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Smart Grid Glossary

AMI: Advanced Metering Infrastructure is a term denoting electricity meters that measure and record usage data at a minimum, in hourly intervals, and provide usage data to both consumers and energy companies at least once daily.

AMR: Automated Meter Reading is a term denoting electricity meters that collect data for billing purposes only and transmit this data one way, usually from the customer to the distribution utility.

ancillary services: Services that ensure reliability and support the transmission of electricity from generation sites to customer loads. Such services may include: load regulation, spinning reserve, non-spinning reserve, replacement reserve, and voltage support.

APPLIANCE: A piece of equipment, commonly powered by electricity, used to perform a particular energy-driven function. Examples of common appliances are refrigerators, clothes washers and dishwashers, conventional ranges/ovens and microwave ovens, humidifiers and dehumidifiers, toasters, radios, and televisions. Note: Appliances are ordinarily self-contained with respect to their function. Thus, equipment such as central heating and air conditioning systems and water heaters, which are connected to distribution systems inherent to their purposes, are not considered appliances.

CAPITAL COST: The cost of field development and plant construction and the equipment required for industry operations.

CARBON DIOXIDE (CO2): A colorless, odorless, non-poisonous gas that is a normal part of Earth’s atmosphere. Carbon dioxide is a product of fossil-fuel combustion as well as other processes. It is considered a greenhouse gas as it traps heat (infrared energy) radiated by the Earth into the atmosphere and thereby contributes to the potential for global warming. The global warming potential (GWP) of other greenhouse gases is measured in relation to that of carbon dioxide, which by international scientific convention is assigned a value of one (1).

carbon footprint - A carbon footprint is the measure of the environmental impact of a particular organization's operation, measured in units of carbon dioxide.

carbon neutral - To be considered carbon neutral, an individual or organization must reduce its carbon footprint to zero.

carbon offset - Credits achieved through financial support of projects that reduce the emission of greenhouse gases. 

carbon trading - Practice of purchasing carbon offsets in order to advertise a building, organization or event as being "carbon neutral." Practice is regulated in countries that signed the Kyoto Protocol. Carbon trading in the U.S. is not overseen by industry-wide standards or certification. 

CLIMATE CHANGE: A term used to refer to all forms of climatic inconsistency, but especially to significant change from one prevailing climatic condition to another In some cases, “climate change” has been used synonymously with the term “global warming”; scientists, however, tend to use the term in a wider sense inclusive of natural changes in climate, including climatic cooling.

compressed air energy storage - A way to store massive amounts of renewable power by compressing air at very high pressures and storing it in large underground caverns, depleted wells or acquifers.

CONGESTION: A condition that occurs when insufficient transfer capacity is available to implement all of the preferred schedules for electricity transmission simultaneously.

DSM: This Demand-Side Management category represents the amount of consumer load reduction at the time of system peak due to utility programs that reduce consumer load during many hours of the year. Examples include utility rebate and shared savings activities for the installation of energy efficient appliances, lighting and electrical machinery, and weatherization materials. In addition, this category includes all other Demand-Side Management activities, such as thermal storage, time-of-use rates, fuel substitution, measurement and evaluation, and any other utility-administered Demand-Side Management activity designed to reduce demand and/or electricity use

DISTRIBUTED GENERATOR: A generator that is located close to the particular load that it is intended to serve. General, but non-exclusive, characteristics of these generators include: an operating strategy that supports the served load; and interconnection to a distribution or sub-transmission system.

DISTRIBUTION: The delivery of energy to retail customers.

DISTRIBUTION SYSTEM: The portion of the transmission and facilities of an electric system that is dedicated to delivering electric energy to an end-user.

ELECTRIC GENERATION INDUSTRY: Stationary and mobile generating units that are connected to the electric power grid and can generate electricity. The electric generation industry includes the “electric power sector” (utility generators and independent power producers) and industrial and commercial power generators, including combined-heat-and-power producers, but excludes units at single-family dwellings.

ELECTRIC GENERATOR: A facility that produces only electricity, commonly expressed in kilowatthours (kWh) or megawatthours (MWh) Electric generators include electric utilities and independent power producers.

electric grid - A network of synchronized power providers and consumers that are connected by transmission and distribution lines and operated by one or more control centers. When most people talk about the power "grid," they're referring to the transmission system for electricity.

electric power: The rate at which electric energy is transferred. Electric power is measured by capacity and is commonly expressed in megawatts (MW). A megawatt (MW) is one million watts.

ELECTRIC POWER GRID: A system of synchronized power providers and consumers connected by transmission and distribution lines and operated by one or more control centers. In the continental United States, the electric power grid consists of three systems: the Eastern Interconnect, the Western Interconnect, and the Texas Interconnect. In Alaska and Hawaii, several systems encompass areas smaller than the State (e.g., the interconnect serving Anchorage, Fairbanks, and the Kenai Peninsula; individual islands).

