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PostPosted: Sat Jun 22, 2013 1:20 pm 
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Joined: Mon Apr 16, 2012 7:29 pm
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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 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 cos(phi).
The phase shift of inverters is sometimes expressed as Tan(phi), positive for reactive power generation (capacitive) and negative for reactive power absorption (inductive).

Therefore we have E_GridApp [kVAh] = E_Grid [kWh] / Cos(Phi)
Technically, producing Reactive energy should be programmed in the inverter device. This is fixed for a given time.

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.

In PVsyst, since Version 6.11 the Power factor may be specified by pressing the "Miscellaneous" 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.

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