Glossary

  • aggregation — Bundling several wind energy projects together so that they are treated as one larger project (for example, when purchasing turbines, interconnecting or maintaining a project) to distribute costs among more turbines or projects.  This practice can improve project economics.
  • airfoil — The cross section profile of the leeward side of a wind generator blade, designed to provide low drag and good lift. Also found on an airplane wing.
  • anemometer — An instrument used to measure the velocity, or speed, of the wind.
  • angle of attack — The angle of relative air flow to a wind turbine’s blade.
  • armature — The moving part of an alternator, generator or motor. In many alternator designs, it carries the magnets and is attached to the blades and hub. Also called a Rotor.
  • availability factor — The percentage of time that a wind turbine is able to operate and is not out of commission due to maintenance or repairs.
  • average capacity (also known as capacity factor) — A measure of a wind turbine’s productivity, calculated by the amount of power that a wind turbine produces over a set time period, divided by the amount of power that would have been produced if the turbine had operated at full capacity during that same time interval.
  • average wind speed (velocity) — The mean wind speed over a specified period of time.
  • balancing — Adjusting wind turbine blades’ weight and weight distribution through two axes so that all blades are the same. Unbalanced blades create damaging vibration.
  • Betz Coefficient — 59.3 percent. This is the theoretical maximum efficiency at which a wind generator can operate, by slowing the wind down.  If the wind generator slows the wind down too much, air piles up in front of the blades and is not used for extracting energy.
  • blades — The flat panels on a wind turbine that are connected to a center shaft that converts the push of the wind into a circular motion in a wind turbine.
  • braking system — A device to slow a wind turbine’s shaft speed down to safe levels (electrically or mechanically).
  • capacity factor — see average capacity.
  • chord — The width of a wind turbine blade at a given location along the length.
  • commercial scale wind — Wind energy projects greater than 100 kilowatts in which the electricity is sold rather than used on-site. This category includes large arrays of 100 or more turbines owned by large corporations and a single locally-owned wind turbine greater than 100 kilowatts in size.
  • community wind —Locally-owned, commercial-scale wind projects that optimize local benefits. Locally-owned means that one or more members of the local community has a significant direct financial stake in the project other than through land-lease payments, tax revenue, or payments in lieu of taxes.
  • cut-in speed — The wind speed at which the turbine blades begin to rotate and produce electricity, typically around 10 miles per hour.
  • cut-out speed — The wind speed, usually around 55 to 65 miles per hour, at which some wind turbines automatically stop the blades from turning and rotates out of the wind to avoid damage to the turbine.
  • distributed generation — A small-scale power generation technology that provides electric power at a site closer to customers than central power plant generation. The term is commonly used to indicate non-utility sources of electricity, including facilities for self-generation.
  • downwind turbine — Refers to a horizontal-axis wind turbine in which the hub and blades point away from the wind direction; the opposite of an upwind turbine.
  • furling — The act of a wind generator yawing out of the wind, either horizontally or vertically, to protect itself from high wind speeds.
  • gigawatt — A unit of power equal to 1 billion Watts, 1 million kilowatts, or 1,000 megawatts.
  • green pricing — A practice utilized by some power providers in which electricity produced from clean, renewable resources is sold at a higher cost than electricity produced from conventional fuels to buyers willing to pay a premium for clean power.
  • grid — An electricity transmission and distribution system.
  • grid-connected system — A residential electrical system, such as solar panels or wind turbines, which is connected to the electric utility system. The utility system serves as a backup source of electricity if the residential system is not producing power.
  • guy anchor — A concrete or metal base that secures wind tower guy wires to the earth.
  • guy wire — A strong metal cable or wire that attaches some towers (typically those of small residential wind turbines) to the ground.
  • horizontal axis wind turbine — A wind turbine design in which the shaft (axis of rotation) is parallel to the ground and the blades are perpendicular to the ground.
  • hub — The central part of the wind turbine, which supports the turbine blades on the outside and connects to the low-speed rotor shaft inside the nacelle.
  • hub height — Measuring from the ground, the tower height of the hub, or central part of a horizontal-axis wind turbine.
  • hybrid system — The combination of multiple energy-producing technologies such as photovoltaic solar electric systems combined with small wind turbine systems.
  • independent power producer — An electricity generator that sells electricity but is not owned by a utility.
  • installed capacity — The total capacity of electrical generation devices in a system. Learn more about the installed capacity of wind energy in the United States here.
  • inverter — A device that converts direct current electricity to alternating current, either for stand-alone systems or to supply power to an electric utility system.
  • Investment Tax Credit — A tax credit granted for specific investment types, such as investment in wind projects.
  • investor-owned utility (IOU) — A power provider owned by stockholders or other investors rather than government agencies or cooperatives.
  • kilowatt — A standard unit of electrical power, equal to 1,000 Watts.
  • kilowatt-hour A unit or measure of electricity supply or consumption of 1,000 Watts for a period of 1 hour.
