ArtifactAn object produced or shaped by human beings and of archaeological or historical interest.
AshThe non-combustible residue of a combusted substance composed primarily of alkali and metal oxides.
ASHRAEAbbreviation for the American Society of Heating, Refrigeration, and Air-Conditioning Engineers.
ASTMAbbreviation for the American Society for Testing and Materials, which is responsible for the issue of many standard methods used in the energy industry.
Asynchronous GeneratorA type of electric generator that produces alternating current that matches an existing power source.
AtlatlA wood or bone shaft implement, held in one hand, and used to throw a spear. The tool functions as a lever, giving greater thrust and distance.
AtmosphereThe gaseous envelope surrounding the Earth, which consists almost entirely of nitrogen (78.1% volume mixing ratio) and oxygen (20.
Atmospheric absorptionAttenuation of sound during its passage through air, during which its sound energy is gradually converted into heat by a number of molecular processes in…
Atmospheric PressureThe pressure of the air at sea level; one standard atmosphere at zero degrees centigrade is equal to 14.695 pounds per square inch (1.
AttainmentAn area considered to have air quality as good as or better than the National Ambient Air Quality Standards for a given pollutant.
Attainment areaA geographic region where the concentration of a specific air pollutant does not exceed federal standards.
AttenuationA mechanism for controlling gene expression in prokaryotes that involves premature termination of transcription.
AtticThe usually unfinished space above a ceiling and below a roof.
Attic FanA fan mounted on an attic wall used to exhaust warm attic air to the outside.
Attic VentA passive or mechanical device used to ventilate an attic space, primarily to reduce heat buildup and moisture condensation.
Audit (Energy)The process of determining energy consumption, by various techniques, of a building or facility.
AugerA rotating, screw-type device that moves material through a cylinder. In alcohol production, it is used to transfer grains from storage to the grinding…
Augmentation PlanA court-approved plan that allows a junior water user to divert water out of priority so long as adequate replacement is made to the affected stream…
Augmentation waterWater used for the replacement of out of priority depletions.
Autoignition TemperatureThe lowest temperature at which a flammable gas vapor will ignite spontaneously, without a source of ignition, after several minutes of exposure to…
Automated mitigation procedureA procedure under which the bids of individual suppliers are capped under certain predetermined conditions.
Automatic (or Remote) Meter Reading SystemA system that records the consumption of electricity, gas, water, etc, and sends the data to a central data accumulation device.
Automatic DamperA device that cuts off the flow of hot or cold air to or from a room as controlled by a thermostat.
Automatic generation controlThe automatic regulation of the power output of electric generators within a prescribed range in response to a change in system frequency, or tie-line…
Auxiliary Energy or SystemEnergy required to operate mechanical components of an energy system, or a source of energy or energy supply system to back-up another.
AvailabilityA reflection of the form and location of nutritional elements and their suitability for absorption.
Available HeatThe amount of heat energy that may be converted into useful energy from a fuel.
Average Annual Daily Traffic (AADT)(AADT)A measurement representing the total number of vehicles passing a given location, based upon 24-hour counts taken over an entire year.
Average CostThe total cost of production divided by the total quantity produced.
Average DemandThe demand on, or the power output of, an electrical system or any of its parts over an interval of time, as determined by the total number of…
Average megawatt (MWa, aMW)(MWa, aMW)One megawatt of capacity produced continuously over a period of one year. 1 aMW = 1 MW x 8760 hours/year = 8,760 MWh = 8,760,000 kWh.
Avoided CostThe incremental cost to an electric power producer to generate or purchase a unit of electricity or capacity or both.
Avoided costsAn investment guideline describing the value of a conservation or generation resource investment by the cost of more expensive resources that a utility…
AWGThe abbreviation for American Wire Gauge; the standard for gauging the size of wires (electrical conductors).
AwningA metal frame clad with fabric attached over a window, door, porch opening or storefront to provide protection from the weather.
Axial FansFans in which the direction of the flow of the air from inlet to outlet remains unchanged; includes propeller, tubaxial, and vaneaxial type fans.
Axial Flow CompressorA type of air compressor in which air is compressed in a series of stages as it flows axially through a decreasing tubular area.
Axial Flow TurbineA turbine in which the flow of a steam or gas is essentially parallel to the rotor axis.
Azimuth (Solar)The angle between true south and the point on the horizon directly below the sun.
B20A mixture of 20% biodiesel and 80% petroleum diesel based on volume.
BackdraftingThe flow of air down a flue/chimney and into a house caused by low indoor air pressure that can occur when using several fans or fireplaces and/or if the…
Background levelThe average amount of a substance present in the environment. Originally referring to naturally occurring phenomena. Used in toxic substance monitoring.
Background level noiseNoise in the environment (other than noise emanating from the source of interest).
Backup Energy SystemA reserve appliance; for example, a stand-by generator for a home or commercial building.
Backup rateA utility charge for providing occasional electricity service to replace on-site generation.
Bacteria(bak-TEER-ee-uh) A large group of single-cell microorganisms. Some cause infections and disease in animals and humans.
