By K.S. Jayaraman 

Bengaluru, Jul 26 (IANS): Scientists have found a new source of clean energy that will join the existing list of solar, wind, and hydropower, says a report in Nanowerk News, a leading nanotechnology portal.

The new source -- called osmotic power -- is generated by a process called "osmosis" that occurs when fresh water comes into contact with salt water through a thin membrane.

During osmosis, the salt "ions" pass through the membrane into the fresh water until both fluids have the same salt concentration. And since an ion is simply an atom with an electrical charge, the movement of the salt ions constitutes a current that can be harnessed to generate electricity.

According to the report, "researchers at Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland have developed an osmotic power generation system that delivers never-before-seen yields."

Key to their discovery is a few atoms thick membrane made of molybdenum disulfide which they developed. The membrane has tiny holes, or nanopores, through which salt ions pass into the fresh water until the two fluids' salt concentrations become equal. As the ions pass through the nanopores, their electrons are transferred to an electrode.

Thanks to its properties, the membrane allows positively-charged ions to pass through, while pushing away most of the negatively-charged ones. That creates voltage between the two liquids as one builds up a positive charge and the other a negative charge. This voltage is what causes the current -- generated by the transfer of ions -- to flow.

According to the report, this is the first time a two-dimensional material has been used for this type of application.

The power generation potential of the new system is huge. According to their calculations, a one square metre membrane with 30 per cent of its surface covered by nanopores should be able to produce 1-MW of electricity, enough to power 50,000 standard energy-saving light bulbs, the report said.

"And since molybdenum disulfide, used for making the membrane, is easily found in nature or can be grown by chemical vapour deposition, the system could feasibly be ramped up for large-scale power generation."

The researchers were able to run a nano-transistor from the current generated by a single nanopore and thus demonstrated a self-powered nanosystem.

The report says that once the systems become more robust, osmotic power could play a major role in the generation of renewable energy by harnessing the potential of estuaries which are bodies of river water with a free connection to the open sea whose water is salty.

While solar panels require adequate sunlight and wind turbines adequate wind, osmotic energy can be produced just about any time of the day or night provided there's an estuary nearby, it says.