Material Insights · Understanding the Material World

Tidal and ocean-current power: Techniques

Barrages, underwater kites and turbines aimed at the Gulf Stream

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.

Barrages are mature and supply almost all tidal electricity. Tidal stream turbines and kites are moving into the first small arrays; ocean current turbines remain at research stage.

Comparison

MethodEfficiencyCostLife-cycle emissionsMaturityScale
Tidal barrages and lagoons23468Hydraulic turbines 70-90%; capacity factor about 25-40%Sihwa about USD 298 million for 254 MW, about USD 1,170/kW (calculated); proposed schemes USD 150-800/kW in IRENA's 2014 brief, whose per-kW figure for La Rance is internally inconsistent; production cost EUR 0.02-0.12/kWh across sources17 g CO2e/kWh (ocean energy median, range 5.6-28)mature Sihwa 254 MW and La Rance 240 MW make up most of the roughly 513 MW of ocean power operating at the end of 2024
Tidal stream turbines and tidal kites15678Rotor about 50% of the flow's kinetic energyUSD 200-450/MWh (2020)17 g CO2e/kWh (ocean energy median)early commercial Europe: almost 32 MW installed since 2010, 12.7 MW still generating; MeyGen 6 MW; Minesto Dragon 12 kite 1.2 MW (Faroe Islands)
Ocean current turbines7930% device efficiency assumed in US resource estimatesNo published figure foundNo study found; likely similar to tidal streamresearch None in IRENA's 2020 database (calculated from its technology totals)

Barrages are cheap to run once built, and La Rance has generated since 1966, but they need rare sites and transform estuaries, so few have been built. Tidal stream, at USD 200-450/MWh, costs several times as much as new wind and solar; IRENA expects about USD 110/MWh once deployment grows. All have low life-cycle emissions; for barrages most comes from the dam's concrete.

How each method works

Tidal barrages and lagoons

A dam across an estuary, or a walled lagoon, holds back water as the tide turns, creating a head of several metres. Sluices and bulb turbines release it to generate on the ebb, the flood or both.23468

Tidal stream turbines and tidal kites

Underwater rotors, usually horizontal-axis like wind turbines, sit in fast tidal channels on gravity bases, piles or floating platforms. Kites carry a turbine under a tethered wing that flies figure-of-eight loops, moving faster than the current.15678

Ocean current turbines

Moored turbines held below the surface by buoyancy and tethers would sit in steady one-way currents such as the Gulf Stream, which flow more slowly than tidal channels but all the time.79

Sources

  1. Tidal Turbines (Maths Inside) London Mathematical Society
  2. Wave Energy: Technology Brief (turbine efficiencies, p. 11) IRENA, 2014
  3. Tidal Energy: Technology Brief IRENA, 2014
  4. La Rance Tidal Barrage (Annex IV site page) PNNL Tethys, 2024
  5. Ocean Energy: Key Trends and Statistics 2024 Ocean Energy Europe (copy hosted by PNNL Tethys), 2025
  6. Climate Change 2014: Mitigation, Annex III Technology-specific cost and performance parameters, Table A.III.2 IPCC AR5 Working Group III, 2014
  7. Innovation Outlook: Ocean Energy Technologies IRENA (copy hosted by PNNL Tethys), 2020
  8. Renewables 2025 Global Status Report: Ocean power REN21, 2025
  9. Marine Energy in the United States: An Overview of Opportunities (Kilcher, Fogarty and Lawson, NREL/TP-5700-78773) NREL / US DOE, 2021