Mixing saltwater and fresh water: Japan's unique way of generating electricity in Asia

(Dan Tri) - Imagine a day when estuaries and seaports will not only be the meeting place between fresh water and salt water, but also "natural power plants" providing a stable source of energy for millions of people.

Imagine a world where electricity is generated simply by mixing fresh and salt water, no fuel, no emissions, no waste.

This seemingly sci-fi scenario has just been realized in Japan with the inauguration of the first osmotic power plant in Asia, only second globally.

The forgotten clean energy source

According to The Guardian , Osmotic Power, also known as salinity gradient energy, has long been classified by scientists as a potential renewable energy source.

Its mechanism originates from the natural process of osmosis: water moves from a low-salt area (freshwater) to a high-salt area (seawater) through a semi-permeable membrane, creating pressure that can be used to turn turbines and produce electricity.

The plant in Fukuoka is designed to produce about 880,000kWh of electricity per year (Photo: TG).

This principle is already happening in nature every day – it is the way plants absorb water from the soil to nourish their cells. But it was not until the 21st century that semi-permeable membrane technology became durable and sophisticated enough to allow humans to exploit this phenomenon to create a stable current.

However, in the global race towards green energy, osmotic power has received less attention than wind, solar or hydropower. The reason is the challenge of efficiency and initial investment costs.

However, with Japan's efforts, this "forgotten" energy source is returning to a promising position.

Recently, Japan officially put into operation an osmotic power plant in Fukuoka city, Kyushu island. This is the first project in Asia and the second in the world, after the Mariager osmotic power plant (Denmark) launched in 2023.

Building on its long-standing expertise in hydropower, Japan has “upgraded” osmosis technology to an industrial scale.

The Fukuoka plant is designed to produce around 880,000kWh of electricity per year. This is equivalent to the electricity consumption of around 220 households – not a large amount, but paving the way for future expansion.

Notably, all the electricity generated will be used to power a nearby desalination plant, ensuring fresh water for Fukuoka City. This is considered a dual-combined model: generating electricity while solving the need for clean water, especially useful for coastal cities where fresh water is scarce.

Unique operating mechanism

In Fukuoka, fresh water or treated wastewater is fed into one side of a semi-permeable membrane, while seawater is fed into the other. The difference in salt concentration causes water to move through the membrane, increasing the pressure on the seawater side.

This pressure is converted into kinetic energy, rotating a turbine connected to a generator, creating a continuous current.

Professor Sandra Kentish, University of Melbourne (Australia), commented: “What is special about the Japanese project is that they use concentrated seawater, the remaining brine after the desalination process, to increase the concentration difference. This method helps maximize efficiency and take advantage of the by-products from the desalination plant.”

Unlike wind or solar power, which are dependent on the weather, osmotic power can be produced 24 hours a day, year-round. Oceans and rivers offer a virtually endless supply of raw materials, promising a steady, low-carbon, and completely renewable flow of electricity.

Challenges and prospects

Despite its clear potential, electroosmosis still faces significant technological challenges. Pump systems require a lot of energy to push water through the membrane, while the membrane itself is susceptible to friction and impurities.

It is these factors that make the cost of producing osmotic power still higher than that of popular renewable sources.

However, according to experts, these barriers are not insurmountable. New materials, advanced wastewater treatment technology and optimal system design are gradually removing difficulties.

Several countries, including Norway, South Korea, Spain and Qatar, have also launched pilot projects, looking to Japan as a model to learn from.

The Fukuoka event is not just significant for Japan. It shows that osmotic power has moved from the laboratory to the real world, becoming a viable option in the global energy diversification strategy.

As humanity strives to reduce greenhouse gas emissions and confront climate change, any clean energy source has strategic value.

Researchers believe that if scaled up, osmotic power could become an important supplementary energy source, especially in coastal countries rich in rivers.

Source: https://dantri.com.vn/khoa-hoc/tron-nuoc-man-va-nuoc-ngot-cach-tao-dien-doc-nhat-chau-a-cua-nhat-ban-20250906074019738.htm