Commercial Solar Glossary UK 2026: 60+ Terms Explained

UK commercial solar comes with a dense terminology stack — DNO certificates, capital allowance schedules, EREC standards, BNEF tiers, IETF scoring criteria, and cell-architecture acronyms (TOPCon, HJT, IBC, PERC). This glossary defines the 63 terms you're most likely to meet in a real commercial solar proposal, contract, or grant application — written in plain English by the engineers who deliver UK commercial PV every week, not by a content team.

Terms are grouped by category. Use the in-page links to jump straight to what you need.

Accreditation (5) Standards (4) Regulation (4) Finance (15) Reporting (2) Grid (2) Electrical (1) Technical (10) Modules (8) Engineering (7) Installation (5)

Accreditation

MCS: Microgeneration Certification Scheme. The UK quality assurance scheme that certifies low-carbon products and installation companies. MCS commercial certification (different from domestic MCS) is required for any system above 4 kW to qualify for Smart Export Guarantee tariffs and most UK public sector funding.
NICEIC: National Inspection Council for Electrical Installation Contracting. UK trade body certifying electrical contractors against BS 7671 standards. NICEIC Approved Contractor is the gold standard for commercial electrical work, including solar AC tie-in.
RECC: Renewable Energy Consumer Code. UK consumer-protection code for businesses selling renewable energy equipment to domestic and small commercial buyers. Required for any business that sells to consumers below the £100,000 threshold.
TrustMark: UK government-endorsed quality scheme covering domestic and small-scale commercial trades. TrustMark licensing is required for any installer working on grant-funded schemes including ECO4 and certain Salix-funded local authority programmes.
IWA: Independent Warranty Association. Provides insurance-backed workmanship warranties on UK construction and renewables installations. An IWA-backed 10-year warranty is enforceable even if the installer goes out of business — important for 25-year solar assets.

Standards

BS 7671: British Standard for electrical installation, currently in its 18th Edition. Sets the legal compliance bar for all UK electrical work including solar PV AC tie-in. All commercial solar AC work must be signed off against BS 7671 18th Edition by a qualified electrician.
EREC G98: Engineering Recommendation G98 covers Type-Tested generators below 17 kW per phase (or 100 kW total across three phases). A G98 install requires only a notification to the DNO — no formal application. Most sub-100 kW commercial solar projects fall under G98.
EREC G99: Engineering Recommendation G99 covers generators above 17 kW per phase or 100 kW total. Requires a formal connection application to the DNO. Connection offer must be issued within 65 working days. Most commercial solar above 100 kW is G99.
EREC G100: Engineering Recommendation G100 covers export limitation control schemes — automated systems that prevent solar export exceeding a permitted threshold. Used when DNO connection capacity is insufficient for full system export.

Regulation

MEES (Minimum Energy Efficiency Standards): UK regulations prohibiting non-domestic landlords from letting commercial property below EPC band E. Proposed tightening to band C in 2027, band B in 2030. Solar PV is one of the few measures that can lift commercial EPC by 1-3 bands in a single capital event.
EPC (Energy Performance Certificate): UK building energy efficiency rating A (best) to G (worst). Commercial EPCs use SBEM or DSM modelling software. Required at letting / sale of commercial property. Validity: 10 years. Solar PV typically lifts commercial EPC by 1-3 bands.
EICR (Electrical Installation Condition Report): BS 7671 inspection certifying that an electrical installation meets current safety standards. Required at solar commissioning to certify the AC tie-in. Typically reissued every 5 years for commercial installations.
CDM 2015: Construction (Design and Management) Regulations 2015. UK health & safety law covering all construction projects including commercial solar. Requires a Principal Designer and Principal Contractor for any project exceeding the notification threshold.

