As installed wind capacity around the world increases, and turbines get ever taller, so the potential for conflict between wind-farm developers and civil and military aviation authorities is growing.
In France, the armed forces are imposing tougher restrictions on turbines being installed near radar sites and in low-altitude flight training zones that threaten to block wind deployment in up to 60% of the country, the industry has warned. High-level discussions have yielded some movement, but real progress needs political support to ensure long-term solutions. In countries such as the UK and the US, such a collaborative approach seems to be working.
There is no denying that turbines can cause interference to radar and other navigation aids, making it difficult for air-traffic controllers and military operators to identify and track aircraft through the "clutter", and for aircraft to accurately identify their location. Civil and military aviation authorities are increasingly concerned as wind turbines reach heights of over 150 metres and developers turn to sites closer to radars, airports and training zones, as those further away are already in use. There is also a cumulative effect on radars as more turbines are installed.
While various technical and procedural solutions to mitigate the impact are available, or in development, uptake has been slow, partly because of cost and sometimes also through lack of procedures for constructive dialogue. No global figure is available for the number of megawatts blocked by radar interference concerns, but even in 2011 the European Wind Energy Association (EWEA) estimated 19GW throughout Europe.
Trade body RenewableUK believes that consent applications for more than 12GW of projects in the UK are currently subject to aviation objections, while German wind federation BWE believes more than 4GW is blocked because of air-traffic safety concerns. In France, up to 6.5GW is affected by proximity to a military radar or low-altitude training zone, according to the renewable energy trade association SER.
In France, since 2011, turbines have been banned or heavily constrained within 30 kilometres of radars. And projects have to obtain consent from the defence ministry. Until last year the ministry generally approved those beyond the 30-kilometre limit and outside certain zones used for low-level flight training. In 2013, however, the ministry started applying stricter criteria for the training zones, objecting to 3GW of projects, including 2.5GW it had previously approved, according to French wind energy association FEE.
The army, which said the turbines were beginning to seriously disrupt its operations, now wants to draw up specific rules covering these areas, even though it already has the power of veto. The ministry wants to enlarge the exclusion zone around military radars to up to 60 kilometres - without showing any technical evidence for this requirement. The wind industry believes that, in total, this would block deployment in over half the country (see map, below). France's current installed capacity stands at 8.5GW.
Following appeals from the wind industry to energy minister Segolene Royal, in September Royal and defence minister Jean-Yves Le Drian agreed to draw up a map showing training zones that could be released for wind-power deployment - largely because they already contain a lot of turbines - and those reserved for the military. Le Drian also said he would define clear criteria for banning turbines near defence radar. While the industry awaits further details, these high-level discussions have at least brought some progress. "It is the first time we have seen such a rapid and effective response on a technical issue," said Marion Lettry, deputy head of renewable energy at trade body SER.
"If there is the political will for wind-farm and radar operators to work together they can find a solution in most cases," says Jacopo Moccia, head of political affairs at EWEA. While every radar and every site is different, and military radars present particular problems, "radars and wind turbines can co-exist", he insists.
Step-change in the UK
Constructive dialogue began in the UK around 2008, when the government, wind industry and air navigation service providers (ANSPs), including the military, signed an agreement allowing for greater cooperation and sharing of resources to investigate the problem. A 2011 update moved from research to implementing site-specific mitigations to radar objections.
"Everyone realised that the two parties had a common goal," says Mark Balsdon, head of data solutions at National Air Traffic Services (NATS). "The ANSPs wanted safety, and the developers wanted to build wind farms." The discussions were key to getting together government departments, national agencies and the aviation and wind industries for mutual gain, agrees RenewableUK: "It helped to instil a more cooperative working approach from aviation stakeholders such as NATS, the Ministry of Defence and airports."
This led to some key mitigation strategies and technologies being agreed, including the deployment of TPS-77 radars for air-defence mitigation, which because it can distinguish between aircraft and wind turbines freed up more than 3GW of offshore capacity; and the Project RM mitigation programme for civilian air traffic.
Following this, utilities SSE and Vattenfall agreed to help foot the bill to upgrade two en-route radars with a technical fix developed by Canadian firm Raytheon. If enough developers come on board, this solution could be extended to other radars, releasing up to 2.2GW of potential capacity, according to NATS.
Various manufacturers are also working on solutions for airport-based radars, such as Danish company Terma's Scanter system, which was trialled earlier this year, with promising results. NATS now wants to fully integrate the system at an airport, but need a developer to fund it, raising once again the issue of who should be paying for these mitigations.
Dialogue in the US
The US has followed a similar path to the UK, with concerns by radar operators first surfacing in 2005. The government imposed a ban on turbines anywhere near defence radars while they studied the potential impact and possible mitigations, explains Tom Vinson, director of regulatory affairs for the American Wind Energy Association. Discussions with the industry followed, but without much progress being made until 2011, when the government established the Siting Clearinghouse within the Department of Defense (DoD), a one-stop shop where developers can determine early on if there are likely to be objections. The DoD is also required to consider mitigation before refusing a project and to explain its decision, backed by a report to Congress. "The good thing is that we have a workable process, the Department of Defense has to consider how to mitigate and has the requirement to conduct technical analysis to explain their objection at a high level," says Vinson.
Government departments and agencies have also been exploring remedies through research programmes. The inter-agency Field Test & Evaluation assesses near-term and off-the-shelf solutions to mitigate the impact of turbines. Among technologies tested are Lockheed Martin's TPS-77 radar and Aveillant's Holographic Radar, which removes turbines from the display of tracking radar systems. While some technologies are promising, and the TPS-77 is installed in the UK, none has yet been certified for use in the US. Certification for new technology is proving difficult, says Vinson.
Other technologies in the pipeline include different forms of radar, stealth blades and using multiple sensors. It is unlikely that any will provide a "silver bullet", but real progress on the ground can only be made once constructive discussions take place over which mitigations to consider, how to integrate them and who will pay for them. And that requires political will.
