SeaGen: The Strangford Lough Tidal Turbine That Proved Tidal Stream Power Could Work

For about eight years, anyone taking the short ferry between Strangford and Portaferry in Northern Ireland could see a strange structure standing in the water about a kilometre to the south. It looked a little like a lighthouse with a crossbar on top. Most of it was hidden. Below the surface, a steel pile held two underwater rotors, each 16 metres across, that turned in the fierce tidal currents rushing in and out of Strangford Lough. This was SeaGen, built by the Bristol company Marine Current Turbines, and it is widely regarded as the world's first large-scale, commercial, grid-connected tidal stream generator.

SeaGen was rated at 1.2 megawatts. That is small by the standards of modern wind turbines. But when it reached full power in December 2008 it was several times more powerful than any tidal stream device before it, and it ran long enough to show that tidal turbines could produce useful amounts of electricity, survive in hostile water, and coexist with protected wildlife under careful monitoring. Over its life it exported more than 11.6 gigawatt-hours of electricity to the grid. It was then dismantled in stages between 2016 and 2019, becoming the first commercial-scale tidal turbine project to be fully decommissioned.

This article covers SeaGen's history, how it worked, how it performed, the environmental programme that surrounded it, the business story of the company that built it, and what the tidal energy industry learned from it.

Quick facts

Why tidal stream power?

The tides as an energy source

The tides are driven by the gravitational pull of the Moon and, to a lesser extent, the Sun, combined with the Earth's rotation. Around much of the British Isles, the sea rises and falls roughly twice a day. Where large volumes of water have to squeeze through narrow gaps, such as the mouths of sea loughs, channels between islands, or headlands, the flow speeds up and produces strong currents.

That flow carries kinetic energy. A tidal stream generator is essentially an underwater turbine placed in such a current to capture some of it, in much the same way that a wind turbine captures some of the energy in moving air.

There are two broad ways to get power from the tides:

• Tidal range schemes, such as barrages and lagoons, trap water behind a wall at high tide and release it through turbines, exploiting the difference in height between high and low water.
• Tidal stream devices sit in the moving current and extract energy from its speed.

SeaGen was a tidal stream device.

Why water is attractive

Water is roughly 800 times denser than air. Because the power in a moving fluid is proportional to its density, a tidal turbine can produce substantial power from currents that would be a gentle breeze if they were air. The standard formula for the power available to a turbine is:

P = ½ × ρ × A × V³ × Cp

where ρ is the density of the fluid (about 1,027 kg/m³ for seawater), A is the area swept by the rotor, V is the flow speed, and Cp is the fraction of the energy the turbine actually captures.

The cube in the formula matters. Doubling the current speed increases the available power eightfold. That is why developers look for the fastest flows they can find, and why a site like Strangford Narrows, where currents reach up to about 4 metres per second, was attractive.

An illustration using SeaGen's own dimensions

The following is a worked example, not a measured result. Take one SeaGen rotor, 16 metres across, sweeping about 201 square metres. At a current of 2.4 m/s, the speed at which Marine Current Turbines said SeaGen reached its full rating, the kinetic power flowing through that area is:

½ × 1,027 × 201 × 2.4³ ≈ 1.43 million watts.

Each rotor was rated at 600 kW, so at that speed the machine needed to convert a little over 40 percent of the passing kinetic power into electricity, after gearbox and generator losses. Above that speed, the blades were controlled to hold output at the rated level instead of producing more.

Predictability

The single biggest selling point of tidal energy is predictability. Wind and sunshine depend on the weather. Tides follow astronomical cycles that can be forecast years in advance. Output still varies, rising and falling with each tide, dropping to almost nothing at slack water, and changing between spring and neap tides over the lunar month. But a grid operator can know when that variation will happen. Supporters of tidal power argue that this makes it a valuable complement to wind and solar, even if it is more expensive.

Before SeaGen: Marine Current Turbines

Peter Fraenkel

The engineer most associated with SeaGen is Peter Fraenkel, who founded Marine Current Turbines in 2000. Fraenkel had previously been a founder partner of IT Power, an energy consultancy. MCT was based in Bristol and remained a small company; Wikipedia records it as employing 15 people in 2007.

