Subsea buoyancy gravity energy storage systems (SBGESS) could take advantage of large water depth to store energy in the form of potential energy. In the proposed system, drum hoists mounted on a semisubmerged support structure simultaneously lift concrete cylinders with hundreds of tonnes and lower floaters with equivalent buoyancy force, which can be released with high round trip efficiencies by inverting the motor operation. The present study addresses the potential effect of the vortex-induced vibration (VIV) produced by current velocities on the behaviour of the energy storage modules. In order to analyse the system response, a state-of-the-art VIV model was integrated with a spherical pendulum and tuned with experimental results from the literature. The numerical model allows estimating amplitudes and frequencies of oscillation for a single module in both in-line and cross-flow directions. Results are used to assess the risk between modules of collisions on a previously designed SBGESS.

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This article presents a preliminary assessment of a subsea buoyancy and gravity energy storage system (SBGESS). The storage device is designed to power an off-grid subsea water injection system to be installed at the Libra oil field in Brazil at 2000 m below sea level. Two 12MW floating wind turbines provide the energy supply. The system performance is evaluated according to historical wind data from reanalysis models, the water injection pumps power curves, the required daily water flow rate, and the maximum number of shutdowns allowed per year. A control strategy with three different operation modes and one energysave sub-mode was implemented to optimise the size of the proposed energy storage system.

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Around 5% of the global offshore oil and gas production is consumed as fuel to power the platforms emitting around 200 million tons of CO2 per year. Adopting renewable energy can increase the oil and gas available for export by reducing internal consumption and opening space for the processing plant. This work presents an improvement to the classical analytical hierarchy process multi-criteria decision analysis method, where a viability check phased is introduced before the criteria weighting. The proposed methodology is then applied to a case in Brazil, where 10MW of continuous electrical power is required by a subsea CO2 separation and reinjection system to be installed at 2000m water depth and 160 km from shore. The selection criteria include technical, economic, and environmental aspects weighted with the contribution of experts. The resulting ranking is offshore wind followed by wave energy, subsea small modular nuclear reactors, and ocean thermal energy conversion.@en