Source Count: 14 | Weighted Score: 30 | Source Confidence: [4/5] | Primary Tier: 2 | Last Updated: March 12, 2026
Keywords: ocean energy, tidal power, wave energy, tidal barrage, tidal stream, OTEC, ocean thermal energy conversion, marine energy, renewable energy, tidal range, La Rance, Sihwa, MeyGen, oscillating water column, point absorber, overtopping device, blue energy, salinity gradient, offshore wind, capacity factor, levelized cost
Category Tags: oceanography, energy, engineering, sustainability, climate
Cross-References: ZF_1_15 — Wave Physics · S_3_06 — Renewable Energy · ZF_1_14 — Ocean-Atmosphere Coupling · ZF_5_05 — UNCLOS · Q_4_10 — Thermodynamics

QUICK SUMMARY

Ocean energy encompasses a family of renewable energy technologies that harvest the ocean's vast stores of kinetic, thermal, and chemical energy — including tidal power (predictable tidal flow and range), wave energy (wind-generated surface waves), ocean thermal energy conversion (OTEC) (temperature difference between warm surface water and cold deep water), and salinity gradient power (osmotic energy from mixing fresh and salt water). The theoretical global ocean energy resource vastly exceeds human energy demand — estimated at 20,000–80,000 TWh/year for wave energy alone and 800 TWh/year extractable from tidal streams — but practical exploitation has proven technically and economically challenging. As of 2025, ocean energy contributes a negligible fraction of global electricity (approximately 0.5 GW installed capacity worldwide, mostly from tidal barrages). The two operational tidal barrages of significant scale — La Rance (France, 240 MW, operating since 1966) and Sihwa Lake (South Korea, 254 MW, 2011) — demonstrate proven technology but require exceptional tidal ranges (>5m) and have significant environmental impacts on estuarine ecosystems. Tidal stream turbines (underwater turbines driven by tidal currents, analogous to underwater wind turbines) and wave energy converters (oscillating water columns, point absorbers, attenuators) have been demonstrated at prototype and small array scale — the MeyGen project (Scotland, 6 MW tidal stream array) is the world's largest — but the harsh marine environment, high capital costs, maintenance challenges, and competition from rapidly cheapening onshore and offshore wind and solar have slowed commercial deployment. OTEC — exploiting the ~20°C temperature difference between tropical surface water and deep water (~1,000m depth) — was demonstrated at small scale in Hawai'i (Natural Energy Laboratory, 1979, 2013) but remains far from commercial viability due to enormous infrastructure requirements and low thermodynamic efficiency. Ocean energy's primary advantages are its predictability (tides) and energy density (waves), but achieving cost-competitive, reliable, survivable systems remains the defining challenge.

1. VERIFIED CLAIMS (Tier 1 — Peer-Reviewed / Experimentally Confirmed)

1.1 Tidal Power: Barrages

• Tidal barrages exploit tidal range (the vertical difference between high and low tide) by enclosing an estuary or bay with a dam and running water through turbines as the tide fills and empties the basin:
• La Rance Tidal Power Station (Brittany, France, 1966): the world's first large-scale tidal barrage — 240 MW capacity, 24 bulb-type turbines operating on both ebb and flood tides. Generates approximately 540 GWh/year — capacity factor ~25%. Has operated reliably for nearly 60 years
• Sihwa Lake Tidal Power Station (South Korea, 2011): 254 MW — the world's largest tidal barrage by installed capacity. Built on an existing sea wall/reclamation dike; flood-tide generation only. Annual output ~550 GWh
• Annapolis Royal (Nova Scotia, Canada, 1984): 20 MW barrage exploiting the Bay of Fundy's extreme tides (>12m range)
• Requirements: tidal range ≥5m for economic viability; suitable estuary/bay geography for dam construction
• Environmental impacts: significant — altered tidal range and timing, changed sedimentation patterns, fish passage obstruction, loss of intertidal habitat. La Rance's estuary ecology took decades to reach a new equilibrium

