How it is calculated: Panel area = panel length × panel width. Incident solar power = panel area × solar irradiance. Solar panel efficiency = rated panel power ÷ incident solar power × 100. At standard test conditions, solar modules are typically rated using an irradiance of 1000 W/m². The calculated value represents module conversion efficiency based on the entered rated power and physical area. Actual field performance varies with temperature, irradiance, angle of incidence, soiling, degradation and other operating conditions.