Monitoring of photovoltaic systems: Good practices and systematic analysis

Over the last 20 years, the statistical average performance ratio of a new photovoltaic (PV) installation in moderate climates has improved from 0.65 to approximately 0.85. This continuous improvement in the field would not have been possible without operational monitoring and the continued analysis of monitoring data by the PV system community. The paper starts with a historical review of the performance of PV systems. It documents the current state of the art and good practices in PV system monitoring. Finally, it presents periodic linear regression as a simple though systematic approach for the visual and mathematical analysis of monitoring data.