Ocean Grazer
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The start-up Ocean Grazer is focused on the multi-purpose use of sustainable energy locations in oceans. That is what Marijn van Rooij, CTO of Ocean Grazer, attests to as being badly needed when it comes to meeting energy targets. “With our system for offshore wind farms, we are also able to generate energy from waves, as well as store excess energy which gets used at some other point in time.”

Prior to this large system being expanded upon, the company first wants to put separate components on the market. Starting with a storage system which harnesses excess energy from wind. This system will be placed underwater in offshore wind farms. It works like a mini hydropower plant. “It pumps water out of an internal reservoir under low pressure, counter to the pressure of the ocean. Actually, it acts like a balloon that is being blown up. By opening a valve, the water from the ocean is pushed back into the reservoir. We are able to harness energy through a hydropower turbine this way,” van Rooij explains.

How does your product distinguish itself in the market?

By using a reservoir for energy, whereby variances between supply and demand are dealt with. “Sustainable energy sources such as wind and sun are variable sources. When the wind blows, energy is generated, otherwise it isn’t.  A buffer of gas-powered energy then compensates for any shortage,” Van Rooij explains further. “By storing this sustainable energy in our system, that buffer of gas-powered energy is needed less and less.”

The variances in supply and demand of energy can vary per microsecond, per season and everything that lies in between. “On a microsecond level, it is important to keep the grid frequency stable at 50 Hz, as here the system must be able to react extremely quickly. The smaller the time scale, the more charge and discharge cycles you have within the storage system,” explains van Rooij.

“Our system has an almost infinite number of charge and discharge cycles. This means that the amount of storage space does not/barely deteriorates over time. This makes our system more practical and durable than lithium-ion batteries. In effect, battery capacities are significanty reduced within a few years. That makes the use of batteries extremely expensive and hazardous to the environment.” Moreover, Ocean Grazer’s reservoir system can be implemented on a huge scale according to van Rooij. That’s also much more diffuicult for batteries.

Yet batteries and other forms of energy storage are still needed, finds van Rooij. “We need energy storage on every level. We can also make use of CAES (compressed air energy storage) for storage over long periods of time, such as days, weeks or seasons. For instance, for water reservoirs or for hydrogen.”

What is your greatest motivation?

“We stand for the multi-purpose use of available space. The North Sea is being filled up with wind farms that are affecting shipping and fishing, among other things. These windmills do not always generate sufficient energy to meet the targets regarding sustainable energy. If we want to achieve these goals, we must link technologies up with each other in order to harvest enough from the various locations. In addition, by using our storage system, we are able to ensure that energy generated by wind turbines, for instance, is not lost.”

What was the biggest obstacle that you had to overcome?

“The biggest challenge was finding the balance between developing the technology and getting funding. The amount of time that you invest in securing financial resources leads to a stagnation in technological development. You have several possibilities in the Netherlands where this is concerned, such as subsidies, loans and investors. Yet applying for these requires special skills. We’ve been working hard on this over the past year, so that should now start to pay off.”

“The investments are really needed in order to be able to develop the product further. We have recently been doing tests mainly in a laboratory and now really want to do tests in a harbour. That requires a lot of money. Which poses a dilemma. On the one hand you need the finacial resources to be able to keep on developing, yet on the other, you need to show what the product is and what has been developed in order to get those resources,. ”

What was the most rewarding moment for you?

“It was a wonderful moment for me when we managed to get the investment we needed to really get this start-up going. For this, we went from thinking in terms of  university research to thinking in terms of business. We have succeeded in bringing these two things together. After that, we had several wonderful moments, for example, when the prototypes were ready. We had worked on them for quite a long time, so when we put them in the water and they actually work -that feels great.”

What can we expect from you in the coming year?

“We have already tested the system on a smaller scale and are now scaling up the tests. Currently, we are also busy with a prototype for a storage system that will be tested in a deep water tank in the laboratory. Next year, we want to test the new storage system in an actual harbour. We have Eemshaven in mind for this. It is a major challenge to apply for licences approving tests in a real-world setting. We have now started that process on time.”

What is your ultimate goal?

“We are now busy with specialized technologies that we can put on the market one by one. Ultimately, we are working towards developing the Hybrid Ocean Grazer, a system in which all of these technologies come together. This is how we will make optimum use of a location in order to generate and harness sustainable energy.  Following that, we are looking at a global roll out so that it really ends up in all of the big oceans of the world.”

Ocean Grazer

Background information


Anthonis Vakis, Bayu Jayawardhana, Marijn van Rooij and Frits Bliek. Bliek has a background in the industry. The others come from the Nation University of Groningen. A professor at the university first launched the concept.

We still do a lot of research into this concept at the university. More than 70 students there have taken part so far.

Year founded

Research began in 2014. It was not until 2018 that the company was actually established.


Revenue is one of the difficult issues. A lot of money must first be invested in the project before it can yield a profit.


There are currently two students doing internships with us, one from France and one from the Netherlands. We are also looking for two new employees.

Ultimate goal in a few words

The realization of hybrid systems, linking diverse resources together with a storage technology.

Need inspiration? All of our earlier Start-ups of the Day can be found here.