In which test condition is the voltage of a solar system typically the highest?

The voltage of a solar system is typically the highest under Standard Test Conditions (STC). STC represents a defined set of conditions used to measure and report the performance of solar panels, specifically at a temperature of 25 degrees Celsius (77 degrees Fahrenheit), with solar irradiance of 1000 watts per square meter, and under an air mass of 1.5. Under these optimal conditions, solar panels can generate their maximum output, which includes the highest voltage levels.

In practice, STC provides a consistent benchmark to compare the performance of different solar panels in a controlled environment, ensuring that differences in voltage and other parameters are due to the panels themselves rather than external factors. Other test conditions, such as PTC (PVUSA Test Conditions), NOCT (Nominal Operating Cell Temperature), and CEC (California Energy Commission), represent different ways to evaluate solar module performance, often accounting for real-world factors like temperature, irradiance levels, and system configuration, which can lead to lower voltage outputs compared to STC.