Based out of our state-of-the-art R&D facility in Kiel, Germany, the company has grown significantly in recent years to become an established leader in the design and manufacture of commercial off-the-shelf (COTS) and custom subsea battery solutions. In our quest to provide the ocean sector with, as per our mission statement, “Technologies for the Marine Environment and Sustainable Measuring Strategies for the Ocean,” one of our more recent focuses has been on developing an industry-first Energy Storage System (ESS).
SUBSEA ENERGY STORAGE
ESS technology is not widely deployed offshore, but today, amid mounting pressures to cut CO2 emissions and usher in a new era of environmental sustainability and operational efficiency to offshore practices, developers are turning to outfits like SubCtech to conceive, manufacture, and integrate scalable ESS solutions into standardized ways of working. Subsea ESS present distinct advantages over their onshore counterparts; land-based battery parks require considerable space, close to large urban areas—given that over 70% of the planet is covered by water, subsea ESS not only optimizes the use of available space but also offer substantial cost savings and significantly lower CO2 emissions compared to land-based solutions, making them a sustainable and economically viable alternative.
We believe that the development of a scalable and reliable offshore EES that harnesses abundant renewable energy sources can prove a game-changer to the energy transition, bringing safe and secure largescale energy supply to critical offshore infrastructure, both as a backup energy source for offshore applications with high energy demands (>1 Mwh) and critical control systems and sensors that require uninterrupted power.
ESS BREAKTHROUGH
Over the last two and a half years, SubCtech has been developing a modular Li-ion Energy Storage System (ESS) designed for deployments of up to 25 years. From the beginning, SubCtech’s ESS has been designed with two integrated 1 Mwh units, as reported by this magazine in 2023. We are now excited to highlight the successful implementation of this dual-unit configuration, offering a flexible and robust 2 Mwh ESS solution. This setup underscores the reliability and scalability of our energy storage systems, tailored to meet the stringent demands of the subsea environment. It has now successfully passed its final field-testing stage: the system has been commissioned and tested in situ and, therefore, has already reached the Technology Readiness Level 6 (TRL 6), according to API17Q.
This ESS is a true first-of-its-kind, reaching full API17F qualification as well as UN T38.3 certification for air, sea, and road transport, as well as DNV 2.7-3 as Portable offshore units. The maximum operating depth is currently 2,000 m, with options for 3,000 m, 6,000 m, and shallow waters.
A CONCERTED EFFORT
This has been a substantial undertaking for the SubCtech team— developing a unique subsea battery system that achieves the highest international manufacturing standards in little under thirty months demands an all-hands-on-deck effort. It has, by all accounts, been a labor of love for the dedicated team members, the details of which have been regularly published in a project blog hosted on our corporate website, which maps out all the major milestones from conception right through to final subsea testing.
The key to the ESS design is its modularity. Each Battery Storage Skid (BSS) has a total power of 1 Mwh. By connecting two of them alongside each other, you now have a total output of 2 Mwh. At present, the current design can be extended to 6 units, meaning the power capacity is scalable to 6 Mwh in total.
The ESS operates with an advanced redundancy concept and is equipped with innovative features such as AC or DC charging, a 3 phases AC output converter, and auto-configuration via our SmartBMS™ and BCM (Battery Control Module, based on our proven NetDI® control technology). The data and power interfaces were adapted and tested to the corresponding systems.
The redundancy concept of the ESS ensures an uninterrupted power supply. This design enables our client to minimize downtime for his entire subsea system and helps cut OPEX costs significantly. Using fewer vessel operations not only reduces costs considerably but also helps curb the CO2 footprint.
Of particular note is the auto-configuration via SmartBMS. This intelligent battery management system (BMS) automatically optimizes the operation of the energy systems from cell level to module level and adapts to the respective requirements. This not only maximizes efficiency but also extends the lifespan of the batteries and, thus, the availability and reliability of the subsea facility.
A so-called Power Skid acts as the converter module and interface between the user’s subsea system and the ESS. An Acoustic Telemetry Modem (ATM) is used as a backup for underwater wireless communication over long distances, for example, up to 6,000 m.
SUBSEA APPLICATIONS
The implications of a unique and scalable ESS of this nature are far-reaching, delivering an uninterrupted power supply and ESS in support of general energy production, power for CCS and other injection systems, buffering for renewable energy facilities such as wave power, solar, wind, and water current generators, and, of course, long tiebacks.
EES of this scale also helps bring the notion of subsea residency into clearer focus, with the potential to incorporate docking stations for charging subsea assets, such as AUVs and ROVs, stationed around offshore infrastructure for long inspection and intervention work for long deployments.
SAFETY FIRST
Safety, as always, remains our priority at SubCtech, which is why this ESS concept was conceived, built, and tested with full DNV oversight and approval, meaning that not only does our ESS offer the highest energy and power density, but it is already fully API17F certified. Our engineers like to jest; our ESS is the safest way to cut offshore operational costs— reducing CAPEX by minimizing the need for extensive cables and umbilicals, and OPEX by ensuring less downtime and more efficient operations.
This feature appeared in ON&T Magazine’s 2025 Special Edition, The Future of Ocean Technology, Vol. 5, to read more access the magazine here.
