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Dictionary of Energy

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hybrid poplar

humus Ecology. decomposed organic matter in which the remains of specific plants and animals are not identifiable and thus the form and appearance of the material is relatively uniform.

hunting and gathering Sustainable Development. the practice of obtaining food by hunting wild animals and by collecting wild plants and other naturally occurring foodstuffs, rather than by agriculture and the raising of domestic livestock; a strategy thought to be common to all early human cultures but today found in only a few isolated groups. Thus, hunter-gatherer, hunting-and- gathering society, and so on.

hunting and gathering Although true huntergatherer societies are rare today, some of their methods survive, as in this African technique of hut building from materials gathered in the bush.

Hütter, Ulrich 1910–1990, Austrian engineer who first described in mathematical detail the theoretical basis for the construction of modern wind turbines with twoand threerotor blades.

Hutton, James 1726–1797, Scottish scientist considered to be the founder of modern geology. In the rocks of Scotland, Hutton found neatly deposited layers of sedimentary rocks overlaying rock layers that were almost vertical. The lower layers of rock, he concluded, must have been deposited eons before, and then later upturned. He thus was the first to describe the vast expanses of time in earth’s history.

Huygens, Christiaan 1629–1695, Dutch scientist who invented the pendulum clock and was the first to identify Saturn’s rings and largest moon, Titan. He also built several pendulum clocks to determine longitude at sea, and derived the law of centrifugal force for uniform circular motion.

HVAC an acronym for heating, ventilation, and air-conditioning.

HVDC Electricity. high voltage direct-current electrical transmission, the preferred mode in various specilaized contexts such as undersea cables, long-haul bulk power transmission in remote areas, and power transmission between unsynchronized AC distribution systems.

hybrid Renewable/Alternative. 1. relating to or involving a hybrid energy system, hybrid vehicle, and so on (see below). 2. short for


hybrid analysis Measurement. a method to calculate the embodied energy of a good or service that combines input–output analysis and process energy analysis.

hybrid electric vehicle (HEV) Renewable/ Alternative. 1. a vehicle that derives part of its propulsionpowerfromaninternal-combustion engine and part of its propulsion power from an electric motor. 2. a vehicle using an internal combustion engine to power a generator that charges a battery, which will in turn power one or more electric-driven motors.

hybrid energy system Renewable/Alternative. a system that combines two or more forms of energy or power to provide a particular energy service. This may include an energy storage component; e.g., a home powered by a combination of a diesel generator, wind power, and battery storage.

hybrid lighting Lighting. a lighting system in which a rooftop collector concentrates and sends sunlight through optical fibers to special lighting fixtures that contain both electric lamps and fiber optics to distribute sunlight directly. When the transmitted sunlight is sufficient to illuminate a room to the desired level, the electric lights do not go on.

hybrid poplar Biomass. a hybrid tree of the genus Populus that has significant potential as a renewable fuel source because of its fastgrowth characteristics.

hybrid propulsion



hybrid propulsion Renewable/Alternative. a combination of two different power sources for vehicle propulsion; one source derives its power from fuel, such as an internal combustion engine or a fuel cell; the second is a device that stores and reuses energy. This can be electrical energy or electromechanical energy, such as a hydraulic accumulator or a flywheel.

hybrid solar lighting Lighting. a lighting system in which a rooftop collector concentrates and sends sunlight through optical fibers to special fixtures inside a building, which contain both electric lamps and fiber optics to distribute sunlight directly. When the transmitted sunlight completely illuminates each room, the electric lights stay off.

hybrid system see HYBRID ENERGY SYSTEM.

hybrid vehicle Renewable/Alternative. any vehicle that employs two sources of propulsion, especially a vehicle that combines a conventional internal combustion engine with an electric motor (see HYBRID ELECTRIC


hydrate Materials. 1. a substance that contains water combined in the molecular form. 2. crystalline substance that contains molecules of water of crystallization. 3. to form or become such a substance.

hydraulic Hydropower. 1. of or relating to water or another liquid in motion. 2. relating to or resulting from the pressure created by forcing water through a relatively small pipe, orifice, or other channel.

hydraulic fracturing Oil & Gas. a oil-well stimulation technique in which high fluid pressure is applied to the face of an underground well with low permeability to force the strata apart, allowing oil to flow toward the well.

