For solar panel inspection, the minimum irradiance is specified as:

• A. 400 W/m^2
• B. 700 W/m^2
• C. 550 W/m^2
• D. 600 W/m^2

Answer: (D)

In solar panel infrared inspection, you need enough sunlight to generate noticeable heat patterns on the modules so defects like hotspots or poor connections reveal themselves in the thermal image. Irradiance is the amount of solar energy per unit area hitting the panel, so higher irradiance means more current and more heating, which helps produce clear, repeatable temperature contrasts that you can interpret reliably. If irradiance is too low, the panels won’t heat enough and the thermal differences become faint or noisy, making it hard to distinguish real defects from normal variation. About 600 W/m^2 is used as the practical minimum because it represents a moderate, sunny condition—enough to drive measurable heating and stable thermal behavior without requiring perfect, full-strength sun. On days with lower irradiance, or on partially shaded panels, the infrared image may not show defects clearly, while very high irradiance is not always necessary in field inspections. So the minimum of 600 W/m^2 balances detectability with practicality, making it the best choice for reliable PV inspections.