# Wave energy converters: Techniques

Buoys, flaps, ramps and air columns put to the test

Source page: https://www.materialinsights.org/energy/e_wave_power/techniques/

What this tab covers The methods used to capture this energy: how each works, and how they compare on efficiency, cost, life-cycle emissions, maturity and scale.

Five families of device compete; all remain at prototype or demonstration stage.

#### Comparison

| Method | Efficiency | Cost | Life-cycle emissions | Maturity | Scale |
|---|---|---|---|---|---|
| **Oscillating water columns**^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[4](https://www.ren21.net/gsr-2025/technologies/ocean-power/)^[5](https://tethys-engineering.pnnl.gov/sites/default/files/publications/IRENA_Innovation_Outlook_Ocean_Energy_2020.pdf)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7) | 2-71% in tests (Pico sea trial 20%); air turbines 50-60% | No device-specific figure; wave overall USD 300-550/MWh (IRENA, 2020) | 17 g CO2e/kWh (ocean energy median, range 5.6-28) | pilot | Mutriku, Spain: 16 turbines of 18.5 kW (296 kW), 210 MWh in 2024 |
| **Point absorbers (buoys)**^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7) | 3-51% | EUR 4,840-9,680/kW capital (2010-2012 estimates, all wave) | 17 g CO2e/kWh (ocean energy median) | pilot | Single demonstration units |
| **Attenuators**^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7) | 14-21% | No current figure | 17 g CO2e/kWh (ocean energy median) | pilot | Pelamis 750 kW prototype (UK) |
| **Overtopping devices**^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7) | 18-27% (Wave Dragon); hydro turbines 70-90% | No current figure | 17 g CO2e/kWh (ocean energy median) | pilot | Wave Dragon prototype tested in Denmark |
| **Oscillating wave surge converters (flaps)**^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[4](https://www.ren21.net/gsr-2025/technologies/ocean-power/)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7) | 35-65% in tank tests | No current figure | 17 g CO2e/kWh (ocean energy median) | pilot | Oyster 315 kW (2009) and 800 kW (2011), Orkney; a 2 MW WaveRoller array funded in Portugal |

Flaps and some point absorbers absorb the most power per metre of width, overtopping devices the least, but none has a cost track record: IRENA puts wave electricity at USD 300-550/MWh, against USD 200-450/MWh for tidal stream. Of 13.5 MW installed in Europe since 2010, only 830 kW was in the water at the end of 2024. Life-cycle emissions are low because the main input is steel.

#### How each method works
**Oscillating water columns**

A chamber open to the sea below traps air. Waves push the water column up and down, forcing air through a turbine that turns the same way in both directions. Built into breakwaters or floating hulls.^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[4](https://www.ren21.net/gsr-2025/technologies/ocean-power/)^[5](https://tethys-engineering.pnnl.gov/sites/default/files/publications/IRENA_Innovation_Outlook_Ocean_Energy_2020.pdf)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7)
**Point absorbers (buoys)**

A buoy small relative to the wavelength bobs on the surface; its motion against a seabed anchor or submerged body drives a hydraulic pump or linear generator. Suits water deeper than about 40 m.^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7)
**Attenuators**

Long jointed floating structures lie along the wave direction; the sections flex at the hinges, pumping hydraulic fluid through motors.^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7)
**Overtopping devices**

Ramps guide waves into a reservoir above sea level; the water drains back through low-head turbines under a 1-2 m head.^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7)
**Oscillating wave surge converters (flaps)**

A buoyant flap hinged to the seabed in shallow water rocks with the surge of the waves, driving hydraulic pistons.^[1](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf)^[4](https://www.ren21.net/gsr-2025/technologies/ocean-power/)^[6](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7)

#### Sources

1. [Review on Power Performance and Efficiency of Wave Energy Converters (Aderinto and Li, Energies 12, 4329), Tables 3-8](https://tethys-engineering.pnnl.gov/sites/default/files/publications/Aderintoetal2019.pdf) MDPI (copy hosted by PNNL Tethys), 2019
2. [Wave Energy: Technology Brief](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Wave-Energy_V4_web.pdf) IRENA, 2014
3. [Renewables 2025 Global Status Report: Ocean power](https://www.ren21.net/gsr-2025/technologies/ocean-power/) REN21, 2025
4. [Innovation Outlook: Ocean Energy Technologies](https://tethys-engineering.pnnl.gov/sites/default/files/publications/IRENA_Innovation_Outlook_Ocean_Energy_2020.pdf) IRENA (copy hosted by PNNL Tethys), 2020
5. [Climate Change 2014: Mitigation, Annex III Technology-specific cost and performance parameters, Table A.III.2](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7) IPCC AR5 Working Group III, 2014

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_wave_power/index.md)
- [Overview](https://www.materialinsights.org/energy/e_wave_power/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_wave_power/correlation/index.md)
- [Efficiency](https://www.materialinsights.org/energy/e_wave_power/efficiency/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_wave_power/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_wave_power/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_wave_power/links/index.md)