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Energy Industry Words and Acronyms

Our glossary is designed to provide you with helpful definitions for the many words and acronyms used in the energy industry.

If you would like to see a new word or term added please let us know.

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Active Solar Energy System

A system designed to convert solar radiation into usable energy for producing electricity, space heating, water heating, or other uses. It requires mechanical devices, usually, photovoltaic cells, pump or fan to collect the sun's energy.


An entity registered with the PURA that brings a group of consumers together to buy energy in bulk. The group of consumers is called a buying group.

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 Pollution

Unwanted particles, mist, or gases put into the atmosphere as a result of motor vehicle exhaust, heating systems, electric generators; the operation of industrial facilities or other human activity.

Alternating Current (AC)

Flow of electricity that constantly changes electric wave direction between positive and negative sides. Almost all power produced by electric utilities in the United States moves in current that shifts direction at a rate of 60 times per second.

Alternative Fuel Vehicle (AFV)

A motor vehicle that runs on fuels other than petroleum-based fuels.

Alternative 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.

Ambient Air Temperature

Surrounding temperature, such as the outdoor air temperature, around a building.

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).

Anaerobic Digestion

A biological process where bacteria decomposes organic matter in the absence of oxygen. For more information, please visit Anaerobic Digestion.

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 creating a type of biomass energy.


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.


Inorganic, non-flammable substance left over after combustible material has been completely burned.


The smallest unit of an element consisting of a dense positively charged nucleus consisting of protons (which have a positive charge) and neutrons (which have a neutral charge) orbited by negatively charged electrons.


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.

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A device that provides starting voltage and limits the current during normal operation in electrical discharge lamps (such as fluorescent lamps).


In the petroleum industry, a barrel is 42 U.S. gallons. One barrel of oil has an energy content of 6 million British thermal units (Btu).

Barrels Per Day Equivalent

A unit of measure that tells how much oil would have to be burned to produce the same amount of energy.


A device that stores energy and produces electric current by chemical action.


Processes that use plants or micro-organisms to change one form of energy into another. For example, an experimental process uses algae to convert solar energy into gas that could be used for fuel.


A transportation fuel for use in diesel engines that is produced through the transesterification of organically-derived oil or fats. It may be used either as a replacement for or as a component in diesel fuel.


A mixture of methane and carbon dioxide produced by the bacterial decomposition of organic wastes and used as a fuel.


Energy resources derived from organic matter. These include wood, agricultural waste and other living-cell material that can be burned to produce heat energy. They also include algae, sewage, and other organic substances that may be used to make energy through chemical processes. For more information please visit, Biomass.


Electricity generated through burning biomass directly, or through turning biomass into fuels (gaseous or liquid) that burn more efficiently.

Bituminous Coal

Soft coal containing large amounts of carbon. It has a luminous flame and produces a great deal of smoke. Bituminous coal is the most abundant coal in active U.S. mining regions. The heat content of bituminous coal consumed in the United States averages 24 million Btu per ton.


A power loss affecting electricity consumers over a large geographical area for a significant period of time.

Blanket Insulation

A type of insulation consisting of flexible fibers that is available in batts (pre-cut) or rolls, with or without facings. Blanket insulation is the most common and widely available type of insulation.

Blown-in Insulation

Small particles of fiber, foam, or other materials that can be blown in for insulation purposes. A good choice for adding insulation to retrofits and difficult locations, as it can conform to any space without disturbing the structures or finishes.


A closed vessel in which water is converted to hot water or pressurized steam. The steam is then subsequently used to heat a building or to turn a turbine.

Bottled Gas

The liquefied petroleum gases including propane and butane, contained under moderate pressure in cylinders.


A nuclear reactor that produces more fuel than it consumes. The breeder, invented in the United States, is used as a power source in several European countries.

British Thermal Unit (BTU)

The standard measure of heat energy. It takes one Btu to raise the temperature of one pound of water by one degree Fahrenheit at sea level. One Btu is equivalent to 252 calories, 778 foot-pounds, 1055 joules, and 0.293 watt-hours.


A third party that may manage the sale of electric energy from a generation company to a consumer, but generally does not hold title to the power.


A controlled power reduction in which the utility decreases the voltage on the power lines so customers receive lower voltage electricity. Brownouts can be used if total power demands exceed the maximum available supply.

Bundled or Fully Bundled Rates

All generation, transmission, and distribution services provided by one entity for a single charge. This would include all ancillary and retail services.

Bunker C Fuel Oil

A very heavy substance, left over after other fuels have been distilled from crude oil. Also called NO. 6 FUEL, it is used in power plants, ships, and large heating installations. Bunker C fuel oil has high sulfur content, which causes air quality concerns when burned as fuel.

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One energy calorie is equivalent to 4.2 joules. One food calorie equals 1,000 energy calories.


The maximum amount of electricity that a generating unit, power plant, or utility can produce under specified conditions. Capacity is measured in megawatts and is also referred to as the nameplate rating.

Carbon Dioxide (CO2)

A colorless, odorless, non-poisonous gas that is a normal part of the air. Carbon dioxide, also called CO2, is exhaled by humans and animals, is emitted when burning fossil fuels, and is absorbed by plants and the sea.

Carbon Monoxide (CO)

A colorless, odorless, highly poisonous gas made up of carbon and oxygen molecules formed by the incomplete combustion of carbon or carbonaceous material, including gasoline. It is a major air pollutant on the basis of weight.


A temperature scale based on the freezing (0 degrees) and boiling (100 degrees) points of water. Abbreviated as C in second and subsequent references in text and was formerly known as Centigrade. To convert Celsius to Fahrenheit, multiply the Celsius number by 9, divide by 5, and add 32.

Chemical Energy

The energy generated when a chemical compound combusts, decomposes, or transforms to produce new compounds.


One complete run of a set of electric conductors from a power source to various electrical devices (appliances, lights, etc.) and back to the same power source.

