What does the unit kilowatt-peak (kWp) mean?

Kilowatt-peak stands for the peak performance of a solar module under specified standard test conditions and serves as a neutral benchmark for performance evaluation.

Among the standard conditions (STC) are a cell temperature of 25° C and a solar irradiance of 1,000 watts per square metre. The temperature indication is particularly important because solar cells provide more power at lower temperatures and less at higher temperatures.

The peak performance is also referred to as "nominal power” or “rated power" by most manufacturers. Since the testing is executed under optimal conditions, the peak performance does not necessarily correspond to the peak performance under real irradiation conditions. Due to the irradiation-induced heating of the solar cells, the latter usually is about 15 to 20 percent below the STC values. However, due to weather-related factors, such as frost, performance can also be above peak performance.