Innovatia

enough pressure that it causes the level in the saltwater chamber to rise. This heightened pressure is then used to drive a turbine. Alas the operating costs were too high and it was back to the drawing board. Then in 2014 another plant opened, this time using Reverse Electrodialysis (RED). In RED, alternating layers of saltwater and freshwater are separated by ion-exchange membranes—ones that allow either positive or negative ions to pass through but not both. When the ions naturally move from the salt-

water to the freshwater, an electric current is generated. Again, it worked, but was too ex- pensive to run. Enter nanotechnology. A membrane was finally produced in 2016 that only allowed salt ions to cross. One square metre of this membrane could potentially produce one megawatt of power, enough for 50,000 en- ergy-efficient lightbulbs. And while this is still difficult to scales, it could potentially be used to power small devices. Small-scale RED devices could be integrated into monitoring systems placed in estuaries or rivers. These systems could power themselves by using the naturally occurring salinity gradient between river water and seawater to generate electric- ity. In remote locations or settings where access to the grid or traditional charging methods is inconvenient, reverse electrodialysis could be a potential power source for Internet of Things devices. These devices typically re- quire only a small amount of energy, making them well-suited for RED applications. The same principles are being used in “ion- tronics”. Unlike traditional electronics that depend on the movement of electrons to transmit and process information or perform tasks, iontronic devices rely on the flow on ions. Some possible applications of this new technology include the creation of energy-ef- ficient displays for phones, tablets or TVs, or the production of batteries that can store more energy. If “blue energy” were to be fully harnessed, it could potentially generate 80 percent of the world’s energy consumption needs.

ENERGY By Rose Lane T hese days, we hear a lot about “green” energy. But have you heard of “blue en- ergy”? Also called “osmotic power” it occurs when salt meets fresh water, as at the mouth of a river. It involves passing the water either side of a membrane. If salt water passes a semipermeable membrane on the other side of which is fresh water, the two solutions will try to even up: the law of osmosis. This move- ment across the membrane thus generates electricity. Provided the fresh water is kept at a constant volume it will keep moving across the membrane. There are a couple of ways to do this and they have so far been successful, albeit cur- rently difficult to scale. The original mem- branes were originally too expensive to pro- duce so development faltered. In 2009 Norway opened a power station run on blue energy by using Pressure Retarded Osmosis. In this method, freshwater is pumped into a chamber separated from a saltwater chamber but under

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