Climate Change

Any significant change in global or regional climate patterns lasting for an extended period of time. It includes major changes in temperature, precipitation, or wind patterns that occur over several decades. Increased levels of atmospheric carbon dioxide produced by the use of fossil fuels is recognized as the major cause of the change from the mid to late 20th century and onwards.


Black or brown rock, formed under pressure from organic fossils in prehistoric times that is mined and burned to produce heat energy. Coal is a fossil fuel.


The combustion of a solid or gas biofuel along with a traditional petroleum-based fuel. Co-firing reduces the amount of greenhouse gases that are released and can be done in existing power plants with little or no modification.


Cogeneration, also known as Combined Heat and Power (CHP), is the use of energy for the simultaneous production of electrical and useful thermal energy. The sequence can be thermal use followed by power production or the reverse, subject to the following standards: (a) At least 5 percent of the cogeneration project's total annual energy output shall be in the form of useful thermal energy. (b) Where useful thermal energy follows power production, the useful annual power output plus one-half the useful annual thermal energy output equals not less than 42.5 percent of any natural gas and oil energy input.


A porous solid left over after the incomplete burning of coal or of crude oil.

Combined Cycle Plant

An electric generating station that uses waste heat from its gas turbines to produce steam for a conventional steam turbine generator.

Combined Heat and Power Systems (CHP)

See cogeneration.


Burning - Rapid oxidation, with the release of energy in the form of heat and light.

Comfort Zone

The range of temperatures over which the majority of persons feel comfortable (neither too hot nor too cold).

Compact Fluorescent Lamp (CFL)

A type of energy efficient light bulb that uses a tube filled with argon and a small amount of mercury vapor. When an electric current is driven through the tube the bulb emits visible light. A CFL bulb lasts a minimum of 10,000 hours but should only be used in secure locations to avoid breakage. To learn more, visit Types of Light Bulbs.  

Competitive Transition Assessment (CTA)

The part of a consumer's electric bill that allows the electric distribution company to recover stranded costs.

Concentrating Solar Power (CSP)

Solar power generated by using mirrors or lenses to concentrate a large area of sunlight, or solar thermal energy, onto a small area called a receiver. CSP system configurations include parabolic trough, linear fresnel, power tower, and dish engine.


The transfer of heat energy through a material (solid, liquid, or gas) by the motion of adjacent atoms and molecules without gross displacement of the particles.

Conductivity (K)

The quantity of heat that will flow through one square foot of homogeneous material, one inch thick, in one hour, when there is a temperature difference of one degree Fahrenheit.


A substance or medium that transmits heat, light, electrons, or sound.


Steps taken to cause less energy to be used than would otherwise be the case. These steps may involve avoidance of waste, reduced consumption, etc. They may involve installing equipment (such as computerized controls to ensure efficient energy use), modifying equipment (such as making a boiler more efficient), adding insulation, changing behavior patterns etc.


Transferring heat by moving air, or transferring heat by means of upward motion of particles of liquid or gas heat from beneath.

Cooling Degree Day

A unit of measure that indicates how heavy the air conditioning needs are under certain weather conditions. For a day where the temperature averages about 71 degrees you accumulate 1 cooling degree day.


A measure of volume, 4 by 4 by 8 feet, used to define amounts of stacked wood available for use as fuel. Burned, a cord of wood produces about 5 million calories of energy.

Crude Oil

Petroleum as found in the earth before it is refined into oil products. Crude oil is refined to produce petroleum products, including heating oils; gasoline, diesel and jet fuels; lubricants; asphalt; ethane, propane, and butane; and many other products used for their energy or chemical content.

Cubic Feet per Minute (CFM)

A measure of flow rate for gaseous substances.

Cubic Foot

The most common unit of measurement of natural gas volume. It equals the amount of gas required to fill a volume of one cubic foot under stated conditions of temperature, pressure, and water vapor. One cubic foot of natural gas has an energy content of approximately 1,000 Btus. One hundred (100) cubic feet equals one therm (or 100,000 Btu).


A measure of radioactivity.

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Day lighting

The use of sunlight to supplement or replace need for electric lighting during the daytime hours.


Breaking the link between an electric company's earnings and its sales of electricity.

Degree Day

A unit, based temperature difference and time, used in estimating fuel consumption and specifying nominal annual heating load of a building. When the mean temperature is less than 65 degrees Fahrenheit the heating degree days are equal to the total number of days that average temperature is less than 65 degrees Fahrenheit for an entire year.


The level at which electricity or natural gas is delivered to users at a given point in time. Electric demand is expressed in kilowatts.

Demand Side Management (DSM)

The planning, implementation, and evaluation of conservation and load manipulation to use electricity more efficiently.

Department of Energy (DOE)

The federal department established by the Department of Energy Organization Act to consolidate the major federal energy functions into one cabinet-level department that would formulate a comprehensive, balanced national energy policy.

Department of Energy and Environmental Protection (DEEP)

The Connecticut Department of Energy and Environmental Protection (DEEP) is charged with conserving, improving and protecting the natural resources and the environment of the state of Connecticut as well as making cheaper, cleaner and more reliable energy available for the people and businesses of the state. DEEP was established on July 1, 2011 with the consolidation of the Department of Environmental Protection, the Department of Public Utility Control, and energy policy staff from other areas of state government.

Department of Public Utility Control (DPUC)

The predecessor of the Public Utilities Regulatory Authority (PURA). PURA replaces the former Department of Public Utility Control (DPUC) and along with the Bureau of Energy and Technology Policy, is part of the Energy Branch of the Department of Energy and Environmental Protection (DEEP). DEEP was created in July 2011 and brings together the state's Department of Environmental Protection (DEP), the Department of Public Utility Control (DPUC) and an energy policy group that had been based at the Office of Policy and Management. See PURA for more information.


The elimination of regulation from a previously regulated industry or sector of an industry. The dissolving of a regulated monopoly structure.


The removal of salt from saline or sea water.

Diesel Oil

Fuel for diesel engines obtained from the distillation of petroleum. It is composed chiefly of aliphatic hydrocarbons its efficiency is measured by a cetane number.


The solid and liquid digested material that is produced through Anaerobic Digestion.