hydraulic gradient Physics. a pressure head gradient (rate of change per unit distance of flow) measured at a specific point and in a given direction, often due to frictional effects along the flow path.

hydraulic head Hydropower. the vertical distance between the surface of a dam’s reservoir and the surface of the waters immediately downstream from the dam.

hydraulic mining Mining. the use of directed, high-pressure jets of water to break loose minerals of interest from a hillside or mountainside,

stream bed, underground deposit, and so on; a historic method of gold mining that has had severe ecological consequences.

hydraulic pressure Hydropower. the pressure created by forcing water or another liquid through a relatively small pipe, orifice, or other channel.

hydraulic turbine Consumption & Efficiency. a turbine that converts the potential energy of falling or fast-flowing water to mechanical energy; most hydraulic turbines today are used to generate electricity in hydropower installations.

hydride Chemistry. a binary compound of hydrogen with another element or a complex species containing hydrogen bound to another element; common examples are the hydrides of boron, lithium, and sodium.

hydrocarbon (HC) Chemistry. a compound composed of only carbon and hydrocarbon; these are the most abundant molecules in most crude oils and refined fuels. Hydrocarbons can be solid (asphalt), liquid (crude oil), or gas (natural gas). They are a diverse mixture of linear, branched, and cyclic saturated compounds with 1–80 carbon atoms, together with aromatic compounds, most commonly with more than one ring and with multiple alkyl substituents.

hydrochlorofluorocarbon (HCFC) Environment. a compound containing hydrogen, fluorine, chlorine, and carbon atoms; they are ozone-depleting substances but are less destructive of the stratospheric ozone layer than chlorofluorocarbons (CFCs) and thus have been introduced as temporary replacements for CFCs in aerosols and in appliances such as refrigerators. The Montreal Protocol calls for the reduction and eventual phasing out of HCFCs.

hydrocracking Oil & Gas. a catalytic, highpressure refinery process that involves the cracking of heavy petroleum fractions in the presence of an excess of hydrogen in which special catalysts are used, such as platinum on a solid base of mixed silica and alumina; the process may be considered as a combination of hydrogenation and catalytic cracking. Thus, hydrocracker.

hydrodesulfurization Materials. a catalytic process for the removal of sulfur compounds from hydrocarbons using hydrogen.



hydrogen electrode

hydrodynamic Hydropower. involving or caused by the motion of a fluid, especially the motion of water through a constricted channel.

hydrodynamics Physics. the study of the motion of fluids and of interactions at fluid boundaries.

hydroelectric Hydropower. describing electric current produced from water power, especially the force or pressure of falling water. Thus, hydroelectricity, hydroelectric power.

hydrofinishing Materials. a catalytic treating process carried out in the presence of hydrogen to improve the properties of naphthenic oils.

hydrofluoric acid Health & Safety. a solution of hydrogen fluoride in water that is released during coal burning; e.g., for electrical power; it is corrosive and highly poisonous, and when concentrated it can pass through the skin and cause serious burns.

hydrofluorocarbon (HFC) Environment. a compound containing only hydrogen, fluorine, and carbon atoms; HFCs have been promoted as alternatives to ozone-depleting substances such as CFCs and HCFCs for various industrial purposes. Though HFCs do not significantly deplete the stratospheric ozone layer, they are greenhouse gases with major global warming potentials and also have other negative environmental implications.

hydrofoil Transportation. 1. an airfoil-shaped plate fitted to the underside of a boat to provide lift at high speeds, reducing hull displacement and associated friction. 2. a vessel equipped with such a plate.

hydroforming Oil & Gas. a high-temperature refining method in which naphthas contact a catalyst in the presence of hydrogen to yield high-octane aromatics for motor fuel or chemical manufacture.

hydrogasification Conversion. the gasification of a fuel by reaction with hydrogen; e.g., the production of methane from pulverized coal at high temperature and pressures (above 1200°F and 500 psi).

hydrogen Chemistry. a nonmetallic element having the symbol H, the atomic number 1, an atomic weight of 1.007 97, a melting point of about 259°C, and a boiling point of about 253°C. It is the lightest and most abundant

hydrofoil Hydrofoil vessels are typically used for passenger ferry service on bays, rivers, lakes, and so on.

