Subsea Pumped Hydro Energy Storage : Exploring the need, possibilities, and limitations in the Energy Transition

Abstract

In light of the global challenges posed by climate change and the required mitigation of its effects, the transition from conventional fossil fuels to renewable energy sources has accelerated, albeit with significant challenges. This thesis investigates the crucial role of energy storage, specifically Subsea Pumped Hydro Storage (SPHS), in facilitating this transition by increasing the flexibility and reliability of power systems dominated by intermittent renewable energy sources. SPSH, not yet a commercial application, could open up the ocean space for large scale energy storage and mitigate the shortcomings of existing energy storage concepts. The ongoing shift towards renewable energy, with geopolitical tensions and the need for energy security increasing the complexity, creates new requirements on the power supply system. This system must be able to reliably supply power when there is a demand even when a majority of the power comes from intermittent power plants while it must also use the opportunities provided by intermittent power plants to its fullest extent. Energy storage emerges as a pivotal solution to the intermittency challenge, offering the dual capability to store excess energy during periods of low demand and supplement the grid during high demand. This thesis examines the benefits of energy storage, towards achieving the goal of limiting the effects of climate change. The thesis introduces a novel thermodynamic model for SPHS, defining key operational parameters such as the Compression Ratio (CR), State of Charge (SOC), and degree of filling. This model not only advances our understanding of SPHS but also sets the stage for future developments in subsea energy storage technology. The research bridges the gap between the industrial know-how, and the academic know-why, evidenced by the collaboration between the University of Stavanger and Subsea7. Only by addressing the gaps will the outcome be a successful product. Several areas for future research and development are identified, including the design of detailed system architectures for SPHS, Life Cycle Assessments (LCA) to evaluate environmental impacts, and the engineering, procurement, construction, and installation (EPCI) aspects of SPHS units. The thesis offers significant contributions to the field, including a general model for analysing SPHS systems, insights into the output profiles of wind turbines in relation to energy storage, and a foundation for the development of subsea hydropower turbines. These contributions not only advance the academic discourse on renewable energy storage solutions but also provide practical pathways for industry application and environmental sustainability.