Glossary of Terms - I

• Ignite - To heat a gaseous mixture to the temperature at which combustion takes place.
• Ignition Point - The minimum temperature at which combustion of a solid or fluid can occur.
• Illuminance - A measure of the amount of light incident on a surface; measured in foot-candles or Lux.
• Imbalance Energy - Discrepancy between the amount that a seller contracted to deliver and the actual volume of power delivered. Imbalances are resolved through monetary payment.
• Immediate or Cancel - An order which must be filled immediately or be canceled. IOC orders need not be filled in their entirety.
• Implied Volatility - A measurement of the market's expected price range of the underlying commodity futures based on market-traded options premiums.
• Impulse Turbine - A turbine that is driven by high velocity jets of water or steam from a nozzle directed to vanes or buckets attached to a wheel. (A pelton wheel is an impulse hydro turbine).
• Inadvertent Energy - The imbalance of energy flows back and forth that are on-going and routine between a generator of power and the centers of demand. These imbalances are typically settled through exchanges of physical product.
• Incandescent - These lights use an electrically heated filament to produce light in a vacuum or inert gas-filled bulb.
• Incentive - A rebate or some form of payment used to encourage people to implement a given demand-side management (DSM) technology. The incentive is calculated as the amount of the technology costs that must be paid by the utility for the participant test to equal one and achieve the desired benefit/cost ratio to drive the market.
• Incident Solar Radiation - The amount of solar radiation striking a surface per unit of time and area.
• Incremental Effects - The annual effects in energy use (measured in megawatthours) and peak load (measured in kilowatts) caused by new participants in existing DSM programs and all participants in new DSM programs during a given year. Reported Incremental Effects should be annualized to indicate the program effects that would have occurred had these participants been initiated into the program on January 1 of the given year. Incremental effects are not simply the Annual Effects of a given year minus the Annual Effects of the prior year, since these net effects would fail to account for program attrition, degradation, demolition, and participant dropouts.
• Independent - Term generally applies to a non-integrated oil or natural gas company, usually active in only one or two sectors of the industry. An independent marketer buys petroleum products from major or independent refiners and resells them under his own brand name or buys natural gas from producers and resells it. There are also independents which are active exclusively either in oil or gas production or refining.
• Independent Power Producers (IPPs) - These are private entrepreneurs who develop, own or operate electric power plants fueled by alternative energy sources such as biomass, cogeneration, small hydro, waste-energy and wind facilities.
• Independent System Operator (ISO) - An ISO is the entity charged with reliable operation of the grid and provision of open transmission access to all market participants on a non-discriminatory basis.
• Indirect Solar Gain System - A passive solar heating system in which the sun warms a heat storage element, and the heat is distributed to the interior space by convection, conduction, and radiation.
• Indirect Utility Cost - A utility cost that may not be meaningfully identified with any particular DSM program category. Indirect costs could be attributable to one of several accounting cost categories (i.e., Administrative, Marketing, Monitoring & Evaluation, Utility-Earned Incentives, Other). Accounting costs that are known DSM program costs should not be reported under Indirect Utility Cost, rather those costs should be reported as Direct Utility Costs under the appropriate DSM program category.
• Indirect Water Heater - A type of water heater that circulates water through a heat exchanger in a boiler. The heated water then flows into an insulated storage tank.
• 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 - The production of an electric current in a conductor by the variation of a magnetic field in its vicinity.
• Induction Generator - A device that converts the mechanical energy of rotation into electricity based on electromagnetic induction. An electric voltage (electromotive force) is induced in a conducting loop (or coil) when there is a change in the number of magnetic field lines (or magnetic flux) passing through the loop. When the loop is closed by connecting the ends through an external load, the induced voltage will cause an electric current to flow through the loop and load. Thus rotational energy is converted into electrical energy.
• Induction Motor - A motor in which a three phase (or any multiphase) alternating current (i.e. the working current) is supplied to iron-cored coils (or windings) within the stator. As a result, a rotating magnetic field is set up, which induces a magnetizing current in the rotor coils (or windings). Interaction of the magnetic field produced in this manner with the rotating field causes rotational motion to occur.
