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UK solar glossary (plain English)

Quick definitions of common solar and battery terms you will see in quotes, apps, and guides.

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Core solar terms

  • kW (kilowatt): a unit of power. Think “how fast” electricity is being produced or used at a moment in time.
  • kWh (kilowatt-hour): a unit of energy. Think “how much” electricity over time (for example, 1 kW for 1 hour = 1 kWh).
  • kWp (kilowatt-peak): the rated size of a solar array under standard test conditions. In the UK, real output is usually lower than the kWp rating at any moment.
  • PV (photovoltaic): solar panels that convert light into electricity.
  • Array: the full set of panels on your roof (or ground mount).
  • Inverter: converts the panels’ DC electricity into AC electricity used in your home and the grid.
  • String inverter: one central inverter for the system. Efficient and common, but performance can be affected if part of the array is shaded.
  • Microinverters: small inverters attached to individual panels. Helpful for complex roofs or shading, typically higher cost.
  • Optimisers: electronics on panels that can reduce shading losses and improve monitoring when paired with a compatible inverter.
  • MPPT (maximum power point tracking): inverter function that continually finds the best operating point for the panels.
  • Generation: the electricity your solar system produces (kWh).
  • Self-consumption (self-use): the share of your solar generation that you use in your home rather than export.
  • Export: electricity you send back to the grid because you are generating more than you are using at that moment.
  • Import: electricity you buy from the grid (when solar is not covering your use).

Performance and real-world output

  • STC (standard test conditions): lab conditions used for panel ratings. Not typical of UK rooftops, so “rated output” is not what you normally see day-to-day.
  • NOCT (nominal operating cell temperature): a more realistic temperature and operating condition than STC.
  • System losses: real-world losses from temperature, wiring, inverter conversion, dirt, mismatch between panels, and other factors.
  • Shading: reduced sunlight on part of the array (trees, chimneys, nearby buildings). Even partial shading can reduce output depending on system design.
  • Degradation: panels slowly produce less over time. Degradation is normal and usually small year-to-year.
  • Clipping: when the panels could produce more, but the inverter caps output (common in some designs and not always “bad”).

Batteries

  • Battery capacity (kWh): how much energy the battery can store.
  • Usable capacity: the amount you can actually use day-to-day (often less than the headline capacity).
  • Depth of discharge (DoD): how much of the battery can be used before it should stop discharging.
  • Round-trip efficiency: how much energy you get back after charging and discharging (always less than 100%).
  • Charge/discharge power (kW): how fast the battery can charge or supply power at a moment in time.
  • Cycle: one full charge and discharge (roughly). Batteries have a finite cycle life.

UK grid and payments

  • SEG (Smart Export Guarantee): export payment scheme where suppliers pay you for electricity you export. Rates vary by supplier and tariff.
  • DNO (distribution network operator): the company that runs the local electricity network in your area.
  • G98 / G99: UK rules for connecting small-scale generation to the grid. Some installs are “notify after”, others require approval first, depending on system size and export capability.
  • Export limit: a cap on how much you are allowed to export to the grid. Some systems are configured to limit export even if panels could generate more.
  • Unit rate: the price you pay per kWh for imported electricity.
  • Standing charge: the daily fixed charge you pay to have an electricity connection.

Quotes, warranties, and paperwork

  • MCS: a UK certification scheme that is commonly required for SEG export payments and used as a quality signal for installers and products.
  • Workmanship warranty: covers installation work (separate from product warranties).
  • Product warranty: covers defects in equipment (panels, inverter, battery).
  • Performance warranty: a long-term promise that panels will still produce at least a stated percentage of their original output after many years.

If you want the “how to interpret this properly” version, start with our guides and the methodology page.