Finance

AIA (Annual Investment Allowance): 100% capital allowance on plant and machinery up to £1 million per year. Solar PV qualifies — limited companies can deduct 100% of solar capex from taxable profits in year one. At current 25% corporation tax rate, this returns 25p per £1 invested as year-one tax relief. The strongest commercial solar tax route.
SEG (Smart Export Guarantee): Ofgem-mandated scheme requiring all UK energy suppliers above 150,000 customers to offer an export tariff for exported electricity. Rates vary 4p/kWh (smart floor) to 15p/kWh (Octopus Outgoing Fixed). MCS certification required to qualify.
PPA (Power Purchase Agreement): Long-term contract (typically 15-25 years) where a funder pays 100% of installation cost and owns the system. The buyer pays only for the electricity it generates, at a fixed rate 30-60% below grid retail. Zero capex on the buyer's balance sheet.
Salix Finance: Non-departmental public body that delivers low-carbon project finance to the UK public sector. Administers the Public Sector Decarbonisation Scheme (PSDS) and the Salix Recycling Fund. Eligible bodies: schools, NHS, councils, universities, emergency services.
PSDS (Public Sector Decarbonisation Scheme): 100% grant funding from DESNZ delivered via Salix Finance. Competitive rounds typically £230-£500m per phase. Award sizes £50k to £20m+. Funded projects must reduce carbon and demonstrate value for money. UK public sector only.
IETF (Industrial Energy Transformation Fund): UK government grant programme funding 15-30% of energy efficiency and decarbonisation capex for energy-intensive manufacturing (SIC codes 10-26 typical). Phase 3 active 2024-2027 with ~£500m budget. Awards £100k to £30m+.
ECO4: Energy Company Obligation Phase 4. Obliges large UK energy suppliers to deliver carbon-reduction measures to qualifying households. Domestic only — not applicable to commercial solar but often confused with commercial schemes.
IRR (Internal Rate of Return): The discount rate at which a project's Net Present Value equals zero. UK commercial solar in 2026 typically achieves 12-22% IRR over 25 years, depending on system size, tariff and financing. Investment-committee preference over simple payback for capital allocation decisions.
NPV (Net Present Value): The sum of discounted cash flows over an asset life. For a 100 kW commercial solar install: typical 25-year NPV £80-£180k at 5% discount rate. NPV is the standard investment-committee comparison metric for capital projects.
Simple payback: Years to recover initial investment from undiscounted cash flows. Capex divided by annual saving. Commercial solar simple payback typically 5-8 years in UK 2026. Quick screening metric, but doesn't reflect time-value-of-money or electricity-price inflation.
OZEV: Office for Zero Emission Vehicles. UK government body administering the Workplace Charging Scheme (WCS) — up to £350 per EV charging socket, capped at 40 sockets per business. Often paired with commercial solar installs.
Capital allowance: UK tax mechanism allowing businesses to deduct the cost of qualifying capital purchases from taxable profits. Solar PV qualifies for the 100% Annual Investment Allowance. Different rates apply for different asset types (Main Pool, Special Rate Pool, etc.).
WDA (Writing Down Allowance): Capital allowance applied at a percentage of an asset's remaining value each year. Solar PV that doesn't qualify for AIA (above the £1m annual cap) falls into the Main Pool with 18% WDA per year.
Special Rate Pool: Capital allowance category for integral features and long-life assets — currently 6% WDA per year. Solar PV generally does NOT fall into this pool (it's Main Pool / AIA qualifying).
GBER (General Block Exemption Regulation): EU/UK subsidy control framework defining maximum public support for projects without state aid notification. UK commercial solar grants typically operate within GBER thresholds.

Reporting

SECR (Streamlined Energy and Carbon Reporting): UK mandatory annual energy and carbon disclosure for large UK companies. Includes Scope 1 and Scope 2 emissions. Solar PV directly reduces Scope 2 reported emissions.
Scope 1, 2, 3 emissions: GHG Protocol categorisation. Scope 1: direct emissions from owned sources. Scope 2: purchased electricity emissions. Scope 3: value chain (supplier, customer) emissions. Commercial solar reduces Scope 2 (and Scope 3 if a supplier installs it).

Grid

DNO (Distribution Network Operator): The licensed company that owns and operates the local electricity distribution network. Six UK DNOs: Northern Powergrid, UK Power Networks, SP Energy Networks, NGED (Western, East Midlands, South West, South Wales), Electricity North West, SSEN. Every commercial solar install requires DNO notification or application.
ANM (Active Network Management): DNO-operated real-time control system that throttles distributed generators when network constraints arise. Common condition of G99 connection offers in constrained areas. Typically results in 1-5% annual generation curtailment in the UK.

Electrical

Three-phase supply: Industrial-grade electrical supply with three live conductors at 120-degree phase offset. Most UK commercial sites have three-phase supply (400V line-to-line). Solar above 17 kW per phase requires three-phase distribution.

Technical

kWp (kilowatt-peak): The peak power output of a solar PV system under Standard Test Conditions (1,000 W/m² irradiance, 25°C cell temperature, AM1.5 spectrum). The standard rating unit for solar modules and systems. 1 kWp typically produces 950-1,150 kWh per year in the UK.
kWh (kilowatt-hour): Energy unit equal to 1 kW of power consumed (or generated) for 1 hour. UK commercial electricity is billed in pence per kWh. A typical 100 kWp commercial solar system generates ~95,000 kWh per year.
MWh / GWh: 1,000 kWh = 1 MWh; 1,000 MWh = 1 GWh. Large commercial installs (above 250 kWp) typically report annual generation in MWh. Industrial energy consumers report total annual electricity demand in GWh.
BESS (Battery Energy Storage System): A complete battery storage system including cells, battery management, inverter (or shared inverter), control system, and enclosure. Commercial BESS in UK 2026 typically uses lithium-iron-phosphate (LFP) chemistry, GivEnergy / Tesla Powerwall Commercial / SolarEdge Energy Bank / Sungrow common brands.
Inverter: Device that converts solar DC into AC for the building distribution and grid. UK commercial market dominated by SolarEdge, SMA, Huawei, Fronius, Sungrow string inverters; large projects use central inverters (SMA Sunny Central, Huawei SUN8000).
String inverter: Inverter that handles a string of panels connected in series. Most common commercial solar inverter type. Single-point-of-failure on a string — if one panel fails, the string output drops.
Central inverter: Large inverter handling multiple strings, typically used on systems above 500 kW. Higher efficiency, lower cost-per-kW, but single-point-of-failure across the whole array. Common in utility-scale and large ground-mount.
Microinverter: One inverter per solar panel. Each panel produces independently — partial shading or single panel failure doesn't affect others. More expensive per kW than string inverters. Common in residential, less common in commercial.
Optimiser: Per-panel DC-DC converter (e.g. SolarEdge P-Series) that allows individual panel-level MPPT. Combines benefits of microinverters (panel-level performance) with central inverter cost efficiency.
MPPT (Maximum Power Point Tracking): Inverter / optimiser algorithm that continuously adjusts the operating voltage to extract maximum power from the panels. Commercial inverters typically have 2-12 MPPT channels.

