The Numerical Model of a PV System Supported by Experimental Validation

Photovoltaic (PV) module manufacturers typically provide electrical parameters at Standard Test Conditions (STCs), while real operation is strongly influenced by irradiance and module temperature. This paper presents a MATLAB-based numerical model that simulates the operation of a real PV string composed of 19 series-connected modules (8.645 kWp). Each module has 72 PV cells arranged as two parallel cell groups, each group consisting of 36 cells connected in series, and a rated maximum power of 455 Wp. The validated string belongs to a PV site comprising 140 modules (63.7 kWp); however, the experimental verification is intentionally performed at the string level to avoid aggregation effects. The model implements the single-diode equivalent circuit and computes the I–V and P–V characteristics at any time step, using 500 points for curve plotting. Measured irradiance and module temperature are used as inputs, while DC voltage, current, and power recorded at the inverter MPPT are used as reference quantities. Model performance is evaluated over two representative operating days, and the verification includes point-by-point comparisons between measured and simulated electrical quantities at 25 operating points, with accuracy quantified through MAE, RMSE, and MRE. The obtained errors are: MAE—power 92.94 W (1.08% of maximum power), voltage 8.33 V (1.07% of maximum voltage), current 0.12 A (1.17% of maximum current); RMSE—power 111.78 W (1.29%), voltage 10.15 V (1.30%), current 0.15 A (1.46%); and MRE—power 2.6%, voltage 1.18%, current 2.57%. These results indicate close agreement between simulated and measured string behavior under the tested conditions, supporting the use of the proposed approach for string-level performance analysis and diagnostic assessment when irradiance and temperature are available from measurements or scenario inputs, without extending conclusions to plant-level generalization beyond the validated subsystem. Photovoltaic panel manufacturers usually provide electrical parameters in a single operating condition, but in reality, PV cells operate under very diverse weather conditions. For this reason, the manufacturer’s information is not sufficient to determine the performance of PV plants.