Long term measurement accuracy analysis of a commercial monitoring system for photovoltaic plants

In order to monitor the correct operation and evaluate the energetic performance of a photovoltaic (PV) power plant, as well as to be able to compare with other PV installations, operational monitoring with appropriate measurement accuracy is necessary. Mainly due to economic reasons, in the majority of cases PV electrical parameters are measured directly by inverters. Measurements acquired with commercial monitoring systems are expected to be less accurate than those acquired with a dedicated monitoring system, which has been specifically designed to perform this kind of measurements. This work aims to verify this aspect through a comparison of operational data from the same PV plants acquired by means of two monitoring systems - a commercial and a dedicated ones - over a period of almost three years. Results show that average differences between the measured values are lower than the tolerances maximum error stated by the inverters' manufacturer and therefore the electrical measurements performed by commercial monitoring systems are sufficiently accurate.