Renewable energy powered membrane technology: Brackish water desalination system operated using real wind fluctuations and energy buffering

Abstract

The performance of a wind-powered membrane filtration system using a brackish water reverse osmosis (BW30) module and synthetic brackish (5500mg/L NaCl) feed water was determined. When tested with real wind speed data (average wind speed 6.1 m/s; interval of 1 s) over one day of realistic fluctuation levels, the wind-membrane system produced 0.78m3 of water with a final concentration of 191mg/L NaCl at an average specific energy consumption (SEC) of 7.2kWh/m3. When a single bank of supercapacitor (SC) energy buffers were added to the system, performance increased to 0.93m3 of permeate produced and a final concentration of 173mg/L NaCl at average SEC of 4.2kWh/m3. Tripling the size of the SC bank further increased productivity to 1.15m3 (47% increase) at a final concentration 172mg/L NaCl and average SEC of 3.1kWh/m3 (57% reduction). The time spent within the safe operating window (SOW) per day, increased from 8h12m under the poorest operating conditions up to 19h56m with the triple SC bank. Importantly, the results indicate that steady-state system performance at an average wind speed can be used as a very good indicator of the expected performance under fluctuating wind conditions. The results described can assist with the design of autonomous, decentralised, off-grid renewable energy powered water treatment systems and help decide whether to include energy buffering components.