Earth Berm
A mound of dirt next to exterior walls to provide wind protection and insulation.

Earth Cooling Tube

A long, underground metal or plastic pipe through which air is drawn. As air travels through the pipe it gives up some of its heat to the soil, and enters the house as cooler air.

Earth-Coupled Ground Source (Geothermal) Heat Pump

A type of heat pump that uses sealed horizontal or vertical pipes, buried in the ground, as heat exchangers through which a fluid is circulated to transfer heat.

Earth Sheltered Houses

Houses that have earth berms around exterior walls.


A registered trademark name for houses built with tires, aluminum cans, and earth.


An incorporated right, liberty, privilege, or use of another entity’s property, distinct from ownership, without profit or compensation; a right-of-way.


A device for converting continuous circular motion into reciprocating rectilinear motion.


A heat exchanger for recovering heat from flue gases for heating water or air.

Edge-Defined Film-Fed Growth (EFG)

A method for making sheets of polycrystalline silicon (for solar photovoltaic devices) in which molten silicon is drawn upward by capillary action through a mold.


The amount of energy service or useful energy delivered per unit of energy input. Often used in reference to lighting systems, where the visible light output of a luminary is relative to power input; expressed in lumens per Watt; the higher the efficacy value, the higher the energy efficiency.

Effective Capacity

The maximum load that a device is capable of carrying.


Under the First Law of Thermodynamics, efficiency is the ratio of work or energy output to work or energy input, and cannot exceed 100 percent. Efficiency under the Second Law of Thermodynamics is determined by the ratio of the theoretical minimum energy that is required to accomplish a task relative to the energy actually consumed to accomplish the task. Generally, the measured efficiency of a device, as defined by the First Law, will be higher than that defined by the Second Law.

Efficiency (Appliance) Ratings

A measure of the efficiency of an appliance’s energy efficiency.

Elasticity of Demand

The ratio of the percentage change in the quantity of a good or service demanded to the percentage change in the price.

Electrical Energy

The energy of moving electrons.

Electrical Charge

A condition that results from an imbalance between the number of protons and the number of electrons in a substance.

Electrical System

All the conductors and electricity using devices that are connected to a source of electromotive force (or generator).

Electrical System Energy Losses

A measure of the amount of energy lost during the generation, transmission, and distribution of electricity.

Electric Circuit

The path followed by electrons from a generation source, through an electrical system, and returning to the source.

Electric Energy

The amount of work accomplished by electrical power, usually measured in kilowatt-hours (kWh). One kWh is 1,000 Watts and is equal to 3,413 Btu.

Electric Furnace

An air heater in which air is blown over electric resistance heating coils.

Electricity Generation

The process of producing electricity by transforming other forms or sources of energy into electrical energy; measured in kilowatt-hours.

Electricity Grid

A common term referring to an electricity transmission and distribution system.

Electric Rate

The unit price and quantity to which it applies as specified in a rate schedule or contract.

Electric Rate Schedule

A statement of the electric rate(s), terms, and conditions for electricity sale or supply.

Electric System

The physically connected generation, transmission, and distribution facilities and components operated as a unit.

Electric System Loss(es)

The total amount of electric energy loss in an electric system between the generation source and points of delivery.

Electric Power Plant

A facility or piece of equipment that produces electricity.

Electric Power Sector

Those privately or publicly owned establishments that generate, transmit, distribute, or sell electricity.

Electric Power Transmission

The transmission of electricity through power lines.

Electric Resistance Heating

A type of heating system where heat, resulting when electric current flows through an “element” or conductor, such as Nichrome, which has a high resistance, is radiated to a room.

Electric Utility

A corporation, person, agency, authority or other legal entity that owns and/or operates facilities for the generation, transmission, distribution or sale of electricity primarily for use by the public. Also known as a power provider.

Electric Vehicles

A battery-powered electrically driven vehicle.

Electricity Industry Restructuring

The process of changing the structure of the electric power industry from one of guaranteed monopoly over service territories, as established by the Public Utility Holding Company Act of 1935, to one of open competition between power suppliers for customers in any area.

Electrochemical Cell

A device containing two conducting electrodes, one positive and the other negative, made of dissimilar materials (usually metals) that are immersed in a chemical solution (electrolyte) that transmits positive ions from the negative to the positive electrode and thus forms an electrical charge. One or more cells constitute a battery.


A conductor that is brought in conducting contact with a ground.


Electrolytic process in which a metal is deposited at the cathode from a solution of its ions.


A chemical change in a substance that results from the passage of an electric current through an electrolyte. The production of commercial hydrogen by separating the elements of water, hydrogen, and oxygen, by charging the water with an electrical current.


