Wind powered desalination

This thesis investigates the technical problems associated with large-scale stand-alone wind powered desalination employing a short-term energy store, particularly the complexities associated with the intermittent operation of the desalination plant. To achieve this, a non-linear, time domain system model of an existing wind powered desalination plant has been developed using the propriety code Simulink. Two desalination techniques have been considered: reverse osmosis and electrodialysis, due firstly to their relatively low specific energy consumption, and secondly, their efficient coupling to a wind turbine generator. As a way of reducing power mismatch, optimising water production, and above all reducing the switching rates of the desalination units, operation of the reverse osmosis and electrodialysis units under variable power conditions is suggested. Little information is available on plant performance under such conditions. A mathematical model has therefore been developed to ascertain the performance of reverse osmosis and electrodialysis processes under transient power conditions. The model consists of the set of partial differential equations (PDEs) describing the conservation of mass, momentum and chemical species coupled with the appropriate boundary conditions. A numerical solution based on the finite volume method has been employed to solve for the system of PDEs, as no analytical solution is available for the particular set of model equations derived. Sensitivity of plant performance to key design parameters (such as operating pressure and energy storage capacity) and operational strategies is predicted from simulation results. This technology is economically attractive for islands where wind energy density is high and water resources are scarce.