Sustainable Marine Structures

Coastal Pumped Hydroelectric Energy Storage: A Variable Volume Floating Tank Design for the Lower Reservoir

Dimitrios Elias Katsareas

R&D Department, Tejas Tubular Products Inc., Houston, TX 77028, USA

Anastasios George Youtsos

Institute of Nuclear Technology & Radioprotection, NCSR Demokritos, 15310 Agia Paraskevi, Greece

DOI: https://doi.org/10.36956/sms.v8i3.3297

Received: 1 May 2026 | Revised: 29 May 2026 | Accepted: 2 July 2026 | Published Online: 28 July 2026

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Abstract

An innovative freshwater storage tank design is considered the key element of the lower reservoir for coastal pumped hydroelectric energy storage (PHES) plants. The cylindrically shaped open-top tank is constructed entirely of recyclable plastic materials; it floats on the sea surface and has flexible walls and a bottom that is impermeable to seawater. The design incorporates a retractable wall that allows for a variable volume capacity of the tank, and as such, it expands and retracts just like a concertina. The lower reservoir is envisaged as modular construction, comprising an array of floating tanks, connected and anchored at the bottom of the sea by a grid mooring system, not unlike those used in coastal fish farms. In fact, a great deal of aquaculture technology has been adopted in the present design, and components like the cage collar (float), sinker tube, connecting grid and mooring systems are the same as those used for decades in fish farming. Key considerations such as modularity, construction costs, installation time, environmental impact, flexibility, and recyclability led to the adoption of this innovative solution, as the lower reservoir of coastal PHES plants uses fresh or desalinated water. As proof-of-concept, a fully functional scale model of the tank was built and assessed in real-life coastal conditions, with results that not only met but also proved to be beyond the author’s expectations. The proposed design concept, fabrication of the tank model, tests performed, experimental data and their evaluation are described in detail. Finally, future work is suggested.

Keywords: Reservoir; PHES; PSH (Pumped Storage Hydropower); Coastal; Floating; Collapsible; Desalinated; Recyclable

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