Subsea Batteries for Green, Leaner Offshore Infrastructure Inspection

Subsea Inspection, Monitoring, Maintenance, and Repair (IMMR) services for offshore wind infrastructure management are in high demand right now as developers seek to prioritize the integration of renewable energy sources into power grids around the world. Central to planned IMMR operations is the periodic examination of the array and export cables—a network of submarine cables installed to transfer the generated power from turbine to offshore substation to onshore substation—to ensure operational optimization and reliability.

AUTOMATED TECHNOLOGIES

Current IMMR campaigns for offshore wind installations are increasingly leveraging automation technologies originally developed and fielded to enhance offshore oil well survey and intervention practices. Autonomous underwater vehicles (AUVs) have become a popular option given that they minimalize topside vessel size and the duration of at-sea operations, resulting in significant savings in terms of operating costs and carbon emissions.

Central to the success of AUVs (and other remotely operated IMMR technologies) is the proximity of their power source—subsea batteries.

Recent advances in subsea battery technology have transformed the applicability of AUVs and other remotely piloted assets for efficient underwater inspection. Certain intervention tasks are better suited to remotely operated vehicles (ROVs), which typically draw their power via an umbilical to topside support. However, improved efficiency, additional tools or equipment, and localized power are also evolving ROVs to use on board subsea batteries to support any required additional bursts of power or even to fuel fully electric ROVs, or eROVs, such as the Nereid UI, developed by Woods Hole Oceanographic Institution for under ice surveys in the Artic.

The development of subsea “resident” AUV systems—equipped with seafloor battery-powered charging stations—extends the notion of subsea inspection to the next level. Subsea residency allows for ongoing scheduled survey operations and on-demand investigation from a remote command center without the need for any topside deployment.

Topping up the battery bank charging system for the AUV can be implemented with a slow rate charge from a topside (platform if viable) or even a wave-based energy generating buoy. Such slow rate charge line minimizes the wire gauge required to carry the power and therefore saves on electrical umbilical size and cost. Meanwhile, the subsea charged battery system is ready for immediate high-powered pulses to meet any vehicle need, hence mitigating the need for any long, bulky cables to transport power to the seabed.

SUBSEA BATTERIES FOR IMMR

Subsea batteries for such IMMR applications can be categorized into three types. The first type is 1 Atmosphere batteries, which are not pressure tolerant—hence the term 1 atmosphere—and so require a pressure vessel. The battery modules are inter-connected with classic electrical connectors and the pressure vessel features a bulkhead mount subsea connector. This style is typical in smaller AUVs for shallow deployment as small pressure vessels are manageable in cost and design.

The other two types of subsea batteries are both pressure tolerant, designed to resist the forces presented at depths of up to 6,000 m (tested to 10,000 psi). Some pressure tolerant types can be configured within a pressure balanced oil filled (PBOF) case. Such types are used for larger configuration battery systems used at greater depths, typically 1,000–6,000 m. The battery modules are inter-connected with classic electrical connectors within the PBOF case, connected in series for voltage increments, and in parallel for power and capacity increments. The case is then oil filled. A panel mount subsea connector presents the battery system power and communications to the subsea application connection.

The third type of subsea battery is also pressure tolerant, but it does not require the use of a PBOF case. It can be used directly in the water. It utilizes subsea ready cables and connectors for subsea interconnect. Such a battery type is very easy to use in subsea applications as it avoids both the pressure vessel requirement and the PBOF case and oil fill requirement. However, resulting subsea cables and connectors can become challenging when configuring a larger series and parallel modules battery system from the battery modules.

SMART SUBSEA BATTERY MODULES

Southwest Electronic Energy (SWE) has been developing and manufacturing batteries for the oil and gas industry for over 40 years, and capitalized on lessons learned from building ruggedized, reliable, downhole MWD batteries with the introduction of the SeaSafe battery product line. While the portfolio has evolved since its launch 12 years ago, today we offer 3 types of SeaSafe subsea batteries as well as a series of accessories primed for underwater robotics and IMMR systems.

For more information, visit: www.swe.com or contact Leon Adams at ladams@swe.com.

This story was originally published in ON&T Magazine's May 2023 Issue. Click here to read more.