Ten years ago a planning application was submitted for a wind turbine in the vicinity of a Civil Airport in England. The Airport did not object to the proposed wind turbine. The wind turbine was consented, built and is now operational.
The Airport is equipped with an Air Traffic Control (ATC) Primary Surveillance Radar (PSR). The wind turbine occasionally appears on the radar screen as clutter.
However, during the last 10 years many more wind farms were built near the Airport which also cause radar clutter (Figure 1). The Airport’s ATC manager currently objects to any further wind developments in the area that are likely to affect the radar due to the cumulative impact.
Figure 1: An example of how cumulative impact has grown over the last years
The Cumulative Impact in a Nutshell
The Cumulative Impact of wind turbines on Aviation usually starts with accepting the impact of a single turbine, as in the example above, and ends with tens or hundreds of turbines in the vicinity of a radar or other aviation facilities.
The two main cumulative concerns on aviation usually are:
- Radar impacts: wind turbines appear as clutter on the radar screen. Radar operators may be concerned by the possibility of multiple areas of clutter in the vicinity of an aircraft’s path.
- Aerodrome and airfield impacts: safety of flying concerns due to the physical structure and turbulence.
So at what stage are we in the UK currently?
The Cumulative Impact in the UK
Many planned turbines are currently receiving aviation objections on cumulative grounds and it is likely that the objections rates will go up because:
- There are 4,842 operational and 3,464 turbines under construction or have received planning consent onshore wind turbines ;
- There are approximately 20GW of wind turbines in the planning system waiting to be determined;
- Very often new sites are planned in the vicinity of operational, under construction or consented turbines which may already impact aviation;
- There are over 1,000 operational aerodromes, airfields, radar and radio facilities that can be affected by wind turbines;
Operational, under construction or consented turbines and aviation constraints are presented in figure 2 below.
Figure 2: UK Onshore wind turbines vs Aviation Constraints
|Development Stage||Number of Wind Turbines / MW||Per Country|
|Country||Number of Turbines||MW|
|Operational||4,842 / 8,056.43||England||1,223||1,973.89|
|Under Construction & Consented||3,464 / 6,940.64||England||704||1,146.44|
Table 1: Onshore operational, under construction and consented turbines in the UK
Official Guidance on Cumulative Impact?
In Table 2 below we have extracted text from the Civil Aviation Authority’s (CAA’s) Civil Aviation Publication (CAP) 764 and Eurocontrol Guidelines to see some of the things these mention on cumulative impacts on aviation.
|Guidelines||What do they say?|
|CAA CAP 764 ||“…while developments with small numbers of wind turbines can have an adverse effect on aviation operations, it is the proliferation of developments, and the resulting cumulative effect, that is of far more significant concern…the combined effect of numerous individual turbines or multiple wind turbine developments can be hard, if not impossible, to mitigate. Therefore it is feasible that service providers may lodge objections to subsequent developments in areas where they had previously been able to accommodate proposed wind turbine developments (paragraph 2.39)”.|
|“…The cumulative effect of geographically separated wind turbine developments may have more impact on aviation than if such developments were located in close proximity to each other. For example, individual areas of clutter separated by 5 NM could have more impact on the provision of ATS than one slightly larger area of clutter…(paragraph 2.40).”|
|“For aerodrome operators or en route service providers, there is a difficulty in protecting aviation activity from these cumulative effects because planning applications … are generally dealt with on a ‘first come, first served’ basis. The use of suspensive conditions significantly reduces the clarity of the planning situation….This could lead to the situation whereby more viable applications are objected to on the grounds of cumulative effect as a result of less viable projects that have been previously approved through a suspensive condition (paragraph 2.41).”|
|“The basis for an objection based on cumulative effect would be that the safety and efficiency of the aerodrome or en-route service may not be maintained or that the growth of an aerodrome or en-route service may be constrained…(paragraph 2.42).|
|It is recognised that many potential developments fail to reach maturity within the formal planning stage. Nevertheless, it is in the interests of aviation stakeholders to take all developments about which they are aware into account until they have been formally notified that a proposal has been abandoned. Therefore, it is in a wind turbine developer’s interest to inform all involved parties when such developments are abandoned or postponed (paragraph 2.43).|
|Eurocontrol Guidelines ||“…the impact of wind turbines on the operational service provided by a radar depends on the number of wind turbines located in the radar line of sight. Therefore it is strongly recommended that ANSP’s keep an accurate tracking of all the approved wind energy projects. With this information they will be able to conduct the impact assessment of the new project in conjunction with the neighbouring approved projects that may already affect the performance of radars (paragraph 4.25, page 33).|
Table 2: CAP 764 & Eurocontrol guideline extracts mentioning cumulative wind turbine impact
How Can I Quickly Assess, Avoid or Solve Cumulative Impacts on Aviation?
Let’s quickly look at how a developer can initially assess the cumulative impact on radar. We would recommend undertaking the following steps:
- Identify which radar may be affected by your wind turbine(s). If your turbine is unlikely to affect any radar then you don’t need to worry for cumulative impacts.
- If your turbine affects one or more radar then investigate further whether the technical impact can be avoided by micrositing the turbine(s), or by means of additional shielding (trees, buildings) or more in depth analysis.
- Undertake radar impact analysis (i.e. a good starting point is radar line of sight) for the specific radar that your turbine may affect.
- Identify operational, under construction and consented wind turbines within the operational range of that radar which are likely to be considered by the aviation stakeholder.
- Undertake a radar impact analysis for the identified turbines (a good starting point is radar line of sight). Pager Power built a radar screen simulator to enable air traffic controllers to determine the cumulative impact of wind turbines. Wind turbine coordinates are programmed in and the radar simulator then shows the expected level clutter at the wind turbine locations. This simulator has enabled a number of wind farm radar objections to be withdrawn in North East England.Normally a simulator can be appropriate after radar line of sight analysis has been undertaken. Output from the line of sight analysis is used to configure the simulator. You can watch the simulator in action in the video below.
- Gather the results. If it appears that it is likely for a cumulative impact to occur which will be unacceptable to the aviation stakeholder then you will need to look at technical mitigation such as Aveillant, C-Speed, Terma, radar blanking or other?
The number of wind turbines in the UK is expected to double in the next few years. As a result of, aviation objections on cumulative grounds are also expected to increase. Unless solutions for mitigating the impacts of the operational turbines are found and implemented then it is considered that in most cases aviation stakeholders will not be able to accept additional impacts.
Editors Note: This post was first published on 26th February 2015, but has been updated for accuracy and comprehensiveness.
 RenewableUK Wind Energy Database (Last accessed 24/02/2015).
 Civil Aviation Authority, CAA (June 2013): CAA Policy and Guidelines on Wind Turbines – CAP 764.
 EUROCONTROL (September 2014): EUROCONTROL Guidelines: How to Assess the Potential Impact of Wind Turbines Surveillance Sensors.
What would be the effect of smaller turbines ?
Hello Jim and thank you for your comment.
In short it varies and it depends on the aviation/radar stakeholder. For example the Ministry of Defence requests that:
"Developers and local planning authorities should consult with the MOD if a proposed turbine is 11 metres to blade tip or taller, and/or has a rotor diameter of 2 metres or more."
In practice, both small and medium wind turbines (15-55 metre total height) can raise aviation/radar concerns.
Is there a specific turbine height you are interested in?