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Fresh water is one of the basic materials for the survival and development of human society. At present, less than 0.36% of the fresh water only exists in rivers, lakes and underground water that can be directly used by human beings.
More than 97% of the earth’s total water volume is sea water. Because the salinity is too high to be directly drunk or irrigated, less than 3% of the remaining fresh water is extremely unevenly distributed, of which 3 / 4 is frozen in the glaciers of the earth’s poles and alpine zone, and the remaining fresh water contains 37 times more groundwater than the surface water.
With the development of social economy and the acceleration of industrialization, the demand for fresh water resources is increasing day by day. Some islands and coastal saline areas, as well as inland brackish water areas, have always been areas lacking fresh water.
In order to solve the contradiction in the development, especially in the water shortage areas, desalination of seawater or brackish water nearby has become one of the effective ways to expand the source of fresh water.
Of course, there are many methods for desalination of seawater or brackish water, such as conventional distillation, ion exchange (we provide customized service for wedge wire resin trap screen filter of ion exchanger), dialysis, reverse osmosis membrane and freezing. These traditional methods not only consume a lot of fuel or electricity, but also pollute the air and cause greenhouse effect.
Therefore, 95% of the energy consumption comes from solar energy, almost no oil, natural gas, coal and other conventional energy, green and pollution-free, the solar desalination technology with high purity of fresh water has been widely used.
In 2018, the U.S. Department of Energy announced funding of 21 million US dollars to support research and development projects of solar thermal desalination technology, aiming to accelerate innovation breakthroughs in solar thermal desalination technology and reduce the cost of solar thermal desalination.
In 2019, the Ministry of industry and information technology and the Ministry of water resources jointly issued the catalogue of industrial water-saving technologies, technologies and equipment encouraged by the state (2019), “solar energy, light and heat, low temperature and multi effect desalination technology” was mentioned.
In 2013, China’s first solar thermal seawater desalination demonstration project was completed and put into operation in Hainan, with a daily output of distilled water of about 30 tons, which can meet the demand of about 5000 people for healthy drinking water, and its water production cost is about 45% of the traditional device
In 2020, Saudi Arabia’s first “solar dome” desalination plant will start construction, which will use concentrated solar energy technology for desalination, with a production cost of about US $0.34/ton, far lower than the production cost of the desalination plant using reverse osmosis method.
In addition to production cost, efficiency is also the focus of solar desalination. Previously, researchers at Rice University in the United States used cheap plastic lenses to focus sunlight on “hot spots”, which improved the efficiency of solar desalination system by about 50%.
They said the typical way to improve the performance of solar desalination system is to increase solar concentrator and light, and the biggest advantage of this method is to use the same amount of light, which can not only redistribute power at a low cost, but also greatly improve the productivity of purified water.
The all passive solar desalination technology is one of the effective technologies to solve the adaptability of desalination because of its simple structure and convenient materials.
In recent years, solar energy interfacial evaporation has provided a new idea for efficient portable desalination, which has become a research hotspot in energy science, material science and thermal science, but its efficiency is also very limited (about 100%).
The research team pointed out that systematic energy transfer optimization is the key to achieve ultra-efficient solar desalination, rather than high-performance materials.
Their proposed “interface local heating multi-stage solar distillation architecture”, which combines the local heating of solar interface and the recovery of steam enthalpy, significantly improves the efficiency of passive solar desalination, which is more than two times higher than the previous research results.
The research team further said that the estimated cost of the device, which can meet the daily drinking water demand of a family, is about $100, and it has great application potential in areas with limited infrastructure but abundant sunshine and sea water.
Therefore, the research results provide a more practical and effective solution to the problem of fresh water shortage in remote or off grid areas, and also provide a new idea and theoretical framework for the practical and efficient interface solar evaporation.
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