For the simple system shown in Fig. 1, if the PV unit connected at k-th node produces PkPV amount of real power and the load connected at this node is PkL+jQkL, then the net active power injection into the grid, (PkPV - PkL), can be negative, zero or positive depending on the amount of PV generation. A four quadrant P-Q diagram presented in Fig. 2, can be used to illustrate this situation.