Shining light on osmosis holds hope for renewable energy

The Betsiboka estuary links the Betsiboka River with the Mozambique Channel, part of the Indian Ocean. How can we maximise the energy producing effects of osmosis at estuaries? European Space Agency/science Photo Library

Light could hold the key to harnessing osmosis as a viable energy source according to Swiss researchers. Recently tested under real-world conditions, the findings offer hope for renewable energy that does not rely on specific weather conditions in contrast to wind and solar.

ResearchersExternal link from the Laboratory of Nanoscale BiologyExternal link (LBEN) at the Swiss Federal Institute of Technology Lausanne (EPFL) have discovered that light helps harness production of power from the natural occurring process of osmosis.

Recreating the conditions at estuaries, the researchers shined light on a system combining water, salt and a membrane to generate electricity. Under the effect of light, the system produces twice as much power as it does in the dark. The research findings have been published in the scientific journal JouleExternal link.

The way it works is that a low-intensity laser light releases embedded electrons and causes them to accumulate at the membrane’s surface, which increases the surface charge of the material. According to the researchers, a system of mirrors and lenses could be used to direct this light onto the membranes at river estuaries. Similar systems are used for solar photovoltaics.

Osmosis is a natural process whereby molecules migrate from a concentrated to a more diluted solution across a semi-permeable membrane. At river estuaries, osmosis happens when electrically charged salt ions move from the salty seawater to fresh river water.

“Essentially, the system could generate osmotic power day and night,” explains Michael Graf, the lead author of the paper on the EPFL website. “Output would double during daylight hours.”

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This builds on LBEN researchExternal link published in 2016, which demonstrated the role of nanomaterials in producing osmotic power. To achieve high power generation, the researchers had to operate in an alkaline environment, with high pH levels that are far from the levels found in estuaries.

This time around, instead of using chemical treatments, the researchers discovered that light could be used, allowing them to operate in real-world conditions.

The potential

This could unlock significant opportunities for renewable energy production. In contrast to most renewable power technologies, like wind and solar, that are weather dependent, the method being developed at EPFL captures an energy source that’s constantly available at river estuaries: osmotic power, also known as blue energy.

The team indicates that there is still a lot of work to do before the technology can be used for real-world applications including stabilising the membrane.