The osmotic or blue energy arises from taking advantage of the difference in salinity between the water of the rivers and that of the sea. The progress in nanotechnology science has given a second chance to osmotic or blue energy, a technique discovered fifty years ago but which had not been developed so far due to its high cost and technological requirements.
The basics of the osmotic or blue energy
The process is basically simple and is based on filtering the water of estuaries, where seawater meets with the water of the rivers, by means of a semipermeable membrane that goes from the liquid with the highest salt concentration to the lowest and prevents the entry of sediments or particles that can cause the circuit to run aground.
The osmotic pressure generated is derived to a turbine connected to a generator to produce electricity, without intermittences and without the need of storage inherent to other renewable processes, among which are solar photovoltaic or wind.
The new advances point towards an efficient and competitive system and the key is to reduce the size of the membranes’ pores for the ions to cross the membrane at an atomic scale.
Two complementary systems of this renewable energy source are currently being developed, both based on the use of membranes, an element where the improvements have been made, namely, delayed pressure osmosis and reverse electrodialysis.
The first uses technologies focused on contacting the two fluids (river water and seawater) through a specific membrane that allows water to pass through but not the salts.
On the contrary, in reverse electrodialysis, it is the dissolved salt and not the water that passes through the membrane.
In both cases, however, a pressure difference is generated that can be used to produce energy.
Nanotechnology helps the osmotic or blue energy production
In this regard, a study was conducted by the researchers of the Nanometric Biology Laboratory of the Federal Polytechnic School of Lausanne, in Switzerland.
The innovative procedure consists of separating two compartments filled with liquid by means of an ultra-thin membrane of molybdenum disulfide (MoS2) of barely three atoms of thickness that has a nanopore through which the ions of the seawater pass toward those of the river water until the salt concentrations in both liquids equalize.
The MoS2 is easily found in nature or can be created by the deposition of chemical vapors, something that makes large-scale production of the system feasible. In addition to its low costs, among the advantages of the innovative membrane is the one that it could be placed directly in the estuaries of the rivers to generate electricity.
Osmotic energy or blue energy plants can be built anywhere a stream of fresh water flowing into the sea is present, as long as the salt concentration is high enough.
Norway and the Netherlands are the countries that have opted for the development of blue energy, so far
The Norwegian company Statkraft launched a pilot plant in a fjord 60 kilometers from Oslo in 2009 at the Sodra Cell Tofte facility, a paper manufacturer in the city of Hurum.
In the same line, the Netherlands inaugurated in 2014 a salinity power plant at the mouth of the Rhine, where it channels water from the North Sea and the river to take advantage of its potential.
According to the researchers’ calculations, the potential of the new method is immense as a membrane of only one square meter, build with nanotechnology, should generate 1 megawatt of electricity, enough energy to light 50,000 modern bulbs. In the same line, an osmotic or blue energy plant the size of a football stadium could supply electricity to around 30,000 homes. It would not generate pollutants into the atmosphere or the water streams and could be built underground, minimizing the visual impact.