Scientists solve the problem of solar saltwater desalination and provide an example for energy storage desalination of salt-rich brine
Recently, He Wei, associate professor at King's College London, and his collaborators, developed a new type of highly flexible electrodialysis technology that improves the application efficiency of solar desalination technology and alleviates the impact of solar intermittent power generation characteristics on technical performance and economy.
As a new type of "energy storage" desalination technology, the electrodialysis technology developed this time can efficiently convert intermittent solar energy like energy storage technology and store it in purified drinking water.
Through this, energy supply and drinking water production energy consumption can be decoupled to meet the water resources needs of residents in specific areas.
It can also provide a sustainable drinking water solution for remote rural areas that lack stable power grid supply.
At the same time, compared with traditional desalination technology that relies on grid power or expensive battery energy storage systems, this research aims to use "energy storage" desalination technology to directly convert solar energy into drinking water, thus bidding farewell to batteries. Dependence on energy storage.
Since the cost of water storage is far lower than the cost of battery energy storage, this technology can also improve the economics of solar desalination technology while improving energy efficiency.
Recently, a related paper was published in Nature Water [1] with the title "Flexible batch electrodialysis for low-cost solar-powered brackish water desalination".
He Wei is the first author and co-corresponding author, and Professor Amos G. Winter V of the Massachusetts Institute of Technology serves as co-corresponding author.
Specifically, this electrodialysis technology is expected to be used in the following scenarios:
First, it is used for drinking water supply in remote areas.
As mentioned before, because this technology can directly convert solar energy into desalinated water, it is particularly suitable for remote areas where the power grid is unstable or is not yet covered by the power grid.
By then, residents in these areas will be able to obtain safe drinking water directly from underground saline sources, thus improving the supply of drinking water.
Second, it is used for agricultural irrigation.
In water-stressed agricultural areas, the technology could be used to provide fresh water for irrigation.
Especially in areas with a lot of saline-alkali soil, the use of electrodialysis technology to desalinate water can effectively reduce soil salinity, thereby improving crop yield and quality.
Third, it is used for recycling industrial salt-rich wastewater.
Many industrial processes, such as food processing, generate large amounts of salt-rich wastewater. In the recovery and treatment of salt-rich wastewater, electrodialysis technology can significantly improve its efficiency.
Fourth, it is used to extract lithium from salt lakes.
Electrodialysis technology can efficiently extract lithium ions from salt lakes, and can integrate the lithium extraction process with new energy sources such as solar energy, thereby converting solar energy (including discarded light) into high-value lithium materials, thereby delivering low-emission, high-quality way to extract lithium ions.
About 1.7 billion people live in water-stressed areas
According to reports, this study is based on the severe background of global water scarcity, with particular attention to the drinking water shortage challenges faced by rural areas in developing countries.
Currently, more than 2 billion people worldwide rely on groundwater as a source of drinking water, but approximately 1.7 billion people live in water-stressed areas.
Due to salinization caused by natural and man-made factors, the quality of groundwater is gradually deteriorating, causing many water sources to become salty or salty and unfit for direct drinking.
Although traditional seawater/salt water desalination technology is adopted, fresh water can be effectively extracted. However, it generally relies on grid power supply and infrastructure, which limits its application in remote areas.
Especially in many developing countries, such as remote areas in India, there is either no power grid coverage or power outages. In addition, most of the electricity comes from coal-fired power plants, resulting in high carbon emissions.
However, these areas usually have abundant sunshine, so distributed solar desalination technology can be used as a sustainable and universal solution to deal with water shortages in remote areas.
According to reports, this research originated from a project of He Wei’s collaborator, Amos G. Winter V of the Massachusetts Institute of Technology.
The latter has previously collaborated with India's Tata Corporation on a series of research projects targeting water scarcity for drinking water and agricultural irrigation.
Later, Professor Tonio Buonassisi of MIT also joined the above project.
Through this, the technical route of using solar energy for underground salt water desalination and agricultural drip irrigation has been established, which is expected to expand the utilization of water resources and reduce water consumption.
At the same time, the economic advantages of using photovoltaic-electrodialysis technology for solar saltwater desalination were also clarified. At this time, He Wei joined the above project.
In order to further reduce the cost of photovoltaic-electrodialysis technology, they established the design theory of photovoltaic-electrodialysis technology using first principles, and optimized the design of the photovoltaic-electrodialysis technology system based on this theory.
