Low Cost Locally Manufactured Marine Pumped Hydro Energy Storage Systems

J. Cotrell
RCAM Technologies, Inc.,
United States

Keywords: marine pumped hydro-electric storage, offshore wind, subsea, long duration energy storage


RCAM's marine pumped hydroelectric (MPH) subsea energy storage system is a flexible and scalable technology that can be used for various applications including hybrid offshore generation/storage plants, grid stabilization and peak shaving, island electrification, and backup power for offshore oil and gas platforms. Its potential to support the transition to a Net Zero future and provide reliable, secure energy for coastal communities internationally make it a promising solution in the growing offshore energy storage industry. In this presentation, RCAM will describe the operating principles of the MPH system, discuss the global market opportunity, present a case study illustrating technology costs and benefits, and discuss ongoing research and development efforts towards commercialization. The offshore renewable energy industry is constantly evolving, and it is essential to identify and evaluate technologies that can increase sustainability and cost-effectiveness. RCAM Technologies, a cleantech start-up specializing in the development of low-cost, locally manufactured energy storage systems for offshore renewable energy generation, is committed to finding innovative solutions for a more sustainable and independent energy future. RCAM's MPH energy storage system uses a series of large, hollow interconnected concrete spheres joined to a reversible pump/turbine and motor/generator unit installed at depths of 750-2000 m on the seafloor. MPH operates similarly to conventional onshore pumped storage hydroelectric energy systems but utilizes the high hydrostatic pressure present in deep offshore waters rather than the elevation difference between reservoirs. The system charges by pumping seawater out of the spheres, reaching a minimum 1 bar internal pressure to prevent cavitation and maximum internal pressure of 10 bar. The surrounding hydrostatic pressure is 100 bar at 1000 m. To discharge energy back to the grid, the system is run in reverse (turbine/generator mode), re-filling the spheres with seawater. The external pressure is always greater than the internal pressure providing an elegant solution that ensures the sphere is subjected only to compressive stresses, for which concrete is a near-ideal, low-cost material. A typical MPH unit uses three 30-m diameter spheres interconnected in a “tri-sphere pod” configuration to provide 37,000m3 inner volume. When commercialized, the performance characteristics of each MPH pump/turbine unit include a charge/discharge power of 5 MW and a round-trip efficiency of 80% providing 10+ hours duration. RCAM is utilizing 3D concrete printing (3DCP) technology to manufacture the largest cost component of MPH – the concrete spheres. This digital fabrication method, which involves the use of a robotic arm or gantry equipped with specialized software to deposit cementitious materials layer by layer, allows for the automated production of complex geometries that would be difficult or impossible to achieve using traditional construction methods. The use of 3DCP significantly reduces construction costs and enables lean, reliable manufacturing using corrosion-resistant materials. A relocatable 3DCP manufacturing facility can be quickly set up at a port near the offshore renewable energy generation plant. Additionally, co-locating the manufacturing process at a quayside facility supports domestic supply chains and provides skilled labor job opportunities in the local community.