Net zero emissions

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Net_zero_emissions

Estimated global warming by 2100 associated with various scenarios: Green dots: The International Energy Agency's proposal for reducing energy-related emissions to net zero by 2050 is consistent with limiting global warming to 1.5°C. Blue dots: Net-zero pledges and other pledges to reduce emissions would limit temperature rise to around 1.7°C. Yellow dots: Since many climate pledges are not backed by policies, policies announced as of 2022 would limit temperature rise to around 2.5°C. Red dots: Before the 2015 Paris Agreement, the world was on a trajectory for global warming of 3.5°C.

Global net zero emissions describes the state where emissions of carbon dioxide due to human activities and removals of these gases are in balance over a given period. It is often called simply net zero. In some cases, "emissions" refers to emissions of all greenhouse gases, and in others it refers only to emissions of carbon dioxide (CO₂).

To reach net zero targets requires actions to reduce emissions. One example would be by shifting from fossil fuel energy to sustainable energy sources. Organizations often offset their residual emissions by buying carbon credits. People often switch between the terms net zero emissions, carbon neutrality, and climate neutrality with the same meaning. However in some cases, these terms have different meanings from each other. Some standards for carbon neutral certification allow heavy carbon offsetting, however net zero standards require reducing emissions to >90% and then only offsetting the remaining <10% to fall in line with 1.5°C targets.

In the last few years, net zero has become the main framework for climate ambition. Both countries and organizations are setting net zero targets. Today more than 140 countries have a net zero emissions target. They include some countries that were resistant to climate action in previous decades. Country-level net zero targets now cover 92% of global GDP, 88% of emissions and 89% of the world population. 65% of the largest 2,000 publicly traded companies by annual revenue have net zero targets. Among Fortune 500 companies the percentage is 63%. Company targets can result from both voluntary action and government regulation.

Net zero claims vary enormously in how credible they are. Most have low credibility. This is despite the increasing number of commitments and targets. While 61% of global carbon dioxide emissions are covered by some sort of net zero target, credible targets cover only 7% of emissions. This low credibility reflects a lack of binding regulation. It is also due to the need for continued innovation and investment to make decarbonization possible.

To date, 27 countries have enacted domestic net zero legislation. These are laws that legislatures have passed which contain net zero targets or equivalent. There is currently no national regulation in place that legally requires companies based in that country to achieve net zero. Several countries including Switzerland are developing such legislation.

History and scientific justification

The idea of net zero came out of research in the late 2000s into how the atmosphere, oceans and carbon cycle were reacting to CO₂ emissions. This research found that global warming will only stop if CO₂ emissions are reduced to net zero. Net zero was basic to the goals of the Paris Agreement. This stated that we must "achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century". The term "net zero" gained popularity after the Intergovernmental Panel on Climate Change published its Special Report on Global Warming of 1.5 °C (SR15) in 2018, this report stated that "Reaching and sustaining net zero global anthropogenic [human-caused] CO₂ emissions and declining net non-CO₂ radiative forcing would halt anthropogenic global warming on multi-decadal timescales (high confidence)."

The idea of net zero emissions is often confused with "stabilization of greenhouse gas concentrations in the atmosphere". This is a term that dates from the 1992 Rio Convention. The two concepts are not the same. This is because the carbon cycle continuously sequesters or absorbs a small percentage of cumulative historical human-caused CO₂ emissions into vegetation and the ocean. This happens even after current CO₂ emissions are reduced to zero. If the concentration of CO₂ in the atmosphere were kept constant, some CO₂ emissions could continue. However global average surface temperatures would continue to increase for many centuries due to the gradual adjustment of deep ocean temperatures. If CO₂ emissions that result directly from human activities are reduced to net zero, the concentration of CO₂ in the atmosphere would decline. This would be at a rate just fast enough to compensate for this deep ocean adjustment. The result would be approximately constant global average surface temperatures over decades or centuries.

It will be quicker to reach net-zero emissions for CO₂ alone rather than CO₂ plus other greenhouse gases like methane, nitrous oxide and fluorinated gases. The net-zero target date for non-CO₂ emissions is later partly because modellers assume that some of these emissions such as methane from farming are harder to phase out. Emissions of short-lived gases such as methane do not accumulate in the climate system in the same way that CO₂ does. Therefore there is no need to reduce them to zero to halt global warming. This is because reductions in emissions of short-lived gases cause an immediate decline in the resulting radiative forcing. Radiative forcing is the change in the Earth's energy balance that they cause. However, these potent but short-lived gases will drive temperatures higher in the short term. This could possibly push the rise in temperature past the 1.5 °C threshold much earlier. A comprehensive net-zero emissions target would include all greenhouse gases. This would ensure that we also urgently reduce non-CO₂ gases.

Terminology

Countries, local governments, corporations, and financial institutions may all announce pledges for achieving to reach net zero emissions.

In climate change discussions, the terms net zero, carbon neutrality, and climate neutrality are often used as if they mean the same thing. In some contexts, however, they have different meanings from each other. The sections below explain this. People often use these terms without rigorous standard definitions.

