4 June 2020
Alternative Energy Glossary Minimize
Alternative Energy Glossary

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Absorber: The blackened surface in a collector that absorbs the solar radiation and converts it to heat energy.

Alternating current (AC): Electric current in which the direction of flow is reversed at frequent intervals, usually 100 or 120 times per second (50 or 60 cycles per second or 50//60 Hz).

Ampere/amp(A): The unit for the electric current; the flow of electrons. One amp is 1coulomb passing in one second. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm. Sometimes this is abbreviated as I for intensity.

Ampere-hour (Ah): Quantity of electrical energy equal to the flow of one ampere of cur-rent for one hour. Typically used to quantify battery bank capacity.

Array: Any number of photovoltaic modules connected together to provide a single electrical output at a specified voltage. Arrays are often designed to produce significant amounts of electricity.

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Battery Bank: An array of Batteries connected in series, parallel, or both.

Battery capacity: The total number of ampere-hours that can be withdrawn from a fully charged cell or battery.

Battery cycle life: The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.

Battery self-discharge: The rate at which a battery, without a load, will lose its charge.

Battery: Two or more “cells” electrically connected for storing electrical energy. Common usage permits this designation to be applied also to a single cell used independently, as in a flashlight battery.

Bearing: A device that transfers a force to structural supports. In a wind generator, bearings allow the Shaft to rotate freely, and allow the machine to Yaw into and out of the wind.

Belt: A device for transferring power from a rotating shaft to a generator. Allows the use of Pulleys to change the ratio of shaft speed to and from the generator.

British Thermal Unit (BTU): The quantity of heat needed to raise the temperature of one pound of water one degree Fahrenheit.

Brushes: Devices for transferring power to or from a rotating object. Used in DC motors and usually made of graphite.

Bypass diode: A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. Alternatively, a diode connected anti-parallel across a part of the solar cells of a PV module. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.

Cell: The basic unit of a photovoltaic module. This word is also commonly used to describe the basic unit of batteries (i.e., a 6-volt battery has three 2-volt cells).

Charge controller: A device that controls the charging rate and/or state of charge for batteries.

Charge rate: The current applied to a cell or battery to restore its available capacity.

Circuit Breaker: A device used to interrupt or break an electrical circuit when an overload condition exists. Circuit breakers are used to protect electrical equipment from potential damage.

Circuit: A device, or system of devices, that allows electrical current to flow through and voltage to occur across positive and negative terminals.

Collector Efficiency: The ratio of usable heat energy extracted from a collector to the solar energy striking the cover.

Collector: A device that collects solar radiation and converts it to heat.

Combined Heat and Power (CHP) Plant: A plant designed to produce both heat and electricity from a single heat source.

Combined Heat and Power: Also known as CHP or Cogeneration, this refers to the production of thermal energy and electrical power simultaneously.

Compact Fluorescent Lamp: Also known as CFLs or energy saving lamps/light bulbs, these efficient lamps generate five times more light than their filament equivalent.

Compact fluorescent lights (CFL): Lights that use a lot less energy than regular light bulbs We can use compact fluorescent lights for reading lights and ceiling lights.

Concentrating Collector: A device which concentrates the sun's rays on an absorber surface which is significantly smaller than the overall collector area.

Conduction: The flow of heat due to temperature variations within a material.

Conductivity: A measure of the ability of a material to permit conduction of heat flow through it.

Conductivity: This is the term used to calculate heat transfer rates for materials and to measure the extent to which a material can transmit electrical energy.

Conduit: A tubular material used to encase and protect electrical conductors.

Constant-Speed Wind Turbines: Wind turbines that operate at a constant RPM (rotor revolutions per minute). They are designed for optimal energy capture at a specific rotor diameter and at a particular wind speed.

Convection: The motion of fluid such as gas or liquid by which heat may be transported.

Cross-Flow: A cross-flow turbine is drum-shaped and uses an elongated, rectangular-section nozzle directed against curved vanes on a cylindrically shaped runner. It resembles a "squirrel cage" blower. The cross-flow turbine allows the water to flow through the blades twice. The first pass is when the water flows from the outside of the blades to the inside; the second pass is from the inside back out.

