Wave power is the process of capturing energy from wind-driven ocean waves to perform tasks such as generating electricity, removing salt from seawater, or moving water. A device used to harness this energy is called a wave energy converter (WEC).

Ocean waves are created mainly by wind blowing across the surface of the sea, as well as by forces such as the gravitational pull of the moon and sun, changes in water temperature, and other natural factors. When waves move slower than the wind above them, energy is transferred from the wind to the waves. Differences in air pressure on the top and bottom of a wave, along with wind friction, help waves grow larger.

Wave power is different from tidal power, which focuses on capturing energy from ocean currents caused by the gravitational forces of the sun and moon. However, wave power and tidal power share some similarities in the technologies used to capture their energy. Other natural forces, such as waves breaking, wind, the Coriolis effect, and differences in water temperature and salt content, can also create ocean currents.

As of 2023, wave power is not widely used for large-scale energy production, despite many early experiments. Efforts to use wave energy began in the 1890s or earlier, partly because waves carry a large amount of energy. Just below the ocean surface, the average energy flow from waves is about five times greater than the energy flow from wind 20 meters above the sea and 10 to 30 times greater than the energy flow from sunlight.

In 2000, the world’s first commercial wave power device, the Islay LIMPET, was built on the coast of Islay, Scotland, and connected to the UK’s electricity grid. In 2008, the first experimental wave energy farm with multiple generators, the Aguçadoura Wave Farm in Portugal, was opened. Both projects have since been discontinued. For more information about other wave power stations, see the List of wave power stations.

Wave energy converters can be grouped based on how they work, such as:

History

The first patent for using ocean waves to produce energy was filed in 1799 in Paris by Pierre-Simon Girard and his son. Around 1910, Bochaux-Praceique built a device in Royan, France, to power his home. This device is believed to be the first of a type called an oscillating water-column wave-energy system. Between 1855 and 1973, 340 patents related to wave energy were filed in the United Kingdom alone.

In the 1940s, Yoshio Masuda began experiments to explore wave energy. He tested many designs and built hundreds of units to power navigation lights. One idea involved using the movement at the joints of a floating raft, which Masuda proposed in the 1950s.

The oil crisis of 1973 increased interest in wave energy. Governments in several countries, especially the United Kingdom, Norway, and Sweden, started major programs to develop wave energy. Scientists, including Stephen Salter, Johannes Falnes, Kjell Budal, Michael E. McCormick, David Evans, Michael French, Nick Newman, and C. C. Mei, studied how to use waves to generate energy.

In 1974, Stephen Salter invented a wave-energy device called the Edinburgh Duck or nodding duck. Tests showed that the duck’s curved body could stop 90% of wave motion and convert 90% of that into electricity, achieving 81% efficiency. In the 1980s, other early prototypes were tested, but interest declined as oil prices dropped. Later, climate change renewed interest in wave energy.

The first wave energy test facility was created in Orkney, Scotland, in 2003 to help develop wave and tidal energy industries. The European Marine Energy Centre (EMEC) has supported more wave and tidal energy devices than any other site. After 2003, test facilities were also built in other countries worldwide.

A prize called the Saltire Challenge offered £10 million to the first team that could generate 100 gigawatt-hours of energy from waves over two years by 2017 (about 5.7 megawatts on average). The prize was not given. A 2017 study by Strathclyde University and Imperial College found that despite over £200 million in UK government funding over 15 years, wave energy devices were not yet ready for the market.

During the 2010s, public funding for wave energy research increased in many countries, including the European Union, the United States, and the United Kingdom. Annual funding typically ranged from 5 to 50 million USD. Combined with private investments, this supported many wave energy projects (see List of wave power projects).

Physical concepts

Ocean waves and energy converters interact in a complex way, similar to how fluids move. Scientists use special equations called Navier-Stokes equations to describe this interaction. These equations explain how fluid velocity, pressure, density, and external forces like gravity affect motion. Under normal conditions, ocean wave movement is described by Airy wave theory, which assumes:

• Fluid motion is mostly without swirling (irrotational).
• Pressure at the water surface is nearly constant.
• The depth of the seabed is nearly constant.

These assumptions are often valid when harvesting energy from ocean waves.

The first assumption means fluid motion can be described using a velocity potential, a mathematical function that helps predict movement. This potential must follow the Laplace equation, a rule that helps describe wave shapes. In ideal conditions, where viscosity (fluid thickness) is very small and only gravity acts on the fluid, the Navier-Stokes equations simplify to a form related to the Bernoulli conservation law. This law connects changes in velocity, pressure, and height to a constant value.

For small waves, a term involving the square of velocity can be ignored, leading to the linear Bernoulli equation. Airy wave theory then uses boundary conditions at the water surface and seabed to find solutions. These solutions describe waves as sine-shaped patterns, with wave height, wavelength, and depth determining specific values.

