Ministerial guidelines
Wind Energy Development Guidelines
Siting, design, noise and shadow flicker for wind farms. A revised draft was published for consultation in 2019.
Department of the Environment, Heritage and Local Government · June 2006 · 119 pages
Ask this document
Answers come only from the text of Wind Energy Development Guidelines, each claim linked to its page. They are not advice; check the page itself.
Free, with a daily limit.
- 25 Planning Guidelines 5.2.1 Habitats Habitats that may be impacted by wind energy developments include peatlands (mainly blanket bog, heaths, flushes and various other wetland habitats including water courses and lakes), sand dune systems, including machair, semi-natural grasslands and woodlands. All are vulnerable, but those located in the uplands are particularly so owing to their location in high rainfall areas and where the growing season is short. The main potential impacts on habitats that can result in the reduction, or loss, of biodiversity are: • Direct loss of habitat to the developments’ infrastructure, including turbine foundations, buildings, roads, quarries and borrow pits; • Degradation of habitats through alteration or disturbance, in particular arising from changes to hydrology that may alter the surface or groundwater flows and levels, and drainage patterns critical in peatlands and river headwaters; • Fragmentation of habitats and increased edge effects; and • Degradation and loss of habitats outside the development site, especially wetland habitats that may arise from pollution, siltation and erosion originating from within the development site. 5.2.2 Species Birds The extent to which birds will be impacted by wind energy developments will vary depending on species, season and location, and these impacts may be temporary or permanent. Those species groups considered to be most at risk are raptors, Swans, Geese, Divers, breeding waders and concentrations of waterfowl. Potential impacts on migratory birds and local bird movements between breeding, feeding and roosting areas require careful consideration.
- 26lanning Guidelines The main potential impacts to birds from wind energy developments have been identified as: • Disturbance during the construction and operational phases leading to the temporary or permanent displacement of birds from the development site and its environs; • Collision mortality, although studies have shown this to be low risk; • Barrier to movement, although studies have indicated that the response by birds to wind energy development may be variable and related to species and/or season; and • Direct loss or degradation of habitats for breeding, feeding and/or roosting purposes, particularly in wetland sites. Other Species The potential impact on other rare flora, mammals, birds, and amphibians and fish including those listed for protection in the Flora (Protection Order), 1999, would also need to be assessed. 5.3 Ground Conditions/Geology In assessing wind energy developments, the underlying geology is a critical factor. Information on the following issues must be submitted as part of a planning application to enable the planning authority to adequately assess the impact of the proposed wind energy development and any mitigating measures proposed to counter the impacts: • A geological assessment of the locality; • A geotechnical assessment of the overburden and bedrock; • A landslide and slope stability risk assessment for the site for all stages of the project, with proposed mitigation measures where appropriate (this should also consider the possible effects of storage of excavated material);
- 27 Planning Guidelines • An assessment of whether the development could create a bog burst or landslide hazard; • Location of the site in relation to any area or site that has been identified by the Geological Survey of Ireland as a geological Natural Heritage Area, a proposed Natural Heritage Area or as a County Geological Site. (If so, are there any impacts discussed, or mitigation measures proposed); • Location of the site in relation to areas of significant mineral or aggregate potential; • An assessment of any potential impacts of the development on groundwater, and • Details of any borrow-pits proposed on site should be shown on the planning application and details given where blasting is proposed, such as on the avoidance and remediation of land slippage. Provision must be made for carrying out site-specific geo-technical investigations in order to identify the optimum location for each turbine. These investigations may suggest minor adjustments to turbine location. In order to accommodate this practice there should be a degree of flexibility built into the planning permission and EIS. The extent of flexibility will be site specific but should not generally extend beyond 20 metres. Any further changes in location beyond the agreed limits would require planning permission. In order to ensure that the above issues have been fully addressed, a developer should consult with the Geological Survey of Ireland and obtain professional advice/source reports from suitably qualified geotechnical engineers, engineering geologists or geologists as appropriate. If upland sites are proposed, the application should be accompanied by a statement from a geologist, a hydro-geologist or an engineer with expertise in soil mechanics.
