It is important that the solar irradiance meter is correctly positioned in relation to the PV system under test to ensure that meaningful data is collected. Varying the angle between the reference cell and the sun can cause significant changes in measured irradiance. The irradiance meter must be positioned so that it is in the same plane as the PV module within ± 2°. The irradiance meter must be positioned so that it does not shade any part of the PV system under test. Accurate and repeatable measurements are best achieved by mechanically securing the irradiance meter to the PV module framework.