1.2 Tidal Stream Technology

• Tidal stream (tidal current) turbines extract kinetic energy from tidal flows in channels and straits — no barrage needed:
• Power available is proportional to the cube of current velocity (P ∝ ρAv³), so even modest current-speed sites can generate significant power at high velocity
• MeyGen project (Pentland Firth, Scotland): world's largest tidal stream array — Phase 1 deployed four 1.5 MW turbines (2016–2018); planned expansion to 86 MW. Demonstrates feasibility of seabed-mounted horizontal-axis turbines in strong tidal flows (~3–5 m/s)
• Other notable projects: EMEC (European Marine Energy Centre) test site in Orkney, Scotland; OpenHydro (Ireland, suspended); Sabella D_5_03 (France, 1 MW); SIMEC Atlantis (MeyGen developer)
• Key advantage: predictability — tidal currents are governed by celestial mechanics and are precisely predictable decades in advance, unlike wind and solar. Capacity factors of 25–40% are achievable
• Challenges: extreme marine environment (corrosion, biofouling, storm loading), subsea installation/maintenance costs, electrical connection to shore, potential impacts on marine life (collision risk, noise, habitat alteration)

1.3 Wave Energy

• Wave energy converters (WECs) capture the kinetic and potential energy of ocean surface waves:
• Major device types:
• Oscillating Water Column (OWC): waves entering a partially submerged chamber compress and decompress air, driving an air turbine (e.g., Limpet, Mutriku breakwater, OceanEnergy OE35)
• Point Absorber: a floating buoy heaves up and down with waves, with the relative motion driving a power take-off (e.g., Corpower, WaveSpring, Ocean Power Technologies PowerBuoy)
• Attenuator: an elongated floating structure oriented parallel to wave direction, with segments articulating at joints as waves pass (e.g., Pelamis Wave Power — the first offshore WEC to deliver electricity to a national grid, 2004, Portugal; company failed 2014)
• Overtopping Device: waves wash over a ramp into a raised reservoir, draining through turbines (e.g., Wave Dragon)
• Global wave energy resource: approximately 2–3 TW theoretically; practical extractable fraction is much smaller — estimated at 500–1,000 TWh/year (IRENA)
• Status: despite decades of development and hundreds of device concepts, no wave energy technology has achieved commercial-scale deployment. The harsh marine environment destroys under-engineered devices, while over-engineering increases cost. Levelized cost of energy (LCOE) for wave energy remains approximately $0.20–$0.55/kWh — far above onshore wind ($0.03–0.05/kWh) and solar ($0.03–0.05/kWh)

2. CREDIBLE CLAIMS (Tier 2 — Supported by Multiple Scholars / Strong Circumstantial Evidence)

2.1 OTEC (Ocean Thermal Energy Conversion)

• OTEC exploits the temperature difference between warm tropical surface water (~25–28°C) and cold deep water (~4–5°C at >600m depth):
• Closed-cycle OTEC: warm surface water evaporates a working fluid (ammonia); the vapor drives a turbine; cold deep water condenses the vapor — a Rankine cycle
• Open-cycle OTEC: warm seawater is flash-evaporated under reduced pressure; steam drives a turbine; cold deep water condenses the steam (producing desalinated water as a byproduct)
• History: concept proposed by Jacques-Arsène d'Arsonval (1881); first demonstration by Georges Claude (1930, Cuba, 22 kW). Modern demonstration: Natural Energy Laboratory of Hawaii Authority (NELHA) — 1 MW Makai Ocean Engineering demonstration plant (2015)
• Theoretical resource: virtually unlimited in tropical oceans (40°N–40°S) — estimated at 3–5 TW potential
• Practical challenges: enormous water flow rates required (OTEC efficiency is inherently low — ~3–5%, compared to ~30–45% for thermal power plants — due to small temperature difference); massive cold water pipe (>1m diameter, extending >600m depth); high capital cost; distance from load centers; environmental concerns (nutrient upwelling, cold water discharge, working fluid leakage)
• OTEC may be most viable for small island developing states (SIDS) with expensive imported fossil fuels, year-round warm surface water, and proximity to deep water

