Electroluminescence imaging of PV devices: uncertainty due to optical and perspective distortion

Electroluminescence (EL) images taken from on-field measurements often suffer from optical and perspective distortion affecting the interpretation and quantification of the images taken. Methods to correct these distortions are presented as well as a method to assess the associated uncertainties. This method uses the uncertainty of pixel position as intermediate step. The influence of pixel deflection, re-projection error and depth-of-field blur is evaluated. Three different camera systems are compared regarding tilt angle dependence. The re-projection error and the camera’s focal length are identified as major influence on the resulting uncertainty. It was shown that EL images with sufficient quality can be recovered, from images taken at high perspective misalignments with tilt angles of about 50°.