Wind Power Glossary

An explanation of technical terms used in the wind power industry and on these pages

The author of these pages is not beholden to any company, lobby group, or government. *

Created about 2008/03/01, last edited 2023/09/27
Contact: David K. Clarke – ©

Also see Energy Units, an explanation of some energy units, definitions, and conversions – or Google search Ramblings

Wind power pages...

Wind power in Australia
 Wind farms in NSW
 Wind farms in Qld
 Wind farms in SA
 Wind farms in Victoria
 Wind farms in Tasmania
 Wind farms in WA
Wind news
Wind power potential in Oz
Wind power problems

Wind farm photo pages...

Canunda/Lake Bonney
Mount Millar
Starfish Hill
Wattle Point

Some of these definitions were taken from ReNew, the quarterly journal of the Alternative Technology Association
16 point compass rose To describe the location of wind farms, in relation to well known towns and cities, I have used the 16 point compass rose. In this system, north-east (NE) is the direction half way between north and east (45° 'true') and nor-nor-east (NNE) is the direction half way between north and north-east (22.5° true), etc.
Putting it another way, starting at north and moving clockwise we have: N, NNE, NE, ENE, E, ESE, SE, SSE, S, SSW, SW, WSW, W, WNW, NW, NNW, and back to N.
AEMO The Australian Energy Market Operator "delivers an array of gas and electricity market, operational, development and planning functions". The data the AEMO provide on power generation are difficult to make use of. AEMO replaced NEMMCO.
ALG Australian landscape guardians (ALG), a group opposed to wind power and apparently not much concerned about any other 'threats to Australian landscapes'. They have connections to the Waubra Foundation, the mining industry, and the right wing think tank the Institute of Public Affairs and its misleadingly named off-shoot the Australian Environment Foundation.
Amp or Ampere The SI unit of electric current; the symbol is A or I. Compare to volt.
Anemometer A device used to measure wind speed
Annual production As used in these pages, the annual average energy production of a particular wind farm. Generally measured in GWh.
Attenuation (of sound) Air absorbs some energy from sound waves (this is on top of the reduction in sound energy due to the inverse-square-law). Higher frequencies are attenuated much more than lower frequencies; thus the sound of a nearby lightning strike is a sharp 'crack', while distant thunder is a low rumble. The rate of attenuation will be greater if there is dust or mist in the air. A calculator for attenuation of sound in air is at Tontechnik-Rechner.
Availability The percentage of time that the particular power station, wind farm, or wind turbine, is in an operational condition.
Axial-flow turbine A turbine in which the air moves in the direction of the axis of rotation of the turbine. All utility scale wind turbines in Australia are axial flow. Compare to cross-flow turbine.
Base load A base-load power station is one that can provide the load that is always present on a power grid; base-load can be supplied by generators such as nuclear and coal-fired power stations. A base-load power station cannot necessarily quickly change its rate of generation to follow the varying demand on a power grid. Base load power should be compared to much more valuable peaking power, which is available on demand, and variable power, such as wind and solar PV, available only when the wind blows or the light is bright.

See also Timing of wind power generation. Wikipedia base load.

In mid 2017 there had been much ignorant referencing of base load; I wrote a dedicated page on the subject.
Betz Limit The maximum theoretical power that can be captured by a wind turbine from the wind. Equal to 59.3% of the energy in the wind.
The part of a turbine that air reacts against to cause the turbine to spin. Most electricity-generating turbines have two or three blades (all utility-scale turbines in Australia have three), whereas water-pumping wind turbines – the traditional windmills – will usually have around 20.
Capacity factor Sometimes called load factor; the percentage of potential generation that is actually achieved. (See also Wind is variable.) For example; A wind farm consisting of ten 2 MW turbines could theoretically generate 175 200 MWh of electricity per year (10×2×24×365=175 200) if all the turbines were to work at 100% of their capacity 100% of the time. In practice turbines do not work at full capacity all the time (no power generation system does) and such a wind farm in Australia would probably generate around 60 000MWh per year (a capacity factor of 34%). See also notes on actual capacity factors in Australian wind farms.

