Kilowatt-peak (kWp)
The DC power rating of a PV module or array under Standard Test Conditions; the conventional unit of installed solar capacity.
Kilowatt-peak is the rated output of PV modules measured at Standard Test Conditions: 1,000 W/m² irradiance, 25 °C cell temperature and the AM1.5G spectrum. A module labelled 450 Wp delivers 450 W under those laboratory conditions; ten of them make a 4.5 kWp array. Utility plants are rated in MWp, national fleets in GWp.
The rating is not a maximum: modules can briefly exceed it on cold, very clear days or under cloud-edge enhancement. Under typical operating conditions output is lower, because cells run hotter than 25 °C (see temperature coefficient) and irradiance is usually lower.
Useful conversions:
- Annual energy (kWh) = kWp × specific yield (kWh/kWp).
- Typical 2025 residential modules: 400–450 Wp; utility modules: 550–720 Wp on 182–210 mm wafers.
- Ground-mounted plants need about 1–2 hectares per MWp including row spacing, more at high latitudes.
Capacity statistics can mix DC (kWp) and AC (kWac) ratings. IRENA and most European statistics report DC; US EIA data use AC. The difference equals the DC/AC ratio, often 1.2–1.35, which matters when comparing capacity factors and costs per watt.
Related terms
All terms →- Standard Test Conditions (STC)
The reference conditions for rating PV modules: 1,000 W/m² irradiance, 25 °C cell temperature and an AM1.5G solar spectrum.
- DC/AC ratio
Ratio of a PV array DC nameplate capacity at STC to its inverter AC rating; also called inverter loading ratio (ILR).
- Specific yield
Annual energy produced per unit of installed PV capacity, expressed in kWh/kWp per year; combines solar resource and system performance.
- Capacity factor
The ratio of the energy a power plant actually produces over a period to the energy it would produce running at full nameplate capacity for the whole period.
- Watt (W)
The SI unit of power, equal to one joule per second; it measures the rate at which energy is produced, transferred or used.