Can flexible operation of brackish desalination facilities reduce the cost of desalted water? A case study in Southern California

Desalination can be an important component of drought-resilient regional water systems, however, energy costs are significant contributors to the cost of desalinated water. The time-varying nature of electricity prices represents an opportunity for desalination facilities to reduce their energy-related costs through operating such facilities to exhibit time-varying electric loads that maximize load when electricity is cheap and minimize load when electricity is expensive. Here, we investigate the extent to which flexible operation of a brackish water desalination facility, represented by the Chino Desalter Authority II facility, in response to time-varying electricity tariffs can reduce the cost of desalinated water. We show that flexible operation does not reduce the cost of desalinated water under current electricity tariffs but may net cost of desalinated water by up to 16.1% on an all-cost basis of the facility under more aggressive real-time pricing tariffs. If the facility was designed to accommodate flexible operation with larger feed pumps and lower minimum flow rates, potential cost reductions increased to 47% under aggressive tariff structures. Further, installing a battery energy storage system instead of operating treatment trains flexibly provided similar benefits as that of flexible operation. Finally, we show that flexible operation to minimize costs does not necessarily reduce greenhouse gas emissions. Overall, we show that there is potential for flexible operation of brackish water desalination facilities to reduce their cost of desalinated water, but these reductions are only realized when electricity tariffs are sufficiently aggressive and when the facility is designed to accommodate flexible operation. • Chino II flexible RO yields no savings under current TOU tariffs • Up to 16.1% reduction in an all-cost basis of desalinated water under aggressive RTP • Pump oversizing and lower minimum-flow limits raise savings up to 47% • Battery storage delivers similar bill savings while keeping RO steady-state • Cost-optimal flexibility may not cut GHG; emissions signals are needed