In 2017, the first prototype system was built and tested in a village called Chelluru in India.
Through this, they not only verified the theory of photovoltaic-electrodialysis technology model and system design, but also gained an in-depth understanding of the specification requirements and cost considerations of saltwater desalination systems in rural India.
They found that although photovoltaic-electrodialysis technology costs less than solar reverse osmosis (PV-RO, Photovoltaic-Reverse Osmosis) systems. However, compared with grid-driven reverse osmosis (on-grid RO, on-grid Reverse Osmosis) systems, the cost advantage is not outstanding enough.
The on-grid RO system has been commercialized in rural areas of India, which shows that photovoltaic-electrodialysis technology has not yet reached an acceptable cost in the market, or that it has not been able to form a local business model for saltwater desalination systems.
Although the cost of the first prototype system has not yet reached the level of commercialization, the field test in India not only confirmed their design theory, but also provided valuable field information.
Based on this information, the research team further innovated electrodialysis technology and proposed a more flexible electrodialysis technology that can flexibly adjust water production according to changes in solar energy supply.
They then built a new prototype system at the Brackish Groundwater National Desalination Research Facility in India.
And use relevant test platforms to conduct more precise monitoring and evaluation of this technology.
Test results show that the system's energy efficiency has been significantly improved, with 77% of available solar energy being directly utilized. This is 91% higher than traditional systems while reducing battery dependence by 92%.
When these field test results were combined with the team's understanding of village-scale desalination projects in India, they found a 22% reduction in water costs, making the technology comparable to on-grid RO systems currently in widespread use.
During the field trip to India, while testing the first prototype system, something happened that made He Wei feel very "counter-intuitive".
At the time of testing, the entire system was powered by solar photovoltaic panels. However, the lights at the experimental site are connected to the power grid and will only automatically connect to the solar system when there is a power outage, and will make a "beep" sound when switching.
This makes them feel grid outages more frequently. Especially at night, they are often the only ones with the lights on.
"The intermittent nature of new energy sources that was once criticized has become a reliable power source here, while the power grids in many countries that are supposed to provide stable power have become truly intermittent energy sources," he said.
This experience enhanced his and his collaborators' understanding of new energy sources, that is, although the sun is a distributed energy source, it can significantly improve the stability of energy supply in remote areas.
In the next step, they plan to expand the application of flexible electrodialysis technology beyond salt water desalination.
Considering the versatility and high efficiency of electrodialysis technology, its potential applications in different fields will undoubtedly bring significant positive impacts, such as agricultural irrigation, lithium extraction from salt lakes, and the use of liquid alkali to capture carbon dioxide. wait.
The new energy industry chain is mainly concentrated in China, and we look forward
to cooperating with domestic units.
It is also reported that as a native of Xi'an, although he does not live in a city near the sea. However, it was while studying in Xi'an that He Wei began to understand seawater/salt water desalination technology.
He graduated from Xi'an Jiaotong University with both bachelor's and master's degrees, and later received his doctorate from Queen Mary, University of London, UK.
He said: "Although I felt a little confused when filling out my application for the college entrance examination, I may have been influenced by reports on environmental protection since I was a child, but I already had a vision for the future in my mind: new energy will become a key technology in the future."
Guided by this belief, he chose the energy and power engineering major at Xi'an Jiaotong University.
During his graduate studies, he participated in a water treatment research project funded by an enterprise, and was exposed to seawater and saltwater desalination technology for the first time, and began to explore how to obtain fresh water from saltwater more efficiently from an energy perspective.
After coming to the UK to study for a PhD, he further studied the integration mechanism and application of seawater desalination technology and various new energy sources.
While working as a postdoctoral fellow at the Massachusetts Institute of Technology in the United States, he shifted his research focus to solar electrodialysis technology.
“It was my research in this field that led me to receive a Research Fellowship from the Royal Academy of Engineering, and started my research career as an independent PI,” he said.
As a key hard technology, energy technology covers a large number of hardware and software research and development in the context of intelligence and digitalization.
Especially in the process of technology industrialization, hardware development inevitably relies on the support of the industry chain and supply chain.
At present, the new energy industry chain is mainly concentrated in China, and he is full of strong interest in exploring and establishing new energy industry transformation opportunities including new electrodialysis technology. “At the same time, we also look forward to cooperation with domestic universities and enterprises.” He said.