The Loch Linnhe proof of concept

Fraenkel's interest in tidal currents predates MCT. In 1994 and 1995 he tested a 3.5-metre-diameter turbine in the Corran Narrows of Loch Linnhe in western Scotland. It generated about 15 kW at a current of 2.25 m/s. The test was primarily funded by Scottish Nuclear. The turbine was later donated to the National Museum of Scotland, in 2010.

SeaFlow, 2003

The next step was SeaFlow, a single-rotor test turbine installed off Lynmouth on the north Devon coast in May 2003. It had an 11-metre rotor and was rated at 300 kW. SeaFlow was commissioned in August 2003 but was never connected to the grid; its output was fed to a dump load. It was nevertheless one of the first offshore tidal turbines of its size, and it set a tidal stream record of 300 kW that SeaGen would later break.

SeaFlow established the basic layout that SeaGen would use: a turbine mounted on a pile drilled into the seabed, with a mechanism to raise the rotor above the water for maintenance. That feature turned out to be important. Working underwater in fast currents is dangerous, expensive and limited to brief windows at slack tide. Lifting the machinery into the air turned maintenance into a much more manageable job.

Choosing Strangford Lough

The site

Strangford Lough is a large sea inlet on the east coast of County Down, about 150 square kilometres in area. It connects to the Irish Sea through a narrow channel, the Strangford Narrows, which the Strangford to Portaferry ferry crosses in a few minutes. As the tide rises and falls, a huge volume of water must pass through this gap, producing some of the strongest tidal currents in the British Isles.

People have used those currents for a long time. Wikipedia notes the remains of a tide mill at Nendrum Monastery on the lough dating from around 787 CE, one of the oldest known tide mills.

Why there?

Frank Fortune, a technical director at Royal Haskoning, the consultancy that led SeaGen's environmental work, summarised the reasons in a 2012 presentation. Strangford offered a significant tidal resource, easy access, a grid connection, the Queen's University Belfast marine station at Portaferry, and a local skills base for assembly and maintenance.

Why it was difficult

The same presentation also listed the problem. Strangford Lough is one of the most protected marine areas in the United Kingdom. It is a European Special Area of Conservation and a Special Protection Area, and in 2013 it became Northern Ireland's first Marine Conservation Zone. It hosts harbour (common) seals, grey seals and harbour porpoises, all protected species, along with important seabed habitats and large numbers of wintering birds; Wikipedia notes that a large share of the world's pale-bellied brent geese winter there.

In other words, MCT chose to put a novel, large, fast-moving machine in the middle of a busy shipping channel inside a wildlife sanctuary. That decision shaped everything that followed.

Design and engineering

The overall layout

SeaGen consisted of:

• a steel tubular monopile about 3 metres in diameter, drilled into the rock seabed in about 24 metres of water and rising some metres above the surface;
• a horizontal crossbeam mounted on the pile, which could slide up and down it;
• two powertrains, one at each end of the crossbeam, each consisting of a rotor, gearbox and generator.

The rotors were 16 metres in diameter, each sweeping about 200 square metres. Each drove a generator through a three-stage gearbox, with two planetary stages and one spur stage, giving a speed increase of 69.8 to 1, according to Wikipedia. Wikipedia gives the rotor speed as about 12 rpm, while the US PRIMRE projects database gives 14 rpm. Even at their maximum, the blade tips moved at about 12 m/s, according to PRIMRE, which is slow compared with the tips of a large wind turbine.

Working both ways

A tidal current reverses direction about every six hours as the tide floods in and ebbs out. Many tidal turbines solve this by rotating the whole machine to face the flow, or by using blades that work in either direction. SeaGen used pitch control: its blades could rotate through 180 degrees around their own axes, so the rotor could generate on both flood and ebb tides without the whole structure turning.

Pitch control also let the machine regulate its power. As the current rose above the speed needed for rated output, the blades could be pitched to shed excess energy and keep the generators within their limits.

Getting into the air

The crossbeam and both powertrains could be raised up the pile until the rotors were clear of the water. This allowed technicians to inspect and repair the rotors and drivetrains from a boat or from the structure itself, without divers. For a first-of-a-kind machine in a fast current, this was an important design choice. It made it possible to fix early problems relatively quickly and to examine how components had fared after months underwater.

Construction

SeaGen was assembled at the Harland and Wolff shipyard in Belfast, the yard famous for building the Titanic. According to the Tethys project record maintained by the US Pacific Northwest National Laboratory, mooring installation took place in February and March 2008, the structure was placed on the seabed on 2 April 2008, and pin piles were drilled and assembly completed between mid-April and late May 2008.

