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| Fig. 1: Tidal Power Plant in the Eastern Scheldt storm in the Netherlands. This is the largest such plant in the country and has five turbines. (Source: Wikimedia Commons) |
The world's oceans represent one of the largest untapped renewable energy sources. Technologies such as tidal energy, wave energy, and ocean thermal energy conversion (OTEC) have the potential to provide continuous, carbon-free power. This report examines ocean-based renewable energy systems and their potential.
Oceans cover more than 70% of the Earth's surface, storing vast amounts of kinetic, potential, and thermal energy. Various ocean-based systems convert this natural energy into electricity using physical processes driven by gravity, wind, and temperature gradients. [1]
Tidal energy harnesses predictable tidal movements through dams or underwater turbines. It is highly predictable and can generate consistent baseload power. However, construction costs, ecological concerns, and site restrictions have limited its widespread deployment. For instance, according to researchers at Guangdong Ocean University, the cost of a single 6 MW turbine is approximately $7.2 million. [2]
Wave energy originates from wind transferring energy to the ocean surface. This energy propagates as waves, carrying both potential and kinetic energy. Theoretical understanding of wave propagation stems from early work by D'Alembert, Airy, and Stokes, whose models describe the relationship between wave height (h), period (T), and energy per meter of wave crest (P). The power of a wave per meter of crest can be expressed as
| P | = | ρg2h2T 32π |
where g is the acceleration due to gravity. [3]
A prominent wave energy technology is the Oscillating Water Column (OWC), which uses the movement of waves to compress and decompress air inside a chamber. This airflow drives a bidirectional Wells turbine to generate electricity. One of the most studied devices, the LIMPET system in Scotland, achieved 49% energy conversion efficiency, approaching the theoretical turbine maximum of 59%. [3]
OTEC exploits temperature gradients between warm surface seawater (253°C) and cold deep seawater (around 5°C). Two main types exist:
Closed-Cycle OTEC, which uses a working fluid (like ammonia) that evaporates and condenses in a continuous loop.
Open-Cycle OTEC, which directly evaporates seawater under low pressure, driving a turbine with the resulting vapor and simultaneously producing freshwater. [1]
Unlike wind and solar systems, OTEC can operate continuously, providing a reliable renewable energy source. However, it is geographically limited to tropical waters where the temperature differential exceeds 20°C. [1]
Commercial tidal plants like La Rance Barrage in France (240 MW) and Sihwa Lake Tidal Station in South Korea (254 MW) demonstrate the large-scale feasibility of tidal power. Also, the such techology has been implemented in the Netherlands as seen in Fig. 1. [2] However, high costs, maintenance, and ecological impacts limit real-world deployment.
According to studies, the U.S. coastline receives approximately 2,100 TWh/year of incident wave energy comparable to half of the nation's current electricity demand. Even accounting for spatial constraints and 49% conversion efficiency, capturing just one-third of that energy could yield around 343 TWh/year, or roughly 3% of total U.S. electricity consumption. [3] While wave energy systems like LIMPET create energy, scaling them is not possible yet because of significant maintenance costs. For just operating, annual maintenance costs are around $240,000/unit and at the moment, the return on this investment is not economical. [2]
Ocean-based renewables remain in a developmental phase compared to wind and solar. However, their predictability, energy density, and coastal proximity make them attractive long-term options. Future progress depends on cost reduction and feasibility improvements.
For coastal and island regions, the synergy between energy production, freshwater generation, and cooling applications could make ocean energy systems cornerstones of sustainable local economies.
Tidal, wave, and OTEC systems showcase the oceans' vast but complex renewable potential. While tidal and wave power can provide intermittent but high-yield electricity, OTEC offers continuous generation with added environmental and community benefits. Each technology faces technical and economic barriers, yet their combined advancement could significantly contribute to a resilient, low-carbon global energy portfolio.
© Kush Arora. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] C. Hyatt, "Ocean Thermal Energy Conversion," Physics 240, Stanford University, Fall 2016.
[2] D. Zhang et al., "Challenges in Tidal Energy Commercialization and Technological Advancements For Sustainable Solutions," iScience 28, 112348 (2025).
[3] E. Bonifacio, "Wave Energy," Physics 240, Stanford University, Fall 2010
