Design strategy and economic analysis on various configurations of stand-alone PV-RO systems

A battery is required in reverse osmosis powered by a photovoltaic system (PV-RO) to prevent inevitable dumping energy and to prolong the operating time of producing water simultaneously. However, the battery is expensive and has a short lifespan. To obtain a competitive water cost, a battery capacity should be as small as possible. This study presents a novel strategy to prevent dumping energy and minimize battery capacity. PV-RO system with battery (PV-RO-Battery) and seasonal water storage tank (SWST) is investigated and its water cost is analyzed. This strategy ensures that all of the daily energy produced by the PV system is used to produce water in less than 24 h, avoiding the accumulation of storing daily excessive energy. Excess daily water production over daily demand is stored in SWST and is supplied to the source of demand when the water production is less than demand. A comparison of a PV-RO-Battery system with and without SWST is also conducted. The reduction of water cost was from 10.21 $/m(3) to 2.31 $/m(3) and 36.96 $/m(3) to 3.06 $/m(3) for the constant and variable demand, respectively. It means that the water cost from the system with SWST is only 20.5% and 8.3% of the system without SWST.