Wave power is the capture of energy of wind waves to do useful work – for example, electricity generation, water desalination, or pumping water. A machine that exploits wave power is a wave energy converter (WEC).
Wave power is distinct from tidal power, which captures the energy of the current caused by the gravitational pull of the Sun and Moon. Waves and tides are also distinct from ocean currents which are caused by other forces including breaking waves, wind, the Coriolis effect, cabbeling, and differences in temperature and salinity.
Wave-power generation is not a widely employed commercial technology, although there have been attempts to use it since at least 1890.
In 2000 the world's first commercial Wave Power Device, the Islay LIMPET was installed on the coast of Islay in Scotland and connected to the National Grid. In 2008, the first experimental multi-generator wave farm was opened in Portugal at the Aguçadoura Wave Park.
Waves are generated by wind passing over the surface of the sea. As long as the waves propagate slower than the wind speed just above the waves, there is an energy transfer from the wind to the waves. Both air pressure differences between the upwind and the lee side of a wave crest, as well as friction on the water surface by the wind, making the water to go into the shear stress causes the growth of the waves.
Wave height is determined by wind speed, the duration of time the wind has been blowing, fetch (the distance over which the wind excites the waves) and by the depth and topography of the seafloor (which can focus or disperse the energy of the waves). A given wind speed has a matching practical limit over which time or distance will not produce larger waves. When this limit has been reached the sea is said to be "fully developed".
Oscillatory motion is highest at the surface and diminishes exponentially with depth. However, for standing waves (clapotis) near a reflecting coast, wave energy is also present as pressure oscillations at great depth, producing microseisms. These pressure fluctuations at greater depth are too small to be interesting from the point of view of wave power.
The waves propagate on the ocean surface, and the wave energy is also transported horizontally with the group velocity. The mean transport rate of the wave energy through a vertical plane of unit width, parallel to a wave crest, is called the wave energy flux (or wave power, which must not be confused with the actual power generated by a wave power device).
with P the wave energy flux per unit of wave-crest length, Hm0 the significant wave height, Te the wave energy period, ρ the water density and g the acceleration by gravity. The above formula states that wave power is proportional to the wave energy period and to the square of the wave height. When the significant wave height is given in metres, and the wave period in seconds, the result is the wave power in kilowatts (kW) per metre of wavefront length.
Example: Consider moderate ocean swells, in deep water, a few km off a coastline, with a wave height of 3 m and a wave energy period of 8 seconds. Using the formula to solve for power, we get
meaning there are 36 kilowatts of power potential per meter of wave crest.
In major storms, the largest waves offshore are about 15 meters high and have a period of about 15 seconds. According to the above formula, such waves carry about 1.7 MW of power across each metre of wavefront.
An effective wave power device captures as much as possible of the wave energy flux. As a result, the waves will be of lower height in the region behind the wave power device.
where E is the mean wave energy density per unit horizontal area (J/m2), the sum of kinetic and potential energy density per unit horizontal area. The potential energy density is equal to the kinetic energy, both contributing half to the wave energy density E, as can be expected from the equipartition theorem. In ocean waves, surface tension effects are negligible for wavelengths above a few decimetres.
As the waves propagate, their energy is transported. The energy transport velocity is the group velocity. As a result, the wave energy flux, through a vertical plane of unit width perpendicular to the wave propagation direction, is equal to:
with cg the group velocity (m/s). Due to the dispersion relation for water waves under the action of gravity, the group velocity depends on the wavelength λ, or equivalently, on the wave period T. Further, the dispersion relation is a function of the water depth h. As a result, the group velocity behaves differently in the limits of deep and shallow water, and at intermediate depths:
Deep water corresponds with a water depth larger than half the wavelength, which is the common situation in the sea and ocean. In deep water, longer-period waves propagate faster and transport their energy faster. The deep-water group velocity is half the phase velocity. In shallow water, for wavelengths larger than about twenty times the water depth, as found quite often near the coast, the group velocity is equal to the phase velocity.
The first known patent to use energy from ocean waves dates back to 1799, and was filed in Paris by Girard and his son. An early application of wave power was a device constructed around 1910 by Bochaux-Praceique to light and power his house at Royan, near Bordeaux in France. It appears that this was the first oscillating water-column type of wave-energy device. From 1855 to 1973 there were already 340 patents filed in the UK alone.
