Economic analysis of SWRO desalination plant design using three different power systems

Abstract

Countries such as Libya with limited fresh water resources and abundant supply of solar energy should look seriously at the use of alternative energy sources for drinking water production. This paper examines the economic feasibility of a 100 m3/day seawater reverse osmosis desalination plant design in the city of Tripoli – Libya. The paper draws a comparison of using three different types of powering systems: The National Electric Grid (Grid), a Standalone (Off-Grid) Photovoltaic System, and a Grid Connected (On-Grid) Photovoltaic System.ROSA Software was used to determine suitable membrane units for the SWRO plant and the membrane element SW30XLE-440i was chosen based on its low feed pressure requirements of 55.5 bar and 35% recovery with total dissolved solid (TDS) of 133 ppm. The electrical consumption of the plant was 26.2 kW and the specific energy consumption (SEC) was 6.28 kWh/m3. The Cost of product water for the plant powered by the Grid, Off-Grid PV and On-Grid PV were 2.07, 2.82, and 1.21 $/m3 respectively at 8% interest rate.The study showed that the use of Grid Connected (On-Grid) photovoltaic system to power a 100 m3/day capacity SWRO plant yielded the lowest levelized cost per cubic meter of produced water. The study also revealed that despite the high cost associated with energy storage in Off-Grid PV systems, the cost of generating electricity from Off-Grid PV systems in high solar insolation regions such as Libya is only marginally higher than that of purchasing electricity from the national electric grid, 0.186 $/kWh versus 0.176 $/kWh. Due to the nature of operation of the desalination plant, however, 37% of the generated electricity from Off-Grid PV goes unutilized either due to battery charge/discharge cycle losses or as a result of energy overproduction at times of peak irradiance.