Common terms used in distributed and community wind energy.

– A –

Airfoil
A shaped surface, such as an airplane wing or wind turbine blade, that produces lift and drag when moved through the air. See also blade

Alternator
An electric generator for producing alternating current. See also generator

Ambient
Of the surrounding area or environment; completely surrounding; encompassing. Used to distinguish environmental conditions–e.g., temperature or sound–from what is added by mechanical devices.

Anemometer
A device to measure wind speed. See also wind vane

Applicant
One applying for permission, typically used in the context of a building permit or utility connection permit.

Authority Having Jurisdiction (AHJ)
The building authority for the area, generally a city or county building department, including its inspectors.

Availability
A measure of the ability of a wind turbine to make power, regardless of environmental conditions. Generally defined as the time in a period when a turbine is able to make power, expressed as a percentage.

 

– B –

Behind-the-meter / behind-the-fence generation
An electrical generating system connected on the user’s side of a utility meter, primarily for energy usage on site instead of for sale to energy retailers. See also net metering

Betz limit
The maximum power coefficient (Cp) of a theoretically perfect wind turbine equal to 16/27 (59.3%) as proven by German physicist Albert Betz in 1919. This is the maximum amount of power that can be captured from the wind.  In reality, this limit is never achieved because of drag, electrical losses, and mechanical inefficiencies. See also Cp

Blade 
An aerodynamic surface that catches the wind. See also, airfoil, rotor

Building-mounted wind energy systems 
Wind turbines mounted on buildings.
– C –

Certification
A process by which materials or equipment are accredited by an independent body to conform to specified standards. A number of types of certification exist for wind turbines. For additional information, refer to DWEA Certification links at https://distributedwind.org/zoning-resource-center/.

Corrosivity
A measure of oxidation and/or material degradation.

Cp
Power coefficient; the ratio of the power extracted from the wind by a wind turbine relative to the power available in the wind. See also Betz limit

Cut-in wind speed
The wind speed at which a wind turbine begins to produce net positive power output.

Cut-out wind speed
The wind speed at which a wind turbine control system stops or slows the rotor, or otherwise curtails power output, in order to protect the system in high winds.

– D –

Decommissioning
The process of deactivating, removing, or retiring a piece of equipment from active service.

Direct drive   
A blade and generator configuration where the blades are connected directly to the electrical generating device so that one revolution of the rotor equates to one revolution of the electrical generating device.

Distributed generation         
Energy generation projects where electrical energy is generated primarily for on-site consumption.  Term is applied for wind, solar, and non-renewable energy.

Downwind
Describes a point downstream of another point in an airstream.

Downwind rotor
A horizontal-axis wind turbine with a propeller that is located downwind of the tower; a wind turbine with an architecture such that the wind flow passes the tower prior to flowing through the propeller.

Drag
An aerodynamic force that acts in the direction of the airstream flowing over an airfoil.

 
– E –

Electric utility company
A company that engages in the generation, transmission, and distribution of electricity for sale, generally in a regulated market. Electric utilities may be investor owned, publicly owned, cooperatives, or nationalized entities.

Energy production
Energy is power exerted over time. Energy production is hence the energy produced in a specific period of time. Electrical energy is generally measured in kilowatt-hours (kWh). See also power

Environmental conditions
Of or pertaining to ambient state of the environment. See also temperature, wind, humidity, corrosivity

-F-

FAA regulations
Rules prescribed by the Federal Aviation Administration (FAA) governing aviation activities in the United States.

Feed-in tariff
An economic policy created to promote active investment in renewable energy sources. Feed-in tariffs typically make use of long-term agreements and pricing tied to costs of production for renewable energy producers.

 

– G –

Gearbox
A compact, enclosed unit of gears or the like for the purpose of transferring force between machines or mechanisms, often with changes of torque and speed. In wind turbines, gearboxes are used to increase the low rotational speed of the turbine rotor to a higher speed required by many electrical generators.

