Turning the tide at the European Marine Energy Centre

9 min read

In the dramatic, windswept landscape of Orkney, Scotland, engineers are helping to harness some of the most powerful waves and tides in the world to produce renewable marine energy.

The European Marine Energy Centre is based in a converted school perched above the harbour of Stromness, a small town on the west coast of the Orkney island of Mainland. It’s a quiet spot in a sleepy town, which belies the awe-inspiring natural resources it is working to exploit.

‘We’ve got both waves and tides here, so we can look at both technologies at the same time; or at least from the same office,’ said Neil Kermode, managing director of EMEC. ‘Waves and tides’, however, is an understatement. There are good reasons for EMEC being sited in Orkney, chief among them that the waves and tides are some of the most powerful in the world.

It seems fitting that Orkney will be one of the first places to benefit from marine energy, as traditionally the Orcadians have been pragmatic and willing to try new ideas. ‘Wealth has come out of the sea in Orkney for many generations,’ said Kermode. ‘It has been massive in terms of trade; there were huge herring fleets based here; the British fleet anchored at Scapa Flow in both world wars. I think Orcadians who’ve been through university have thought, “here’s a landscape that’s entirely sculpted by energy — the wind, the waves and the tide have shaped the landscape. Why not get the energy from the sea?”’

The world of wave and tidal power, neglected since the early 1980s, is becoming one of the fastest-moving areas in the energy sector. There are now some 80 devices around the world in various stages of development — and 60 per cent of the development is in the UK.

This is fitting because, through quirks of geography, the UK has some of the richest marine energy reserves in the world. Its position on the edge of western Europe means it is exposed to Atlantic waves that have built up over thousands of miles of ocean, while the interaction between the Atlantic and the North Sea, the Irish Sea and the English Channel, along with the many constrained passages between islands and mainland, creates fearsome tidal races where thousands of tonnes of water flow at high speeds four times a day.

The recent UK energy review estimated the country could gather about 20 per cent of its energy requirements from marine renewables. More than half of Europe’s potential tidal energy reserves are in the Pentland Firth, the narrow passage between Scotland and Orkney. Estimates of the energy reserve in these waters range as high as 20GW, which is equivalent to 20 average-sized power stations and almost enough to meet the UK’s mean energy consumption (although not its peak power requirement, which is about 60GW).

But getting the power out of the water is not simple. Of the 80 devices under development, so far only seven have been tested in open water and none has been connected to the National Grid — although the first may be only months off.

That is where EMEC comes in, as the world’s only accredited and independent testing and verification house for wave and tidal renewable generation devices. Despite this it is a small operation, with nine staff whose expertise includes oceanography, electrical and marine engineering and marine biology, to monitor devices’ effects on the fish, whales, seals and dolphins that abound in the clean waters around Orkney.

The centre’s origin was a Foresight report for the government in the 1990s, explained Kermode. ‘Some work was done, which showed that all marine energy devices were going to have some common features: they were going to be in the water; they were going to need a cable coming back to the beach; and you’d need to do something with the electricity when it gets back to the beach. And doing all of those things is going to be quite hard.’

The decision was taken to find a site where the infrastructure — terminals on the seabed, cabling and a substation on shore to receive and condition the power and channel it into the National Grid — could be installed, so device developers could concentrate on making sure their equipment worked, without having to worry about how to test it. ‘It’s a lot easier for people to get their first commercial devices into the water if the data they generate the first time around are credible,’ said Kermode.

Orkney is the most northerly point on the UK’s National Grid, which makes it easier to get the power into the system. And EMEC has wave and tidal testing sites, both with four ‘berths’ for devices to plug in and the complete infrastructure to bring the power to shore. So far, said Kermode, some £15m has been invested in the facilities, mostly via the Highlands and Islands Development Board.

Wave machines are berthed just over a mile (2km) off Billia Croo, a beach a few miles along the Mainland coast from Stromness. ‘There’s nothing west of Billia Croo until you hit Canada,’ said Kermode. ‘The waves come in uninterrupted and there’s a huge energy impingement, of the order of 25kW/linear metre of wave.’

