Hybrid system must include operation strategies that describe the energy flow between the generator and the load. The operation decision variables to be optimized represent routing and operation decisions that are based on the power flow modeled for the hybrid system. The main operation decision variables of the hybrid system model are presented as follows:

CSCPV, CSCW, CSIN, SOCmin, SOCmax, CSL, Vmax-off, Vmax-on, Vmin-off, Vmin-on

Some of these decision variables may be set before optimization of the hybrid system. To protect the battery against overcharging, PV array or wind generator is disconnected from the system, when the DC bus voltage increases above Vmax-off and when the current required by the load is less than the current generated by the PV array and wind generators. They are connected again when DC bus voltage decreases below Vmax-on. To protect the battery against excessive discharging, the load is disconnected when the DC bus voltage falls below Vmin-off and when the current required by the load is greater than the current generated by the PV array and wind generators. The load is connected again when DC bus voltage increase above Vmin-on. Control switch and charger controller operation strategies are described below.

Charger control switch of PV, CSCPV,

CSCPV = 0, If V> Vmax-off and ILOAD<IPV CSCPV = 1, If V< Vmax-on Charger control switch of wind generator, CSCW,

CSCW = 0, If V> Vmax-off and ILOAD<IW CSCW = 1, If V< Vmax-on Load control switch, CSL,

CSCW = 0, If V< Vmin-off and ILOAD>IW + IPV CSCW = 1, If V>Vmin-on

The hybrid system model has many constrains such as technological, socio-economic, legal or physical. The constraints in the presented approach are given by technical characteristics of battery operation and by matching demand and generated energy. Constraints can be formulated as follows;

SOCmax > SOC(t) > SOCmin

IPV (t) + IW (t) + IBD (t) > Iload(t) + IBC (t)

At all times, equation 13 can not be proved. According to the application, the load may not be served with desired amount of energy. This situation is described as loss of load probability. LLP of the energy system can be calculated using equation 14. Also, LLP is the size of system reliability.

T T n Energy _ Demand

LLi —

Energy _ Served (14)

The object of optimization procedure is to achieve hybrid system that generates energy with the lowest cost. The objective function of the hybrid system model considered LCC function that was defined with in costing model of hybrid system. The hybrid system model needs to be optimized with respect to the decision variables and operation strategies such that the minimum life-cycle cost is achieved.