. Applied and Environmental Geophysics Technical Report, University of Keele, (link), last accessed September 2023
[8] Scotcourts.gov, Opinion of Lord Tyre (2020), P1176/19, (link) last accessed 2023
[9] Xi Engineering Consultants, 2013, Eskdalemuir Wind Turbine Seismic Vibration Calculations to confirm maximum turbine seismic level to deploy minimum of 1GW deployment, document number SGV-205-LimitSet-TechReport-v13 (link), last accessed September 2023
[10] Onshore Wind Policy Statement 2022, Scottish Government (link), last accessed September 2023
[11] Landscape of a wind farm, Alfo Madeiros (January 2023) from Pexels.com. Last acccessed on 4th October 2023. Available at: https://www.pexels.com/photo/landscape-of-a-wind-farm-15268778/