A nonmetallic (liquid or solid) conductor that carries current by the movement of ions (instead of electrons) with the liberation of matter at the electrodes of an electrochemical cell.

Electromagnetic Energy

Energy generated from an electromagnetic field produced by an electric current flowing through a superconducting wire kept at a specific low temperature.

Electromagnetic Field (EMF)

The electrical and magnetic fields created by the presence or flow of electricity in an electrical conductor or electricity consuming appliance or motor.

Electromotive Force

The amount of energy derived from an electrical source per unit quantity of electricity passing through the source.


An elementary particle of an atom with a negative electrical charge and a mass of 1/1837 of a proton; electrons surround the positively charged nucleus of an atom and determine the chemical properties of an atom.

Electronic Ballast

A device that uses electronic components to regulate the voltage of fluorescent lamps.

Electron Volt

The amount of kinetic energy gained by an electron when accelerated through an electric potential difference of 1 Volt; equivalent to 1.603 x 10^-12; a unit of energy or work; abbreviated as eV.

Electrostatic Precipitator

A device used to remove particulate matter from the waste gasses of a combustion power plant.

Ellipsoidal Reflector Lamp

A lamp where the light beam is focused 2 inches ahead of the lamp reducing the amount of light trapped in the fixture.


A substance(s) or pollutant emitted as a result of a process.

Emission Factor

A measure of the average amount of a specified pollutant or material emitted for a specific type of fuel or process.


The ratio of the radiant energy (heat) leaving (being emitted by) a surface to that of a black body at the same temperature and with the same area; expressed as a number between 0 and 1.


The housing around a motor that supports the active parts and protects them. They come in different varieties (open, protected) depending on the degree of protection required.


A heat absorbing reaction or a reaction that requires heat.

End Use

The purpose for which useful energy or work is consumed.


To send electricity through a electricity transmission and distribution network; a conductor or power line that is carrying current.


The capability of doing work; different forms of energy can be converted to other forms, but the total amount of energy remains the same.

Energy Audit

A survey that shows how much energy you use in your house or apartment. It will help you find ways to use less energy.

Energy Charge

That part of an electricity bill that is based on the amount of electrical energy consumed or supplied.

Energy Contribution Potential

Recombination occurring in the emitter region of a photovoltaic cell.

Energy Crops

Crops grown specifically for their fuel value. These include food crops such as corn and sugarcane, and nonfood crops such as poplar trees and switchgrass. Currently, two energy crops are under development: short-rotation woody crops, which are fast-growing hardwood trees harvested in 5 to 8 years; and herbaceous energy crops, such as perennial grasses, which are harvested annually after taking 2 to 3 years to reach full productivity.

Energy Efficient Mortgages

A type of home mortgage that takes into account the energy savings of a home that has cost-effective energy saving improvements that will reduce energy costs thereby allowing the homeowner to more income to the mortgage payment. A borrower can qualify for a larger loan amount than otherwise would be possible.

Energy Efficiency Ratio (EER)

The measure of the instantaneous energy efficiency of room air conditioners; the cooling capacity in Btu/hr divided by the watts of power consumed at a specific outdoor temperature (usually 95 degrees Fahrenheit).

Energy Density

The ratio of available energy per pound; usually used to compare storage batteries.

Energy Factor (EF)

The measure of overall efficiency for a variety of appliances. For water heaters, the energy factor is based on three factors: 1) the recovery efficiency, or how efficiently the heat from the energy source is transferred to the water; 2) stand-by losses, or the percentage of heat lost per hour from the stored water compared to the content of the water: and 3) cycling losses. For dishwashers, the energy factor is defined as the number of cycles per kWh of input power. For clothes washers, the energy factor is defined as the cubic foot capacity per kWh of input power per cycle. For clothes dryers, the energy factor is defined as the number of pounds of clothes dried per kWh of power consumed.

Energy End-Use Sectors

Major energy consuming sectors of the economy. The Commercial Sector includes commercial buildings and private companies. The Industrial Sector includes manufacturers and processors. The Residential Sector includes private homes. The Transportation Sector includes automobiles, trucks, rail, ships, and aircraft.

Energy Guide Labels

The labels placed on appliances to enable consumers to compare appliance energy efficiency and energy consumption under specified test conditions as required by the Federal Trade Commission.

Energy Intensity

The relative extent that energy is required for a process.

Energy Policy Act of 1992 (EPAct)

A comprehensive legislative package that mandates and encourages energy efficiency standards, alternative fuel use, and the development of renewable energy technologies. Public Law 102-486, October 24th, 1992. Also authorized the Federal Energy Regulatory Commission (FERC) to order the owners of electric power transmission lines to transmit or “wheel” power for power generators including electric power providers, federal power marketing authorities, and exempt wholesale generators.