Generator
A machine that converts mechanical energy to electricity. The mechanical power for an electric generator is usually obtained from a rotating shaft. In a wind turbine, the mechanical power comes from the wind causing the blades on a rotor to rotate. Generators that use permanent magnets to provide the magnetic field used to create electrical current are called permanent magnet generators, PMGs. See also blade, rotor, stator, alternator

Governor
A device used to limit the RPM of the rotor.  Limiting RPM serves to reduce centrifugal forces acting on the wind turbine and rotor as well as limit the electrical output of the generating device.  Governors can be electrical, also known as “dynamic braking,” or mechanical.  Mechanical governors can be “passive,” using springs to pitch the blades out of their ideal orientation, or an offset rotor that pitches out of the wind, or “active” by electrically or hydraulically pitching blades out of their ideal orientation.

Grid-connected        
Energy generating systems that are connected to the electricity distribution system. Wind turbines often require a power-conditioning unit that makes their output electrically compatible with the utility grid. See also inverter

Guyline
A guyline (or guy wire) support guyed towers, which are the least expensive way to support a wind turbine. Guyed towers can consist of lattice sections, pipe, or tubing. Because the guy radius must be one-half to three-quarters of the tower height, guyed towers require more space to accommodate them than monopole or self-standing lattice towers.

– H –

Horizontal-axis wind turbine (HAWT)
 A wind turbine with a rotor axis that lies in or close to a horizontal plane. Often called a “propeller-style” wind turbine.

Hub    
That component of a wind turbine to which the blades are affixed. See also rotor, blade

Hub Height
The distance from the foundation to which the tower is attached to the center of the hub of a HAWT.

Humidity
A measure of moisture content in the air.

 

– I –

Induction generator
An asynchronous AC motor designed for use as a generator.  Generates electricity by being spun faster than the motor’s standard “synchronous” speed.  Must be connected to an already-powered circuit to function (i.e. the grid), but does not require an inverter to produce grid-ready electricity when driven at constant speed.

Interconnection standards
Specifies the technical and procedural process by which a customer connects an electricity-generating device to the grid. Such standards include the technical and contractual terms that system owners and utilities must abide by. State public utility commissions typically establish standards for interconnection to the distribution grid, while the Federal Energy Regulatory Commission (FERC) establishes standards for interconnection to the transmission grid. While many states have adopted interconnection standards, some states’ standards apply only to investor-owned utilities and not to municipal utilities or electric cooperatives.

Intermittency
Stopping or ceasing for a time; alternately ceasing and beginning again. Wind and solar resources are described as intermittent because they change without regard to peoples’ needs or wants.

International Electrotechnical Commission (IEC) 
The international wind-industry standards body.
 

– K –

Kilowatt (kW)
A measure of power. Utility customers sometimes pay a demand charge for the maximum power they demand during a period in addition to the energy they pay for. See also peak power

Kilowatt hour (kWh)
A measure of energy. Utility customers are generally charged for the kilowatt hours that they consume. See also energy production

 

 

– L –

Lattice
A structure of crossed wooden or metal strips usually arranged to form a diagonal pattern of open spaces between the strips. Lattice towers, either guyed or freestanding, are often used to support small wind turbines.

Lift
An aerodynamic force that acts at right angles to the airstream flowing over an airfoil.

 

– M –

Monopole      
A freestanding type of tower that is essentially a tube, often tapered.

 

– N –

Nacelle          
The enclosed part of a wind turbine that houses the generator and often a gearbox or power converter.

Nameplate capacity
The power capacity of a generating device that is typically affixed to the generating device.  Nameplate capacity typically, but not necessarily, represents the maximum continuous power output of the generating device.

National Electrical Code (NEC)
Also known as National Fire Protection Association document NFPA 70, is the standard for the safe design, installation, and inspection of electrical wiring and equipment in the United States. Currently adopted in all 50 states.