  • megawatt — A standard measure of electric power plant generating capacity equal to 1,000 kilowatts or 1 million watts.
  • met tower — A tower with a group of instruments (including anemometers and wind vanes) attached that collectively measure various meteorological parameters such as wind speed, wind direction, and temperature at various heights above the ground. The term met is short for meteorological.
  • nacelle — The structure at the top of the wind turbine tower just behind (or, in some cases, in front of) the wind turbine blades. It houses the key components of the wind turbine, including the rotor shaft, gearbox and generator.
  • net metering — Measuring both consumption and generation of electricity by a small generation facility (such as a small wind system). The net energy produced or consumed is purchased from or sold to the power provider.
  • payback period — The amount of time required for the savings resulting from a renewable energy system to equal the system cost.
  • peak wind speed — The maximum instantaneous wind speed (or velocity) that occurs within a specific time period.
  • power curve — A graphic displaying the instantaneous power output of a specific turbine design at various wind speeds; used with wind resource data to determine the potential for electricity generation at a project site.
  • Production Tax Credit (PTC) — A provision included in the Energy Policy Act of 1992: a commercial tax credit that applies to wholesale electrical generators of wind energy facilities based on the amount of energy generated.
  • renewable energy certificates — Also known as green tags, certificates representing the environmental attributes of power produced from renewable resources. By separating the environmental attributes from the power, clean power generators are able to sell the electricity they produce to power providers at a competitive market value. The additional revenue generated by the sale of the certificates can be applied to the above-market costs associated with producing power made from renewable energy sources.
  • Public Utilities Regulatory Policy Act (PURPA) — A 1978 law that requires electric utilities to purchase electricity produced from qualifying power producers that use renewable energy resources or are co-generators.
  • rated wind speed — The wind speed at which a wind turbine reaches its nameplate-rated level of power production. For most small wind turbines, this is around 30 to 35 miles per hour.
  • rotor — The visible spinning parts of a wind turbine, including the turbine blades and the hub.
  • start-up speed — The wind speed at which a wind turbine rotor starts to rotate. The turbine does not necessarily produce any power until the wind reaches cut-in speed.
  • thrust bearing — A bearing that is designed to handle axial forces along the centerline of the shaft; in a wind generator, the axial force is the force of the wind pushing back against the blades.
  • tower — The base structure that supports and elevates a wind turbine rotor and nacelle.
  • turbine — A device for converting the flow of a fluid (air, steam, water or hot gases) into mechanical motion that can be utilized to produce electricity.
  • twist — In a wind generator blade, the difference in pitch between the blade root and the blade tip. Generally, the twist allows more pitch at the blade root for easier startup and less pitch at the tip for better high-speed performance.
  • utility-scale wind — Wind energy projects greater than 100 kilowatts in capacity in which the electricity is sold rather than used on-site. This category includes large arrays of turbines owned by corporations and a single locally-owned wind turbine greater than 100 kilowatts in size.
  • vane — A large, flat piece of material used to align a wind turbine rotor correctly into the wind. Usually mounted vertically on the tail boom. Sometimes called a tail.
  • variable pitch turbine — A type of wind turbine rotor where the attack angle of the blades can be adjusted either automatically or manually.
  • vertical axis wind turbine — A wind generator design in which the rotating shaft (axis of rotation) is perpendicular to the ground and the cups or blades rotate parallel to the ground.
  • watt — The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).
  • watt-hour — A unit of electricity supply or consumption of one Watt over the period of one hour.
  • waveform — The shape of the phase power at a certain frequency and amplitude.
  • wind monitoring system — An instrument or group of instruments (including anemometers and wind vanes) that collectively measure various meteorological parameters, such as wind speed, wind direction and temperature at various heights above the ground.
  • wind power class — A system designed to rate the quality of the wind resource in an area, based on the average annual wind speed. The scale ranges from 1 to 7 with 1 being the poorest wind energy resources and 7 representing exceptional wind energy resources.
  • wind resource — The wind energy available for use based on historical wind data, topographic features and other parameters.
  • wind resource assesment — The process of characterizing the wind resource and its energy potential for a site of geographical area. Wind resource maps for the U.S. are available here.
  • wind rose — A circular plot used to portray certain characteristics about wind speed and direction observed at a monitoring location.
  • wind shear — A term and calculation used to describe how wind speed increases with height above the surface of the earth. The degree of wind shear is a factor of the complexity of the terrain as well as the actual heights measured. Wind shear increases as friction between the wind and the ground becomes greater. Wind shear is not a measure of the wind speed at a site.
  • wind speed — The rate at which air particles move through the atmosphere, commonly measured with an anemometer.
  • wind vane — A device used to measure wind direction.
  • windmill — A device that uses wind power to mill grain into flour. Informally used as a synonym for wind generator or wind turbine, and to describe machines that pump water with wind power.
  • yaw — The rotation of a horizontal-axis wind turbine about its tower or vertical axis

AWEA has prepared a Wind Energy Acronyms guide (PDF 107 KB).