A–Z

Energy glossary

Short, plain-English definitions of the terms you meet in energy news and bills.

A

Albedo: The share of incoming sunlight that a surface reflects, on a scale from 0 (absorbs everything) to 1 (reflects everything).
Anaerobic digestion: A process in which microbes break down organic material such as food waste, slurry and crops without oxygen, producing biogas and a fertiliser called digestate.

B

Balancing Mechanism: The real-time market the National Energy System Operator uses to pay generators, batteries and large users to change their output so supply matches demand every second.
Baseload power: The minimum level of electricity demand that exists around the clock, and the power stations that run more or less continuously to meet it.
Battery energy storage system (BESS): A bank of rechargeable batteries connected to the grid that stores electricity when it is plentiful and releases it when it is needed.
Bifacial solar panel: A solar panel that generates electricity from light hitting both its front and its back, picking up sunlight reflected from the ground or surfaces behind it.
Bioenergy with carbon capture and storage (BECCS): Burning or processing biomass for energy while capturing the resulting carbon dioxide and storing it underground, with the aim of removing CO2 from the atmosphere.
Biomethane: Biogas that has been cleaned and upgraded to almost pure methane, so it can be injected into the gas grid and used in place of fossil natural gas.

C

Capacity factor: How much electricity a power plant actually produced over a period, as a share of what it would have produced running flat out the whole time.
Capacity Market: A scheme that pays power stations, batteries, interconnectors and flexible demand to be available when Great Britain's electricity system is under stress.
Carbon border adjustment mechanism (CBAM): A charge on the carbon emitted in making certain imported goods, so they face a carbon cost similar to products made under the UK's own carbon market.
Carbon budget: A legally binding cap on the UK's total greenhouse gas emissions over a five-year period, set under the Climate Change Act 2008.
Carbon capture and storage (CCS / CCUS): Capturing carbon dioxide from power stations or factories before it reaches the air, then piping it for permanent storage deep underground.
Carbon intensity (of electricity): How much carbon dioxide is emitted to produce one unit of electricity, usually given in grams of CO2 per kilowatt-hour (gCO2/kWh).
Clean Power 2030: The UK government's mission for Great Britain's electricity to come overwhelmingly from clean sources by 2030, set out in an action plan published in December 2024.
Climate Change Levy (CCL): A UK tax on the electricity, gas and other fuels that businesses and the public sector use, added to their energy bills by the supplier.
Coefficient of performance (COP and SCOP): The ratio of heat a heat pump delivers to the electricity it uses; SCOP is the same ratio averaged over a whole heating season.
Contracts for Difference (CfD): The UK government's main scheme for new low-carbon power: generators get a fixed strike price per MWh, topped up or paid back against the market price.
Curtailment and constraint payments: Curtailment is when a power station, usually a wind farm, is told to cut output because the grid cannot carry its power; constraint payments compensate it.

D

Demand flexibility: Changing when electricity is used, rather than how much, so that demand moves to times when power is cheaper, cleaner or easier for the grid to supply.
Distribution network operator (DNO): The company that owns and runs the local electricity network of poles, cables and substations that carries power from the national grid to homes and businesses.

E

Economy 7: An electricity tariff with two unit rates: a cheaper rate for seven hours, usually at night, and a higher rate for the rest of the day.
Electrolyser: A device that uses electricity to split water into hydrogen and oxygen; powered by renewable electricity, it produces green hydrogen.
Energy Company Obligation (ECO4): A Great Britain scheme that requires larger energy suppliers to fund insulation and heating upgrades for low-income homes. ECO4 ends on 31 December 2026 with no successor obligation.
Energy Performance Certificate (EPC): A certificate that rates how energy efficient a building is on a scale from A (best) to G (worst), with recommendations for improving it.
Energy price cap: The maximum unit rates and daily standing charges that suppliers in Great Britain can charge households on default tariffs, set by Ofgem every three months.
Energy security: Having reliable access to the energy a country needs, at prices households and businesses can afford, and being able to withstand supply shocks.

F

Feed-in Tariff (FIT): A former Great Britain scheme that paid small-scale generators for electricity they produced and exported. It closed to new applicants in 2019, but existing payments continue.
Floating offshore wind: Wind turbines mounted on floating platforms anchored to the seabed, which lets wind farms be built in water too deep for fixed foundations.

G

Gate 2 (grid connections reform): The reformed process for connecting projects to Great Britain's grid, giving firm dates only to projects that are ready to build and fit Clean Power 2030.
Great British Energy: A publicly owned, operationally independent clean energy company set up by the UK government and headquartered in Aberdeen.
Great British Energy – Nuclear: The UK government body, formerly Great British Nuclear, that leads new nuclear projects, including the small modular reactor programme with Rolls-Royce SMR at Wylfa.
Green Gas Support Scheme (GGSS): A government scheme that pays tariffs to new anaerobic digestion plants in Great Britain for biomethane they inject into the gas grid, funded by the Green Gas Levy.
Grid connection queue: The list of generation, storage and demand projects waiting for a connection to Great Britain's electricity network, now being reordered under the Gate 2 reforms.
Grid inertia: The stored energy in the spinning machines connected to the grid, which slows down how fast the system frequency changes when supply and demand suddenly diverge.

H

Heat network: A system of insulated pipes that carries heat from a central source to several buildings or homes, also called district or communal heating.
Heat pump: An electric device that moves heat from the outside air, the ground or water into a building, delivering more heat energy than the electricity it uses.
Home battery storage: A rechargeable battery installed in a home to store electricity from solar panels or the grid and use it later, usually in the evening.
Hydrogen colours (green, blue, grey…): An informal colour code describing how hydrogen was produced, from grey hydrogen made from unabated natural gas to green hydrogen made with renewable electricity.