A typical capacity factor for a small photovoltaic system in Australia, for comparison, is around 18%. The capacity factor concept used for wind farms is very similar to the load factor used in electrical engineering.

Cross-flow turbine A turbine where the flow of air is at right angles to the axis of rotation of the turbine. Also see vertical axis turbine and compare to axial-flow turbine.
Current The rate at which electricity flows in a conductor. Analogous to the volume of water flowing through a pipe. Measured in Amperes, or Amps. (A current of one Amp implies a flow of 6.25 E18 electrons per second past a point.) Compare to volt.
Darrieus rotor or turbine A form of vertical-axis wind turbine that uses thin blades; Wikipedia.
dB, Decibel The decibel is a unit of sound volume, or more accurately, sound pressure. The decibel scale is logarithmic, so 40dB is ten times as 'loud' as 30dB, 50dB is ten times as loud as 40dB and 100 times as loud as 30dB, etc. (Also see dB(A), below.)
Sound volume, as perceived by humans, is dependent of the pitch of the sound. A sound reading shown as dB(A), or dBA, indicates that the scale is adjusted to match human perception. The dB(A) scale adjusts absolute dB readings of sound levels from very low frequency sounds, infrasound, downward because of this human perception. So an infrasound level of, say 110dB on the absolute scale, would be adjusted to something well below 110 on the dB(A) scale.
Diameter When applied to a wind turbine it is the diameter of the area swept by the turbine blades: the diameter of the Swept area. The blade length will be less than half of the diameter.
Dispatchability This term is used in the electricity supply industry to describe how readily power generation is increased or decreased to follow changes in demand. Some forms of gas-fired generators are the most dispatchable (flexible), coal-fired generators are only slowly varied, while nuclear is usually run at a constant rate. Output from wind and solar PV installations are normally entirely dependent on how much wind there is or the brightness of the light.

Many forms of generation (or forms of energy storage) can be varied, but there is an economic compromise between producing the maximum amount of power as often as posible or producing a smaller amount of power when prices are higher. See also base load.

Distributed generation technology Small-scale power generation or storage technologies (typically in the range of 1 kW to 10,000 kW) used to provide an alternative to or an enhancement of the traditional electric power system with large power stations that may be remote from the energy markets.

Compare to Utility-scale, or centralised power generation.