2.2 Salinity Gradient Power

• Osmotic power exploits the chemical potential difference between fresh water and seawater at river mouths:
• Pressure Retarded Osmosis (PRO): a semipermeable membrane separates fresh and salt water; osmotic pressure drives fresh water through the membrane into the saltwater side, pressurizing it to drive a turbine. First prototype: Statkraft (Norway, 2009) — 4 kW demonstration plant; closed 2013 due to low membrane performance and high cost
• Reverse Electrodialysis (RED): ions migrate through ion-exchange membranes, generating an electrical current directly. Demonstration projects in the Netherlands (REDstack, Afsluitdijk prototype)
• Theoretical resource is enormous (~2.6 TW globally from river runoff mixing with the ocean), but membrane technology is insufficient for economic power generation. Research continues but commercial deployment is not imminent

2.3 Environmental Considerations

• Ocean energy environmental impacts are generally lower than fossil fuels but include:
• Tidal barrages: major estuarine habitat alteration, fish entrainment in turbines
• Tidal stream: collision risk for marine mammals and diving birds, noise, electromagnetic field effects from subsea cables, benthic habitat disturbance. Evidence to date from MeyGen and EMEC suggests impacts are modest but monitoring is limited
• Wave energy: potential entanglement risk for marine mammals, noise, visual impact, alteration of wave regime in the lee of arrays (affecting nearshore sediment transport)
• OTEC: discharge of nutrient-enriched deep water could alter surface ocean ecology; thermal plumes; potential for biocide release

3. SPECULATIVE CLAIMS (Tier 3 — Limited Evidence / Emerging Hypotheses)

3.1 Large-Scale Tidal Lagoons

• The concept of tidal lagoons — artificial impoundments in the open sea (not across estuaries) — has been proposed as an alternative to barrages with lower environmental impact:
• Swansea Bay Tidal Lagoon (Wales): proposed 320 MW project that underwent extensive planning and environmental assessment but was rejected by the UK government in 2018 on cost grounds (estimated £1.3 billion)
• Whether tidal lagoons can achieve cost-competitiveness with offshore wind remains unproven. Proponents argue that 120+ year asset lifetimes and predictable output justify higher upfront costs

3.2 Hybrid Ocean Energy Systems

• Concepts for combining wave, tidal, wind, and OTEC technologies on shared offshore platforms — reducing infrastructure costs — are in conceptual/early design stages. No significant hybrid systems have been deployed

4. DUBIOUS CLAIMS (Tier 4 — Fringe / Not Supported by Evidence)

4.1 Ocean Energy Can Replace All Fossil Fuels

• While the theoretical ocean energy resource vastly exceeds global energy demand, the practical, economic, and engineering constraints are severe. Ocean energy will contribute to the energy mix in favorable locations but is not expected to be a dominant global energy source in the foreseeable future, given the rapid cost declines in solar, onshore wind, and offshore wind

4.2 Free Energy from the Ocean

• Claims of unlimited "free energy" from perpetual motion ocean devices or "zero-point energy" extraction from seawater have no scientific basis and violate fundamental thermodynamic principles

COUNTER-ARGUMENTS

• Commercial viability debate: Whether marine renewable energy technologies — wave energy, tidal stream, tidal barrage, and ocean thermal energy conversion (OTEC) — can achieve cost-competitiveness with offshore wind and solar remains uncertain. Wave energy has attracted decades of R&D investment but has yet to produce a commercially viable device at scale, leading some analysts to question whether the engineering challenges (survivability in storm seas, maintenance access, grid connection) are fundamentally more difficult than for other renewables
• Tidal barrage environmental impact: The proposed Severn Estuary tidal barrage — which would generate substantial predictable power — has been repeatedly shelved due to concerns about impacts on internationally important intertidal habitats, fish migration, and sediment dynamics, illustrating the tension between renewable energy goals and environmental protection

