French company building osmotic power plants. Sweetch Energy's technology relies on membranes that let through charged particles (ions) rather than water molecules. The movement of ions creates an electric potential difference, which is the basis of a battery; the resulting charge is then used to produce a current directly.
The company's generators are built by stacking together a series of ion-selective membranes and flowing through them fresh and salty water extracted from different points in a river delta. Although the ion-transfer process has been known about for years, the cost of making the required membranes had been prohibitive. Sweetch says it has developed cheaper and more effective versions using nanotube structures made from natural materials, such as wood. The details remain proprietary.
Sweetch Energy is constructing a trial plant on the river delta where the Rhone meets the Mediterranean Sea in southern France. If the trial succeeds, the company aims to build a larger installation over the next decade with a generating capacity of 500 megawatts—enough to supply the 1.9m people of Marseille and its surrounding districts. The company is led by Nicolas Heuzé and is also working on similar projects in other parts of the world.
Sweetch eventually hopes to generate electricity at a levelised cost below $100 per megawatt hour.
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