Cost and funding

The project's cost is usually reported as about £12 million. A Northern Ireland Assembly research paper from January 2009, citing the Belfast Telegraph, gave that figure, and noted that MCT had received a £5.2 million grant from the UK government's Department for Business, Enterprise and Regulatory Reform (BERR) and £500,000 of financial assistance from Northern Ireland Electricity. Earlier, pre-construction estimates put the project at about £8.5 million, with the Department of Trade and Industry expected to fund half; the gap illustrates how first-of-a-kind marine projects tend to cost more than initially planned. MCT also received money from the Carbon Trust's Marine Renewables Proving Fund, according to trade press reports.

Installation and commissioning

First power, and a setback

SeaGen first fed electricity into the grid in July 2008. Sources give 14 July and 17 July, the latter being the date reported in the press. The Northern Ireland Assembly paper notes that the initial plan was to run at reduced power, around 150 kW, increasing over the summer.

Things did not go entirely to plan. Shortly after start-up, a software fault caused damage to the blades on one of the two rotors. The machine ran on one rotor, at half its rated power, while the damaged rotor was repaired and replaced. Full power was finally reached on 18 December 2008.

Full power

When SeaGen hit 1.2 MW for the first time, it set a new record for a tidal stream device, comfortably beating the 300 kW set by SeaFlow in 2003. MCT's managing director, Martin Wright, said at the time: "SeaGen is now running exactly as we said it would." He described the achievement as showing "the commercial potential of tidal energy as a viable alternative source of renewable energy."

The electricity was purchased by ESB Independent Energy, part of the Irish ESB group, for customers in Northern Ireland and the Republic of Ireland.

Accreditation

SeaGen was accredited by Ofgem, the UK energy regulator, as a UK power station, making it eligible for Renewables Obligation Certificates, the main support mechanism for renewable electricity in the UK at the time. Industry reports describe it as the first tidal power system to secure this accreditation.

Operating under a microscope

Licence conditions

SeaGen was licensed under the Food and Environment Protection Act (FEPA). Its environmental statement had been submitted in 2005, and the licence was first granted in December 2005 and revised in later years. The licence was for a temporary installation of five years. The Northern Ireland Assembly paper reported that, although the technology had a design life of around 20 years, MCT considered removal at the end of the licence term the most appropriate course given the area's environmental importance.

Because nobody knew how seals, porpoises, fish and diving birds would react to large rotors in a narrow channel, the licence imposed several layers of precaution:

• Marine mammal observers were stationed on the pile with authority to stop the turbine.
• Operation was initially limited to daylight, when observers could see.
• Active sonar was developed by the Sea Mammal Research Unit (SMRU) as a further way of detecting animals approaching the rotors.
• An environmental monitoring programme ran in parallel to assess whether those precautions were needed, and to adjust them.

How the shutdown system worked

Under the original protocol, if an observer saw a seal, porpoise or shark within a set distance of the turbine, an MCT engineer shut the rotors down. The observer watched until the animal had left, the turbine was restarted, and each incident was reported to a liaison at Queen's University Belfast, who passed the information to regulators, consultants and scientists.

Fortune's presentation included a log of early emergency stops. Between July 2008 and July 2009 it lists shutdowns triggered by common seals and unidentified targets at distances from about 20 metres to 130 metres, some called by the human observers and some by the active sonar operator. Over time, as evidence accumulated, the shutdown distance was progressively reduced. The sonar was run alongside human observers, compared with them, and then allowed to take over. A trade report from February 2010 notes that from autumn 2009 SeaGen was running automatically without marine mammal observers on board.

Who oversaw it

Fortune described the governance of the programme in some detail. A Science Group, with an independent chairman, Dr David Erwin, included the Northern Ireland Environment Agency as regulator, the Joint Nature Conservation Committee, Royal Haskoning, Queen's University Belfast and SMRU. It met in confidence to review results and agree changes to mitigation. A separate Liaison Group, with the same chairman, was open to the public and other interested bodies. Results were reported to the Science Group twice a year.

This approach is called adaptive management: start with cautious restrictions, collect evidence on clearly defined questions, and relax or tighten the restrictions as the evidence warrants. SeaGen became one of the best-known real-world examples of it in marine renewable energy.

