A new stream of reliable renewable energy: osmotic power

Renewable energy is still enjoying a period of robust expansion, despite the best efforts of Donald Trump (or, arguably, because of them).

But a relatively new and little-known source of renewable power is starting to come of age: osmotic power. While it might sound like a fictitious concept, or something the Power Rangers might invoke, the idea of the power of osmosis has been around for decades. Norway may be credited with the proof of concept of a practical power plant employing the notion, and Denmark opened the first fully-functioning osmotic power plant in 2023. But it is only with the recent commissioning of a full-scale, efficient, commercial plant at Fukuoka, Japan, that the real potential of the idea has become clear.

Osmosis is the movement of water from areas of low salt concentration to areas of high salt concentration through a membrane of some sort. It is the same principle that allows plants to draw water from the soil, and that keeps our own cells hydrated. In the context of power generation, as at Fukuoka, the difference in saltiness of seawater and freshwater is used to pull water across a membrane, increasing the pressure on the saltwater side. This pressure gradient can then be used to drive a turbine, thereby generating electricity.

In the case of Fukuoka, the saltwater is super-concentrated by using the brine left over from the operation of a nearby desalination plant, making the whole process much more efficient. The electricity generated is then fed back into the power-hungry desalination plant, as well as to supply a few hundred local homes. The power it generates is equivalent to about two soccer fields of solar panels, and it runs day and night, regardless of the weather. It produces zero carbon dioxide and no other harmful by-products.

The trick is to produce enough power to outweigh the energy cost of pumping the two streams of water into the power station, and the frictional loss across the membrane, which is what the Fukuoka plant has achieved. The idea is gathering steam [sic], and pilot projects are starting up in Norway, South Korea, Spain, Qatar and Australia. 

Right now, the modality is still in its infancy but, as technical challenges are gradually overcome and the concept comes of age, researchers say that it could eventually meet up to 15% of global energy demand by 2050 - not to be sniffed at. This prediction is probably overly optimistic, but it certainly represents yet another string to the essential bow of renewable energy.