Crystalline silicon: A type of PV cell made from a single crystal or polycrystalline slice of silicon.

Current at maximum power (Imp): The current at which maximum power is available from a module.

Current: The flow of electric charge in a conductor between two points having a difference in potential (voltage).

Cut-In: The rotational speed at which an alternator or generator starts pushing electricity hard enough (has a high enough voltage) to make electricity flow in a circuit.

Cycle life: Number of discharge-charge cycles that a battery can tolerate under specified conditions before it fails to meet specified criteria as to performance (e.g., capacity decreases to 80-percent of the nominal capacity).

Cycles per Second: Measured in Hertz. In electricity, it is the number of times an AC circuit reaches both minimum and maximum values in one second.

Days of autonomy: The number of consecutive days a standalone system battery bank will meet a defined load without solar energy input.

DC to DC converter: Electronic circuit to convert DC voltages (e.g., PV module voltage) into other levels (e.g., load voltage). Can be part of a maximum power point tracker (MPPT).

Deep cycle battery: Type of battery that can be discharged to a large fraction of capacity many times without damaging the battery.

Delta: A 3-phase alternator wiring configuration in which all phases are connected in Series.

Depth of discharge (DOD): The amount of ampere hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity.

Diffused Radiation: Indirect sunlight that is scattered from air molecules, dust and water vapor.

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

Diode: Electronic component that allows current flow in one direction only.

Direct current (DC): Electric current in which electrons flow in one direction only. Opposite of alternating current.

Direct Radiation: Solar radiation that comes straight from the sun, casting shadows on a clear day.

Discharge rate: The rate, usually expressed in amperes over time, at which electrical cur-rent is taken from the battery.

Disconnect: Switch gear used to connect or disconnect components of a PV system for safety or service.

Draft tube: A water conduit, which can be straight or curved depending upon the turbine installation, that maintains a column of water from the turbine outlet and the downstream water level.

Drain back System: The solar heat transfer fluid automatically drains into a tank by gravity. Drain back systems are available in one or two tank configurations. A heat exchanger is necessary, because the city inlet pressure would prevent draining.

Drain down System: Freeze protection is provided by solenoid valves opening and dumping the water in the system to drain at a preset low temperature. Collectors and piping must be pitched or sloped so that the system can drain down using gravity.

Dump Load: A device to which wind generator power flows when the system batteries are too full to accept more power, usually an electric heating element. This diversion is performed by a Shunt Regulator, and allows a Load to be kept on the Alternator or Generator.

Duty Cycle: In a circuit, the ratio of off time to on time.

Duty cycle: The ratio of active time to total time. Used to describe the operating regime of appliances or loads.

Efficiency: The ratio of desired output to required input.

Efficiency: The ratio of output power to input power. Expressed as a percent.

Circuit: Path followed by electrons from a power source (generator or battery) through an external line (including devices that use the electricity) and returning through another line to the source.

Grid: An integrated system of electricity distribution, usually covering a large area; most typically in the USA, owned and operated by a public utility.

Electrolyte: A liquid conductor of electricity in which flow of current takes place by migration of ions. The electrolyte for a lead-acid storage cell is an aqueous solution of sulfuric acid.

Emittance: A measure of the propensity of a material to emit thermal radiation.

Energy density: The ratio of energy available from a battery to its volume (Wh/1) or mass (Wh/kg).

Energy: The ability to do work. Stored energy becomes working energy when we use it.

Equalization: The process of mixing the electrolyte in batteries by periodically overcharging the batteries for a short period to “refresh” cell capacity.

Evacuated tube solar collectors: These utilize parallel rows of glass tubes to absorb energy from the sun. Each tube is transparent and consists of an outer tube and a metal absorber tube attached to a fin. The coating of the fin absorbs energy from the sun.

Evacuated tube solar collectors: These utilize parallel rows of glass tubes to absorb energy from the sun. Each tube is transparent and consists of an outer tube and a metal absorber tube attached to a fin. The coating of the fin absorbs energy from the sun.

Evacuated tube: The absorber tube in a solar thermal collector through which collector fluid flows.