What the monitoring found

The SeaGen Environmental Monitoring Programme final report, prepared by Royal Haskoning for MCT and dated January 2011, summarised several years of baseline and post-installation work. The Tethys database summarises its main conclusions:

• Collisions: No major impacts on marine mammals were detected over three years of post-installation monitoring, based in part on shoreline carcass surveys.
• Seals: Telemetry tags were fitted to 36 harbour seals in three deployments (2006, 2008 and 2010). Combined with sonar data, the results suggested that seals tended to pass the turbine during slack tide, when the rotors were slow or stopped, which was interpreted as a degree of avoidance. Seals still passed regularly, and aerial surveys found no major changes at haul-out or breeding sites.
• Porpoises: Harbour porpoise activity declined during the installation phase, but no long-term change in abundance was attributed to the device. Passive acoustic monitoring recorded porpoises regularly passing the operating turbine, with no barrier effect.
• Birds: There was some small-scale displacement of diving birds immediately around the device, but overall bird numbers in the Narrows stayed stable.
• Seabed: Changes to the seabed community were gradual and consistent with natural variation, and the area lost to the foundations during construction was recolonised.
• Water flow: There was no significant change in ambient flow speed or direction, and the surface wake did not extend through the water column. Shipping between Strangford and Portaferry was judged unlikely to be affected.

The report's overall finding was of relatively small-scale behavioural changes, suggestive of some local avoidance, without population-level effects attributable to SeaGen.

Why this mattered

The environmental results were arguably as important as the engineering results. Before SeaGen, regulators and conservation groups had no real data on how a large tidal turbine would affect marine mammals. Every future project would face the same questions. SeaGen gave them their first substantial dataset from a commercial-scale machine in a sensitive site. Fortune's presentation noted that mitigation measures had been progressively removed as evidence accumulated, and that a decision on removing the shutdown protocol entirely was expected.

At the same time, it is important not to overstate what SeaGen proved. It was one machine, with two rotors, in one channel. The behaviour of seals at Strangford may not predict the behaviour of other species at other sites, and the effects of a single turbine may not scale linearly to arrays of dozens or hundreds. Researchers have generally treated SeaGen as a valuable starting point rather than a final answer.

Performance

Milestones

Capacity factor claims

Capacity factor is the ratio of what a power plant actually produces to what it would produce running at full power all the time. For context, onshore wind farms in the UK typically achieve capacity factors well below 50 percent.

MCT reported in early 2010 that SeaGen had achieved a capacity factor of 66 percent. The Wikipedia article cites a figure of 0.59 based on the average of the last 2,000 hours. MCT also said that SeaGen's average output was comparable to a wind turbine of about twice its rated power.

These were impressive numbers, but they need careful reading. They describe periods when the machine was available and operating. They do not describe the full lifetime of the project, which included commissioning delays, a period running on one rotor, daylight-only operation under the early licence conditions, maintenance downtime and testing.

A rough lifetime calculation

The following is a simple calculation for illustration, not an official figure. If a 1.2 MW machine ran at full power every hour for eight years, it would produce about 84 GWh (1.2 MW × 8,760 hours × 8 years). SeaGen exported a little over 11.6 GWh across its working life. That suggests a lifetime average output of roughly 14 percent of its rating.

The gap between this figure and the 59 to 66 percent claims is not a contradiction. A first-of-a-kind demonstration machine spends much of its life not operating normally: being commissioned, repaired, modified, tested under restrictions or waiting for maintenance. The high figures show what the turbine could do when it ran. The lifetime total shows how much of the time a pioneering machine actually spent running in that mode. Both numbers are useful, for different questions.

Homes powered

Press reports often described SeaGen as enough to power about 1,000 homes. The PRIMRE database notes that the 5 GWh produced by September 2012 was said to equal the annual electricity needs of about 1,500 households. Such "homes powered" figures depend heavily on what average household consumption is assumed, and they should be treated as rough illustrations rather than precise measures.

Daily operation

Wikipedia records that SeaGen generated for 18 to 20 hours a day as the tides moved through the Narrows. MCT said in 2008 that it would move to full operating mode for periods of up to 22 hours a day. The remaining time corresponds to the periods around slack water, when the current is too slow to turn the rotors usefully. PRIMRE notes that the rotors started generating once the current exceeded about 1 m/s.