element in the universe, comprising about 90% of it by weight, but it is only a minute fraction of dry air on earth. Hydrogen in combination with oxygen as water (H2O) is essential to life and is present in all organic compounds; it also occurs in acids, bases, alcohols, petroleum, and other hydrocarbons. In nature at standard conditions it is a colorless, odorless, and highly flammable gas. RSee next page.

hydrogen-2 Chemistry. another name for DEU-


hydrogen-3 Chemistry. another name for TRI-


hydrogenation Chemistry. 1. a general reaction in which hydrogen is added to the unsaturated molecules of hydrocarbons or fatty acids, normally by use of a catalyst. 2. any process in which hydrogen is combined with another substance.

hydrogen balloon see HELIUM BALLOON.

hydrogen bomb Nuclear. an extremely powerful type of nuclear weapon, in which the fusion of deuterium and tritium (heavy isotopes of hydrogen) releases enormous amounts of energy in the form of heat.

hydrogen economy Hydrogen. the concept of an energy system based primarily on the use of hydrogen as an energy carrier, especially for transportation vehicles.

hydrogen electrode Chemistry. a standard reference electrode, usually consisting of a platinum surface coated with platinum black

hydrogen passivation


hydropower resettlement

Rhydrogen Hydrogen’s atomic structure of one proton, and one electron makes it the lightest of the elements. Identified as an element by Cavendish and named by Lavoisier, hydrogen’s historic use is as an industrial chemical. Much of its current use is in improving crude oil in refineries. However, hydrogen was considered for energy even in the 19th Century—by Jules Verne, as well as by contemporary scientists. Hydrogen is like electricity in that it is an energy carrier, not a primary source—it is derived from the conversion of some other form of energy. It can be manufactured from a variety of sources, including natural gas, coal, nuclear energy and all forms of renewable energy. When used as a fuel in combustion processes or in fuel cells, hydrogen has minimal emissions relative to conventional fuels. Although hydrogen has about

that is bathed with a stream of hydrogen gas bubbles and immersed in a solution of hydrogen ions. It has a potential of zero when the activity of all species is unity, and it is used to measure hydrogen–ion concentrations.

hydrogen passivation Photovoltaic. the injection of hydrogen into a mixture of silicon being made for photovoltaic cells; the hydrogen inactivates crystal defects such as grain boundaries and lattice dislocations to improve overall cell performance.

hydrogen-rich Hydrogen. describing a type of fuel that contains a significant amount of hydrogen, such as gasoline, diesel fuel, methanol, ethanol, natural gas, or coal.

hydrogen sulfide Chemistry. HS, a toxic, colorless gas that has an offensive odor and that is soluble in water; a dangerous fire and explosion hazard and a strong irritant. It occurs naturally in crude petroleum, natural gas, volcanic gases, and hot springs, and results from the bacterial breakdown of organic matter and human and animal wastes. It also is generated by industrial activities; e.g., food processing, coke ovens, paper mills, and tanneries.

hydrogen vehicle Hydrogen. a transportation vehicle powered by hydrogen, either by means of an internal combustion engine (hydrogen engine) or electricity-generating fuel cells.

hydrologic(al) cycle Earth Science. the process of water constantly moving through a vast

three times the energy density of gasoline per kilogram, making it ideal as a rocket fuel, it has a very low energy density on a volumetric basis. This poses significant economic and technical challenges to the transmission and storage of hydrogen. Potential end uses of hydrogen include fuel cell vehicle technology as well as stationary power generation. Research and development of hydrogen energy centers on reducing the costs associated with its manufacture and storage. As a potential complement to electricity as one of the two primary long-term energy carriers, hydrogen ultimately could offer a transition from today’s energy mix that is as significant as that from wood to coal, or coal to oil.