Flat Plate Collector: A device, usually a box, in which sunlight is collected and converted into heat by a dark absorber plate under glass or plastic, without the aid of reflecting surfaces to concentrate the rays.

Flat Plate Collector: A device, usually a box, in which sunlight is collected and converted into heat by a dark absorber plate under glass or plastic, without the aid of reflecting surfaces to concentrate the rays.

Flat Plate Collector: A solar collection device in which sunlight is converted into heat on a plane surface without the aid of reflecting surfaces to concentrate the rays.

Float charge: Float charge is the voltage required to counteract the self-discharge of the battery at a certain temperature.

Float life: Number of years that a battery can keep its stated capacity when it is kept at float charge.

Flow: Volume of water, expressed as cubic feet or cubic meters per second, passing a point in a given amount of time.

Galvanic Corrosion: A condition caused as a result of a conducting liquid making contact with two different metal which are not properly isolated physically and/or electrically.

Gassing current: Portion of charge current that goes into electrolytical production of hydrogen and oxygen from the electrolytic liquid in the battery. This current increases with increasing voltage and temperature.

Gel-type battery: Lead-acid battery in which the electrolyte is composed of a silica gel matrix.

Geothermal: Energy from reservoirs in the Earth’s surface, such as geysers or ground water that is ‘heat energy’.

Gigawatt (gW): One billion watts. One million kilowatts. One thousand megawatts.

Green credit: Green credits are a new way to purchase renewable electric generation that divides the generation into two separate products: the commodity energy and the renewable attributes. The green credit represents the renewable attributes of a single megawatt of renewable energy. Also known as green tags, renewable energy credits, or renewable energy certificates.

Green Power: popular term for energy produced from renewable energy resources.

Grid (also “Power Grid” and “Utility Grid”): A common term referring to an electricity transmission and distribution system.

Grid-tie: A PV, wind or hydroelectric systems that supplies power directly to the utility grid. Also called grid-connected, grid-interactive, utility-inter-tie and other similarly descriptive terms.

Ground Source Heat Pump (GHP): Electrically powered systems that tap the stored energy of the earth. These systems use the earth's relatively constant temperature to provide heating, cooling, and hot water for homes and commercial buildings.

Ground Source: Solar heat stored in the ground that can be utilized by heat pumps (see Borehole).

Head: Vertical change in elevation, expressed in either feet or meters, between the head water level and the tailwater level.

Heat Exchanger: A device, such as a coiled copper tube immersed in a tank of water, that is used to transfer heat from one fluid to another through a separating wall.

Heat Pump: An energy efficient electric compressor that takes a high volume of low-level heat from one source. This is then transferred to another place as a lower volume of high-grade heat. It operates as a heating and air-conditioning system that uses a refrigeration cycle (where a refrigerant is compressed as a liquid and expanded as vapor to absorb and emit heat.) The heat pump transports heat to a space to be heated during Winter and reabsorbs heat from the same space to be cooled during the Summer. Heat can be absorbed from the air, ground or ground water (see Borehole). Types of heat pump:

Heat Sink: A medium or container to which heat flows.

Heating, Ventilation, and Air Conditioning (HVAC): Controls the ambient environment (temperature, humidity, air flow, and air filtering) of a building and must be planned for and operated along with other data center components such as computing hardware, cabling, data storage, fire protection, physical security systems, and power.

Hybrid system: A PV system that includes other sources of electricity generation, such as wind or fossil fuel generators.

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Impulse Turbine: The impulse turbine generally uses the velocity of the water to move the runner and discharges to atmospheric pressure. The water stream hits each bucket on the runner. There is no suction on the down side of the turbine, and the water flows out the bottom of the turbine housing after hitting the runner. An impulse turbine is generally suitable for high head, low flow applications. Include pelton and crossflow turbines.

Insolation: Sunlight, direct or diffuse; from ‘incident solar radiation.’ Usually expressed in watts per square meter. Not to be confused with ‘insulation.’

Insulation: A material with high resistance (R-value) to heat flow.

Interconnect: A conductor within a module or other means to provide an electrical connection between the solar cells.

