Ocean waves and tides are both renewable energy sources, but they work on different physical principles. Waves are created by wind blowing across open water, so wave power is ultimately a form of wind energy stored in the sea. Tidal energy is driven by the gravitational pull of the Moon and Sun combined with the Earth’s rotation, which makes it predictable years in advance.
Neither technology is yet as widespread as solar or onshore wind. The UK has a pioneering tidal stream array, MeyGen in the Pentland Firth, which its owner says delivers over 90% of UK tidal output each year, and a major test centre for wave and tidal devices in Orkney, but wave energy has not yet won a government contract. Understanding how these systems convert the ocean’s motion into electricity, and why some projects have succeeded while others failed, shows where marine energy fits in the energy mix.
How it works: turning ocean motion into electricity
Tides are caused by the gravitational pull of the Moon and Sun, combined with the Earth’s rotation. In some places, near-shore water levels rise and fall by up to about 12 metres (40 feet), according to the US Energy Information Administration (EIA). This movement supports two types of tidal power:
- Tidal range (barrages and lagoons): A wall across an estuary or bay holds water back and releases it through turbines as the tide rises and/or falls. The EIA says producing tidal energy economically requires a tidal range of at least 10 feet (about 3 metres).
- Tidal stream: Underwater turbines, similar to wind turbines but submerged, placed where tidal currents are fast. The EIA describes them as sturdier and costlier than wind turbines.
Wave energy devices capture the up-and-down or back-and-forth motion of waves. They can sit on or below the surface, or be anchored to the seabed. The main types, as described by the European Marine Energy Centre (EMEC), include:
- Attenuators: Long floating devices that lie along the direction of the waves and generate power from the flexing between their sections (for example, the former Pelamis).
- Point absorbers: Floating buoys that capture energy from waves arriving from any direction through the motion of their top relative to their base (for example, CorPower).
- Oscillating water columns: Partly submerged hollow chambers where rising and falling water pushes air back and forth through a turbine.
- Overtopping devices: Waves spill into a raised reservoir, and the water returns to sea through a low-head turbine, like a mini hydro dam.
- Oscillating wave surge converters: Hinged flaps that swing with the surge of the waves.
For students asking how the energy in waves becomes electricity, the chain is: wind gives energy to the water (the kinetic and potential energy of waves) → the device moves → this mechanical motion drives a hydraulic system, air turbine or direct-drive generator → electricity is produced → it travels by subsea cable to the shore. Overtopping devices work in a similar way to hydropower, using a head of water to turn a turbine.
Real-world examples: UK projects and global benchmarks
Most UK marine energy deployment is in Scottish waters.
MeyGen (Inner Sound, Pentland Firth)
Located about 2 km offshore between the Scottish mainland’s north-east tip and the island of Stroma, MeyGen was reported to be the first tidal stream array in the world to pass 50 GWh of cumulative generation. Phase 1 consists of four 1.5 MW turbines (6 MW in total) of two designs, each with an 18-metre rotor. It first generated power in 2016–2017 and has been fully operational since March 2018. The project has consent for 86 MW. Its owner, Ampeak Energy, estimates it supplies about 6,000 homes.
Figures for cumulative output differ. Ampeak’s MeyGen page says “over 51GWh” without a date, while a later secondary report, citing Ocean Energy Europe figures, gives 83.6 GWh by the end of 2025.
In the first half of 2026, generation was 4.4 GWh, down from 7.9 GWh in the same period of 2025, because one turbine was brought ashore for servicing; the other three ran throughout. MeyGen Phase 2 holds Contracts for Difference (CfDs) for 59 MW from the AR4, AR5 and AR6 rounds, with target commissioning in 2027, 2028 and 2029. It is not under construction, and Ampeak’s September 2026 interim report says future phases “remain challenging”.
Orbital O2 (Orkney)
Launched from Dundee on 22 April 2021, Orbital Marine Power’s O2 is a 2 MW floating tidal turbine, described by the company as “the most powerful tidal turbine in the world”. It has two 1 MW nacelles on retractable legs and a hull weighing 680 tonnes. Its first export of power to the grid at EMEC was announced on 28 July 2021, with enough output for around 2,000 UK homes a year, according to EMEC. Orbital has won CfDs for planned projects at Eday totalling 16.8 MW, according to ORE Catapult.
Nova Innovation (Shetland)
Nova Innovation runs the Shetland Tidal Array in Bluemull Sound, between Yell and Unst. Its first 100 kW turbines were installed from 2016, and the company describes it as the world’s first offshore tidal array to deliver electricity to the grid. After the original turbines were decommissioned by October 2023, the site operates three 100 kW M100-D turbines (300 kW in total). In 2018 Nova added a Tesla battery, which the company describes as creating the first grid-connected tidal “baseload” station.
Global benchmarks
- La Rance (France): A 240 MW tidal barrage that has operated since 1966, producing about 600 GWh a year.
- Sihwa Lake (South Korea): The world’s largest tidal power plant at 254 MW, operating since August 2011 with annual output of about 550 GWh.
What the numbers say: output, resource and costs
Tidal stream power is currently far more expensive than established renewables.
