Peak power in kilowatts peak (kWp) is the standard metric for rating solar PV systems and individual panels. It represents output under laboratory Standard Test Conditions rather than typical real-world operating conditions, where irradiance levels are lower and cell temperatures vary. Actual AC output is lower than the kWp rating due to inverter losses, temperature derating, cable losses, and system availability.
For commercial solar PV structural assessments, the total array kWp informs the approximate panel count, which combined with panel dimensions and weight determines the array layout and dead load imposed on the roof structure. Arrays are sized to the available roof area, structural capacity, and DNO export limit, all confirmed during pre-construction surveys.