Wave energy is strongest at the surface and decreases with depth. However, near reflective coasts, standing waves can create pressure changes deep underwater, causing small ground vibrations called microseisms. These deep pressure changes are too weak to be useful for energy conversion.

Airy waves behave differently in deep and shallow water. In deep water (where depth is more than half the wavelength), waves spread out based on their size, with longer waves moving faster. In shallow water (where wavelength is much longer than depth), waves travel without spreading out.

Wave power depends on wave height and energy period. For example, waves 3 meters high with an 8-second energy period produce about 36 kilowatts of power per meter of wave crest. Larger storms with 15-meter waves and 15-second periods can generate about 1.7 megawatts of power per meter of wavefront.

Wave energy is proportional to the square of wave height, as described by linear wave theory. Waves carry energy horizontally, with crests moving at phase velocity and energy moving at group velocity. The energy flux (power) depends on wavelength, water depth, and gravity.

Wave height is influenced by wind speed, how long the wind blows, the distance over which wind affects waves (fetch), and seabed shape. Waves reach a "fully developed" state when wind conditions no longer increase their size. Larger waves are more powerful, but wave power also depends on wavelength, water density, depth, and gravity.

Wave energy converters

Wave energy converters (WECs) are grouped based on how they work, where they are placed, and the system that takes energy from waves. Locations include shoreline, nearshore, and offshore. Power take-off systems include: hydraulic ram, elastomeric hose pump, pump-to-shore, hydroelectric turbine, air turbine, and linear electrical generator.

The four most common types are:

• point absorber buoys
• surface attenuators
• oscillating water columns
• overtopping devices

Point absorber buoys float on the ocean surface and are secured with cables attached to the ocean floor. These buoys are smaller than the waves they capture. They absorb energy by creating a wave that cancels out the incoming waves. Buoys use the rising and falling motion of waves to generate electricity through linear generators, mechanical converters, or hydraulic pumps. Energy from waves can affect the shoreline, so these devices are usually placed far from the coast.

One point absorber design tested by CorPower includes a feature called a negative spring, which improves performance and protects the buoy during large waves. It also has a pneumatic cylinder that keeps the buoy at a fixed distance from the ocean floor, regardless of the tide. Under normal conditions, the buoy moves up and down twice as much as the wave’s height by adjusting its timing. It rises slightly after the wave passes, which helps it capture more energy. Tests in 2024 showed a 300% increase in power generation compared to a buoy without this feature.

Surface attenuators use multiple floating sections connected together. They are placed perpendicular to waves, and their movement from swells drives hydraulic pumps to create electricity. The Pelamis Wave Energy Converter is a well-known example of this type, though it is no longer in development.

Oscillating water column devices are fixed at one end to a structure or the ocean floor, while the other end moves freely. Energy is captured from the movement between the fixed point and the device. These systems often use floats, flaps, or membranes. Some designs use curved reflectors to focus wave energy at the capture point. They collect energy from the rising and falling motion of waves.

Oscillating water column devices can be placed onshore or offshore. Waves push air into a chamber, which forces the air through a turbine to create electricity. Air moving through turbines can create noise that may affect nearby birds and marine life. Marine animals might also become trapped in the air chamber. These devices use energy from the entire water column.

Overtopping devices are long structures that use wave speed to fill a reservoir with water higher than the surrounding ocean. The stored water’s height is used to generate electricity through low-head turbines. These devices can be placed on or offshore.

Submerged pressure differential converters use flexible membranes, often made of reinforced rubber, to capture wave energy. These systems use the difference in water pressure below waves to create a pressure difference inside a closed hydraulic system. This pressure difference drives a turbine and electrical generator. The flexible membranes are lightweight and can move easily, which helps them work well with wave energy. Their flexibility allows the working surface to change shape, which can be adjusted to match specific wave conditions or protect the device from extreme forces.

Submerged converters can be placed on the ocean floor or in midwater. In both cases, they are protected from strong water forces that occur at the ocean surface. Wave forces decrease as the depth increases, so placing the device at the right depth can balance protection from extreme forces and access to wave energy.

Floating in-air converters may be more reliable because they are above water, making them easier to inspect and maintain. Examples include:

• roll damping systems with turbines in compartments holding sloshing water
• horizontal axis pendulum systems
• vertical axis pendulum systems

In early 2024, a fully submerged wave energy converter using point absorber technology was approved in Spain. The device includes a buoy attached to the ocean floor and placed underwater, away from storm waves and out of public view.