David Hart

Imperial College, UK

global cycle in which it evaporates from lakes and oceans, forms clouds, precipitates as rain or snow, and then flows back to the ocean.

hydrology Earth Science. the science of water; the study of the properties, distribution, and effects of water on the earth’s surface, in the soil and underlying rocks, and in the atmosphere. Usually applies to studies of water in relation to land surfaces as opposed to the waters of the open ocean (oceanography).

hydrolysis Chemistry. 1. a chemical reaction in which water is chemically combined into a reactant and the reactant is broken down into smaller molecules. 2. a reaction of water with a salt to create an acid or base. Thus, hydrolytic.

hydromagnetic wave see ALFVÉN WAVE.

hydrometer Measurement. an instrument used to measure the specific gravity of a liquid.

hydronic HVAC. referring a heating or cooling system that transfers heat by circulating a fluid through a closed system of pipes. Thus, hydronic heating.

hydropower energy derived at a variety of scales from water pressure, especially the force or pressure of falling water used to power a water wheel, turbine, and so on.

hydropower resettlement Hydropower. the large-scale forced relocation of households and communities as a result of the construction of large hydropower dams and their associated reservoirs; e.g., it is estimated that




hydropower Historically the main use of water power was for mechanical tasks such as grinding grain, but in modern society it has been used mainly for electrical power.

the construction of the Three Gorges Dam in China will require about 1.2 million people to be resettled.

hydroretort Oil & Gas. a retort in which oil shale is thermally decomposed in the presence of hydrogen under pressure.

hydroscopic Chemistry. capable of absorbing moisture from its surroundings.

hydrosphere Earth Science. the portion of the earth that is water, especially liquid water, ice, and water vapor on the surface, but also including subsurface and atmospheric water.

hydrostat see HUMIDISTAT.

hydrostatic Physics. having to do with liquids at rest. Thus, hydrostatic pressure.

hydrostatics Physics. the scientific study of liquids at rest, as well as the forces and pressures associated with them.

hydrostatic test Materials. a strength and tightness for a drain, vessel, pipe, or other such closed hollow object; the item is filled with a test liquid and subjected to pressure.

hydrothermal Earth Science. relating to or caused by heated water, especially the action of water heated by natural processes rather than by industrial activity.

hydrothermal vent Earth Science. a geyser on the sea bottom through which superhot aqueous solutions rise from the magma beneath the crust; this creates a surrounding system of mineral-rich water that helps to support a distinctive type of ecosystem not found in typical cold-water environments at the same ocean depth.

hydrotreating Oil & Gas. an oil refinery catalytic process in which hydrogen is contacted with petroleum product streams to remove impurities.

hydrous Chemistry. containing water.

hydrous ethanol Transportation. an alternative transportation fuel consisting of ethanol mixed with some fraction of water.

hygrometry Measurement. the scientific study and calculation of the relative humidity of the atmosphere. Thus, hygrometer.

Hypercar Transportation. a conceptual motor vehicle that is able to have ultralight weight and ultralow drag by the utilization of advanced composite materials; developed by Hypercar Inc. and the Rocky Mountain Institute.

hypereutrophy Ecology. the ultimate stage of eutrophication; the “old age” of a lake; i.e., a condition of an excessively large supply of nutrients, resulting in a high production of organic matter by plants and animals and murky, odorous water approaching wetlands status. Thus, hypereutrophic.

hypersonic Transportation. describing an object (e.g., a spacecraft) moving at speeds far above the speed of sound (greater than Mach 5). The space shuttle reenters the atmosphere at high hypersonic speeds (at or near Mach 25).

hypocaust History. an ancient Roman method of heating baths and other buildings by means of circulating heated air beneath the floor; considered the first system of central heating.

hypolimnion Earth Science. the lowest water layer of a thermally stratified lake or reservoir; it is isolated from wind mixing, often too deep for sunlight penetration and plant photosynthesis, and typically cooler and less oxygenated than the epilimnion layer above.

hypothetical resources



hypothetical resources Coal. a classification for undiscovered coal resources that may reasonably be expected to exist in known coal mining areas under known geologic conditions.

hypsithermal Climate Change. relating to or occurring in a climatic period on earth occurring about 10,000 to 5000 years ago, characterized by generally warmer temperatures and decreased or increased rainfall in various areas.

hypsometry Earth Science. the science of height; the study or measurement of the elevation or depth of features on the earth, especially natural features. Also, hypsography.

hysteresis Physics. 1. a condition in which the state of a system depends on its previous history, generally the retardation or lagging of

an effect behind the cause of the effect. 2. specifically, the inclination of a magnetic material to saturate and retain some of its magnetism after the alternating magnetic field to which it is subjected reverses polarity.

hysteresis coupling Electricity. an electric coupling in which torque is transmitted by hysteresis; i.e., forces from the resistance of magnetic fields within a ferromagnetic material.

hysteresis loss Physics. an energy loss in magnetic material due to an alternating magnetic field, as elementary magnets within the material align themselves with the reversing magnetic field.

hythane Oil & Gas. hydrogen–methane; a commercial gas product that contains 20% hydrogen and 80% natural gas.

