Seawater reverse osmosis (SWRO) as deferrable load in micro grids

Seawater desalination in the capacity range 100-1000 m(3)/day is globally of increasing importance, especially when it comes to in remote costal regions. By meeting the energy demand of desalination plants by using renewable energy technologies, the environmental impact can be minimised. For water production of more than a few cubic meters per day, usually conventional constantly operating desalination systems are used requiring the implementation of expensive energy storage systems and/or a grid-connection. Variable operating SWRO plants could eventually increase the efficiency of an energy supply system by minimising the otherwise unavoidable dump load and the capacity of energy storage systems. To provide evidence for this thesis, data of the Cape Verdean Island Brava were used and three main scenarios compared. Simulations using hourly data-sets show that energy supply systems with a high wind share can benefit from deferrable loads like a variable desalination plant. Based on their flexibility, such processes are very attractive to implement as dynamic load in stochastically fluctuating renewable energy supply systems. Technological requirements for a variable operation of a SWRO plant are described, considering pressure changes and interruptions of the energy supply and water flow. For the simulation, a preliminary plant design configured by SYNLIFT Systems is used. A detailed analysis of levelised costs of water and electricity highlights options, how desalination could be applied as deferrable load in grid-connected systems in a technologically feasible and economically profitable way.