It is required to predict the performance of the heat exchangers network HRSG and HSSG during sunny days while the solar radiation varies. In these calculations several initial values were guessed before arriving iteratively at the final heat balance and the duty added to the steam generation. The design value of \(\left(\text{UA}\right)_{d}\) is corrected by using appropriate factors for gas properties and heat balance of each section. First, the temperature correction factor \(F\)which reflects gas properties for each surface is computed, and then the transferred heat\(\ \)using the expression: