What Is Ocean Power?

Ocean power, also called marine energy, refers to the generation of electricity or useful mechanical work by converting the kinetic and thermal energy stored in the ocean's waves, tidal flows, currents, salinity gradients, and temperature differences. Unlike solar and wind resources, many ocean energy forms are predictable on daily and seasonal cycles, offering the potential for baseload and peaking capacity from a renewable source. The global ocean covers more than 70 percent of Earth's surface and continuously absorbs solar energy, making its energy content vast; the practical challenge is extracting it reliably and economically in a corrosive, high-force marine environment.

Ocean power research draws from marine engineering, hydrodynamics, electrical power systems, and materials science. Engineering systems must withstand biofouling, saltwater corrosion, mechanical fatigue from wave and tidal loading, and the logistical difficulty of offshore installation and maintenance.

Wave Energy Conversion

Wave energy converters (WECs) extract power from the oscillatory motion of ocean surface waves. Device architectures include oscillating water columns, which trap air above a water surface and force it through a turbine as waves raise and lower the water level; oscillating body converters, which use the relative motion between floating structures and sea anchors to drive generators; and overtopping devices that capture water elevated by waves into a reservoir and release it through turbines. The U.S. Department of Energy Marine Energy program estimates that wave resources off U.S. coasts could contribute substantially to national electricity generation, though most commercial-scale WEC projects remain in the demonstration phase as of the mid-2020s. Wave energy density is highest along western continental margins in temperate latitudes, where prevailing winds generate persistent swell.

Tidal and Current Energy

Tidal energy converters exploit the periodic rise and fall of sea level caused by lunar and solar gravitational forces. Tidal barrage systems dam a tidal estuary or bay, capturing water at high tide and releasing it through turbines during the ebb; the Rance Tidal Power Station in France, operational since 1966, remains the largest barrage installation. Tidal stream turbines, conceptually similar to submerged wind turbines, extract energy from fast-moving tidal currents without requiring impoundment. Strong tidal streams occur at headlands and in channels between islands or across sounds, with the Pentland Firth between mainland Scotland and Orkney recognized as one of Europe's most energetic tidal resources. Ocean current energy converters target slow but continuous deepwater flows such as the Florida Current, part of the Gulf Stream system. The International Renewable Energy Agency (IRENA) tracks global installed capacity and technology readiness across these categories.

Ocean Thermal Energy Conversion

Ocean thermal energy conversion (OTEC) exploits the temperature difference between warm surface water and cold deep water to drive a heat engine and generate electricity. A closed-cycle OTEC system vaporizes a low-boiling-point working fluid such as ammonia using surface water, drives a turbine, then condenses the vapor using cold water pumped from depths of 800 to 1,000 meters. A temperature differential of at least 20 degrees Celsius is required, limiting viable sites to tropical and subtropical latitudes. OTEC produces a continuous power output independent of waves or tides, and its deep-water cold supply can also support aquaculture and air conditioning as co-products. The U.S. GAO Renewable Ocean Energy spotlight reviews OTEC alongside wave and tidal technologies in the context of federal research investment priorities.

Applications

Ocean power has applications in a range of fields, including:

• Grid electricity generation from predictable renewable sources
• Remote island and offshore facility power supply
• Marine operations support and offshore platform electrification
• Desalination powered by wave, tidal, or OTEC systems
• Deep-sea aquaculture using OTEC cold-water co-products