Engineers have developed a solar-powered desalination system capable of generating significant amounts of clean water, even as sunlight fluctuates throughout the day. This innovative system is more cost-effective than other solar-powered designs since it doesn’t rely on additional batteries for energy storage.
MIT engineers have created a groundbreaking desalination system that operates in tandem with the sun’s cycles.
The newly designed system effectively removes salt from water based on the intensity of solar energy available. As sunlight increases during the day, the desalination process intensifies, automatically adjusting its operation in response to changes in sunlight, such as decreasing output when clouds pass or ramping up when the skies clear.
This rapid adaptation allows the system to efficiently utilize solar energy, resulting in the production of substantial quantities of clean water despite daily variations in sunlight. Unlike other solar-based desalination technologies, this MIT system does not need additional batteries or supplementary power from the grid.
Engineers conducted tests on a community-scale prototype at groundwater wells in New Mexico over a six-month period, experimenting with different weather conditions and water types. On average, the system captured more than 94 percent of the electrical energy generated by its solar panels, producing as much as 5,000 liters of water daily, even amidst significant weather changes.
“Traditional desalination technologies require a consistent power supply and utilize batteries to manage the fluctuations associated with sources like solar energy. By continuously adjusting energy consumption to align with sunlight, our system effectively directly uses solar power to produce clean water,” says Amos Winter, the Germeshausen Professor of Mechanical Engineering and director of the K. Lisa Yang Global Engineering and Research (GEAR) Center at MIT. “The ability to generate drinking water from renewable sources without the need for battery storage is a monumental challenge we have successfully tackled.”
The system is specifically designed for desalinating brackish groundwater, which is saltier than fresh water and is found in underground reservoirs. The researchers consider brackish groundwater to be a vastly untapped potential source of drinking water, especially as fresh water reserves deplete in many regions globally. They believe this novel, battery-free system could deliver essential drinking water at low costs, particularly in inland communities lacking access to seawater and traditional power grids.
“Most of the population lives too far from the coast for seawater desalination to be practical, making them heavily reliant on groundwater, especially in remote, low-income areas. Unfortunately, due to climate change, this groundwater is becoming increasingly saline,” states Jonathan Bessette, a PhD student in mechanical engineering at MIT. “This technology has the potential to provide sustainable and affordable clean water to underserved regions worldwide.”
The details of the new system are outlined in a paper published today in Nature Water. Co-authors of the study include Bessette, Winter, and staff engineer Shane Pratt.
Pump and flow
This new desalination method builds upon a previous design reported earlier this year, where Winter and his colleagues aimed to desalinate water using a “flexible batch electrodialysis” approach.
Electrodialysis and reverse osmosis are the two primary techniques for desalinating brackish groundwater. Reverse osmosis employs pressure to force saline water through a membrane, filtering out the salt, while electrodialysis uses an electric field to extract salt ions as water moves through a set of ion-exchange membranes.
Researchers have explored harnessing renewable energy for both methods, but reverse osmosis systems usually require a steady power supply, which is incompatible with variable energy sources like solar.
Winter, He, and their team focused on improving electrodialysis to create a more flexible, responsive system that could adapt to fluctuations in solar energy.
In their previous design, they implemented a system with water pumps, an ion-exchange membrane stack, and a solar panel array, including a model-based control mechanism that utilized sensor data to determine the optimal water pumping rate and voltage needed for effective salt extraction.
When tested in real-world scenarios, this system was able to adjust its water output based on sunlight variations. On average, it utilized 77 percent of the electrical energy generated by the solar panels—91 percent more than traditionally-designed solar electrodialysis systems.
However, the researchers believed they could achieve even better results.
“We could only process data every three minutes, meaning that a passing cloud could disrupt operations,” Winter explains. “The system might indicate a need for high power, but if sunlight diminishes suddenly, we would have to compensate for that drop using batteries.”
Solar commands
In their latest developments, the researchers aimed to eliminate the dependence on batteries by drastically reducing the system’s response time to mere fractions of a second. Now, the system can adjust its desalination rate three to five times every second, allowing it to better respond to shifts in sunlight without needing to supplement power with batteries.
The key to this swift adjustment lies in a newly devised control strategy called “flow-commanded current control.” In this approach, the system gauges the solar power being generated and, if the panels produce more energy than necessary, it automatically commands an increase in pumping rates and electrical current to enhance salt extraction.
“If the sun is increasing every few seconds, we monitor the solar panels rapidly to maximize flow rates and current,” Winter elaborates. “By continuously adjusting our power consumption in line with available solar energy throughout the day, we significantly reduce our reliance on batteries.”
The engineers have rolled out this updated control strategy in a fully automated system designed to desalinate enough brackish groundwater to serve approximately 3,000 people daily. The prototype was tested over six months at the Brackish Groundwater National Research Facility in Alamogordo, New Mexico, where it effectively utilized over 94 percent of the solar panel’s energy for desalination, regardless of varying solar conditions.
“Compared to conventional solar desalination systems, we have nearly eliminated the need for battery capacity,” Winter states.
The engineers are looking to further test and scale this technology with the goal of providing larger communities and entire municipalities with low-cost, fully solar-powered drinking water.
“While this represents significant progress, we are committed to continuing our efforts in developing more affordable and sustainable desalination solutions,” Bessette mentions.
“Our current focus is on testing for reliability and developing a product line that can supply desalinated water using renewable energy across multiple global markets,” adds Pratt.
The team plans to establish a company based on their new technology soon.
This research received partial funding from the National Science Foundation, the Julia Burke Foundation, and the MIT Morningside Academy of Design. Further support came from Veolia Water Technologies and Solutions as well as Xylem Goulds.
