Glossary of UK solar terms
Solar has an unusually large amount of jargon for something most people buy once. This is what the terms actually mean.
Every term here is written to be understood without reading anything else first. Where a term has a full explainer page, the entry links to it.
Entries carry the date a human last checked them against a primary source. Where that has not happened yet, the entry says so — an unverified definition that admits it is more useful than a confident one that is out of date.
8
800 VA cap
Also written: 800W cap, 800W limit, 800 VA limit
The output limit on a plug-in solar device. The instrument sets 800 watts of rated alternating current output per device; the specification sets 800 VA of apparent power and 3.5 A. The specification anticipates one such device per household circuit, but the government made that conditional on an amendment to G98, and said the existing one-device-per-household limit applies until the amendment is made.
A
Anti-islanding
Also written: Islanding protection, Anti-islanding protection
The protection that makes an inverter shut down when the grid supply fails, so it cannot keep energising a section of network that engineers may believe is dead. For plug-in solar the specification requires the inverter to disconnect within 100 milliseconds of losing the mains.
Apparent power
Also written: VA, Volt-amperes
Power measured in volt-amperes, the product of voltage and current irrespective of how well they are in phase. Real power, in watts, is apparent power multiplied by the power factor, so the two are close but not interchangeable — which matters when one document sets a limit in watts and another sets it in VA.
Article 4 direction
A direction made by a local planning authority that withdraws permitted development rights in a defined area. Where one is in force, work that would normally need no application does need one. They are commonly used in conservation areas and are easy to miss.
Azimuth
Also written: Aspect, Orientation
The compass direction a panel faces, given in degrees away from due south in UK and European modelling: 0° is south, 90° is west, −90° is east and 180° is north. Together with tilt it fixes how much of the available sunlight the panel can intercept.
B
Balcony solar
Plug-in solar mounted on a balcony, railing, wall or fence rather than a roof. The term is often used interchangeably with plug-in solar, though strictly it describes where the panels are mounted rather than how they connect.
BREL report
Also written: Building Regulations England Part L report
The as-built compliance report for Part L of the Building Regulations in England. It matters to a buyer because Approved Document L paragraph 5.78 requires any photovoltaic array falling short of the standard in paragraphs 5.73 or 5.74 to be highlighted in it — so a shortfall is recorded in a document about your specific home.
BS 1363
Also written: 13A plug, UK three-pin plug
The British Standard for the UK 13 A plug, socket outlet and fused connection unit — the standard three-pin domestic plug. It matters in the plug-in solar context because it defines the connection a plug-in kit uses to reach a household circuit.
BS 7671
Also written: IET Wiring Regulations, Wiring Regulations
The British Standard for electrical installations, also known as the IET Wiring Regulations. It is not statute, but compliance is the accepted way of demonstrating that an electrical installation meets the safety requirements of the Building Regulations.
C
Complete kit
Also written: Certified kit
A plug-in solar product sold and certified as a single assembly — panels, microinverter, cabling and mounting supplied together and tested as one product. The distinction matters because the regulatory position for a complete certified kit differs from that of components bought separately.
Conservation area
An area designated by a local planning authority for its special architectural or historic interest. Designation restricts what can be done without permission, and solar on elevations facing a highway is among the things that commonly need a planning application inside one.
Consumer unit
Also written: Fuse box, Distribution board
The board that distributes electricity around a property and houses its protective devices. Installing solar sometimes requires the consumer unit to be upgraded, which is a cost that does not always appear clearly in a quotation.
D
DC:AC ratio
Also written: Overpanelling, Over-panelling, Inverter loading ratio
The ratio of installed panel capacity in kWp to the inverter's rated alternating current output in kW. Fitting more panels than the inverter can pass at once — a ratio above 1 — is normal practice, because a UK array reaches its rated output for very few hours a year. Where it does, the inverter limits the output, which is called clipping.
Degradation
The gradual decline in a panel's output over its life. Manufacturers publish a performance warranty stating the output they guarantee after a given number of years, and those figures vary between products, so the warranty is worth reading rather than assuming.
DESNZ
Also written: Department for Energy Security and Net Zero
The UK government department responsible for energy policy, including domestic solar, grants and the schemes that fund them. Its announcements and statistical releases are the primary source for policy changes.