Direct Combustion

The process that converts biomass material to heat energy, most commonly through the use of a boiler or furnace.

Direct Current (DC)

Electricity that flows continuously in the same direction. Battery cells produce DC.

Distillate Fuel Oil

A general classification for one of the petroleum fractions produced in conventional distillation operations. It includes diesel fuels and fuel oils. Products known as No. 1, No. 2, and No. 4 diesel fuel are used in on-highway diesel engines, such as those in trucks and automobiles, as well as off-highway engines, such as those in railroad locomotives and agricultural machinery. Products known as No. 1, No. 2, and No. 4 fuel oils are used primarily for space heating and electric power generation.

Distillate Fuel Oil No. 1 Diesel Fuel

A light distillate fuel oil that has distillation temperatures of 550 degrees Fahrenheit at the 90 percent point and meets the specifications defined in ASTM Specification D 975. It is used in high-speed diesel engines, such as those in city buses and similar vehicles.

Distillate Fuel Oil No. 2 Diesel Fuel

A fuel that has distillation temperatures of 500 degrees Fahrenheit at the 10 percent recovery point and 640 degrees Fahrenheit at the 90 percent recovery point and meets the specifications defined in ASTM Specification D 975. It is used in high-speed diesel engines, such as those in railroad locomotives, trucks, and automobiles. Low Sulfur Diesel Fuel: No. 2 diesel fuel that has a sulfur level no higher than 0.05 percent by weight. It is used primarily in motor vehicle diesel engines for on-highway use. High Sulfur Diesel Fuel: No. 2 diesel fuel that has a sulfur level above 0.05 percent by weight. Fuel oil (Heating Oil): A distillate fuel oil that has distillation temperatures of 400 degrees Fahrenheit at the 10 percent recovery point and 640 degrees Fahrenheit at the 90 percent recovery point and meets the specifications defined in ASTM Specification D 396. It is used in atomizing type burners for domestic heating or for moderate capacity commercial/industrial burner units.

Distillate Fuel Oil No. 4 Fuel

A distillate fuel oil made by blending distillate fuel oil and residual fuel oil stocks. It conforms with ASTM Specification D 396 or Federal Specification VV-F-815C and is used extensively in industrial plants and in commercial burner installations that are not equipped with preheating facilities. It also includes No. 4 diesel fuel used for low- and medium-speed diesel engines and conforms to ASTM Specification D 975.

Distributed Wind

Refers to smaller turbines that produce 100 kilowatts or less and are primarily used to power a home, farm, or small business. However, the proximity to End-Use and point of interconnection can overrule the amount of kilowatts produced for distributed wind, meaning that a multi-megawatt turbine at a manufacturing facility can be considered distributed wind if it is installed at or near the point of end-use in order to meet the onsite energy demand.


The delivery of electricity to the retail customer's home or business through low voltage distribution lines. Voltages range from 4200V to 66KV (KV = Kilo Volts)

Distribution System

The substations, transformers, and lines that convey electricity from high-power transmission lines to consumers and businesses.

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Electric Utility

Any organization with a monopoly franchise (including any municipality), which sells electric energy to end-use customers.

Electric Vehicle (EV)

An electric vehicle (EV) uses one or more electric motors or traction motors for propulsion, as opposed to an internal combustion engine. Three main types of electric vehicles exist, those that are directly powered from an external power station, those that are powered by stored electricity originally from an external power source, and those that are powered by an on-board electrical generator, such as an internal combustion engine (a hybrid electric vehicle) or a hydrogen fuel cell.


A property of the basic particles of matter. A form of energy having magnetic, radiant, and chemical effects. Electric current is created by a flow of charged particles (electrons).

Electricity Congestion

A condition that occurs when insufficient transmission capacity is available to transmit electricity from one location to another and to implement all of the desired transactions simultaneously.

Electricity Demand

The rate at which energy is delivered to meet the electric loads requiring generation, transmission, and distribution facilities.


Breaking a chemical compound down into its elements by passing a direct current through it. Electrolysis of water, for example, produces hydrogen and oxygen.

Electromagnetic Fields (EMF)

Electricity produces magnetic and electric fields. These 60 Hertz fields (fields that go back and forth 60 times a second) are associated with electrical appliances, power lines and wiring in buildings.

Emission Standard

The maximum amount of a pollutant legally permitted to be discharged from a single source.


The capacity for doing work. Forms of energy include thermal, mechanical, electrical and chemical. Energy may be transformed from one form into another.

Energy Budget

A requirement in the Building Energy Efficiency Standards that a proposed building be designed to consume no more than a specified number of British thermal units (Btus) per year per square foot of conditioned floor area.

Energy Efficient

Using less energy to do the same amount of work. Learn why Energy Efficiency is important!

Energy Efficient Technology

Equipment that uses less energy to perform the same functions, i.e. a high efficiency boiler. 

Energy Efficient Behavior 

Also known as Conservation. 

Energy Reserves

The portion of total energy resources that is known and available that can be provided to the electric grid with presently available technology at an affordable cost.

Environmental Protection Agency (EPA)

The primary federal agency charged with protecting the environment.

Ethanol (CH3CH2OH)

A liquid that is produced chemically from ethylene or biologically from the fermentation of various sugars from carbohydrates found in agricultural crops and residues from crops or wood. Used in the United States as a gasoline octane enhancer and oxygenate, it increases octane 2.5 to 3.0 numbers at 10 percent concentration. Ethanol can also be used in higher concentration (E85) in vehicles optimized for its use. Also known as Ethyl Alcohol or Grain Alcohol.

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The covering sometimes found on one side of insulation, often made of material such as kraft paper, foil-kraft paper, or vinyl. Facing serves as a vapor barrier and prevents moisture from moving from a heated space to a colder space.

Fahrenheit (F)

A temperature scale in which the boiling point of water is 212 degrees and its freezing point is 32 degrees. To convert Fahrenheit to Celsius, subtract 32, multiply by 5, and divide the product by 9.