Efficiency of wind turbines The Betz Limit gives a theoretical maximum to wind turbine efficiency of 59.3%. The efficiency of wind turbines varies greatly – must vary greatly – depending on wind speed; it is discussed in more depth elsewhere on these pages.
Energy Energy in physics is the capacity for doing work. Compare to Power. In the SI metric units energy is measured in Watt-hours (Wh), kilowatt-hour (kWh), etc. As examples, an amount of energy is used to pump a quantity of water from a low place to a high place; an amount of energy is required to move a vehicle from point A to point B; an amount of energy is required to boil a litre of water. Also see Units of energy. Many people, even in the energy business, confuse power and energy.
Energy return on investment Defined as the ratio between the useful energy got out of a process against the energy needed for that process; in simple terms, energy out against energy in.
EPC Engineering, Procurement and Construction; refers to the major sections in the setting-up of a wind farm.
ESIPC (SA) The Electricity Supply Industry Planning Council has been established to monitor the electricity supply industry in South Australia. At 1 July 2009 ESIPC became a part of AEMO.
Exawatt-hour, EWh A unit of energy equal to one billion billion (1018) Watt-hours. Also see Metric system multipliers.
Expected life A wind turbine and a wind farm has a limited life expectancy. Parts wear out and, in a fast developing field such as wind power, machinery becomes out-dated. Underground electrical cabling deteriorates with time. Some parts can be replaced as they wear or fail, but there comes a time when the most economic option is to replace, or scrap, the whole wind farm. We in Australia must be careful that failed turbines never litter our ridge-lines.
Footing The footing is the base, usually concrete, that secures the turbine in place. This is sometimes called the foundation, but that term is more accurately applied to the geological formation around the footing. There are two main types of wind turbine footings. If a turbine is built on bed-rock it can make use of rock anchors to secure a relatively small concrete footing (about 220 tonnes for a 2MW turbine) to the underlying bed-rock. If there is no shallow bed-rock, or the bed-rock is shattered, then heavier footings (gravity footings: about 800 tonnes for a 2MW turbine), that are capable of holding the turbine in place without any attachment to underlying materials, must be used.
Furling A method of preventing damage to horizontal-axis wind turbines by automatically turning them out of the wind using a spring-loaded tail or other device. Utility-scale wind turbines do not use such devices; they are computer-controlled.
Gigawatt, GW A unit of power equal to one billion (109) Watts. Also see Metric system multipliers.
Greenhouse gas saving
The amount of carbon dioxide that would have been released into the atmosphere by a fossil fuel fired power station had the particular wind farm not been generating power. Every MWh of electricity generated by a wind farm replaces a MWh that would have been generated by some other means. In the case of a coal fired power station around one tonne of carbon dioxide is released into the atmosphere for every MWh or electricity generated. See CO2 abatement for more information.
Greenhouse intensity
FuelKg CO2
Natural gas0.45
Black coal0.8
Brown coal1.2
Alternatively Carbon intensity. A measure of the amount of greenhouse gas released into the atmosphere in relation to the amount of useful energy (usually electricity) produced. Some typical values for common fossil fuels, in kilograms of CO2 released per kWh of power generated, are given in the table on the right.

The higher the number for greenhouse intensity, the 'dirtier' the fuel is considered to be in relation to climate change.

The greenhouse intensity of wind power is less than 0.05.

(Also see Carbon intensity.)

Gigawatt-hour, GWh A unit of energy equal to one billion (109) Watt-hours. Also see Metric system multipliers.
HVDC High voltage direct current is used to transmit large amounts of power over long distances; there are smaller power losses and the construction cost of a HVDC line is less than that of a more conventional high voltage alternating current line. HVDC could be used to advantage for some of the longer transmission lines in Australia, especially if full use it to be made of Australia's great wind power potential. Also see Wikipedia.
Horizontal-axis turbine The most common form of wind turbine, in which the axis is parallel to the direction of the wind. Another name for a axial-flow turbine.
Hub The section which connects the turbine blades to the main shaft. At construction it is usually attached to the blades at the base of the turbine tower and then the whole assembly is lifted in one piece.
Infrasound According to the International Electrotechnical Commission's (IEC's) IEC 1994, infrasound is: Acoustic oscillations whose frequency is below the low frequency limit of audible sound (about 16 Hz). However this definition is incomplete as infrasound at high enough levels is audible at frequencies below 16 Hz. Infrasound in relation to health is discussed elsewhere on this site. Also see Wind turbine noise: Infrasound.
Installed capacity The amount of electricity that will be generated by a wind farm when all its turbines are generating at their full capacity.
Inverse square law This physical law has been known since the seventeenth century and applies to things like gravitation, electrostatics, light and sound. It describes how the strength of something such as sound decreases with the distance from the source; putting it simply, doubling the distance from the source causes the strength (loudness) to decrease to a quarter, trebling the distance reduces the strength to a ninth, four times the distance a sixteenth the strength, etc.

The inverse square law applies to anything that radiates from a distinct source.