- 28lanning Guidelines 5.4 Archaeology The potential impact of the proposed wind energy development on the archaeological heritage of the site should be assessed. The assessment should address direct impacts on the integrity and visual amenity of monuments and include appropriate mitigation measures, such as through a desktop study and a field inspection where necessary. 5.5 Architectural Heritage The planning authority should assess the potential impact of the proposed wind energy development on the architectural heritage of the locality and its landscape context, where relevant. This is particularly necessary in the case of structures included in the Register of Protected Structures. 5.6 Noise There are two distinct noise sources associated with the operation of wind turbines; aerodynamic noise caused by blades passing through the air, and mechanical noise created by the operation of mechanical elements in the nacelle - the generator, gearbox and other parts of the drive-train. Aerodynamic noise is a function of many interacting factors including blade design, rotational speed, wind speed and inflow turbulence; it is generally broadband in nature and can display some “character” (swish). Mechanical noise from a wind turbine is tonal in nature. Advances in turbine technology and design have resulted in reduced noise emissions. Aerodynamic refinements that have combined to make turbines quieter include the change from lattice to tubular towers, the use of variable speed operations, and the switch to 3 blade turbine designs. Improvements in gearbox design and the use of anti-vibration techniques in the past ten years have resulted in significant reductions in mechanical noise. The most recent direct drive machines have no high-speed mechanical components and therefore do not produce mechanical noise.
- 29 Planning Guidelines Turbine noise increases as wind speeds increase, but at a slower rate than wind generated background noise increases. The impact of wind energy development noise is therefore likely to be greater at low wind speeds when the difference between noise of the wind energy development and the background noise is likely to be greater. Wind turbines do not operate below the wind speed referred to as cut-in speed, usually around 5 metres per second. Larger and variable speed wind turbines emit lower noise levels at cut-in speed than smaller fixed speed turbines. Noise from wind turbines is radiated more in some directions than others, with areas down-wind experiencing the highest predicted noise levels. At higher wind speeds noise from wind has the effect of largely masking wind turbine noise. Good acoustical design and carefully considered siting of turbines is essential to ensure that there is no significant increase in ambient noise levels at any nearby noise sensitive locations. Sound output from modern wind turbines can be regulated, thus mitigating noise problems, albeit with some loss of power. An appropriate balance must be achieved between power generation and noise impact. Noise impact should be assessed by reference to the nature and character of noise sensitive locations. In the case of wind energy development, a noise sensitive location includes any occupied dwelling house, hostel, health building or place of worship and may include areas of particular scenic quality or special recreational amenity importance. Noise limits should apply only to those areas frequently used for relaxation or activities for which a quiet environment is highly desirable. Noise limits should be applied to external locations, and should reflect the variation in both turbine source noise and background noise with wind speed. The descriptor9, which allows reliable measurements to be made without corruption from relatively loud transitory noise events from other 9 LA90, 10mm
- 30lanning Guidelines sources, should be used for assessing both the wind energy development noise and background noise. Any existing turbines should not be considered as part of the prevailing background noise. In general, a lower fixed limit of 45 dB(A)10 or a maximum increase of 5dB(A) above background noise at nearby noise sensitive locations is considered appropriate to provide protection to wind energy development neighbours. However, in very quiet areas, the use of a margin of 5dB(A) above background noise at nearby noise sensitive properties is not necessary to offer a reasonable degree of protection and may unduly restrict wind energy developments which should be recognised as having wider national and global benefits. Instead, in low noise environments where background noise is less than 30 dB(A), it is recommended that the daytime level of the LA90, 10min of the wind energy development noise be limited to an absolute level within the range of 35-40 dB(A). Separate noise limits should apply for day-time and for nighttime. During the night the protection of external amenity becomes less important and the emphasis should be on preventing sleep disturbance. A fixed limit of 43dB(A) will protect sleep inside properties during the night. In general, noise is unlikely to be a significant problem where the distance from the nearest turbine to any noise sensitive property is more than 500 metres. Planning authorities may seek evidence that the type(s) of turbines proposed will use best current engineering practice in terms of noise creation and suppression. 10 An ‘A-weighted decibel’ - a measure of the overall noise level of sound across the audible frequency range (20Hz-20 kHz) with A- frequency weighting to compensate for the varying sensitivity of the human ear to sound at different frequencies. The decibel scale is logarithmic. A 10 dB(A) increase in sound level represents a doubling of loudness. A change of 3 dB(A) is the minimum perceptible under normal circumstances.
- 31 Planning Guidelines 5.7 Safety Aspects There are no specific safety considerations in relation to the operation of wind turbines. Fencing or other restrictions are not necessary for safety considerations. People or animals can safely walk up to the base of the turbines. There is a very remote possibility of injury to people or animals from flying fragments of ice or from a damaged blade. Most blades are composite structures with no bolts or separate components and the danger is minimised as a result. The build up of ice on turbine blades is unlikely to present problems. Most wind turbines are fitted with anti-vibration sensors, which will detect any imbalance caused by the icing of the blades. The sensors will cause the turbine to wait until the blades have been de-iced prior to beginning operation. 5.8 Proximity to Roads and Railways In general, turbines may distract motorists when they are being constructed or when they are new. Over time the turbines become part of the landscape and in general do not cause any significant distraction to motorists. The provision of appropriately sited laybys for viewing purposes can help reduce distraction by giving an opportunity to view the wind energy development in safety; lay-by size should be adequate to cater for tour buses. Although wind turbines erected in accordance with standard engineering practice are stable structures, best practice indicates that it is advisable to achieve a safety set back from National and Regional roads and railways of a distance equal to the height of the turbine and blade. 5.9 Proximity to Power Lines Adequate clearance between structures and overhead power lines as specified by the electricity undertaker should be provided. It should be noted that there is a statutory obligation to notify the electricity distributor of proposed developments within 23 meters of any transmission or distribution line.
