Tidal on the rise

Tidal energy is moving up a gear, with arrays becoming real and a supply chain being put to the test. But, there’s still more to do. Elaine Maslin reports.

An AR1500 generator and gearbox being assembled at OREC. Photo from Atlantis Resources.

Tidal energy is making huge strides this year. The first commercial array is being built out in Scotland’s Pentland Firth, between Orkney and the Scottish Mainland, by Atlantis Resources, meanwhile OpenHydro is building an array of its openhole devices off France.

Others are eyeing arrays, too, with floating devices starting to play a greater role, as well as concepts for platforms to house multiple original equipment manufacturer supplied turbines, showing the increasing confidence in turbine technology. Confidence in the technology is also helping to breed confidence in the supply chain, with various companies creating and designing bespoke vessels and tools to aid installation and maintenance.

But, for those not as commercially advanced as Atlantis (a stock market-listed outfit with backing from Morgan Stanley), creating a commercially attractive business is still tough, including for those looking to offer bespoke high-end vessels for the installation and maintenance market. Lessons are also being learned and cost savings sought as firms move into bigger projects.

And while the UK’s Energy Technologies Institute predicts tidal energy could supply 20-100 TWh (terawatt hours) of the 350TWh of the UK’s annual electricity demand, it says there’s still some way to go before the technology could supply the 10-20GW it thinks the technology has the potential to supply. This is because the levelized cost of energy (LCOE) for today’s tidal energy converters is estimated to be in the range US$273-410 (£200-300)/ MWh compared to $176-226 (£129-166) for offshore wind projects. Which is why the focus has turned from proving the technology, to reducing the costs. The next hurdle will then be scaling up.

An AR1500 being assembled at OREC. Photo from Atlantis Resources.

Leading the pack

The first 6MW phase (Phase 1a) of what will potentially be a 398MW array is being built out now, with four generators due to be installed and grid connected by yearend. Lessons are being learned, the supply chain tested, and plans for the next phases of the project are being adjusted accordingly.

“The work we are now doing is around supply chain ability to deliver in time to correspond with financial close [on the next phase projects],” says Atlantis’ CEO Tim Cornelius.

In Phase 1a, the four turbines, from two suppliers (1 x Atlantis AR1500 and three Andtritz Hydro Hammerfest devices), each have their own gravity-based foundations. Some of the lessons learned on the project have been around the influence of turbulence on the design of the turbine support structure or foundation, which has driven a need for two different designs, says David Taaffe, project manager.

These structures are currently being built out at Nigg in Scotland. Some 16 of 24 ballast blocks had been manufactured by early May, each weighing 200-tonne, with six for each substructure. Installation is due in August, followed by turbine installation. The subsea power export cables are already laid.

To reduce costs, on the next phase, Phase 1b, Atlantis is looking at having two turbines per foundation, Taaffe told the All Energy conference and exhibition in Glasgow in May. Phase 1c could have up to 50 turbines installed. Other ways to reduce costs could be more standardization around the stabilization and yaw mechanisms, across the industry, Taaffe said.

Nothing is easy

Cardiff-based Tidal Energy Ltd. has its eye on a 10MW array at St David’s Head, in the Ramsay Sound, offshore Pembrokeshire, Wales, using its multiple turbine, gravity-based platform, called DeltaStream, which sway around to meet the tidal flow.

But first, the firm is testing a single device in the Ramsay Sound, a marine special area of conservation, to demonstrate the technology and assess its impact on the marine environment. One was finally installed in December last year, and is exporting power via a 1.2km subsea cable to shore, where it is conditioned before going into the grid.

“It’s not been an easy path,” says Martin Murphy, the firm’s managing director, at All Energy. “One thing we have learned is that it is a long process. It needs stamina.”

The fabrication contractor went into administration soon after fabrication started. Then, in 2015, a problem was found on the subsea cable, meaning that additional funding had to be found for repair work, which was carried out using the Siem Daya I, the same used by Atlantis on the MeyGen project.

The Ramsay Sound site has offered challenges around the nature of the tidal stream there, as well as installation processes and a tough business environment. One of the key issues in the Ramsay Sound is the difference in energy between the ebb and flow regimes. Due to the nature of the seabed, the north flowing flow creates intense turbulence in the environment.

To help understand more about how the device operates and interacts with the environment, an acoustic monitoring platform is being installed, with active sonar (acoustic Doppler current profiler) measuring current speed and data fed to the Delta stream, then via fiber optic cable to shore. There are also passive hydrophones on the device itself.

2 x Scotrenewables SR2000 being launched in May. Photos from Scotrenewables.

See if it floats

Smaller outfit Scotrenewables is making strides, too. Its 2MW, 550-tonne SR2000 device, which it describes as the world’s largest tidal device, was launched in May at Harland & Wolff in Belfast, and is due to be taken to Orkney for a grid-connected test program.

