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 of reactive power doesn't consume any "real" (active) energy.

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.