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Solar glossary

The words you will meet in solar quotes, guides and rules, explained simply.

AC (alternating current): The kind of electricity your home's sockets and appliances use.
AC-coupled battery: A battery with its own inverter, connected to your home's normal wiring. The usual way to add a battery to existing panels.
Array: All the solar panels in a system, together.
Article 4 direction: A council decision that removes permitted development rights in an area, so you need to apply for planning permission.
BMS (battery management system): The electronics inside a battery that protect the cells, for example by stopping charging when they are too cold.
Building warrant: In Scotland, approval for certain building work under the building standards.
Changeover switch: A switch fitted by an electrician that connects house circuits to either the grid or a back-up source such as a generator or portable power station, never both at once.
Clipping: When an inverter limits its output, so some of what the panels could produce is lost.
Commissioning: Testing a system, switching it on and recording the results.
Consumer unit: Your fuse box, where the circuits in your home start.
Cycle life: How many full charges a battery is rated for before its capacity falls to a stated level, such as 80% of new.
DC (direct current): The kind of electricity solar panels and batteries produce and store.
DC to AC ratio: The panels' total rating divided by the inverter's rating.
DC-coupled battery: A battery that shares a hybrid inverter with the solar panels.
Depth of discharge: How much of a battery's capacity can be used before it stops discharging.
DNO (distribution network operator): The company that runs the local power cables in your area. It is not your energy supplier.
Economy 7: A tariff with seven hours of cheaper electricity, typically between midnight and 7am, through a two-rate meter.
ENA register: The Energy Networks Association's list of compliant plug-in solar devices and type-tested equipment.
Export: Electricity you send to the grid.
Export limitation: A setting or device that caps how much a system can send to the grid.
G98: The Great Britain process for connecting small type-tested generation (up to 16 amps per phase): connect, then notify within 28 days.
G98/NI: Northern Ireland's version of G98, for NIE Networks.
G99: The process for larger generation and storage: apply to the network operator before installing.
HIES: Home Insulation and Energy Systems: one of the two consumer codes MCS installers can belong to.
Hybrid inverter: An inverter that handles both solar panels and a battery.
Import: Electricity you buy from the grid.
Inverter: The box that turns DC from panels or a battery into AC for your home.
kW (kilowatt): Power: how fast electricity is made or used.
kWh (kilowatt hour): Energy: how much electricity is made or used. One 'unit' on your bill.
kWp (kilowatt peak): A solar system's rated output under standard test conditions.
LFP (LiFePO4): Lithium iron phosphate: the most common type of home battery. A kind of lithium-ion battery, sometimes called LiFe.
Listed building consent: Separate consent needed for work affecting a listed building.
MCS: The Microgeneration Certification Scheme, which certifies installers and products. Usually needed for export payments.
Microinverter: A small inverter fitted to each panel, or the inverter in a plug-in kit.
MPPT: Maximum power point tracking: how an inverter gets the most from each string of panels.
Network operator: See DNO.
NMC: Nickel manganese cobalt: a lithium-ion battery type used in older home batteries, such as Tesla's Powerwall 2, and many electric cars.
Open-circuit voltage (Voc): The highest voltage a solar panel produces when nothing is connected. It decides how many panels can be linked in series to an input.
Part P: The part of the Building Regulations in England and in Wales that covers electrical work in homes.
PAS 63100: The British fire-safety specification for home batteries, including where they may and may not be installed.
Permitted development: Building work you can do without applying for planning permission, if you meet the conditions.
Plug-in solar: A small solar kit with a three-pin plug that connects to a wall socket, limited to 800 W. Also called balcony solar.
Portable power station: A battery with its own inverter and household sockets, charged from the mains, solar panels or a car; also sold as a solar generator. Nothing is wired into the home.
Power optimiser: A small box fitted to each panel that improves output while still feeding a central inverter.
Prior approval: A lighter application to the council, needed in some protected areas.
RCD: Residual current device: a safety switch that cuts the power when it detects a fault.
RECC: The Renewable Energy Consumer Code: one of the two consumer codes MCS installers can belong to.
Round-trip efficiency: The share of the energy put into a battery that you get back out.
SEG (Smart Export Guarantee): The Great Britain scheme requiring suppliers to offer payment for exported electricity.
Self-consumption: The share of your solar electricity you use as it is made.
Sodium-ion battery: A newer battery type that uses sodium instead of lithium. It copes better with cold and is less prone to overheating, but is bulkier.
Solar generator: A sales name for a portable power station sold with, or able to take, solar panels. It has no engine and makes no fumes.
Standing charge: A fixed daily charge on your bill, whatever you use.
String: A group of panels wired in series.
Surge power: A short burst of power above an inverter's continuous rating, needed when motors and compressors start.
Thermal runaway: When a battery cell overheats and keeps heating itself, which can lead to a fire.
Time-of-use tariff: A tariff with different prices at different times of day, often cheaper overnight.
Type Test Register: The Energy Networks Association's list of equipment tested for connection under G98.
UPS (pass-through) mode: A portable power station feature that runs appliances from the mains and switches to its battery within milliseconds if the power fails.
Usable capacity: The part of a battery's capacity you can actually use.
Wired-in system: A solar system connected by an electrician to its own circuit at the consumer unit, instead of plugged into a socket.

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Updated 2026-10-05.