The report describes activities focused on evaluating the energy performance (on the DC side) of an inverter in which a Maximum Power Point Tracking (MPPT) algorithm, developed by RSE, has been previously implemented in its firmware. This algorithm is capable of quickly identifying the maximum power point (Pmax), even under conditions disrupted by variations in partial shading and solar irradiance.
The tests were conducted in a laboratory using a photovoltaic simulator that emulates the current-voltage characteristics (I-V curves) of a PV string under conditions of partial shading and variable irradiance over time. The aim was to assess the increase in energy production using the RSE inverter compared to that produced by recently developed commercial inverters, some of which claim to use high-performance MPPT algorithms under partial shading conditions. The test utilized two databases of I-V curves: one composed of artificially generated curves, representing highly variable shading and irradiance dynamics, and a second created from a campaign measuring the I-V curves of an actual PV string exposed to shading caused by obstacles with shapes typical of real objects (such as trees, chimneys, antennas, poles) placed nearby.
The experimental results showed that, in the case of complex dynamics of solar irradiance and partial shading variations (artificially created and simulated during the test with a photovoltaic simulator), the energy produced using the RSE inverter was 15% higher than that produced by the tested commercial inverters.
In the case of experiments conducted using the database of experimental curves, due to their lower variability in the considered experimental scenarios, the daily energy increases of the RSE inverter were approximately 4% higher compared to recently developed inverters.
Finally, the report describes the implementation of diagnostic functions in the firmware of the RSE inverter through a routine that scans the I-V curve and automatically processes it to estimate both the series resistance value of the PV string and the average cell temperature (assuming no partial shading). An analysis of the uncertainty in parameter estimation was also carried out, which is strongly influenced by the uncertainty of the sensors integrated into the inverter for measuring voltage and current, as well as by the presence of shading.