Glossary A to F


Alternating current (AC) - Flow of electricity that constantly changes direction between positive and negative sides. Electricity produced in the UK moves in current that shifts direction at a rate of 50 times per second (50 Hertz, 50Hz).


Base load - The minimum load experienced by an electric utility system over a given period of time. Baseload capacity - Generating equipment operated to serve loads 24-hours per day (eg. nuclear power plants).

BETTA – the British Electricity Transmission and Trading Arrangements introduced in April 2005, extending NETA to Scotland.


Capacity - The maximum load a generating unit, generating station, or other electrical apparatus is rated to carry.

Capacity factor - The ratio of the electrical energy produced by a generating unit relative to the electrical energy that could have been produced at continuous full power operation during the same period of time. The Capacity Factor for wind energy in the UK is typically between 20% and 40%.

Capacity value – Sometimes referred to as capacity credit, this is an expression of the percentage of conventional generation that can be displaced by wind generation. The capacity value may be equal to the capacity factor at low levels of wind penetration, but will be lower as penetration increases.

CCGT - Combined cycle gas turbine; modern gas powered electricity generating technology.

Conservation - A foregoing or reduction of electric usage for the purpose of saving natural energy resources and limiting peak demand in order to ultimately reduce the capacity requirements for plant and equipment.

Current (electric) - Flow of electrons in an electric conductor.


Defra - Department of Environment, Food and Rural Affairs

Distributed generation (embedded generation) - A distributed generation system involves small amounts of generation located on a utility's distribution system for the purpose of meeting local (substation level) peak loads and/or displacing the need to build additional (or upgrade) local distribution lines.

DBERR - Department of Business, Enterprise and Regulatory Reform.

Distribution - The system of wires, switches, and transformers that serve neighbourhoods and businesses; classified as 132,000 volts and below in England and Wales (132kV is considered to be part of the Transmission Network in Scotland). A distribution system reduces the voltage from high-voltage transmission lines (275,000 volts or 400,000 volts) to a level that can be distributed to homes or businesses; 132,000V, 33,000V, 11,000V, 3,300V, 440V.

Distribution system - That part of the electric system that delivers electrical energy to consumers.

DSO, DNO - Distribution System (or Network) Operator.


Embedded generation – see distributed generation

Energy - This is broadly defined as the capability of doing work. In the electricity industry, energy is more narrowly defined as electricity supplied over time, normally expressed in kilowatt-hours.

Energy consumption - The amount of energy consumed in the form in which it is acquired by the user. The term excludes electrical generation and distribution losses.

Energy efficiency - Programmes that reduce energy consumption whilst maintaining a given level of output.

Energy mix - the distribution or proportion of different energy sources within the total energy supply.

Energy resources - Everything that could be used by society as a source of energy.

Energy source - A source that provides the power to be converted to electricity e.g. hydro, solar, wind, biomass, fossil fuel, nuclear fuel.

Energy use - Energy consumed during a specified time period for a specific purpose (usually expressed in kWh).