North Hoyle Windfarm Report

Executive Summary

Overview

The Maritime and Coastguard Agency (MCA) has responsibility, on behalf of the Department for Transport of the UK Government, for the safety of navigation under the International Convention for the Safety of Life at Sea (SOLAS), for the direction and co-ordination of search and rescue operations and for the prevention of marine pollution.

In this context MCA has been consulted by the Department for Transport, of which it is an executive agency, and the Department of Trade and Industry’s Offshore Renewables Consents Unit with respect to assessing all foreseeable marine safety risks associated with applications made by wind farm developers.

Since no large-scale off-shore wind farms existed in the United Kingdom until the North Hoyle site was developed, investigation into their potential effect on marine radar, communications and navigation systems was necessarily limited to desk top and laboratory research. The North Hoyle development therefore presented an opportunity for QinetiQ and MCA to carry out experimental field tests for the first time in the United Kingdom, the results of which would be used to inform the offshore wind farm consents process and those whose operations could be affected by resulting developments. MCA’s participation in this research was funded by the Department for Transport’s Shipping Policy Division.

MCA trials

MCA’s programme was intended to assess the effect of the wind farm structures on marine systems in operational scenarios. The trials assessed all practical communications systems used at sea and with links to shore stations, shipborne and shore-based radar, position fixing systems, and the Automatic Identification System (AIS). The tests also included basic navigational equipment such as magnetic compasses.

Theeffectsonthemajority ofsystemstestedbytheMCAwerefoundnottobesignificant enough to affect navigational efficiency or safety, and an on-going collection of data on such systems is expected prove these conclusions. This will be achieved by further trials, where seen to be necessary and through the collation of data observed by mariners.

Some reported effects, such as those on short range radio devices, will be further investigated as will some scenarios which could not be assessed during the trials period, such as helicopter search and rescue operations within wind farms.

The only significant cause for concern found by the MCA during the trials was the effect of wind farm structures on shipborne and shorebased radar systems. It was determined that the large vertical extent of the wind turbine generators returned radar responses strong enough to produce interfering side lobe, multiple and reflected echoes. While reducing receiver amplification (gain) would enable individual turbines to be clearly identified from the side lobes - and hence limit the potential of collisions with them - its effect would also be to reduce the amplitude of other received signals such that small vessels, buoys, etc., might not be detectable within or close to the wind farm. Mariners will require guidence on these potential effects. Bearing discrimination was also reduced by the magnitude of the response and hence the cross range size of displayed echoes. If on passage close to a wind farm boundary or within the wind farm itself, this could in some circumstances affect a vessel’s ability to fully comply with the International Regulations for the Prevention of Collisions at Sea. For full compliance, mariners will need to pay particular attention to the determination of a safe speed and to assessing risk of collision when passing near or through wind farms, particularly in restricted visibility. The cited Regulations are contained in Appendix C of which the relevant sections are Rule 6(b) (ii) (iii) (iv) and (v), Rule 7 (b) and (c), Rule 19 (a) (b) (c) and (d). It was also found that the performance of a vessel’s automatic radar plotting aid (ARPA) , referred to in Rule 7 (b) ,could be affected when tracking targets in or near the wind farm.

With respect to the multiple and reflected echoes produced when wind farm structures lie between the observing radar and a relatively high sided vessel, gain reduction will have similar effects to those described above. If, as in the trial undertaken, a shore or platform based radar is intended to detect and track traffic in port approaches, Vessel Traffic Services (VTS) or in the proximity of off-shore oil or gas installations, the effects could be significant.

QinetiQ trials

The QinetiQ trials were designed to test the theoretical results calculated in previous work [1]. The previous work had calculated the expected effects of the wind turbines at the North Hoyle wind farm on marine communications, GPS and radar systems. In this report the experimental tests carried out to validate the theoretical results [1] are described. This work has been funded by NPower Renewables Ltd.

Four trials, covering the areas of GPS, VHF communications and radar tracking and radar clutter were performed by QinetiQ.

The QinetiQ GPS trial involved traversing previously defined courses through and around the wind farm. Along each course, the number of satellites visible to two different GPS systems (a Garmin 152 and a Garmin GPSIII) and the position of the ship were recorded. Our results show that on average between 8 and 11 satellites were visible at any one time providing accurate positioning to within 5 metres.