Modern scientific pursuit of wave energy was pioneered by Yoshio Masuda's experiments in the 1940s. He tested various concepts of wave-energy devices at sea, with several hundred units used to power navigation lights. Among these was the concept of extracting power from the angular motion at the joints of an articulated raft, which was proposed in the 1950s by Masuda.
A renewed interest in wave energy was motivated by the oil crisis in 1973. A number of university researchers re-examined the potential to generate energy from ocean waves, among whom notably were Stephen Salter from the University of Edinburgh, Kjell Budal and Johannes Falnes from Norwegian Institute of Technology (now merged into Norwegian University of Science and Technology), Michael E. McCormick from U.S. Naval Academy, David Evans from Bristol University, Michael French from University of Lancaster, Nick Newman and C. C. Mei from MIT.
Stephen Salter's 1974 invention became known as Salter's duck or nodding duck, although it was officially referred to as the Edinburgh Duck. In small scale controlled tests, the Duck's curved cam-like body can stop 90% of wave motion and can convert 90% of that to electricity giving 81% efficiency.
In the 1980s, as the oil price went down, wave-energy funding was drastically reduced. Nevertheless, a few first-generation prototypes were tested at sea. More recently, following the issue of climate change, there is again a growing interest worldwide for renewable energy, including wave energy.
The world's first marine energy test facility was established in 2003 to kick-start the development of a wave and tidal energy industry in the UK. Based in Orkney, Scotland, the European Marine Energy Centre (EMEC) has supported the deployment of more wave and tidal energy devices than at any other single site in the world. EMEC provides a variety of test sites in real sea conditions. Its grid-connected wave test site is situated at Billia Croo, on the western edge of the Orkney mainland, and is subject to the full force of the Atlantic Ocean with seas as high as 19 metres recorded at the site. Wave energy developers currently testing at the centre include Aquamarine Power, Pelamis Wave Power, ScottishPower Renewables and Wello.
Wave power devices are generally categorized by the method used to capture or harness the energy of the waves, by location and by the power take-off system. Locations are shoreline, nearshore and offshore. Types of power take-off include: hydraulic ram, elastomeric hose pump, pump-to-shore, hydroelectric turbine, air turbine, and linear electrical generator. When evaluating wave energy as a technology type, it is important to distinguish between the four most common approaches: point absorber buoys, surface attenuators, oscillating water columns, and overtopping devices.
This device floats on the surface of the water, held in place by cables connected to the seabed. The point-absorber is deﬁned as having a device width much smaller than the incoming wavelength λ. A good point absorber has the same characteristics as a good wave-maker. The wave energy is absorbed by radiating a wave with destructive interference to the incoming waves. Buoys use the rise and fall of swells to generate electricity in various ways including directly via linear generators, or via generators driven by mechanical linear-to-rotary converters or hydraulic pumps. EMF generated by electrical transmission cables and acoustics of these devices may be a concern for marine organisms. The presence of the buoys may affect fish, marine mammals, and birds as potential minor collision risk and roosting sites. Potential also exists for entanglement in mooring lines. Energy removed from the waves may also affect the shoreline, resulting in a recommendation that sites remain a considerable distance from the shore.
These devices act similarly to point absorber buoys, with multiple floating segments connected to one another and are oriented perpendicular to incoming waves. A flexing motion is created by swells that drive hydraulic pumps to generate electricity. Environmental effects are similar to those of point absorber buoys, with an additional concern that organisms could be pinched in the joints.
These devices typically have one end fixed to a structure or the seabed while the other end is free to move. Energy is collected from the relative motion of the body compared to the fixed point. Oscillating wave surge converters often come in the form of floats, flaps, or membranes. Environmental concerns include minor risk of collision, artificial reefing near the fixed point, EMF effects from subsea cables, and energy removal effecting sediment transport. Some of these designs incorporate parabolic reflectors as a means of increasing the wave energy at the point of capture. These capture systems use the rise and fall motion of waves to capture energy. Once the wave energy is captured at a wave source, power must be carried to the point of use or to a connection to the electrical grid by transmission power cables.
