The increasing development of floating wind turbines has paved the way for exploiting offshore wind resources at locations with greater depth and energy potential. The study presents a novel Subsea Buoyancy Gravity Energy Storage System (SBGESS) that combines buoyancy energy storage and gravity energy storage technologies to overcome the intermittent nature of wind energy. The proposed system is assessed for time-shifting power delivery applications in two Brazilian offshore wind farm sites with varying wind conditions and water depths. The performance of the SBGESS is evaluated by considering different numbers of units, water depths, and control strategies. The results demonstrate that the SBGESS can effectively enhance offshore wind farms’ capacity factor and power output during peak times, particularly in regions with lower wind potential and higher profundity.

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.

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.