Glossary of Terms - A

• Above-market Cost - The cost of a service in excess of the price of comparable services in the market.
• Absorber - The component of a solar thermal collector that absorbs solar radiation and converts it to heat, or, as in a solar photovoltaic device, the material that readily absorbs photons to generate charge carriers (free electrons or holes). Dark-colored objects that soak up heat in solar collectors.
• Absorption Chiller - A type of air cooling device that uses absorption cooling to cool interior spaces.
• Absorption Coefficient - In reference to a solar energy conversion devices, the degree to which a substance will absorb solar energy. In a solar photovoltaic device, the factor by which photons are absorbed as they travel a unit distance through a material.
• Absorption Cooling - A process in which cooling of an interior space is accomplished by the evaporation of a volatile fluid, which is then absorbed in a strong solution, then desorbed under pressure by a heat source, and then recondensed at a temperature high enough that the heat of condensation can be rejected to a exterior space.
• Absorption Refrigeration - A system in which a secondary fluid absorbs the refrigerant, releasing heat, then releases the refrigerant and reabsorbs the heat. Ammonia or water is used as the vapor in commercial absorption cycle systems, and water or lithium bromide is the absorber.
• Absorptivity - In a solar thermal system, the ratio of solar energy striking the absorber that is absorbed by the absorber to that of solar energy striking a black body (perfect absorber) at the same temperature. The absorptivity of a material is numerically equal to its emissivity.
• Acceptor - A dopant material, such as boron, which has fewer outer shell electrons than required in an otherwise balanced crystal structure, providing a hole, which can accept a free electron.
• Access Charge - A charge for a power supplier, or its customer, for access to a utility's transmission or distribution system. It is a charge for the right to send electricity over another's wires.
• Account Executive - The agent of a commission house who serves customers/traders by entering their commodity futures and options orders, reporting trade executions, advising on trading strategies, etc.
• Acid Rain - Also called acid precipitation or acid deposition, acid rain is precipitation containing harmful amounts of nitric and sulfuric acids formed primarily by nitrogen oxides and sulfur oxides released into the atmosphere when fossil fuels are burned. It can be wet precipitation (rain, snow, or fog) or dry precipitation (absorbed gaseous and particulate matter, aerosol particles or dust). Acid rain has a pH below 5.6. Normal rain has a pH of about 5.6, which is slightly acidic. The term pH is a measure of acidity or alkalinity and ranges from 0 to 14. A pH measurement of 7 is regarded as neutral. Measurements below 7 indicate increased acidity, while those above indicate increased alkalinity.
• Active Cooling - The use of mechanical heat pipes or pumps to transport heat by circulating heat transfer fluids.
• Active Power - The power (in Watts) used by a device to produce useful work. Also called input power.
• Active Solar Heater - A solar water or space-heating system that moves heated air or water using pumps or fans.
• Active Solar Heating Systems - A solar water or space-heating system that use pumps or fans to circulate the heat-transfer fluid from the solar collectors to a storage tank subsystem.
• Actual Peak Load Reductions - The actual reduction in annual peak load (measured in kilowatts) achieved by consumers that participate in a utility DSM program. It reflects the real changes in the demand for electricity resulting from a utility DSM program that is in effect at the same time the utility experiences its annual peak load, as opposed to the installed peak load reduction capability (i.e., Potential Peak Load Reduction). It should account for the regular cycling of energy efficient units during the period of annual peak load.
• Adiabatic - Without loss or gain of heat to a system. An adiabatic change is a change in volume and pressure of a parcel of gas without an exchange of heat between the parcel and its surroundings. In reference to a steam turbine, the adiabatic efficiency is the ratio of the work done per pound of steam, to the heat energy released and theoretically capable of transformation into mechanical work during the adiabatic expansion of a unit weight of steam.
• Adjustable Speed Drive - An electronic device that controls the rotational speed of motor-driven equipment such as fans, pumps, and compressors. Speed control is achieved by adjusting the frequency of the voltage applied to the motor.
• ADP - Alternative Delivery Procedure. A provision of a futures contract that allows buyers and sellers to make and take delivery under terms or conditions that differ from those prescribed in the contract. An ADP may occur at any time during the delivery period, once long and short futures positions have been matched for the purpose of delivery.
• Affiliate - A company that is controlled by another or that has the same owner as another company.
