A comparison between two different techniques to estimate the uncertainty of the low irradiance test

The purpose of the test “Performance at low irradiance” is to determine how the electrical performance of the module varies with load at 25°C and at irradiance of 200Wm-2, using natural sunlight or a simulator class BBB or better conforming to the requirements of IEC 60904-9, instead of 1000 Wm-2 standard conditions. A device to change the irradiance to 200Wm-2 is required; its implementation shan't affect the relative spectral irradiance distribution and the spatial uniformity in accordance with IEC 60904-10. To this purpose the IEC 60904-10 recommends the use of mesh filters or neutral density filters. Mesh filters are believed to be the best method for large surfaces. It would be important to compare results and uncertainties related to the different solutions and discuss about pros and cons. This paper matches the results of two laboratories that adopt two different approaches. The low irradiance performance test has gained importance due to the always extensive use of PV as integration elements on buildings.