Solar updraft tower technology as clean and renewable energy source

Abstract

Solar energy is renewable, clean and practically non-depletable energy source - it is estimated that we will have steady, unlimited supply of sunlight for another 5 billion years. Efficient utilization of solar energy and development of solar systems in that purpose are the research topics of many scientists and engineers worldwide. Solar updraft tower (SUT) technology is attracting interest in many regions worldwide, being a compelling prospect for producing clean and renewable energy. Very import operational parameters of SUT systems are mass flow rate and pressure difference inside the tower. Based on the assumption of one-dimensional (1D) flow, a comprehensive mathematical model for buoyancy driven air flow inside the SUT power plant is developed. It consists of system of nonlinear differential equations which describes the flow inside collector and the tower, and algebraic equations which describes the flow in collector to tower transition section and turbines. Validity of the model is confirmed by numerical solution of the equations for the case of Manzaneres SUT, where good agreement is found between obtained solution and available experimental data. Dimensionless form of model equations are further developed which enables the performance analysis of SUT systems. It is found that only large-scale systems are feasible, and that increase in tower height increase the mass flow rate only to some extent. Additionally, CFD computations based on Boussinesq model for buoyancy-driven flow and using Reynold-Averaged Navier-Stokes (RANS) equations are performed where good agreement is found with derived 1D model.