To compare the ability of solar panels, there are standard conditions established: at an irradiance of 1 kW/m², of which the spectrum corresponds to the spectrum of sunlight at an air mass of 1.5 (this means that the sunlight passing the atmosphere is equal to one and a half times the average thickness of the atmosphere), and a cell temperature of 25°C.

The maximum electrical power from a solar panel under these conditions is called the peak power (Pmax) and is shown in Wp (Watt-peak).