MIT engineers have developed an innovative desalination system that operates in sync with the sun’s cycles.
This solar-powered system efficiently extracts salt from water, adjusting its desalination process to align with the fluctuations in solar energy. As sunlight intensifies throughout the day, the system accelerates its desalination capabilities, seamlessly adapting to sudden changes in sunlight, such as cloud cover or clear skies.
Thanks to its ability to respond promptly to subtle shifts in sunlight, this system maximizes the use of solar energy, generating substantial quantities of clean water despite varying sunlight levels. Unlike other solar-driven desalination technologies, the MIT system eliminates the need for additional batteries for energy storage or supplementary power sources from the grid.
The engineers rigorously tested a cutting-edge community-scale prototype on groundwater wells in New Mexico over six months. Despite unpredictable weather conditions and varying water types, the system impressively harnessed over 94 percent of the electrical energy generated from its solar panels. This enabled it to consistently produce up to 5,000 liters of water per day, even in the face of significant fluctuations in weather and available sunlight.
“Conventional desalination technologies require steady power and need battery storage to smooth out a variable power source like solar. By continually varying power consumption in sync with the sun, our technology directly and efficiently uses solar power to make 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. “Being able to make drinking water with renewables, without requiring battery storage, is a massive grand challenge. And we’ve done it.”
The researchers have developed the revolutionary system designed to desalinate brackish groundwater, a vast but often overlooked source of water. With fresh water reserves under increasing strain in many parts of the world, the team sees brackish groundwater as a promising solution for providing clean drinking water. Their innovative, renewable, and battery-free system has the potential to deliver affordable drinking water, especially in inland communities with limited access to seawater and grid power.
“The majority of the population actually lives far enough from the coast that seawater desalination could never reach them. They consequently rely heavily on groundwater, especially in remote, low-income regions. And unfortunately, this groundwater is becoming more and more saline due to climate change,” says Jonathan Bessette, MIT PhD student in mechanical engineering. “This technology could bring sustainable, affordable clean water to underreached places around the world.”
The innovative system represents a significant advancement from the previous design, showcasing a remarkable approach to desalinating water through “flexible batch electrodialysis.” This method, along with reverse osmosis, is a primary technique for desalinating brackish groundwater. Unlike reverse osmosis, which relies on steady power levels, the team’s focus on electrodialysis has led to the development of a more adaptable, “time-variant” system that can effectively harness renewable solar power.
In their initial design, the team integrated water pumps, an ion-exchange membrane stack, and a solar panel array to create the electrodialysis system. The true innovation, however, lies in the implementation of a model-based control system that leverages sensor data from every component to predict the optimal water pumping rate and voltage application. This approach maximizes the extraction of salt from the water while adapting to the natural variations in solar energy.
Field tests demonstrated the system’s ability to adjust water production in response to fluctuations in solar energy, achieving a remarkable direct utilization of 77 percent of the electrical energy generated by the solar panels. This represents a staggering 91 percent improvement compared to conventional solar-powered electrodialysis systems. Despite these impressive results, the researchers are already striving for further enhancements.
“We could only calculate every three minutes, and in that time, a cloud could literally come by and block the sun,” Winter says. “The system could be saying, ‘I need to run at this high power.’ But some of that power has suddenly dropped because there’s now less sunlight. So, we had to make up that power with extra batteries.”
The cutting-edge desalination system with a faster response time can adjust to changes in sunlight throughout the day without the need for batteries. This innovative system can adjust its desalination rate three to five times per second, thanks to a revolutionary control strategy called “flow-commanded current control.”
This strategy allows the system to optimize its pumping and salt removal based on the amount of solar power being produced, making it incredibly efficient and sustainable.
After rigorous testing at the Brackish Groundwater National Desalination Research Facility in New Mexico, the system proved to harness over 94 percent of the solar panel‘s electrical energy to directly power desalination. This breakthrough has the potential to revolutionize access to clean water for communities around the world.
“Compared to how you would traditionally design a solar desal system, we cut our required battery capacity by almost 100 percent,” Winter says.
The engineers are gearing up to conduct extensive testing and expand the system to bring affordable, completely solar-powered drinking water to larger communities and entire municipalities.
“While this is a major step forward, we’re still working diligently to continue developing lower cost, more sustainable desalination methods,” Bessette says.
“Our focus now is on testing, maximizing reliability, and building out a product line that can provide desalinated water using renewables to multiple markets around the world,” Pratt adds.
Journal reference:
- Jonathan Tae-Yoon Bessette, Shane Richard Pratt & Amos G. Winter V. Direct-drive photovoltaic electrodialysis via flow-commanded current control. Nature Water, 2024; DOI: 10.1038/s44221-024-00314-6