| 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. |
| Impermeable | does not allow liquids to pass through easily. Certain rock types and clay soil are impermeable. |
| 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. |
| Incandescent Light | An electric lamp that is evacuated or filled with an inert gas and contains a filament (commonly tungsten). The filament emits visible light when heated to extreme temperatures by electric current through it. Incandescent lightbulbs are one of the most inefficient ways to light a home. They produce a great deal of heat along with the light, and use three to four times as much energy for the same light output as compact fluorescent lightbulbs. |
| Incident Light | Light that shines on to the surface of a PV cell or module. |
| 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. |
| Independent Power System | A power generation system that is independent of the mains grid. |
| Indirectly Conditioned Space | See conditioned space, indirectly. |
| Indium Oxide | A wide band gap semiconductor that can be heavily doped with tin to make a highly conductive, transparent thin film. Often used as a front contact or one component of a heterojunction solar cell. |
| Induction Generator | A generator that produces energy by the production of a magnetic field by the proximity of a electric charge. Commonly made from old induction motors. |
| Induction Motor | An AC motor in which the rotating armature has no electrical connections to it and consists of alternating plates. |
| Induction Motor (Ac) | A type of electric motor that requires a high surge to start, and a stable voltage supply, making it a challenge to run using a solar-electric system. |
| 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 |
| Infrared Light. | Electromagnetic radiation whose wavelengths lie in the range from .75 micrometers to 1000 micrometers. |
| Infrared Radiation | Electromagnetic radiation whose wavelengths lie in the range from 0.75 micrometer to 1000 micrometers; invisible long wavelength radiation (heat) capable of producing a thermal or photovoltaic effect, though less effective than visible light. |
| 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 Well | a well through which geothermal water is returned to an underground reservoir after use. Geothermal production and injection wells are constructed of pipes layered inside one another and cemented into the earth and to each other. This protects any shallow drinking water aquifers from mixing with deeper geothermal water. |
| Input Voltage | This is determined by the total power required by the alternating current loads and the voltage of any direct current loads. Generally, the larger the load, the higher the inverter input voltage. This keeps the current at levels where switches and other components are readily available. |
| 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 amount of sunlight reaching an area, usually expressed in Watt hours per square meter per day. |
| Installer | Usually a retailer and installer of PV Systems |
| Insulation | A material used to prevent the flow of electricity. Normally used on electrical wires to prevent electric shock. Typical materials used include plastics such as PVC and polypropylene. |
| Insulation, Thermal | A material having a relatively high resistance of heat flow and used principally to retard heat flow. See R-VALUE. |
| Insulator | A material (such as plastic or glass) that does not permit electricity to pass through it readily. |
| Intake | In a hydro system, the structure that receives the water and feeds it into the penstock (pipeline). Usually incorporates screening or filtering to keep debris and aquatic life out of the system. |
| 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. |
| 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. |
| Integrator | Integrates PV components in to a complete PV System |
| 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. |
| Interconnect | A conductor within a module or other means of connection which provides an electrical interconnection between the solar cells. [UL 1703] |
| 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. |
| Inter-Connector | A transmission line or group of transmission lines that connects the transmission networks in adjacent regions. |
| 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. |
| Intrinsic Layer | A layer of semiconductor material, used in a photovoltaic device, whose properties are essentially those of the pure, undoped, material. |
| Intrinsic Semiconductor | An undoped semiconductor. |
| Inverter | A device that converts DC electricity (anywhere from 12 to 600 VDC) to AC electricity (typically 120/240 VAC). |
| Investor-Owned Utilities | A private company that provides a utility, such as water, natural gas or electricity, to a specific service area. |
| Ion | An atom that has lost or gained electrons and by doing so, becomes 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. |
| IPP | INDEPENDENT POWER PRODUCER. An private entity that operates a generation facility and sells power to electric utilities for resale to retail customers. |
| Irradiance | The direct, diffuse, and reflected solar radiation that strikes a surface. Usually expressed in kilowatts per square meter. Irradiance multiplied by time equals insolation. |
| ISC | See SHORT CIRCUIT CURRENT. |
| 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 that may 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. |
| Ispra Guidelines | Guidelines for the assessment of photovoltaic power plants, published by the Joint Research Centre of the Commission of the European Communities, Ispra, Italy. |
| I-Type Semiconductor | Semiconductor material that is left intrinsic, or undoped so that the concentration of charge carriers is characteristic of the material itself rather than of added impurities. |
| I-V Curve | A graph that plots the current versus the voltage from a PV cell as the electrical load (or resistance) is increased from short circuit (no load) to open circuit (maximum voltage). The shape of the curve characterizing cell performance. Three important points on the I-V curve are the open-circuit voltage, short-circuit current, and peak or maximum power (operating) point. |
| I-V Data | The relationship between current and voltage of a photovoltaic device in the power-producing quadrant, as a set of ordered pairs of current and voltage readings in a table, or as a curve plotted in a suitable coordinate system |
