Shutter array technique for real-time non-invasive extraction of individual channel responses in multi-channel CPV modules

Abstract

ABSTRACT Concentrator photovoltaic (CPV) solar energy systems use optics to concentrate direct normal incidence (DNI) sunlight onto multi -junction photovoltaic (MJPV) cells fabricated from III -V compound semiconductors on germanium substrat es. The MJPV receiver, which integrates cell and bypass diode, is then mated with its concentrating optic to form a channel, and several such channels form a CPV module, in which the receivers are connected electrically in series. The two ends of the modul e receiver string are brought out to a single pair of electrical connections, at which point the light -current -voltage ( L -I-V ) response of the entire module can be tested. With commercial CPV modules commonly sealed against outdoor exposure, there are no o ther accessible test points, and field installation on trackers further complicates access to performance data. There are many physical phenomena influencing module performance, and in early development and commercialization some of these may not yet be co mpletely under control. Unambiguous diagnosis of such phenomena from one full -module L -I-V curve is problematic. Simple, fast test methods are needed to develop more detailed information from full -module on -tracker testing, without opening up modules in th e field. We describe a test protocol, using a simple optical shutter array constructed to fit mechanically over the module. When module L -I-V curves are recorded for each of various combinations of open and closed shutters, the information can be used to i dentify one or more anomalous channels, and to further identify the kind of anomaly present, such as optical misalignment, conductor failure, series or shunt resistance, and so on. Simulated results from anomaly models can be compared with the measured res ults to identify the anomalous behaviour. Results herein are compared with direct single -channel measurements to verify the technique. The L -I-V response curves were obtained in continuous real time, an approach found to be more helpful than single -shot ca pture in understanding field response. A triangular wave function generator is used to drive the DC power supply, and a four -channel digital sampling oscilloscope displays and stores the real time response. Where modules exhibit unstable or intermittent re sponse under certain conditions, this is immediately obvious in real -time display . Keywords: concentrator photovoltaic; CPV; test method; L -I-V curve; shutter array technique; continuous dynamic display ; solar energy