Inverter: Device that converts DC electricity into AC electricity (single or multiphase), either for off-grid standalone systems or for grid-tie systems.

Junction box: An electrical box designed to be a safe enclosure in which to make proper electrical connections. On PV modules this is where PV strings are electrically connected.

Kilowatt (kW): 1000 watts.

Kilowatt-hour (kWh): One thousand watt-hours. The kWh is a unit of energy. 1 kWh=3600 kJ.

Life cycle cost: An estimate of the cost of owning and operating a system for the period of its useful life; usually expressed in terms of the present value of all lifetime costs.

Light emitting diode (LED): LEDs produce light at low temperatures. This reduces wasted heat energy and makes them very efficient.

Load: Anything in an electrical circuit that, when the circuit is turned on, draws power from that circuit.

Low Voltage Disconnect: Senses battery voltage and prevents the battery from deep discharge by turning off the loads connected to it. In the case of a charge controller, the LVD can control DC loads only. An LVD in an inverter can control AC loads.

Maximum power point tracker (MPPT): Means of a power conditioning unit that automatically operates the PV generator at its MPP under all conditions.

Mean Wind Speed: The average wind speed over a specified time period and height above the ground.

Median Wind Speed: The wind speed with 50% probability of occurring.

Megawatt (MW): One million watts; 1000 kilowatts.

Modified Sine Wave: An AC electricity waveform that approximates (to varying degrees of smoothness) smooth sine wave current. Modified sine wave has voltage "steps" between equal positive and negative extremes of the AC waveform. Modified sine wave current is produced by some types of inverters in off-grid systems.

Multi-crystalline: Material that is solidified at such as rate that many small crystals form. The atoms within a single crystallite are symmetrically arranged, whereas crystallites are jumbled together.

Nacelle: The cover for the gearbox, drive train, and generator of a wind turbine.

Nominal operating cell temperature (NOCT): The reference PV module operating temperature presented on manufacturer’s literature. Generally the NOCT is referenced at 25°C, 77°F.

Nominal voltage: Voltage stated on a photovoltaic (PV) module. This indicates the corresponding nominal battery the panel will charge. A nominal 12v panel will charge a 12v battery. The actual voltages are closer to 14.4V for the battery and 17V for the panel.

Ohm: The unit of resistance to the flow of an electric current.

One-axis tracking: A system capable of rotating about one axis, also referred to as single axis. These tracking systems usually follow the sun from east to west throughout the day.

Open Loop: A system where water is pumped from a water well, pond, lake or other surface source for a ground source heat pump or solar water heater. The water is heated or cooled for use.

Open-circuit voltage (Voc): The maximum possible voltage across a photovoltaic cell or module; the voltage across the cell in sunlight when no current is flowing.

Parallel: In DC electrical circuits such as a battery bank or solar panel array, this is a connection where all negative terminals are connected to each other, and all positive terminals are connected to each other. Voltage stays the same, but amperage is increased. In AC circuits such as a wind generator alternator, each parallel coil is connected to common supply wires, again increasing amperage but leaving voltage the same. Opposite of Series.

Passive solar: The design of buildings so that they capture or exclude the Sun’s heat in order to reduce fossil fuel consumption for heating or cooling.

Payback: The time it takes for positive cash flow to match capital costs. Can be from energy efficient or renewable energy measures.

Peak Load:The greatest demand placed on an electric system; measured in kilowatts or megawatts; also, the time of day or season of the year when that demand occurs.

Peak Wind Speed: The maximum instantaneous wind speed that occurs within a specific period of time.

Pelton wheel: Has one or more free jets discharging water into an aerated space and impinging on the buckets of a runner. Draft tubes are not required for impulse turbine since the runner must be located above the maximum tailwater to permit operation at atmospheric pressure. A Turgo Wheel is a variation on the Pelton. The Turgo runner is a cast wheel whose shape generally resembles a fan blade that is closed on the outer edges. The water stream is applied on one side, goes across the blades and exits on the other side.

Penstock: A closed conduit or pipe for conducting water to the powerhouse.

