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Alternative Fuel Vehicle (AFV):

A vehicle with an engine designed to run on a fuel other than gasoline or diesel.


The unit of measurement of electrical current produced in a circuit.

Bi-Fuel Natural Gas Vehicle:

A vehicle with an engine capable of running on either natural gas or some other fuel (usually gasoline).


The amount of electric power delivered or required for which a generator, turbine, transformer, transmission circuit, station, or system is rated by the manufacturer.

Carbon Dioxide (CO2):

Carbon Dioxide is the main product from the combustion of fossil fuels, such as gas, oil and coal. While CO2 has been implicated as having a possible role in the global greenhouse debate, it is not currently regulated.


The sequential or simultaneous process in which useful heat/steam is generated, used in a variety of process applications, and then directed into a turbine to generate electricity and/or mechanical work from the useful thermal energy still available for use.

Combined Cycle:

A cogeneration technology in which additional electricity is produced sequentially from otherwise lost waste heat exiting from one or more gas-fired turbines. The exiting heat flow is routed to an exhaust-fired conventional boiler or to a heat recovery steam generator for utilization by a steam turbine in the production of electricity. This process increases the efficiency of an electric generating system by turning the rejected heat into thermal steam rather than discharging it into the atmosphere.

Compressed Natural Gas (CNG):

This is a natural gas that is highly compressed and stored in high-pressure surface containers. Compressed natural gas is used extensively as a transportation fuel for automobiles, truck and buses.


A flow of electrons in an electrical conductor. The strength or rate of movement of the electricity is measured in amperes.

Dedicated NGV:

A vehicle that can be fueled only by natural gas.

Direct Use:

Direct use involves burning natural gas directly at end-use applications such as furnaces, water heaters and other natural gas appliances or vehicles. This is as opposed to burning natural gas for electric generation which would then be used to power the same appliances or electric vehicles in a less efficient manner due to energy losses incurred during generation and transportation.


The capacity for doing work as measured by the capability of doing work (potential energy) or the conversion of this capability to motion (kinetic energy). Energy has several forms, some of which are easily convertible and can be changed to another form useful for work. Most of the world's convertible energy comes from fossil fuels that are burned to produce heat that is then used as a transfer medium to mechanical or other means in order to accomplish tasks. Electrical energy is usually measured in kilowatt hours, which heat energy is usually measured in British thermal units.

Energy Source:

The primary source that provides the power that is converted to electricity through chemical, mechanical, or other means. Energy sources include coal, petroleum and petroleum products, gas, water, uranium, wind, sunlight, geothermal, and other sources.

Fossil Fuel:

Any naturally occurring organic fuel, such as coal, crude oil, and natural gas.

Fuel Cell:

A device that produces electrical energy directly from the controlled electrochemical oxidation of the fuel. It does not contain an intermediate heat cycle, as do most other electrical generation techniques.

Gas Gallon Equivalent (GGE):

A unit for measuring compressed natural gas sold at public fueling stations and comparing fuel efficiencies.


The process of producing electric energy by transforming other forms of energy; also, the amount of electric energy produced, expressed in kilowatt hours.

Geothermal Energy:

Energy from the internal heat of the earth may be residual heat, friction heat, or a result of radioactive decay. The heat is found in rocks and fluids at various depths and can be extracted by drilling and/or pumping.


The layout of an electrical distribution system.

Home Fueling Appliance:

A natural gas fueling component that contains both compressor and fueling equipment which is sized for residential time fill use.

Kilowatt (kW):

One thousand watts.

Load (Electric):

The amount of electric power delivered or required at any specific point or points on a system. The requirement originates at the energy-consuming equipment of the customers.

Megawatt (MW):

One million watts.

Natural Gas:

A naturally occurring mixture of hydrocarbon and non-hydrocarbon gases found in porous geological formations beneath the earth's surface, often in association with petroleum. The principal constituent is methane.

Natural Gas Vehicle (NGV):

A vehicle powered by compressed natural gas.