The tidal site, meanwhile, is at the Falls of Warness, a submerged reef just off the northern Orkney island of Eday, where twice a day the North Atlantic tide rushes into the North Sea through the narrow gap between the islands at speeds exceeding eight knots (4m/sec)

OpenHydro's quarter scale tidal generator at the falls of Warness
OpenHydro’s quarter scale tidal generator at the falls of Warness

Billia Croo is a site of special scientific interest, with fossilised fish deposits between the strata of the cliffs, so the substation that receives the energy from wave devices and channels in to the grid is almost invisible, buried in the shoreline. The cable, capable of handling up to 9MW of power, splits into four as it runs along the seabed, out to individual berths in the deep water. To the north and south of these berths, ‘waverider’ buoys bob up and down in the swell, transmitting data on wave height and wave length back to the offices in Stromness. This, explained test engineer Chris White, allows the developers to correlate their devices’ performance to the wave conditions on the site.

Billia Croo looks peaceful, with a 2m swell rolling in over the metre-diameter boulders on the beach, but the energy is readily apparent. ‘We often get 5-6m waves, or even higher,’ said White. ‘And when they come in, those boulders just get rolled around like pebbles.’

At the moment, there are no devices moored off Billia Croo but, within the next few weeks, one of the berths will be occupied by Pelamis, a wave-energy converter developed by Edinburgh-based Ocean Power Delivery and one of the machines furthest along the development pathway. Pelamis is a long, articulated structure with a torpedo-shaped nose and is surprisingly large — about the size of a London Underground train. Its segments — six in the model now moored off the island of Hoy on sheltered Scapa Flow and awaiting a tow up to Billia Croo — are linked by universal joints, allowing the structure to flex as waves flow under and past it.

Inside the three short segments are the power-conversion units. ‘There are two hydraulic rams, one at the top and one at the bottom,’ explained project manager Jacob Ahlqvist. ‘As the machine moves, these rams expand and contract and they suck oil from a low-pressure cylinder, compress it and pump it into a hydraulic accumulator. We allow the pressure in there to build up to 300bar and, once we have a sufficient volume at that pressure, we open a valve to drain the oil through a motor, which spins a generator.’ The three-module Pelamis generates 750kW of power in a 5-6m swell.

The Pelamis mechanism is developed from an older generation of wave-power converter, known as Salter’s Duck. Developed in the 1970s by wave power pioneer Stephen Salter of Edinburgh University, the ‘duck’ was a cam-shaped body on the surface of the sea, linked to a similar hydraulic generator system. The Duck was highly efficient, extracting most of the energy from the waves, but this was believed to make it vulnerable to high seas. Pelamis’s torpedo nose is designed to let it ‘dive through’ the largest waves rather than flexing with them. Although this reduces its efficiency, it makes it a more robust and ‘survivable’ design, said Ahlqvist.

Pelamis is the closest wave-power device to commercialisation. It is about to undergo four weeks of testing at Billia Croo, allowing Ahlqvist’s team to correlate power generation to wave conditions and gather data about the operations of hydraulics and electronics and the stresses that develop in the machine’s steel body as the joints flex.

Already, three machines are awaiting deployment for a wave farm off Portugal and, last month, the Scottish Executive announced £4m funding for a four-Pelamis wave farm off Orkney. Initially, the machines will be run at Billia Croo, said Kermode, to test how they interact with each other. Then a permanent wave farm will be established, possibly off Hoy, where submarine cables carry the National Grid over the Pentland Firth, with the option to increase the number of machines to twenty.

Wave power has long been seen as running ahead of tidal, but this may soon change. At EMEC’s tidal site, a two-legged superstructure supports a device that looks like a giant Polo Mint — a tidal turbine owned by Dublin-based developer OpenHydro. From the sea, the power in the water is obvious — the tide streams past the legs of the superstructure, leaving a speedboat-style wake streaking across the surface of the sea.

The OpenHydro turbine, six metres in diameter, is about to be lowered into the water and plugged into the seabed terminal, making it the world’s first tidal device connected to the National Grid. Generating 250kW and about a quarter of the size of OpenHydro’s projected full-scale unit, it will supply most of the energy for the 150 people who live on Eday.