ELECTRIC SYSTEM RELIABILITY: The degree to which the performance of the elements of the electrical system results in power being delivered to consumers within accepted standards and in the amount desired. Reliability encompasses two concepts, adequacy and security Adequacy implies that there are sufficient generation and transmission resources installed and available to meet projected electrical demand plus reserves for contingencies. Security implies that the system will remain intact operationally (i.e., will have sufficient available operating capacity) even after outages or other equipment failure. The degree of reliability may be measured by the frequency, duration, and magnitude of adverse effects on consumer service.

ELECTRIC UTILITY: Any entity that generates, transmits, or distributes electricity and recovers the cost of its generation, transmission or distribution assets and operations, either directly or indirectly, through cost-based rates set by a separate regulatory authority (e.g., State Public Service Commission), or is owned by a governmental unit or the consumers that the entity serves. Examples of these entities include: investor-owned entities, public power districts, public utility districts, municipalities, rural electric cooperatives, and State and Federal agencies.

ELECTRICITY CONGESTION: A condition that occurs when insufficient transmission capacity is available to implement all of the desired transactions simultaneously.

ELECTRICITY DEMAND: The rate at which energy is delivered to loads and scheduling points by generation, transmission, and distribution facilities.

ENERGY EFFICIENCY, ELECTRICITY: Refers to programs that are aimed at reducing the energy used by specific end-use devices and systems, typically without affecting the services provided. These programs reduce overall electricity consumption (reported in megawatthours), often without explicit consideration for the timing of program-induced savings. Such savings are generally achieved by substituting technologically more advanced equipment to produce the same level of end-use services (e.g. lighting, heating, motor drive) with less electricity. Examples include high-efficiency appliances, efficient lighting programs, high-efficiency heating, ventilating and air conditioning (HVAC) systems or control modifications, efficient building design, advanced electric motor drives, and heat recovery systems.

ENERGY SAVINGS: A reduction in the amount of electricity used by end users as a result of participation in energy efficiency programs and load management programs.

ENERGY SERVICE PROVIDER: An energy entity that provides service to a retail or end-use customer.

FERC: The Federal agency with jurisdiction over interstate electricity sales, wholesale electric rates, hydroelectric licensing, natural gas pricing, oil pipeline rates, and gas pipeline certification. FERC is an independent regulatory agency within the Department of Energy and is the successor to the Federal Power Commission.

fuel cell: A device capable of generating an electrical current by converting the chemical energy of a fuel (e.g., hydrogen) directly into electrical energy. Fuel cells differ from conventional electrical cells in that the active materials such as fuel and oxygen are not contained within the cell but are supplied from outside. It does not contain an intermediate heat cycle, as do most other electrical generation techniques.

GENERATION: The process of producing electric energy by transforming other forms of energy; also, the amount of electric energy produced, expressed in kilowatthours.

GLOBAL WARMING: An increase in the near surface temperature of the Earth. Global warming has occurred in the distant past as the result of natural influences, but the term is today most often used to refer to the warming some scientists predict will occur as a result of increased anthropogenic emissions of greenhouse gases.

GREENHOUSE GASES: Those gases, such as water vapor, carbon dioxide, nitrous oxide, methane, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride, that are transparent to solar (short-wave) radiation but opaque to long-wave (infrared) radiation, thus preventing long-wave radiant energy from leaving Earth’s atmosphere. The net effect is a trapping of absorbed radiation ’s surface.

INTERMITTENT ELECTRIC GENERATOR OR INTERMITTENT RESOURCE: An electric generating plant with output controlled by the natural variability of the energy resource rather than dispatched based on system requirements. Intermittent output usually results from the direct, non-stored conversion of naturally occurring energy fluxes such as solar energy, wind energy, or the energy of free-flowing rivers (that is, run-of-river

INTERRUPTIBLE LOAD: This Demand-Side Management category represents the consumer load that, in accordance with contractual arrangements, can be interrupted at the time of annual peak load by the action of the consumer at the direct request of the system operator. This type of control usually involves large-volume commercial and industrial consumers. Interruptible Load does not include Direct Load Control.

LINE LOSS: Electric energy lost because of the transmission of electricity. Much of the loss is thermal in nature. 

LOAD (ELECTRIC): The amount of electric power delivered or required at any specific point or points on a system. The requirement originates at the energy-consuming equipment of the consumers.

LOAD CONTROL PROGRAM: A program in which the utility company offers a lower rate in return for having permission to turn off the air conditioner or water heater for short periods of time by remote control. This control allows the utility to reduce peak demand.

NERC: North American Electric Reliability Corporation, an institution that oversees and regulates the reliability of the North American electrical grids.

OFF PEAK: Period of relatively low system demand These periods often occur in daily, weekly, and seasonal patterns; these off-peak periods differ for each individual electric utility.