Hz hertz.


IAEA International Atomic Energy Agency (est. 1957); an intergovernmental organization that serves as a center of cooperation in the nuclear energy field. It was set up as the world’s Atoms for Peace organization within the United Nations.

IAEE International Association for Energy Economics (est. 1977), a nonprofit professional organization that provides an interdisciplinary forum for the exchange of ideas, experience, and issues among professionals interested in energy economics.

ice Earth Science. water in the solid state, produced by the freezing of liquid water, by the condensation of water vapor directly into crystals, or by the compaction and recrystallization of fallen snow.

ice age or Ice Age Earth Science. 1. an interval of geologic time during which a large portion of the earth’s surface was covered by glaciers; characterized by a significantly cold worldwide climate and widespread glacial advance toward the equator. 2. specifically, a name for the Pleistocene epoch, because of its widespread glacial ice.

ice-charcoal History. an ancient Chinese term for coal.

ice core Earth Science. an extensive column of ancient ice, drilled out of an ice sheet or glacier for the purpose of obtaining various types of data, especially indications of past climate trends.

ice front Earth Science. 1. a high, steep vertical cliff that forms the boundary of an ice sheet as it meets the sea, beyond which there is open water. 2. another term for GLACIAL MAXIMUM; i.e., the point of farthest advance of a glacier.

ice sheet Earth Science. a broad, thick sheet of glacial ice that covers an extensive land area

for a long period of time, sufficiently deep to overlie most of the bedrock topography, so that its shape is mainly determined by its internal dynamics.

ice shelf Earth Science. a continuous and more or less permanent sheet of fast ice, generally level and sometimes extending hundreds of kilometers from the shore, fed by glaciers and by annual accumulation of snow. Although attached to land on one side, an ice shelf’s edge is chiefly supported by the water on which it floats.

ice slurry storage Storage. the use of small ice crystals and a binary solution consisting of water and a freezing point depressant, such as ethylene glycol, ethanol, or sodium chloride in cooling applications; e.g., chilled water systems, air conditioning, or district cooling.

ICRP International Commission on Radiological Protection (est. 1928); an independent registered charity established to advance for the public benefit the science of radiological protection.

ideal gas Chemistry. a theoretical gas whose molecules are infinitely small and exert no force upon each other. This means that their motion is completely chaotic and does not depend on any mutual interaction, but only on completely elastic collisions, which cause a transfer of energy from one molecule to

ice shelf In the past several decades scientists have observed a series of retreats and collapses by Antarctic ice shelves; this has been attributed to a strong climate warming trend in the region.

ideal gas law



another and a change of their direction and velocity. Also called a PERFECT GAS.

ideal gas law Chemistry. an expression of the relationship of temperature, pressure, and volume for an ideal gas; pV = nRT, in which p is the pressure of the system, V is the volume, n is the number of moles of the sample, R is the gas constant for the gas in question, and T the absolute temperature. Many actual gases will approximately obey this law at sufficiently low pressures or high temperatures.

ideal rocket Physics. a theoretical rocket that would operate perfectly at a velocity equal to that of its jet gases; used to provide ideal parameters to be compared to practice.

identified resources Coal. a collective term for the sum of coal resources whose location, quality, and quantity have been established from geologic evidence supported by engineering measurement.

IDLH Health & Safety. immediately dangerous to life or health; describing the maximum concentration of a hazardous material from which one could escape within 30 minutes, without any symptoms impairing the escape or any irreversible health effects.

IEA International Energy Agency (est. 1974), an intergovernmental body that seeks to advance the security of energy supply, economic growth, and environmental sustainability through energy policy cooperation. It was formed in response to the oil crisis in 1973–1974.

IEA Bioenergy (est. 1978), an organization of the International Energy Agency (IEA) that seeks to improve cooperation and information exchange between countries that have national programs in bioenergy research, development, and deployment.

IECC Policy. International Energy Conservation Code; a code of standards developed by the International Code Council (ICC) that facilitates energy conservation through efficiency in envelope design, mechanical systems, lighting systems, and the use of new materials and techniques.

