Prediction of energy production is crucial for the design and installation of PV plants. In
this study, five free and commercial software tools to predict photovoltaic energy production are
evaluated: RETScreen, Solar Advisor Model (SAM), PVGIS, PVSyst, and PV*SOL. The evaluation
involves a comparison of monthly and annually predicted data on energy supplied to the national
grid with real field data collected from three real PV plants. All the systems, located in Castile and
Leon (Spain), have three different tilting systems: fixed mounting, horizontal-axis tracking, and
dual-axis tracking. The last 12 years of operating data, from 2008 to 2020, are used in the evaluation.
Although the commercial software tools were easier to use and their installations could be described
in detail, their results were not appreciably superior. In annual global terms, the results hid poor
estimations throughout the year, where overestimations were compensated by underestimated
results. This fact was reflected in the monthly results: the software yielded overestimates during
the colder months, while the models showed better estimates during the warmer months. In most
studies, the deviation was below 10% when the annual results were analyzed. The accuracy of the
software was also reduced when the complexity of the dual-axis solar tracking systems replaced the
fixed installation.