IMAGES

BIBLIOGRAPHY

1. Bahaj, AbuBakr S | 2011 | "Generating Electricity from the Oceans" | Renewable and Sustainable Energy Reviews | ∅ | 15::3399–3416 | ∅ | ∅ | doi:10.1016/j.rser.2011.04.032 | ∅ | ∅ | ∅
2. Charlier, Roger H. | 1982 | ∅ | Tidal Energy | ∅ | ∅ | Van Nostrand Reinhold | ∅ | isbn:9781119014447 | ∅ | ∅ | ∅
3. Charlier, Roger H.; Charles W | 2009 | ∅ | Ocean Energy: Tide and Tidal Power | ∅ | ∅ | Finkl | ∅ | doi:10.1007/978-3-540-77932-2_8 | ∅ | ∅ | Springer
4. Drew, Benjamin, Andrew R | 2009 | "A Review of Wave Energy Converter Technology" | Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy | ∅ | 223::887–902 | Plummer, and M | ∅ | doi:10.1243/09576509jpe782 | ∅ | ∅ | Necip Sahinkaya
5. Falcão, António F. de O | 2010 | "Wave Energy Utilization: A Review of the Technologies" | Renewable and Sustainable Energy Reviews | ∅ | 14::899–918 | ∅ | ∅ | doi:10.1016/j.rser.2009.11.003 | ∅ | ∅ | ∅
6. IRENA. (corp.) | 2020 | ∅ | Ocean Energy: Technology Readiness, Patents, Deployment Status, and Outlook | ∅ | ∅ | International Renewable Energy Agency | ∅ | doi:10.1787/afbc8c1d-en | ∅ | ∅ | ∅
7. Khan, Nasir, Amina Kalair, Naeem Abas; Aun Haider | 2017 | "Review of Ocean Tidal, Wave and Thermal Energy Technologies" | Renewable and Sustainable Energy Reviews | ∅ | 72::590–604 | ∅ | ∅ | ∅ | ∅ | ∅ | ∅
8. Lewis, Anthony, et al | 2011 | "Ocean Energy" | IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation | ∅ | ∅ | In , ed | ∅ | ∅ | ∅ | ∅ | Edenhofer et al; Cambridge University Press
9. Nihous, Gérard C | 2007 | "An Estimate of Atlantic Ocean Thermal Energy Conversion (OTEC) Resources" | Ocean Engineering | ∅ | 34::2210–2221 | ∅ | ∅ | ∅ | ∅ | ∅ | ∅
10. Post, Jan W., et al | 2007 | "Salinity-Gradient Power: Evaluation of Pressure-Retarded Osmosis and Reverse Electrodialysis" | Journal of Membrane Science | ∅ | 288::218–230 | ∅ | ∅ | ∅ | ∅ | ∅ | ∅
11. Rourke, Fergal O., Fergal Boyle; Anthony Reynolds | 2010 | "Tidal Energy Update 2009" | Applied Energy | ∅ | 87::398–409 | ∅ | ∅ | ∅ | ∅ | ∅ | ∅
12. SIMEC Atlantis Energy | 2023 | "MeyGen Tidal Energy Project: Operational Update " | ∅ | ∅ | ∅ | Company report, 2023 | ∅ | ∅ | ∅ | ∅ | ∅
13. Vining, Joseph G.; Annette N | 2009 | "Economic Factors and Incentives for Ocean Wave Energy Conversion" | IEEE Transactions on Industry Applications | ∅ | 45::547–554 | Muetze | ∅ | ∅ | ∅ | ∅ | ∅
14. Avery, William H.; Chih Wu | 1994 | ∅ | Renewable Energy from the Ocean: A Guide to OTEC | ∅ | ∅ | Oxford University Press | ∅ | ∅ | ∅ | ∅ | ∅

CROSS-REFERENCE INDEX

• Wave Physics → ZF_1_15 — Wave Physics
• Renewable Energy → S_3_06 — Renewable Energy
• Ocean-Atmosphere Coupling → ZF_1_14 — Ocean-Atmosphere Coupling
• UNCLOS → ZF_5_05 — UNCLOS
• Coastal Geomorphology → ZF_5_08 — Coastal Geomorphology
• Deep-Sea Ecosystems → ZF_2_01 — Deep-Sea Ecosystems

Last updated: March 12, 2026

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