Recognition

In 2009, MCT was named Renewable Energy Developer of the Year at the UK Renewable Energy Association awards, and it was ranked the top tidal energy company in the Guardian and Cleantech Group's Global 100 survey.

The business story

Big plans

SeaGen was always intended as a stepping stone. In February 2008 MCT announced a joint project with npower renewables, part of RWE, to install seven SeaGen-type turbines in a 10.5 MW tidal farm at the Skerries, off Anglesey in north Wales. The Northern Ireland Assembly paper describes plans for completion by around 2011. MCT also planned a project at Kyle Rhea, between Skye and the Scottish mainland, through a subsidiary called Sea Generation (Kyle Rhea) Ltd, with four turbines of up to 2 MW each. In Canada, the company signed an agreement in 2007 with the Maritime Tidal Energy Corporation for the Bay of Fundy, and planned at least three 1.2 MW turbines at Campbell River in British Columbia.

None of these projects reached construction.

Siemens

In February 2012, the German engineering group Siemens increased its stake in MCT from 45 percent to more than 90 percent, and the company later became wholly owned by Siemens. The move was widely seen as a vote of confidence in tidal power by one of the world's largest power engineering firms.

It did not last. In September 2014, Siemens suspended work on the Skerries project. Later that year it decided to exit tidal energy altogether.

Atlantis

In April 2015 Atlantis Resources, which was developing the MeyGen tidal project in the Pentland Firth off northern Scotland, agreed to buy MCT from Siemens in an all-share deal. Its chief executive said at the time that the company would explore options for developing the Anglesey Skerries site further.

In practice, Atlantis did not continue MCT's development programme. In 2016 it relinquished the seabed leases for both the Skerries and Kyle Rhea. Wikipedia notes that MCT's €18.4 million of European NER 300 funding was transferred to MeyGen in 2015. Atlantis effectively wound the company down. The business later became SIMEC Atlantis Energy, then SAE Renewables, and now trades as Ampeak Energy.

Why the business did not take off

There is no single official explanation for why MCT's commercial projects stalled, but several factors are visible in the record.

• Cost. First-of-a-kind marine projects are expensive, and costs per megawatt are far higher than for mature technologies such as onshore wind. SeaGen's own cost rose from early estimates of about £8.5 million to a reported £12 million.
• Scale. Investors and utilities need confidence that costs will fall with volume. That requires building many machines, which requires money, which requires confidence: a classic chicken-and-egg problem.
• Competition. Offshore wind was scaling rapidly during the same period, and its costs were falling quickly. Tidal stream was competing for the same pool of investment and policy support.
• Corporate strategy. When Siemens decided to concentrate on other businesses, its tidal subsidiary lost its main backer.

None of this means SeaGen failed technically. It worked, and it worked for years. The difficulty was turning a successful prototype into a profitable product line.

Decommissioning

The decision

In January 2016 Atlantis announced that SeaGen would be decommissioned, starting that summer. According to Atlantis's later statements, the device was considered to have served its research and development purpose.

Removing a turbine from a tidal race

Decommissioning SeaGen was itself an engineering challenge. The same fierce currents that made the site attractive also made it hard to work in. Subsea work could only be done during brief slack-tide windows. Keynvor MorLift Ltd (KML), a UK marine contractor, was appointed principal contractor for the engineering, planning and offshore works.

The work was done in phases:

In the final lift, KML rigged, cut and lifted what Atlantis described as a structure of over 500 tonnes. Atlantis announced completion on 26 July 2019, saying SeaGen was the first commercial-scale tidal turbine development to be fully decommissioned. The company's chief executive, Tim Cornelius, said: "SeaGen's successful decommission represents a major milestone moment for the tidal power industry."

An environmental statement prepared for the decommissioning concluded that removal was not predicted to result in any medium- to long-term environmental impacts.

Why decommissioning mattered

Decommissioning is easy to overlook, but for regulators and investors it matters a great deal. A new marine technology is much easier to license if there is evidence that it can be removed cleanly at the end of its life. SeaGen showed that a large tidal turbine and its foundation could be taken out of a fast tidal channel, and that the costs, methods and timescales involved could be planned. That is useful information for every future project.

