The Blue Energy or osmotic energy is the energy that is obtained by the difference of salinity between the sea water and the river water. This type of energy has great potential to become a clean source of renewable energy, thus contributing to the fight against global warming and the depletion of traditional energy sources.
What is it and how do you get the Blue Energy?
Blue Energy uses the amount of energy released when fresh water comes into contact with seawater. The difference in salinity between these two kinds of water creates a clean renewable energy source. The process consists in the permeation of the water with low salinity to another with a higher concentration of salt, since the greater the saline difference between both solutions, the greater the amount of energy produced.
The first research on this type of osmotic energy is due to the American scientist Sidney Loeb. In the 1950s, this scientist developed a procedure for obtaining potable water through the effect of osmosis, using a synthetic membrane, sea water and high pressures.
A few years later, Loeb introduced in his research the use of a tank with two chambers separated by a semipermeable membrane. In one of the chambers was stored the salt water, and in the other the fresh water. The salt of the sea water made it to the fresh water through the membrane, generating an increase of the pressure of the side of the sea water. This pressure increase, equivalent to a water column of 120 meters, was used to move a turbine and generate electricity.
Based on this discovery, there are currently two lines of research, one based on Loeb’s technology, and another that seeks the effect of reverse electrodialysis.
Based on the prototype of Loeb, an experimental blue power plant is in operation in Tofte (Norway) since 2009. This plant tests and investigates the use of different types of membranes and designs. Also, the Lumière Matière Institute of Lyon has developed an experimental device that is supposed to be a thousand times more efficient than any other system.
On the other hand, Dr. Mauro Pasta’s research line focuses on the creation of a device called Entropy Battery.
Entropy as a way to generate electricity
Every system contains entropy, that is, some measure of disorder. In a closed system the entropy tends to increase according to the second principle of thermodynamics. Based on this premise, if we take a glass of pure water and a crystal of salt separately, each of them contains less entropy than if we mix them. Once mixed, to separate them again we have to use energy.
If energy is needed to separate the water from the salt, energy can also be obtained by mixing the water with the salt. From this arises the research on the generation of electricity thanks to the difference between the salinity of the fresh water and the sea water.
The advantage of Dr. Mauro Pasta’s research compared to the membrane prototypes noted above is that, for the moment, the membranes are fragile and the implementation of such systems is a great investment. While creating an entropy battery is very simple. It is based on two electrodes immersed in a liquid containing ions, ie an electrolyte. The interaction of fresh water ions with salt water gives rise to such a salt water concentration that there comes a time when the electrodes can not contain more ions. When we reach this phase, it is when we can produce electrical energy.
This research has focused on the use of manganese dioxide as a positive electrode because it is not harmful to the environment. On the other hand, the negative electrode, which until now we have used, is silver, with which we have obtained very good results. The only obstacle to developing the project is that the use of silver electrodes can make the process more expensive.
For this reason, Mauro Pasta continues to research in the same line, to develop the operation of the entropy battery. Studies have shown that you can achieve a 74% efficiency in the extraction of energy using this type of battery.
The energy potential that can be obtained is 2TW, which means 13% of the total energy consumed in the entire planet.
