Dear Giovani,
SAM calculates those loss percentages to display in the diagram on the Losses tab. The losses are annual values, and the percentages apply to annual totals. They are meant to make it easier to compare different sources of losses and to identify the largest sources of losses in your system design.
For example, your results suggest that relatively more power is lost from converting DC power from the photovoltaic array to AC through the inverter than converting battery power between AC and DC.
The AC losses (AC battery loss, AC wiring, transformer loss, and AC availability and curtailment) apply to the gross AC energy value.
Please see these posts for related discussions:
Losses section and sankey diagram doesn't make sense or add up
Module loss
Loss diagram calculations
Best regards,
Paul.