• Affiliated Power Producer - A generating company that is affiliated with a utility. 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 fueled vehicles, it refers to conversion devices or kits for conventional fuel vehicles.
• AGA - American Gas Association. Major natural gas industry trade association, based in Alexandria, Virginia. AGA conducts technical research and helps create standards for equipment and products involved in every facet of the natural gas industry. It also compiles statistics which are considered industry standards.
• Aggregation - The process of organizing small groups, businesses or residential customer into a larger, more effective bargaining unit that strengthens their purchasing power with utilities.
• Aggregator - An entity that puts together customers into a guying group for the purchase of a commodity service. The vertically integrated investor owned utility, municipal utilities and rural electric cooperatives perform this function in today's power market. Other entities such as buyer cooperatives or brokers could perform this function in a restructured power market.
• Air Collector - In solar heating systems, a type of solar collector in which air is heated in the collector.
• Air Infiltration Measurement - A building energy auditing technique used to determine and/or locate air leaks in a building shell or envelope.
• Air mass - The ratio of the mass of atmosphere in the actual observer-sun path to the mass that would exist if the observer was at sea level, at standard barometric pressure, and the sun was directly overhead. Note--(sometimes called air mass ratio). Air mass varies with the zenith angle of the sun and the local barometric pressure, which changes with altitude. For sun zenith angle, Z, of 62 degrees or less and local atmospheric pressure, P, where Po is standard atmospheric pressure, AM approximately equal sec Z(P/Po). [ASTM E 772] Alternatively, the path length of light through the atmosphere is described in terms of an equivalent relative air mass. AM0 corresponds to the solar spectrum in outer space; at the equator, the average spectrum is AM1, and the reference spectrum for STC was defined to be AM1.5 (average spectrum at 45-degrees latitude).
• Air mass 1.5 (AM1.5) standard reference spectrum - The solar spectral irradiance distribution (diffuse and direct) incident at sea level on a sun-facing 37-degree tilted surface. The atmospheric conditions for AM1.5 are: precipitable water vapor, 14.2 mm; total ozone, 3.4 mm; turbidity (base e, lambda=0.5 mm), 0.27. [ASTM E 892, Table 2]
• Air Pollution - The presence of contaminants in the air in concentrations that prevent the normal dispersive ability of the air, and that interfere with biological processes and human economics.
• Air Pollution Control - The use of devices to limit or prevent the release of pollution into the atmosphere.
• Air Quality Standards - The prescribed level of pollutants allowed in outside or indoor air as established by legislation.
• Air Register - The component of a combustion device that regulates the amount of air entering the combustion chamber.
• Air Retarder/Barrier - A material or structural element that inhibits air flow into and out of a building's envelope or shell. This is a continuous sheet composed of polyethylene, polypropylene, or extruded polystyrene. The sheet is wrapped around the outside of a house during construction to reduce air in-and exfiltration, yet allow water to easily diffuse through it.
• Air Space - The area between the layers of glazing (panes) of a window.
• Air-Source Heat Pump - A type of heat pump that transfers heat from outdoor air to indoor air during the heating season, and works in reverse during the cooling season.
• Air-to-Water Heat Pump - A type of heat pump that transfers heat in outdoor air to water for space or water heating.
• Alaskan System Coordination Council (ASCC) - One of the ten regional reliability councils that make up the North American Electric Reliability Council (NERC).
• Alcohol - A group of organic compounds composed of carbon, hydrogen, and oxygen; a series of molecules composed of a hydrocarbon plus a hydroxyl group; includes methanol, ethanol, isopropyl alcohol and others.
• All or None - A trading order which must be filled in its entirety or not at all.
• Allowance for Funds Used During Construction (AFUD) - Construction activities may be financed from internally generated funds (primarily earnings retained in the business), or from funds provided by other external sources (short- and long-term debt). The allowance for funds used during construction is intended to recognize the cost of these funds dedicated to construction activities during the construction period. To arrive at the "allowance", a common procedural method makes use of a formula that is based on the assumption that short-term debt is the first source of construction funds. The cost rate for short-term debt is based on current costs. Since a utility plant is subject to depreciation, the allowance for funds used during construction is recovered in the form of depreciation from ratepayers over the service life of the plant to which it applies. A noncash item representing the estimated composite interest costs of debt and a return on equity funds used to finance construction. The allowance is capitalized in the property accounts and included in income.
• Alternating Current (AC) - Flow of electricity that constantly changes director between positive and negative sides. Almost all power produced by electric utilities: --usually 100 or 120 times per second (50 or 60 cycles per second or 50//60 Hz).
• Alternative Fuels - A popular term for "non-conventional" transportation fuels derived from natural gas (propane, compressed natural gas, methanol, etc.) or biomass materials (ethanol, methanol).
• Alternator - A generator producing alternating current by the rotation of its rotor, and which is powered by a primary mover.
• Ambient Air - The air external to a building or device.
• Ambient Temperature - The temperature of a medium, such as gas or liquid, which comes into contact with or surrounds an apparatus or building element.
• American Option - An option contract that may be exercised at any time prior to expiration. This differs from a "European option," which may only be exercised on the expiration date. The Exchange options contracts are "American."
• American Public Power Association (APPA) - The trade association of publicly-held/municipal power entities. Public power is a collection of more than 2,000 community-owned electric utilities, serving over 40 million citizens, or about 15 percent of electricity consumers.
• Ammonia - A colorless, pungent, gas (NH3) that is extremely soluble in water, may be used as a refrigerant; a fixed nitrogen form suitable as fertilizer.
• Amorphous Semiconductor - A non-crystalline semiconductor material that has no long-range order.
• Ampere - A unit of measure for an electrical current; the amount of current that flows in a circuit at an electromotive force of one Volt and at a resistance of one Ohm. 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. Abbreviated as amp.
• Amp-Hours - A measure of the flow of current (in amperes) over one hour. Quantity of electricity or measure of charge. (1 Ah = 3600 C [Coulomb])
• Anaerobic Digester - A device for optimizing the anaerobic digestion of biomass and/or animal manure, and possibly to recover biogas for energy production. Digester types include batch, complete mix, continuous flow (horizontal or plug-flow, multiple-tank, and vertical tank), and covered lagoon.
• Anaerobic Digestion - The complex process by which organic matter is decomposed by anaerobic bacteria. The decomposition process produces a gaseous byproduct often called "biogas" primarily composed of methane, carbon dioxide, and hydrogen sulfide.
• Anaerobic Lagoon - A holding pond for livestock manure that is designed to anaerobically stabilize manure, and may be designed to capture biogas, with the use of an impermeable, floating cover.
• Ancillary Services - Ancillary services are those services necessary to support the transmission of energy from resources to loads while maintaining reliable operation of the Transmission Provider's transmission system in accordance with Good Utility Practice.
• Anemometer - An instrument for measuring the force or velocity of wind; a wind gauge.
• Angle of Incidence - In reference to solar energy systems, the angle at which direct sunlight strikes a surface; the angle between the direction of the sun and the perpendicular to the surface. Sunlight with an incident angle of 90 degrees tends to be absorbed, while lower angles tend to be reflected.
• Angle of Inclination - In reference to solar energy systems, the angle that a solar collector is positioned above horizontal.
• Angstrom Unit - A unit of length named for A.J. Angstome, a Swedish spectroscopist, used in measuring electromagnetic radiation equal to 0.000,000,01 centimeters.
• Anhydrous Ethanol - One hundred percent alcohol; neat ethanol.
• Annual Effects - The total effects in energy use (measured in megawatthours) and peak load (measured in kilowatts) caused by all participants in the DSM programs that are in effect during a given year. It includes new and existing participants in existing programs (those implemented in prior years that are in place during the given year) and all participants in new programs (those implemented during the given year). The effects of new participants in existing programs and all participants in new programs should be based on their start-up dates (i.e., if participants enter a program in July, only the effects from July to December should be reported). If start-up dates are unknown and cannot be reasonably estimated, the effects can be annualized (i.e., assume the participants were initiated into the program on January 1 of the given year). The Annual Effects should consider the useful life of efficiency measures, by accounting for building demolition, equipment degradation and attrition.
• Annual Equivalent - An equal cash flow amount that occurs every year.
• Annual Fuel Utilization Efficiency (AFUE) - The measure of seasonal or annual efficiency of a residential heating furnace or boiler. It takes into account the cyclic on/off operation and associated energy losses of the heating unit as it responds to changes in the load, which in turn is affected by changes in weather and occupant controls. A measure of heating efficiency, in consistent units, determined by applying the federal test method for furnaces. This value is intended to represent the ratio of heat transferred to the conditioned space by the fuel energy supplies over one year.
