Simulation Results for a Hybridizes Operation of a Gas Turbine or a Burner for a Small Solar Tower Power Plant

To the group of solar thermal power systems belongs the solar tower where a field of two-axis tracking heliostats reflects the sun arrays to the receiver aperture. In the receiver high temperatures are reached which can generate steam for a Rankine cycle or ultimately even high enough temperatures to use the heat in a gas turbine system of a combined cycle power plant. Germany’s first and only solar tower power plant for experimental and demonstration purposes has been erected in the town of Jülich. The plant, which has been designed with an open volumetric receiver, supplies the grid with a nominal power of 1.5 MWe. A further upgrade to a hybrid system by combining the solar operation with combustion process for natural gas or biogas is currently being taken into account. The advantage of the solar-fossil hybrid power plants, compared to solar-only systems, lies in low additional investment costs due to an adaptable solar share and reduced technical and economical risks. For that reason an advanced software tool library is developed for the modeling of such hybrid power plants. This library includes components of the solar and steam cycle as well as a gas turbine and a burner. From this library components are used to develop a simulation model for the calculation of a small hybrid power plant. This tool enables the calculation of the energy output of not only individual operating points but also of chosen days and a whole year. In this paper a simulation model for two hybrid concepts with a burner or a gas turbine of the solar tower power plant of Jülich are described. The newly developed additions to the model library have been validated with results from another software tool as well as with design calculations at steady state conditions. Special operation strategies for these two hybrid concepts and simulation results for parts of the small solar tower power plant are described and discussed. Emphasis is given in the understanding of the different parameters that have a direct influence on the thermal heat entering the heat recovery steam generator of the solar tower power plant