Energy Security Act of 1980

Legislation authorizing a U.S. biomass and alcohol fuel program, and that authorized loan guarantees and price guarantees and purchase agreements for alcohol fuel production.

Energy Service Company (ESCO)

A company that specializes in undertaking energy efficiency measures under a contractual arrangement whereby the ESCO shares the value of energy savings with their customer.

Energy Storage

The process of storing, or converting energy from one form to another, for later use; storage devices and systems include batteries, conventional and pumped storage hydroelectric, flywheels, compressed gas, and thermal mass.


A thermodynamic property of a substance, defined as the sum of its internal energy plus the pressure of the substance times its volume, divided by the mechanical equivalent of heat. The total heat content of air; the sum of the enthalpies of dry air and water vapor, per unit weight of dry air; measured in Btu per pound (or calories per kilogram).

Entrained Bed Gasifier

A gasifier in which the feedstock (fuel) is suspended by the movement of gas to move it through the gasifier.


A measure of the unavailable or unusable energy in a system; energy that cannot be converted to another form.


All the natural and living things around us. The earth, air, weather, plants, and animals all make up our environment.

Epitaxial Growth

In reference to solar photovoltaic devices, the growth of one crystal on the surface of another crystal. The growth of the deposited crystal is oriented by the lattice structure of the original crystal.


The two times of the year when the sun crosses the equator and night and day are of equal length; usually occurs on March 21st (spring equinox) and September 23 (fall equinox).


A unit of work done by the force of one dyne acting through a distance of one centimeter.

Ethanol — Ethyl alcohol (C
A colorless liquid that is the product of fermentation used in alcoholic beverages, industrial processes, and as a fuel additive. Also known as grain alcohol.

Ethyl Tertiary Butyl Ether (ETBE)

A chemical compound produced in a reaction between ethanol and isobutylene (a petroleum-derived by-product of the refining process). ETBE has characteristics superior to other ethers: low volatility, low water solubility, high octane value, and a large reduction in carbon monoxide and hydrocarbon emissions.


A mixture of substances that has a melting point lower than that of any mixture of the same substances in other proportions.

Eutectic Salts

Salt mixtures with potential applications as solar thermal energy storage materials.

Evacuated-Tube Collector

A collector is the mechanism in which fluid (water or diluted antifreeze, for example) is heated by the sun in a solar hot water system. Evacuated-tube collectors are made up of rows of parallel, transparent glass tubes. Each tube consists of a glass outer tube and an inner tube, or absorber. The absorber is covered with a selective coating that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn (“evacuated”) from the space between the tubes to form a vacuum, which eliminates conductive and convective heat loss. Evacuated-tube collectors are used for active solar hot water systems.


The conversion of a liquid to a vapor (gas), usually by means of heat.

Evaporative Cooling

The physical process by which a liquid or solid is transformed into the gaseous state. For this process a mechanical device uses the outside air’s heat to evaporate water that is held by pads inside the cooler. The heat is drawn out of the air through this process and the cooled air is blown into the home by the cooler’s fan.

Evaporator Coil

The inner coil in a heat pump that, during the cooling mode, absorbs heat from the inside air and boils the liquid refrigerant to a vapor, which cools the house.


The power required to energize the magnetic field of a generator.

Exempt Wholesale Generator

An unregulated subsidiary of a power provider that is allowed to generate and sell wholesale power as an independent energy producer, and is exempt from the Public Utility Holding Company Act of 1935.


A reaction or process that produces heat; a combustion reaction.

Expanded Polystyrene

A type of insulation that is molded or expanded to produce coarse, closed cells containing air. The rigid cellular structure provides thermal and acoustical insulation, strength with low weight, and coverage with few heat loss paths. Often used to insulate the interior of masonry basement walls.

Expansion Tank

A tank used in a closed-loop solar heating system that provides space for the expansion of the heat transfer fluid in the pressurized collector loop.

Expansion Valve

The device that reduces the pressure of liquid refrigerant thereby cooling it before it enters the evaporator coil in a heat pump.

External Combustion Engine

An engine in which fuel is burned (or heat is applied) to the outside of a cylinder; a Stirling engine.


The environmental, social, and economic impacts of producing a good or service that are not directly reflected in the market price of the good or service.

Extruded Polystyrene

A type of insulation material with fine, closed cells, containing a mixture of air and refrigerant gas. This insulation has a high R-value, good moisture resistance, and high structural strength compared to other rigid insulation materials.