Solar panels receive their ratings under specific testing conditions known as "Standard Testing Conditions" or "STCs". These conditions serve as the industry standard for evaluating solar panels, making it easier t. The Wattage rating of a solar panel is the most fundamental rating, representing the. Solar panels come with two Current (or Amperage) ratings that are measured in Amps: 1. The Maximum Power Current, or Imp for short. 2. And the Short Circuit Current, or Isc fo. Solar panels are classified by their nominal voltages (e.g., 12 Volts or 24 Volts), but these voltages are only used as a reference for designing solar systems. For example, the following sola.