Implementation

Since 2015, there has been significant growth in the number of actors pledging net zero emissions. Many standards have emerged that interpret the net zero concept and aim to measure progress towards net zero targets. Some of these standards are more robust than others. Some people have criticized weak standards for facilitating greenwashing. The UN, UNFCCC, International Organization for Standardization (ISO), and the Science Based Targets initiative (SBTi) promote more robust standards.

Types of greenhouse gas

Some targets aim to reach net zero emissions only for carbon dioxide. Others aim to reach net zero emissions of all greenhouse gases. Robust net zero standards state that all greenhouse gases should be covered by a given actor's targets.

Some authors say that carbon neutrality strategies focus only on carbon dioxide, but net zero includes all greenhouse gases. However some publications, such as the national strategy of France, use the term "carbon neutral" to mean net reductions of all greenhouse gases. The United States has pledged to achieve "net zero" emissions by 2050. As of March 2021 it had not specified which greenhouse gases will be included in its target.

Scopes of emissions sources

The Greenhouse Gas Protocol is a group of standards that are the most common in GHG accounting. These standards reflect a number of accounting principles. They include relevance, completeness, consistency, transparency, and accuracy. The standards divide emissions into three scopes:

• Scope 1 covers all direct GHG emissions within a corporate boundary (owned or controlled by a company). It includes fuel burned by the company, use of company vehicles, and fugitive emissions.
• Scope 2 covers indirect GHG emissions from consumption of purchased electricity, heat, cooling or steam. As of 2010, at least one third of global GHG emissions are Scope 2.
• Scope 3 emission sources include emissions from suppliers and product users (also known as the "value chain"). Transportation of goods, and other indirect emissions are also part of this scope. Scope 3 emissions these were estimated to represent 75% of all emissions reported to the Carbon Disclosure Project, though that percentage varies widely amongst business sectors.

Corporate net zero targets vary in how widely they cover emissions related to the company's activities. This can greatly affect the volume of emissions that are counted. Some oil companies, for instance, claim that their operations (Scopes 1 and 2) produce net zero emissions. These claims do not cover the emissions produced when the oil is burned by its customers, which are 70 - 90% of oil-related emissions. This is because they count as Scope 3 emissions.

Robust net zero standards require Scope 3 emissions to be counted, but "carbon neutrality" standards do not.

Approaches

The terms 'carbon neutral' and 'net zero' are often used interchangeably by politicians, businesses and scientists. Some experts use the terms differently, as illustrated by this graphic.

A given actor may plan to achieve net zero emissions through a combination of approaches. These would include (1) actions to reduce their own emissions, (2) actions to directly remove carbon dioxide from the atmosphere, and (3) purchasing carbon credits.

Reducing emissions

Robust net zero standards require actors to reduce their own emissions as much as possible following science-based pathways. They must then balance their residual emissions using removals and offsets. This typically involves shifting from fossil fuels to sustainable energy sources. Residual emissions are emissions that are not practical to reduce for technological reasons.

Experts and net zero frameworks disagree over the exact percentage of residual emissions that may be allowed. Most guidance suggests this should be limited to a small fraction of total emissions. Sector-specific and geographical factors would determine how much. The Science Based Targets initiative says that residual emissions across most sectors should fall between 5-10% of an organization's baseline emissions. It should be even lower for some sectors with competitive alternatives like the power sector. Sectors such as heavy manufacturing where it is harder to mitigate emissions will probably have a higher percentage of residual emissions by 2050.

The ISO and British Standards Institution (BSI) publish "carbon neutrality" standards that have higher tolerance for residual emissions than "net zero" standards. For example, BSI PAS 2060 is a British standard for measuring carbon neutrality. According to these standards, carbon neutrality is a short-term target, and net zero is a longer-term target.

Carbon removals and offsets

To balance residual emissions, actors may take direct action to remove carbon dioxide from the atmosphere and sequester it. Alternatively or in addition they can buy carbon credits that "offset" emissions. Carbon credits can be used to fund carbon removal projects such as reforestation.

Strong standards such as the ISO and BSI "net zero" standards only allow removal-based offsets that have the same permanence as the greenhouse gases that they balance. We call this concept "like for like" removals. Permanence means that removals must store greenhouse gases for the same period as the lifetime of the GHG emissions they balance. For example, methane has a lifetime of around 12 years in the atmosphere. Carbon dioxide lasts between 300 and 1,000 years. Accordingly, removals that balance carbon dioxide must last much longer than removals that balance methane.

Carbon credits can also fund initiatives that aim to avoid emissions. One example would be energy efficiency retrofits or renewable energy projects. Avoided emissions offsets result from actions that reduce emissions relative to a baseline or status quo. But they do not remove emissions from the atmosphere. Weak standards such as ISO and BSI "carbon neutrality" standards allow organizations to use avoided-emissions carbon credits. They do not specify how permanent or durable a credit must be.

