The PV system consists of several EPUs in parallel to supply electricity to the power grid. With the UGF for each EPU, the UGF representing the
capacity distribution for the entire PV system can be calculated by using the parallel composition operator Q :
UsysiZ) = £ pk ■
where m, M, pk and w k are the number of EPUs, the state number of the PV system and the probability, and capacity level of state k for the PV system, respectively.
The general technique for determining the UGF of the PV system is based on a state enumeration approach. This approach is usually extremely resource consuming. Fortunately, the PV system can be divided into subsystems (string, array and EPU) and the UGF method allows one to obtain the system UGF recursively. This property of the UGF method is based on the associative property of many practically used structure functions. The recursive approach presumes the UGF of subsystems containing several basic components and then treating the subsystem as a single component with the obtained UGF when the UGF of a higher level subsystem is computed . The recursive approach provides a drastic reduction of the computational resources needed to obtain the capacity distribution of a complex MSS.
The yearly expected energy production (YEEP) of the PV system EEpv is defined as the product of the expected capacity of the system Ew and yearly peak sun hours PSH:
EE = E x psh
The operator 5 is used to calculate Ew and defined as
^ Pk ■ zw4 = ^ Pk ■ wk
k=l J k=1
where U is obtained from (16).