Tidal stream costs
The UK government supports tidal stream through a ring-fenced part of the Contracts for Difference auctions. Strike prices are not all on the same price basis:
| Round (results) | Tidal stream capacity | Strike price | Price basis |
|---|---|---|---|
| AR4 (7 July 2022) | 40.82 MW | £178.54/MWh | 2012 prices |
| AR5 (8 September 2023) | 53.04 MW | £198/MWh | 2012 prices |
| AR6 (3 September 2024) | 28 MW | £172/MWh | 2012 prices |
| AR7a (10 February 2026) | 20.9 MW | £265/MWh | 2024 prices (ORE Catapult) |
ORE Catapult says the AR7a price is about 10% higher than AR6 in like-for-like terms. In the same AR7a round, onshore wind cleared at £72.24/MWh and solar at £65.23/MWh (2024 prices), so tidal stream remained about 3.5 to 4 times the price. Across the rounds, over 140 MW of CfD-backed tidal stream is expected to be commissioned by 2030, compared with about 10 MW operating in February 2026, according to ORE Catapult.
Wave energy status
No wave project has won a CfD in the UK, and no wave farm has yet reached commercial scale in the UK. There is no reliable published figure for the UK wave resource. In the US, the EIA estimates theoretical annual wave energy off the coasts at up to 2.64 trillion kWh, equivalent to about 63% of US utility-scale generation in 2023.
Resource potential
Estimates of the UK’s tidal stream resource differ. A 2021 study by Coles et al. puts the practical resource at about 34 TWh a year, equivalent to 11% of UK annual electricity demand, needing about 11.5 GW installed by 2050. ORE Catapult (2018) estimated a practical resource of 15 GW.
Limitations and honest assessment
Cost and funding: Marine devices work in a harsh environment, which adds to capital and servicing costs. Pelamis Wave Power, developer of the snake-like Pelamis attenuator, entered administration on 21 November 2014 after failing to secure further development funding, with debts of almost £16 million.
Environmental and site constraints: According to the EIA, tidal barrages can affect estuary wildlife, change tidal levels in the basin and increase turbidity. Suitable sites are limited: tidal range needs a range of at least about 3 metres, and tidal stream needs fast currents, such as the speeds of up to about 4 m/s reported at EMEC’s Fall of Warness site.
Maintenance and durability: Devices face storms, corrosion and servicing needs. MeyGen’s lower output in the first half of 2026, while one turbine was ashore for servicing, shows the effect on generation.
Capital-intensive tidal range: The Swansea Bay Tidal Lagoon (proposed 320 MW, £1.3 billion) was rejected by the government on 25 June 2018. Business and Energy Secretary Greg Clark said it did not meet value-for-money requirements: its capital cost per unit of annual generation would be three times that of Hinkley Point C. The developer, Tidal Lagoon Power, disputed this, putting the figure at 1.5 times.
Predictability: Tides follow astronomical cycles, and Ampeak cites tidal energy’s “predictability and complementary role alongside other renewable technologies”. Waves depend on the wind and are more variable than tides.
The UK angle: where does Britain stand?
The European Marine Energy Centre in Orkney, established in 2003, has grid-connected test sites for tidal (Fall of Warness) and wave (Billia Croo) devices. It is described as the world’s only ISO/IEC 17025-accredited test laboratory for ocean energy, and EMEC says more ocean energy converters have tested there than at any other site in the world.
Crown Estate Scotland manages Scottish seabed leasing; its 2010 Pentland Firth and Orkney Waters round was described as the world’s first commercial wave and tidal leasing round. The tidal ring-fence in CfD auctions has so far backed over 140 MW of capacity expected online by 2030, which ORE Catapult says would take UK installed tidal stream capacity above 150 MW, still a small share of Britain’s electricity mix.
Frequently asked questions
How do waves generate electricity?
Devices capture the motion of the waves. An oscillating water column uses rising and falling water to push air through a turbine. A point absorber buoy moves with the waves, driving a hydraulic system or direct-drive generator. The electricity is sent to shore by subsea cable.
What is the difference between wave energy and tidal energy?
Wave energy harnesses surface waves created by wind, which vary with the weather. Tidal energy comes from the gravitational pull of the Moon and Sun. Tidal stream turbines capture moving currents, while tidal barrages and lagoons use the height difference between high and low tide. Tides are predictable years ahead; waves are not.
What are the advantages and disadvantages of wave energy?
Advantages include a large theoretical resource (off the US coasts, equal to about 63% of US utility-scale generation in 2023, according to the EIA), no fuel and no direct emissions while operating. Disadvantages include high costs, harsh operating conditions that drive maintenance needs, company failures such as Pelamis in 2014, and no commercial-scale wave farm yet in the UK.
What is the biggest tidal energy project in the UK?
MeyGen in the Pentland Firth is the UK’s largest operating tidal stream array, with 6 MW across four turbines. Its owner says it has generated “over 51GWh” (undated); a secondary report gives 83.6 GWh by the end of 2025. The owner estimates it supplies about 6,000 homes.
Why was the Swansea Bay tidal lagoon rejected?
The government rejected it on 25 June 2018 on value-for-money grounds. It said the capital cost per unit of annual generation would be three times that of Hinkley Point C and that a six-lagoon programme would cost more than £50 billion. The developer disputed the figures.
How much does tidal power cost compared with wind and solar?
In the AR7a auction (results February 2026), tidal stream cleared at £265/MWh, against £72.24/MWh for onshore wind and £65.23/MWh for solar, all in 2024 prices. That makes tidal stream about 3.5 to 4 times as expensive, and its AR7a price was about 10% higher than AR6 in like-for-like terms.