Carbon offsetting has been critizied on several fronts. One important concern is that offsets may delay active emissions reductions. In a 2007 report from the Transnational Institute, Kevin Smith likened carbon offsets to medieval indulgences. He said they allowed people to pay "offset companies to absolve them of their carbon sins." He said this permits a "business as usual" attitude that stifles required major changes. Many people have criticized offsets for playing a part in greenwashing. This argument appeared in a 2021 watchdog ruling against Shell.

Loose regulation of claims by carbon offsetting schemes combined with the difficulties in calculating greenhouse gas sequestration and emissions reductions has also given rise to criticism. This argument is that this can result in schemes that do not adequately offset emissions in reality. There have been moves to create better regulation. The United Nations has operated a certification process for carbon offsets since 2001. This is called the Clean Development Mechanism. It aims to stimulate "sustainable development and emission reductions, while giving industrialized countries some flexibility in how they meet their emission reduction limitation targets." The UK Government's Climate Change Committee says reported emissions reductions or removals may have happened anyway or. not last into the future. This is despite an improvement in standards globally and in the UK.

There has also been criticisms of non-native and monocultural forest plantations as carbon offsets. This is because of their "limited—and at times negative—effects on native biodiversity" and other ecosystem services.

Most of the carbon credits on the voluntary market today do not meet UN, UNFCCC, ISO or SBTi standards for permanent carbon dioxide removals. So significant investment in carbon capture and permanent geological storage will probably be necessary to achieve net-zero targets by mid-century.

Timeframe

To achieve net zero, actors are encouraged to set net zero targets for 2050 or earlier. Long-term net zero targets should be supplemented by interim targets for every one to five years. The UN, UNFCCC, ISO, and SBTi all say that organizations should prioritize early, front-loaded emissions reduction. They say they should aim to halve emissions by 2030. Specific emissions reduction targets and pathways may look different for different sectors. Some may be able to decarbonize more quickly and easily than others.

Many companies often claim a commitment to reach net zero emissions by the year 2050. These promises are often made at the corporate level. Both governments and international agencies encourage businesses to contribute to a national, or international, net zero pledge. The International Energy Agency says that global investment in low carbon substitutes for fossil fuels needs to reach US$4 trillion annually by 2030 for the world to get to net zero by 2050.

Some groups have raised concerns that net zero cannot be achieved worldwide by 2050.

Comprehensive accounting

The guidance from standards institutions says that organizations should choose a base year to measure emissions reductions against. This should be representative of their typical greenhouse gas profile. They should explain the choice of baseline and how they will account for changes in conditions since the baseline. Financial organizations should also include emissions within their portfolio. This should include all organizations they have financed, invested in, or insured. Countries and regions should include both territorial emissions released within their boundaries and consumption emissions related to products and services imported and consumed within their boundaries.

Cities and countries pose a challenge when it comes to calculating emissions. This is because the production of products and services within their boundaries might be linked to either internal consumption or exports. At the same time the population also consumes imported products and services. So it is important to state explicitly whether emissions are counted at the location of production or consumption. This helps to prevent double counting. The lengthy manufacturing chains of a globalised market might make this challenging. There are additional challenges with looking at renewable energy systems and electric vehicle batteries. This is because the necessary embodied energy and other effects of raw material extraction are often significant when measuring life-cycle emissions. However the local emissions at the place they are used may be small.

Equity and impact

The concept of net zero has attracted criticism for the impact it could have on equity and distribution. The use of removals or carbon credits for offsetting has been particularly controversial. This is because of the possibility that offset projects themselves could have harmful effects. The ISO Net Zero Guidelines say that net zero strategies should align with the United Nations Sustainable Development Goals.This is in order to "support equity and global transition to a net zero economy, and any subsequent UN global goals which supersede the 2030 SDGs." The UNFCCC's Race to Zero campaign says emissions reductions and removals should "safeguard the rights of the most vulnerable people and communities". It says that organizations should disclose how they will support communities affected by climate impacts and climate transition.

Alignment with the global net zero goal

The United Nations High-Level Expert Group on the Net Zero Emissions Commitments of Non-State Entities has made several recommendations for non-state actors. Non-state actors include cities, regional governments, financial institutions, and corporations. One of these is not financing new fossil fuel development. Another is supporting strong climate policy. And another is ensuring that business activities and investments do not contribute to deforestation.

Country examples

A number of countries have net zero, or even net negative carbon emissions. These generally have a high level of forestation.

• Bhutan
• Comoros
• Gabon
• Guyana
• Madagascar
• Niue
• Panama
• Suriname

For example, Costa Rica sources much of its energy needs from renewables and is undertaking reforestation projects. In 2007, the Costa Rican government announced the commitment for Costa Rica to become the first carbon neutral country by 2021. Costa Rica would be, according to its leaders, the first country in the world to have launched in 2019 a comprehensive decarbonization plan (zero carbon emissions by 2050).

Standards for products

Leading standards and guidance allow official accreditation bodies to certify products as carbon neutral but not as net zero. The rationale behind this is that until organizations and their supply chains are on track for net zero, allowing a product to claim to be net zero at this point would be disingenuous and lead to greenwashing.