The effect of wind turbines on VHF communications was investigated by QinetiQ using a hand-held VHF transceiver that was run in series with an adjustable attenuator. A link margin of 1 dB was achieved in free-space (away from any turbines). This required an attenuation of 16dB to be added to the transceiver.

To explore the shadow region behind the wind turbines, four link margins, 2dB, 3dB, 4dB and 5dB were used. These link margins correspond to a total attenuation of 15dB, 14dB, 13dB and 12dB added to the transceiver. The closest approach to turbine 21 was 500 metres and approximately 5m behind turbine 26. As expected the depth of shadow was greater when closer to a turbine. When behind turbine 21 the shadow was found to be approximately 2dB to 3dB lower than the attenuation needed to give a 1dB link margin in free space. For turbine 26 the shadow was deeper due to the closer proximity of the VHF system. It was found that behind turbine 26 the depth of shadow was approximately 10dB below the link margin in free space. The shadow depths are shallower than predicted theoretically confirming the worst case expectations of the theoretical work.

The QinetiQ radar shadowing trials provided very little evidence that shadowing of targets would present any significant problems. In particular the shadowing observed was, like the VHF trials, less than predicted in the theoretical study. Clutter in the radar display due to the presence of wind turbines was found to be quite considerable. Both ring-around and false plots were observed (referred to by mariners as side-lobe, multipleandreflected echoes). The observed problems could be suppressed successfully by using the gain and range settings of the radar. However, thismayhave the unwanted side-effect of no longer being able to detect some small targets.

Conclusions

The general findings were as follows:

i Global Positioning System (GPS)

No problems with basic GPS reception or positional accuracy were reported during the trials.

ii Magnetic compasses

The wind farm generators and their cabling, interturbine and onshore, did not cause any compass deviation during the MCA trials. As with any ferrous metal structure, however, caution should be exercised when using magnetic compasses close to turbine towers.

iii Loran C

Although a position could not be obtained using Loran C in the wind farm area, the available signals were received without apparent degradation.

iv Helicopter radar and communications systems

These trials were not carried out due to helicopter call-outs to emergencies on the trial days. The emergency services are keen that they should be undertaken when convenient. MCA will co-operate with RAF Valley and other emergency services to ensure that this is done.

v VHF and other communications

The wind farm structures had no noticeable effects on any voice communications system, vessel to vessel or vessel to shore station. These included shipborne, shorebased and hand held VHF transceivers and mobile telephones. Digital selective calling (DSC) was also satisfactorily tested. The VHF Direction Finding equipment carried in the lifeboats did not function correctly when very close to turbines (within about 50 metres) and the BHP telemetry or short range radio link to and from its deployed RIB (rigid inflatable boat) was similarly reported to suffer interruptions.

vi The Automatic Identification System (AIS) carried aboard MV "Norbay" and monitored by HM Coastguard MRSC Liverpool was fully operational.

vii Small Vessel radar performance.

1. The wind turbine generators (WTG) produced blind and shadow areas in which other turbines and vessels could not be detected unless the observing vessel was moving.
2. Detection of targets within the wind farm was also reduced by the cross and down-range responses from the WTGs which limited range and bearing discrimination.
3. The large displayed echoes of WTGs were due to the vertical extent of the turbine structures.
4. These returned strong responses from sectors of the main beam outside the half power (-3dB) points and the side lobes outside 10° from the main beam.
5. Although such spurious echo effects can be limited to some extent by reducing receiver amplification (gain) this will also reduce the amplification of other targets, perhaps below their display threshold levels.
6. Sea and rain clutter will present further difficulties to target detection within and close to wind farms. Weather conditions at the time of the trials were such that these effects could not be examined.

viii Shore based radar performance

Short range performance (less than 6 nm)
When a small shore based radar was sited such that the height of its antenna was about six metres above sea level, its performance with respect to small vessels was similar to that of the vessel-mounted systems in terms of range and bearing discrimination and target detection within the wind farm.

When moved to a height of 200 metres above sea level there was an improvement in range discrimination.

When the higher powered and narrower beam width BHP Billiton radar was used, at the same height, the visual detection of targets within, and beyond, the wind farm was again improved.

