The term peak power (Wp) is used in solar technology to evaluate the performance of solar cells. It is the optimum peak power that a solar cell or photovoltaic system
achieves under location-dependent criteria and specified test conditions. When determining the peak power, the test conditions
, the Standard Test Conditions (STC), should correspond to the real ambient conditions during operation of an installed solar cell, but they represent idealized ambient conditions. Peak power refers to the solar irradiance, the temperature of the solar cell and the density of the atmosphere. It is expressed in watts
peak (Wp), kilowatts peak (kWp), or megawatts peak (MWp). Thestandard test condition (STC) is a solar irradiance of 1,000 W/sq m, an ambient temperature of 25 °C and a wind speed of 1 m/s
. More realistic values for the ambient temperature are obtained with the Normal Operating Cell Temperature (NOCT) and show that with the NOCT rating, the cell performance is lower than that indicated by the peak power.