| Term | Definition |
| Absorbed Glass Mat (AGM) Batteries | Employ a micro-fibrous silica glass mat envelope to immobilize their electrolyte. This makes them non-spillable and gives them a lower self-discharge rate than conventional flooded lead-acid batteries. |
| Absorber | 1) In a photovoltaic device, the material that readily absorbs photons to generate charge carriers (free electrons or holes). 2) The absorber is that part of a solar thermal collector that receives the incident radiant energy and transforms it into heat energy. |
| Absorbers | Dark coloured objects that soak up heat in solar collectors. |
| Absorptance | The ratio of the radiation absorbed by a surface to the total energy falling on that surface described as a percentage. |
| Absorption Coefficient | The factor by which photons are absorbed as they travel a unit distance through a material. |
| AC (Alternating Current) | A type of electrical current, the direction of which is reversed at regular intervals or cycles. Alternating current is abbreviated as AC. |
| Acceptor | An element (like boron) that is missing outer shell electrons to be used in solar panel construction. |
| Access Charge | A charge paid by all market participants withdrawing energy from the ISO controlled grid. The access charge will recover the portion of a utility’s transmission revenue requirement not recovered through the variable usage charge. |
| Acid Rain | Precipitation that has become acidic as the result of chemical reactions. Sulfur dioxide emissions from fossil fuel burning power plants react with the water, oxygen, and other chemicals in the air to cause acid rain. |
| Activated Shelf Life | The period of time, at a specified temperature, that a charged battery can be stored before its capacity falls to an unusable level. |
| Activation Voltage(S) | The voltage(s) at which a charge controller will take action to protect the batteries. |
| Active Solar Energy System | Solar radiation used by special equipment to provide space heating, hot water or electricity. |
| Active Solar Heater | A water or space heating system that moves heated air or water using pumps or fans. |
| 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. |
| Addition | An alteration to an existing building that increases conditioned space. |
| Adjustable Set Point | A feature allowing the user to adjust the voltage levels at which a charge controller will become active. |
| Adjustment Bid | A bid that is used by the ISO to adjust supply or demand when congestion is anticipated. |
| Adverse Hydro | Water conditions limiting the production of hydroelectric power. In years having below-normal levels of rain and snow, and in seasons having less-than-usual runoff from mountain snowpack, there is then less water available for hydro energy production. |
| Aeolus | The god of the winds in Greek mythology. |
| After-Market | broad term that applies to any change after the original purchase, such as adding equipment not a part of the original purchase. As applied to alternative fuel vehicles, it refers to conversion devices or kits for conventional fuel vehicles. |
| Aggregator | An entity responsible for planning, scheduling, accounting, billing, and settlement for energy deliveries from the aggregator’s portfolio of sellers and/or buyers. Aggregators seek to bring together customers or generators so they can buy or sell power in bulk, making a profit on the transaction. |
| AGM (Adsorbed Glass Mat) | a newer type of battery construction that uses saturated adsorbant glass mats rather than gelled or liquid electrolyte. AGM batteries are typically more expensive than flooded (liquid), but offer enhanced reliability. |
| Agriculture | the growing (farming) of plants, flowers, trees, grains, and other crops. Greenhouses can be heated with hot water from geothermal reservoirs. In some places pipes of hot water are buried under the soil. Geothermal heat is also used to dry crops. |
| AIC | See amperage interrupt capability. |
| Air | The mixture of gases that surrounds the earth and forms its atmosphere. Air is composed primarily of oxygen and nitrogen. |
| Air Change | The replacement of a quantity of air in a space within a given period of time, typically expressed as air changes per hour. If a building has one air change per hour, this is equivalent to all of the air in the building being replaced in a one-hour period. |
| Air Conditioner | An assembly of equipment for air treatment consisting of a means for ventilation, air circulation, air cleaning, and heat transfer (either heating or cooling). The unit usually consists of an evaporator or cooling coil, and an electrically-driven compressor and condenser combination. |
| Air Film | A layer of still air adjacent to a surface which provides some thermal resistance. |
| Air Film Coefficient | A measure of the heat transfer through an air film. [See ASHRAE Table 1, ASHRAE Handbook, 1985 Fundamentals] |
| Air Mass | The length of the path of solar radiation through the atmosphere. E.g. Air mass of 1 means the sun is overhead (goes trough 1 atmosphere). |
| Air Pollution | Air with contaminants in it that prevent the air from dispersing as it normally would, and interfere with biological processes. |
| Air-To-Air Heat Exchanger | A device with separate air chambers that transfers heat between the conditioned air being exhausted and the outside air being supplied to a building. |
| Alcohol Fuels | A class of liquid chemicals that have certain combinations of hydrogen, carbon and oxygen, and that are capable of being used as fuel. |
| Alteration | Any change or modification to a building’s construction. [See Addition]. |
| Alternating Current | An electric current that reverses directions at regular intervals (typically 60 times a second); abbreviated "AC." This current found in homes. |