DNO
Also written: Distribution Network Operator
The Distribution Network Operator, the company that owns and runs the local electricity network in your area. It is not your supplier, and you do not choose it — it is determined by where you live. Connecting generation to the grid means dealing with the DNO, not the supplier.
E
ECO4
Also written: Energy Company Obligation, ECO
The fourth phase of the Energy Company Obligation, the scheme requiring larger energy suppliers to fund efficiency improvements in qualifying households. It is targeted at low income and vulnerable households rather than being generally available, which is frequently misrepresented.
EPC
Also written: Energy Performance Certificate
The Energy Performance Certificate, which rates a property's energy efficiency and is required when a home is sold or let. Solar affects the rating, and the register of certificates is an open dataset used to track solar uptake across the country.
ESQCR
Also written: Electricity Safety, Quality and Continuity Regulations 2002
The Electricity Safety, Quality and Continuity Regulations 2002, which govern the safety of electricity networks and of generation connected to them. One of the two sets of regulations amended by SI 2026/848 to accommodate plug-in solar.
Euroclass B-s3, d2
Also written: Euroclass, Reaction to fire classification, BS EN 13501-1
A reaction-to-fire classification under BS EN 13501-1. The plug-in solar specification requires the outermost substantial layer of a module — usually the backsheet — to achieve a performance equivalent to it, and requires the test procedures used to demonstrate that to appear in the product documentation.
Export limitation
Also written: Export limiting, Export limitation device
Configuring a system so it cannot export more than an agreed amount to the grid, usually to stay within what the local network can accept. It is a common condition of a DNO connection agreement and it can cap what a system earns from export, so it is worth checking before installation.
Export tariff
The rate a supplier pays for each unit of electricity you export to the grid. Some are fixed, some vary by time of day, and some are only available if you also buy your electricity from the same supplier. You do not have to use the same supplier for import and export.
F
Feed-in Tariff
Also written: FiT
The scheme that preceded the Smart Export Guarantee, paying both a generation and an export rate. It closed to new applicants, but existing agreements continue to run for their original term, which is why buying a house with panels can involve an inherited Feed-in Tariff agreement.
Final ring circuit
Also written: Ring final circuit, Ring main
A domestic wiring arrangement in which socket outlets are connected in a loop back to the consumer unit, rather than on a radial run. It is characteristic of UK wiring and it matters wherever a limit is defined per circuit rather than per property.
Future Homes Standard
Also written: FHS
The standard intended to raise the energy performance of new homes in England, delivered through changes to the Building Regulations. It is the route by which solar generation becomes a requirement on new build homes rather than an option.
Future Homes Standard
Also written: FHS, Future Homes and Buildings Standards
The set of building regulations changes for new homes in England given effect by SI 2026/335 and the 2026 editions of Approved Documents L and F. For solar, its operative part is requirement L3: a new dwelling must have on-site renewable electricity generation. It takes effect on 24 March 2027, with transitional arrangements running to 24 March 2028.
G
G100
Also written: EREC G100, Export limitation scheme, Customer limitation scheme
The Energy Networks Association engineering recommendation setting the technical requirements for schemes that limit how much electricity a customer's installation exports to, or imports from, the network. A G100-compliant scheme is what allows more generating capacity to be installed than the connection is permitted to export.
G98
The Energy Networks Association engineering recommendation covering the connection of small generation that can be notified to the DNO after installation rather than approved in advance. Domestic solar within the size limit is normally connected under G98. It is also where the number of plug-in solar devices a home may have is decided: the government response states that G98's one-device-per-household limit continues to apply until G98 is amended to permit one per circuit.
G98 Type Test Register
Also written: Type Test Register, ENA Type Test Register
The Energy Networks Association list of generation equipment assessed as meeting G98 requirements. The government response states that plug-in solar products will be listed on it, and that only devices identified as compliant on the register are considered to have demonstrated compliance — so a manufacturer's own claim is not the test.
G99
The Energy Networks Association engineering recommendation covering generation above the G98 threshold, which requires the DNO's approval before it is connected rather than notification afterwards. Larger domestic and most commercial systems fall under G99.
Ground floor area
Also written: GFA, AGRND
In Approved Document L 2026, the measure the solar output target is derived from: 40% of it, at 0.22 kWp per square metre, defines the notional array. Measured to the internal face of the external perimeter wall, including certain unheated spaces. For a building containing dwellings it is the gross internal area divided by the number of storeys.
