Active-salinity-control reverse osmosis desalination as a flexible load resource

Abstract

The proposed active-salinity-control reverse osmosis (ASCRO) system dynamically controls energy consumption by operating across a range of feed salinity, allowing it to shift over a wide range of pump feed flows and pressures. ASCRO utilizes feedwater from both low- and high-salinity sources. Enabling a dynamic power consumption profile can enhance demand-response capabilities, compensating for stressors on the grid. Moreover, ASCRO can improve the integration of renewable energy (RE) by responding to power fluctuations without compromising permeate production. This system can include on-site RE and energy storage to power the ASCRO plant and provide services to the grid. We considered the following grid-connected scenarios: 1) ASCRO, 2) ASCRO and battery storage, 3) ASCRO and photovoltaics (PV), and 4) ASCRO, battery storage, and PV. The levelized cost of water (LCOW) was minimized by providing load-shifting and regulation capacity services in the California Independent System Operator (CAISO) market. We quantified that the ASCRO plant can ramp from minimum to maximum load within 84 s, which is adequate for participation in fast-timescale markets. The LCOW for these scenarios ranged from 49 to 59 cents/m3. We also present sensitivity analyses showing the effects of capital cost, CAISO market prices, and PV size on LCOW.