Solar panel glossary

This glossary explains the UK solar terms you will meet when buying panels, from kWp and kWh to the Smart Export Guarantee, MCS and self-consumption. Each definition is short and jargon-free so you can read any quote with confidence.

kWp (kilowatt-peak): The maximum output, or size, of a solar system under standard test conditions. UK systems are typically 3 to 7 kWp.
kWh (kilowatt-hour): A unit of energy: the amount of electricity generated or used. UK panels produce about 850 kWh per kWp each year.
kW (kilowatt): A unit of power: how fast energy is used or produced at a moment in time, as opposed to kWh which is energy over time.
AC / DC: Panels produce direct current (DC); your home and the grid use alternating current (AC). The inverter converts DC to AC.
Array: The full set of solar panels installed together on your roof or ground mount.
Irradiance: The amount of solar energy hitting a surface. UK irradiance varies modestly by region, around 15% between the sunniest and least sunny areas.
Yield (kWh/kWp): How much electricity each kWp of panels produces per year. The UK average is around 850 kWh/kWp, adjusted for region, direction and shading.
Inverter: The device that converts panel DC into home AC electricity. Types include string, hybrid (battery-ready) and microinverters.
Hybrid inverter: An inverter that also manages a battery, so you can add storage without a separate battery inverter.
Microinverter: A small inverter fitted to each panel, so shading on one panel does not reduce the output of the others.
Power optimiser: A unit fitted to each panel that lets it perform independently, reducing the impact of shading, used with a string inverter.
Smart Export Guarantee (SEG): The UK scheme that pays you for solar electricity exported to the grid, around 15p per kWh on a competitive tariff.
Feed-in Tariff (FiT): The legacy UK scheme that paid for generation. It closed to new applicants in 2019 and was replaced by the SEG.
MCS: The Microgeneration Certification Scheme: the UK quality standard for solar installers, required to claim the SEG.
DNO: Distribution Network Operator: the company running your local electricity network, which must be notified of your solar system.
G98 / G99: The processes for connecting solar to the grid. G98 covers smaller systems (notify after); G99 covers larger systems (approve before).
Self-consumption: The share of your generated solar you use yourself rather than export. Around 37% without a battery, roughly 70% with one.
Export: Solar electricity sent to the grid because you are not using it, paid for under the SEG at around 15p per kWh.
Import: Electricity you buy from the grid, at around 27p per kWh, which solar reduces.
Monocrystalline: The most common, higher-efficiency panel type (around 20%+), made from single-crystal silicon. Now the UK standard.
Polycrystalline: An older, slightly cheaper and less efficient panel type made from multi-crystal silicon, now increasingly rare.
Bifacial panel: A panel that also captures light on its rear side, useful on reflective or ground-mounted installations.
In-roof vs on-roof: On-roof panels mount above the tiles (cheaper, common); in-roof panels sit flush within the roof for a sleeker look.
Mounting rail: The aluminium rails fixed to your rafters that the panels clamp onto.
Battery capacity: The energy a home battery stores, measured in kWh. Most UK homes suit 5 to 13 kWh.
Depth of discharge (DoD): The share of a battery's capacity you can safely use. A higher usable DoD means more of the nominal capacity is available.
Degradation: The slow fall in panel output over time, around 0.5% a year, so panels still produce ~85% of original output at 25 years.
Solar diverter: A device that sends surplus solar to your immersion heater, heating water for free instead of exporting at the lower rate.
Immersion heater: An electric element in a hot water cylinder. A solar diverter can power it with surplus solar.
EPC: Energy Performance Certificate: a rating of a home's energy efficiency. Solar PV typically improves the score.
Smart meter: A meter that measures your import and export half-hourly, required to claim the SEG and to use time-of-use tariffs.
Generation meter: A meter that records the total electricity your solar system generates.
Time-of-use tariff: An electricity tariff with different prices at different times, ideal with a battery or EV for cheap overnight charging.
Consumer unit: Your fuse board. Older or full boards may need upgrading (£300 to £600) to connect a solar system safely.
Bird mesh: Protective mesh fitted around panels to stop pigeons nesting underneath, an optional extra of £200 to £500.
Payback period: The time for energy savings to repay the system cost. UK solar typically pays back in 6 to 10 years.
Return on investment (ROI): The financial return from solar over its life, combining bill savings and export income against the upfront cost.