ON PEAK: Periods of relatively high system demand. These periods often occur in daily, weekly, and seasonal patterns; these on-peak periods differ for each individual electric utility.

OUTAGE: The period during which a generating unit, transmission line, or other facility is out of service.

PEAK DEMAND OR PEAK LOAD: The maximum load during a specified period of time. 

PEAKER PLANT OR PEAK LOAD PLANT: A plant usually housing old, low-efficiency steam units, gas turbines, diesels, or pumped-storage hydroelectric equipment normally used during the peak-load periods.

PEAKING CAPACITY: Capacity of generating equipment normally reserved for operation during the hours of highest daily, weekly, or seasonal loads. Some generating equipment may be operated at certain times as peaking capacity and at other times to serve loads on an around-theclock basis.

RATE BASE: The value of property upon which a utility is permitted to earn a specified rate of return as established by a regulatory authority. The rate base generally represents the value of property used by the utility in providing service and may be calculated by any one or a combination of the following accounting methods: fair value, prudent investment, reproduction cost, or original cost. Depending on which method is used, the rate base includes cash, working capital, materials and supplies, deductions for accumulated provisions for depreciation, contributions in aid of construction, customer advances for construction, accumulated deferred income taxes, and accumulated deferred investment tax credits.

RATE CASE: A proceeding, usually before a regulatory commission, involving the rates to be charged for a public utility service. 

RATE FEATURES: Special rate schedules or tariffs offered to customers by electric and/or natural gas utilities. 

RATE OF RETURN: The ratio of net operating income earned by a utility is calculated as a percentage of its rate base. 

RATE OF RETURN ON RATE BASE: The ratio of net operating income earned by a utility, calculated as a percentage of its rate base. 

RATE SCHEDULE (ELECTRIC): A statement of the financial terms and conditions governing a class or classes of utility services provided to a customer. Approval of the schedule is given by the appropriate rate-making authority.

RATEMAKING AUTHORITY: A utility commission’s legal authority to fix, modify, approve, or disapprove rates as determined by the powers given the commission by a State or Federal legislature.

RATES: The authorized charges per unit or level of consumption for a specified time period for any of the classes of utility services provided to a customer 

RELIABILITY (ELECTRIC SYSTEM): A measure of the ability of the system to continue operation while some lines or generators are out of service. Reliability deals with the performance of the system under stress.

RENEWABLE ENERGY RESOURCES: Energy resources that are naturally replenishing but flow-limited. They are virtually inexhaustible in duration but limited in the amount of energy that is available per unit of time. Renewable energy resources include: biomass, hydro, geothermal, solar, wind, ocean thermal, wave action, and tidal action 

SOLAR ENERGY: The radiant energy of the sun, which can be converted into other forms of energy, such as heat or electricity. 

SMART GRID: A generic label for the application of computer intelligence and networking abilities to a dumb electricity distribution system.

TARIFF: A published volume of rate schedules and general terms and conditions under which a product or service will be supplied. 

THERMAL ENERGY STORAGE: The storage of heat energy during utility off-peak times at night, for use during the next day without incurring daytime peak electric rates.

THERMAL LIMIT: The maximum amount of power a transmission line can carry without suffering heat-related deterioration of line equipment, particularly conductors. 

TIME-OF-DAY PRICING: A special electric rate feature under which the price per kilowatthour depends on the time of day. 

TIME-OF-DAY RATE: The rate charged by an electric utility for service to various classes of customers. The rate reflects the different costs of providing the service at different times of the day.

TRANSMISSION AND DISTRIBUTION LOSS: Electric energy lost due to the transmission and distribution of electricity. Much of the loss is thermal in nature.

TRANSMISSION (ELECTRIC) (VERB): The movement or transfer of electric energy over an interconnected group of lines and associated equipment between points of supply and points at which it is transformed for delivery to consumers or is delivered to other electric systems. Transmission is considered to end when the energy is transformed for distribution to the consumer. 

UTILITY GENERATION: Generation by electric systems engaged in selling electric energy to the public.

UTILITY-SPONSORED CONSERVATION PROGRAM: Any program sponsored by an electric and/or natural gas utility to review equipment and construction features in buildings and advise on ways to increase the energy efficiency of buildings. Also included are utility-sponsored programs to encourage the use of more energy-efficient equipment. Included are programs to improve the energy efficiency in the lighting system or building equipment or the thermal efficiency of the building shell.

WIND ENERGY: Kinetic energy present in wind motion that can be converted to mechanical energy for driving pumps, mills, and electric power generators.


See also: Smart Grid Technology Overview, Smart Grid Tutorial: What IT Managers Need to Know

Many of the definitions in this glossary are from The Smart Grid: An Introduction.  They are reprinted with the permission of the U.S. Department of Energy.  Visit the official DOE website for more information on Smart Grids initiatives. 

This was last updated in April 2011
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