H
Higher-risk building
Also written: HRB
A category of building subject to the Building Safety Regulator's gateway process. It matters here only for timing: the 2026 building regulations changes come into force for higher-risk building work on 24 September 2027, six months later than for ordinary work, with their own transitional test.
I
IDNO
Also written: Independent Distribution Network Operator
An Independent Distribution Network Operator, which owns and runs distribution networks built on newer developments in competition with the incumbent DNO. If you live on a recent estate, your network operator may be an IDNO rather than the regional DNO.
Interim Product Specification
Also written: IPS, IPS v2, Plug-in Solar Device Interim Product Specification
The specification a plug-in solar device must comply with for the permission in SI 2026/848 to apply. Published by the Secretary of State, version 2 dated 16 July 2026. It is explicitly interim, applying while longer-term standards are developed, and no end date has been given.
Inverter
The device that converts the direct current produced by solar panels into the alternating current a property and the grid use. It is usually the first component of a system to need replacing, so its specification and warranty matter more than most buyers expect.
Irradiance
Also written: Irradiation, Insolation
The power of sunlight falling on a given area, measured in watts per square metre. It varies with location, season, time of day, weather and the orientation of the surface. It is the input every generation estimate is built on, which is why estimates are location-specific.
K
kWh
Also written: Kilowatt hour, Unit of electricity
The kilowatt hour, the unit electricity is measured and billed in. It is a quantity of energy, not a rate — one kilowatt of power sustained for one hour. A system's annual generation, your consumption and your bill are all in kilowatt hours, which is why it is the number that actually matters.
kWp
Also written: Kilowatt peak, Watt peak, Wp, Peak power
Kilowatt peak, the rated output of a solar array under standard test conditions. It describes capacity, not production — a system's kWp is what it could produce at that instant under laboratory conditions, and tells you nothing on its own about how much electricity it will generate over a year. That is measured in kilowatt hours.
L
Listed building
A building on the statutory list of buildings of special architectural or historic interest. Listing covers the whole building, inside and out, and works affecting its character require listed building consent — which is a separate consent from planning permission, and is required regardless of permitted development rights.
M
MCS
Also written: Microgeneration Certification Scheme
The Microgeneration Certification Scheme, the UK quality assurance scheme for small-scale renewable technologies and the companies that install them. An MCS certificate for the installation is what most export tariffs and grant schemes ask for, which is why the certification matters to buyers as well as to installers.
MCS Installation Database
Also written: MID
The register of installations certified under MCS. It is the source of the installation counts used in UK solar deployment statistics, and it is where an installer's certification status and scope can be checked.
Micro-generation
Also written: Microgeneration
Small-scale generation of electricity or heat, typically at a single property, below the thresholds that apply to commercial generation. It is the category domestic solar sits in, and the term the certification scheme and connection rules are built around.
Microinverter
Also written: Micro-inverter, Micro inverter
A small inverter fitted to an individual panel rather than to the array as a whole, so each panel operates independently. This limits the effect of shading on one panel, at the cost of more components on the roof. Plug-in solar kits use a microinverter integrated into the kit.
Monocrystalline
Also written: Mono
A solar cell made from a single continuous crystal of silicon. Mono cells are the dominant technology in current domestic panels, and are generally more efficient per square metre than the polycrystalline cells they replaced.
MPAN
Also written: Meter Point Administration Number, Supply Number
The Meter Point Administration Number, the unique reference for an electricity supply point. A property that exports electricity generally needs an export MPAN as well as an import one, and a missing or incorrect export MPAN is a common reason export payments fail to start.
O
Ofgem
Also written: Office of Gas and Electricity Markets
The energy regulator for Great Britain. Ofgem administers the Smart Export Guarantee, sets the energy price cap, and regulates suppliers and network companies. Its publications are a primary source for tariff and scheme rules.
P
Part L
Also written: Approved Document L, Part L of the Building Regulations
The part of the Building Regulations for England covering conservation of fuel and power. It sets the energy efficiency standards new and altered buildings must meet, and it is the mechanism through which requirements for solar on new homes are applied.
Part P
Also written: Approved Document P
The part of the Building Regulations for England covering electrical safety in dwellings. Notifiable electrical work must be either carried out by someone registered with a competent person scheme or notified to building control.