IEEE Institute of Electrical and Electronics Engineers (est. 1884), a nonprofit technical professional association recognized as an authority in technical areas ranging from computer engineering, biomedical technology

and telecommunications, to electric power, aerospace and consumer electronics, among others.

IEI International Energy Initiative (est. 1991), an independent nongovernmental publicpurpose organization led by international energy experts, with regional offices in Latin America, Africa, and Asia.

IETA International Emissions Trading Association (est. 1999), a nonprofit organization that established the first functional international framework for trading greenhouse gas emission reductions. Its mission is a trading regime that results in real and verifiable greenhouse gas emission reductions, balancing economic efficiency with environmental integrity and social equity.

IGA International Geothermal Association (est. 1988), a nongovernmental organization whose objective is to encourage research, development, and utilization of geothermal resources worldwide.

IGCC integrated gasification combined cycle.

igneous Earth Science. of or relating to a rock that was formed by solidification from molten or partly molten material; one of the three principal classifications of rocks along with


ignition Chemistry. the point at which a substance begins a process of combustion, or the means by which this process begins.

ignition energy Chemistry. the amount of external energy that must be applied in order to ignite a combustible fuel mixture.

ignition system Transportation. a collective term for the components of an internal combustion engine that produce the spark to ignite the mixture of fuel and air; i.e., the battery, ignition coil, spark plugs, distributor, and associated switches and wiring.

IGY International Geophysical Year.

IIASA International Institute for Applied Systems Analysis (est. 1972); a nongovernmental research organization located near Vienna, Austria that conducts interdisciplinary scientific analyses of environmental, economic, technological, and social issues in the context of human dimensions of global change.

IIR International Institute of Refrigeration (est. 1954), an intergovernmental organization that



incandescent lamp

pools international scientific and industrial knowledge in all areas of refrigeration.

IISD International Institute for Sustainable Development (est. 1990), a nonprofit group whose mission is to promote change towards sustainable development.

illuminance Lighting. the photometric equivalent of irradiance used as the standard metric for lighting levels; the amount of luminous flux striking a unit area of a surface, measured in lumens per square meter and expressed in lux (lx) or foot-candles (fc).

illuminating oil History. an earlier name for


illumination Lighting. 1. lighting; the application and distribution of light to a subject. 2. another term for ILLUMINANCE.

ILW intermediate-level waste.

image-dissection Communication. a type of television picture tube in which an image is swept past an aperture that dissects it section by section, instead of its being scanned by an electron beam; based on the Image Dissector technology developed by U.S. television pioneer Philo T. FARNSWORTH in 1927.

imbalance energy Electricity. the real-time change in generation output or demand requested by an independent system operator to maintain reliability of the grid.

Imhoff tank Environment. an underground sedimentation tank used in wastewater treatment; designed to remove settleable solids from the wastewater and then anaerobically digest these solids in the lower portion of the tank.

immiscible Chemistry. not able to be mixed; describing two liquids that do not mix with each other, such as oil and water; the converse of MISCIBLE. Thus, immiscibility.

immobilized electrolyte Storage. describing a type of lead–acid battery in which the electrolyte (the acid) is held in place against the plates instead of being a free-flowing liquid. The two most common techniques are geltype and glass mat batteries.

immunotoxic Health & Safety. harmful to the immune system; describing an agent that suppresses normal immune function. Thus, immunotoxin, immunotoxicity.

impedance Electricity. the effective resistance to the flow of electric current at a given fre-

quency in an alternating current circuit; the reciprocal of ADMITTANCE.

impeller Conversion. 1. a rotor for transmitting motion, as in a centrifugal pump, blower, turbine, agitator vessel, or fluid coupling. 2. a rotating member of a centrifugal flow compressor or supercharger.

imperial Measurement. describing a system of liquid and dry measure traditionally used in Great Britain and certain Commonwealth countries, in which a gallon is equivalent to 1.2 U.S. gallons and a bushel to 1.03 U.S. bushels.

impingement Ecology. the process in which an aquatic organism strikes against the intake structure of a power plant after being drawn in along with the inflowing water.

impoundment Environment. an enclosed wetland that is hydrologically isolated from the surrounding ecosystem; this can be due to a combination of natural features (e.g., beach ridge, natural levee ridge) and anthropogenic ones (e.g., road embankment, spoil bank).

