Navigation:  Project design > Grid-connected system definition > Power Factor

The energy E_grid calculated by the PVsyst simulation is the active (or real) energy, expressed in [kWh].

Now the grid manager may require to produce some reactive energy for compensating the unbalances of the other users (expressed in [kVARh]).

The Apparent energy is the product U * I expressed in [kVAh].

If the voltage is sinusoidal, the active (or real) energy is U * I * cos(phi)  [kWh], where phi is the phase shift between current and voltage.

The Power Factor is the ratio of the Active energy to the Apparent energy. In the sinusoïdal case, it is equal to cos(phi).

The phase shift  produced by inverters is sometimes expressed as Tan(phi), positive for reactive power generation (capacitive, Phi>0, named "Leading") and negative for reactive power absorption (inductive, Phi<0, named "Lagging").

In the simulation results:

Therefore we have E_GridApp [kVAh] = E_Grid [kWh] / Cos(Phi):  the Apparent energy has always a higher value than the Active energy E_Grid calculated by the simulation.

If you specify a phase shift in the simulation  (button "Energy management"), the Apparent energy will appear at the bottom of the  Loss diagram.

This quantity has no influence up to the E_Grid calculation, but it produces an increase of the real current in the AC lines, and therefore an increase of the Wiring loss in the AC circuit (and also in the external inverter in any).  

NB: Technically, producing Reactive energy is a parameter which should be programmed in the inverter device. This is fixed for a given period.

Effect on PNom

Now a question arises with the overload conditions. There are 2 possibilities:

- either the Pnom specified by the inverter's manufacturer corresponds to an active power. In this case the usual simulation takes correctly the overpower conditions into account.

- or the Pnom specified by the inverter's manufacturer is an apparent power. In this case the power limitation should occur for PnomApp [kVA] = Pnom [kW] / cosPhi. Therefore the simulation has to adjust the Pnom specified in the inverter's definition, by dividing it by the required CosPhi.

NB: the limitation on the Apparent power is sometimes specified as a current limitation. At a given time this depends on the output voltage, i.e. the grid voltage. However during the simulation the grid voltage evolution is not known ; therefore the power limitation cannot be applied by using this current criteria.

Procedure

In PVsyst, the Power factor may be specified by pressing the "Energy management" button, either as Cos(phi) or as Tan(phi). It may also be specified in monthly values.

This will act on the inverter Pnom limitation if specified as Apparent power limit, and the apparent energy is mentioned on the loss diagram.

Leading and Lagging currents

Let us define Phi as the phase shift between the current and the voltage.

When an inductance (motor) is connected to the grid, it will create  a delay on the phase of the absorbed current. This is named Lagging  and corresponds to Phi < 0.  

When a capacitance is connected to the grid it will absorb a current in advance with respect to the voltage. This is named Leading and corresponds to Phi  > 0.  

The numerous motors present on the grid (inductive load) "consume"  reactive power. The electronic power generation of the solar inverters makes it easy to produce reactive power. Therefore the grid manager often requires that the inverters produce reactive power (i.e. generate a leading current, phi > 0) for compensating.