kWp

Kilowatt-peak — the rated maximum DC power output of a solar PV array under standard test conditions (1,000W/m², 25°C cell temp).

kWp (kilowatt-peak) is how solar arrays are sized. A "4kWp system" produces 4kW of DC power at standard test conditions: 1,000W/m² irradiance, 25°C cell temperature and AM1.5 spectrum. Real-world output is almost always lower than nameplate because UK irradiance rarely hits 1,000W/m² and cells get hot.

For Cornwall, expect roughly 950-1,050 kWh per kWp per year on a south-facing 30-40° pitch. A 4kWp array therefore generates about 3,800-4,200 kWh/year. East-west splits typically lose 10-15%, north-facing roofs 30-40%.

Modern n-type TOPCon panels reach 440-460W per panel, so a 4kWp array is typically 9-10 panels covering around 18-20m² of roof. A 6kWp array (around 13-14 panels) is now the typical "comfortable" residential sizing in Cornwall — large enough to cover most daytime base load and charge a battery, but small enough to fit on a single roof slope. See our solar installation page.