What is blue energy?

Much has rained since the middle of the last century when Professor Pattle ventured that the saline differential between the compositions of the salt water of the sea and the fresh water of the rivers at its mouth could generate a variation of osmotic pressure called blue energy.

That is, by separating both liquids by a special semi-permeable membrane, the fresh water would naturally flow into the chamber with salt water to decrease the salt concentration. By maintaining the volume of this fixed chamber, the pressure on this side of the salt water would increase and could theoretically be used to move a turbine that, in turn, would generate electricity.

And we are not talking about a testimonial production: there are studies that indicate that, if it were used, it could cover 80% of the world's energy needs. Until then, the eureka moment arrived, because, at that time, there was no technology that could take advantage of such an energetic torrent. It was necessary to go into practice.

In the year 73, an American professor named Sidney Loeb, inspired by the differential salt differential between the Dead Sea and the Jordan River, developed a membrane system based on delayed osmotic pressure, the so-called PRO system, which uses developed membranes ad hoc to apply the principle pointed out by Professor Pattle.

Very high cost

The problem was that the cost of manufacturing the membranes was prohibitive. It would take years for this to be reduced significantly.

Finally, in 2009, a plant with this technology was inaugurated in Tofte (Norway). However, it was also not the time to uncork the champagne: it barely produced 10 KW of electricity, with a yield of 1 W / m2.

In addition, due to the bacterial action, the orifices of the membranes were clogging and losing effectiveness. In 2013 they decided to close the project. It was time to try another complementary technology.

It was Loeb himself who, four years after developing the PRO system, announced the technique of reverse electrodialysis (RED). This time, instead of taking advantage of the water pressure, the focus was to take advantage of the positive and negative charges in a body of salt water and another of fresh water, separated by a membrane with an applied electric current.

With this system, it is the salts that pass through the membrane in such a way that one side allows only positive ions to pass to the cathode, while the other only passes the negative ones towards the anode. From there, the movement of the electric charge is generated and exploited.

The first plant with the RED system was inaugurated in Holland in 2014, thanks to a project by Wetsus, the Dutch Water Institute, in Leeuwarden. stack, the resulting company, has been working on electricity generation since then, with a production of 50 KW.

Nanotechnology comes to the rescue

However, new advances point towards a truly efficient and competitive system to capitalize, once and for all, the energy potential of osmosis.

The key was to reduce the size of the holes for the ions to cross the membrane at an atomic scale. Thus, at the end of 2016, the development of a new molybdenum disulfide membrane of three atoms in thickness with the potential capacity to produce 1 MW per square meter was published in Nature.

That is, that surface could light 50,000 low-energy bulbs. Apart from its low cost, another advantage of this material is that industrial plants would not be needed, but that the membranes could be placed directly in the estuaries of the rivers to generate electricity.