I

Interconnector: A high-voltage cable that links one country's electricity grid to another's, so power can flow in either direction between them.

K

Kilowatt-hour (kWh): A unit of energy equal to using 1,000 watts of power for one hour; it is the unit used on UK gas and electricity bills.
Kilowatt-peak (kWp): The rated power of a solar panel or array under standard laboratory test conditions, used to compare system sizes rather than to predict real output.

L

Levelised cost of electricity (LCOE): The average cost of each megawatt-hour a power plant produces over its whole life, including building, running, fuel and decommissioning.
Levelised cost of heat (LCOH): The average lifetime cost of producing one unit of heat from a heating system, usually given in pounds per megawatt-hour of heat.
Long-duration energy storage (LDES): Storage that can hold electricity and release it for many hours or days, helping cover long periods of low wind and sun. Ofgem's scheme defines it as eight hours or more.

M

MCS certification: The UK quality scheme for small-scale renewable systems such as solar panels, heat pumps and home batteries, covering products, installers and installations.
Megawatt (MW) and gigawatt (GW): Units of power: a megawatt is one million watts and a gigawatt is one thousand megawatts, used to rate power stations, wind farms and the grid.
Mine water heat: Low-carbon heat taken from water in flooded former coal mines, usually boosted by heat pumps and supplied to buildings through a heat network.

N

National Energy System Operator (NESO): The publicly owned body that balances Great Britain's electricity system in real time and plans the wider energy system, including gas, for the long term.
National Grid: Both the everyday name for Great Britain's high-voltage electricity network and a listed company that owns the part of it in England and Wales.
Net zero: The point at which a country's greenhouse gas emissions are balanced by the amount removed from the atmosphere. UK law requires net zero by 2050.
Nuclear fusion: The process that powers the sun: light atoms such as hydrogen isotopes join to form heavier ones, releasing energy. Fusion power stations remain experimental.

O

Offshore wind: Electricity generated by wind turbines installed at sea, now the UK's largest renewable source of power and the core of its 2030 clean power plan.
Ofgem: The independent regulator for the gas and electricity markets in Great Britain, responsible for protecting consumers, setting the price cap and regulating network companies.
Onshore wind: Electricity generated by wind turbines on land, a mature and low-cost technology whose growth in England was held back by planning rules until 2024.

P

Photovoltaic (PV) cell: A thin semiconductor device, usually made of silicon, that turns sunlight directly into direct-current electricity; it is the basic building block of every solar panel.
Power purchase agreement (PPA): A long-term contract in which a buyer, often a large business, agrees to buy electricity from a specific generator at an agreed price.

R

Renewable Energy Guarantees of Origin (REGO): A certificate issued by Ofgem for each megawatt-hour of renewable electricity generated in the UK, used by suppliers to show how much of their power is renewable.
Renewables Obligation (RO): The UK's main support scheme for large-scale renewable electricity from 2002 until it closed to new capacity in April 2017. Payments continue until 2037.
Run-of-river hydropower: Hydroelectric generation that diverts part of a river's natural flow through a turbine and back into the river, with little or no water stored behind a dam.

S

Sand battery: A thermal store that uses surplus electricity to heat sand or crushed rock in an insulated silo, then releases the heat later, usually into a district heating network.
Small modular reactor (SMR): A nuclear fission reactor designed to be built mostly in a factory as standard modules, with an output of up to about 300 MW of electricity per unit.
Smart Export Guarantee (SEG): A Great Britain scheme that requires larger electricity suppliers to pay small-scale generators, such as homes with solar panels, for electricity they export to the grid.
Smart meter: A gas or electricity meter that records how much energy you use in short intervals and sends the readings to your supplier automatically.
Solar inverter: The device that converts the direct current (DC) produced by solar panels into the alternating current (AC) used in homes and on the grid.
Standing charge: A fixed daily amount on a gas or electricity bill that you pay regardless of how much energy you use, even on days when you use none.
Strategic Spatial Energy Plan (SSEP): A plan being prepared by NESO for the UK, Scottish and Welsh governments that maps where new electricity and hydrogen generation and storage should go in Great Britain.

T

Thermoelectric generator (TEG): A solid-state device with no moving parts that turns a temperature difference directly into electricity, using the Seebeck effect.
Tidal stream energy: Electricity generated by underwater turbines that are turned by fast-flowing tidal currents, a predictable renewable source the UK has been testing for two decades.
Time-of-use tariff: An electricity tariff that charges different unit rates at different times of day, so power is cheaper when demand is low or supply is plentiful.
Transmission network: The highest-voltage part of the electricity grid, carrying bulk power over long distances from large generators to the local distribution networks.

U

UK Emissions Trading Scheme (UK ETS): The UK's carbon market: power stations, heavy industry, aviation and shipping must hold one allowance for every tonne of CO2e they emit, under a shrinking cap.

V

Vehicle-to-grid (V2G): Technology that lets a parked electric car send electricity from its battery back to the grid, not just draw power from it to charge.

W

Warm Homes Plan: The UK government's programme of grants, loans and other support to upgrade homes with insulation, heat pumps, solar panels and batteries, replacing supplier-funded schemes such as ECO4.
Wave energy: Electricity generated from the up-and-down and back-and-forth motion of ocean waves, a technology the UK has tested for decades but not yet deployed at commercial scale.
Wholesale electricity price: The price at which generators sell electricity to suppliers before it reaches homes. In Great Britain it is often set by gas power stations.

Z

Zonal pricing: A wholesale electricity market split into regional zones, each with its own price. The UK government decided in July 2025 to keep a single national price instead.