Wind Energy

Wind power captures the natural wind in our atmosphere and converts it into mechanical energy, then into electricity. Wind power started with windmills, which pumped water, ground grain and did other work. Today’s wind turbine typically has three blades, sit atop a steel tower and range in height from 35 feet to over 300 feet tall.

Watch Energy 101: Wind Turbines

Wind Definitions

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.

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).

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 some wind turbines automatically stop the blades from turning and rotates out of the wind to avoid damage to the turbine, typically around 55 to 65 miles per hour.

Furling – The act of a wind generator yawing out of the wind, either horizontally or vertically, to protect itself from high wind speeds.

Horizontal Axis Wind Turbine (HAWT) – 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.

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.

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.

Power Curve – A graphic displaying the instantaneous power output of a specific turbine design at various wind speeds; used with the 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.

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.

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.

Vertical Axis Wind Turbine (VAWT) – 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.

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 Assessment – The process of characterizing the wind resource and its energy potential for a site of geographical area.

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 Vane – A device used to measure wind direction.

Yaw – The rotation of a horizontal axis wind turbine about its tower or vertical axis.

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