Legacy

MeyGen and the next generation

Atlantis said that lessons from SeaGen informed later tidal turbine development and its MeyGen project. MeyGen, in the Inner Sound of the Pentland Firth between the island of Stroma and the Scottish mainland, began operating in 2018 with four 1.5 MW turbines on gravity foundations, each with an 18-metre rotor. By August 2025 it had exported about 80 GWh in total, according to Wikipedia, and further phases have won Contracts for Difference, the UK's current support mechanism for renewable electricity.

MeyGen's design differs from SeaGen in important ways. Its turbines sit on the seabed on heavy three-legged foundations rather than on a single pile that breaks the surface, and they cannot be raised out of the water. Each turbine has its own cable to shore. These differences reflect the industry's movement towards fully submerged machines that do not obstruct shipping or alter the seascape, at the cost of more difficult maintenance.

The wider industry

SeaGen was not the very first tidal turbine to supply a grid. A 300 kW turbine at Kvalsund in Norway delivered power to the grid in 2003. Nor was it the last large single device: other developers, including Orbital Marine Power in Orkney, have since built larger machines. But SeaGen was the first to combine megawatt scale, grid connection, commercial power sales and multi-year operation. It defined what a credible tidal project looked like for years afterwards.

Its most enduring legacy may be in the environmental and regulatory field. The SeaGen monitoring programme is regularly cited in reviews of tidal energy impacts. The adaptive management approach, with clear monitoring questions, independent scientific oversight and progressive relaxation of precautions, has become a template for how regulators handle uncertainty about new marine technologies.

Lessons learned

Drawing on the project record, several broad lessons stand out.

1. Access matters. The ability to raise SeaGen's rotors out of the water made early problems fixable. Designs that are harder to maintain need to be more reliable from the start.
2. Commissioning takes time. The blade damage in 2008 shows how software and control errors can damage hardware in a new machine. Months passed before full output was reached.
3. Environmental uncertainty can be managed. The combination of cautious mitigation and serious monitoring allowed a turbine to operate in a highly protected site.
4. Technical success is not commercial success. SeaGen performed, but its developer's follow-on projects did not proceed. Policy, investment and corporate strategy matter as much as engineering.
5. Plan for the end. SeaGen showed decommissioning was feasible, but also that it took more than three years in phases and required specialist marine contractors.

Criticism and limits

Cost per unit of energy

The most persistent criticism of tidal stream power is cost. A £12 million machine producing about 11.6 GWh over its life works out, as a rough illustration, at around £1 per kilowatt-hour of lifetime output on capital cost alone, before operation, maintenance and decommissioning. That is a crude calculation for a single demonstration device, not a meaningful estimate of what commercial tidal power would cost. But it highlights why tidal developers emphasise economies of scale and learning, and why critics argue that money spent on tidal power could cut more carbon if spent on cheaper technologies.

Limited suitable sites

Strong tidal currents are found in relatively few places. A tidal stream industry can only ever be as large as the number of suitable channels, and many of those are environmentally sensitive, busy with shipping, or far from grid connections.

One device does not tell you everything

As noted above, SeaGen's environmental findings came from a single installation. Arrays of many turbines may have cumulative effects on wildlife, sediment movement and water flow that a single machine does not reveal.

Visual and navigational impact

Because SeaGen's pile broke the surface, it was visible and had to be marked as a navigation hazard. Some people found it an interesting landmark; others considered such structures an intrusion into a natural seascape. Later designs have moved towards fully submerged machines partly to address these concerns.

Common misconceptions

"SeaGen was a tidal barrage."

No. Tidal barrages, such as the La Rance scheme in France, use dams to hold back water. SeaGen was a free-standing turbine in an open current, with no dam or wall.

"Tidal turbines spin fast and chop up fish."

SeaGen's rotors turned at about 12 to 14 revolutions per minute, with tip speeds of around 12 m/s at most. Collision risk was taken seriously, which is why the monitoring and shutdown regime existed, but the three-year post-installation monitoring found no major impacts on marine mammals. That is not proof that collisions never happen at any tidal site, but it does contradict the image of a high-speed blender.

"SeaGen was the first tidal turbine ever connected to a grid."

It is more accurate to call it the first large-scale commercial tidal stream generator. Smaller devices, such as the turbine at Kvalsund in Norway in 2003, had already delivered electricity to a grid.

"SeaGen was removed because it failed."