Credibility

Status of net-zero carbon emissions targets as of October, 2023 . The inclusion criteria for net-zero commitments may vary from country to country.

More and more nations and private and public-sector organizations are committing to net zero. But the credibility of these claims remains low. There is no binding regulation requiring a transition to net zero. So the overwhelming majority of net zero commitments have been made on a voluntary basis. The lack of an enforcement mechanism surrounding these claims means that many are dubious. In many sectors such as steel, cement, and chemicals, the pathway to reaching net zero in terms of technology remains unclear. Further investment in research and innovation and further regulation will probably be necessary if net zero claims are to become more credible.

A consortium of climate scientists has tracked net zero commitments. Their research found that net pledges drafted in law or policy documentation have grown from 7% of countries in 2020 to 75% in 2023. However, very few have met the minimum requirements for a "decent pledge". The UN Race to Zero campaign calls them "starting line criteria". This states that they must have a "plan and published evidence of action taken towards reaching the target" besides a stated pledge.

The role of carbon credits

One of the main reasons for the low credibility of many net zero claims is their heavy reliance on carbon credits. Carbon credits are often used for offsetting. They reduce or remove emissions of carbon dioxide or other greenhouse gases in order to compensate for emissions made elsewhere. Many fossil fuel companies have made commitments to be net zero by 2050. At the same time they continue to increase greenhouse gas emissions by extracting and producing fossil fuels. They claim that they will use carbon credits and carbon capture technology in order to continue extracting and burning fossil fuels. The UN has condemned such pledges as dangerous examples of greenwashing.

Criticism

Climate scientists James Dyke, Bob Watson, and Wolfgang Knorr argue that the concept of net zero has been harmful for emissions reductions. This is because it allows actors to defer present-day emissions reductions by relying on future, unproved technological fixes. Examples are carbon offsetting, carbon dioxide removal and geoengineering. "The problems come when it is assumed that these [technological fixes] can be deployed at vast scale. This effectively serves as a blank cheque for the continued burning of fossil fuels and the acceleration of habitat destruction," they said. By tracing the history of previous failures in climate policy at reducing emissions from 1988 to 2021, they said they "[arrive] at the painful realisation that the idea of net zero has licensed a recklessly cavalier 'burn now, pay later' approach which has seen carbon emissions continue to soar". They concluded: "Current net zero policies will not keep warming to within 1.5 °C because they were never intended to. They were and still are driven by a need to protect business as usual, not the climate. If we want to keep people safe then large and sustained cuts to carbon emissions need to happen now. [...] The time for wishful thinking is over."

In March 2021, Tzeporah Berman, chair of the Fossil Fuel Non-Proliferation Treaty Initiative, argued that the Treaty would be a more genuine and realistic way to achieve the goals of the Paris Agreement than the net zeron approach. She described net zero as "delusional and based on bad science".

In his 2021 report, Dangerous Distractions, economist Marc Lee said that net zero had the potential to be a dangerous distraction that reduced political pressure to reduce emissions. "A net zero target means less incentive to get to 'real zero' emissions from fossil fuels, an escape hatch that perpetuates business as usual and delays more meaningful climate action," he said. "Rather than gambling on carbon removal technologies of the future, Canada should plan for a managed wind down of fossil fuel production and invest public resources in bona fide solutions like renewables and a just transition from fossil fuels," he said.

Marine energy

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/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.

Global potential

There is the potential to develop 20,000–80,000 terawatt-hours per year (TWh/y) of electricity generated by changes in ocean temperatures, salt content, movements of tides, currents, waves and swells

Global potential

Form	Annual generation
Tidal energy	>300 TWh
Marine current power	>800 TWh
Osmotic power Salinity gradient	2,000 TWh
Ocean thermal energy Thermal gradient	10,000 TWh
Wave energy	8,000–80,000 TWh
Source: IEA-OES, Annual Report 2007

Indonesia, as an archipelagic country that is three quarters ocean, has 49 GW recognized potential ocean energy and has 727 GW theoretical potential ocean energy.

Forms of ocean energy

The oceans represent a vast and largely untapped source of energy in the form of surface waves, fluid flow, salinity gradients, and thermal differences.

Marine and Hydrokinetic (MHK) or marine energy development in U.S. and international waters includes projects using the following devices:

• Wave power converters in open coastal areas with significant waves;
• Tidal turbines placed in coastal and estuarine areas;
• In-stream turbines in fast-moving rivers;
• Ocean current turbines in areas of strong marine currents;
• Ocean thermal energy converters in deep tropical waters.

Marine current power

Main article: Marine current power

Strong ocean currents are generated from a combination of temperature, wind, salinity, bathymetry, and the rotation of the Earth. The Sun acts as the primary driving force, causing winds and temperature differences. Because there are only small fluctuations in current speed and stream location with no changes in direction, ocean currents may be suitable locations for deploying energy extraction devices such as turbines.