Katabatic wind A cold wind that flows downhill and is powered by gravity. The term is generally used for winds that blow off the Antarctic Plateau toward the coast, although it could also be applied to gully winds.
kilowatt, kW A unit of power equal to one thousand Watts. Also see Metric system multipliers.
kilowatt-hour, kWh A unit of energy equal to one thousand Watt-hours. One kWh is sufficient to heat about 11 litres of water from room temperature (20°) to boiling point, or to run a 20 Watt light bulb for 50 hours. Also see Metric system multipliers.
Load factor An electrical engineering term very similar to capacity factor.
Latitude Distance south of the equator expressed in degrees. In these pages I have used decimal degrees rather than degrees, minutes and seconds because I believe the latter to be archaic: as pounds, shillings and pence are archaic currency.
Longitude Distance east of the Prime Meridian expressed in degrees. See also latitude, above.
Minimum operational wind speed
The lightest breeze that a particular turbine can use. See also Productive wind speeds and wind speed range of turbines.
Minimum wind speed for full output The lightest wind sufficient for a particular turbine to produce its maximum rated electricity generation. Also see wind speed range of turbines.
MRET Mandatory Renewable Energy Target; (as of March 2015 Australia's MRET is in question because of the Abbott government's opposition to renewable energy).
Megawatt, MW A unit of power equal to one million Watts. One MW is enough power for around 430 electric kettles (2300W) or 45 000 compact fluorescent light bulbs (22W each). Also see Metric system multipliers.
Megawatt-hour, MWh A unit of energy equal to one thousand kWh one million Watt-hours. Also see Metric system multipliers.
Nacelle That part of the turbine that houses the gearbox (not all wind turbines have a gearbox), electrical generator, cooling system etcetera, at the top of the tower.
NEMMCO The National Electricity Market Management Company is the market operator of the National Electricity Market (NEM) and the system operator of the national grid. Has been replaced by AEMO.
Nocebo effect The placebo effect is a beneficial effect produced by a placebo drug or treatment, which cannot be attributed to the properties of the placebo itself, and must therefore be due to the patient's belief in that treatment. The Nocebo effect is the opposite, it is when negative expectations cause real symptoms. The Skeptic's Dictionary has a fuller explanation. Also see The link between health complaints and wind turbines: support for the nocebo expectations hypothesis; Fiona Crichton, Simon Chapman, Tim Cundy, Keith J. Petrie; 2014/11/11.
Peak load Peak load (or peak demand) is that time when the demand for electricity is at its greatest. In Australia it tends to come at around 6pm on exceptionally hot days, when many people are coming home from work, switching on air conditioners, and preparing dinner. It is important because it is the time when both the electrical generation system and transmission system is under greatest stress. They are largely designed with the aim of coping as well as possible with peak demand. The wide-spread take-up of household solar PV power has tended to make the time of peak load come later in the day than previously.
Peaking power Peaking power, dispatchable power, or 'on demand' power is power that can be made available as required, such as power from hydro, pumped hydro, or batteries. It should be compared to base load base load power (from inflexible genertion sources) and variable power (from sources such as wind, solar, tidal, and wave generators).
Petawatt-hour, PWh A unit of energy equal to one million billion (1015) Watt-hours. Also see Metric system multipliers.
Power Compare to energy. Power is a flow of energy; an amount of energy per unit time. In the SI metric units, it is measured in Watts (W), kilowatts (kW), etc. Also see Units of Power. As examples, an amount of power is required to push a car at a given speed (under specific conditions) and an amount of power is required to run an electric jug. Many people, even in the energy business, confuse power and energy.
Power purchase agreement
The operator of a wind farm makes an agreement to sell power to a distributor of electricity. This is a Power purchase agreement. In these pages I have usually given only the name of the distributor who has agreed to purchase the power against this phrase.
Price elasticity of electricity demand A measure of how electricity demand responds to changes in the price of electricity. For example the AEMO in 2011 estimated the price elasticity in South Australia "to be -0.25, with slightly less than half this applying to peak demand (that is, a 4% real rise in prices is expected to lead to a 1% reduction in sales and a 0.5% reduction in peak demands)".
