How mixing salt and fresh water can be an energy source

The term "blue energy" is a relatively new term. It owes its birth to a widespread natural phenomenon - the mixing of fresh and sea water at the places where rivers flow into the sea.

The essence of "blue" or osmotic energy is as follows. Imagine that two liquids, brine and water, are separated by a semi-permeable membrane. The membrane itself is designed in such a way that only water passes through, that is, it works in one direction. The resulting pressure of the water flow can be used to rotate the turbines.

Several power plants were built using this technology. But their effectiveness turned out to be extremely low.

Osmotic power plant in Norway

Researchers at the Dutch water institute Wetsus began mastering the osmotic method in a slightly different direction, which they called reverse electrodialysis. Its difference is that it is not water molecules that pass through the membrane, but salt ions.

There are 2 types of membranes in the installation: positively charged sodium ions pass through one, and negatively charged chloride ions pass through the other. The membranes form a kind of sandwich decks, in which the layers of salt and fresh water alternate with each other, thanks to two types of ion-transporting membranes. All this contributes to the generation of electricity.

Scientists are studying the effectiveness of the capacitive mixing method, when fresh and seawater are alternately fed into special chambers with two electrodes acting as capacitors, which also creates a voltage.

Thermal power plants, emitting huge amounts of carbon dioxide, could become an inexhaustible source of fossil fuels here. It turns out that by dissolving it in water, you can get carbonic acid, which decomposes into hydrogen and bicarbonate ions. Then, by capacitive mixing, a huge amount of energy can be extracted from it.