Ocean currents are instrumental in determining the climate in many regions around the world. While little is known about the effects of removing ocean current energy, the impacts of removing current energy on the farfield environment may be a significant environmental concern. The typical turbine issues with blade strike, entanglement of marine organisms, and acoustic effects still exists; however, these may be magnified due to the presence of more diverse populations of marine organisms using ocean currents for migration purposes. Locations can be further offshore and therefore require longer power cables that could affect the marine environment with electromagnetic output.

Osmotic power

Main article: Osmotic power

At the mouth of rivers where fresh water mixes with salt water, energy associated with the salinity gradient can be harnessed using pressure-retarded reverse osmosis process and associated conversion technologies. Another system is based on using freshwater upwelling through a turbine immersed in seawater, and one involving electrochemical reactions is also in development.

Significant research took place from 1975 to 1985 and gave various results regarding the economy of PRO and RED plants. It is important to note that small-scale investigations into salinity power production take place in other countries like Japan, Israel, and the United States. In Europe the research is concentrated in Norway and the Netherlands, in both places small pilots are tested. Salinity gradient energy is the energy available from the difference in salt concentration between freshwater with saltwater. This energy source is not easy to understand, as it is not directly occurring in nature in the form of heat, waterfalls, wind, waves, or radiation.

Ocean thermal energy

Main article: Ocean thermal energy conversion

Water typically varies in temperature from the surface warmed by direct sunlight to greater depths where sunlight cannot penetrate. This differential is greatest in tropical waters, making this technology most applicable in water locations. A fluid is often vaporized to drive a turbine that may generate electricity or produce desalinized water. Systems may be either open-cycle, closed-cycle, or hybrid.

Tidal power

Main article: Tidal power

The energy from moving masses of water – a popular form of hydroelectric power generation. Tidal power generation comprises three main forms, namely tidal stream power, tidal barrage power, and dynamic tidal power.

Wave power

Main article: Wave power

Solar energy from the Sun creates temperature differentials that result in wind. The interaction between wind and the surface of water creates waves, which are larger when there is a greater distance for them to build up. Wave energy potential is greatest between 30° and 60° latitude in both hemispheres on the west coast because of the global direction of wind. 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.

The wave energy sector is reaching a significant milestone in the development of the industry, with positive steps towards commercial viability being taken. The more advanced device developers are now progressing beyond single unit demonstration devices and are proceeding to array development and multi-megawatt projects. The backing of major utility companies is now manifesting itself through partnerships within the development process, unlocking further investment and, in some cases, international co-operation.

At a simplified level, wave energy technology can be located near-shore and offshore. Wave energy converters can also be designed for operation in specific water depth conditions: deep water, intermediate water or shallow water. The fundamental device design will be dependent on the location of the device and the intended resource characteristics.

Environmental effects

Common environmental concerns associated with marine energy developments include:

• the risk of marine mammals and fish being struck by tidal turbine blades
• the effects of EMF and underwater noise emitted from operating marine energy devices
• the physical presence of marine energy projects and their potential to alter the behavior of marine mammals, fish, and seabirds with attraction or avoidance
• the potential effect on nearfield and farfield marine environment and processes such as sediment transport and water quality

The Tethys database provides access to scientific literature and general information on the potential environmental effects of marine energy.

Wave power

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Wave_power

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).

Waves are generated primarily by wind passing over the sea's surface and also by tidal forces, temperature variations, and other factors. As long as the waves propagate slower than the wind speed just above, energy is transferred from the wind to the waves. Air pressure differences between the windward and leeward sides of a wave crest and surface friction from the wind cause shear stress and wave growth.

Wave power as a descriptive term is different than tidal power, which seeks to primarily capture the energy of the current caused by the gravitational pull of the Sun and Moon. However, wave power and tidal power are not fundamentally distinct and have significant cross-over in technology and implementation. Other forces can create currents, including breaking waves, wind, the Coriolis effect, cabbeling, and temperature and salinity differences.

As of 2022, wave power is not widely employed for commercial applications, after a long series of trial projects. Attempts to use this energy began in 1890 or earlier, mainly due to its high power density. Just below the ocean's water surface the wave energy flow, in time-average, is typically five times denser than the wind energy flow 20 m above the sea surface, and 10 to 30 times denser than the solar energy flow.

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 UK national grid. In 2008, the first experimental multi-generator wave farm was opened in Portugal at the Aguçadoura wave park. Both projects have since ended.

Wave energy converters can be classified based on their working principle as either:

• oscillating water columns (with air turbine)
• oscillating bodies (with hydroelectric motor, hydraulic turbine, linear electrical generator)
• overtopping devices (with low-head hydraulic turbine)

History

The first known patent to extract energy from ocean waves was in 1799, filed in Paris by Pierre-Simon Girard and his son. An early device was constructed around 1910 by Bochaux-Praceique to power his house in Royan, France. It appears that this was the first oscillating water-column type of wave-energy device. From 1855 to 1973 there were 340 patents filed in the UK alone.

Modern pursuit of wave energy was pioneered by Yoshio Masuda's 1940s experiments. He tested various concepts, constructing hundreds of 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 Masuda proposed in the 1950s.