Modules

Tier 1: Bloomberg New Energy Finance (BNEF) quarterly classification of bankable solar module manufacturers. Includes the most-financed manufacturers — JinkoSolar, Longi, JA Solar, Trina, Canadian Solar, REC, Q CELLS, etc. Important for project finance acceptance.
TOPCon: Tunnel Oxide Passivated Contact. N-type solar cell architecture, dominant commercial spec in 2026. Higher efficiency than older PERC (22-24% vs 20-22%), better low-light performance, lower temperature coefficient.
HJT (Heterojunction): Premium N-type cell architecture combining crystalline silicon with thin-film amorphous silicon layers. Industry-leading efficiency (22-24% module) and temperature coefficient. Higher cost than TOPCon — premium installs only.
PERC: Passivated Emitter and Rear Cell. Older P-type cell architecture, dominant 2015-2023, now being replaced by N-type TOPCon. Still available at 5-10% cost discount but lower efficiency and worse light-induced degradation.
IBC / Back-contact: Interdigitated Back Contact cell. Premium architecture with all electrical contacts on the rear face (no front-side busbars). Maxeon, Aiko, Longi Hi-MO X10 use back-contact technology. Highest efficiency commercial modules.
Bifacial module: Solar panel that generates electricity from both front and rear faces. Rear gain 5-15% on reflective ground (white membrane, snow); 2-5% on dark substrate. Best for ground-mount and elevated rooftop installations.
Performance warranty: Manufacturer guarantee that the module will produce at least X% of its rated output after Y years. Commercial-grade Tier 1 modules typically guarantee 85-89% at year 25-30, with 0.4-0.55% annual degradation.
Product warranty: Separate from performance warranty — covers manufacturing defects. Typical commercial-grade Tier 1: 12-15 years. REC offers 20-year product warranty as standard; Maxeon offers 40 years.

Engineering

PVSyst: Industry-standard commercial solar yield modelling software. Combines location-specific meteorological data, panel and inverter specifications, shading analysis, and degradation curves to model expected lifetime yield. All commercial proposals should include PVSyst output.
PVGIS: EU Commission free solar yield modelling tool (Photovoltaic Geographical Information System). Lower-fidelity than PVSyst but free — useful for initial desk feasibility estimates.
Half-hourly meter data: Electricity consumption data recorded at 30-minute intervals throughout the day. Required for accurate commercial solar self-consumption modelling. UK commercial sites above 100 kVA typically have half-hourly metering as standard.
Self-consumption: The percentage of solar-generated electricity used on-site (vs exported to grid). Sector typical: cold storage 90-95%, manufacturing 70-85%, offices 55-65%, schools 45-55%. Higher self-consumption = faster payback because self-consumed kWh saves full grid retail tariff.
Self-sufficiency: The percentage of a site's total electricity needs met by on-site solar. Always lower than 100% unless the site has battery storage and significant array oversizing. Typical commercial site self-sufficiency: 20-40%.
Irradiance: Solar power per unit area (W/m²). Standard Test Conditions use 1,000 W/m². UK average daily irradiance varies 950-1,150 kWh/m²/year depending on region.
Temperature coefficient: Rate at which module output decreases as cell temperature rises above 25°C. Modern N-type TOPCon: ~-0.30%/°C. P-type PERC: ~-0.35%/°C. HJT: ~-0.25%/°C. Better (less negative) coefficient = stronger summer performance.

Installation

Profiled steel roof: Industrial roof type with ridge-and-valley steel sheeting. Standard on UK industrial estates 1990s-onwards. Accepts modern PV mounting cleanly via direct clamping or rail systems.
Single-ply membrane roof: Flat roof type using TPO / PVC / EPDM rubber membrane. Standard on modern UK commercial buildings. PV typically mounted via ballasted systems to avoid roof penetrations that could compromise waterproofing.
Asbestos cement roof: Pre-2000 industrial roof material. Solar PV install typically requires roof replacement first due to load capacity and end-of-life timing. Asbestos survey required before any work — typically £400-£900.
Ballasted mounting: PV mounting system that uses concrete blocks or weighted plates to hold panels in place without penetrating the roof membrane. Standard on flat commercial roofs. Wind-load engineering critical for UK zone 4-5 coastal sites.
Rail mounting: PV mounting using aluminium rails fixed to roof structure via penetrations sealed with EPDM gaskets. Common on profiled steel and trapezoidal roofs. K2 Systems, Schletter, GSE are common UK suppliers.

UK Commercial Solar Glossary 2026: 60+ Terms Explained