A team of researchers at Penn State have been studying this relatively unused source of energy. It isn’t new because the sources have always been there, but it was extremely inefficient to use. Methods used to extract that electricity were either difficult to do or it wasn’t worth the effort in achieving it.
Those methods are pressure-retarded osmosis, reverse electrodialysis, and capacitive mixing. PRO is where freshwater is removed from saltwater through a semipermeable membrane process, which is osmosis. RED pushes the water through cation and anion membranes on a slope which sparks that electricity. CapMix also creates that voltage when electrodes are placed into a saline solution with varying salt levels.
PRO has been the most successful process of the three, but membranes go bad in the process. Christopher Gorski, Penn State’s Assistant Professor in Environmental Engineering, “that bacteria grows on them or particles get stuck on their surfaces, and they no longer transport water through them.” The other two processes don’t have the blockage problem, but it also doesn’t create enough electricity.
How are those last two processes fixed? By simply combining them together. There are two channels created and are separated by a membrane. Electrodes are placed in both channels, and each of them get the flow of either freshwater or saltwater. That flow alternates down the channels, and graphite foil is put in the path to be a current collector.
Gorski explains that electricity generation is achieved due to “salt going to the electrodes” and “chloride transferring across the membrane.” With the customized process of using both methods at one, that creates much more electricity than doing it separately. According to the report, they created 12.6 watts per square meter.
That’s much higher than the 2.9 watts per square meter obtained through RED and surpases the record high for PRO at 9.2 watts per square meter. In theory, this process being used at coastal convergences could create roughly 40 percent of the global energy requirement.
More testing needs to be done in order for that to become a reality, however. How long will the electrodes last in the separate channels? Will other aspects of the seawater degrade the performance of this method? Ultimately, the process sounds like another potential big hit for hydroelectricity.