• Industrial - The industrial sector is generally defined as manufacturing, construction, mining, agriculture, fishing, and forestry establishments (Standard Industrial Classification [SIC] codes 01-39). The utility may classify industrial service using the SIC codes, or based on demand or annual usage exceeding some specified limit. The limit may be set by the utility based on the rate schedule of the utility.
• Industrial Process Heat - The thermal energy used in an industrial process.
• Inert Gas - A gas that does not react with other substances; e.g. argon or krypton; sealed between two sheets of glazing to decrease the U-value (increase the R-Value) of windows.
• 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.
• Insolation - The solar power density incident on a surface of stated area and orientation, usually expressed as Watts per square meter or Btu per square foot per hour.
• Installed capacity - The total generating units' capacities in a power plant or on a total utility system. The capacity can be based on the nameplate rating or the net dependable capacity.
• Instantaneous Efficiency (of a Solar Collector) - The amount of energy absorbed (or converted) by a solar collector (or photovoltaic cell or module) over a 15 minute period.
• Insulation Blanket - A pre-cut layer of insulation applied around a water heater storage tank to reduce standby heat loss from the tank.
• Insulator - A device or material with a high resistance to electricity flow.
• Intangible Transition Charge - The amounts on all customer bills, collected by the electric utility to recover transition bond expenses.
• Integrated Collector/Storage (ICS) Solar Systems - ICS solar systems are also called "batch" or "breadbox" water heaters. They combine the collector and storage tank in one unit. The sun shining into the collector strikes the storage tank directly, heating the water. The large thermal mass of the water, plus methods to reduce heat loss through the tank, prevent the stored water from freezing.
• Integrated Heating Systems - A type of heating appliance that performs more than one function, for example space and water heating.
• Integrated Resource Plan (IRP) - A comprehensive and systematic blueprint developed by a supplier, distributor, or end-user of energy who has evaluated demand-side and supply-side resource options and economic parameters and determined which options will best help them meet their energy goals at the lowest reasonable energy, environmental, and societal cost.
• Integration - A term that describes the degree in, and to, which one given company participates in all phases of the petroleum industry.
• 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 utility, enabling power to be moved in either direction. Interconnections allow the utilities to help contain costs while enhancing system reliability.
• Interdepartmental Service (Electric) - Interdepartmental service includes amounts charged by the electric department at tariff or other specified rates for electricity supplied by it to other utility departments.
• Intermediate Load (Electric System) - The range from base load to a point between base load and peak. This point may be the midpoint, a percent of the peakload, or the load over a specified time period.
• Intermittent Generators - Power plants, whose output depends on a factor(s) that cannot be controlled by the power generator because they utilize intermittent resources such as solar energy or the wind.
• Intermittent Resources - Resources whose output depends on some other factory that cannot be controlled by the utility e.g. wind or sun. Thus, the capacity varies by day and by hour.
• Internal Combustion Electric Power Plant - The generation of electric power by a heat engine which converts part of the heat generated by combustion of the fuel into mechanical motion to operate an electric generator.
• Internal Combustion Plant - A plant in which the prime mover is an internal combustion engine. An internal combustion engine has one or more cylinders in which the process of combustion takes place, converting energy released from the rapid burning of a fuel-air mixture into mechanical energy. Diesel or gas-fired engines are the principal types used in electric plants. The plant is usually operated during periods of high demand for electricity.
• Internal Gain - The heat produced by sources of heat in a building (occupants, appliances, lighting, etc).
• Internal Mass - Materials with high thermal energy storage capacity contained in or part of a building's walls, floors, or freestanding elements.
• Internal Rate of Return - A widely used rate of return for performing economic analysis. This method solves for the interest rate that equates the equivalent worth of an alternative's cash receipts or savings to the equivalent worth of cash expenditures, including investments. The resultant interest rate is termed the internal rate of return (IRR).
• Interruptible Gas - Gas sold to customers with a provision that permits curtailment or cessation of service at the discretion of the distributing company under certain circumstances, as specified in the service contract.