Phase: The timing of AC current cycles in different wires. 3-phase alternators produce current that is cyclically timed between 3 different wires and a common wire, while single phase produces it in only 1 wire and a common.

Photovoltaic (PV): Pertaining to the direct conversion of photons of sunlight into electricity.

Photovoltaic array: An interconnected system of PV modules that function as a single electricity producing unit. The modules are assembled as a discrete structure, with common support or mounting. In smaller systems, an array can consist of a single module.

Photovoltaic module: The smallest environmentally protected, essentially planar assembly of solar cells – including ancillary parts such as interconnections, terminals and protective devices such as diodes – intended to generate DC power under unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate).

Photovoltaic peak watt: Maximum “rated” output of a cell, module, or system. Typical rating conditions are 0.645 watts per square inch (1000 watts per square meter) of sunlight, 68 degrees F (20 degrees C) ambient air temperature and 6.2 x 10-3 mi/s (1m/s) wind speed.

Photovoltaic system: A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components.

Polycrystalline: See ‘multicrystalline.'

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.

Power factor: The ratio of the average power and the apparent volt-amperes. pulse-width-modulated wave inverter (PWM): Pulse-width-modulated wave inverters are the most expensive, but produce a high quality of output signal at minimum current harmonics. The output voltage is very close to sinusoidal.

Prevailing Wind Direction: The direction from which the wind predominantly blows as a result of the seasons, high and low pressure zones, the tilt of the earth on its axis, and the rotation of the earth.

PV: Abbreviation for photovoltaic.

Pyranometer: An calibrated instrument for measuring solar radiation.

Radiation: The flow of energy through open space via electromagnetic waves, such as visible light.

Reaction Turbine: A reaction turbine develops power from the combined action of pressure and moving water. The runner is placed directly in the water stream flowing over the blades rather than striking each individually. Reaction turbines are generally used for sites with lower head and higher flows than compared with the impulse turbines. Inculdeds Kaplan and Francis turbines.

Resistance (R): The property of a conductor which opposes the flow of an electric current resulting in the generation of heat in the conducting material. The unit of resistance is ohms.

Rotor: The blades and other rotating components of a wind energy conversion turbine.

RPM: Revolutions Per Minute. The number of times a shaft completes a full revolution in one minute.

Series: A way of joining electrical equipment by connecting positive leads to negative leads; such a configuration increases the voltage while current remains the same.

Series regulator: Type of battery charge regulator where the charging current is controlled by a switch connected in series with the PV module or array.

Shaft: The rotating part in the center of a wind generator or motor that transfers power.

Short Circuit: Parts of a circuit connected together with only the impedance of the leads between them. 2) In wind generators, connecting the output leads directly together so as to heavily load a generator in high winds. This creates a "short" circuit path back to the generator, bypassing all other loads.

short-circuit current (Isc): The current flowing freely from a photovoltaic cell through an external circuit that has no load or resistance; the maximum current possible.

Shunt regulator: Type of a battery charge regulator where the charging current is controlled by a switch connected in parallel with the PV generator. Overcharging of the battery is prevented by shorting the PV generator.

Shunt: An electrical bypass circuit that proportionally divides current flow between the shunt and the shunted equipment. It also allows high current measurements with low-current equipment.

Silicon (Si): A chemical element, atomic number 14, semi-metallic in nature, dark gray, an excellent semiconductor material. A common constituent of sand and quartz (as the oxide). Crystallizes in face centered cubic lattice – like a diamond. The most common semiconductor material used in making photovoltaic devices.

Sine wave inverter: An inverter that produces utility quality, sine wave power forms.

Solar constant: The strength of sunlight; 1353 watts per square meter in space and about 1000 watts per square meter at sea level at the equator at solar noon.

Solar energy: Energy from the sun in the form of electro-magnetic radiation.

Square wave inverter: The inverter consists of a DC source, four switches, and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating. The switches are turned on and off at a correct sequence, at a certain frequency. The square wave inverter is the simplest and the least expensive to purchase, but it produces the lowest quality of power.

Standalone: An autonomous or hybrid photovoltaic system not connected to a grid. Some standalone systems require batteries or some other form of storage. “Standalone” is virtually synonymous with “off-grid” when applied to energy systems.