1. Larger vessel detection
   A larger vessel was easily detected within and beyond the wind farm. However, while it was broadside on to the direction of the shore radar, reflections from the turbines produced strong multiple echoes. At an oblique aspect to the radar, multiple echoes did not occur, but some reflected echoes were observed.
2. Long range radar (more than 12 nm)
   When the wind farm was observed at long range by the Mersey docks and Harbour Board radar the vessel was easily detected and tracked

ix Radar and ARPA carried on larger vessels

As with small vessel radars, range and bearing discrimination were affected by the response from the WTGs. Definition was less on S band radar than on X band. Numerous spurious echoes from side lobes and reflections were reported by MV "Norbay" starting at a range of about 1.5 nm. The ship’s ARPA had difficulty tracking a target vessel within the wind farm due to target swop to the stronger response. This substantiated a similar report with respect to the BHP Billiton radar’s own tracking system

x Non type-tested radar, communications and navigational equipment

The effects on such systems will be similar to those tested during the trials but will vary individually with respect to transmitted power, antenna performance, radar beam width, etc. The Royal Yachting Association is assisting MCA by providing ongoing information through the experiences of its membership.

With the exception of those noted in the next paragraph, most of the effects of offshore wind farm structures on the practical operation of marine radar, communications and navigation systems are not anticipated to significantly compromise marine navigation or safety. Where questions are raised about specific systems during the on-going collection of data they will, when possible, continue to be monitored and assessed.

There are however concerns about the use of both shipborne and shorebased radar as an effective aid to both vessel and mark detection and, consequently, for ship-to-ship collision avoidance in the proximity of wind farms. Wind farm structures generally have high vertical extents and therefore will return very strong responses when observing radars are close. The magnitude of such responses will vary according to transmitted radar power and proximity to the structures but can prevent both the visual detection of targets and the effective operation of automatic radar plotting aids (ARPA). These effects can be mitigated by vessels keeping well clear of wind farms in open water or, where navigation is restricted, keeping the wind farm boundaries at suitable distances from established traffic routes, port approaches, routing schemes, etc. Other technical solutions may be employed, particularly in port approaches.

For a particular wind farm these boundary distances should be determined in consultation with the Maritime and Coastguard Agency’s Southampton HQ in conjunction with other stakeholders and included in the Environmental Statement submitted with the consent application. A Department of Trade and Industry (DTI) funded navigational risk assessment project is about to be undertaken. This will produce a methodology for assessing navigational risk - and marine risk in general - in and around offshore wind farms. It is intended to be used by government agencies for the assessment and, where appropriate, acceptance of offshore wind farm applications, and for the guidance of developers in the preparation of such applications. Included in this will be recommendations on suitable distances of wind farm boundaries from traffic routes . In the meantime, a set of recommendations based on domain theory, and taking into account the above effects, has been produced as a draft working template by MCA.

With respect to shorebased or offshore platform based systems, the careful siting of radar scanners in relation to traffic routes and wind farm configurations should enable any degrading effects to be minimised. Again, the location or relocation of required radar systems and their funding should be determined in consultation with the relevant organisations, these data included in the Environmental Statement, and submitted with the consent application.

Further work needs to be done, as for example identified in the report with respect to adverse weather conditions, helicopter search and rescue operations, short range radio systems, non type-tested systems, etc. These should be carried out as soon as is practical.

Acknowledgements

Many individuals, companies and organisations took part in these trials. In particular the QinetiQ and the Maritime and Coastguard Agency would like to record their appreciation for the contributions of the following:

Broken Hill Proprietary Billiton Ltd., its staff and the crew of the "Clwyd"

The Chamber of Shipping

Denbridge Marine Ltd

The Environment Agency and its staff in Buckley, North Wales.

Mersey Docks and Harbour Board

NPower Renewables and the crews of "Celtic Wind" and "Fast Cat"

The P & O Steamship Company Ltd., and the officers of M.V."Norbay"

The Trinity House Lighthouse Service and its staff.

The Royal National Lifeboat Institution with the shore and sea crews of the Rhyl and Hoylake lifeboats.

Paul Frost 2nd Mechanic of Rhyl Lifeboat Station for video camera work

The Royal Yachting Association