• Interruptible Load - Refers to program activities that, in accordance with contractual arrangements, can interrupt consumer load at times of seasonal peak load by direct control of the utility system operator or by action of the consumer at the direct request of the system operator. It usually involves commercial and industrial consumers. In some instances the load reduction may be affected by direct action of the system operator (remote tripping) after notice to the consumer in accordance with contractual provisions. For example, loads that can be interrupted to fulfill planning or operation reserve requirements should be reported as Interruptible Load. Interruptible Load as defined here excludes Direct Load Control and Other Load Management. (Interruptible Load, as reported here, is synonymous with Interruptible Demand reported to the North American Electric Reliability Council on the voluntary Office of Energy Emergency Operations Form OE-411, ÏCoordinated Regional Bulk Power Supply Program Report, with the exception that annual peak load effects are reported on the Form EIA-861 and seasonal (i.e., summer and winter) peak load effects are reported on the OE-411).
• Interruptible Power - This refers to power whose delivery can be curtailed by the supplier, usually under some sort of agreement by the parties involved.
• Interruptible Rates - These provide power at a lower rate to large industrial and commercial customers who agree to reduce their electricity use in times of peak demand.
• Interruptible Service - Utility service which expects and permits interruption on short notice, generally in peak-load periods, in order to meet the demand by firm service customers. Interruptible service customers usually pay a lower rate than firm service customers. Opposite of Firm Service.
• Interval Metering - The process by which power consumption is measured at regular intervals in order that specific load usage for a set period of time can be determined.
• In-the-Money - An option that can be exercised and immediately closed out against the underlying market for a cash credit. The option is in-the-money if the underlying futures price is above a call option's strike price, or below a put option's strike price.
• Intrinsic Layer - A layer of semiconductor material (as used in a solar photovoltaic device) whose properties are essentially those of the pure, undoped, material.
• Intrinsic Semiconductor - An undoped semiconductor.
• Intrinsic Value - The amount by which an option is in-the-money. An option which is not in-the-money has no intrinsic value. For calls, intrinsic value equals the difference between the underlying futures price and the option's strike price. For puts, intrinsic value equals the option's strike price minus the underlying futures price. Intrinsic value is never less than zero.
• Introducing Broker - A firm engaged in soliciting or in accepting orders for the purchase or sale of any commodity for future delivery.
• Inverted Market - A futures market is said to be inverted when distant contract months are selling at a discount to nearby contract months; also known as backwardation.
• Inverter - A device that that converts direct current electricity (from for example a solar photovoltaic module or array) to alternating current for use directly to operate appliances or to supply power to a electricity grid.
• Investment Tax Credit - A tax credit granted for specific types of investments.
• Investor Owned Utility (IOU) - A utility owned by stockholders or other investors; sometimes referred to as a private utility, in contrast to a public utility that is owned by a government agency or cooperative.
• Invisible Supply - Uncounted stocks of a commodity in the hands of wholesalers, manufacturers and producers which cannot be identified accurately; stocks outside commercial channels but theoretically available to the market.
• In-well Transfer - An inventory transfer of propane held in underground caverns or storage.
• Ion - An electrically charged atom or group of atoms that has lost or gained electrons; a loss makes the resulting particle positively charged; a gain makes the particle negatively charged.
• Ionizer - A device that removes airborne particles from breathable air. Negative ions are produced and give up their negative charge to the particles. These new negative particles are then attracted to the positive particles surrounding them. This accumulation process continues until the particles become heavy enough to fall to the ground.
• Irradiance - The direct, diffuse, and reflected solar radiation that strikes a surface.
• Isolated Solar Gain System - A type of passive solar heating system where heat is collected in one area for use in another.
• ISPRA guidelines - Guidelines for the assessment of PV Plants, published by the Joint Research Centre of the Commission of the European Communities, Ispra, Italy.
• I-Type Semiconductor - A 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 graphical plot or representation the current and voltage output of a solar photovoltaic cell or module as a load on the device is increased from short circuit (no load) condition to the open circuit condition; used to characterize cell/module performance.
• 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 (i.e., Cartesian). [ASTM E 1036]