SOFC System Modelling in the Hybrid Power Plant Project

Kurzfassung

Hybrid power plants offer a promising way to deliver electricity at very high efficiencies. The aim of the DLR project Hybrid Power Plant is to push this technology towards a pre-commercial state. Therefore a dynamic model is being developed which will enable us to gain a deep insight into the power plant without risking hardware. A stationary model has been developed to perform system efficiency analysis as described in [1]. To fully understand the processes in the fuel cell system detailed modelling is crucial. The models generated will be used for control design and a model based control of a gas turbine system installed on site in Stuttgart, therefore they have to be able to run in real time. It is noted that detailed modelling and real time modelling are incompatible as commonly experience in modelling activities. The presentation will focus on stack modelling performed in 2008. The detailed model is based on a conventional Nernst and Tafel approach [2]. The stack is modelled from single cell models each used as a representative for a bundle in the system. In order to reduce model complexity and to speed up calculation time electrochemistry was integrated into the model as a four dimensional look up table [3], which was derived from the single cell model. Pressure influence on cell performance will be discussed based on modelling results from a short element of a tubular cell. The pressure dependence of two modes of operation with distinct behaviours is presented. Validation of the stack model was performed on a Siemens SFC 5 Alpha system installed in Stuttgart. Several load steps as well as voltage current curves obtained during operation where used for model validation. The model is in good agreement with the experimental results. A further focus will be on system modelling demonstrating the dynamic behaviour of the coupled components.