Wave Power: Renewable Marine Energy

Wave power is a type of renewable energy which can be harvested from the ocean. We outline the main types of marine technologies which are still in their infancy, including floating buoys. Read about the challenges and future prospects of sustainable oceanic wave power and how it could help remote islands become more environmentally friendly.
Floating wave farm in India
View of a prototype 1-megawatt wave energy farm off the coast of Southern India. Photo: © Oscilla Power Inc

The Power of the Sea

The ocean is vast and powerful, and if we could harvest its energy we could supply enough green electricity to meet four times the global electricity demand of today. 1 With climate change intensifying, the race is on to find sources of clean renewable energy to replace fossil fuels like coal, oil and gas. Could the blue economy, led by wave power be the answer? Possibly, but the challenges are great and our climate crisis is worsening by the day.

What Is Wave Power?

Wave power refers to the renewable energy derived from the bobbing motion of ocean waves. It is one of several different types of marine energy. The others include, tidal power which is driven by movements of tides; ocean thermal energy conversion (OTEC), which exploits differences in sea temperatures; and osmotic energy which exploits differences in salinity levels. (Note: Wave and tidal energy are forms of hydropower, as both harness the kinetic energy of moving water.)

Ocean waves contain a huge amount of power. The concept of harnessing that energy to generate electricity, is known as wave power, or oceanic wave energy (OWE). A machine that exploits wave power is called a wave energy converter (WEC) or wave energy harvester.

As 71 percent of the Earth is covered by ocean, wave power is one of the most widely available types of sustainable energy. For example, the EIA conservatively estimates that 64 percent of the United States’ electricity requirements in 2019 could be generated (theoretically) by wave power (2.64 trillion kilowatthours). 2

Despite this, only a minuscule portion of marine power is harvested worldwide. This is because the technology is still in the early stages of research and development. Deployment at scale remains a long way off.

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How Much Electricity Does Wave Power Currently Provide?

Very little, to date.

As of January 2021, total global marine energy generation capacity is only about 500 MW, most of which comes from tidal power (495 MW), while wave power accounts for a mere 2 MW. 3

Europe is currently the world leader in wave power generation. But even then, oceanic wave energy produces less than 0.2 percent of the European Union’s electrical output and this is forecast to rise to a mere 1.1 percent by 2030. 4 5.

Put simply, wave power has barely made a ripple and the consensus among industry experts is that it lags about two decades behind other renewable technologies such as wind power and solar power.

Types of Wave Energy Converters

There are hundreds of wave energy converter designs (WEC), in all shapes and sizes but only a small percentage ever make it through to full prototype testing. 6 No WEC stands out yet as the definitive answer to harvesting energy from waves. Scaled testing of the WECs in real seas has proven extremely difficult and expensive, hence a lack of funding and commercialization to date.

Presently, there are three main types of WECs: (1) point absorbers (2) overtopping or terminator devices and (3) oscillating water columns.

Point Absorbers

Point absorbers utilize a sophisticated system of floats and hydraulic pistons to generate electricity. They are considered the most cost-effective WEC currently, because they can produce considerable energy with a relatively small device. There are different examples of point absorbers, the best known is the ‘Power Buoy’, but all essentially work in the same manner. These devices float on the water, and the up and down movement of the oscillating waves moves the hydraulic piston which in turn runs a generator which produces electricity.

Overtopping Device

Overtopping devices are large structures, rather like big floating bags that catch waves and their energy – hence they ‘terminate’ the waves. The water falls through a hole in the middle of the structure, turning a turbine which is connected to a rotating electrical generator.

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Oscillating Water Column

An oscillating water column (OWC) is a chamber or hollow which is used to harness energy caused by the action of waves. First developed in the 1940s, OWCs consist of a hollow structure built into the side of a cliff. Open to the sea below the water surface, air is trapped in the chamber above. The wave action compresses and depresses the trapped air, forcing air flow through a turbine generator which spins to create electricity.