| Alternating Current (Ac) | An electrical current in which the direction of electron flow reverses periodically, usually many times per second. Most U.S. household electrical systems use AC current rated at 120 volts and 60 cycles per second. |
| Alternative (Transportation) Fuels | as defined by the National Energy Policy Act (EPAct) the fuels are: methanol, denatured ethanol and other alcohols, separately or in mixtures of 85 percent by volume or more (or other percentage not less than 70 percent as determined by U.S. Department of Energy rule) with gasoline or other fuels; CNG; LNG; LPG; hydrogen; "coal-derived liquid fuels;" fuels "other than alcohols" derived from "biological materials;" electricity, or any other fuel determined to be "substantially not petroleum" and yielding "substantial energy security benefits and substantial environmental benefits." |
| Alternative Energy Sources | See RENEWABLE ENERGY. |
| Alternative Fuel Vehicle (Afv) | motor vehicles that run on fuels other than petroleum-based fuels. As defined by the National Energy Policy Act (EPAct), this excludes reformulated gasoline as an alternative fuel. |
| Alternative Fuels | A popular term for “non-conventional”transportation fuels like propane that are derived from natural gas or biomass materials. |
| Alternator | A device for producing Alternating Current ("AC") electricity. Usually driven by a motor, but can also be driven by other means, including water and wind power. |
| Altitude Angle | The angle of the sun above the horizon, measured in degrees. In winter, the sun is at a low solar altitude, and in the summer, the sun is at a high solar altitude. |
| Ambient | The surrounding atmosphere; encompassing on all sides; the environment surrounding a body but undisturbed or unaffected by it. |
| Ambient Air Temperature | Surrounding temperature, such as the outdoor air temperature around a building. |
| Ambient Temperature | The temperature of the surrounding area. |
| American Wire Gauge (Awg) | American Wire Gauge, a set of standards in the U.S. specifying the diameter of wire. A higher number indicates smaller wire. |
| Ammeter | A device used for measuring the current (amperage) at any point in an electrical circuit. |
| Amorphous Semiconductor | A non-crystalline semiconductor material that has no long-range order. |
| Amorphous Silicon | A thin-film solar PV cell material which has a glassy rather than crystalline structure. Made by depositing layers of doped silicon on a substrate normally using plasma-enhanced chemical vapor deposition of silane. |
| Amp Hour | The quantity of electrical energy corresponding to the flow of current of one ampere for one hour. The term is used to quantify the energy stored in a battery. Most batteries are rated in Ah. |
| Ampacity | Refers to the highest safe amount of electrical current through conductors, overcurrent devices, or other electrical equipment. Ampacity is determined by the cross-sectional area and the material of the conductor, or the manufacturer’s equipment rating. |
| Amperage Interrupt Capability (AIC) | direct current fuses should be rated with a sufficient AIC to interrupt the highest possible current. |
| Ampere (A) Or Amp | The unit for the electric current; the flow of electrons. One amp is 1 coulomb passing in one second. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm. |
| Ampere (A)(Amp) | Unit of electrical current, the flow of electrons. |
| Ampere (Amp) | The unit of measure that tells how much electricity flows through a conductor. It is like using cubic feet per second to measure the flow of water. For example, a 1,200 watt, 120-volt hair dryer pulls 10 amperes of electric current (watts divided by volts). |
| Ampere Hour Meter | An instrument that monitors current with time. The indication is the product of current (in amperes) and time (in hours). |
| Ampere, Amps | The measurement of the flow of an electric current through a conductor. |
| Ampere-Hour (Amp-Hour; Ah) | A measure of electron flow over time, used to measure battery capacity and state of charge. For example, a current of 1 amp drawn from a battery for 10 hours would result in 10 amp-hours of charge cycling through the battery. |
| Ampere-Hour Meter | An instrument that monitors electron flow over time. Amp-hours are the product of electron flow (in amperes) and time (in hours). |
| Amp-Hour (Ah) | Unit of electrical energy, the flow of 1 Amp for 1 Hour. Often used to describe the quantity of energy stored in a battery. |
| Amplitude | Generally refers to the maximum and minimum voltage attained by an alternating or pulsed current in each complete cycle or pulse of that current. |
| Ancillary Services | The services other than scheduled energy that are required to maintain system reliability and meet WSCC/NERC operating criteria. Such services include spinning, non-spinning, and replacement reserves, voltage control, and black start capability. |
| Anemometer | An instrument for measuring and indicating the force or speed of the wind. |
| Angle Of Incidence | The angle that the sun’s rays make with a line perpendicular to a surface. The angle of incidence determines the percentage of direct sunshine intercepted by a surface. |
| Animal Waste Conversion | Process of obtaining energy from animal wastes. This is a type of biomass energy. |
| Annual Maximum Demand | The greatest of all demands of the electrical load which occurred during a prescribed interval in a calendar year. |
| Annual Solar Savings | The annual solar savings of a solar building is the energy savings attributable to a solar feature relative to the energy requirements of a non-solar building. |
| Anode | The positive electrode in an electrochemical cell (battery). Also, the earth or ground in a cathodic protection system. Also, the positive terminal of a diode. |
| 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 itself. |
