Photovoltaic system testing techniques and results

Over the past three years, the New Mexico Solar Energy Institute (NMSEI) has tested and collected data on eight intermediate-size flat-plate photovoltaic systems. These data are now included in a valuable database for determining component reliability and system degradation trends. The specific test techniques used by NMSEI and the reliability of photovoltaic modules revealed by this testing are described and discussed. These methods are: I-V curve plotting, operating voltage and current measurements, and shading tests. These use of I-V curve data are important in determining array peak power rating and quickly locating large system faults. Operating voltage and current measurements are used in determining the location of module level faults. Bypass diode current measurements in conjunction with intentional module shading are used for isolating module faults in intermediate-size systems and systems with inaccessible module wiring. Of the 64000 modules tested, 362 modules (0.6%) were not contributing power