Federally-Mandated Congestion Costs (FMCC)

Effective January 1, 2004, federal law requires that two line item charges for congestion costs, energy-related and/or reliability-related costs be added to customer bills. They are defined as charges to the consumer resulting from deficiencies in the electricity transportation system. Congestion costs occur when a more costly generator is dispatched before a less costly one because there isn't adequate transmission capacity to get the generation from the less costly plant to the load center that needs it.


A release of energy caused by the splitting of an atom's nucleus. This is the energy process used in conventional nuclear power plants to make the heat needed to run steam electric turbines.

Fissionable Material

A substance whose atoms can be split by slow neutrons. Uranium-235, plutonium-239 and uranium-233 are fissionable materials.

Flat Plate

A device used to collect solar thermal energy. It is a box with a metal surface painted black on the side facing the sun, to absorb the sun's heat.

Flue Gas

Gas that is left over after fuel is burned and which is disposed of through a pipe or stack to the outer air.


A tubular electric lamp that is coated on its inner surface with a phosphor and that contains mercury vapor whose bombardment by electrons from the cathode provides ultraviolet light which causes the phosphor to emit visible light either of a selected color or closely approximating daylight.


A unit of luminance measured on a work surface that is one foot from a uniform point source of light of one candle and is equal to one lumen per square foot.

Fossil Fuel

Oil, coal, natural gas, or their by-products. Fuel that was formed in the earth in prehistoric times from remains of living-cell organisms.


A substance that can be used to produce heat or power.

Fuel Cell

An electrochemical device that converts the chemical energy of a fuel, such as hydrogen, and an oxidant, such as oxygen, directly into electricity. The principal components of a fuel cell are catalytically activated electrodes for the fuel (anode) and the oxidant (cathode) and an electrolyte to conduct ions between the two electrodes, thus producing electricity. Waste heat from the chemical process can be used to meet thermal loads.

Fuel Oil

Petroleum products that are burned to produce heat or power.

Fuel Rod

A long slender tube that holds fissionable material (fuel) for nuclear reactor use. Fuel rods are assembled into bundles called fuel elements or assemblies, which are loaded individually into the reactor core.

Fully Bundled Service

All generation, transmission, and distribution services provided by one entity for a single charge. This would include all ancillary and retail services.

Fusion Energy

A power source, now under development, based on the release of energy that occurs when atoms are combined under the most extreme heat and pressure. It is the energy process of the sun and the stars.

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A unit of volume. A U.S. gallon has 231 cubic inches or 3.785 liters.


Gaseous fuel (usually natural gas) that is burned to produce heat energy. The word is also used colloquially to refer to gasoline.

Gas Utility

Any person engaged in, or authorized to engage in, distributing or transporting natural gas, including, but not limited to, any such person who is subject to the regulation of the Public Utilities Commission.


The process where biomass fuel is reacted with sub-stoichiometric quantities of air and oxygen usually under high pressure and temperature along with moisture to produce gas which contains hydrogen, methane, carbon monoxide, nitrogen, water and carbon dioxide. The gas can be burned directly in a boiler, or scrubbed and combusted in an engine-generator to produce electricity. The three types of gasification technologies available for biomass fuels are the fixed bed updraft, fixed bed downdraft and fluidized bed gasifies. Gasification is also the production of synthetic gas from coal.


In the United States, gasohol (E10) refers to gasoline that contains 10 percent ethanol by volume. This term was used in the late 1970s and early 1980s but has been replaced in some areas of the country by terms such as E10, Super Unleaded Plus Ethanol, or Unleaded Plus.


A light petroleum product obtained by refining oil and is used as motor vehicle fuel.

Gasoline Grades

The classification of gasoline by octane ratings. Each type of gasoline (conventional, oxygenated, and reformulated) is classified by three grades - Regular, Mid-grade, and Premium. In general, automotive octane requirements are lower at high altitudes. Therefore, in some areas of the United States, such as the Rocky Mountain States, the octane ratings for the gasoline grades may be 2 or more octane points lower. Regular gasoline: Gasoline having an antiknock index, i.e., octane rating, greater than or equal to 85 and less than 88. Mid-grade gasoline: Gasoline having an antiknock index, i.e., octane rating, greater than or equal to 88 and less than or equal to 90. Premium gasoline: Gasoline having an antiknock index, i.e., octane rating, greater than 90.

Generation Company (GenCo)

A regulated or non-regulated entity (depending upon the industry structure) that operates and maintains existing generating plants. The Genco may own the generation plants or interact with the short-term market on behalf of plant owners. In the context of restructuring the market for electricity, Genco is sometimes used to describe a specialized marketer for the generating plants formerly owned by a vertically-integrated utility.

Geographic Information System (GIS)

An organized collection of computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information.

Geothermal Energy

Energy obtained from within the earth's crust, originating in its core. Includes water or steam extracted from geothermal reservoirs that can be used for geothermal heat pumps, water heating, or electricity generation. For more information, please visit Geothermal Energy.

Geothermal Gradient

The change in the earth's temperature with depth. As one goes deeper, the earth becomes hotter.

Geothermal Heat Pump (GHP)

Provides highly efficient heating and cooling through the use of the earth's constant temperature.  Also known as Ground Source Heat Pump (GSHP).

Gigawatt (GW)

One thousand megawatts (1,000 MW) or one million kilowatts (kW) or one billion watts (1,000,000,000 watts) of electricity. One gigawatt is enough to supply the electric demand of about 2,000,000 average homes.

Global Warming

An increase in the near surface temperature of the Earth. Global warming has occurred in the distant past as the result of natural influences, but the term today most often used to refer to the warming that scientists predict is occurring as a result of increased emissions of greenhouse gases.

Greenhouse Effect

The presence of trace atmospheric gases make the earth warmer than would direct sunlight alone. These gases (carbon dioxide [CO 2], methane [CH 4], nitrous oxide [N 2O], tropospheric ozone [O 3], and water vapor [H 2O]) allow visible light and ultraviolet light (shortwave radiation) to pass through the atmosphere and heat the earth's surface. This heat is re-radiated from the earth in form of infrared energy (longwave radiation). The greenhouse gases absorb part of that energy before it escapes into space. This process of trapping the longwave radiation is known as the greenhouse effect. Scientists estimate that without the greenhouse effect, the earth's surface would be roughly 54 degrees Fahrenheit colder than it is today -- too cold to support life as we know it.

