Abstract:In this paper the problem of increasing the capacity of an already constructed solar thermal power plant has been studied through the concept of lost available work. The required increased capacity has been proposed to be achieved by means of a new large size collector and an auxiliary boiler. Two different schemes along with an extra scheme for night operation of the power plant have been considered in the present work. For each scheme, three different operating conditions have been assumed, resulting in a total of nine operating options. For these options, results of analysis based on the second law of thermodynamics have been presented. These results might then be used to choose the optimum solar hybrid power plant configuration.