Hydroelectric station on seabed to store energy

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Pioneering SME: Ocean Grazer

Ocean Grazer has developed a hydraulic battery to optimally match the supply and demand of electricity. The Ocean Battery is operating on water pressure and can reduce electricity costs by 15%. The underwater hydroelectric station is also scalable, environmentally friendly and solves congestion problems. A prototype will soon be tested in the Eemshaven, says director Frits Bliek.

What is the problem that you have found a solution for?

“The offshore wind industry has a great need for techniques to transform intermittent renewable energy sources into dispatchable power generators to allow delivery precisely when the market demands it. Because the supply of wind energy fluctuates and is not accurately predictable, imbalance can arise. This disrupts both the electricity grid and the electricity market. Moreover, energy prices regularly fall so sharply that it is unattractive to supply electricity. The temporary storage of electricity can solve this. At the moment there are super capacitors that store and supply electricity with a very sort response time. However, these lithium-ion super batteries degrade over time. They are at the end of their lifespan after 3,500 - 15,000 charges and discharges. Considering that there are an average of 10 cycles per day, or 3500 times a year, they should be replaced after about one to four years. Offshore, this is an expensive operation. In addition, flow batteries are on the rise. Due to the chemical liquids, it can be expected that these electrochemical batteries will cause the necessary problems with permits. Finally, there are plans for hydrogen conversion and energy islands to create energy buffers. Apart from the billions of euros in investments, these will always be one-off, unique designs. Our solution does not have all these disadvantages.”

What is the core of your solution?

“We have developed a kind of hydropower plant that stores and supplies electricity on the seabed, for minutes to several days. It is a closed ‘box’ with a tubing and a rubber roof. When the battery is fully charged, the water has the same pressure as the sea water. The surplus of renewable electricity generated by a wind turbine, floating solar panels or wave energy can drive the pumps in the engine room to move water into the flexible reservoir (the space between the pipes and the roof). When discharged, the hydraulic pumps drive turbines to produce electricity. The deeper the water, the higher the differential pressure and the better the price/performance ratio. The rubber roof is made of EPDM which is also used for inflatable flood defenses in rivers. The Ocean Battery is 70x70x10 meters in size and has a storage volume of about 10 MWh.

The Ocean Battery builds on an idea from the University of Groningen in 2011 for a hybrid wave generation and energy storage system. In order to accelerate market introduction, we have decided to focus on the most advanced and demanded energy storage system first; after 30 years of development, wave energy has not led to large scale commercialization. ”

What is so pioneering about your product?

“The Ocean Battery is an out-of-the-box solution. We bring existing techniques together into a complex closed system in such a way that it meets the high technology and market requirements. The shape of the membrane for the roof is also unique. This is not because of the high forces - the pressure on both sides of the membrane is the same - , but you don't want it to crack because it folds in half and wrinkles when charging and discharging. It is not without reason that we have applied for two patents. ”

What are the benefits of your system?

“The Ocean Battery is scalable, environmentally friendly and avoids congestion. An average wind farm of 750 MW requires an estimated 150 MWh  of storage. That means 15 installations. The closed ‘box’ requires little maintenance and can last 15-20 years without any problems. Because only water is pumped around, it is environmentally friendly. So even if the roof leaks, at most water is released. A hydraulic battery also better matches the electromechanical nature of the offshore wind industry than electrochemical variants.

The system runs within 30 seconds to 2 minutes and can be tuned. Not as fast as super capacitors of Li-ion, but fast enough for frequency control. The Ocean Battery can reduce the Level Cost of Electricity by 15% under the current market conditions. That is a significant cost reduction. We achieve this through a combination of congestion management (avoiding switching of wind turbines), limiting imbalance costs (due to the unpredictable behaviour of the wind) and trading on the electricity market.”

What are your challenges?

“Developing a business model that suits all of our customers is the biggest challenge for energy storage. The added value for producers and wind farm owners is evident, but we believe that it is also a solution for end users such as data centers, that need 100% renewable energy to keep their  license to operate. Moreover, our system is attractive to a network operator like TenneT to manage grid congestion. However, the regulatory framework does not allow grid operators to own storage assets as they could influence the market prices. On the other hand, the availability of storage capacity has to be guaranteed over a long period of time for such applications. A business model with (partial) asset ownership would normally be the first solution to look into. Technically, the validation and upscaling are our biggest challenges.”

How far are you now?

“In September we will install and test a prototype on the bottom of the Eemshaven in the north of the Netherlands. That will succeed certainly. Together with knowledge institutes Deltares and Marin, we carry out a series of tests to investigate the reliability and the offshore installation procedures. We are also in one of the two remaining consortia for the Hollandse Kust Noord V site. The interest  of potential customers is certainly quite high.”

What are your next steps?

“It makes the most sense to integrate the Ocean Battery into the design of future wind farms. We aim to test a full-scale battery by 2022. At that time, we prefer to work together with producers, wind farm owners, end users or network operators for efficient upscaling.”

What are the benefits of Offshore Wind Innovators and TKI Wind at Sea?

“They are very valuable for building a network. They link us with interested customers and give us the opportunity to increase our awareness. We have not yet applied for a subsidy via TKI Wind op Zee, but we are working on that.”