Oscillating Water Column devices can be located on shore or in deeper waters offshore. With an air chamber integrated into the device, swells compress air in the chambers forcing air through an air turbine to create electricity. Significant noise is produced as air is pushed through the turbines, potentially affecting birds and other marine organisms within the vicinity of the device. There is also concern about marine organisms getting trapped or entangled within the air chambers.
Overtopping devices are long structures that use wave velocity to fill a reservoir to a greater water level than the surrounding ocean. The potential energy in the reservoir height is then captured with low-head turbines. Devices can be either on shore or floating offshore. Floating devices will have environmental concerns about the mooring system affecting benthic organisms, organisms becoming entangled, or EMF effects produced from subsea cables. There is also some concern regarding low levels of turbine noise and wave energy removal affecting the nearfield habitat.
Submerged pressure differential based converters are a comparatively newer technology  utilizing flexible (usually reinforced rubber) membranes to extract wave energy. These converters use the difference in pressure at different locations below a wave to produce a pressure difference within a closed power take-off fluid system. This pressure difference is usually used to produce flow, which drives a turbine and electrical generator. Submerged pressure differential converters frequently use flexible membranes as the working surface between the ocean and the power take-off system. Membranes offer the advantage over rigid structures of being compliant and low mass, which can produce more direct coupling with the wave’s energy. Their compliant nature also allows for large changes in the geometry of the working surface, which can be used to tune the response of the converter for specific wave conditions and to protect it from excessive loads in extreme conditions.
A submerged converter may be positioned either on the sea floor or in midwater. In both cases, the converter is protected from water impact loads which can occur at the free surface. Wave loads also diminish in non-linear proportion to the distance below the free surface. This means that by optimizing the depth of submergence for such a converter, a compromise between protection from extreme loads and access to wave energy can be found. Submerged WECs also have the potential to reduce the impact on marine amenity and navigation, as they are not at the surface. Examples of submerged pressure differential converters include M3 Wave, Bombora Wave Power's mWave, and CalWave.
Common environmental concerns associated with marine energy developments include:
The worldwide resource of coastal wave energy has been estimated to be greater than 2 TW. Locations with the most potential for wave power include the western seaboard of Europe, the northern coast of the UK, and the Pacific coastlines of North and South America, Southern Africa, Australia, and New Zealand. The north and south temperate zones have the best sites for capturing wave power. The prevailing westerlies in these zones blow strongest in winter.
Estimates have been made by the National Renewable Energy Laboratory (NREL) for various nations around the world in regards to the amount of energy that could be generated from wave energy converters (WECs) on their coastlines. For the United States in particular, it is estimated that the total energy amount that could be generated along its coastlines is equivalent to , which would account for nearly 33% of the total amount of energy consumed annually by the United States. While this sounds promising, the coastline along Alaska accounted for approx. 50% of the total energy created within this estimate. Considering this, there would need to be the proper infrastructure in place to transfer this energy from Alaskan shorelines to the mainland United States in order to properly capitalize on meeting United States energy demands. However, these numbers show the great potential these technologies have if they are implemented on a global scale to satisfy the search for sources of renewable energy.
WECs have gone under heavy examination through research, especially relating to their efficiencies and the transport of the energy they generate. NREL has shown that these WECs can have efficiencies near 50%. This is a phenomenal efficiency rating among renewable energy production. For comparison, efficiencies above 10% in solar panels are considered viable for sustainable energy production. Thus, a value of 50% efficiency for a renewable energy source is extremely viable for future development of renewable energy sources to be implemented across the world. Additionally, research has been conducted examining smaller WECs and their viability, especially relating to power output. One piece of research showed great potential with small devices, reminiscent of buoys, capable of generating upwards of of power in various wave conditions and oscillations and device size (up to a roughly cylindrical 21 kg buoy). Even further research has led to development of smaller, compact versions of current WECs that could produce the same amount of energy while using roughly one-half of the area necessary as current devices.
