Renewable Energy Glossary

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Absolute Humidity

A measure of the water vapor content of air.

Absorber

The part of a solar thermal collector that receives the sun's radiant energy and transforms it into heat energy.

Absorber Plate

The component of a collector that absorbs the solar energy and distributes it to a storage tank or heat-delivery system. Liquid collector absorbers use tubes or heat pipes to transport the heat.

AC

Alternating current (AC) is the cyclical flow of electrical current, reversing direction as it flows. It is the type of electrical current provided by utility companies.

AC Module

A complete assembly that includes the PV module, microinverter, cabling, and grounding in an integrated, plug-and-play product designed to generate AC power. An AC module is tested and certified by a nationally recognized test laboratory as a complete assembly. The inverter is factory-integrated with the PV module, and the entire unit carries one end-to-end warranty from the module manufacturer.

AC Service Panel

An electrical box which is the central point of electrical distribution throughout a building.

AC Watts Output

The array STC-rated watts multiplied by the inverter efficiency; also known as the minimum inverter size.

Active Solar Thermal System

A system that traps the sun's energy with solar collectors and uses an electromechanical subsystem to move that energy to its point of intended use for water heating, space heating, pool heating, industrial process heat, electrical generation, and space cooling.

Active Tracker

Follows the sun's path through the day by using motors, controls, sensors, or timers.

Adobe

A sun-dried earthen, un-compressed brick used for wall construction. Traditional adobe blocks are a standard 10"x14"x4" size.

AEO

Annual energy output. A turbine depends on the average windspeed of the site. Expressed in kilowatt-hour units of electrical energy per year, this is the most important indicator of the value of a turbine to its owner, but it's difficult to determine the average windspeed of a site until a tower has been there long enough to measure it.

Ah

An amp-hour (Ah) is one amp of current flowing for one hour. An amp-hour is the unit of measurement for capacity of a battery.

AHJ

Authority having jurisdiction (AHJ) is an individual or organization who enforces codes and standards in a particular area, typically via plan review, granting permits, and performing inspections.

Air Barrier

A material or structural element that inhibits air flow into and out of a building's envelope or shell. Often it allows water to diffuse through it. See also Vapor Barrier.

Air Leakage

The uncontrolled infiltration or exfiltration of air into buildings through cracks and joints in any building section, and around windows and doors of a building, caused by temperature or pressure differentials.

Air Vent

A device used to eliminate air in SWH system piping. It can have automatic or manual operation.

Albedo

A measurement of reflected radiation.

Alternating Current

The cyclical flow of electrical current, reversing direction as it flows. It is the type of electrical current provided by utility companies.

Alternator

An electromechanical device that generates AC electricity.

Altimeter

A device that measures altitude (based on air pressure), and can be used to measure head on a hydro site. Readings are relative to background air pressure that may be changing. Altimeters can have varying levels of accuracy. It is advisable to use more than one technique to measure head.

Altitude Angle

The sun's height above the horizon measured in degrees. The altitude angle value increases as the sun rises above the horizon. (0 degrees would be sunrise, and 90 degrees would be directly overhead.)

Altitude Angle

Measure of the angle formed between the sun and the horizon.

Ambient Air Temperature

The average surrounding air temperature.

American Wire Gauge

A standardized nomenclature used to designate the cross-sectional diameter of electrically conducting wire; the cross-sectional area associated with a particular gauge is an important factor for determining its current-carrying capacity (or ampacity).

AMM

An analog multimeter (AMM) is an electrical meter with analog dial screen used to measure values such as voltage, current, and resistance.

Amp-Hour

One amp of current flowing for one hour. An amp-hour is the unit of measurement for capacity of a battery.

Ampacity

The current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

Amperage

The rate of the flow of electrons through a conductor, denoted by the electrical symbol A.

Analog Multimeter

An electrical meter with an analog dial screen used to measure values such as voltage, current, and resistance.

Annual Energy Output

The AEO of a turbine depends on the average windspeed of the site. Expressed in kilowatt-hour units of electrical energy per year, this is the most important indicator of the value of a turbine to its owner, but it's difficult to determine the average windspeed of a site until a tower has been there long enough to measure it.

Anode

(Battery) The electrode within a battery cell that undergoes the chemical process of oxidation. Electrically, the anode is the cell's positive terminal. (Water heater) An aluminum or magnesium sacrificial rod installed within steel tanks that is used to help prevent corrosion of the tank.

ANSI

The American National Standards Institute (ANSI) oversees the making, broadcasting, and use of thousands of guidelines and standards that impact businesses in the United States.

Antifreeze System

Indirect forced circulation system that utilizes a nontoxic heat transfer fluid.

Antiscald Valve

A safety valve that limits hot water output by mixing cold water at a set maximum temperature.

Aquastat

An electromechanical device that opens and closes a switch based on the temperature of a fluid.

Arc Flash

A dangerous rapid release of energy from an electrical fault that overcomes the resistance of air, at temperatures high enough to vaporize conductors and create an arc blast of molten metal and expanding plasma.

Array Size

Refers to the total DC array wattage at standard test conditions (STC), also known as system size or array nameplate wattage.

Array Tilt Angle

A solar array's inclination as measured in degrees from horizontal. Modules collect the most solar radiation when they are angled perpendicular to the sun.

Array-to-Inverter Power Ratio

The STC rated watts of the array divided by the rated continuous power output of the inverter, used to evaluate if an inverter is the appropriate size for a system.

Asynchronous Generator

An asynchronous motor will back-feed the grid if driven faster than its motoring speed. Coils in the motor's body produce a magnetic field that rotates with the frequency of the grid.

Authority Having Jurisdiction

An individual or organization that enforces codes and standards in a particular area, typically via plan review, granting permits, and performing inspections.

Automatic Voltage Regulator

An electronic control circuit used on stand-alone synchronous generators powered by hydro turbines. The AVR adjusts the current in the field coils to regulate the output voltage under changing load conditions.

Average Daily Amp-Hours Required

The amount of battery energy (amp-hours) needed to run the loads for one day.

Average Daily Load

The average amount of energy used in a day; this value is critical for off-grid system sizing.

AVR

An automatic voltage regulator (AVR) is an electronic control circuit used on stand-alone synchronous generators powered by hydro turbines. The AVR adjusts the current in the field coils to regulate the output voltage under changing load conditions.

AWG

American wire gauge (AWG) is a standardized nomenclature used to designate the cross-sectional diameter of electrically conducting wire; the cross-sectional area associated with a particular gauge is an important factor for determining its current-carrying capacity (or ampacity).

Azimuth

The horizontal aspect of the sun's position relative to a defined direction is called its solar azimuth angle. In the Northern Hemisphere, it is measured in degrees east or west of true south.

1 A B C D E F G H I J K L M N O P Q R S T U V W Y

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