The oil crisis in 1973 renewed interest in wave energy. Substantial wave-energy development programmes were launched by governments in several countries, in particular in the UK, Norway and Sweden. Researchers re-examined waves' potential to extract energy, notably Stephen Salter, Johannes Falnes, Kjell Budal, Michael E. McCormick, David Evans, Michael French, Nick Newman, and C. C. Mei.

Salter's 1974 invention became known as Salter's duck or nodding duck, officially the Edinburgh Duck. In small-scale 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, several other first-generation prototypes were tested, but as oil prices ebbed, wave-energy funding shrank. Climate change later reenergized the field.

The world's first wave energy test facility was established in Orkney, Scotland in 2003 to kick-start the development of a wave and tidal energy industry. The European Marine Energy Centre(EMEC) has supported the deployment of more wave and tidal energy devices than any other single site. Subsequent to its establishment test facilities occurred also in many other countries around the world, providing services and infrastructure for device testing.

The £10 million Saltire prize challenge was to be awarded to the first to be able to generate 100 GWh from wave power over a continuous two-year period by 2017 (about 5.7 MW average). The prize was never awarded. A 2017 study by Strathclyde University and Imperial College focused on the failure to develop "market ready" wave energy devices – despite a UK government investment of over £200 million over 15 years.

Public bodies have continued and in many countries stepped up the research and development funding for wave energy during the 2010s. This includes both EU, US and UK where the annual allocation has typically been in the range 5-50 million USD. Combined with private funding, this has led to a large number of ongoing wave energy projects.

Physical concepts

Main article: Airy wave theory

Like most fluid motion, the interaction between ocean waves and energy converters is a high-order nonlinear phenomenon. It is described using the incompressible Navier-Stokes equations

$${\displaystyle \begin{array}{rl}\frac{\mathrm{\partial }\overrightarrow{u}}{\mathrm{\partial }t}+(\overrightarrow{u}\cdot \overrightarrow{\mathrm{\nabla }})\overrightarrow{u}& =\nu \mathrm{\Delta }\overrightarrow{u}+\frac{\overrightarrow{F_{\text{ext}}}-\overrightarrow{\mathrm{\nabla }}p}{\rho }\\ \overrightarrow{\mathrm{\nabla }}\cdot \overrightarrow{u}& =0\end{array}}$$

where $\overrightarrow{u}(t,x,y,z)$ is the fluid velocity, $p$ is the pressure, $\rho$ the density, $\nu$ the viscosity, and $\overrightarrow{F_{\text{ext}}}$ the net external force on each fluid particle (typically gravity). Under typical conditions, however, the movement of waves is described by Airy wave theory, which posits that

• fluid motion is roughly irrotational,
• pressure is approximately constant at the water surface, and
• the seabed depth is approximately constant.

In situations relevant for energy harvesting from ocean waves these assumptions are usually valid.

Airy equations

The first condition implies that the motion can be described by a velocity potential $\varphi (t,x,y,z)$:

$${\displaystyle \overrightarrow{\mathrm{\nabla }}\times \overrightarrow{u}=\overrightarrow{0}\iff \overrightarrow{u}=\overrightarrow{\mathrm{\nabla }}\varphi \text{,}}$$

which must satisfy the Laplace equation,

$${\displaystyle {\mathrm{\nabla }}^2\varphi =0\text{.}}$$

In an ideal flow, the viscosity is negligible and the only external force acting on the fluid is the earth gravity ${\displaystyle \overrightarrow{F_{\text{ext}}}=(0,0,-\rho g)}$. In those circumstances, the Navier-Stokes equations reduces to

$${\displaystyle \frac{\mathrm{\partial }\overrightarrow{\mathrm{\nabla }}\varphi }{\mathrm{\partial }t}+\frac{1}{2}\overrightarrow{\mathrm{\nabla }}(\overrightarrow{\mathrm{\nabla }}\varphi {)}^2=-\frac{1}{\rho }\cdot \overrightarrow{\mathrm{\nabla }}p+\frac{1}{\rho }\overrightarrow{\mathrm{\nabla }}(\rho gz),}$$

which integrates (spatially) to the Bernoulli conservation law:

$${\displaystyle \frac{\mathrm{\partial }\varphi }{\mathrm{\partial }t}+\frac{1}{2}(\overrightarrow{\mathrm{\nabla }}\varphi {)}^2+\frac{1}{\rho }p+gz=(\text{const})\text{.}}$$

Linear potential flow theory

Motion of a particle in an ocean wave.

A = At deep water. The circular motion magnitude of fluid particles decreases exponentially with increasing depth below the surface.
B = At shallow water (ocean floor is now at B). The elliptical movement of a fluid particle flattens with decreasing depth.
1 = Propagation direction.
2 = Wave crest.
3 = Wave trough.

