Billions of people depend on brackish groundwater as their primary drinking source — yet turning that water clean with solar power has always come with a catch: batteries. Without them, a passing cloud can cripple a desalination system mid-operation.
MIT engineers say they’ve found a way around that constraint. Their prototype doesn’t store solar energy — it moves with the sun in real time, adjusting its desalting rate several times per second. Tested over six months at a research facility in New Mexico through shifting weather and varying water conditions, the system kept running without a backup power supply in sight.
The battery problem that has held solar desalination back
Conventional desalination demands a steady power supply. Reverse osmosis — the most widely used method — forces salty water through membranes under continuous high pressure. Any interruption disrupts the process. Solar energy, which rises and falls with clouds, seasons, and time of day, is inherently incompatible with that requirement. Batteries have served as the traditional fix, but they add significant cost, require maintenance, and degrade over time — barriers that put solar desalination out of reach for many low-income or remote communities.
Electrodialysis offers a different path. Rather than using pressure, it applies an electric field to pull salt ions out of water as it passes through a stack of ion-exchange membranes. The process is more tolerant of variable power — a more natural match for solar — and that flexibility is what the MIT team chose to build on.
The need is real and growing. Brackish groundwater sits in underground reservoirs across much of the world, saltier than fresh water but far less saline than seawater. As climate change stresses freshwater reserves, it’s becoming the default source for many inland populations — the same populations often farthest from grid infrastructure and least able to afford expensive energy storage.
How the MIT system learned to follow the sun
The MIT team had already made meaningful progress before this latest work. An earlier design using “flexible batch electrodialysis” achieved 77 percent direct utilization of available solar electrical energy — roughly 91 percent better than traditionally designed solar electrodialysis systems. But the system updated its operating parameters only once every three minutes, leaving a real vulnerability: a cloud passing in that window could cut available power before the system had time to respond, requiring battery buffering to compensate.
The new solution came from PhD student Jonathan Bessette and staff engineer Shane Pratt. They developed what they call “flow-commanded current control” — an approach that ditches complex predictive models entirely. The system continuously reads how much power the solar panels are actually generating and immediately acts on that information.
When available power rises, the controller increases the pumping rate, pushing more water through the electrodialysis stack while raising the electrical current to pull more salt from the faster-moving water. This loop runs three to five times per second — fast enough to track solar variations in near real time, with no lag that would require a battery to fill.
Six months in New Mexico: what the prototype proved
To move beyond the lab, the team deployed a community-scale prototype at the Brackish Groundwater National Research Facility in Alamogordo, New Mexico. Over six months, the system ran continuously on several wells, operating through variable weather, shifting seasons, and different water compositions.
The results were significant. On average, the system directly harnessed over 94 percent of the electrical energy generated by its solar panels. At peak conditions, it produced up to 5,000 liters of clean water per day — enough to supply roughly 3,000 people — maintaining that performance across a wide range of sunlight conditions without drawing on any supplemental power source.
The most pointed figure came from the researchers directly: compared to a traditionally designed solar desalination system, the new approach cut required battery capacity by “almost 100 percent.” That near-total elimination of energy storage is what reshapes the economics.
Who stands to benefit — and how far the technology could reach
The system is designed specifically for communities that existing infrastructure has failed to reach: inland, remote, and low-income populations without access to seawater or reliable grid power. As Bessette noted, the majority of the global population lives too far from coastlines for seawater desalination to be a realistic option. They depend on groundwater — and that groundwater is getting saltier.
The current prototype is sized for around 3,000 people, but the team’s ambitions extend further. They’re working to scale toward full municipalities and developing a broader product line for multiple global markets. Shane Pratt described the focus as “testing, maximizing reliability, and building out a product line that can provide desalinated water using renewables to multiple markets around the world.”
The team plans to launch a company based on the technology in the coming months. The technical barrier that once made battery-free solar desalination seem implausible has now been cleared. Whether that translates into widespread deployment will depend on manufacturing scale, regulatory pathways, and local adoption.
