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 named after the French physicist André-Marie Ampère (1775-1836); 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.

Angle of inclination

Is the angle between the solar cell and the horizontal. According to degree of latitude of the installation location of the solar power plant, there is a different optimum angle of inclination.

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.

Battery array

An array is composed of a number of electrical storage devices (batteries) inter-connected either in parallel or series in order to achieve the desired potential difference or current. Batteries do not make electricity, they only store electricity.

Betz limit

In 1919, a German physicist, Albert Betz, calculated that there's a limit to how much power a turbine blade can extract from the wind. If a wind turbine's performance of wind energy extract exceeds the Betz Limit of 59.26% energy extraction, more and more air tends to go around the turbine rather than through it, with air pooling up in front the turbine. In other words, the wind will consider the turbine as an obstacle and will tend to go around the turbine, thus, rendering the turbine an ineffective wind energy device. In theory, if 100% of the wind energy were extracted from the wind, the wind would simply stop.

Blades

The aerodynamic surface that catches the wind.

BOS

The Balance of System or the components beyond the "front-end" energy generation comprised of wind turbine(s) and or photovoltaic systems required to complete the renewable energy technology solution. The BOS components typically include inverter(s), rectifer(s), DC-panels, AC-panels, controllers, resistive load diversion, isolation switches, etc. dependent upon the architecture of the RETS deployed.

Brake

Various systems used to stop the rotor from turning.

Charge controller

A component of a renewable energy system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge. The charge controller may also indicate the system operational status.

Converter

See Inverter.

Coriolis Force

Effect of the earth's rotation tending to turn the direction of motion of any object or fluid toward the right in the Northern Hemisphere and the left in the Southern Hemisphere.

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.

Diode

A solid-state device that allows electricity to flow in only one direction.

DOD

Depth of discharge

Downwind

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

Electric field

The effect produced by the existence of an electric charge, such as an electron, ion, or proton, in the volume of space or medium that surrounds it.

Electron

An electron is a negatively charged subatomic particle. It can be either free (not attached to any atom), or bound to the nucleus of an atom. Electrons in atoms exist in spherical shells of various radii, representing energy levels. The larger the spherical shell, the higher the energy contained in the electron.

Electromagentic energy/radiation

Radiation made up of oscillating electric and magnetic fields and propagated with the speed of light. Includes gamma radiation, X-rays, ultraviolet, visible, and infrared radiation, and radar and radio waves.

Freewheeling

A wind generator that is NOT connected to a Load is freewheeling, and in danger of self-destruction from overspeeding.

Front-end

This refers to the "visible" renewable energy generating facilities including the wind turbine(s), solar modules, solar thermal or bio-mass.

Furling

A passive protection for the turbine where typically the rotor folds either up or around the tail vane, or yawing out of the wind either horizontally or vertically to protect itself from high wind speeds.

Generator set (genset)

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

Greenhouse effect

A term used to describe the heating of the atmosphere owing to the presence of carbon dioxide and other gases.

Greenhouse gases (GHG)

GHG are gaseous components of the atmosphere that contribute to the greenhouse effect. The major natural greenhouse gases are water vapor, which causes about 36-70% of the greenhouse effect on Earth (not including clouds); carbon dioxide, which causes between 9-26%; and ozone, which causes between 3-7%. Other greenhouse gases include, but are not limited to: methane, nitrous oxide, sulfur hexafluoride, and chlorofluorocarbons.

Grid

The energy distribution network. The network that connects electricity generators to electricity users.

Grid-interactive

A grid-tied configuration that uses "grid interactive" inverters will match the phase and voltage delivered by the grid, and which allows the current to flow through a bi-directionally registering utility meter allowing the RETS user to not only export power to the grid, but which can also draw energy from the grid should the need arise. A configuration that utilizes "net metering" is said to be "grid-tied".

Grid-noninteractive

A configuration that uses both the renewable energy generated and the power utility to service the power needs of the client. This configuration does not feed excess power generated into the utility and therefore, will require a voltaged resistive diversion load to dissipate the excess power generated.

Guy anchor

The guy anchor is a foundation designed to secure a tower's guy wire connection to the earth.

Guy cable

Is the cable or wire used as a tension support between a guy anchor and a tower in order to stabilize the tower and to maintain its vertical aspect in wind.

Guy tower

Is a tower that requires the use of external guy supports in order to maintain its vertical aspect.

HAWT

Horizontal axis wind turbine in which the rotors rotate in a plane perpendicular to the ground, on a horizontal axis.

