Salt Water Osmosis: Will Our Deltas Help Solve the Energy Crisis?

As the planet gradually recognizes the threat of global climate change, innovators and experts in nearly every country are proposing and testing a wide array of renewable energy solutions. One of these options involves the reversed osmosis of salt and chlorine between saltwater and freshwater supplies.

Salt Water Osmosis: Will Our Deltas Help Solve the Energy Crisis?
By: Anthony Pannullo

REDstack

“Blue energy”, the nickname of this potential renewable, is currently undergoing small-scale testing by a Dutch research company, REDstack BV. Universities representing the countries of Italy, Spain, Poland, and the Netherlands are on board with this test, known as Capmix. Test plants and projects are essential to figuring out how a renewable energy source would operate as a large-scale, real life solution. So far, one blue energy plant is expected to power nearly one hundred homes.  

How does it work?

The process creates a “battery” using a basic chemistry concept known as osmosis. As you may remember from chemistry class, osmosis applied to this case refers to the movement of water molecules across a membrane. Molecules will move from areas of high concentration, to areas of low concentration. This source uses what is known as “reversed electrodialysis”, or the RED in REDstack BV.  

Saltwater and freshwater are divided by filters. The sodium ions in the saltwater have a positive charge. Sodium ions pass through the filter toward the freshwater side, while chlorine ions holding a negative charge pass from the freshwater to the saltwater side. Just like an ordinary household battery, this process uses the energy transfer between a cation and an anion.
Let’s refer to this diagram for a visual representation of reversed osmosis:
Reverse Electrodyalisis

In this reversed osmosis diagram, we see the high sodium concentrations of negatively charged chlorine (Cl-) anions moving toward areas of low chlorine concentration. Simultaneously, the positively charged sodium (Na+) cations are moving from areas of high concentration toward low concentration in the opposite direction. The filters placed within the system will regulate the flow between the two ions.

Energizing Deltas

The Dutch, who already hold a global reputation in the field of water security, are presently experimenting with a related renewable hydropower model of “Energizing Deltas”. A delta is the site of sediment deposition, typically found at the end of a river or lake as it empties into another body of water. In the Netherlands, engineers are studying the prospects of placing turbines where the Ijssel Lake empties into the Wadden Sea.  Dikes, or levees, are already used in the region for flood control. These dikes are a sort of dam which is used to control water levels. The idea of Energizing Deltas in the city of Afsluitdijk, Netherlands aims to use an already-existing system that could be modified to produce clean, renewable energy.
http://www.dutchwatersector.com/uploads/2014/11/dws-redstack-demo-opening-fresh-salt-scheme2-350px.jpg

Is Reversed Electrodialysis too Good to be True?

Here’s the catch. The first RED plant opened only within the last five years. Much like many of the solutions we may see in the next decade, this is still undergoing the testing phase to study the capabilities of the system. In fact, even the membrane filters themselves are still subject to tests. After the technology within the system proves plausible, scientists and engineers will have to determine its affect on local wildlife, the human population, and of course the economic consequences. In a sustainable system, the goal is to develop RED technology to be economically beneficial. The final result should not harm the local ecosystem, or interfere negatively with humans.  
A bit of initial energy is required to jumpstart the process, but from that point, the flow between saltwater and freshwater should happen automatically. The process will require a pump to continue the flow through the system, but the plan is clearly to get a higher energy return than the invested initial energy.

ConclusionThe consensus is that reversed electrodialysis is possible to at least provide some energy to local communities. This technology would so far only be helpful in large delta regions, such as the Mississippi River delta in the United States for example. It would not produce enough power to drive the state of Mississippi, but any little bit helps to reduce our carbon footprint. The bottom line is to create a large-scale plant that will not use more energy and resources than it produces. No renewable energy source can solve the global energy and climate crisis alone. The goal is to diversify our options, and to use the best form of renewable energy that is appropriate in a particular area.

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