Comparison of modelling approaches and layouts for solar chimney turbines

The turbogenerator is a core component of any solar chimney power plant. Various layouts for the turbogenerator have been proposed in the literature. In this paper the performance of these layouts is compared using analytical models and optimization techniques, and the important design parameters are discussed. The turbine layouts under consideration are single rotor and counter rotating turbines, both with or without inlet guide vanes.In contrast to similar investigations found in the literature, various radial sections along the blades are analysed in the turbine model. This approach is more appropriate than using a simple mean line analysis when dealing with turbines with high blade aspect ratio and low hub to tip ratio. Furthermore, a limit to the degree of reaction of the turbine has been introduced to avoid diffusion at the hub.It is shown in this paper that these slight changes in modelling approach have a significant impact on the performance prediction. Further it can be concluded that the single rotor layout without guide vanes performs very poorly; the efficiency of the other three layouts is much better and lies in a narrow band. The counter rotating layouts provide the highest peak efficiencies, but at relatively low speeds, which leads to an undesirable higher torque for the same power output.