What Are The Challenges of Wave Power?

The ocean energy market is still in its infancy, and the sector has to overcome a number or challenges to prove the reliability and affordability of its technologies. There are several obstacles that still need to be overcome.

Challenge 1: Technology

As of January 2021, there is no commercially successful way of capturing energy from waves. Most of the work done in ocean wave energy harvesting, remains theoretical.

The main problem is, we have not yet figured a way to directly make waves spin a turbine in a scalable way. And spinning a turbine is the best way we know of converting the mechanical energy of a moving substance into electricity.

Aside from solar power, pretty much all our electricity comes from spinning turbines. The most obvious example is a wind turbine, which generates wind power on land and offshore. However, even traditional fossil fuel power plants that use coal, or natural gas, or nuclear energy rely on turbines to generate electricity. The fuel is just there to turn water into steam, to spin a turbine.

Scientists are experimenting with very different wave energy converters to unpack energy from waves. While the devices look very different to each other, the main goal is to try and turn waves into something else that can spin a turbine. For example, as we have seen above, they have built large towers (Oscillating Water Columns) in which waves rise and fall, pressurizing air to drive a turbine. They have created big floating bags (Overtopping Devices), that waves pile into and water flows out, spinning a turbine.

Yet we still have not been able to get these turbines to spin fast enough or consistently enough to make electricity. Or at least, cheap electricity. Building in the ocean is expensive, whatever you build is exposed to storms, salt water and debris.

However, as the potential of wave power is so vast, it is hoped that one day we may figure out how to make turbines more commercially viable. Or even, perhaps, move past the turbine paradigm.

Challenge 2: Survivability

The best wave resources occur in areas where strong winds have traveled over long distances. In Europe this occurs along the western coasts of Great Britain, Ireland, France, Portugal and Spain – known as the Atlantic Arc. But these are rough waters. Harsh sea conditions, especially during storms and extreme weather events raise a lot of structural and survivability questions. You could build nearer the coastline, but wave energy decreases the more inland you go due to friction with the seabed.

Challenge 3: Cost

The high upfront costs associated with ocean energy technologies combined with the unproven status of the technologies have hindered investors’ confidence in the sector. The current costs of both wave and tidal stream energy are considerably higher than conventional and other renewable energy generation. This is not surprising, given the early stage of technologies and that projects tend to be constrained to 10 MW total installed capacity and thus have limited economies of scale.

Challenge 4: Marine Life

Systems need to be built to avoid injury to marine mammals and other ocean life. Conflicts can also arise between use of the ocean for energy and other activities, such as shipping, fishing, recreation and tourism. 

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The Advantages of Wave Power

Predictability, Availability and Abundance

The main advantage of marine energies, compared to other renewables, are predictability, availability and abundance.

Much like wind and solar, wave power provides a sustainable solution to our energy problems. It can be used to create electricity without creating greenhouse gas emissions, or any sort of air pollution. There will always be wind and therefore waves, so it’s inexhaustible and renewable. For each MWh generated by marine energy, 300 kg of carbon dioxide emissions can be avoided. 7

Wave power is consistent day and night. Unlike solar power systems which do not operate at night, or geothermal energy which is mainly only available in specific locations.

Wave energy also has applications for remote islands such as the Caribbean or Canary Islands replacing expensive and polluting oil-powered energy systems. Furthermore, wave energy can power offshore industries such as fish farms, and oil and gas platforms; as well as naval vessels.

Reasonable Payback Period

The Environmental and Physical Sciences at the University of Sienna recently conducted a study on the carbon footprint of building wave energy converters. They considered construction, installation, maintenance and the operational phases in a Life Cycle Assessment.  They concluded that the carbon footprint payback period was 13 months. This is slightly more than wind power which is about 8 months. 8 9

Protects Coastlines

Future marine wave energy farms could play a key role in coastal protection. Farms could extract a considerable amount of wave energy, reducing the amount of energy in the surf zone which causes coastline erosion. 10

Difference between tidal power and wave power
Comparison. Left, a tidal stream generation system. Major tidal flows and ocean currents like the Gulf Stream, can be exploited to extract tidal energy using underwater rotors and turbines. Right, a floating wave energy converter. Images: (L) SeaGen-Sea Generation Tidal Turbine / (R) (CC0 1.0)

What’s the Difference Between Wave Power and Tidal Power?