SeaGen was licensed as a temporary installation, and its developer had said from the outset that removal at the end of the licence term was appropriate given the site's sensitivity. It was decommissioned after it had served its research and development purpose and after its owner changed strategy. It was not removed because it stopped working.

"Tidal power is constant."

Tidal power is predictable, but not constant. Output rises and falls with every tide and drops to near zero around slack water, roughly four times a day at Strangford. It also varies between spring and neap tides.

Frequently asked questions

Where was SeaGen?

In the Strangford Narrows, the channel connecting Strangford Lough to the Irish Sea in County Down, Northern Ireland, about a kilometre south of the Strangford to Portaferry ferry route.

Who built it?

Marine Current Turbines Ltd, a Bristol company founded in 2000 by Peter Fraenkel. The structure was assembled at the Harland and Wolff shipyard in Belfast.

How big was it?

Two 16-metre rotors on a crossbeam mounted to a 3-metre steel pile in about 24 metres of water. The main structure weighed about 300 tonnes, and the final section removed in 2019 weighed over 500 tonnes including subsea elements.

How much electricity did it make?

It was rated at 1.2 MW and exported more than 11.6 GWh over its working life.

How much did it cost?

About £12 million, according to reports at the time of installation, with public support including a £5.2 million government grant.

Did it harm seals?

The monitoring programme found behavioural changes, particularly a tendency for seals to pass the turbine at slack tide, but no major impacts on marine mammals over three years of post-installation monitoring and no population-level effects attributed to SeaGen.

Why was it removed?

Its licence was temporary, it had served its research and development purpose, and its owner, Atlantis, chose to focus on other projects such as MeyGen. Decommissioning ran from 2016 to 2019.

Is anything still there?

According to Atlantis and its contractor, the remaining tower and subsea structure were removed in July 2019, completing the decommissioning.

What replaced it?

Nothing was installed at the same location. The tidal energy industry's attention moved to sites such as the Pentland Firth, where MeyGen operates, and to other test and demonstration areas in Scotland and Wales.

Who owns the technology now?

Siemens sold Marine Current Turbines to Atlantis Resources in 2015. Atlantis, later SIMEC Atlantis Energy and SAE Renewables, now trades as Ampeak Energy.

Summary

SeaGen was a 1.2 MW twin-rotor tidal stream turbine installed in Strangford Narrows, Northern Ireland, in 2008 by Marine Current Turbines. It was the first device to combine megawatt scale, grid connection, commercial electricity sales and years of operation, and when it reached full power in December 2008 it set a record for tidal stream generation. Its rotors could be raised above the water for maintenance, and its pitch-controlled blades worked on both flood and ebb tides.

Because it sat in one of the UK's most protected marine sites, SeaGen operated under strict precautions, including marine mammal observers, shutdowns and active sonar, that were progressively relaxed as monitoring showed no major harm to seals, porpoises or birds. It exported more than 11.6 GWh before operations ended in 2016, and it was removed in stages by 2019, becoming the first commercial-scale tidal turbine to be fully decommissioned.

Commercially, its story is mixed. The follow-on farms its developer planned never went ahead, and the company was absorbed first by Siemens and then by Atlantis. Technically and environmentally, though, SeaGen did what a demonstration project is supposed to do. It showed that a large tidal turbine could work, that it could share a channel with protected wildlife under careful management, and that it could be taken away cleanly when its job was done.

Sources

• SeaGen (Wikipedia)
• Marine Current Turbines (Wikipedia)
• Tethys (PNNL): Strangford Lough MCT SeaGen project site
• Tethys (PNNL): SeaGen Environmental Monitoring Programme final report
• Frank Fortune, Royal Haskoning: SeaGen, Strangford Lough, an adaptive management approach (2012)
• Northern Ireland Assembly Research and Library Services: Update on the SeaGen project (January 2009)
• PRIMRE / OpenEI: SeaGen-S Strangford Lough project record
• Renewable Energy World: MCT's SeaGen reaches full 1.2 MW capacity (December 2008)
• Renewable Energy Magazine: First 1,000 hours converting tidal energy (2010)
• NS Energy: SIMEC Atlantis completes SeaGen decommissioning (July 2019)
• Water Power Magazine: SIMEC Atlantis decommissions 1.2 MW SeaGen tidal system
• Strangford Lough (Wikipedia)
• MeyGen (Wikipedia)
• Tidal stream generator (Wikipedia)