- 32lanning Guidelines 5.10 Interference with Communication Systems Wind turbines, like all electrical equipment, produce electromagnetic radiation, and this can interfere with broadcast communications. The interference with broadcast communication can be overcome by the installation of deflectors or repeaters. Planning authorities should advise the developer to contact the individual broadcasters, both national and local, and inform them of the proposals. A list of the licensed operators is available on the ComReg website at www.comreg.ie. Mobile phone operators should also be advised of the proposed development. 5.11 Aircraft Safety The siting of wind turbines may have implications for the operations of the Communications, Navigation and Surveillance systems used for Air Traffic Control for the separation and safety of aircraft. Wind turbine siting may also have implications for the flight paths of aircraft. Regard must be had to the Irish Aviation Authority's Obstacles to Aircraft in Flight Order, 2002, (S.I. 14 of 2002), as amended, which specifies the criteria used to determine whether or not any object anywhere in the State is deemed to be an obstacle affecting aircraft operations. In addition, in order to assure the safety and efficiency of aircraft operations in the vicinity of airports, the International Civil Aviation Organisation (ICAO) has defined a volume of air space above which new objects are not permitted. No part of the wind turbine should penetrate these defined surfaces. Accordingly, wind energy developers should be advised to contact the Irish Aviation Authority at the pre-planning stage of consultation, with details of locations and proposed heights of turbines, to ensure that the proposed development will not cause difficulties with air navigation safety.
- 33 Planning Guidelines 5.12 Shadow Flicker Wind turbines, like other tall structures, can cast long shadows when the sun is low in the sky. The effect known as shadow flicker occurs where the blades of a wind turbine cast a shadow over a window in a nearby house and the rotation of the blades causes the shadow to flick on and off. This effect lasts only for a short period and happens only in certain specific combined circumstances, such as when: • the sun is shining and is at a low angle (after dawn and before sunset), and • the turbine is directly between the sun and the affected property, and • there is enough wind energy to ensure that the turbine blades are moving. Careful site selection, design and planning, and good use of relevant software, can help avoid the possibility of shadow flicker in the first instance. It is recommended that shadow flicker at neighbouring offices and dwellings within 500m should not exceed 30 hours per year or 30 minutes per day11 . At distances greater than 10 rotor diameters from a turbine, the potential for shadow flicker is very low. Where shadow flicker could be a problem, developers should provide calculations to quantify the effect and where appropriate take measures to prevent or ameliorate the potential effect, such as by turning off a particular turbine at certain times. 11 The shadow flicker recommendations are based on research by Predac, a European Union sponsored organisation promoting best practice in energy use and supply which draws on experience from Belgium, Denmark, France, the Netherlands and Germany.
- 34lanning Guidelines 5.13 Windtake The question of windtake should be dealt with at scoping stage and/or during pre-application discussions, to ensure that any proposed layout of wind turbines takes into account the development potential of an adjoining site for a similar development. In general, to ensure optimal performance and to account for turbulence and wake effects, the minimum distances between wind turbines will generally be three times the rotor diameter (=3d) in the crosswind direction and seven times the rotor diameter (=7d) in the prevailing downwind direction. Bearing in mind the requirements for optimal performance, a distance of not less than two rotor blades from adjoining property boundaries will generally be acceptable, unless by written agreement of adjoining landowners to a lesser distance. However, where permission for wind energy development has been granted on an adjacent site, the principle of the minimum separation distances between turbines in crosswind and downwind directions indicated above should be respected. 5.14 Decommissioning and Reinstatement The decommissioning of a wind energy development once electricity ceases to be generated must be assessed. Plans for decommissioning should be outlined at the planning stage. Issues to be addressed include restorative measures, the removal of above ground structures and equipment, landscaping and/or reseeding roads. It may be appropriate to allow tracks to remain, e.g., as part of a walking route after decommissioning.
Source Department of the Environment, Heritage and Local Government: Wind Energy Development Guidelines (June 2006) · Licence the publisher's termsText read from the publisher’s PDF; tables, maps and drawings do not survive as text, and page numbers are the PDF’s (its first page is 1). Check the original before relying on a passage.