When considering small amplitude waves and motions, the quadratic term ${\left(\overrightarrow{\mathrm{\nabla }}\varphi \right)}^2$ can be neglected, giving the linear Bernoulli equation,

$${\displaystyle \frac{\mathrm{\partial }\varphi }{\mathrm{\partial }t}+\frac{1}{\rho }p+gz=(\text{const})\text{.}}$$

and third Airy assumptions then imply

$${\displaystyle \begin{array}{rl}& \frac{{\mathrm{\partial }}^2\varphi }{\mathrm{\partial }{t}^2}+g\frac{\mathrm{\partial }\varphi }{\mathrm{\partial }z}=0(\text{surface})\\ & \frac{\mathrm{\partial }\varphi }{\mathrm{\partial }z}=0\phantom{\frac{{\mathrm{}}^{\mathrm{}}}{\mathrm{}{}^{\mathrm{}}}}(\text{seabed})\end{array}}$$

These constraints entirely determine sinusoidal wave solutions of the form

$${\displaystyle \varphi =A(z)\sin (kx-\omega t)\text{,}}$$

where ${\displaystyle k}$ determines the wavenumber of the solution and ${\displaystyle A(z)}$ and ${\displaystyle \omega }$ are determined by the boundary constraints (and ${\displaystyle k}$). Specifically,

$${\displaystyle \begin{array}{rl}& A(z)=\frac{gH}{2\omega }\frac{\cosh (k(z+h))}{\cosh (kh)}\\ & \omega =gk\tanh (kh)\text{.}\end{array}}$$

The surface elevation ${\displaystyle \eta }$ can then be simply derived as

$${\displaystyle \eta =-\frac{1}{g}\frac{\mathrm{\partial }\varphi }{\mathrm{\partial }t}=\frac{H}{2}\cos (kx-\omega t)\text{:}}$$

a plane wave progressing along the x-axis direction.

Consequences

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. Pressure fluctuations at greater depth are too small to be interesting for wave power conversion.

The behavior of Airy waves offers two interesting regimes: water deeper than half the wavelength, as is common in the sea and ocean, and shallow water, with wavelengths larger than about twenty times the water depth. Deep waves are dispersionful: Waves of long wavelengths propagate faster and tend to outpace those with shorter wavelengths. Deep-water group velocity is half the phase velocity. Shallow water waves are dispersionless: group velocity is equal to phase velocity, and wavetrains propagate undisturbed.

The following table summarizes the behavior of waves in the various regimes:

Airy gravity waves on the surface of deep water, shallow water, or intermediate depth

Wave power formula

Photograph of the elliptical trajectories of water particles under a – progressive and periodic – surface gravity wave in a wave flume. The wave conditions are: mean water depth d = 2.50 ft (0.76 m), wave height H = 0.339 ft (0.103 m), wavelength λ = 6.42 ft (1.96 m), period T = 1.12 s.

In deep water where the water depth is larger than half the wavelength, the wave energy flux is

${\displaystyle P=\frac{\rho g^2}{64\pi }{H}_{m0}^2{T}_e\approx \left(0.5\frac{\text{kW}}{{\text{m}}^3\cdot \text{s}}\right)H_{m0}^2{T}_e,}$

with P the wave energy flux per unit of wave-crest length, H_m0 the significant wave height, T_e 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.

For 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 s. Solving for power produces

${\displaystyle P\approx 0.5\frac{\text{kW}}{{\text{m}}^3\cdot \text{s}}(3\cdot \text{m}{)}^2(8\cdot \text{s})\approx 36\frac{\text{kW}}{\text{m}},}$

or 36 kilowatts of power potential per meter of wave crest.

In major storms, the largest offshore sea states have significant wave height of about 15 meters and energy period of about 15 seconds. According to the above formula, such waves carry about 1.7 MW of power across each meter of wavefront.

An effective wave power device captures a significant portion of the wave energy flux. As a result, wave heights diminish in the region behind the device.

Energy and energy flux

In a sea state, the mean energy density per unit area of gravity waves on the water surface is proportional to the wave height squared, according to linear wave theory:

${\displaystyle E=\frac{1}{16}\rho g{H}_{m0}^2,}$ 

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.

The waves propagate on the surface, where crests travel with the phase velocity while the energy is 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 the energy flux (or wave power, not to be confused with the output produced by a device), and is equal to:

${\displaystyle P=E{c}_g,}$ with c_g the group velocity (m/s).

Due to the dispersion relation for waves under gravity, the group velocity depends on the wavelength λ, or equivalently, on the wave period T.

Wave height is determined by wind speed, the length of time the wind has been blowing, fetch (the distance over which the wind excites the waves) and by the bathymetry (which can focus or disperse the energy of the waves). A given wind speed has a matching practical limit over which time or distance do not increase wave size. At this limit the waves are said to be "fully developed". In general, larger waves are more powerful but wave power is also determined by wavelength, water density, water depth and acceleration of gravity.

Wave energy converters

Wave energy converters (WECs) are generally categorized by the method, 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.

Different conversion routes from wave energy to useful energy in terms or electricity or direct use.

The four most common approaches are:

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

Generic wave energy concepts: 1. Point absorber, 2. Attenuator, 3. Oscillating wave surge converter, 4. Oscillating water column, 5. Overtopping device, 6. Submerged pressure differential, 7. Floating in-air converters.

