kWp meaning in Physics Related ?

The nominal power is the nameplate capacity of photovoltaic (PV) devices, such as solar cells, modules and systems, and is determined by measuring the electric current and voltage in a circuit, while varying the resistance under precisely defined conditions. The nominal power is important for designing an installation in order to correctly dimension its cabling and converters.

The peak power is not the same as the power under actual radiation conditions. In practice, this will be approximately 15-20% lower due to the considerable heating of the solar cells.Moreover, in installations where electricity is converted to AC, such as solar power plants, the actual total electricity generation capacity is limited by the inverter, which is usually sized at a lower peak capacity than the solar system for economic reasons. Since the peak DC power is reached only for a few hours each year, using a smaller inverter allows to save money on the inverter while clipping (wasting) only a very small portion of the total energy production. The capacity of the power plant after DC-AC conversion is usually reported in WAC as opposed to Wp or WDC.