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There are over 1.6 billion people living in rural, water-stressed areas across the world. Brackish groundwater desalination can expand these stressed freshwater supplies. Compared to conventional reverse osmosis (RO), electrodialysis reversal (EDR) can reduce water wastage and energy consumption in brackish water desalination. The improved energy efficiency and water recovery makes solar photovoltaic (PV)-powered EDR systems promising solutions for locations where grid access is restricted or unavailable. However, state-of-the-art PV-EDR is still prohibitively expensive for cost-constrained communities, largely due to the use of batteries for addressing solar power's intermittence. To reduce a system's dependence on batteries, here we present a novel time-variant EDR technology that can flexibly vary pumping and EDR power to match available intermittent solar power while maximizing the desalination rate. We experimentally demonstrated that the flexible system was able to directly utilize 77% of the available solar energy on average, a 91% improvement compared to the reference conventional PV-EDR operation which operated at constant flowrate and EDR voltage. The flexible system also requires 92% less battery capacity. Using a village-scale desalination case study in India, shifting from constant to flexible operation of PV-EDR systems can reduce the levelized cost of water by 22% and make the technology cost-competitive with currently used on-grid, village-scale RO desalination solutions. Cost projections for EDR membranes and brine disposal show that in the future, PV-EDR could produce water at 60\% the cost achieved by on-grid RO, which would provide an improved sustainable solution for addressing water scarcity in remote areas.

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