Observed voltage spikes on fielded photovoltaic arrays caused by startup and shutdown switching of inverters

Investigators at South Dakota State University and the Florida Solar Energy Center installed a high-speed datalogger on a high-voltage PV series string as part of an experiment to quantify lightning-induced transients in PV arrays. However, during the measurement period, an unexpected result was observed: large voltage spikes appeared at the PV array terminals during the inverter's morning start-up and evening shut-down procedures. This paper describes those observations, probable causes and effects, and mitigation options.