Solar & Home Energy · 11 min read · Beginner

Solar & Battery Glossary: kW, kWh, kWp, MPPT, CT Clamp, EPS, MCS & More

A plain-English glossary of common UK solar, inverter, battery, export and grid-connection terms used in installer quotations and monitoring apps.

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Key points & steps

  1. kW (kilowatt) is power: the rate at which equipment is generating, consuming, charging or discharging electricity at a moment in time.
  2. kWh (kilowatt-hour) is energy: the amount generated, used or stored over time. A 5kWh battery describes an energy quantity, not automatically a 5kW discharge rate.
  3. kWp (kilowatt-peak) is the rated DC peak capacity of a solar-PV array under standard test conditions; actual instantaneous and annual generation vary with real conditions.
  4. Inverter: converts DC electricity from panels/battery into usable AC electricity. Hybrid inverter: an inverter architecture designed to integrate compatible battery storage as well as PV.
  5. String: a group of solar modules electrically connected together. MPPT (maximum power point tracker): inverter control that adjusts electrical operating point to obtain useful power from a connected PV string/array under changing conditions.
  6. Optimiser: module-level electronics used in some systems for monitoring/control and to manage panel-level differences. Microinverter: inverter mounted at/for individual modules rather than one central string inverter.
  7. DoD (depth of discharge): the proportion of battery capacity discharged. Usable capacity: the energy the system makes available in normal operation. Round-trip efficiency: the proportion of input energy recovered after charging and discharging losses.
  8. Clipping: when available panel DC power exceeds what the inverter/system can convert or export at that moment, causing the output to be capped. Export limit: the maximum power permitted to flow from the site to the distribution network under the connection arrangement.
  9. DNO: Distribution Network Operator. G98/G99: engineering-recommendation connection routes for generation/storage. G100: technical requirements for export-limitation schemes.
  10. MCS: the UK certification scheme covering eligible low-carbon installations/installers and associated standards; an MCS certificate is not the same thing as a manufacturer warranty or DNO approval.
  11. SEG: Smart Export Guarantee, the Great Britain framework for eligible small generators to receive supplier payments for metered exports. CT clamp/current transformer: a sensor used by many systems to measure electricity flow at a cable/connection point.
  12. EPS/backup output: an emergency-power function designed to supply selected loads during a grid outage. Islanding: operating a local electrical system separated from the public network; normal grid-tied inverters must stop energising the grid during outages unless an approved backup/islanding arrangement is provided.

Practical tips

  • Installer quotations often mix kW, kWh and kWp; check the unit before comparing two numbers.
  • “10kW system” can be ambiguous unless the quotation states whether it means panel DC capacity, inverter AC power or battery output.
  • Ask for a simple diagram showing panels, inverter, battery, meter/CT and grid connection if the terminology is making a quotation difficult to compare.

What you may need

  • Installer quotation
  • Panel/inverter/battery datasheets
  • MCS/DNO handover documents
  • Monitoring app screenshots if comparing terminology

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