The SR2000 is a floating structure, from which two 1MW turbines are suspended. This means it is nearer to the higher flowrates and away from turbulence on the seabed, says CEO Andrew Scott, as well as having reduced volumes of steel. It can be towed and installed on pre-installed seabed anchors and moorings using a 30-50-tonne bollard pull anchor handler without getting men in the water or on the device, he says. Maintenance is from a non-DP multicat vessel, like those used in the offshore wind industry, Scott says.

Delivery of the SR2000 may have taken slightly longer than planned, however. For Scotrenewables, lessons learned have been around resourcing, Scott told All Energy. “Hard lessons were learned around resourcing. While we have experience and knowledge, there was a shortfall around construction and execution skills and this is a common feature across marine renewables and is a vital learning curve.”

More work also needs to be done around power take off optimization, Scott says. This is an area the wider industry is also focusing on (see Breaking Waves - OE July 2016). Scotrenewables is also looking to go to medium voltage systems to reduce the amount of onboard equipment, he says.

Pontoon platform

OpenHydro’s device being launched off France this year. Photo from DCNS.

A floating, multi-turbine platform is also Cowes and Orkney based Sustainable Marine Energy’s (SME) approach. The firm’s Plat-O platform, comprising three connected semisubmersible “pontoons,” is held beneath the sea surface. Turbines are mounted from the connections between the buoyant structures. The central pontoon contains the controls systems, etc., while the outer pontoons offer buoyancy.

The firm was recently awarded $6.15 million (£4.5 million) funding to help it start building out an array of Plat-O devices at EMEC, Orkney. A first device is due to be installed this summer, followed by a larger, 240kW, platform with Schottel Hydro Instream Turbines (SIT 250), production of which is due to start this summer, also in Scotland. Up to five will be installed. SME recently placed an order in for 16 Schottel tidal turbines, as part of its work.

Christoph Harwood, commercial director, SME, says that the design means vessels with lifting capability are not needed – multicat vessels can tow the devices out for installation and a winch-based pull down systems moves the devices into their moored position.

After looking at gravity anchoring, SME developed a helical anchoring method, effectively creating rawl plugs in the rocky seabed at EMEC, deployed off a multicat vessel using an ROV. It was first trialed in Q1 2016 and results revealed at All Energy.

OpenHydro’s device being launched off France this year. Photo from DCNS.

Openhole goal

One of the earliest tidal units in the water was OpenHydro’s so-called openhole technology. The latest seafloor mounted (a gravity foundation made by pumping tubular steel frames full of concrete) 2MW, 16m-diameter unit weighs 300-tonne.

OpenHydro is working on the Cape Sharpe Tidal project, a joint venture with Emera Energy and OpenHydro in the Bay of Fundy, Nova Scotia, with two 16m diameter, 2MW machines being deployed this year. The export cables, connectors etc., were already installed. Another two machines are being built for the EDF Palpol Brehat project in France, which already has two installed. This 8MW project will help pave the way for the 14MW Normandie Hydro project, also off France, which will see seven tidal turbines in the Raz Blanchard by 2018. With these projects, as well as a plan for a 200MW project in the Pentland Firth and others, OpenHydro has some 900MW of projects in the pipeline, says James Ives the firm’s CEO. Add other prospects the firm is looking at and the number increases to 2GW, he says.

OpenHydro developed its own deployment barge system for installation and maintenance. It takes just hours to deploy a machine, Ives says, with commissioning from the barge.

For OpenHydro, the latest testing has been less around the turbine and more about electronics testing, controls systems and optimizing power output from the turbines, Ives told the European Ocean Energy Conference in Edinburgh earlier this year.

Reduce costs or scale up?

Despite the advances in the sector, arguments remain on the best way forward.

“Unless tidal energy can compete with offshore wind on profitability, it seems obvious they will fail to get interest in finance,” says Peter Fraenkel, co-founder of Marine Current Turbines, a firm credited with helping get the tidal industry off the ground, and now a consultant.

“Wind turbines have grown [in size] because the only way to improve their performance is increasing the rotor swept area, which has grown by a factor of over 100. Costs are a quarter of what they were in 1980 in real terms.

“Today no one considers anything less than 5MW offshore,” he says. “Tidal started scaling up but stopped in 2008. We cannot continue starting small and not scaling up or we will fail. The main message is that costs are not the biggest answer, low costs devices not much use if they are not profitable.”

Fraenkel is involved in a new design, Super SeaGen, which is focused on having a large rotor space. It is a floating device with multiple turbines suspended off it, which can be lifted out of the water.

Jason Hayman, SME’s CEO believes tidal needs has to go the way of fish farming, “using smaller vessels and local skills at a decent cost base.”

“Sometimes we get caught up in the scale thing too much,” Hayman adds. “We want to get the costs out, understand the mechanics and when we understand it, scale up.

“It’s a common misconception we will drive the levelized cost of energy down with scale,” he continues. “It contributes, but it’s about how many times you do something. “They used to say we need DP. But, it is about process and learning and making things a lot cheaper.”

However, Hayman says the problem is not related to the technology. “The problem,” he says, “Is with the financial engineering and right level of government support to enable industry to stand on its own two feet.”

Marine Current Turbines founder, Fraenkel, added a word of caution. “There is also a danger of over-egging the problems.”