Glossary M to S


Megawatt (MW) -One million watts. A large coal-fired power station in the UK typically has an installed capacity of between 2,000 MW and 4,000 MW

Megawatt-hour (MWh) - One thousand kilowatt-hours or one million-watt hours.


NETA - the New Electricity Trading Arrangements introduced in March 2001 for England and Wales, and governed by the Balancing and Settlement Code (see BSC). Now superseded by BETTA.


Off-peak - Periods of relatively low system demands.

OFGEM - the Office of Gas and Electricity Markets; the energy regulator for the GB gas and electricity sectors.

Outage - Time during which service is unavailable from a generating unit, transmission line, or other facility.


Payback - The length of time it takes for the savings received to cover the cost of implementing the technology.

Peak - Periods of relatively high system demands.

Peak demand - Maximum power used in a given period of time.

Phase - One of the characteristics of the electric service supplied or the equipment used. Practically all residential customers have singlephase service at 240 volts. Large commercial and industrial customers typically have threephase service from 440 volts upwards.

Plant - A facility containing prime movers, electric generators, and other equipment for producing electric energy.

Power - The rate at which energy is transferred.

Power plant - A generating station where electricity is produced.

Production - The act or process of generating electric energy.

Pumped storage - A facility designed to generate electric power during peak load periods with a hydroelectric plant using water pumped into a storage reservoir during off-peak periods.


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Regulation - An activity of government to control or direct economic entities by rulemaking and adjudication.

Reliability - Electric system reliability has two components - adequacy and security. Adequacy is the ability of the electric system to supply the aggregate electric demand and energy requirements of the customers at all times, taking into account scheduled and unscheduled outages of system facilities. Security is the ability of the electric system to withstand sudden disturbances such as electric short circuits or unanticipated loss of system facilities.

Renewable energy - the term used to cover those energy flows that occur naturally and repeatedly in the environment, it includes all energy derived from the sun (solar, wind, ocean, and hydro power, plus biomass), and geothermal sources.
Energy that is capable of being renewed by the natural ecological cycle, generally wind, wave, tidal, solar, hydro, biomass.

Renewables Obligation - support mechanism aimed at increasing the percentage of renewable energy generation on the national grid. The Renewables Obligation works by placing an obligation on electricity suppliers to source an increasing percentage of supply from renewables. Separate obligations apply in Scotland and Northern Ireland.

Reserve capacity - Capacity in excess of that required to carry peak load.

ROCs - Renewable Obligation Certificates; the tradable ‘currency’ of the RO.

Running and quick-start capability - Generally refers to generating units that can be available for load within a 30-minute period.


Scheduled outage - An outage that results when a component is deliberately taken out of service at a selected time, usually for the purposes of construction, maintenance, or testing.

Spinning reserve - Reserve generating capacity running at zero load.

Substation - A facility used for switching and/or changing or regulating the voltage of electricity. Service equipment, line transformer installations, or minor distribution or transmission equipment are not classified as substations.

Supplier - A person or corporation, generator, broker, marketer, aggregator or any other entity, that sells electricity to customers, using the transmission or distribution facilities of an electric distribution company.

System (Electric) - Physically connected generation, transmission, and distribution facilities operating as a single unit.