There is a potential impact on the marine environment. Noise pollution, for example, could have negative impact if not monitored, although the noise and visible impact of each design vary greatly. Other biophysical impacts (flora and fauna, sediment regimes and water column structure and flows) of scaling up the technology are being studied. In terms of socio-economic challenges, wave farms can result in the displacement of commercial and recreational fishermen from productive fishing grounds, can change the pattern of beach sand nourishment, and may represent hazards to safe navigation. Waves generate about 2,700 gigawatts of power. Of those 2,700 gigawatts, only about 500 gigawatts can be captured with current technology. Since 2008, Seabased Industry AB (SIAB) has deployed several units of wave energy converters (WECs) manufactured with different designs. Offshore deployments of WECs and underswater substation are being complicated procedures. SIAB discussed these deployments in terms of economy and time efficiency, as well as safety. Certain solutions are suggested for the various problems encountered during the deployments. It is found that the offshore deployment process can be optimized in terms of cost, time efficiency and safety.
A group of wave energy devices deployed in the same location is called wave farm, wave power farm or wave energy park. Wave farms represent a solution to achieve larger electricity production. The devices of a park are going to interact with each other hydrodynamically and electrically, according to the number of machines, the distance among them, the geometric layout, the wave climate, the local geometry, the control strategies. The design process of a wave energy farm is a multi-optimization problem with the aim to get a high power production and low costs and power fluctuations.
The Aegir wave farm was a planned wave farm off the south west of Shetland. The project was developed by Aegir Wave Power, a 2009 formed joint venture of Vattenfall and the wave power technology developer Pelamis Wave Power. The wave farm would have had capacity from 10 MW potentially up to 100 MW. Following the collapse of Pelamis in November 2014, the project was cancelled by Vattenfall in February 2015.Aquamarine Power
Aquamarine Power was a wave energy company, which was founded in 2005 to commercialise a wave energy device concept known as the Oyster wave energy converter. The company's head offices were based in Edinburgh. The company had further operations in Orkney, Ireland, Northern Ireland and the United States. Its chief executive officer was Martin McAdam, who joined the company in 2008. The company was advised by Trevor Whittaker, inventor of the Oyster concept, and Stephen Salter, inventor of the Salter's Duck.
The company ceased to trade on 20 November 2015.Energy in Sweden
Energy in Sweden describes energy and electricity production, consumption and import in Sweden. Electricity sector in Sweden is the main article of electricity in Sweden. Swedish climate bill Feb 2017 aims to make Sweden carbon neutral by 2045. Swedish target is to decline emission of climate gases 63% from 1990 to 2030 and international transportation excluding foreign flights 70%. By 2014 just over half of the country's total final energy consumption in electricity, heating and cooling and transport combined was provided by renewables, the highest share amongst the 28 EU member countries.Swedish government climate and environment investment budget will be ca 1.3 billion euros in 4 years 2017 - 2020 in non fossil travel, renewable energy and international (Annually in Swedish currency : 1.8 billion 2017, 1.5 billion 2018, 4.5 billion 2019 & ca 5 billion 2020.)European Marine Energy Centre
The European Marine Energy Centre (EMEC) Ltd is a UKAS accredited test and research centre focusing on wave and tidal power development based in the Orkney Islands, UK. The Centre provides developers with the opportunity to test full-scale grid-connected prototype devices in unrivalled wave and tidal conditions. The operations are spread over five sites:
Billia Croo wave energy test site, Mainland (wave power)
Fall of Warness tidal energy test site, off the island of Eday (tidal power)
Scale wave test site at Scapa Flow, off St Mary’s Bay
Scale tidal test site at Shapinsay Sound, off Head of Holland
Stromness (office and data facilities)EMEC was established by a grouping of public sector organisations following a recommendation by the House of Commons Science and Technology Committee in 2001. In addition to providing access to areas of sea with high wave and tidal energy potential, the centre also offers various kinds of support regarding regulatory issues, grid connection and meteorological monitoring as well as local research and engineering support.Iberdrola Renovables
Iberdrola Renovables was a subsidiary of Iberdrola, headquartered in Valencia, Spain, which included companies in the domains of renewable energy, particularly wind power. The firm was the world's largest renewable energy firm: it was the world's largest owner-operator of wind farms, but also operated in the solar, hydro, biomass and wave power industries.Islay LIMPET
Islay LIMPET was the world's first commercial wave power device and was connected to the United Kingdom's National Grid.List of power stations in Wales
This is a list of electricity-generating power stations in Wales, sorted by type and name, with installed capacity (May 2007).
