Updated September 2026.
The ocean is always moving, and that motion carries an enormous amount of energy. Tides rise and fall on a timetable you can print years in advance, and waves roll in day and night. Yet after decades of work, ocean energy supplies only a sliver of the world’s electricity. Here is why, and what is finally starting to change.
Tidal power: predictable, proven, pricey
Tides are driven by the pull of the moon and sun, so their timing is known precisely. That predictability is tidal power’s big advantage over wind and solar. There are two main approaches.
- Barrages are low dams across an estuary. Water flows through turbines as the tide comes in and goes out. They work, and they last. France’s 240 MW La Rance station has run since 1966, and South Korea’s 254 MW Sihwa Lake plant, opened in 2011, is the largest in the world. But they transform the estuary behind them, and few sites have both a big enough tidal range and public support. Several British proposals, such as the Severn Barrage and the Swansea Bay lagoon, were shelved over cost and environmental concerns.
- Tidal stream turbines are like underwater wind turbines, set in fast tidal channels. The flagship is MeyGen in Scotland’s Pentland Firth. Its four turbines (6 MW in total) had generated more than 84 GWh by late 2025, and individual turbines have run for years without being hauled out for repair. The developers plan to add tens of megawatts more before the end of the decade.
Wave power: still searching for a winning design
Waves are harder. The sea is violent, and a device must survive storms many times stronger than the conditions it is designed to harvest. Dozens of designs have been tried:
- bobbing buoys
- hinged “snakes”
- oscillating water columns, where waves push air through a turbine
- floaters attached to piers and breakwaters
Unlike wind turbines, which settled on one shape long ago, wave energy has no single design that has clearly won. Several well-funded companies went bust in the 2010s.
Progress now is mostly small and practical. Eco Wave Power has connected floaters on breakwaters to the grid in Israel and started a pilot at the Port of Los Angeles in 2025. In Oregon, PacWave South is being built as the first grid-connected, commercial-scale wave energy test site in the US, where developers can put their devices in real ocean conditions.
The honest verdict
- Cost is the obstacle. Ocean power is still several times more expensive per kilowatt-hour than offshore wind or solar. It needs many more machines in the water to bring prices down the way wind and solar did.
- Its value is in the timing. Tides are perfectly predictable, and waves often peak in winter when solar output is low. That makes it a useful complement to other renewables, especially for islands and remote coastal communities.
- Environmental effects look manageable at today’s scale, but they are still being studied: noise, collisions with marine life and changes to sediment flows.
More: Wave Energy and Hydroelectric Power.
