Wave energy converters: Techniques
Buoys, flaps, ramps and air columns put to the test
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 columns12456 | 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)126 | 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 |
| Attenuators126 | 14-21% | No current figure | 17 g CO2e/kWh (ocean energy median) | pilot | Pelamis 750 kW prototype (UK) |
| Overtopping devices126 | 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)1246 | 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 columnsA 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.12456
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.126
AttenuatorsLong jointed floating structures lie along the wave direction; the sections flex at the hinges, pumping hydraulic fluid through motors.126
Overtopping devicesRamps guide waves into a reservoir above sea level; the water drains back through low-head turbines under a 1-2 m head.126
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.1246
Sources
- Review on Power Performance and Efficiency of Wave Energy Converters (Aderinto and Li, Energies 12, 4329), Tables 3-8 MDPI (copy hosted by PNNL Tethys), 2019
- Wave Energy: Technology Brief IRENA, 2014
- Renewables 2025 Global Status Report: Ocean power REN21, 2025
- Innovation Outlook: Ocean Energy Technologies IRENA (copy hosted by PNNL Tethys), 2020
- Climate Change 2014: Mitigation, Annex III Technology-specific cost and performance parameters, Table A.III.2 IPCC AR5 Working Group III, 2014