Towards a more efficient generation of central tower hybrid thermosolar gas turbine power plants

In this communication we present a novel model for the pre-design of hybrid thermosolar Brayton plants. The plant is described as a whole allowing to predict overall performance. It is considered as composed by three subsystems: solar field and receiver, combustion chamber, and power block. Overall efficiency is obtained as a combination of subsystems efficiencies. Solar field efficiency is computed in detail for any location and any meteorological condition. Most important losses are considered, including shadowing, blocking, spillage, atmospheric attenuation, and so on. A simplified model is taken for the thermal losses in the receiver, including radiation losses. For the power block a detailed thermodynamic model based on an irreversible Brayton cycle is assumed. Multi-stage compression and expansion and regeneration are included in the model. All these ingredients allow for obtaining precise estimations of plant performance at off-design conditions as diary power and efficiency curves, consumption, emissions, and fuel conversion efficiency, in terms of a relatively reduced number of parameters with clear physical meaning, avoiding complex and over-detailed computations. Annual averages are also susceptible to be computed. And so, sensitivity analysis and optimization suggestions can be performed in the framework of the model. Model predictions for several subcritical working fluids (including air, nitrogen, carbon dioxide, and helium) and different plant configurations, are analyzed. The importance of considering the plant as a whole, i.e., to choose the main parameters of the gas turbine (operation temperature, pressure ratio, number of stages, etc.) in concordance to the details of the solar subsystem (concentration ratio, operation temperature of the receiver, etc.) is highlighted.