Solar Energy Glossary
Plain-English definitions for every solar, battery and grid term you'll encounter when getting solar quotes — AIA, G99, MCS, SEG, AC/DC coupling, full expensing and more.
- AC-coupled battery
- A battery system that connects to the existing AC electricity wiring, typically used as a retrofit to an existing solar PV system. Requires its own inverter.
- AIA
- Annual Investment Allowance — UK tax relief letting businesses (companies, sole traders and partnerships) deduct 100% of qualifying plant and machinery, including solar PV and batteries, from profits in year 1, up to £1m a year.
- BIPV
- Building-integrated photovoltaics — solar PV designed as part of the building fabric (roof tiles, facade panels, glazing) rather than mounted on top.
- BoS
- Balance of System — the non-panel, non-inverter components of a solar installation: cabling, isolators, mounting frames, monitoring equipment.
- CAPEX
- Capital Expenditure — the upfront cost of buying and installing a solar system, owned outright.
- CAA
- Civil Aviation Authority — the UK regulator for drone flight. Drone surveys require CAA-approved pilot certification.
- CTL clamp
- Current transformer clamp — fitted around an incoming live cable to measure current draw and feed data to the inverter or export limitation device.
- DC-coupled battery
- A battery system that connects to the DC side of the solar inverter, sharing the inverter with the panels. More efficient than AC-coupled but only feasible at new install.
- DNO
- Distribution Network Operator — the company that owns and operates the regional electricity network (in our area, NGED (formerly Western Power Distribution) / National Grid Electricity Distribution / Northern Powergrid).
- EPS
- Emergency Power Supply — battery system feature allowing the battery to power critical home circuits during a grid outage. Requires correct inverter spec.
- Export limitation
- A control mechanism that prevents the solar inverter from exporting more than a set amount of power to the grid. Allows installation on grid-constrained sites without full DNO reinforcement.
- Full Expensing
- UK tax relief letting companies deduct 100% of spending on new main-rate plant and machinery in year 1, with no cap; permanent since November 2023. It does not cover solar panels or batteries, which are special-rate plant — their relief comes through AIA.
- G98
- DNO notification standard for small-scale embedded generation up to 3.68 kW per phase. Fast-track 28-day notification.
- G99
- DNO application standard for embedded generation above the G98 threshold. Requires full engineering submission and DNO approval before commissioning.
- G100
- DNO standard for export-limited generation. Allows installation on grid-constrained sites by limiting export below a fixed threshold.
- Hybrid inverter
- A single inverter that handles both solar PV and battery storage on one device with one grid connection. Standard for new domestic installs.
- kWh
- Kilowatt-hour — the unit of electrical energy consumed or generated. 1 kWh = running a 1 kW kettle for 1 hour.
- kWp
- Kilowatt-peak — the rated output of a solar panel array under standard test conditions. The headline 'size' of a solar system.
- LFP
- Lithium iron phosphate — the battery chemistry now used in virtually all home and small-commercial batteries. Safer than older NMC chemistry.
- MCS
- Microgeneration Certification Scheme — the UK certification body for renewable installers. MCS certification is required for SEG eligibility on domestic installs.
- MPAN
- Meter Point Administration Number — the unique reference for a UK electricity supply. Quoted as a 21-digit string starting with a 'profile class' digit.
- MPRN
- Meter Point Reference Number — the equivalent for gas supplies.
- Optimiser
- A small device fitted to each solar panel that maximises output even when other panels are shaded or dirty. Standard on shaded roofs.
- OZEV
- Office for Zero Emission Vehicles — the UK government body administering EV charger grants and workplace charging schemes.
- Permitted Development
- UK planning rights allowing certain works (including most rooftop solar PV) without a planning application.
- PPA
- Power Purchase Agreement — third-party finance where the funder owns the solar system and you pay only for the kWh you consume at a fixed tariff below grid.
- PSDS
- Public Sector Decarbonisation Scheme — UK government grant funding for net-zero capital projects in the public sector.
- RCD
- Residual Current Device — safety switch detecting earth faults. Required upgrade for many older properties when adding EV chargers or solar.
- REGO
- Renewable Energy Guarantees of Origin — UK certificates evidencing renewable generation. The basis of '100% renewable' electricity contracts.
- Salix
- UK government public-sector finance body. Salix offers 0% interest loans for energy-saving projects in schools, NHS and councils.
- SBA
- Structures and Buildings Allowance — UK tax relief at 3% per year on qualifying non-residential building costs (including some solar-related roof works).
- SEG
- Smart Export Guarantee — the UK scheme requiring all major electricity suppliers to offer an export tariff to small-scale generators.
- Self-consumption ratio
- The percentage of generated solar energy that is used on-site rather than exported. Higher is better for ROI.
- String inverter
- A single inverter handling all panels in a 'string' (typically 8–22 panels). Cheaper than micro-inverters but less tolerant of shading.
- Tier 1 panel
- A panel manufacturer ranked by BloombergNEF as financially stable enough to be considered bankable. Roughly the top 15 global manufacturers.
- UPS
- Uninterruptible Power Supply — battery-backed protection for sensitive electronics. Can coexist with solar and home battery systems.
- V2H / V2G
- Vehicle-to-home / Vehicle-to-grid — using your EV battery to power your home or to export to the grid. Limited UK availability in 2026.
- WCS
- Workplace Charging Scheme — UK grant covering up to 75% of the cost of workplace EV chargepoints, capped at £500 per socket (installs completed from 1 April 2026) and 40 sockets per applicant (£20,000).
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