AC

Alternating current, where the electrical current switches directions a fixed number of times per second (such as 60 times per second or 60 Hz)

Airfoil

The shape of the blade cross-section, which for most modern horizontal axis wind turbines, is designed to enhance the lift and improve turbine performance.

Ampere (A)

A measure of electric current; one A of current represents one coulomb of electrical charge moving past a specific point in one second (1 C/s = 1 A).

Ampere-hour

A unit of for the quantity of electricity obtained by integrating current flow in amperes over the time in hours for its flow; used as a measure of battery capacity.

Anemometer

A device to measure the wind speed.

Annual energy output (AEO)

The total energy produced by a wind turbine over the course of a year.

Average wind speed

The mean wind speed over a specified period of time.

Blades

The aerodynamic surface that catches the wind.

Brake

Various systems used to stop the rotor from turning.

Converter

See Inverter.

Cut-in wind speed

The wind speed at which a wind turbine begins to generate electricity.

Cut-out wind speed

The wind speed at which a wind turbine ceases to generate electricity.

DC

direct current

Density

Mass per unit of volume.

DOD

Depth of discharge

Downwind

On the opposite side from the direction from which the wind is blowing.

Furling

A passive protection for the turbine where typically the rotor folds either up or around the tail vane.

Generator set (genset)

Machine using an internal combustion engine (gasoline or diesel) and generator to produce AC or DC electricity.

Grid

The utility distribution system. The network that connects electricity generators to electricity users.

HAWT

Horizontal axis wind turbine.

Inverter

A device that converts direct current (DC) to alternating current (AC).

kW

Kilowatt, a measure of power for electrical current (1,000 watts).

kWh

Kilowatt-hour, a measure of energy equal to the use of one kilowatt in one hour.

MW

Megawatt, a measure of power (1,000,000 W or 1,000 kW).

Nacelle

The body/shell/casing of a propeller-type wind turbine, covering the gearbox, generator, blade hub, and other parts.

O&M Costs

Operation and maintenance costs.

Photovoltaics (PV)

The direct conversion of sunlight into electricity.

Power Coefficient

The ratio of the power extracted by a wind turbine to the power available in the wind stream.

Power curve

A chart showing a wind turbine's power output across a range of wind speeds.

PUC

Public Utility Commission, a state agency which regulates utilities. In some areas known as Public Service Commission (PSC).

Rated output capacity

The output power of a wind machine operating at the rated wind speed.

Rated wind speed

The lowest wind speed at which the rated output power of a wind turbine is produced.

Rotor

The rotating part of a wind turbine, including either the blades and blade assembly or the rotating portion of a generator.

Rotor diameter

The diameter of the circle swept by the rotor.

Rotor speed

The revolutions per minute of the wind turbine rotor.

Start-up wind speed

The wind speed at which a wind turbine rotor will begin to spin. See also cut-in wind speed.

Swept area

The area swept by the turbine rotor, A = π R 2 , where R is the radius of the rotor.

Tip speed ratio

The speed at the tip of the rotor blade as it moves through the air divided by the wind velocity. This is typically a design requirement for the turbine.

Turbulence

The changes in wind speed and direction, frequently caused by obstacles.

Upwind

On the same side as the direction from which the wind is blowing—windward.

VAWT

Vertical axis wind turbine.

W

watt, a measure of power for electrical current (1,000 watts = 1 kW).

Wind farm

A group of wind turbines, often owned and maintained by one company. Also known as a wind power plant.

Yaw

The movement of the tower top turbine that allows the turbine to stay into the wind.