Greenhouse Gases

Those gases, such as water vapor, carbon dioxide, nitrous oxide, methane, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride, that are transparent to solar (short-wave) radiation but opaque to long-wave (infrared) radiation, thus preventing long-wave radiant energy from leaving Earth's atmosphere. The net effect is a trapping of absorbed radiation and a tendency to warm the planet's surface.


A system of interconnected transmission power lines and generators that is managed so that the generators are dispatched as needed to meet the requirements of the customers connected to the gird at various points. The independent system operator (ISO) is sometimes used to identify a company responsible for the operation of the grid for

Ground Source Heat Pump (GSHP)

See Geothermal Heat Pump (GHP). 

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Heat Gain

An increase in the amount of heat contained in a space, resulting from direct solar radiation, heat flow through walls, windows, and other building surfaces, and the heat given off by people, lights, equipment and other sources within the space.

Heat Loss

A decrease in the amount of heat contained in a space, resulting from heat flow through walls, windows, roof and other building surfaces and from exfiltration of warm air through leaks in the structure.

Heat Pump

A refrigeration unit, similar to an air-conditioning unit that is capable of heating by refrigeration; transferring heat from one (often cooler) medium to another (often warmer) medium. This reversible-cycle air conditioner usually provides cooling in summer and heating in winter.

Heating Degree Day

A unit that measures the space heating needs during a given period of time. It is calculated by adding together the number of degrees under 65 degrees that occurs within a given time period. This total is the number of heating degree days.

Heating Ventilation and Air Conditioning (HVAC)

A system that provides heating, ventilation and/or cooling within or associated with a building.

Heavy Water

A type of hydrogen atom that may be used as fuel for fusion power plants. Also called deuterium, it is found in abundance in the seas.


Using solar radiation to cause chemical reactions.


A process that uses the sun's rays to produce heat


A unit of electromagnetic wave frequency that is equal to one cycle per second. It is named after Henrich R. Hertz.

High Sulfur Coal

Coal whose weight is more than one percent sulfur.

High Voltage

High power transmission line service of 110 kilovolts (kV) to 765 kV that is used as a primary service for industrial applications.

Horsepower (HP)

A unit for measuring the rate of doing work. One horsepower equals about three-fourths of a kilowatt (745.7 watts).

Hybrid Vehicle

Usually a hybrid EV, a vehicle that employs a combustion engine system together with an electric propulsion system. Hybrid technologies expand the usable range of EVs beyond what an all-electric-vehicle can achieve with batteries only. Hybrid EVs charge their batteries with their engine and breaking system.

Hydroelectric Power

Electricity produced by falling water that turns a turbine generator. Also referred to as HYDRO. For more information, please visit Hydropower.

Hydrogen (H)

A colorless, odorless, highly flammable gaseous element. It is the lightest of all gases and the most abundant element in the universe, occurring chiefly in combination with oxygen in water and also in acids, bases, alcohols, petroleum, and other hydrocarbons.

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A facility that uses a dam built across a river to store water in a reservoir until it is needed. When water is released from the reservoir, it flows through a turbine, spins its blades, and powers a generator that produces electricity.

Incandescent Lamp

An electric lamp in which a filament is heated by an electric current until it emits visible light. Much of the energy is converted into heat; therefore, this class of lamp is a relatively inefficient source of light.

Independent System Operator (ISO)

An independent entity that operates the electric power grid to coordinate generation and transmission. For the New England states, it is ISO-New England.


The total amount of solar radiation (direct, diffuse, and reflected) striking a surface exposed to the sky.


Material designed to prevent heat from being transmitted from one area to another. It reduces heat loss or gain by serving as a barrier between areas that have significant differences in temperature. For more information, please visit Insulation.

Insulation Concrete Forms (ICFs)

Cast-in-place (usually reinforced) concrete walls that are sandwiched between two layers of insulation.

Integrated Resource Plan (IRP)

Public Act 11-80 required the Department of Energy and Environmental Protection (DEEP) to prepare an Integrated Resource Plan. An Integrated Resource Plan (IRP) is comprised of an assessment of the future electric needs and a plan to meet those future needs. It is integrated in that it looks at both demand side (conservation, energy efficiency, etc.) resources as well as the more traditional supply side (generation/power plants, transmission lines, etc.) resources in making its recommendations on how best to meet future electric energy needs in the state.

Internal Combustion Engine

An engine in which fuel is burned inside the engine. A car's gasoline engine or rotary engine is an example of an internal combustion engine.

Interruptible Service

Electricity or natural gas supplied under agreements that allow the supplier to curtail or stop service under contracted, pre-agreed market or supply conditions.


An atom or group of atoms that is electrically charged.

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Joule (J)

A unit of work or energy equal to the amount of work done when the point of application of force of 1 newton is displaced 1 meter in the direction of the force. It takes 1,055 joules to equal a British thermal unit.

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A light petroleum distillate that is used in space heaters, cook stoves, and water heaters and is suitable for use as a light source when burned in wick-fed lamps.

Kilovolt (kV)

One thousand volts (1,000). Distribution lines in residential areas are usually from 4.8 to 38 kV (4800v to 38000v).

Kilowatt (kW)

One thousand (1,000) watts. A unit of measure of the amount of constant electricity needed to operate given equipment. On a hot summer afternoon a typical home, with central air conditioning and other equipment in use, might have a demand of 4 kW.

Kilowatt-Hour (kWh)

The most commonly used unit of measure that measures energy consumed over time. It means one kilowatt of electricity supplied for one hour. In 2007 a typical household consumed about 700 kWh in an average month.  An energy measurement (one kilowatt for one hour).

