When do we reach out to such renewables. Miraculously Saline water generating electricity

Japan has launched its first osmotic power plant in Fukuoka, becoming only the second country after Denmark to generate electricity from the meeting of seawater and freshwater. The facility, which began operating on August 5, will produce around 880,000 kilowatt-hours annually, powering a desalination plant and marking a milestone in renewable energy.

Japan has officially entered the global race to generate energy from the meeting of saltwater and freshwater, unveiling its first osmotic power plant in Fukuoka earlier this month.

The facility, operated by the Fukuoka District Waterworks Agency, is only the second in the world after Denmark’s pioneering project in 2023.

Experts see it as a crucial development in the search for renewable energy sources that can function continuously without weather limitations or carbon emissions.

What we know about Japan’s first osmotic power plant

The newly launched installation in Fukuoka uses the difference in salinity between seawater and freshwater to produce electricity.

According to the waterworks agency, the plant is expected to deliver about 880,000 kilowatt-hours per year, a volume of energy equivalent to the consumption of approximately 220 Japanese households.

The agency highlighted osmotic generation as “a next-generation renewable energy source that is not affected by weather or time of day and emits no carbon dioxide.”

By relying on the natural flow of water molecules across a semipermeable barrier, the technology avoids the intermittency problems faced by solar and wind power, which depend on sunlight or favourable weather conditions.

The science behind osmotic power

The principle of osmosis, known to science for centuries, is at the heart of the system. When freshwater and saltwater are placed on either side of a semipermeable membrane, water molecules naturally flow toward the saltier side to balance concentrations.

Osmotic power plants exploit this process by placing two water streams with different salinities opposite each other, separated by specialised membranes that allow only water molecules to pass.

In the case of the Fukuoka facility, the freshwater side comes from treated wastewater sourced from a sewage plant, while the saltwater side is composed of concentrated 

As the freshwater crosses the barrier, pressure builds on the saltwater side. This pressure is then used to drive a turbine connected to a generator, producing electricity.

The concept is straightforward but technically demanding. Large amounts of water must be pumped into the system, and membranes must withstand high pressure while maintaining selectivity to avoid impurities passing through.

The Fukuoka plant’s design reflects recent advances in both areas, including improvements in hollow-fibre forward-osmosis membranes that enhance efficiency.

What hurdles does the method face

Despite the enthusiasm, experts acknowledge that significant challenges remain. Energy must be expended to pump both saltwater and freshwater into the facility, and frictional resistance inside the membranes causes additional losses.

 “While energy is released when the salt water is mixed with fresh water, a lot of energy is lost in pumping the two streams into the power plant and from the frictional loss across the membranes. This means that the net energy that can be gained is small.”

Japan’s decision to use concentrated seawater brine, the residual from desalination plants, was a smart approach because it increases the difference in salt concentration between the two streams, thereby enhancing the amount of energy available.

The advances in membrane and pump technology are gradually reducing inefficiencies.

Why this method is sustainable

Unlike solar and wind energy, osmotic power plants can operate continuously, as long as there is access to freshwater and seawater. This quality makes them particularly attractive for regions seeking stable renewable energy sources.