As we’ve mentioned previously, obtaining energy from water is one of the oldest and most effective methods. But today we’re not talking about water mills or underwater turbines—instead, it’s the relationship between freshwater and saltwater that takes center stage.
Osmosis. Freshwater, saltwater, and a semipermeable membrane. Of course, the water doesn’t need to be "salty"—any other solute works (sugar, for example), but the general idea remains: part of the freshwater "passes" through the membrane into the saltwater side, creating extra pressure. As a physical process so critical to life, many of our readers have probably seen it in small experiments during biology or natural science classes, but osmosis could become an extraordinary energy source if the cost-benefit relationship is right. The Statkraft group built a prototype osmotic plant in Hurum (Norway), and although it managed to produce about 4 kilowatts, Statkraft decided to shut it down for several reasons: low energy, high maintenance, more competitive technologies, and a long etcetera.
A Membrane Just Three Atoms Thick
According to a study published in Nature by researchers from Switzerland’s EPFL and the University of Illinois (Urbana-Champaign), a new type of ultra-thin semipermeable membrane far surpasses all previous developments. What does 'ultra-thin' mean? Just three atoms —and the main material is molybdenum disulfide, something we usually see used as a lubricant. The nanopores in this membrane become "osmotic generators" with outstanding energy density. The official text mentions one megawatt per square meter of membrane, enough for about 750 homes.
The big problem this technology faces (for now) is in creating the membrane itself. The researchers conducted experiments with a single nanopore, and to reach that desired megawatt of energy, a square meter of membrane would need millions—which need to be drilled with precision, and economically. In a few years, we’ll likely be talking about osmosis again. Patience.
Source: Popular Science