• Annual Load Fraction - That fraction of annual energy demand supplied by a solar system.
• Annual Maximum Demand - The greatest of all demands of the electrical load which occurred during a prescribed interval in a calendar year.
• Annual Transmission Costs - The total annual cost of the Transmission System shall be the amount specified in Schedule 1 until amended by the Transmission Provider or modified by the Commission.
• Annuity - A series of equal cash flows over a number of years.
• Anode - The positive pole or electrode of an electrolytic cell, vacuum tube, etc. (see also sacrificial anode).
• Anthracite (coal) - A hard, dense type of coal, that is hard to break, clean to handle, difficult to ignite, and that burns with an intense flame and with the virtual absence of smoke because it contains a high percentage of fixed carbon and a low percentage of volatile matter.
• Anthropogenic - Referring to alterations in the environment due to the presence or activities of humans.
• Antireflection Coating - A thin coating of a material applied to a photovoltaic cell surface that reduces the light reflection and increases light transmission.
• Aperture - An opening; in solar collectors, the area through which solar radiation is admitted and directed to the absorber.
• API - American Petroleum Institute. The primary U.S. oil industry trade association, based in Washington, D.C. API conducts research and sets technical standards for industry equipment and products from wellhead to retail outlet. It also compiles statistics which are regarded as industry benchmarks.
• API Gravity - Gravity (weight per unit volume) of oils as measured by the API scale whereby: API Gravity =141.5 specific gravity at 60o F=- 131.5
• Apparent Day - A solar day; an interval between successive transits of the sun's center across an observer's meridian; the time thus measured is not equal to clock time.
• Apparent Power (kVA) - This is the voltage-ampere requirement of a device designed to convert electric energy to a non-electrical form.
• Appliance Energy Efficiency Ratings - The ratings under which specified appliances convert energy sources into useful energy, as determined by procedures established by the U.S. Department of Energy.
• Appliance Saturation - The percentage of households or buildings in a service area that have the type of equipment to which the demand-side technology applies. For example, if 50 percent of the residential customers have a central air conditioner, the appliance saturation is 50 percent.
• Appliance Standards - Standards established by the U.S. Congress for energy consuming appliances in the National Appliance Energy Conservation Act (NAECA) of 1987, and as amended in the National Appliance Energy Conservation Amendments of 1988, and the Energy Policy Act of 1992 (EPAct). NAECA established minimum standards of energy efficiency for refrigerators, refrigerator-freezers, freezers, room air conditioners, fluorescent lamp ballasts, incandescent reflector lamps, clothes dryers, clothes washers, dishwashers, kitchen ranges and ovens, pool heaters, television sets (withdrawn in 1995), and water heaters. The EPAct added standards for some fluorescent and incandescent reflector lamps, plumbing products, electric motors, and commercial water heaters and Heating, Ventilation, and Air Conditioning (HVAC) systems. It also allowed for the future development of standards for many other products. The U.S. Department of Energy (DOE) is responsible establishing the standards and the procedures that manufacturers must use to test their models. These procedures are published in the Code of Federal Regulations (10 CFR, Ch. II, Part 430), January 1, 1994 (Federal Register).
• Applicability Factor - The percentage of end-use energy and demand used by a technology to which the demand-side management (DSM) measure applies. For example, the high-efficiency fluorescent lighting DSM measure applies to fluorescent lighting but not all lighting. Applicability therefore represents the percent of the lighting end-use attributable to fluorescence for which there could be high-efficiency replacements installed.
• Arbitrage - The simultaneous purchase of one commodity against the sale of another in order to profit from fluctuations in the usual price relationships. Variations include the simultaneous purchase and sale of different delivery months of the same commodity; of the same delivery month, but different grades of the same commodity; and of different commodities.
• Area Load - The total amount of electricity being used at a given point in time by all consumers in a utility's service territory.
• Argon - A colorless, odorless inert gas sometimes used in the spaces between the panes in energy efficient windows. This gas is used because it will transfer less heat than air. Therefore, it provides additional protection against conduction and convection of heat over conventional double -pane windows.
• Array (Solar) - Any number of solar photovoltaic modules or solar thermal collectors or reflectors connected together to provide electrical or thermal energy.
• Ash - Impurities consisting of silica, iron, alumina, and other noncombustible matter that are contained in coal. Ash increases the weight of coal, adds to the cost of handling, and can affect its burning characteristics. Ash content is measured as a percent by weight of coal on an "as received" or a "dry" (moisture-free, usually part of a laboratory analysis) basis.
