Optimization of solar-driven systems for off-grid water nanofiltration and electrification

Abstract

The work described is motivated by an inability to extend central infrastructure for power and water to low-population-density areas of the Navajo Nation and elsewhere. It is estimated that 35% of the Navajo population haul water for household use, frequently from unregulated sources of poor initial quality. The proposed household-scale, solar-driven nanofiltration (NF) system designs are economically optimized to satisfy point-of-use water purification objectives. The systems also provide electrical energy for a degree of nighttime household illumination. Results support rational design of multiple-component purification systems consisting of solar panels, a high-pressure pump, NF membranes, battery storage and an electrical control unit subject to constraints on daily water treatment and excess energy generation. The results presented are conditional (based on initial water quality, membrane characteristics and geography) but can be adapted to satisfy alternative treatment objectives in alternate geographic, etc. settings. The unit costs of water and energy from an optimized system that provides 100 gpd (1 gallon is 3.78 L) and 2 kWh/day of excess electrical energy are estimated at $0.16 per 100 gallons of water treated and $0.26 per kWh of nighttime electrical energy delivered. Methods can be used to inform dispersed infrastructure design subject to alternate constraint sets in similarly remote areas.