New diagnostic functions have been developed and implemented in the firmware of a prototype inverter (RSE inverter) in which a Maximum Power Point Tracking (MPPT) algorithm for the photovoltaic (PV) string connected to it had been developed and implemented by RSE in previous System Research activities. They allow real-time analysis and identification of the degradation of the PV string connected to the RSE inverter. In particular, a procedure has been implemented (called “mismatch_identification”) by which the current losses of the individual PV substrings due to effects of shading, fouling, or damage to the modules can be identified. Based on the results of the mismatch_identification procedure, a new analysis method has been developed which allows predicting the energy benefits achievable following a partial maintenance intervention by the system maintainer, i.e., an intervention carried out not on the entire system but on a limited number of substrings.
A procedure has also been implemented (called “temperature_identification”) capable of estimating the average temperature of the photovoltaic cells of each PV substring, even in partial shading conditions, using a single room temperature sensor, applying a set of formulas that use some electrical parameters of the PV string and the results of the mismatch identification procedure.
The new diagnostic functions have been validated through tests carried out at the RSE inverter laboratory; a Spitzenberger photovoltaic simulator has been used to simulate the IV curves of strings affected by partial shading. The new routines implemented in the inverter have correctly identified the current and temperature values set in the simulator SW.
After the indoor test campaigns on the RSE inverter carried out in previous System Research activities, for the first time outdoor tests have been performed in operating conditions: the RSE inverter has been connected to a PV string affected by artificial partial shading caused by purpose-built obstacles for the test, having typical shapes of real objects such as trees, chimneys, antennas, poles. The results of the experimentation have proven that the RSE inverter is reliable, as no malfunctions (such as machine downtime, stalls, and/or unjustified shutdowns) have occurred, and confirmed the excellent performance of the MPPT RSE algorithm, implemented in inverter firmware, which has identified the correct maximum power point in 99.1% of the experimental cases analyzed.