Energy Glossary

Energy Glossary of Terms

Base load

The minimum amount of electric power delivered or required over a given period of time at a steady rate.


Carbon Dioxide (CO2)

A colorless, odorless, non-poisonous gas that is a normal part of Earth’s atmosphere. CO2 is required as a natural part of plant growth.  Carbon dioxide is a product of natural causes (for example, decomposition, ocean release, respiration and volcanoes.) and fossil-fuel combustion. It is considered a greenhouse gas as it traps heat (infrared energy) radiated by the Earth into the atmosphere and thereby contributes to the potential for global warming. The global warming potential (GWP) of other greenhouse gases is measured in relation to that of carbon dioxide, which by international scientific convention is assigned a value of one (1).


Carbon Sequestration (or Carbon Capture and Storage)

The fixation of atmospheric carbon dioxide in a carbon sink through biological or physical processes. Carbon dioxide capture and sequestration (CCS) is a set of technologies that can greatly reduce CO2 emissions from new and existing coal- and gas-fired power plants and large industrial sources. CCS is a three-step process that includes:


  • Capture of CO2from power plants or industrial processes.  Removal technologies are not yet proven at a commercial scale.
  • Transport of the captured and compressed CO2(usually in pipelines).
  • Underground injection and geologic sequestration (also referred to as storage) of the CO2into deep underground rock formations. These formations are often a mile or more beneath the surface and consist of porous rock that holds the CO2. Overlying these formations are impermeable, non-porous layers of rock that trap the CO2 and prevent it from migrating upward



An easily burned black or brownish-black “rock” made up of more than 50 percent by weight and more than 70 percent by volume of carbonaceous material. It is formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geologic time.  Coal provides a great deal of heat even when small amounts are burned.



Chemical oxidation accompanied by the generation of light and heat.


Customer-Owned Generation

The term used for customer-generated solar, wind, biomass, and other renewable energy generating sources as well as combined heat and power devices installed at the site where they will be used, usually at homes and small businesses.  Also called “Distributed Generation.”


Distributed Generation

(See Customer-Owned Generation, above)


Electric power grid

A system of synchronized power providers (generators) and consumers connected by transmission and distribution lines. In the continental United States, the electric power grid consists of three systems: the Eastern Interconnect, the Western Interconnect, and the Texas Interconnect. In Alaska and Hawaii, several systems encompass areas smaller than the State (e.g., the interconnect serving Anchorage, Fairbanks, and the Kenai Peninsula; individual islands).


Electric power plant

A building with equipment for converting mechanical, chemical, and/or fission energy into electric energy.


Electric rate

The price set for a specified amount and type of electricity as well as the other terms for the sale of electricity to a group or class of customers who have similar ways of using electricity.



A form of energy characterized by the presence and motion of electrons (i.e., sub-atomic or elementary charged particles) generated by friction, induction, or chemical change.


Electricity generation

The process of producing electric energy or the amount of electric energy produced by transforming other forms of energy, commonly expressed in kilowatt-hours (kWh) or mega-watt hours  (Mwh).


Integrated gasification-combined cycle technology

Coal, water, and oxygen are fed to gasifier, which produces synthetic natural gas, called “syngas”. This medium-Btu gas is cleaned (particulates and sulfur compounds removed) and is fed to a gas turbine. The hot exhaust of the gas turbine and heat recovered from the gasification process produce steam, which drives a steam turbine to produce electricity.


Kilowatt (kW)

One thousand watts.


Kilowatt-hour (kWh)

A measure of electricity defined as a unit of work or energy, measured as 1 kilowatt (1,000 watts) of power expended for 1 hour. One kWh is equivalent to 3,412 BTUs.


Megawatt (MW)

One million watts of electricity.


Megawatt hour (MWh)

One thousand kilowatt-hours or 1 million watt-hours.


Net Metering

Net Metering is a policy that allows electric customers to sell excess electricity generated by their distributed generation system to their electric company most often at prices above others who sell power to electric companies.  To take advantage of net metering, distributed generation customers must be connected to the electric grid just like other customers.


Under net metering, electric companies are required to buy power from distributed generation customers at the full retail rate.  The retail rate is the price customers pay to buy electricity from a utility.  However, the retail rate includes not just the cost of electricity itself, but also the cost of delivering it to customers through the electric grid, i.e., the fixed costs of the poles, wires, meters, advanced technologies and other infrastructure as well as people who operate and repair this infrastructure that make the electric grid safe and reliable for everyone.


Peak demand

The maximum amount of electricity used by a customer or a group of customers during a specified period of time.  To reliably serve customers, electric companies must have enough electric generation to match the peak demand of all its customers at the moment that they need that electricity.


Photovoltaic cell (PVC)

An electronic device consisting of layers of semiconductor materials fabricated to form a junction (adjacent layers of materials with different electronic characteristics) and electrical contacts.  PVC is capable of converting sunlight or other incident light directly into electricity.


Renewable energy resources

Renewable energy resources include biomass, hydro, geothermal, solar, wind, ocean thermal, wave action, and tidal action.  While these sources are naturally replenished, they may be intermittent and cannot be depended upon to produce electricity 24 hours a day, 365 days a year.



An electrical device for changing voltage.


Transmission (electric)

An interconnected group of wires and associated equipment for the movement or transfer of electric energy between points of supply and points at which it is transformed for delivery to customers or is delivered to other electric systems.



A machine for generating rotary mechanical power from the energy of a stream of fluid (such as water, steam, or hot gas).  Turbines convert the kinetic energy of fluids to mechanical energy through the principles of impulse and reaction, or a mixture of the two.


Watt (W)

The unit of electrical power equal to one ampere under a pressure of one volt. A Watt is equal to 1/746 horsepower.


For a more comprehensive Energy Glossary, visit the Energy Information Administration.