BaffleA device, such as a steel plate, used to check, retard, or divert a flow of a material.
Baffle chamberIn incinerator design, a chamber designed to settle fly ash and coarse particulate matter by changing the direction and reducing the velocity of the…
BagasseThe fibrous material remaining after the extraction of juice from sugarcane; often burned by sugar mills as a source of energy.
BaghouseAn air pollution control device used to filter particulates from waste combustion gases; a chamber containing a bag filter.
BajadaA broad sloping deposit caused by the joining together of alluvial fans. These occur on the lower slopes of mountains and are often characterized by loose…
Balance PointAn outdoor temperature, usually 20 to 45 degrees Fahrenheit, at which a heat pump's output equals the heating demand.
Balance-of-SystemIn a renewable energy system, refers to all components other than the mechanism used to harvest the resource (such as photovoltaic panels or a wind…
BalancingThe requirement imposed by electricity grids or natural gas pipelines that supply and demand be equal over a certain time period.
Bald and Golden Eagle Protection ActThis Act was originally enacted in 1940 as the Bald Eagle Protection Act to protect bald eagles and later amended to include golden eagles.
BalingA means of reducing the volume of a material by compaction into a bale.
BallastA device used to control the voltage in a fluorescent lamp.
Ballast Efficacy FactorThe measure of the efficiency of fluorescent lamp ballasts. It is the relative light output divided by the power input.
Ballast FactorThe ratio of light output of a fluorescent lamp operated on a ballast to the light output of a lamp operated on a standard or reference ballast.
Band GapIn a semiconductor, the energy difference between the highest valence band and the lowest conduction band.
Band Gap EnergyThe amount of energy (in electron volts) required to free an outer shell electron from its orbit about the nucleus to a free state, and thus promote it…
Bar screenA screen made of parallel bars set 3/4" to 2" apart used to filter out large objects.
barkThe outer protective layer of a tree including the inner bark and the outer bark.
barrel (of oil)A liquid measure equal to 42 U.S. gallons, or typically about 306 lb of oil. One barrel equals 5.6 ft3; for crude oil, one barrel contains about 5.
Barrel (petroleum)42 U.S. gallons (306 pounds of oil, or 5.78 million Btu).
Barrel of oil equivalentA unit of energy equal to the amount of energy contained in a barrel of crude oil. Approximately 5.78 million Btu or 1,700 kWh.
Basal MetabolismThe amount of heat given off by a person at rest in a comfortable environment; approximately 50 Btu per hour (Btu/h).
BasaltVolcanic rock (or lava), characteristically dark in color and containing 45 to 54% silica and generally rich in iron and magnesium (mafic composition).
baseOne of the components of nucleosides, nucleotides and nucleic acids . Four different bases are found in naturally occurring DNA - the purines A (adenine )…
Base campA site occupied by several families or more on either a year round or a seasonal basis.
Base PowerPower generated by a power generator that operates at a very high capacity factor.
Baseboard RadiatorA type of radiant heating system where the radiator is located along an exterior wall where the wall meets the floor.
baselineAn initial measurement that is taken at an early time point to represent a beginning condition, and is used for comparison over time to look for changes.
BaseloadThe minimum level of electric power demand of a utility, region, or utility customer delivered or required over a given period of time at a steady rate…
Baseload CapacityThe power output of a power plant that can be continuously produced.
Baseload DemandThe minimum demand experienced by a power plant.
Baseload Power PlantA power plant that is normally operated to generate a base load, and that usually operates at a constant load; examples include coal fired and nuclear…
Baseload UnitAn electric power plant, or generating unit within a power plant, that is normally operated continuously to meet the base load of a utility.
BasementAny area of the building, including any sunken room or sunken portion of a room, having its floor below ground level (subgrade) on all sides.
Basement complexThe suite of mostly crystalline igneous and/or metamorphic rocks that generally underlies the sedimentary rock sequence.
Basement rockThe oldest rocks in a given area; a complex of metamorphic and igneous rocks that underlies the sedimentary deposits.
Basin: (1) A depression in the Earth's surface that collects sediment. (2) The area of land that drains to a particular river.
Batch HeaterThis simple passive solar hot water system consists of one or more storage tanks placed in an insulated box that has a glazed side facing the sun.
Batch ProcessA process for carrying out a reaction in which the reactants are fed in discrete and successive charges.
Batt/BlanketA flexible roll or strip of insulating material in widths suited to standard spacings of building structural members (studs and joists).
BatteryA beating or wrongful physical violence. The threat to use force is an "assault;" the actual use of force is a battery, which usually includes an assault.
Battery capacityThe maximum total electrical charge, expressed in ampere-hours, which a battery can deliver to a load under a specific set of conditions.
Battery Energy StorageEnergy storage using electrochemical batteries. The three main applications for battery energy storage systems include spinning reserve at generating…
Beadwall&##8482;A form of movable insulation that uses tiny polystyrene beads blown into the space between two window panes.
Beam RadiationSolar radiation that is not scattered by dust or water droplets.
Bearing WallA wall that carries ceiling rafters or roof trusses.