Wave power harnesses the energy of wind through waves. Usually, a device for harnessing wave energy sits on the surface of the ocean where it can make use of the up and down bobbing motion of water to move mechanical pieces in the shaft and drive a generator. Tidal power harnesses the power of tides – namely, the gravitational forces of the moon and the sun. Usually, a device for harnessing tidal power is placed under water where it can directly make use of the back-and-forth movement of tides to spin a turbine and drive a generator.

Future Prospects

Most of the world still relies heavily on dirty fossil fuels to generate electricity. Yet global warming is linked directly to the burning of those fuels. It is estimated that, by the end of the 21st century, the average temperature of Earth will have increased by as much as 5.8 °C triggering a rise in sea levels, hurricanes and other extreme weather events. 11.

With the ever-growing political pressure to develop renewable energy solutions, solar and wind power – with per-kilowatt prices dropping by the day – look increasingly more like a viable bet for the future.

That does not however, mean there is no place for marine energies like wave and tidal power. After all, wind and solar are not perfect since the sun doesn’t always shine and the wind doesn’t always blow.

In time, the renewable energy mix is likely to be strengthened by the addition of marine energies. The good news is, developers are planning and building the first wave energy farms around Europe, most notably in the UK, Portugal and Ireland. 12 Once built, these pilot farms will serve as a basis for commercializing wave energy technology and in time perhaps, for building a new industry.

YOU MIGHT BE INTERESTED IN: Another renewable power source that is receiving more attention, is hydrogen energy, thanks to its ability to ‘store’ unused intermittent energies, such as wind and solar. For details, see: Hydrogen Energy: Tomorrow’s Clean Fuel.

The latest energy development is nuclear fusion, a very costly quest for low carbon energy which involves the fusion of two isotopes of hydrogen. Theoretically, it could be the renewable energy of the future.

References

  1. IRENA and “Ocean Energy Europe Partner to Drive Ocean Energy Industry”. December 2020 []
  2. U.S. Energy Information. []
  3. “Marine Energy Marine energy (or ocean energy) encompasses wave, tidal stream, tidal range, ocean thermal, ocean current, run-of-river, and salinity, etc., through which energy can be harnessed from oceans.” Energy for Sustainable Development, 2020 []
  4. Oceans of energy: European Ocean Energy Roadmap 2010–2050[]
  5. SETIS Marine Energy Report. (PDF) https://setis.ec.europa.eu/system/files/Marine_Energy.pdf []
  6. “A review of wave energy converter technology”. B Drew et al. August 2016 []
  7. Update of the Technology Map for the SET-Plan EU.[]
  8. “Lifecycle Environmental Impact Assessment of an Overtopping Wave Energy Converter Embedded in Breakwater Systems”. Nicoletta Patrizi et al.  April 2019 []
  9. Evaluating the Environmental Impacts and Energy Performance of a Wind Farm System Utilizing the Life-Cycle Assessment Method: A Practical Case Study. Mohamed R. Gomaa, Hegazy Rezk et al. August 2019 []
  10.  “Evaluating the Future Efficiency of Wave Energy Converters along the NW Coast of the Iberian Peninsula”  by Americo S. Ribeiro et al 2020 []
  11. “The share of cooling electricity in global warming: Estimation of the loop gain for the positive feedback.” Hamed Shakouri G.ab 2019  []
  12. Ocean Energy Europe, 2020 https://www.oceanenergy-europe.eu/ocean-energy/wave-energy/ []
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