Letter I

IMBALANCE ENERGY - The real-time change in generation output or demand requested by the ISO to maintain reliability of the ISO-controlled grid. Sources of imbalance energy include regulation, spinning and non-spinning reserves, replacement reserve, and energy from other generating units that are able to respond to the ISO's request for more or less energy.

ILEV (Inherently Low Emission Vehicle) - Term used by federal government for any vehicle that is certified to meet the California Air Resources Board's Low Emission Vehicle (LEV) standards for non-methane organic gases and carbon monoxide, ULEV standards for nitrogen oxides and does not emit any evaporative emissions.

IMPORTS (Electric utility) - Power capacity or energy obtained by one utility from others under purchase or exchange agreement.

IMPOUNDMENT - A body of water confined by a dam, dike, floodgate or other artificial barrier.

INCANDESCENT LAMP - An electric lamp in which a filament is heated by an electric current until it emits visible light.

INDEPENDENT POWER PRODUCER -- An Independent Power Producer (IPP) generates power that is purchased by an electric utility at wholesale prices. The utility then resells this power to end-use customers. Although IPPs generate power, they are not franchised utilities, government agencies or QFs. IPPs usually do not own transmission lines to transmit the power that they generate.

INDIGENOUS ENERGY RESOURCES - Power and heat derived from sources native to California. These include geothermal, hydro, biomass, solar and wind energy. The term usually is understood to include cogeneration facilities.

INDIRECTLY CONDITIONED SPACE - See conditioned space, indirectly.

INFILTRATION - The uncontrolled inward leakage of air through cracks and gaps in the building envelope, especially around windows, doors and duct systems.

INFILTRATION BARRIER - A material placed on the outside or the inside of exterior wall framing to restrict inward air leakage, while permitting the outward escape of water vapor from the wall cavity. [See California Code of Regulations, Title 24, Section 2-5302]

INFRASTRUCTURE - generally refers to the recharging and refueling network necessary to successful development, production, commercialization and operation of alternative fuel vehicles, including fuel supply, public and private recharging and refueling facilities, standard specifications for refueling outlets, customer service, education and training, and building code regulations.

INJECTION - (Petroleum) - Forcing gas or water into an oil well to increase pressure and cause more oil to come to the surface. See THERMALLY ENHANCED OIL RECOVERY.

IN-SITU COMBUSTION - An experimental means of recovering hard-to-get petroleum by burning some of the oil in its natural underground reservoir. Also called FIREFLOODING.

IN-SITU GASIFICATION - Converting coal into synthetic gas at the place where the coal is found in nature.

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

INSULATION, THERMAL - A material having a relatively high resistance of heat flow and used principally to retard heat flow. See R-VALUE.

INTERCHANGE (Electric utility) - The agreement among interconnected utilities under which they buy, sell and exchange power among themselves. This can, for example, provide for economy energy and emergency power supplies.

INTERCONNECTION (Electric utility) - The linkage of transmission lines between two utilities, enabling power to be moved in either direction. Interconnections allow the utilities to help contain costs while enhancing system reliability.

INTERESTED PARTY - any person whom the commission finds and acknowledges as having a real and direct interest in any proceeding or action carried on, under, or as a result of the operation of, this division.

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 a internal combustion engine. It differs from engines having an external furnace, such as a steam engine.

INTERRUPTIBLE SERVICE (Electric utility) - Electricity supplied under agreements that allow the supplier to curtail or stop service at times.

INTERTIE - A transmission line that links two or more regional electric power systems.

INVESTOR-OWNED UTILITIES - A private company that provides a utility, such as water, natural gas or electricity, to a specific service area. The investor-owned utility is regulated by the California Public Utilities Commission. In California the investor-owned utilities supplying energy are:

ION - An atom or group of atoms that is electrically charged.

IOU - An investor owned utility. A company, owned by stockholders for profit, that provides utility services. A designation used to differentiate a utility owned and operated for the benefit of shareholders from municipally owned and operated utilities and rural electric cooperatives.

INTEGRATED RESOURCE PLANNING(IRP) - A public planning process and framework within which the costs and benefits of both demand- and supply-side resources are evaluated to develop the least-total-cost mix of utility resource options. In many states, IRP includes a means for considering environmental damages caused by electricity supply/transmission and identifying cost-effective energy efficiency and renewable energy alternatives. IRP has become a formal process prescribed by law in some states and under some provisions of the Clean Air Act amendments of 1992.

INTEGRATED RESOURCE PLANNING PRINCIPLES - The underlying principles of IRP can be distinguished from the formal process of developing an approved utility resource plan for utility investments in supply- and demand-side resources. A primary principle is to provide a framework for comparing a variety of supply- and demand-side and transmission resource costs and attributes outside of the basic provision (or reduction) of electric capacity and energy. These resources may be owned or constructed by any entity and may be acquired through contracts as well as through direct investments. Another principle is the incorporation of risk and uncertainty into the planning analysis. The public participation aspects of IRP allow public and regulatory involvement in the planning rather than the siting stage of project development.

IPP - INDEPENDENT POWER PRODUCER. An private entity that operates a generation facility and sells power to electric utilities for resale to retail customers.

ISDN - INTEGRATED SERVICES DIGITAL NETWORK. A 128 Kbps(kilobytes per second) digital telephone service available in many parts of the country though not universally available thatmay be able to substitute for fiber optic cable in every respect except possibly television transmission.

ISO - INDEPENDENT SYSTEM OPERATOR. A neutral operator responsible for maintaining instaneous balance of the grid system. The ISO performs its function by controlling the dispatch of flexible plants to ensure that loads match resources available to the system.