Productive wind speeds That range of wind speeds that are useable by a particular wind turbine for electricity generation. The power available from wind is proportional to cube of the wind's speed: double the speed, eight times the energy. So as the speed of the wind falls the amount of energy that can be got from it falls very rapidly. On the other hand, as the wind speed rises, so the amount of energy in it rises very rapidly; very high wind speeds can overload a turbine. Productive wind speeds for a modern turbine might be from around 5m/sec to 30m/sec (18km/hr to 108km/hr). See also Survival wind speed.
Renewable energy Energy that is produced from a renewable source, such as sunlight, flows of wind or water, or sustainably grown plants.
Rock anchor If suitable rock is situated beneath the turbine footing steel rods are used to anchor the turbine and footing to the underlying bedrock, reducing the amount of concrete that would otherwise be necessary. If there is no bedrock within a few metres of the surface, or if the bedrock is highly weathered or fractured, then gravity footing are needed.
Rotor The blades and hub at the centre of the blades - the part that rotates in front of the Nacelle.
Rotor diameter The diameter of the circle swept-out by the tips of the turbine's blades.
Savonius turbine or rotor A type of vertical-axis turbine that uses half-drum shaped 'blades' to catch the wind and turn a shaft. Generally a low-speed turbine with high torque, usually used for water pumping.
Shut down wind speed The maximum wind speed at which a particular turbine can generate electricity. With higher wind speeds the turbine must be shut-down to avoid damage.
SOO; Statement of opportunities, NEMMCO
NEMMCO state that "The SOO is intended to assist existing and potential National Electricity Market (NEM) participants when assessing the future need for:
- electricity supply capacity;
- demand-side participation (DSP); and
- transmission network augmentation in support of NEM operations.
The SOO incorporates the Annual National Transmission Statement (ANTS). The SOO is published each year in October and can be downloaded from the NEMMCO Net site.
Spinning reserve In order to assure electrical supply it is necessary to keep some generation plant (usually fossil-fuelled) running, but not generating, so that it will be able to be brought into production at short notice. (The need for spinning reserve would be greatly reduced by introducing Supply Dependent Load, which is discussed in my Sustainable Electricity page.)
Survival wind speed The maximum wind speed that a turbine is designed to withstand before sustaining damage. See also Productive wind speeds
Swept circle and swept area The circle through which the turbine blades rotate and the area of that circle.
Terawatt-hour, TWh A unit of energy. One TWh is a million-million Watt-hours. Also see Metric system multipliers.
Tip-speed ratio The ratio of the blade tip speed to wind speed
Turbine A device that converts the energy in a stream of moving fluid into mechanical energy.
Turbulence Airflow that varies in speed and direction rapidly and violently that can cause damage to wind turbines. Often caused by objects such as trees or buildings.
Utility-scale power generators Very large facilities; possibly distant from the energy markets, aimed at interacting with a power grid. Compare to distributed generation technology.
Variable power Power from renewable sources such as wind, solar PV, wave and tide is available at varying rates, depending on the strength of the light, the brightness of the light, etcetera. Is should be compared with inflexible base load power and peaking power that is available on demand.
Vertical-axis turbine A wind turbine with the axis or main shaft mounted vertically. This type of turbine does not have to turn to face the wind. Types include the Darrieus and Savonius.
Volt, voltage The volt is the SI unit of electric potential. Voltage is analogous to the pressure of water in a pipe. Compare to Amp and current.
Watt The basic SI metric unit of power; equal to one Joule of work performed per second; also, in electricity, the power dissipated in an electrical conductor carrying one ampere current between points at one volt potential difference. Also see Units of power.
Watt-hour, Wh A unit of energy, generally electrical energy, equal to a flow of power of one Watt for a period of one hour.
Wind farm An integrated group of wind turbines that feed electricity into one or more electrical sub-stations and thence, usually, into the electricity grid.
Wind turbine A turbine designed to convert the energy in a stream of moving air into mechanical, and then electrical, energy.

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