Osmotic energy is a type of energy that does not depend on the wind, nor the sun, nor giant turbines. Its source is in something as everyday as water, and more specifically, in the meeting between fresh water and salt water.
The curious thing is that, despite being a relatively little known technology for the general public, it is one of the most promising for the coming years. Why? Because it is clean, stable, silent, does not depend on meteorological conditions and is constantly available. Each river that flows into the sea generates an exact point where this energy can be harnessed. Let us see what osmotic energy is.
What is osmotic energy?
The best way to understand what osmotic energy is to imagine the two types of water with different salinity, the fresh water coming from a river and the salt water coming from the sea. When these two waters meet, a physical phenomenon called osmosis occurs, a natural process in which fresh water tends to pass into salt water to balance the salt concentration.
That movement is so powerful that it can be transformed into energy. In fact, osmotic energy is based precisely on taking advantage of that difference in concentration between the two types of water to generate electricity. The most important thing is that this type of energy:
- Is renewable, because rivers and seas will always exist.
- Is predictable, since it does not depend on the weather.
- Is constant, something that does not happen with solar or wind.
- Is clean, without emissions or waste.
How osmotic energy or blue energy works
The basis of osmosis energy is simple, although its practical application requires advanced engineering. The process works thanks to a semipermeable membrane, designed to let only fresh water pass but not salt water. Let us see it step by step.
1. Two tanks separated by a special membrane are placed
On one side fresh water is put and on the other salt water. The membrane allows fresh water to cross towards the salt water, but not the other way around.
2. Fresh water begins to pass towards the salt water
Nature seeks balance, so water with lower salt concentration flows towards the one with higher concentration. That movement generates osmotic pressure, which is the key to everything.
3. The generated pressure moves a turbine
When the water passes to the salty side, the volume increases and creates enough pressure to move a hydraulic turbine. The turbine, in turn, produces electricity. This process is known as PRO (Pressure Retarded Osmosis), one of the most used methods to generate blue energy.
4. Electricity is generated continuously
Unlike other renewable energies, this osmotic flow:
- Does not depend on whether it is day or night
- Does not depend on the weather
- Does not generate noise
- Does not alter the landscape
It only needs the constant presence of fresh water entering the sea, something that happens in thousands of points on the planet every second.
5. The RED method also exists
In addition to the PRO method, there is RED (Reverse Electrodialysis). It works through membranes that allow the passage of salt ions, generating a direct electrical current without turbines. Both methods have significant advances and are being tested in places like Norway, Japan and the Netherlands.
Summarizing all this, osmotic energy works taking advantage of the natural movement of fresh water towards salt water, transforming that physical process into renewable energy.
Advantages of osmosis energy
Now that we know what osmotic energy is within renewable energies, it is undeniable that it has a set of unique advantages that make it a very serious candidate to complement the energy matrix of the future. The most important are these:
- It is a constant and predictable energy. Unlike the sun and wind, which can vary depending on the time of day or the weather, the meeting between a river and the sea is constant. This makes osmotic energy stable, ideal as base energy for the grid and perfect for compensating the intermittency of other renewables.
- It does not alter the landscape. Blue energy plants can be built near river mouths, semi buried or integrated into existing structures. They do not require giant turbines or infrastructures visible from miles away.
- It does not produce polluting emissions. There is no combustion, no smoke, no CO2, the process is completely clean.
- Takes advantage of natural resources that already exist. It does not need external raw material. It only uses fresh water and salt water, two abundant and renewable elements.
- It is silent. This detail may seem minor, but noise pollution is a clear disadvantage in wind energy. Osmosis energy does not generate noise.
- It can work continuously. That means it is perfect to complement electrical grids, give stability to hybrid systems and work as a backup for solar energy.
- It has a huge untapped potential. The International Energy Agency points out that osmotic energy could generate up to 2000 TWh per year, almost the same as all current hydroelectric power.
Disadvantages of blue energy
Although it is promising, it still has important challenges to explain to be completely honest.
- The technology is still expensive. Semipermeable membranes, especially in large installations, are expensive and require maintenance. In addition the membranes can get dirty, in fact there is the phenomenon known as fouling, caused by sediments, microorganisms and particles, which reduces performance having to give it periodic maintenance.
- Lack of scalability and need for specific locations. There are still few industrial scale plants and, to work, it requires a stable flow of fresh water, which is close to the sea and that there is an absence of extreme pollution that can damage the membranes.
- Moderate energy production. Although stable, its energy density is lower than other sources such as traditional hydroelectric. Its ideal role is that of complementary energy, not substituting all the others.
What differentiates osmotic energy from other types of energy?
This is very important because it helps to situate osmotic energy within the current renewable map. Let us see these differences.
1. Compared to solar energy
Solar generates more energy in less space but it is intermittent and depends on the weather. Osmotic is constant and predictable.
2. Compared to wind energy
Wind can produce huge energy peaks but the wind is very irregular. Osmosis energy does not fluctuate.
3. Compared to hydroelectric
Hydro needs dams, large flows and huge works while osmotic can be built without major environmental impacts.
4. Compared to tidal energy
Tidal depends on cyclic tides, so it produces but not always. Osmotic does not depend on the state of the sea, only on the mixture with fresh water.
5. Compared to geothermal
Geothermal requires specific geological zones and, on the other hand, osmotic is available in thousands of rivers in the world.
As you have already seen what osmotic energy is, you will have reached the same conclusion as us, and it is that this energy does not compete with other renewables, it complements them. Thanks to its stability, its ideal role is to balance the grid and guarantee continuous supply when other sources drop.
