The effect of wind speed fluctuations on the performance of a wind-powered membrane system for brackish water desalination

Abstract

A wind-powered reverse osmosis membrane (wind-membrane) system without energy storage was tested using synthetic brackish water (2750 and 5500 mg/L NaCl) over a range of simulated wind speeds under both steady-state and fluctuating conditions. The parameters varied were: i) average wind speed from 3.7 (system start-up) to 8.7 m/s; ii) wind turbulence intensity from 0.0 (steady-state conditions) to 0.6 (extreme fluctuations); and iii) period of oscillation from 15 to 90 s. With a feed water of 2750 mg/L NaCl, the wind-membrane system produced good-quality permeate (<600 mg/L) over the full range of wind speeds and fluctuations. The system performance (in terms of permeate flux and NaCl concentration) at average wind speeds of 7.0 m/s or more was unaffected by fluctuations up to a turbulence intensity of 0.4 and was independent of the period of fluctuation within this operating range. With a feed water of 5500 mg/L NaCl an average wind speed of 7.0 m/s or more was required to produce adequate-quality permeate (<1000 mg/L) under fluctuating conditions. It is concluded that this wind-membrane system can be operated within a safe operating window with large power fluctuations, but further control strategies are required to deal with intermittent operation, especially with higher salinity feed waters.