Coupling electrodialysis desalination with photovoltaic and wind energy systems for energy storage: Dynamic simulations and control strategy

Abstract

The presence of desalination systems in polygeneration facilities is usually limited by important difficulties in operating under non-stationary regimes typical of renewable energy sources. Reverse osmosis, namely the most common desalination technology, is characterised by slow dynamics that rarely adapts to the power fluctuations of renewables. Therefore, the possibility of using electrodialysis coupled with a hybrid photovoltaic/wind energy source was investigated in this work. In particular, the combination of photovoltaic and wind energy is very attractive in order to achieve a more stable energy production, while electrodialysis is claimed to be a more flexible process compared to reverse osmosis. For this reason, the aim of this work was to analyse the technical advantages of using electrodialysis in the aforementioned scenarios, Suitable transitory simulation models are implemented for modelling electrodialysis units, photovoltaic panels and wind turbines. Dynamic scenarios were analysed, looking at two different time scales. Quasi steady-state simulations were used to study the yearly operation of 4 electrodialysis units operating in parallel, demonstrating process flexibility over a wide range of produced flowrates (from 920 to 230 m3/d) and power inputs (5–45 kW) when producing drinking water at a constant NaCl outlet concentration of 0.25 g/l. Dynamic simulations were adopted to study the daily time scale, where the desalination unit control system, purposely designed and tuned, was able to maintain a relatively stable target value in presence of disturbances in power availability, i.e. with a fluctuation of the outlet concentration lower than ± 10%, in between 0,23 and 0,27 g/l. Simulation results show how the electrodialysis process is particularly suitable for the integration within polygeneration systems as energy-buffer.