Hub

The component to which the rotor blades are attached. The hub is then attached to the horizontal shaft of the wind turbine extending into the nacelle to the generator.

Induction generator

A device which converts the mechanical energy produced by the wind turbine into useable electrical energy by alternating the direction of a magnetic field around an iron core, induces the flow of electrons (current).

Insolation

A measure of the solar energy incident on a given area over a specific period of time. Usually expressed in kilowatt-hours per square metre per day or indicated in peak sun hours.

Inverter

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

Joule

One joule is defined as the amount of work or energy exerted when a force of one newton is applied over a displacement of one metre. One joule is the equivalent energy of one watt of power radiated or dissipated for one second. The joule was named after the British physicist James Prescott Joule (1818-1889).

Kinetic energy

The energy possessed by a moving object, in this case, the wind. The formula for kinetic energy is 1/2 (mass) x (velocity)².

kW

Kilowatt, a measure of power for electrical current (1,000 watts). Kilowatt is calculated by the product of current (amperage) and voltage (potential difference) resulting in the formula P = I x V where P = power (watts); I = current (amps); V = voltage (volts).

kWh

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

Laminar wind

Airflow free of turbulence, that is to say, free of any eddying motion - a smooth stream.

Magnetic declination

The magnetic declination at any point on the Earth is the angle between the local magnetic field -- the direction the north end of a compass points -- and true north. To calculate magnetic declination, use the NRCan's Magnetic Declination Calculator.

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.

Net metering

Net Metering is a program whereby eligible customers with specific generation facilities can reduce their net energy costs by exporting surplus generated energy back onto the utility distribution system for credit against the energy the customer consumes from the distribution system. Click Net Metering to read an article describing its details.

O&M Costs

Operation and maintenance costs.

Ohm (Ω )

One ohm is the resistance that requires a potential difference of one volt per ampere of current. The amount of the current depends on the potential difference and the resistance to the flow of current. This property of a circuit, the electric resistance, is measured in ohms. The unit was name after the German physicist Georg Simon Ohm (1787-1854).

Open circuit voltage (Voc)

The maximum possible voltage across a solar module or array. Open circuit voltage occurs in sunlight when no current is flowing.

Orientation

Position with respect to the cardinal directions, N, S, E, W.

Peak power (Wp)

The amount of power a solar cell module can be expected to deliver at noon on a sunny day (i.e. at Standard Test Conditions) when it is facing directly towards the sun.

Photon

A particle/wave composed of light and other forms of electromagnetic radiation, sometimes called light quantum. The photon has no charge and no mass.

Photovoltaic (PV)

The direct conversion of sunlight into electricity. photo = light, volt = electricity. Abbreviation: PV

Pitch

The angle at which the wind strikes the blades of the rotor. By changing the angle, the rotor can experience "stalling" in high winds in order to protect the turbine from excessive wind speed.

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.

Rectifier

An electrical circuit used to convert AC into DC current. A rectifier is a diode that causes the current to flow in only one direction. The output of the rectifier is essentially half-AC current, which is then filtered into DC.

RETS

Renewable Energy Technology Solutions.

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.

Solar array

A collection of solar modules, typically roof-mounted or a top-of-pole mount.

Solar cell

A semiconductor device that converts the energy of sunlight into electric energy. Also called a "photovoltaic cell" or PVC.

Solar constant

The power density of solar radiation on a plane perpendicular to the direction of the sun at the mean earth-sun distance outside the earth's atmosphere; its value is 1.37 kW per square meter.

Solar module

An electrical device consisting of a large array of connected solar cells used to convert light from the sun directly into DC electricity by using the photovoltaic effect. Usually made of multiple solar cells bonded between glass and a backing material. A typical Solar Module would be 100 Watts of power output (but module powers can range from 1 Watt to 300 Watts) and have dimensions of 2 feet by 4 feet.

Solar tracker

A mounting rack for a PV array that automatically tilts to follow the daily path of the sun through the sky. A "tracking array" will produce more energy through the course of the day, than a "fixed array" (non-tracking) particularly during the long days of summer.

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, the most common variant is the Darrieus configuration which looks like a vertical "egg-beater". For more details and photos on VAWT, visit What Are Vertical-Axis Wind Turbines (VAWTs)?, 1998 by the American Wind Energy Association.

W

watt, a measure of power for electrical current (1,000 watts = 1 kW), which can be calculated with the formula: W = V * A.

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.