• ASHRAE - Abbreviation for the American Society of Heating, Refrigeration, and Air-Conditioning Engineers.
• Ask - A motion to sell. The same as offer.
• Asset - An economic resource, tangible or intangible, which is expected to provide benefits to a business.
• Assignment - The process by which the seller of an option is notified of a buyer's intention to exercise the rights associated with the option.
• Associated Gas - Natural gas present in a crude oil reservoir, either separate from or in solution with the oil.
• ASTM - American Society for Testing Materials. Grade and quality specifications for petroleum products and metals are determined by the ASTM in test methods.
• Asynchronous Generator - A type of electric generator that produces alternating current that matches an existing power source.
• Atmospheric Pressure - The pressure of the air at sea level; one standard atmosphere at zero degrees centigrade is equal to 14.695 pounds per square inch (1.033 kilograms per square centimeter).
• Atrium - An interior court to which rooms open.
• At-the-Market - An order to buy or sell a futures contract at whatever price is obtainable when the order reaches the trading floor. Also called a market order.
• At-the-Money - An option whose exercise, or strike, price is closest to the futures price.
• Attributes - Attributes are the outcomes by which the relative "goodness" of a particular expansion plan is measured e.g. fuel usage. Some attributes, such as fuel usage, are measured in well-defined parameters. Other attributes (e.g. public perception of a technology) are more subjective. Attributes may be grouped in several ways. Categories include financial, economic, performance, fuel usage, environmental, and socioeconomic. The attributes chosen must measure issues that directly concern the utility and have an impact on its planning objectives. Limiting the number of attributes reduces the complexity and cost of a study.
• Audit (Energy) - The process of determining energy consumption, by various techniques, of a building or facility.
• Automatic (or Remote) Meter Reading System - A system that records the consumption of electricity, gas, water, etc, and sends the data to a central data accumulation device.
• Automatic Damper - A device that cuts off the flow of hot or cold air to or from a room as controlled by a thermostat.
• Automatic Exercise - Following options expiration, an option which is in-the-money by $100 or more is exercised automatically by the clearinghouse, unless the holder of the option submits specific instructions to the contrary.
• Autonomous System - A stand-alone PV system that has no back-up generating source. May or may not include storage batteries.
• Auxiliary Energy or System - Energy required to operate mechanical components of an energy system, or a source of energy or energy supply system to back-up another.
• Availability - Describes the reliability of power plants. It refers to the number of hours that a power plant is available to produce power divided by the total hours in a set time period, usually a year.
• Available but not Needed Capability - Capability of generating units that are operable but not necessary to carry load.
• Available Heat - The amount of heat energy that may be converted into useful energy from a fuel.
• 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 includes operations and maintenance, tax, and fuel expenses.
• Average Demand - The 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 kilowatt-hours divided by the units of time in the interval.
• Average Revenue per Kilowatt-hour - The average revenue per kilowatt-hour of electricity sold by sector (residential, commercial, industrial, or other) and geographic area (State, Census division, and National), is calculated by dividing the total monthly revenue by the corresponding total monthly sales for each sector and geographic area.
• Average Wind Speed (or Velocity) - The mean wind speed over a specified period of time.
• Avoided Costs - These are costs that a utility avoids by purchasing power from an independent producer rather than generating power themselves, purchasing power from another source or constructing new power plants. A Public Utility Commission calculates avoided costs for each utility, and these costs are the basis upon which independent power producers are paid for the electricity they produce. There are two parts to an avoided cost calculation: the avoided capacity cost of constructing new power plants and the avoided energy cost of fuel and operating and maintaining utility power plants. The minimum amount an electric utility is required to pay an independent power producer, under the PURPA regulations of 1978, equal to the costs the utility calculates it avoids in not having to produce that power (usually substantially less than the retail price charged by the utility for power it sells to customers).
• Avoirdupois Unit - Customary U.S. weights. 1 troy ounce = 1.09 ounces avoirdupois.
• AWG - The abbreviation for American Wire Gauge; the standard for gauging the size of wires (electrical conductors).
• Axial Fans - Fans 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 Compressor - A type of air compressor in which air is compressed in a series of stages as it flows axialy through a decreasing tubular area.
• Axial Flow Turbine - A 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.