Blue Energy: the next big thing

Sustainable and widely available. What’s not to love?

Klara Zietlow
6 min readOct 26, 2020
Covering 70% of the earth’s surface, water has so much untapped potential. Photo via Pixabay.

Blue might be the new green. At least when it comes to energy.

When a river empties into the sea, huge volumes of freshwater meet salty seawater to spark a kind of chemical shock. A process called osmosis (hence the name ‘Blue-’ or ‘Osmotic Energy’), causes the freshwater to quickly disperse itself throughout the saltwater, evening out its saltiness. 🧂

The natural flow of energy generated is equal to the same volume of water falling from a 250 meter high cliff! And with only a fraction of the space.

Not only does Osmotic Power generate tons of energy, it’s also available to every single continent! A few high potential rivers include Zaire, Ganges, Nile, and Mississippi but there are many more all around the world. The best places have long coastlines or large salt lakes.

Read on to find out how this amazing process works…

It’s all thanks to our friends semipermeable membranes

There are two main ways to control the diffusion (dispersing) and harvest energy. Both rely on osmosis and semipermeable membranes.

Semipermeable membranes allow water to slip through but block solubles, such as salt, from entering*. They’re kind of like super tiny sieves.

*It’s important to note there are many types of semipermeable membranes and not all have the same functions as the one described above.

No. 1: Pressure Retarded Osmosis (PRO)

Although the name Pressure Retarded Osmosis is a mouth full, it is actually quite simple to understand.

When a semipermeable membrane is put between freshwater and saltwater, the freshwater will cross over to the saltwater to equal out the salt levels in both sections of the tank. This flow of extra water to the saltwater side builds up a vast amount of pressure. Enough pressure to spin a turbine and generate electricity. 🔌

A model of Pressure Retarded Osmosis (PRO)
A very basic model of Pressure Retarded Osmosis. Diagram by yours truly ;)

In 2009 a state-owned Norwegian company, Statkraft, opened a pilot PRO plant on the Oslo Fjord. But it only produced 5 kWh, 1/1000th of what a small nuclear plant generates, so it shut down after 4 years due to cost concerns. Even so, the plant wasn’t intended to run for the long haul and worked well as a proof-of-concept.

No. 2: Reverse Electrodialysis (RED)

While PRO uses pressure to generate electricity, Reverse Electrodialysis, or RED, takes another approach that’s a bit more complicated. Instead of using a semipermeable membrane that lets water through, RED uses membranes that let either anions or cations through, but not water.

Onions and captions, what?? I got you. Anions and cations are atoms that are either have extra or are missing electrons, making them an ion. This means they are either negatively charged (anions) or positively charged (cations). Anions and cations usually form when two atoms bond and move around their electrons.

You can think of RED as a seawater sandwich 🥪. It uses layers of water separated by semipermeable membranes to form something like a battery. The “bread” on the outside is freshwater and the “filling” on the inside is saltwater. Between the “bread” and “filling” there’s a membrane that lets either anions or cations in, like cheese with veeery small holes.

Salt is made of sodium and chloride, so in this case the anion is chloride and the cation is sodium. Dry salt molecules are hard to separate, but when they dissolve in water, atoms can float around freely separating and combining at will. Kind of like an awkward party where you only know half the people ;)

Sometimes ions in the saltwater tank will find a hole in their corresponding membrane just big enough for them to fit through. They use this to escape the party and join “their people” in the private, freshwater side room. Because each membrane only lets either anions or cations in, only ions with the same charge will be in the same room.

Over time, there will be more anions on one side and more cations on the other side as the atoms discover their secret VIP rooms. This separation of charges builds up an electrical potential that we can use on the spot or send to the electrical grid.

A model of Reverse Electrodialysis (RED)
A single section of a Reverse Electrodialysis generator. Usually there would be more sections stacked. (Created by me just for you)

Although the output of a single membrane is small, we can increase its power by stacking up lots of layers, like a club sandwich on steroids. Most of the research and development on REDs right now focuses on increasing the number of membranes working together at the same time.

Reverse Electrodialysis is happening now!

There are a couple of companies already attempting to use RED technology.

The Netherlands took their hand at it in 2014. They opened their plant, REDstack BV, on the Afsluitdijk dam, a perfect location with sea on one side and freshwater on the other. It’s still going strong today! 💪

The Afsluitdijk dam from above. Photo from Wikipedia Commons taken by MD van Leeuwen.

The EU ran a project called REAPower from 2010–2014 . It was set up at a saltworks in Sicily with reserves of highly concentrated brine (super salty water). They used this brine instead of ocean saltwater and replaced the freshwater with seawater, because of availability.

The flexibility of RED means it is compatible with lots of different places. It could even partner with desalination water plants to use their waste brine!

Ao Nang, Thailand. Photo via Unsplash.

So how close are we to a blue future?

Energy receives only a fraction of the funding that other renewable energy sources get which means there’s still lots of research needed. Still, it has made some great strides since it was first attempted in 1973.

If we want to improve the two methods of osmotic energy described above, we must first improve the membranes we use in them. Researchers around the world are hustling to come up with new membrane materials to find the most efficient match.

In December of 2019, scientists at Rutgers University made a membrane development breakthrough. Using nanotechnology, they created a membrane 8,000 times more power dense than the one it was based off of and are working to make it even more efficient. This breakthrough brings hope that Blue Energy could someday provide a big part of the world’s energy.

Rick Sieber, the director of REDstack BV says, “Compared to the development time of solar or wind power we (Blue Energy) are just starting, and we have already made a great deal of progress. When given sufficient time and money, we will continue this progress… since the runoff of rivers isn’t fluctuating on the same timescale as solar and wind power, we believe that Blue Energy can be an important energy source in the future.”

Osmotic Power is consistent, can be switched on or off at will and works at any time of day — a big advantage over solar and wind power.

Blue Energy often goes unmentioned in conversations around renewable energy. Of course it still needs much more research, but considering it has the potential to power 80% of the world’s energy and is to accessible anywhere with saltwater, I think it deserves more funding and discussion. 💙⚡

What do you think? Drop your thoughts and takeaways in the comments and leave some claps if you learned something!

Key Takeaways:

  • There are 2 main types of Osmotic Power: Pressure Retarded Osmosis and Reverse Electrodialysis
  • PRO builds up pressure to spin a turbine
  • RED separates salt molecules to build up an electrical potential
  • In order to improve both methods we need to improve the membranes they use
  • Blue Energy has great potential, it just needs more research and funding

Before you go, I’m a 13-year-old passionate about a more sustainable future and I’d love to connect on LinkedIn or by email ( Thanks so much for reading and I hope you learned something new! 🦄✨




Klara Zietlow

Passionate about the future of food and the environment. Likes animals too :)