Power plant on Afsluitdijk in continual development

Magic. What REDstack does, seems a bit like it. The company’s plant on the Afsluitdijk draws electricity from the water. Not through hydropower, but through the difference in salt content between salt water and fresh water. The Wetsus spin-off is on the eve of a major upscaling.

Rik Siebers, director Redstack. (Photos: Pepijn van den Broeke)

Large barrels, lots of pipes and big machines can be seen in the building on the Breezanddijk, an area of sand land in the middle of the Afsluitdijk. Outside, there are more plants. The sound of running water is ever-present and the smell of seawater wafts by. The electricity produced here flows directly into the grid. Electricity that is made without CO2 emissions, which can be generated continuously and very flexibly, independently of sun and wind.

“We have calculated that ten to fifteen percent of the global energy demand can be met by this system,” says Rik Siebers. He is the director of REDstack, the company that develops this technology. “Our goal is to eventually sell the stacks, which are the systems that extract electricity from fresh and salt water. They can be used in many places around the world, because there are many rivers flowing into the sea.”


The development of this technology has been going on for years to achieve this goal. RED stands for Reverse Electrodialysis, the chemical process that takes place in the plant. It makes use of the difference in salt concentration. By mixing fresh water and salt water in a controlled way, it generates a movement of charged particles. In the plant, positively and negatively charged particles are separated using membranes. This creates, as it were, a large battery with a plus and minus side: Blue Energy.

The theory that this is possible has existed for 65 years, but the question of whether the method can be made profitable in practice has remained unanswered for a long time. Until Jan Post, a Wetsus researcher, gained his doctorate on this subject in 2009. REDstack joined forces with various market parties, governments and funds to create the pilot plant on the Afsluitdijk.

“Then you discover that sometimes it’s just a little bit different in real life than it is in a laboratory,” says Siebers. “We had to deal with barnacles in the water inlet, with all sorts of organisms that affected the operation of the plant. That’s exactly what such a pilot plant is for, to test in practice and solve problems.”


Test location Redstack at the Afsluitdijk. 

International research

For the latter of which a special room has been set up in the building. It is the laboratory, where students, researchers and PhD students from numerous educational institutions can figure out which parts of the technology can be done differently and better. Other ways to filter seawater, for example, ways to make the membranes more effective, and more. “I call this our nursery. This is where great ideas come into being.”

The relationship with knowledge institutions is a bit like the nature of the technology itself. “It’s one big interaction with mutual benefits. We take advantage of all the research while the students and PhD students have the space to do wonderful projects. These are not just researchers from Friesland or the Northern Netherlands. We work closely together with the Eindhoven University of Technology and even with many institutions abroad. Next to the ten or so permanent employees, there are always students and researchers walking around here.”

All of this says something about the potential of the technology, which will soon have to be proven on a larger scale. REDstack is busy finding a site and the funding to scale up the pilot plant. “It’ll take a few more years and then we’ll have a demo plant twenty times the size of this pilot plant. We also want to be able to expand to a commercial power plant on this same site.”


Green hydrogen

An interesting ‘by-catch’ of the way REDstack generates energy is completely green hydrogen. This occurs when the energy is converted into electrical power. REDstack is looking at how the green hydrogen can be extracted and stored at the plant. Hydrogen is suitable for storing energy for a longer period of time. It can improve the flexibility of the power supply.



Wetsus is the European centre of excellence for sustainable water technology, part of the Water Campus Leeuwarden. Companies and knowledge institutes from all over Europe work together here on innovations that help solve water problems in the world and tackle other challenges with the help of water technology.