Payback period
The time taken for the savings and income from a system to equal what it cost. It depends on the price paid, the electricity price assumed, how much generation is self-consumed and the export rate — so any single payback figure quoted without those assumptions stated is not meaningful.
Permitted development
Also written: Permitted development rights, GPDO, General Permitted Development Order
Development allowed by a general order rather than by an individual planning application. Domestic solar in England sits in Part 14 of Schedule 2 to the 2015 Order, which permits equipment on a dwellinghouse or block of flats within limits — including that in a conservation area it must not be installed on a wall which fronts a highway.
Permitted development
Also written: Permitted development rights, PD
A general planning permission granted by legislation rather than by a council decision, which allows certain works without a planning application. Most domestic roof-mounted solar falls within it, subject to conditions and limits — but those conditions are where the exceptions live.
Plug-in microgenerator
The term SI 2026/848 uses for a plug-in solar device: an energy source that generates electricity from the direct conversion of sunlight, operates through a standard plug and socket, and is designed to operate in parallel with a distributor's network.
Plug-in solar
Also written: Plug in solar, Plug-and-play solar
A small solar kit with an integrated microinverter that connects to a household circuit through an ordinary socket, rather than being wired in by an electrician. Widely used in parts of Europe, and the subject of a distinct UK regulatory regime with its own limits and notification requirements.
Power optimiser
Also written: Optimiser, Optimizer
A device fitted to an individual panel that conditions its output before it reaches a central inverter, reducing the effect of shading or mismatch between panels. Unlike a microinverter it does not convert to alternating current itself.
PVGIS
Also written: Photovoltaic Geographical Information System
A modelling tool published by the European Commission's Joint Research Centre that estimates solar generation for a given location, orientation and tilt from long-run climate data. It is the standard open source for location-specific yield estimates.
R
RECC
Also written: Renewable Energy Consumer Code
The Renewable Energy Consumer Code, a consumer code covering the sale of small-scale renewable systems to households. It sets rules on sales conduct, contracts, deposits and cancellation, and it operates a dispute resolution route for consumers whose installer is a member.
Requirement L3
Also written: L3, Part L requirement L3
The functional requirement, inserted into Schedule 1 of the Building Regulations 2010, that when a building containing dwellings is erected a system for on-site renewable electricity generation must be installed on it or within its curtilage, designed so residents can use the electricity and capable of a reasonable output given the building's design and surroundings.
S
SEG
Also written: Smart Export Guarantee
The Smart Export Guarantee, the scheme under which licensed electricity suppliers above a certain size must offer a tariff paying small generators for the electricity they export to the grid. Suppliers set their own rates, so what is on offer varies widely and changes often.
Self-assembled kit
A plug-in system put together from separately purchased components rather than bought as a certified complete kit. It sits outside the regime that covers complete kits, so the safety, notification and insurance position is different and needs checking before buying.
Self-consumption
The share of the electricity you generate that you use yourself rather than exporting. Because electricity bought from a supplier normally costs more per unit than exported electricity earns, using your own generation is usually worth more than selling it — which is what makes timing and storage matter.
SI 2026/848
Also written: The Plugs and Sockets etc. (Safety) Regulations 1994 and Electricity Safety, Quality and Continuity Regulations 2002 (Amendment) Regulations 2026
The statutory instrument that makes plug-in solar lawful to sell with a standard plug in Great Britain. Made on 16 July 2026 and in force from 27 August 2026, it amends the 1994 plug safety regulations and the 2002 electricity safety regulations, permitting a standard plug on a device generating up to 800 watts where it complies with the interim specification.
Solar Together
A group-buying model run in partnership with local authorities, in which residents register together and installers bid to supply the group. It is not a grant and it is not government funding, though it is often described as though it were.
Specific yield
Also written: kWh/kWp, Kk
Annual generation divided by installed capacity, expressed in kilowatt hours per kilowatt peak. It allows systems of different sizes to be compared, and it is the figure that reveals whether a system is underperforming for its location.
Standard test conditions
Also written: STC
The laboratory conditions a panel's headline rating is measured under: 1,000 watts per square metre of irradiance, a cell temperature of 25°C, and a defined light spectrum. The two main conditions rarely occur together outdoors in the UK, because the sunshine bright enough to reach 1,000 W/m² also heats the cell well past 25°C.
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