Environmental effects

Common environmental concerns linked to marine energy are:

• The impact of electric and magnetic fields, as well as underwater noise;
• The possibility that structures may change how marine mammals, fish, and seabirds behave, such as attracting them, causing them to avoid the area, or leading to entanglement;
• Possible effects on natural ocean processes, like the movement of sediment and the quality of water;
• Foundation or mooring systems that may harm ocean floor organisms by causing them to become entangled or trapped;
• Electric forces created by underwater power cables;
• A small risk of collisions;
• The buildup of artificial reefs near fixed structures;
• Possible disturbance to areas where animals rest.

The Tethys database offers access to scientific studies and general information about how ocean current energy might affect the environment.

Potential

Wave energy's worldwide potential is estimated to be more than 2 terawatts. Areas with the highest potential for wave power include the western coast of Europe, the northern coast of the UK, and the Pacific coasts of North and South America, Southern Africa, Australia, and New Zealand. The best places to capture wave energy are in the temperate zones near the North and South Poles. In these areas, the strong winds called westerlies blow most strongly during winter.

The National Renewable Energy Laboratory (NREL) studied how much wave energy could be used in different countries. It found that the United States has the potential to generate about 1,170 terawatt-hours of energy each year, which is nearly one-third of the country's total electricity use. About half of this potential comes from the coastline of Alaska.

The actual energy that can be used from waves will be less than the theoretical maximum because of technical and economic challenges.

Wave energy is a type of energy that comes from the sun indirectly. The sun heats the Earth unevenly, creating wind systems that blow over the ocean. While ocean currents also contribute, wave energy mainly comes from wind. When energy moves from one source to another, some is lost due to the First Law of Thermodynamics, which states that energy cannot be created or destroyed, but some is always lost as heat. However, the energy in waves can be more concentrated than the original source because water is denser than air and energy spreads unevenly. This makes many areas around the world ideal for capturing wave energy.

Challenges

Environmental issues need to be solved. Problems related to society and the economy include fishermen losing their jobs or being forced to move, and dangers to ships and boats. Supporting systems, such as connections to the power grid, must be built. Some wave energy converters (WECs) have not always worked well. For example, in 2019, Seabased Industries AB in Sweden closed because of many problems, including real-world and money-related challenges.

Current wave power technology faces many technical challenges. These problems come from the complicated and changing nature of ocean waves, which require strong and efficient equipment to capture energy. Difficulties include creating wave energy devices that can survive damage from saltwater, severe weather, and very strong waves. Improving the performance and efficiency of wave energy converters, such as oscillating water column (OWC) devices, point absorbers, and overtopping devices, requires solving engineering problems caused by the unpredictable movement of waves. Also, developing systems to keep wave energy devices in place in the ocean and systems that turn wave energy into electricity are major technical challenges. Because a submerged flexible mound breakwater reduces more wave energy than a rigid structure, more wave energy is expected to be reduced when the structure changes shape significantly.

Wave farms

A wave farm, also called a wave power farm or wave energy park, is a group of wave energy devices placed together. These devices work together with water and electricity based on factors like the number of machines, how far apart they are, their arrangement, the type of waves in the area, the shape of the coastline and ocean floor, and how they are controlled. Designing a wave farm requires balancing many goals, such as producing a lot of energy, keeping costs low, and reducing energy changes. Wave farms near the shore can greatly affect how beaches change over time. For example, wave farms help reduce the wearing away of beaches, showing that combining coastal protection with energy production can make wave energy more financially useful. Other studies show that wave farms near lagoons may offer good coastal protection when planning how to use ocean areas.

Patents

• WIPO patent application WO2016032360 — 2016 Pumped-storage system – "Pressure buffering hydro power" patent application
• U.S. patent 8,806,865 — 2011 Ocean wave energy harnessing device – Pelamis/Salter's Duck Hybrid patent
• U.S. patent 4,152,895 — 1979 Wave powered motor – Lockheed Martin's "Dam-Atoll" patent
• U.S. patent 3,928,967 — 1974 Apparatus and method of extracting wave energy – The original "Salter's Duck" patent
• U.S. patent 4,134,023 — 1977 Apparatus for use in the extraction of energy from waves on water – Salter's method for improving "duck" efficiency
• U.S. patent 6,194,815 — 1999 Piezoelectric rotary electrical energy generator
• U.S. patent 1,930,958 — 1932 Wave Motor – Parsons Ocean Power Plant – Herring Cove Nova Scotia – March 1925. The world's first commercial plant to convert ocean wave energy into electrical power. Designer – Osborne Havelock Parsons – born in 1873 Petitcodiac, New Brunswick.
• Wave energy converters utilizing pressure differences US 20040217597 A1 — 2004 Wave energy converters utilizing pressure differences

A UK-based company has developed a Waveline Magnet that can achieve a levelized cost of electricity of £0.01/kWh with minimal levels of maintenance.