Standard test conditions (STC): Conditions under which a solar module is tested in a laboratory

Stand-off mounting: Technique for mounting a PV array on a sloped roof, which involves mounting the modules a short distance above the pitched roof and tilting them to the optimum angle. This promotes air flow to cool the modules.

Sulphation: A condition in lead-acid batteries that is characterized by reduced charge capacity. During the discharge part of its operation cycle, lead sulfate crystals form on both the positive and negative electrodes (plates). This is a normal and manageable consequence of battery operation. If the battery is allowed to remain in a discharged state for a prolonged period of time, the sulfate crystals continue to grow. These larger crystals reduce the effective plate area and are difficult to dissolve back into the electrolyte solution with normal charging. Thus, they reduce the overall capacity of the battery. This condition can be prevented by recharging the battery immediately following a discharge.

Surge capacity: The ability of an inverter or generator to deliver high currents momentarily required when starting a motor.temperature compensation: An allowance made in charge controller set points for changing battery temperatures.

Surge: The momentary start-up condition of a motor requiring a large amount of current.

Thermal Mass: The tendency of a building with large quantities of heavy materials to remain at the same temperature or to fluctuate only very slowly; also the overall heat storage capacity of the building.

Thermal siphon: The natural movement of heat that occurs when a warm fluid rises and a cool fluid sinks under the influence of gravity; makes water circulate automatically between a warm collector and a cooler storage tank above it.

Thermistor: Sensing device which changes its electrical resistance according to temperature. Used in the control system to generate input data on collector and storage temperatures.

Thin film: A layer of semiconductor material, such as copper indium diselenide, cadmium telluride, gallium arsenide, or amorphous silicon, a few microns or less in thickness, used to make photovoltaic cells.

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.

Tilt angle: Angle of inclination of a module as measured in degrees from the horizontal. For maximum performance solar collectors/modules should be set as close as possible to perpendicular to the sun.

Tip Speed Ratio: The ratio of how much faster than the windspeed that the blade tips are moving. Abbreviation TSR.

Total harmonic distortion (thd): The measure of closeness in shape between a waveform and its fundamental component.

Tracking PV array: PV array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are (1) one axis where the array tracks the sun east to west and (2) two-axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy.

Transformer: An electromagnetic device used to convert AC electricity, either to increase or decrease the voltage.

Transformer: Multiple individual coils of wire wound on a laminate core. Transfers power from one circuit to another using magnetic induction. Usually used to step voltage up or down. Works only with AC current.

Trickle charge: A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.

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.

Two-axis tracking: A system capable of rotating independently about two axes and following the sun’s orientation and height in the sky (e.g., vertical and horizontal).utility-

VAC: Volts Alternating Current.

Variable-Speed Wind Turbines: Turbines in which the rotor speed increases and decreases with changing wind speeds. Sophisticated power control systems are required on variable speed tubines to insure that their power maintains a constant frequency compatible with the grid.

VDC: Volts Direct Current.

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.

Voc: Open-circuit voltage (seen entry).

Volt (V): A unit of measure of the force, or ‘push’, given the electrons in an electric circuit. One volt produces one amp of current when acting against a resistance of one ohm.

Voltage at maximum power (VMP): The voltage at which maximum power is available from a module.

Wake Losses: The space behind a wind turbine that is marked by decreased wind power capacity due to the fact that the turbine itself used the energy in turning the blades. The wind behind the turbine, in its wake, is less effective at generating energy for a certain distance in the downwind direction due to turbulence created by the upwind machine.

Watt (W): The unit of electric power, or amount of work. One ampere of current flowing at a potential of one volt produces one watt of power.

Watt-hour (Wh): A quantity of electrical energy when one watt is used for one hour.

Waveform: The shape of the curve graphically representing the change in the AC signal voltage and current amplitude, with respect to time.

Wind Rose: A diagram that indicates the average percentage of time that the wind blows from different directions, on a monthly or annual basis.

Wind Turbine Rated Capacity: The amount of power a wind turbine can produce at its rated wind speed.
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