With its turbine blades the only moving part of the device, the OpenHydro design is deliberately simple, said chief executive James Ives. ‘It’s a permanent magnet generator with magnets in the tips of the turbine blades and coils in the stator around the outside.’

This reduces the cost of the machine, and also boosts its efficiency. ‘We don’t have any losses associated with gear boxes or hydraulic mechanisms. Also, we have no oils, greases or lubricants in there that can act as pollutants and the hole in the middle, while it provides some hydro- dynamic benefits, also provides a passage through the turbine for marine life.’

In addition, claimed Ives, retaining the tips of the turbine within the housing reduces the noise it produces, which is another factor for ‘fish-friendliness’.

The tall superstructure that houses the turbine is purely a developmental tool, explained Ives, so the company can replace the turbine with subsequent models for testing and verification of performance.

The commercial model, however, will sit permanently on the sea bed with nothing showing above the water’s surface; OpenHydro plans to install this version at another EMEC berth in the summer.

The company is also about to commercialise its designs. Ives describes the turbine at EMEC as a ‘pre-commercial model’ but has recently signed contracts for two full-scale tidal stream farms — off Alderney in the Channel Islands and in the Bay of Fundy in Nova Scotia. This latter site, cluttered with floating ice in the winter, is even more challenging than Orkney, he said. Both farms will use an array of turbines of different sizes, and will generate around one MW of power.

Tidal streams are often seen as harsh environments to work in — even more so than wave sites. While waves occasionally die down, the tide is always there. Consequently, many developers have chosen to site experimental turbines in sheltered tidal inlets. But the EMEC site allows developers to work in the North Atlantic, where the environment is unremitting.

‘We’ve learned a huge amount from that and it’s helped us make a very robust design,’ said Ives. ‘A lot of people are scared of working in that marine environment but we have a different view. We respect it and we know how to make it work for us. Yes, it’s tough, but it’s not as bad as people make out.’

Back at EMEC, Neil Kermode is realistic about how much work is needed to establish marine renewables as a part of the UK energy mix. He said: ‘We’re probably about where wind was 20 years ago and we have to understand that sometimes technologies are going to fail; they’ll sink, or end up on the beach. But it’s only a massive challenge if it’s left to small companies; not so much if the corporates come on board and we decide to make it a UK plc imperative.

‘Look back at history, at what this country has managed to achieve when it has set its mind to it. We’ve achieved remarkable feats.’

Pulling energy from the oceans could be one of the most notable.

Bobbing around

Pelamis and OpenHydro are just two of the wave and tidal technologies being tested in the UK. At various points around the country, other developers are sliding their machines into the water and awaiting results.

At Strangford Narrows in Northern Ireland, a sheltered tidal inlet into Strangford Lough, Marine Current Turbines is awaiting the arrival of SeaGen, above, with a pair of twin-blade rotors that will generate one MW of power.

Now being assembled at Harland & Wolff shipyard in Belfast, the device will be installed later this year.

Another version of a tidal turbine is being operated by Lunar Energy, based in East Yorkshire and using technology invented by an Aberdeen company, Rotech. The device uses a six-bladed turbine housed within a double-ended venturi that accelerates the flow through the blades. Lunar Energy announced earlier this month that it is to team up with E.On, the owner of PowerGen, to develop an 8MW tidal farm off the west coast of the UK, using eight 20m-high turbines sited some 120m below the sea’s surface.

Now being installed 10 miles off Hayle on the north coast of Cornwall, Wave Hub is a sea-floor terminal where four arrays of devices will be connected to the grid. Three of its berths are now booked and Ocean Prospect, a Bristol-based firm, is planning an array of Pelamis devices. The other two berths are taken by some 24 PowerBuoy devices, where the waves operate a piston that turns a generator; and Danish firm Fred Olsen’s platform-based device, whose legs house buoyant plastic balls that are forced up and down by the waves, with the motion generating electricity.

In Denmark, meanwhile, the Wave Dragon generator is already grid-connected. This is an overtopping system: the waves wash water up a ramp on to an elevated platform, where it is forced to flow back into the sea under gravity through a series of turbines.