Note that the DBERR maintains a comprehensive list of UK power stations here:List of wave power stations
The following page lists most power stations that run on wave power. Wave farms are classified into 8 types based on the technology used, such as Surface-following attenuator, Point absorber, Oscillating wave surge converter, Oscillating water column, Overtopping/Terminator, Submerged pressure differential, Bulge wave device, and Rotating mass.Marine energy
Marine energy or marine power (also sometimes referred to as ocean energy, ocean power, or marine and hydrokinetic energy) refers to the energy carried by ocean waves, tides, salinity, and ocean temperature differences. The movement of water in the world’s oceans creates a vast store of kinetic energy, or energy in motion. Some of this energy can be harnessed to generate electricity to power homes, transport and industries.
The term marine energy encompasses both wave power i.e. power from surface waves, and tidal power i.e. obtained from the kinetic energy of large bodies of moving water. Offshore wind power is not a form of marine energy, as wind power is derived from the wind, even if the wind turbines are placed over water.
The oceans have a tremendous amount of energy and are close to many if not most concentrated populations. Ocean energy has the potential of providing a substantial amount of new renewable energy around the world.Pelamis Wave Energy Converter
The Pelamis Wave Energy Converter was a technology that used the motion of ocean surface waves to create electricity. The machine was made up of connected sections which flex and bend as waves pass; it is this motion which is used to generate electricity.
Developed by the now defunct
Scottish company Pelamis Wave Power (formerly Ocean Power Delivery), the Pelamis became the first offshore wave machine to generate electricity into the grid, when it was first connected to the UK grid in 2004. Pelamis Wave Power then went on to build and test five additional Pelamis machines: three first-generation P1 machines, which were tested in a farm off the coast of Portugal in 2009, and two second-generation machines, the Pelamis P2, were tested off Orkney between 2010 and 2014. The company went into administration in November 2014, with the intellectual property transferred to the Scottish Government body Wave Energy Scotland.Pelamis Wave Power
Pelamis Wave Power designed and manufactured the Pelamis Wave Energy Converter – a technology that uses the motion of ocean surface waves to create electricity. The company was established in 1998 and had offices and fabrication facilities in Leith Docks, Edinburgh, Scotland. It went into administration in November 2014.Renewable energy in Africa
The developing nations of Africa are popular locations for the application of renewable energy technology. Currently, many nations already have small-scale solar, wind, and geothermal devices in operation providing energy to urban and rural populations. These types of energy production are especially useful in remote locations because of the excessive cost of transporting electricity from large-scale power plants. The applications of renewable energy technology has the potential to alleviate many of the problems that face Africans every day, especially if done in a sustainable manner that prioritizes human rights.
Access to energy is essential for the reduction of poverty and promotion of economic growth. Communication technologies, education, industrialization, agricultural improvement and expansion of municipal water systems all require abundant, reliable, and cost-effective energy access.Renewable energy in Portugal
Renewable energy in Portugal was the source for 25.7% of energy consumption in 2013. In 2014, 63% of Portugal's electricity needs were supplied by renewable sources.
In 2016, 58% of power produced in Portugal came from renewable sources, an increase against the previous year (50.4%), while renewable energy consumption represented 27.2% (early data) of total consumption.In 2001, the Portuguese government launched a new energy policy instrument – the E4 Programme (Energy efficiency and Endogenous Energies), consisting of a set of multiple, diversified measures aimed at promoting a consistent, integrated approach to energy supply and demand. By promoting energy efficiency and the use of renewable energy (endogenous) sources, the programme sought to upgrade the competitiveness of the Portuguese economy and to modernize the country’s social fabric, while preserving the environment by reducing gas emissions, especially the carbon dioxide.While from 2002-2007 the main priorities were focused on the introduction of natural gas (aiming at progressively replacing oil and coal in the energy balance) and liberalization of the energy market (by opening this former state-owned sector to competition and private investment), the emphasis shifted for the next 5 years was on energy efficiency (supply and demand sides) and use of endogenous (renewable) energy.During February 2016, an equivalent to 95% of electricity consumed in Portugal was produced by renewable sources such as biomass, hydropower, wind power and solar power. A total of 4139 GWh was produced by these sources. In May 2016, all of Portugal's electricity was produced renewably for a period of over four days, a landmark achievement for a modern European country.The renewable energy produced in Portugal fell from 55.5% of the total energy produced in 2016 to 41.8% in 2017, due to the drought of 2017, which severely affected the production of hydro electricity. The sources of the renewable energy that was produced in Portugal in 2017 were Wind power with 21.6% of the total (up from 20.7% in 2016), Hydro power with 13.3% (down from 28.1% in 2016), Bioenergy with 5.1% (same as in 2016), Solar power with 1.6% (up from 1.4% in 2016), Geothermal energy with 0.4% (up from 0.3% in 2016) and a small amount of Wave power in the Azores. 24% of the energy produced in the Azores is geothermal.Portugal committed to close all of the country's coal producing facilities by 2030, making it almost completely reliant on renewable energy in the incoming years.Renewable energy in Scotland
The production of renewable energy in Scotland is an issue that has come to the fore in technical, economic, and political terms during the opening years of the 21st century. The natural resource base for renewable energy is extraordinary by European, and even global standards, with the most important potential sources being wind, wave, and tide.
