Night reactive energy production

The "Reactive power" is not a real electrical power: you cannot produce any movement or heat with it.

Reciprocally, the production/consumption of reactive power doesn't reduce nor increase the "real" (active) power.

Now the output electronic circuits of some inverters are able to "produce" a reactive power on the grid, by "absorbing" power from the grid and "reinjecting" it with a phase shift. They may behave in the same way as a capacitor for "absorbing" reactive energy (or possibly an inductor, but this is not useful). This feature is sometimes provided by PV plants to the grid, especially during night.

This extra-PV night contribution is not treated by PVsyst, as it is not related to the PV production. PVsyst only treats the Reactive power associated with a PV "active" power production. The reactive power treated in PVsyst is always proportional to the Active power.