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Ocean energy (also designated marine energy, marine hydrokinetic energy, or marine renewable energy) is the renewable power derived from the kinetic, potential, thermal, and chemical energy of seawater. Governed internationally by technical standards such as the International Electrotechnical Commission (IEC) TS 62600 series, ocean energy captures power from surface waves, tidal currents, ocean thermal gradients, and salinity differentials.
Short answer
Ocean energy encompasses renewable power harvested from seawater movement, temperature differences, and chemical gradients. Major forms include wave energy, tidal stream and barrage power, ocean thermal energy conversion (OTEC), and salinity gradient systems. With an energy density roughly 800 times that of air, ocean energy offers highly predictable baseload and variable power governed by international IEC TS 62600 technical standards.
Definition and scope
According to the U.S. Department of Energy (DOE) Water Power Technologies Office (WPTO) and the International Energy Agency Ocean Energy Systems (IEA-OES), ocean energy encompasses five primary physical conversion domains:
- Wave Energy: Capturing kinetic and potential energy transferred from wind to ocean surface waves.
- Tidal Stream Energy: Harnessing horizontal kinetic flows driven by astronomical tides in coastal straits.
- Tidal Range Energy: Exploiting vertical hydraulic head created by tidal rises using barrages or lagoons.
- Ocean Thermal Energy Conversion (OTEC): Utilizing the thermal gradient between warm surface seawater and cold deep-ocean water.
- Salinity Gradient Energy: Extracting osmotic chemical potential released when freshwater mixes with seawater.
Under IEC Technical Committee 114 (IEC TC 114), marine energy explicitly excludes atmospheric offshore wind (which is governed by IEC TC 88). Within broader oceanographic research, ocean energy focuses on hydrodynamics, power take-off (PTO), survivability, and grid integration. In the United States, recoverable marine energy is equivalent to approximately 57% of all 2019 domestic electricity generation.
How it works or how it is used in practice
Because seawater is roughly 800 times denser than air, marine hydrokinetic systems achieve high energy densities at modest flow velocities, requiring smaller rotor footprints than atmospheric wind turbines. Operational systems rely on four core subsystems:
- Primary Capture Structure: The hydrodynamic body (such as a heaving buoy, oscillating air chamber, or turbine rotor) that directly interfaces with wave or tidal motion.
- Power Take-Off (PTO): The electromechanical, hydraulic, or pneumatic subsystem converting irregular mechanical oscillations into grid-synchronized electricity. Archetypes include permanent-magnet linear generators, hydraulic motor circuits, and bi-directional air turbines.
- Mooring and Foundations: Tension-leg moorings, catenary chains, and seafloor anchors that hold position against extreme cyclic fatigue and 100-year storm wave loads.
- Subsea Power Conditioning: Subsea umbilical cables, dry-mate connectors, and power electronics converting variable electrical output for grid transmission.
Beyond bulk utility grids, ocean energy powers off-grid coastal microgrids, offshore aquaculture monitoring, autonomous underwater vehicle (AUV) charging docks, and marine observation arrays.
Types or related concepts
Ocean energy systems differ by resource mechanism, conversion kinematics, and operating environments. The table below outlines the five primary types based on specifications from DOE WPTO and IEA-OES:
| Ocean Energy Type | Physical Resource Mechanism | Primary Converter Archetypes | Operating Medium | Capacity Factor | Primary Engineering Challenge |
|---|---|---|---|---|---|
| Wave Energy | Kinetic and potential energy of surface waves | Point absorbers, oscillating water columns, attenuators | Surface wave oscillations | 25% – 40% | Survivability under extreme storm wave loads |
| Tidal Stream | Kinetic energy of fast-moving horizontal currents | Horizontal-axis turbines, vertical-axis cross-flow turbines | Tidal flow velocity (> 1.5 m/s) | 30% – 45% | Dynamic turbulence, cavitation, and marine biofouling |
| Tidal Range | Potential energy from hydrostatic head differences | Tidal barrages, tidal lagoons, bi-directional bulb turbines | Vertical tidal elevation (> 5 m) | 20% – 35% | High civil capital costs and estuarine sedimentation |
| Ocean Thermal (OTEC) | Thermodynamic gradient between surface and deep water | Closed-cycle Rankine engines, open-cycle flash evaporators | Temperature gradient (≥ 20°C across 1,000 m depth) | 70% – 90% (Baseload) | Deep cold-water pipe engineering and parasitic pumping loads |
| Salinity Gradient | Chemical osmotic potential between fresh and saline water | Pressure-Retarded Osmosis (PRO), Reverse Electrodialysis (RED) | Salinity differential (river mouth vs seawater) | 70% – 85% (Continuous) | Membrane fouling and high capital cost per m² of membrane |
Point absorbers capture heave along wave crests. Oscillating water columns compress air above a water column to spin bi-directional Wells turbines. Tidal turbines generate predictable power proportional to the cube of current velocity. OTEC systems operate Rankine cycles using low-boiling-point fluids like ammonia, and salinity gradient plants leverage semi-permeable membranes to generate osmotic pressure.