Kilovolt-Amp (kVA)

A unit of electrical power that can be used in rating transformer and generator strength.  One kilovolt-amp is equal to 1,000 volt-amperes. 

Kinetic Energy

Energy of a body or system due to its motion or movement.

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Landfill Gas

Gas generated by the natural degrading and decomposition of municipal solid waste by anaerobic microorganisms in sanitary landfills. The gases produced, carbon dioxide and methane, can be collected by a series of low-level pressure wells and can be processed into a medium Btu gas that can be burned to generate steam or electricity.

Light Emitting Diode (LED)

A small light source that creates light through the movement of electrons through a semiconductor material. LEDs are typically made of durable plastic and can last over 25,000 hours. For more information visit Types of Light Bulbs.


The lowest rank of coal, often referred to as brown coal, used almost exclusively as fuel for steam-electric power generation. It is brownish-black and has a high inherent moisture content, sometimes as high as 45. The heat content of lignite consumed in the United States averages 13 million Btu per ton. The texture of the original wood often is visible in lignite.

Liquefied Gases

Gases that have been or can be changed into liquid form by containing under pressure or at low temperatures. These include butane, butylene, ethane, ethylene, propane and propylene.

Liquefied Natural Gas (LNG)

Natural gas that has been condensed to a liquid, typically, by cryogenically cooling the gas to minus 327.2 degrees Fahrenheit.

Liquefied Petroleum Gas (LPG)

A mixture of gaseous hydrocarbons, mainly propane and butane, that changes into liquid form under moderate pressure. LPG or propane is commonly used as a fuel for rural homes for space and water heating, as a fuel for barbecues and recreational vehicles, and as a transportation fuel. It is normally created as a by-product of petroleum refining and from natural gas production.

Liquid Foam Insulation

Insulation that can be sprayed, foamed-in-place, injected, or poured and creates an effective air barrier with a high R-Value when compared to traditional batt insulation.


The amount of electric power supplied to meet one or more end user's needs or an end-use device or an end-use customer that consumes power.

Load Centers

A geographical area where large amounts of power are drawn by end-users.

Load Management

Steps taken to reduce power demand at peak load times or to shift some of it to off-peak times. This may be with reference to peak hours, peak days or peak seasons. The main effect on electric peaks is air-conditioning usage, which is therefore a prime target for load management efforts. Load management is achieved by persuading consumers to modify behavior or by using equipment that regulates some electric consumption.

Loose-fill Insulation

See Blown-in Insulation.


A special coating that reduces the emissivity of a window assembly, thereby reducing the heat transfer through the assembly.


A measure of the amount of light available from a light source equivalent to the light emitted by one candle.

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Mechanical Energy

The sum of the kinetic energy and the potential energy of a system.

Megawatt (MW)

One thousand kilowatts or one million watts. One megawatt is enough energy to power 200 average homes.

Megawatt Hour (MWh)

One thousand kilowatt-hours or an amount of electricity that would supply the monthly power needs of a typical home having an electric hot water system.


A device for measuring levels and volumes of a customer's gas and electricity use.

Methane (CH4)

The simplest of hydrocarbons and the principal constituent of natural gas. Pure methane has a heating value of 1,012 Btu per standard cubic foot. Methane is the main component of natural gas and marsh gas. It is the product of the anaerobic decomposition of organic matter, enteric fermentation in animals and is one of the greenhouse gases.

Methanol (CH3OH)

A liquid formed by catalytically combining carbon monoxide (CO) with hydrogen (H2) in a 1:2 ratio, under high temperature and pressure. Commercially it is typically made by steam reforming natural gas. Methanol is also formed in the destructive distillation of wood. (Also known as Methyl Alcohol, Wood Alcohol).

Methyl Tertiary Butyl Ether (MTBE)

Ether manufactured by reacting methanol and isobutylene. The resulting ether has a high octane and low volatility. MTBE is a fuel oxygenate and is permitted in unleaded gasoline up to a level of 15 percent. It is one of the primary ingredients in reformulated gasolines.

Municipal Solid Waste

Locally collected garbage that can be processed and burned to produce energy.

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Natural Gas

A gaseous mixture of hydrocarbon compounds, found in the earth, composed of methane, ethane, butane, propane and other gases.


An uncharged particle found in the nucleus of every atom except that of hydrogen.

New England Power Pool (NEPOOL)

A voluntary association of electric utilities in New England that established a single regional network to direct the operations of the major generating and transmission (bulk power system) facilities in the region. Its goals are safety, reliability and economy.


A unit of force. The amount of force it takes to accelerate one kilogram at one meter per second per second.

Nitrogen Oxides (NOx)

Oxides of nitrogen that are a chief component of air pollution that can be produced by the burning of fossil fuels.

Nuclear Energy

Power obtained by splitting heavy atoms (fission) or joining light atoms (fusion). A nuclear energy plant uses a controlled atomic chain reaction to produce heat. The heat is used to make steam run conventional turbine generators.

Nuclear Regulatory Commission (NRC)

An independent federal agency that ensures that strict standards of public health and safety, environmental quality and national security are adhered to by individuals and organizations possessing and using radioactive materials. The NRC is the agency that is mandated with licensing and regulating nuclear power plants in the United States. It was formally established in 1975 after its predecessor, the Atomic Energy Commission, was abolished.

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Ocean Power

Also referred to as marine and hydrokinetic energy, ocean power refers to the energy harnessed from waves, tides, and temperature differences in the ocean. For more information, please visit Ocean Power.

Ocean Thermal Energy Conversion (OTEC)

Uses the natural temperature difference in the ocean to generate power.


A rating scale used to grade gasoline as to its antiknock properties. Also, any of several isometric liquid paraffin hydrocarbons. Normal octane is a colorless liquid found in petroleum boiling at 124.6 degrees Celsius.

Octane Rating

A measure of a gasoline's resistance to exploding too early in the engine cycle, which causes knocking. The higher the rating, the lower the chance of premature ignition.

Office of Consumer Counsel (OCC)

This is an independent state agency that is charged to act as the advocate for consumer interests regarding matters concerning public service companies, electric suppliers and certified telecommunications providers.