Nitrogen Oxides (NOx):

Various oxides of nitrogen are formed in the combustion of fossil fuels, such as gas, oil and coal. Some NOx is formed from the nitrogen bound in the fuel when it is combusted and some NOx (thermal NOx) is formed at high temperatures from the nitrogen in the air. NOx, in combination with volatile organic compounds (VOC) and sunlight, lead to the formation of ozone.

Emissions of NOx are strictly regulated, monitored and enforced by local, state and federal environmental agencies to protect people, animals and vegetation.
North American Electric Reliability Council (NERC):

A council formed in 1968 by the electric utility industry to promote the reliability and adequacy of bulk power supply in the electric utility systems of North America. NERC consists of nine regional reliability councils and encompasses essentially all the power systems of the contiguous United States, Canada, and some in Mexico.


Original Equipment Manufacturer


A mixture of hydrocarbons usually existing in the liquid state in natural underground pools or reservoirs. Gas is often found in association with oil.

Overhead vs. Underground Electric Service:

In most instances, Underground service is generally more reliable than overhead, but maintenance is more difficult and costly. Regardless of whether the lines are constructed overhead or underground, they are built in compliance with all applicable safety rules and regulations.

Pad-mounted Transformer:

A distribution transformer that is installed on the ground on concrete pads and provides underground electrical service to customers.

Peak Load:

The maximum load during a specified period of time.

Peak Load Plant:

A plant usually housing old, low-efficiency equipment normally used during the peak-load periods.

Peaking Capacity:

Capacity of generating equipment normally operated 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.

Petroleum (Crude Oil):

A naturally occurring, oily, flammable liquid composed mostly of hydrocarbons. Crude oil is occasionally found in springs or pools, but usually is drilled from wells beneath the earth's surface.

Photovoltaic Cell:

Device that produces electrical current by converting light or similar radiation.

Public Fueling Station:

Refers to a fueling station that is accessible to the general public.

Prime Mover:

The engine, turbine, water wheel, or similar machine that drives an electric generator.

Quick Fill:

Refers to the process of fueling a vehicle with natural gas in approximately the same time it would take to fuel the same vehicle with liquid fuels such as gasoline or diesel.

Renewable Energy Source:

An energy source that is regenerative or virtually inexhaustible. Typical examples are wind, geothermal and water power.

Scheduled Outage:

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


Substations are like interchanges on interstate highways or intersections on city streets, depending on the voltages involved and the amount of power passing through them. Enclosed by fences, substations contain transformers, switches, circuit breakers and other devices used to control and direct the flow of electric power through the energy delivery grid.

Sulfur Dioxide (SO2):

Sulfur dioxide is a product of fossil fuel combustion, such as the burning of oil or coal. Small amounts of sulfur contained in the fuel is converted into sulfur dioxide in the combustion process.

Emissions of sulfur dioxide are strictly regulated, monitored and enforced by local, state and federal environmental agencies to protect people, animals and vegetation.

A term used to identify a type of electric generating station, capacity, capability, or output in which the source of energy for the prime mover is heat.

Time Fill
A method of fueling a vehicle with natural gas over an extended period of time, usually six to eight hours.

A device used to raise or lower electrical voltage.

Transmission-level Voltage:

There is no specific standard for transmission-level voltage. It refers to that part of the electric system dedicated to the delivery of bulk power from power plants to transmission substations scattered around the transmission grid.

Electric power is transmitted at very high voltages because losses (much like heat losses) are minimized at elevated voltage levels. For a given amount of power delivered, doubling the transmission voltage cuts the electrical losses by 75 percent.

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

Vehicle Conversion:

Retrofitting a vehicle engine to run on natural gas.

Vehicle Refueling Appliance:

A natural gas fueling component that contains both compressor and fueling equipment.


The electrical unit of power.

Sources: Energy Information Administration; 1998; Tampa Electric; 1999; Peoples Gas1999.