Innovative Solar-Powered Desalination System by MIT Promises Freshwater at Costs Below Tap Water Rates

A solar-powered desalination prototype, having a slanted ten-stage layout, is situated within a reservoir resembling a boat. This apparatus effectively transforms seawater into potable water and is believed to do so at a cost below that of producing tap water. Acknowledgment: Jintong Gao and Zhenyuan Xu

Engineers from MIT, in collaboration with Chinese counterparts, have crafted a solar-powered mechanism that sidesteps the salt build-up problems often seen in other desalination technologies.

The engineers, based both at MIT and in China, are working on a fully passive system that desalinates seawater. The design, motivated by oceanic processes, operates solely on solar energy.

Published in the journal Joule on September 27, the research paper describes a novel solar-powered desalination structure. This setup uses natural sunlight to heat saltwater.

The device is configured in such a way that it enables water to circulate in vortex-like currents, mimicking the ocean’s large-scale thermohaline circulation. This current, in synergy with solar heat, causes the water to evaporate while leaving salt residues. Subsequently, the evaporated water is condensed and harvested as clean, potable water. Meanwhile, residual salt is expelled rather than being allowed to accumulate and block the system.

Enhanced Efficacy and Output

This novel design surpasses all other existing passive solar desalination models in terms of water production and salt elimination rates.

Projections indicate that a system of this size—equivalent to a small suitcase—could generate approximately 4 to 6 liters of drinking water per hour and function for many years before requiring maintenance. Given this performance level, the cost of producing drinkable water would undercut that of tap water.

Lenan Zhang, a research scientist at MIT’s Device Research Laboratory, stated, “For the first time, it is possible for water produced by sunlight to be even cheaper than tap water.”

The team envisions that a scaled-up version could fulfill the daily water needs of a small family and could be particularly beneficial for coastal communities without grid connectivity.

Collaborators on the study included Yang Zhong, an MIT graduate student, and Evelyn Wang, the Ford Professor of Engineering, along with researchers from Shanghai Jiao Tong University in China.

Design Evolution

The team’s latest model builds on a prior multi-layered design, which faced issues of salt crystal accumulation and consequently higher maintenance costs. The new version combines features from past designs with enhancements that facilitate both water and residual salt circulation, thereby achieving higher water production and salt rejection rates.

Zhenyuan Xu explained that the design now incorporates a much more potent convection process that is akin to natural oceanic phenomena occurring on a kilometric scale.

The design is influenced by thermohaline convection in the ocean, a process that governs water circulation on a global scale due to variations in temperature and salinity.

System Mechanics

The core of the new design consists of a single stage that looks like a thin box, topped with a material that effectively absorbs solar heat. The box is divided into upper and lower compartments. The top section allows water flow and is fitted with an evaporator layer that uses solar heat to induce evaporation. This evaporated water is directed towards the lower section, where it is condensed into fresh water. The entire setup, tilted within a larger vessel and floated in saltwater, enables water to naturally flow and circulate, propelled by thermal energy and the vessel’s incline.

Prototype tests with one, three, and 10 stages were conducted in waters of varying salinity levels. Calculations based on these tests suggest that the system could operate for several years without salt accumulation and at a cost lower than that of tap water production in the United States.

Guihua Yu, a researcher unaffiliated with the study but specializing in sustainable water and energy storage systems at the University of Texas at Austin, praised the design for its innovation and practical applicability in regions with high salinity water.

Reference and Funding

The study, titled “Extreme salt-resisting multistage solar distillation with thermohaline convection,” was published in the journal Joule on September 27, 2023. The DOI is 10.1016/j.joule.2023.08.012.

Research funding at Shanghai Jiao Tong University was provided by the Natural Science Foundation of China.

Frequently Asked Questions (FAQs) about solar-powered desalination system

More about solar-powered desalination system

• MIT’s Official Announcement on Solar Desalination System
• Journal Article in Joule
• Natural Science Foundation of China
• Shanghai Jiao Tong University Research Publications
• Overview of Desalination Technologies
• U.S. Tap Water Production Costs