The maximum nominal / rated output of the SolarPowa 28 solar charger is rated based on the Standard Test Conditions (STC) – the industry-wide standard for the conditions under which a solar panel is tested. The test conditions are defined as irradiation 1000 W/m², temperature 25°C, and air mass 1.5.
The nominal / rated power refers to the power of the solar charger, which is not equal to the actual output of the solar charger. In fact, the actual power is less than the nominal / rated power, since there will be some power loss in the form of heat during the solar energy conversion, and a few other environmental factors such as the weather conditions, seasonal changes, and location.