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Loss diagram

The loss diagram provides a quick and insightful look into the quality of a PV system design, by identifying the main sources of losses.

It is always present in the Simulation report for the entire year. It is also available for each month using the buttons "Detailed results > Predefined graphs" in the project dialog. This allows evaluation of the seasonal effects and impact of the different losses.

Please refer to Array losses, general considerations for a general explanation of the losses in PVsyst.

The array losses start from the rough evaluation of the nominal energy, using the global effective irradiance and the array MPP nominal efficiency at STC. Then it gives the detail of the PV model behaviour according to the environmental variables.

In stand-alone systems, the diagram provides details of battery use, specifically indicating which portion of energy effectively passes through the battery. Minimizing the battery use is of some importance for the lifetime (number of charge/discharge cycles).

Note: Each loss is defined as a percentage of the previous energy quantity. Therefore, percentage values are not additive: when grouping losses, the overall percentage is not the sum of the detailed values.

Note: Accounting for individual losses is a complex problem. The simulation process and some variable definitions were substantially reformulated to obtain a coherent result. Additionally, some contributions cannot be evaluated rigorously. For example, in stand-alone systems, ohmic losses are evaluated using the standard relation Ploss = R × I². In reality, however, array resistance modifies the PV operating point and overall circuit equilibrium. A more accurate calculation would involve simulating the complete system with and without this resistance and evaluating the differences. Even with this approach, some loss contributions will be shifted to other categories.

Nevertheless, even if some individual losses are not precisely determined, the energy values at each main step of the simulation are, in principle, correctly calculated.

You can refer to the following pages for a detailed description of the individual variables: