The selection of the cost-effective design for energy systems is one of the important issues in the design and optimization of the power generation systems. To achieve this goal, the thermodynamic analysis and fault detection is one of the useful methods. Thus, in this paper, the thermoeconomic diagnosis and fault detection method is used for the selection of effective Double-Solar-Gas-Turbine system (DSGT). In the proposed DSGT system, the heliostat solar system and combustion of fossil fuel are used as a heat source of the power plant. To achieve the research goals, in the first steps, the energy and exergy analysis is performed, and the energy and exergy parameter is evaluated. Then, the thermoeconomic and the exergy cost accounting analysis is performed and based on this analysis; the exergy cost parameters are examined for all the components and flows. Finally, the malfunction of each component is evaluated with the thermoeconomic diagnosis approach and based on this approach, the effects of irreversibility in each component on other components are investigated. Results show that one of the heat exchangers (intercooler in the bottom cycle) has the highest exergetic cost in comparison to other components, but this heat exchanger has a very small impact on the irreversibility of other components. Conversely, the heat recovery heat exchanger (recovery between the two cycles) has a major effect on the irreversibility of other components, and thus the most correction should be performed in this converter.