Daylight Photoluminescence Imaging via Optical String Switching

Abstract

Optical switching of the electrical operating point of individual crystalline silicon modules has previously been demonstrated as an elegant noncontact method for outdoor photoluminescence image acquisition in full daylight, with the important advantage that no modifications to the system wiring are required. Herein, a modified approach for photoluminescence imaging acquisition in large photovoltaic arrays, enabled by simultaneous optical switching of all modules within a series-connected string, is demonstrated. This improved method is a simpler approach and allows for significantly increased measurement throughput. Quantitative assessment of image data acquired in full daylight is possible since all modules in a string are series connected and operate at the same current. Excellent agreement is reported for voltage variations between modules that are inferred from daylight photoluminescence image data and measurements conducted under controlled laboratory conditions.