Point absorber buoy

This device floats on the surface, held in place by cables connected to the seabed. The point-absorber has a device width much smaller than the incoming wavelength λ. Energy is absorbed by radiating a wave with destructive interference to the incoming waves. Buoys use the swells' rise and fall to generate electricity directly via linear generators, generators driven by mechanical linear-to-rotary converters, or hydraulic pumps. Energy extracted from waves may affect the shoreline, implying that sites should remain well offshore.

Surface attenuator

These devices use multiple floating segments connected to one another. They are oriented perpendicular to incoming waves. A flexing motion is created by swells, and that motion drives hydraulic pumps to generate electricity.

Oscillating wave surge converter

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. Converters often come in the form of floats, flaps, or membranes. Some designs incorporate parabolic reflectors to focus energy at the point of capture. These systems capture energy from the rise and fall of waves.

Oscillating water column

Oscillating water column devices can be located onshore or offshore. Swells compress air in an internal chamber, forcing air through a turbine to create electricity. Significant noise is produced as air flows through the turbines, potentially affecting nearby birds and marine organisms. Marine life could possibly become trapped or entangled within the air chamber. It draws energy from the entire water column.

Overtopping device

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 captured with low-head turbines. Devices can be on- or offshore.

Submerged pressure differential

Submerged pressure differential based converters use flexible (typically 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 hydraulic system. This pressure difference is usually used to produce flow, which drives a turbine and electrical generator. Submerged pressure differential converters typically use flexible membranes as the working surface between the water and the power take-off. Membranes are pliant and low mass, which can strengthen coupling with the wave's energy. Their pliancy allows large changes in the geometry of the working surface, which can be used to tune 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 seafloor 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 depth, protection from extreme loads and access to wave energy can be balanced.

Floating in-air converters

Wave Power Station using a pneumatic Chamber

Simplified design of Wave Power Station

Floating in-air converters potentially offer increased reliability because the device is located above the water, which also eases inspection and maintenance. Examples of different concepts of floating in-air converters include:

• roll damping energy extraction systems with turbines in compartments containing sloshing water
• horizontal axis pendulum systems
• vertical axis pendulum systems

Environmental effects

Further information: Environmental impact of electricity generation

Common environmental concerns associated with marine energy include:

• The effects of electromagnetic fields and underwater noise;
• Physical presence's potential to alter the behavior of marine mammals, fish, and seabirds with attraction, avoidance, entanglement
• Potential effect on marine processes such as sediment transport and water quality.
• Foundation/mooring systems can affect benthic organisms via entanglement/entrapment
• Electromotive force effects produced from subsea power cables.
• Minor collision risk
• Artificial reef accumulation near fixed installations
• Potential disuption to roosting sites

Potential

Wave energy's worldwide theoretical potential 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.

World wave energy resource map

The National Renewable Energy Laboratory (NREL) estimated the theoretical wave energy potential for various countries. It estimated that the US' potential was equivalent to 1170 TWh per year or almost 1/3 of the country's electricity consumption. The Alaska coastline accounted for ~50% of the total.

Note that the technical and economical potential will be lower than the given values for the theoretical potential.

Environmental impacts must be addressed. Socio-economic challenges include the displacement of commercial and recreational fishermen, and may present navigation hazards. Supporting infrastructure, such as grid connections, must be provided. Commercial WECs have not always been successful. In 2019, for example, Seabased Industries AB in Sweden was liquidated due to "extensive challenges in recent years, both practical and financial".

Current wave power generation technology is subject to many technical limitations. These limitations stem from the complex and dynamic nature of ocean waves, which require robust and efficient technology to capture the energy. Challenges include designing and building wave energy devices that can withstand the corrosive effects of saltwater, harsh weather conditions, and extreme wave forces. Additionally, optimizing the performance and efficiency of wave energy converters, such as oscillating water column (OWC) devices, point absorbers, and overtopping devices, requires overcoming engineering complexities related to the dynamic and variable nature of waves. Furthermore, developing effective mooring and anchoring systems to keep wave energy devices in place in the harsh ocean environment, and developing reliable and efficient power take-off mechanisms to convert the captured wave energy into electricity, are also technical challenges in wave power generation. As the wave energy dissipation by a submerged flexible mound breakwater is greater than that of a rigid submerged structure, greater wave energy dissipation is expected due to highly deformed shape of the structure.

Wave farms

A wave farm (wave power farm or wave energy park) is a group of colocated wave energy devices. The devices interact hydrodynamically and electrically, according to the number of machines, spacing and layout, wave climate, coastal and benthic geometry, and control strategies. The design process is a multi-optimization problem seeking high power production, low costs and limited power fluctuations.

Gallery of wave energy installations

• 
  Pelamis Wave Energy Converter on site at the European Marine Energy Centre (EMEC), in 2008.
   
• 
  Azura at the US Navy’s Wave Energy Test Site (WETS) on Oahu.
   
• 
  The AMOG Wave Energy Converter (WEC), in operation off SW England (2019).
   
• 
  The mWave converter by Bombora Wave Power.
   
• 
  CalWave Power Technologies, Inc. wave energy converter in California.

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 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.