Where it matters for labs, clinics or supply decisions
Ocean energy testing and deployment govern instrumentation, laboratory protocols, and supply choices across marine engineering facilities:
- Hydrodynamic Testing Facilities: Wave flumes, tow tanks, and directional wave basins evaluate scaled prototypes (1:50 to 1:10 scale). Wave makers and current generators must be calibrated according to IEC TS 62600-103 to replicate spectral sea states accurately.
- Metrology and Sensor Procurement: Quantitative resource assessment requires acoustic Doppler current profilers (ADCPs), acoustic wave and current gauges, load cells, and fiber-optic strain sensors. Testing facilities must maintain ISO 17025 accredited calibration for all metrology equipment.
- Materials Selection and Corrosion Mitigation: Marine test tanks and subsea hardware demand corrosion-resistant alloys, including super duplex stainless steel (UNS S32750), marine-grade aluminum (5083-H116), and titanium, alongside sacrificial zinc/aluminum anodes and biocide-free foul-release coatings.
- Osmotic Membrane Protocol Standards: Laboratories researching salinity gradient power implement strict salinity and conductivity measurement protocols to monitor ion transport, membrane flux, and concentration polarization during Pressure-Retarded Osmosis testing.
- Environmental Compliance and Permitting: Open-water device testing requires adherence to federal statutory mandates, including environmental permitting and marine mammal protections, requiring hydrophone acoustic arrays to monitor underwater noise during converter operations.
Common misunderstandings
Several common misunderstandings surround marine renewable energy:
- Conflating Ocean Energy with Offshore Wind: Offshore wind turbines capture atmospheric airflow above sea level and are governed by IEC TC 88. Ocean energy converters harvest hydrodynamic, thermal, or chemical energy within the water column and are standardized by IEC TC 114.
- Assuming Waves and Tides Share the Same Dynamics: Waves are driven by stochastic wind interactions, resulting in seasonal variation. Tides are governed by celestial gravitational forces of the Earth, Moon, and Sun, enabling precise generation forecasts decades in advance.
- Believing All Tidal Energy Requires Barrages: Modern commercial tidal development prioritizes modular tidal stream turbines placed on seafloor foundations, avoiding the large civil barrages and ecological impoundments of historical designs.
- Assuming OTEC Requires High Boiling Points: Closed-cycle OTEC systems do not boil seawater. Instead, warm surface water (25°C) vaporizes low-boiling-point working fluids such as ammonia (boiling point -33.3°C at atmospheric pressure) inside a closed loop.
FAQ
What are the primary types of ocean energy?
The primary types of ocean energy are wave energy, tidal stream energy, tidal range energy, ocean thermal energy conversion (OTEC), and salinity gradient energy. Each extracts power from a distinct physical, thermodynamic, or chemical marine property.
How does ocean energy differ from offshore wind?
Offshore wind captures kinetic energy from atmospheric winds above the ocean surface using wind turbines (governed by IEC TC 88). Ocean energy captures energy from the seawater column itself, including waves, currents, tides, thermal gradients, and salinity differences (governed by IEC TC 114).
What international standards govern marine energy converters?
IEC Technical Committee 114 (IEC TC 114) publishes the IEC TS 62600 Technical Specifications series, covering terminology (62600-1), design requirements (62600-2), wave converter power performance (62600-100), wave resource assessment (62600-101), and tidal resource characterization (62600-200).
Why does water density matter for ocean energy?
Seawater is approximately 800 times denser than air. This high density provides substantially higher kinetic power density at moderate speeds, allowing compact hydrokinetic turbine rotors to capture significant power.
Can ocean energy systems generate drinking water?
Yes. Open-cycle OTEC systems flash-evaporate warm surface seawater in a partial vacuum to generate steam for electricity, then condense it against deep cold seawater, producing potable desalinated freshwater as a natural co-product.
Sources
- U.S. Department of Energy (DOE) Water Power Technologies Office. "Marine Energy Basics." CMEI Water Resources. Accessed November 9, 2026. https://www.energy.gov/cmei/water/marine-energy-basics
- International Energy Agency – Ocean Energy Systems (IEA-OES). "What is Ocean Energy." OES Technology Collaboration Programme. Accessed November 9, 2026. https://www.ocean-energy-systems.org/ocean-energy/what-is-ocean-energy/
- U.S. Department of Energy (DOE). "International Standards and IEC TC 114: Marine Energy – Wave, Tidal, and Other Water Current Converters." CMEI Water Resources. Accessed November 9, 2026. https://www.energy.gov/cmei/water/international-standards-and-iec-tc-114-marine-energy-wave-tidal-and-other-water-current
- U.S. Department of Energy (DOE). "Marine Energy Glossary." Water Power Technologies Office. Accessed November 9, 2026. https://www.energy.gov/cmei/water/marine-energy-glossary