Offshore Wind

Wind turbines that are not located on land, but within a body of water.


A unit of measure of electrical resistance. One volt can produce a current of one ampere through a resistance of one ohm.

Oil Shale

A type of rock containing organic matter that produces large amounts of oil when heated to high temperatures.

Organic Light Emitting Diode (OLED)

Light emitting panels that are still in development. The panels are made of carbon based materials that emit light when electricity is applied. OLED panels are becoming widely used in cellphones, televisions, and other materials. For more information, visit Types of Light Bulbs.

Organization of Petroleum Exporting Countries (OPEC)

Founded in 1960 to unify and coordinate petroleum polices of the members, its headquarters is in Vienna, Austria.


An interruption of electric service that is temporary (minutes or hours) and affects a relatively small area (buildings or city blocks).


A term used in the petroleum industry to denote octane components containing hydrogen, carbon and oxygen in their molecular structure. Includes ethers such as MTBE and ETBE and alcohols such as ethanol or methanol. The oxygenate is a prime ingredient in reformulated gasoline. The increased oxygen content given by oxygenates promotes more complete combustion, thereby reducing tailpipe emissions.

Ozone (O3)

A kind of oxygen that has three atoms per molecule instead of the usual two. Ozone is a poisonous gas, but the ozone layer in the upper atmosphere shields life on earth from deadly ultraviolet radiation from space. The molecule contains three oxygen atoms.

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Particulate Matter (PM)

Unburned fuel particles that form smoke or soot and stick to lung tissue when inhaled. A chief component of exhaust emissions from heavy-duty diesel engines.

Parts per Million (ppm)

The unit commonly used to represent the degree of pollutant concentration where the concentrations are small.

Passive Solar Energy

Use of the sun to help meet a building's energy needs by means of architectural design (such as arrangement of windows) and materials (such as floors that store heat, or other thermal mass).

Peak Demand

The maximum electric load during a specified period of time. Connecticut's peak demand occurs between noon and 8 p.m., weekdays.

Peaking Capacity

Capacity of generating equipment normally reserved for operation during the hours of highest daily, weekly, or seasonal loads. Some generating equipment may be operated at certain times as peaking capacity and at other times to serve loads on an around-the-clock basis.


Oil as found in its natural state under the ground.


A device that produces an electric reaction to visible radiant energy (light).


A process by which green plants change carbon dioxide into oxygen and organic materials. The energy for this process comes from sunlight.

Photovoltaic Cell (PV)

A semiconductor that converts light directly into electricity. Cells range in size from large solar panels to squares smaller than a postage stamp. 

Potential Energy

The stored capacity for work of an object or a system. For example, the energy stored in a large rock that is ready to fall off a wall, or the energy in a pendulum at the top of its swing.

Power Plant

A central station generating facility that produces energy.


A gas that is both present in natural gas and refined from crude oil. It is used for heating, lighting and industrial applications.

Public Utilities Regulatory Authority (PURA)

The Public Utilities Regulatory Authority (PURA) is statutorily charged with regulating the rates and services of Connecticut's investor owned electricity, natural gas, water and telecommunication companies and is the franchising authority for the state’s cable television companies. In the industries that are still wholly regulated, PURA balances the public’s right to safe, adequate and reliable utility service at reasonable rates with the provider’s right to a reasonable return on its investment. PURA also keeps watch over competitive utility services to promote equity among the competitors while customers reap the price and quality benefits of competition and are protected from unfair business practices.

Pumped Storage

A hydropower technology that pumps water uphill during periods of low electrical demand then releases it when the demand becomes high. The water stored in the high elevation reservoir flows downhill, spins the turbine(s), and generates electricity.


A chemical decomposition of biomass in the absence of oxygen at elevated temperatures.

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One quadrillion (1015) British thermal units (Btus). An amount of energy equal to 170 million barrels of oil. Total U.S. consumption of all forms of energy is (in the 1990s) about 83 quads in an average year.

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A unit of measure of absorbed radiation. Acronym for radiation absorbed dose. One rad equals 100 ergs of radiation energy per gram of absorbing material.

Radiant Energy

Energy transferred by the exchange of electromagnetic waves from a hot or warm object to one that is cold or cooler. Direct contact with the object is not necessary for the heat transfer to occur.


The flow of energy across open space via electromagnetic waves such as light. Passage of heat from one object to another without warming the air space in between.

Rankine Cycle

The steam-Rankine cycle employing steam turbines has been the mainstay of utility thermal electric power generation for many years. The cycle, as developed over the years uses superheat, reheat and regeneration. Modern steam Rankine systems operate at a cycle top temperature of about 1,073 degrees Celsius with efficiencies of about 40 percent.


A device in which a controlled nuclear chain reaction can be maintained, producing heat energy.

Recovered Energy

Reused heat or energy that otherwise would be lost. For example, a combined cycle power plant recaptures some of its own waste heat and reuses it to make extra electric power.

Renewable Energy

Natural resources that constantly renew themselves or that are regarded as practically inexhaustible. These include solar, wind, geothermal, hydro, ocean, and biomass. Visit our Renewable Energy page to learn more.

Renewable Portfolio Standards

The amount in percentage of class 1, class 2, or class 3 renewable energy supply required to be supplied by retail electric energy providers.


A place where things are stored.

Run-of-River System

See Diversion.


The measurement of resistance of heat flow through insulation. Higher R-values indicate a lesser rate of heat transfer, meaning greater insulating power.

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Scheduled Outage

The shutdown of a generating unit, transmission line, or other facility, for inspection or maintenance in accordance with an advance schedule.


A solid crystalline substance, such as silicon, that has electrical conductivity greater than an insulator but less than a conductor.

Smart Thermostat

An advanced, programmable thermostat that allows you to control your thermostat from a smart phone or Wi-Fi compatible device.

Solar Cell

A photovoltaic cell that can convert light directly into electricity. A typical solar cell uses semiconductors made from silicon.

