Utility scale ocean battery, a bedfellow for floating PV


From pv magazine Global. 

Dutch start-up Ocean Grazer grabbed the limelight at the Consumer Electronics Show (CES 2022) in Las Vegas last week, where its new design for an offshore energy storage system based on hydro dam technology garnered the “Best of Innovation” award.

The Ocean Battery is a pumped hydro system in a box. Buried in the seabed, the battery provides storage up to the gigawatt-hour scale by connecting rigid reservoir elements, each with a storage volume of 10MWh. The system can be adapted to various forms of renewable power generation such as floating PV, offshore wind, tidal and wave energy.

“There is a perfect match between the Ocean Battery and floating PV arrays,” Ocean Grazer CEO Frits Bliek told pv magazine. “As we can adapt the charging capacity independently from the discharging capacity, we can tune the capex [capital expenditure cost] to rapidly absorb the solar peak around noun and discharge the accumulated power of the rest of the day. In this way we can optimally tune into the business case of a floating PV array.”

The Ocean Battery features technology that has been in use at hydroelectric dams for more than a century. While it has identical functionality and performance, it comes with one big difference, as the hydrostatic pressure comes for free and there is no need to build an entire hydro dam.

The system

In other words, the Ocean Battery stores energy by pumping water from low-pressure rigid reservoirs, each holding up to 20 million litres of freshwater, into high-pressure flexible bladders installed on the seabed. During discharging, water stored as potential energy flows back from the flexible bladder to the rigid reservoir via hydro turbines that generate electricity.

“Minimal discharging time is 0.5 hours, sufficient for the highest demands in the utility sector,” said Bliek. “Any lower power-capacity-to-storage-capacity can be created, to support bulk shifting, for example. There is no self-discharge whatsoever so power can be stored as long as you want.”

The round trip efficiency of the Ocean Battery stands at around 78%. Its technical lifetime is rated at a minimal 20 years but is most likely 30-50 years, according to its developer. Ocean Grazer said the battery has low maintenance costs and is designed with sustainability in mind, enhancing marine life. It is made from readily available global materials steel, concrete, and rubber/PVC and uses clean water as the energy carrier.


According to its product sheet, the Ocean Battery is able to provide a wide range of grid services including frequency control, black-start power, and energy arbitrage. In addition to the traditional services provided by utility scale storage – such as curtailment prevention and congestion management – Ocean Battery can also allow “over-planting,” to maximise the energy yield of wind farms per square kilometre, ie it can make room for more turbine capacity at the same project, improving its economics.

Developer Ocean Grazer was spun out of the University of Groningen, in the Netherlands. The start-up describes itself as “the only company that provides a reliable, affordable and eco-friendly energy storage system that provides a flexible and modular solution for offshore and inshore energy storage at [a] gigawatt-hour scale.”

Ocean Grazer is developing its first commercial demonstrator for an inshore lake in the north of the Netherlands which hosts a floating solar installation. That system is slated for completion in 2023. “Next to that we are developing an offshore project connected to a wind farm,” Bliek added. “Potentially, a floating solar installation could be included in that project but details [have to be] worked out as we are in the middle of the scoping phase. The project will be completed in 2025.”

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