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Scientists led by the Massachusetts Institute of Technology (MIT) have designed a new photovoltaic desalination system based on time-varying electrodialysis (EDR) inversion technology. The proposed system has a lower levelized water cost than conventional solar desalination technologies.
A global group of scientists led by the Massachusetts Institute of Technology (MIT) has developed a novel, low-cost solar-powered brackish water desalination system that can reportedly reduce levelized costs of water (LCOW). initials in English) compared to conventional photovoltaic desalination systems.
The proposed desalination system uses time-varying electrodialysis inversion (EDR) technology, which the researchers developed as a flexible variation of traditional EDR desalination. “Our research aims to address water scarcity in rural India, where most groundwater is too saline to drink. Access to the electrical grid and its stability are not good and they suffer frequent power outages,” explains Wei He, author of the research, to pv magazine .
“An EDR module is made up of a stack of ion exchange membranes and uses an electric field to move ions from the dilute flow channels to the brine flow channels between each membrane,” explains the research group. “This electric field can be reversed intermittently to prevent scale buildup on the membrane.”
However, due to the intermittent nature of solar energy, classic EDR is not a perfect fit. It requires constant power to operate, so PV-EDR plants need the support of batteries or oversized solar systems, especially at the beginning and end of the day, when solar power is low.
“To overcome these problems, we have developed a flexible batch EDR technology that incorporates time-varying voltage and flow rate adjustment,” the academics explain. “A model-based control method allows the EDR system to align its energy consumption with available solar energy at each time step, while optimizing water production under varying solar conditions.”
To control operation, the team created a model-based main controller that runs in Python and calculates optimal pump flow and EDR stack voltage from real-time sensor readings. A prototype was built at a research center that closely reflected the design parameters and typical operating conditions of a community-scale PV-EDR system with the capacity to produce 6 m3 of fresh water per day. It was powered by a solar panel with a surface area of ??37 m2 and an inclination of 30 degrees.
This pilot system was tested for single-day and six-day analysis and compared to the traditional constant-run EDR system. Both systems were fed with water with an average initial salinity of 970 mg l-1. The system was set to a conservatively low water recovery rate of 60%.
“The flexible system is able to directly use 77% of the available solar energy on average, compared to only about 40% in the conventional system (an increase of 91%),” the scientists highlighted. “This suggests that a conventional system would require much more solar panel surface area to operate directly (i.e. without energy storage), which would increase capital costs.”
Furthermore, the analysis showed that the minimum average battery capacity required for the flexible system was 0.27 kWh, which is a 92% reduction compared to 3.3 kWh for the constant system. “Finally, the results show that the flexible system can reach its production volume up to 54% faster than the conventional system,” they added.
Following the experimental results, the researchers conducted a cost analysis case study for the use of such a system in Chelluru, a rural town in India located near Hyderabad. Using computer simulation and optimization, it was compared with a conventional PV-EDR system, a state-of-the-art constant PV-EDR system, and a commercial networked reverse osmosis (RO) desalination system. “Reverse osmosis uses pressure to force water through a polymer membrane, while its constituent ions are blocked by the membrane,” the group explains.
“The optimized levelized cost of water achieved by the proposed flexible PV-EDR system is $1.66/m3, which improves the cost by 22% compared to the state-of-the-art PV-EDR system and by 46% compared to the conventional PV-EDR system,” the scientists found. “The total cost of ownership (LCOW) of network reverse osmosis is $1.71 m-3, 3% above the LCOW of the flexible PV-EDR system.”
Their findings are presented in “ Flexible batch electrodialysis for low-cost solar-powered brackish water desalination ,” published in Nature Water . The team was made up of researchers from Kings College London (United Kingdom) and the Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (HI ERN) (Germany).
“For the next step, exploring the long-term performance and expanding the scope of our PV-EDR technology beyond brackish water desalination presents a significant opportunity to address a broader range of global challenges related to wastewater treatment.” water and liquid waste,” concluded He. |
