Renewable energy powered membrane technology. 2. The effect of energy fluctuations on performance of a photovoltaic hybrid membrane system
This paper reports on the performance fluctuations during the operation of a batteryless hybrid ultrafiltration – nanofiltration / reverse osmosis (UF-NF/RO) membrane desalination system powered by photovoltaics treating brackish groundwater in outback Australia. The renewable energy powered membrane (RE-membrane) system is designed to supply clean drinking water to a remote community of about 50 inhabitants. The performance of the RE-membrane system over four different solar days is summarised using four different NF membranes (BW30, NF90, ESPA4, TFC-S), and examined in more detail for the BW30 membrane. On an Australian spring day, the system produced 1.1 m3 of permeate with an average conductivity of 0.28 mS.cm-1, recovering 28% of the brackish (8.29 mS.cm-1 conductivity) feedwater with an average specific energy consumption of 2.3 kWh.m-3. The RE-membrane system tolerated large fluctuations in solar irradiance (500 – 1200 W.m-2), resulting in only small increases in the permeate conductivity. When equipped with the NF90 (cloudy day) and ESPA4 (rainy day) membranes, the system was able to produce 1.36 m-3 and 0.85 m-3 of good quality permeate, respectively. The TFC-S membrane was not able to produce adequate water quality from the bore water tested. It is concluded that batteryless operation is a simple and robust way to operate such systems under conditions ranging from clear skies to medium cloud cover.