| Ansi | American National Standards Institute is the national organization that coordinates development and maintenance of consensus standards and sets rules for fairness in their development. ANSI also represents the USA in developing international standards. |
| Anthracite | Hard coal, found deep in the earth. It burns very hot, with little flame. It usually has a heating value of 12,000-15,000 British thermal units (Btus) per pound. |
| Anti-Reflection Coating | A thin coating of a material with a specific refractive index applied to a cell to reduce the reflection of light. |
| Appliance Saturation | A percentage telling what proportion of all households in a given geographical area have a certain appliance. |
| Applicant | Applicant means any person who submits an application for certification pursuant to the provisions of this division, including, but not limited to, any person who explores for or develops geothermal resources. |
| Application | Application means any request for certification of any site and related facility filed in accordance with the procedures established pursuant to this division. An applicant for a geothermal powerplant and related facilities may propose more than one site and related geothermal facilities in the same application. |
| Aquaculture | the farming of fish and other water-dwelling organisms in freshwater or seawater. Geothermal water is used to help speed the growth of fish, prawns and alligators. China is probably has more aquaculture operations than any other country. |
| Aquifer | a large permeable body of underground rock capable of yielding quantities of water to springs or wells. Aquifers provide about 60 percent of American drinking water. Underground aquifers of hot water and steam are called geothermal reservoirs. |
| Aquilo | The Latin word for the North Wind in Greek mythology. |
| Arbor Or Arbor Shaft | An adaptor which converts your motor shaft to a useable threaded bolt |
| Area Load | The total amount of electricity being used at a given point in time by all consumers in a utility’s service territory. |
| Array | Any number of photovoltaic modules connected together electrically to provide a single electrical output. Also see photovoltaic (PV) array. |
| Array Current | The electrical current produced by a photovoltaic array when it is exposed to sunlight. |
| Array Operating Voltage | The voltage produced by a photovoltaic array when exposed to sunlight and connected to a load. |
| Ash | Non-organic, non-flammable substance left over after combustible material has been completely burned. |
| Ashrae | Acronym for American Society of Heating, Refrigerating and Air- Conditioning Engineers. |
| Associated Gas | Natural gas that can be developed for commercial use, and which is found in contact with oil in naturally occurring underground formations. |
| Asynchronous Generator | A type of electric generator that produces alternating current (AC) electricity to match an existing power source. |
| Atgas | Synthetic gas produced by dissolving coal in a bath of molten iron. The process was developed by Applied Technology, Inc. Synthetic gas may be used as a substitute for natural gas in industrial and home uses. |
| Atom | Primary basis of all matter. It has a nucleus consisting of protons and neutrons surrounded by orbiting electrons . |
| Auster | The Latin word for the South Wind in Greek mythology. |
| Autonomous System | A PV System that operates without any other energy generating source. Also see: Stand-Alone System |
| Auxiliary Energy Subsystem | Equipment using conventional fuel to supplement the energy output of a solar system. This might be, for example, an oil- fueled generator that adds to the electrical output of a substitutes for the solar system during long overcast periods when there is not enough sunlight. |
| Auxiliary Equipment | Extra machinery needed to support the operation of a power plant or other large facility. |
| Availability | The quality or condition of a photovoltaic system being available to provide power to a load. Usually measured in hours per year. One minus availability equals downtime. |
| Average Cost | The revenue requirement of a utility divided by the utility’s sales. Average cost typically includes the costs of existing power plants, transmission, and distribution lines, and other facilities used by a utility to serve its customers. It also included operating and maintenance, tax, and fuel expenses. |
| Average Demand | The energy demand in a given geographical area over a period of time. For example, the number of kilowatt-hours used in a 24-hour period, divided by 24, tells the average demand for that period. |
| Average Hydro | Rain, snow and runoff conditions that provide water for hydroelectric generation equal to the most commonly occurring levels. Average hydro usually is a mean indicating the levels experienced most often in a 104-year period. |
| Avoided Cost | (Regulatory) The amount of money that an electric utility would need to spend for the next increment of electric generation to produce or purchase elsewhere the power that it instead buys from a cogenerator or small-power producer. Federal law establishes broad guidelines for determining how much a qualifying facility (QF) gets paid for power sold to the utility. |
| Awg (American Wire Gauge) | a standard system for designating the size of electrical wire. The higher the number, the smaller the wire. Most house wiring is #12 or 14. |
| Azimuth | The Angle between the north direction and the projection of the surface normal into the horizontal plane; measured clockwise from north. As applied to the PV array, 180 degree azimuth means the array faces due south. |
| Azimuth Angle | The angle between true south and the point on the horizon directly below the sun. |
| Azimuth | The Angular Distance Between True South And The Point On The Horizon Directly Below The Sun. Typically Used As An Input For Opaque Surfaces And Windows In Computer Programs For Calculating The Energy Performance Of Buildings. |