Solar Collector

A device designed to receive solar radiation and convert it to thermal energy. Normally, a solar thermal collector includes a frame, glazing, and an absorber, together with appropriate insulation. The heat collected by the solar collector may be used immediately or stored for later use. Solar collectors are used for space heating; domestic hot water heating; and heating swimming pools, hot tubs, or spas.

Solar Energy

Heat and light radiated from the sun.

Solar Heating and Cooling (SHC)

Systems that use solar energy to heat a fluid (liquid or air) and the heat is either stored for later use or transferred directly to the interior of a building.

Solar Power

Power obtained from the energy of the sun's rays that can be used for power or heating purposes. It is one of the cleanest and quietest renewable energy sources available. To learn more, visit Solar Power.

Solar Thermal Power Plant

A thermal power plant in which 75 percent or more of the total energy output is from solar energy and the use of backup fuels, such as oil, natural gas, and coal, does not, in the aggregate, exceed 25 percent of the total energy input of the facility during any calendar year period.

Steam Electric Plant

A power station in which steam is used to turn the turbines that generate electricity. The heat used to make the steam may come from burning fossil fuel, using a controlled nuclear reaction, concentrating the sun's energy, tapping the earth's natural heat or capturing industrial waste heat.

Stranded Costs

Prudent costs incurred by a utility which may not be recoverable under market-based retail competition. Examples are undepreciated generating facilities, deferred costs, and long-term contract costs.

Structural Insulated Panels (SIPs)

Prefabricated insulated structural elements consisting of an insulating foam core sandwiched between two structural facings for residential and light commercial construction. SIPs can offer high energy savings compared to traditional construction methods when properly installed.


A facility that steps up or steps down the voltage in utility power lines. Voltage is stepped up where power is sent through long-distance transmission lines. It is stepped down where the power is to enter local distribution lines.

Sulfur Dioxide (SO2) or SOx

A colorless, toxic and very irritating gas that is a byproduct of fossil fuel combustion. Other forms of sulfur oxides are sometimes called SOx.


A yellowish nonmetallic element, sometimes known as brimstone. It is present at various levels of concentration in many fossil fuels whose combustion releases sulfur compounds that are considered harmful to the environment. Some of the most commonly used fossil fuels are categorized according to their sulfur content, with lower sulfur fuels usually selling at a higher price.


A synthetic material that has very low or no electrical resistance. Such experimental materials are being investigated in laboratories to see if they can be created at near room temperatures. If such a superconductor can be found, electrical transmission lines with no little or no resistance may be built, thus conserving energy usually lost in transmission. Superconductors could also have uses in computer chips, solid state devices and electrical motors or generators.

Systems Benefits Charge (SBC)

The charge on each electric customer's bill that covers certain regulatory and energy public policy costs, such as public education and hardship protection.

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Task Lighting

Lighting designed specifically to illuminate one or more task locations, and generally confined to those locations.


One hundred thousand British thermal units (1 therm = 100,000 Btu).

Thermal Power Plant

Any stationary or floating electrical generating facility using any source of thermal energy, with a generating capacity of 50 megawatts or more, and any facilities appurtenant thereto. Exploratory, development, and production wells, resource transmission lines, and other related facilities used in connection with a geothermal exploratory project or a geothermal field development project are not appurtenant facilities for the purposes of this division. Thermal power plant does not include any wind, hydroelectric, or solar photovoltaic electrical generating facility.


A study of the transformation of energy into other manifested forms and of their practical applications. The three laws of thermodynamics are 1. Law of Conservation of Energy -- energy may be transformed in an isolated system, but its total is constant 2. Heat cannot be changed directly into work at constant temperature by a cyclic process 3. Heat capacity and entropy of every crystalline solid becomes zero at absolute zero (0 degrees Kelvin)


A device that automatically regulates temperature to the desired setting. Some devices allow multiple settings for different time periods and are referred to as programmable thermostats. Smart thermostats allow control from a smart phone or Wi-Fi compatible device. For more information, please visit Thermostats.

Tidal Power

Energy obtained by using the motion of the tides to run water turbines that drive electric generators. Tidal power technologies include barrages or dams, tidal fences, and tidal turbines.

Transitional Standard Offer (TSO)

The 2004 Transitional Standard Offer (TSO) Period began on Jan. 1, 2004 and replaced the Standard Offer Period which expired on Dec. 31, 2003. The 2004 Transitional Standard Offer, effective through Dec. 31, 2004, removed the 10% rate reduction. Its intended result was to encourage more electric suppliers to do business within the state. The 2005 TSO reflects the electric rate increase of 10.3%. The contributing factors for this increase are: the price of crude oil, the price of natural gas and the federally mandated congestion costs.


A machine in which the kinetic energy of a moving fluid or steam is converted into mechanical energy.

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Unbundled Electric Rates

The separating of the total process of electric power service from generation to metering into its component parts for the purpose of separate pricing or service offerings.


A radioactive element, found in ores, of which atoms can be split to create energy.

Utility-Scale Wind

Large wind turbines that produce more than 100 kilowatts.

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Vapor Barrier

Also called vapor diffusion retarders, a thin layer of material that reduces the rate at which a fluid can move through a material. Used to help control moisture in a home or building.


A unit of electromotive force. It is the amount of force required to drive a steady current of one ampere through a resistance of one ohm. Electrical systems of most homes and office have 120 volts.


The electric pressure of a circuit, measured in volts. Based on the maximum normal effective difference of potential between any two conductors of the circuit.

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A unit of measure of electric power at a point in time, as capacity or demand. One watt of power maintained over time is equal to one joule per second. The Watt is named after Scottish inventor James Watt and is capitalized when shortened to w and used with other abbreviations, as in kWh.

Wave Energy

Energy extracted from surface waves or from pressure fluctuations below the surface. There are various types of wave energy converters- the main types include terminators, attenuators, point absorbers, and overlapping devices.

Wind Power

Power obtained from harnessing the wind's energy. For more information please visit Wind Power

Wind Turbine

A machine consisting of long blades connected to a long tower. The wind spins the blades, which generates power.

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