At the start of 2019, Scotland had 10.9 gigawatts (GW) of installed renewable electricity capacity. Renewable electricity generation in Scotland was 26,708 GWh in 2018, making up 74% of gross electricity consumption. Scottish renewable generation makes up approximately 25% of total UK renewable generation. In 2015, Scotland exported over 28.9 per cent of generation.In 2015, Scotland generated 59% of its electricity consumption through renewable sources, exceeding the country's goal of 50% renewable energy by 2015. Moving forward, the Scottish Government's energy plan calls for 100% of electricity consumption to be generated through renewable sources by 2020, and 50% of total energy consumption (including transportation) by 2030.Continuing improvements in engineering and economics are enabling more of the renewable resources to be utilised. Fears regarding peak oil and climate change have driven the subject high up the political agenda and are also encouraging the use of various biofuels. Although the finances of many projects remain either speculative or dependent on market incentives, it is probable that there has been a significant, and in all likelihood long-term change, in the underpinning economics.In addition to planned increases in large-scale generating capacity and microsystems using renewable sources, various related schemes to reduce carbon emissions are being researched. Although there is significant support from the public, private and community-led sectors, concerns about the effect of the technologies on the natural environment have been expressed. There is also an emerging political debate about the relationship between the siting, and the ownership and control of these widely distributed resources.Variable renewable energy
Variable renewable energy (VRE) is a renewable energy source that is non-dispatchable due to its fluctuating nature, like wind power and solar power, as opposed to a controllable renewable energy source such as hydroelectricity, or biomass, or a relatively constant source such as geothermal power or run-of-the-river hydroelectricity.Wave farm
A wave farm – or wave power farm or wave energy park – is a collection of machines in the same location and used for the generation of wave power electricity. Wave farms can be either offshore or nearshore, with the former the most promising for the production of large quantities of electricity for the grid. The first wave farm was constructed in Portugal, the Aguçadoura Wave Farm, consisting of three Pelamis machines. The world's largest is planned for Scotland.Wave power in Australia
Wave power in Australia is being developed as the country has a long and largely deep-water coastline. It is one of several regions of the world where wave power projects are being considered.
In early 2015 the Perth wave energy project was commissioned.Wave power in the United States
Wave power in the United States is under development in several locations off the east and west coasts as well as Hawaii. It has moved beyond the research phase and is producing reliable energy for the Grid. Its use to-date has been for situations where other forms of energy production are not economically viable and as such, the power output is currently modest. But major installations are planned to come on-line within the next few years.Wavegen
Wavegen Limited (later Voith Hydro Wavegen Limited) was a wave energy company based in Inverness, Scotland. It was founded in 1990 by Allan Thomson. It was sold to Voith Hydro in 2005, and they closed the company in 2013.
|Properties of gravity waves on the surface of deep water, shallow water and at intermediate depth, according to linear wave theory|
( h > ½ λ )
( h < 0.05 λ )
( all λ and h )
|phase velocity||m / s|
|group velocity[c]||m / s|
|wavelength||m||for given period T, the solution of:|
|wave energy density||J / m2|
|wave energy flux||W / m|
|angular frequency||rad / s|
|wavenumber||rad / m|