Performance Assessment of Solar Chimneys: Part I – Impact of Chimney Height on Power Output

Abstract

Solar chimney is a truly sustainable and green energy technology, which is a potential alternative to carbon-based energy economy. The working principle of solar chimneys is based on the buoyant nature of air to turn a turbine that produces electrical power. Solar chimneys are highly in the centre of interest among all solar energy applications since they enable both day and night time operation owing to greenhouse and chimney effects. A typical solar chimney consists of three main parts as chimney, collector and turbine. When the in-situ applications of solar chimneys are gone through, it can be easily asserted that the driving force in electricity generation comes from the chimney effect as a consequence of the notable pressure differences between the inlet and outlet of the chimneys. In most cases, the greenhouse effects on power output are considered auxiliary only due to non-optimised geometric properties for the air medium beneath the collector. Within the scope of this CFD research, the impacts of chimney height on power output of a typical solar chimney are evaluated. A commercial and reliable CFD software ANSYS FLUENT is considered for the numerical analyses. For different chimney heights, the average velocity at the inlet of chimney in which the turbine is placed is determined by applying k-e turbulence model, continuity, momentum and energy equations for a 2D model. The results reveal that there is an exponential relationship between the pressure difference and the average air velocity and the solar chimney is found to be practical after a certain value of chimney height. For a chimney and collector diameter of 10 and 1000 m, respectively, the average velocity at the inlet of chimney is calculated to be 25.17 m/s for a chimney height of 100 m, whereas it is 18.06 m/s for the height of 50 m. The findings are of vital importance in terms of feasibility studies on solar chimneys since they give a clear understanding about the influence of chimney height on the electrical power output of any solar chimney power plant.