DC drop reference

What it is

The DC cables between the modules and the inverter have a resistance. The current flowing through them costs voltage, so the inverter terminals sit below the modules by the cable resistance times the current. The inverter sets the voltage at its terminals, and the modules deliver the current that belongs to their own voltage. Every operating point therefore needs the drop, and the drop needs a current. At the maximum-power point the two options give almost the same result. They differ when the inverter holds the array away from that point: at an edge of the MPPT window, on the AC limit or on the DC current limit. The bottom panel of the figure shows the two voltages and the drop between them. On strings that run below the window the choice can change the annual energy by several percent; on strings sized for the window the effect is negligible. The choice is live only with the operating point on the array's I–V curve.

Options

• Drop at the MPP current: the cable drop at the maximum-power current, fixed for the timestep
• Drop at the operating current: the cable drop at the current of the operating point

References

1. PVsyst 8 help, Array ohmic wiring loss

API

inverter.dc_drop_reference = mpp_current | operating_current