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Renewable Energy Glossary

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Ambient NoiseThe average noise level over a given period of time, usually composed of sound from many sources, near and far.
AnemometerEquipment fixed on a mast to measure wind speed over a particular site. Anemometry masts are usually slender structures fixed to the ground with guy wires.
Background Noise LevelA measurement of the noise level already present within the environment in the absence of wind energy development operation.
BermAn extended mound of soils, overburden or structure erected as a barrier to sight, sound or water.
Blade SwishThe modulation of broadband noise at turbine blade passing frequency.
Borrow PitAn area of excavation of rock and/or soil material that is used elsewhere within the site development boundaries.
Cut-In Wind SpeedThe cut-in speed is when the turbine blades start rotating and generating power.
dB (Decibel)Measurement of sound, the scale in which sound pressure level is expressed. When measuring environmental noise, a weighting network is used which filters the frequency of sound, and is expressed as dB(A).
dB(A)(A Weighted Decibel)An 'A-weighted decibel' is a measure of the overall noise level of sound across the audible frequency range (20Hz20kHz) with A- frequency weighting (i.e., 'A' weighting) to compensate for the varying sensitivity of the human ear to sound at different frequencies. The decibel scale is logarithmic. Every 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.
Energy Yield Describes the electrical output from a wind energy project. It is closely related to wind speed; the higher the wind speed, the greater the energy yield.
Hertz (Hz)Unit of frequency of sound, in cycles per second. Frequency determines pitch of sound.
Hub HeightHeight of wind turbine tower from the ground to the centre-line of the turbine rotor.
ImpactDegree of change in an environment resulting from a development.
InfrasoundInfrasound occurs naturally in the environment (e.g. wind sound effects) and is generated by many human activities and the operation of many types of machines (e.g. motor cars, washing machines etc. Infrasound generally occurs at frequencies below the normal range of human hearing , less than 20Hz.
LA90TA-weighted sound pressure level (in decibels, dB) obtained using 'Fast' time-weighting that is exceeded for 90% of the given time interval (T), e.g. for background noise level. The given time interval is ten minutes for LA90.
LAeq,TLAeq,T is the equivalent continuous sound level . It is a type of average and is used to describe fluctuation noise in terms of a single noise level over the sample period (T).
Megawatts and KilowattsUsed as a measurement of electrical generating capacity. A megawatt (MW) is equal to 1,000 kilowatts (kW) or 1,000,000 watts (W).
NacelleThis contains the key mechanical components of the wind turbine including the gearbox and generator. A yaw mechanism is employed to turn the nacelle so that the rotor blades face the prevailing wind.
NoiseAny sound that has the potential to cause disturbance, discomfort or psychological stress to a subject exposed to it. Described as 'unwanted sound'.
Noise Sensitive LocationIn the case of wind energy development, this 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.
PhotomontageA visualisation which superimposes an image of a proposed development upon a photograph or series of photographs.
Shadow FlickerA term used to describe the short-lived effect of shadows cast by rotating blades of wind turbines when the sun passes behind them, which occurs under certain combinations of geographical positions and time of day.
SubstationConnects the local electricity network to the electrical system of the wind energy project through a series of automatic safety switches.
Stall-Regulated TurbineIn a stall-regulated wind turbine when wind speeds are high, the rotational speed and power production decreases with increasing wind speed above a certain value.
TowerThe supporting vertical structure of a wind turbine.
Visual Absorption Capability (VAC)VAC is a classification system used to indicate the ability of any landscape to accept human alteration without loss of character.
Viewshed Reference Points (VRPs)Those locations from where visibility of the proposed wind energy development might be provided.
Yaw DriveA yaw drive is a horizontal mechanical component of a wind turbine which ensures the blades are facing towards the wind.
Zone of Theoretical Visibility (ZTV) ZTV is a computer-generated tool to identify the likely (or theoretical) extent of visibility of a development.
Zone of Visual Influence (ZVI) The determination of the visibility of an object within the surrounding landscape.

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