impulse turbine Conversion. 1. a turbine that produces power when a jet of water from an enclosed diversion pipeline moves with force through a specially shaped nozzle to impact directly onto the turbine blades; e.g., a Pelton turbine. 2. a similar turbine operating on the same principle but employing pressurized steam rather than water as the high-velocity fluid.

inactive pool Hydropower. a condition in which the water stored in a reservoir or lake does not provide enough flow to generate hydroelectric power.

incandescence Lighting. the emission of visible electromagnetic radiation due to the thermal excitation of atoms or molecules.

incandescent Lighting. giving off a glowing light due to a high temperature; having the property of incandescence.

incandescent lamp Lighting. a light bulb with a resistive wire filament, usually made of tungsten, that can be heated until it glows white hot; the filament is enclosed in an evacuated bulb to prevent oxidation. This is the original form of electric lighting and historically the most common. Thus, incandescent lighting.



indirect energy

incendiary Chemistry. 1. a chemical agent designed to cause combustion. 2. employing such an agent, especially as a weapon.

incentive-based Policy. describing a regulation that uses the economic behavior of firms and households to attain desired environmental goals. Incentive-based programs involve taxes on emissions or tradable emission permits.

Inch Lines Oil & Gas. a system of pipelines

(Big Inch and Little Big Inch) constructed during World War II to carry oil from East Texas to the northeastern U.S., a distance of about 1500 miles, to compensate for the fact that the supply of oil by sea was threatened by German submarines. Following the war these lines were converted to natural gas pipelines.

inch of mercury Measurement. a unit of measure for atmospheric pressure, equal to the amount of power pressure exerted by a oneinch column of mercury under standard conditions of temperature and gravity; a term derived from the use of mercury barometers to measure air pressure.

incident Nuclear. a term for any occurrence, or series of occurrences having the same origin, causing nuclear damage or creating a grave and imminent threat of such damage.

incident (incidence) angle see ANGLE OF


incident radiation Solar. incoming radiation; the quantity of radiant energy striking a surface per unit time and unit area.

incinerate Conversion. of a material, to burn or be burned until it is converted to ashes. Thus, incineration.

incinerator Conversion. a furnace that is designed for the destruction of refuse through burning; it may be fired by various means such as gas, oil, or solid fuel.

inclined plane History. a surface sloped at an angle to the horizontal (or some other reference surface), providing a mechanical advantage for raising loads; one of the simple machines along with the lever, screw, and so on.

income elasticity Economics. the degree to which the demand for a good or service changes with respect to income; e.g., a change in the demand for gasoline as a result of a change in income.

incomplete combustion Conversion. the combustion of a fuel in which it is only partially burned, with further burning possible under proper conditions. The incomplete combustion of carbon produces carbon monoxide.

independent power producer (IPP) Electricity. a generator of electricity for public use other than an electric utility, usually a small capacity plant or industrial facility, e.g., a wind farm.




(ISO) Electricity.

an independent, govern-

mentally regulated entity established to coordinate, control, and monitor regional transmission in a nondiscriminatory manner and ensure the safety and reliability of the electric system. Similarly, independent system planner (ISP).

index of sustainable economic welfare (ISEW) Sustainable Development. an alternative measure for assessing the strength of an economy and human well-being. Unlike gross national product and similar indicators, it includes measures for other positive contributions such as the value of household labor, or negative contributions such as income inequality, environmental degradation, and the depletion of nonrenewable resources.

indicated resources Coal. the sum of coal resources for which estimates of the rank, quality, and quantity have been computed to a moderate degree of geologic assurance.

indigenous Sustainable Development. 1. of an organism, native to or occurring naturally in the habitat in which it currently exists. 2. describing a group of people known to have been living in a given area since ancient times; e.g., the Inuit are described as indigenous peoples of the Arctic region.

indirect cooling Electricity. the use of a closed loop water system to reject waste heat from a power plant to the atmosphere.

indirect energy Consumption & Efficiency. all energy requirements not considered to be DIRECT ENERGY; e.g., in the case of automobile transportation, the use of vehicle fuel would be direct energy, while the energy required to manufacture vehicles, build and maintain roads, and so on would be indirect. Also, indirect use.