Osmotic power, also known as salinity gradient energy or blue energy, is an alternative energy form providing renewable and sustainable power. It’s based on naturally occurring processes when fresh water meets salty sea water. When both water bodies mix together they diffuse to reach stability. This process of mixing releases energy. The energy produced relies on the evaporation to separate water from salt.
Our so called ‘blue planet’ consist mainly of water. About 97% of it is salt water, the other 3% is suitable for drinking. However, the chemical difference between salt and fresh water could provide us with an endless supply of energy. This is what’s called salinity gradient energy. The theory has been around since the 50’s but it was not until the 70’s when actual potential power availability was estimated. Since 2014, thanks to technological advancements and lower costs, Blue Energy is becoming a reality.
There are several existing salinity gradient methods to produce energy. The most advanced today is Reverse ElectroDialysis (RED). Energy is harvested from the difference in salt concentrations which pass through a semipermeable membrane. The membrane allows water to pass freely but acts as a barrier to salt. The RED method diverts ions in the water which creates an electric potential between two electrodes. With fresh water on the outside and seawater sandwiched in the middle between the anion and cation membrane, an ion flux will occur. This ultimately creates a saline battery. A series of these batteries are stacked on top of each other to create a higher power output.The RED salinity gradient method is not restricted to only fresh and sea water. Any concentration of salt water will do just fine. This means that energy could be generated out of industrial waste water flows, returning energy back to the industry.
Due to the fact that rivers keep flowing into the sea, salinity gradient power generation is available to produce energy 24/7. Even though it’s a very young technology still under development, Blue Energy does look like a promising additional energy source. It’s both renewable and not fluctuating as solar and wind power. Thanks to this constant energy source it’s possible to switch it on and off depending on the demand of the electricity grid. This is currently only true for coal, gas and nuclear energy production. Combining Blue, wind and solar energy might make up the chain of 100% renewable energy we’ve all been looking for.When planning Blue Energy plants on an industrial level it’s advisable to keep in mind marine and river environments. Aquatic plants and animals are adapted to thrive best in their own specific balanced water environment. Discharging of brackish water, the main waste product of salinity gradient technology, could cause salinity fluctuations. Intolerance of species to these fluctuations might lead to low densities of these populations. However, this effect could be minimised by pumping brackish water out to sea and away from any local ecosystems.