As the oil and gas industry has become increasingly focused on reducing greenhouse gas (GHG) emissions, the concept of leveraging renewable energy sources (RES), such as offshore and floating wind farms, to provide clean power to offshore installations has gained traction. However, many hurdles stand in the way of making this a reality. Mainly, this is because of the need to offset the inherent intermittency associated with electricity generation from renewables.
In 2018, Siemens, Seadrill, and Northern Ocean took an important step toward solving this problem by implementing the world’s first lithium-ion battery solution on the West Mira drilling rig in the North Sea. West Mira is a sixth-generation, ultra-deep-water (10,000-ft) semi-submersible that will operate in the Nova Field, approximately 120 km (75 miles) northwest of Bergen, Norway. It will be the world’s first hybrid rig to operate a low-emissions hybrid (diesel-electric) power plant using lithium-ion storage technology, with DNV-GL Power Notation.
Designing lithium-ion batteries for spinning reserve and safety
The concept of using lithium-ion energy storage solutions in both all-electric and hybrid power systems is not new. However, it has not been until recent years that large megawatt-hour capacity battery solutions have been commercialized for use in marine applications. This is primarily because of the numerous technical hurdles that have had to be addressed, including high capital cost, limited battery range, lifespan and reliability, and so forth. Safety has also been a critically important factor.
Because lithium-ion batteries combine high energy materials with flammable electrolytes, any damage to the separator as a result of mechanic stress or high temperature will lead to an internal short-circuit. This causes the electrolyte inside the cell to begin evaporating, resulting in an increase in internal pressure until the electrolyte vapor is eventually released, either through a relief valve or by the bursting of the cell shell. Without protective measures in place, an explosive gas-air mixture is created and if heating is not ceased, thermal runaway takes place.
Thermal runaway poses a serious safety concern for any facility that uses lithium-ion energy storage. However, in marine vessels and offshore facilities, the risk is magnified as there are limited options for personnel to be evacuated from the area where danger exists. Also, an explosion could cause catastrophic damage to the structure.
Additionally, in oil and gas operations, combustible fuels are present, which increase the risk of fire spreading. For this reason, lithium-ion energy storage solutions used in marine environments must incorporate fail-proof design measures to ensure safety.
Battery solution: BlueVault
This was the primary design objective of the battery solution (formerly named Blue Vault) used for the West Mira drilling rig. Individual cells in battery packs are equipped with propagation protection to prevent large-scale thermal runaway. Gases produced as a result of the thermal event are ducted through the cubicle that holds the battery modules. Any thermal runaway event that occurs within the system is isolated on the cell level. A freshwater cooling system regulates the temperature in the batteries.
The cooling system is designed to work as a passive safety layer to ensure that a faulty battery cell will not propagate to any neighboring battery cells. It also keeps the battery temperature stable and helps to extend its lifespan. The latter is influenced by a variety of factors, including ambient temperature, number of cycles, depth of cycles, and so forth. The typical life expectancy of the battery system is around 10 years.
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