Glossary of Wind Energy Terms

aggregation — Bundling several wind energy projects together so that they are treated as one larger project (when purchasing turbines, interconnecting, or maintaining a project, for example,) in order to spread out costs over more turbines or projects. This can have the effect of improving project economics.

airfoil — The cross section profile of the leeward side of a wind generator blade. Designed to give 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 the blade in a wind turbine.

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 commission due to maintenance or repairs.

balancing — With wind turbine blades, adjusting their weight and weight distribution through 2 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 — A measure of the productivity of a wind turbine, calculated by the amount of power that a wind turbine produces over a set period of time, divided by the amount of power that would have been produced if the turbine had been running at full capacity during that same time interval.

chord — The width of a wind turbine blade at a given location along the length.

commercial scale wind — Wind energy projects greater than 100 kW where the electricity is sold rather than used on-site. This category can include large arrays of 100 or more turbines owned by large corporations, a single locally-owned wind turbine greater than 100 kW in size, or anything in between.

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 other 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 at which the turbine automatically stops the blades from turning and rotates out of the wind to avoid damage to the turbine, usually around 55 to 65 miles per hour.

distributed generation —A small-scale power generation technology that provides electric power at a site closer to customers than the central station 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.

grid-connected system — A residential electrical system such as solar panels or wind turbines which are connected to the electrical grid. In such systems the grid serves as a battery backup for the residential system for those times when there is no sun or wind.

guy anchor — A concrete or metal base which attaches windtower guy wires securely to the earth.

guy wire — A strong metal cable or wire which attaches a tower to the ground.

horizontal axis wind turbine —A "normal" wind turbine design, in which the shaft 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.

hybrid system — The combination of  multiple energy producing technologies such as photovoltaic systems combined with small wind turbine systems.

inverter — A device that converts direct current electricity to alternating current either for stand-alone systems or to supply power to an electricity grid.

met Tower — A 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. 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 that houses the key components of the wind turbine, including the rotor shaft, gearbox, and generator.

power curve — 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— The result of the Energy Policy Act of 1992, a commercial tax credit that applies to whole-sale electrical generators of wind energy facilities based upon the amount of energy generated in a year.

rated wind speed — The wind speed at which the turbine is producing its nameplate-rated power production.  For most small wind turbines this is around 30 to 35 miles per hour.

rotor — Comprises the spinning parts of a wind turbine, including the turbine blades and the hub.

start-up speed — The windspeed at which a wind turbine rotor starts to rotate. It does not necessarily produce any power until it reaches cut-in speed.

tail boom — A strut that holds the tail (Vane) to the wind generator frame.

thrust bearing — A bearing that is designed to handle axial forces along the centerline of the shaft--in a wind generator, this 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.

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 where the rotating shaft 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).

waveform — The shape of the phase power at a certain frequency and amplitude.

wind monitoring system — Also termed met tower, a 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 Powering America (WPA) — A U.S. Department of Energy initiative designed to promote the use of wind energy across the country, with the goal of quadrupling U.S. wind capacity by 2010.

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 rose — A circular plot used to define 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. But informally used as a synonym for wind generator or wind turbine, and to describe machines that pump water with wind power.

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