A thermodynamic model for a hybrid solar gas-turbine power plant is presented. All the subsystems of the plant are modeled, taking into account the most important losses sources: those coming from heat losses in the solar subsystem, those in the combustion chamber, those associated to the Brayton cycle, and those heat losses in the heat exchangers connecting subsystems. Analytical expressions for the overall plant efficiency and its power output are obtained in a general form, for whichever solar share: from the pure combustion mode when solar irradiance is null or small, to the eventual case in which only solar heat input would be enough to ensure that the working fluid reaches the turbine inlet temperature. The gas-turbine model is validated by direct comparison of the model predictions with the output parameters of a commercial turbine. Results are very promising. The real parameters of an existing experimental thermosolar plant are considered and its performance records in stationary irradiance conditions are obtained. A sensitivity analysis of the influence of several turbine losses is performed: recuperator, turbine, compressor, and pressure losses. Finally, the influence of the pressure and temperature ratios on the overall plant efficiency and the fuel conversion rate is discussed. This kind of thermodynamic analysis is necessary in order to design efficient as well as commercially interesting new generations of plants of this type. (C) 2015 Elsevier Ltd. All rights reserved.