Net metering / net billing
For electric customers who generate their own electricity, net metering allows for the flow of electricity both to and from the customer. When a customer’s generation exceeds the customer’s use, electricity from the customer flows back to the grid, offsetting electricity consumed by the customer at a different time during the same billing cycle. In effect, the customer uses excess generation to offset electricity that the customer otherwise would have to purchase at the utility’s full retail rate. Net metering is required by law in most U.S. states, but state policies vary widely. See also behind-the-meter

Noise
Generally defined as unwanted sound. Sound power is measured in decibels, dB. Building and planning authorities often regulate sound power levels from facilities. See also sound, electrical noise

– O –

Obstruction   
A general term for any significant object that would disturb wind flow passing through a turbine rotor.  Most common examples are homes, buildings, trees, silos, and fences.  Topographical features such as hills or cliffs that might also affect wind flow are not called obstructions.

Off-grid          
Energy-generating systems that are not interconnected directly into an electrical grid. Energy produced in these systems is often used for battery charging.

Overall height
The total height of a wind turbine from its base at grade to its uppermost extent. See also total height

Overhead power lines
Structures used in electric power transmission and distribution to transmit electrical energy.

– P –

Peak power
The maximum instantaneous power than can be produced by a power-generating system or consumed by a load. Peak power may be significantly higher than average power.

Power curve  
A graph that shows how much power a wind turbine produces over a given set of wind speeds.  When matched with a wind distribution (which describes how many hours the wind blows at each speed per year at that location), can be used to estimate how much energy will be produced by the turbine annually.

Prevailing wind         
The most common direction or directions that the wind comes from at a site. Prevailing wind usually refers to the amount of time the wind blows from that particular direction but may also refer to the direction the wind with the greatest power density comes from.

– R –

Rated power output
Generally, the nameplate rating of an electrical generating device. Small wind turbines in the United States define rated output as the power output at a constant hub-height wind speed of 11 m/s (25 mph).

 
– S –

Setback
In zoning parlance, the distance required between a structure and another structure, property line, utility easement or other demarcation.

Small wind energy system
A wind energy conversion system consisting of a wind turbine, tower, and associated control or conversion electronics, which has a rated power output of 100 kW or less.

Sound
Pressure waves occurring at a frequency in the audible range of human hearing that are registered as sensory input by the ear, measured in decibels (dB or dBA). See also noise

Stator
The stationary part of a rotary machine or device, especially a generator or motor. Most especially related to the collection of stationary parts in its magnetic circuits. The stator and rotor interact to generate electricity in a generator and to turn the driveshaft in a motor.

Swept area
The projected area perpendicular to the wind direction that a wind turbine rotor will describe during one complete rotation. The swept area limits the amount of wind intercepted by the turbine. See also rotor diameter
– T –

Temperature
A measure of thermal energy. See also ambient

Total height  
The height of the wind system from the top of the foundation to which the tower is attached to the tip of a blade extended upwards. See also overall height

Tower
A structure designed to support a wind turbine at a substantial height above grade in a wind flow. Typical types include monopole, guyed lattice, and self-supporting lattice designs.

 

– U –

Upwind          
Describes a point upstream of another point in an airstream.

Upwind rotor
A horizontal-axis wind turbine whose propeller is located upwind of the tower; a wind turbine with an architecture such that the wind flow passes through the propeller prior to flowing past the tower.

 

– V –

Vertical-axis wind turbine (VAWT)
A wind turbine whose rotor spins about a vertical or near-vertical axis.

 

– W –

Wet stamp
Refers to a specific engineering review of a specific plan or set of drawings by an in-state licensed engineer who subsequently approves the plan or drawings with his/her stamp. A wet stamp implies an original stamped document, not a copy.

Wind
The movement of an air mass.

Wind rose
A visual means of representing the frequency with which the wind blows from different directions.

Wind turbine 
A mechanical device that converts kinetic energy in the wind into electrical energy.

Wind vane
A device to measure wind direction. See also anemometer.

Source: DWEA Permitting and Zoning Committee

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