Wave energy is energy contained in ocean surface waves that can be converted into useful mechanical or electrical energy. Most naturally occurring ocean waves are generated when wind transfers energy to the surface of the water. The resulting waves can travel long distances, carrying energy from regions where winds generated them to distant coastlines. Wave energy technologies attempt to intercept this motion and convert it into electricity.
Unlike tidal energy, which is primarily associated with gravitational interactions between Earth, Moon and Sun, wave energy originates mainly from atmospheric wind energy transferred into the ocean. Waves contain both potential energy associated with the displacement of water above and below its equilibrium position and kinetic energy associated with the movement of water particles. The exact distribution of energy depends on wave height, period, wavelength, depth and other characteristics. Wave energy converters are engineered devices that respond to oscillating water motion, pressure differences or changes in water level. The electricity generated can be transmitted to shore or, in some applications, used offshore.
Ocean waves are described using parameters including significant wave height, wave period, wavelength, frequency and direction. Wave height is the vertical distance between crest and trough, while wave period is the time between successive wave crests passing a fixed location. Longer period waves can carry substantial energy and can travel large distances with relatively low energy loss. Deep water waves behave differently from shallow water waves because the influence of the seabed changes with depth.
As waves approach a shoreline, they undergo shoaling, refraction, diffraction and eventually breaking as their energy interacts with the seabed and coastal geometry. These processes affect the distribution of usable wave energy near shore. Wave energy resources are often strongest in regions exposed to persistent winds and long ocean fetches, particularly higher latitude coastlines where powerful storms generate large waves. However, an energetic wave climate can also impose severe mechanical loads on equipment. A device designed to capture energy efficiently during moderate waves must also survive extreme storms that may contain much greater forces.
Wave energy converters come in several technological categories. Oscillating water column devices use waves to move an enclosed column of air above a water chamber, causing air to flow back and forth through a turbine. Oscillating wave surge converters exploit the horizontal movement of water near the seabed or coast to move a hinged flap or similar structure. Point absorbers are relatively small devices that move in response to waves and extract energy from the relative motion of components.
Attenuators are elongated floating devices oriented broadly along the direction of wave propagation and use flexing or relative movement between sections to generate power. Overtopping devices allow waves to fill an elevated reservoir, after which water flows back through low head turbines. These technologies demonstrate that there is no single wave energy machine. Each design attempts to match mechanical motion to the characteristics of the local wave resource. Hydraulic systems, direct drive generators, air turbines and other power take off mechanisms may be used to convert mechanical motion into electricity.
The amount of energy available in waves depends strongly on wave height and period. For a simplified deep water wave, energy flux is related to the square of wave height and increases with wave period, meaning that larger and longer period waves can contain substantially more energy. Wave energy is therefore highly sensitive to sea conditions. A wave energy converter must capture enough energy to be economically useful while preventing excessive mechanical loads during severe conditions.
Control systems may alter the response of a device depending on wave conditions. Devices can be tuned so that their natural frequencies interact favourably with dominant wave periods, potentially increasing energy capture. However, the same dynamic response can become dangerous during extreme events. Mooring systems must maintain position while withstanding repeated wave forces, and underwater electrical cables must tolerate movement, currents and seabed conditions. The marine environment introduces corrosion, biofouling, fatigue and difficult maintenance requirements. Consequently, successful wave energy technology requires not only high theoretical energy capture but also durability, reliability, maintainability and acceptable lifecycle cost.
Wave energy has potential environmental benefits because electricity can be produced without directly burning fossil fuels. Nevertheless, marine energy devices are not environmentally neutral. Floating or fixed structures can modify local habitats and hydrodynamic conditions, while mooring systems and subsea cables disturb seabed areas during installation. Underwater noise and electromagnetic fields associated with equipment and cables may interact with marine organisms, although the significance varies by technology and site.
Devices can also alter wave energy reaching areas behind the installation, potentially affecting sediment transport or coastal processes. Large arrays could produce effects that differ from those of a single prototype, making cumulative environmental assessment important. On the other hand, some structures may create artificial habitat for marine organisms or exclude certain human activities from parts of the sea. The environmental balance therefore depends on design, location, array density, installation methods, species present and operating conditions.
The exploitation of wave motion for mechanical work has historical precedents, but modern wave energy research expanded substantially during the twentieth century as concerns about energy supply and advances in marine engineering stimulated development. Numerous experimental devices have been constructed and tested in different countries. Wave energy has historically faced difficulties achieving commercial maturity because the same environment that provides the energy also subjects machinery to harsh loads.
Offshore equipment must survive storms, corrosion and repeated cyclic stresses while producing electricity economically during ordinary conditions. Reliability problems can greatly increase maintenance costs because accessing offshore machinery can require specialised vessels and suitable weather windows. Research has therefore concentrated on robust structures, improved power take off systems, advanced control strategies, reliable moorings and better understanding of wave climates. The technology continues to be studied alongside tidal energy as part of the broader field of marine renewable energy.
Wave energy differs from offshore wind energy even though both can operate in the same general marine environment. Offshore wind turbines extract kinetic energy from moving air, whereas wave energy converters extract energy from oscillating water motion. Wave energy also differs from tidal energy because tides arise from astronomical gravitational forces, while most waves are generated by wind. These distinctions matter because the resource characteristics are different.
Wind and waves can be correlated because strong winds often generate larger waves, but they are not identical resources. Wave energy can sometimes continue arriving at a coastline after the local wind has weakened because waves generated elsewhere can propagate over large distances. Wave power is also generally more concentrated than solar energy over the same horizontal surface area, but extracting it requires equipment that can withstand a much harsher physical environment. The technology is consequently a specialised form of renewable energy engineering rather than simply an underwater version of another renewable technology.
The principal challenge of wave energy is balancing energy capture with survival and cost. A converter that extracts every possible unit of energy during calm and moderate conditions may experience damaging loads during extreme storms. Conversely, a very conservative design may survive storms but capture too little energy to be economically competitive. Engineers therefore study wave statistics, structural dynamics, hydrodynamics, fatigue, control systems, mooring behaviour and extreme event probabilities.
The economic value of a wave device depends on annual energy production, capital cost, maintenance requirements, financing, distance from shore, cable costs and reliability. Arrays may provide smoother aggregate output than a single device because individual machines experience different wave phases and local conditions, although the underlying resource remains variable. Integration with electricity networks can also require forecasting and complementary resources. These factors explain why wave energy remains technically promising but comparatively less deployed than mature renewable technologies such as wind, solar and established hydropower.
