Rising tides

Elaine Maslin examines the market for wave and tidal, and reports on industry efforts to drive down costs and eventually scale up.

A Tocardo device, supported on a Damen-built “UFS,” at Hatston Pier, Orkney, earlier this year, before being deployed at the Fall of Warness tidal test site. Photo from Colin Keldie.

The pace at which offshore wind costs have dropped over the last few years has surprised many. The once expensive energy source has taken on the challenge of becoming competitive, hitting sub-£100/MWh (US$129/MWh) levelized cost of energy (LCOE) in 2016, a 32% drop on the previous year and making it cheaper than nuclear power. This year has even seen a wind farm bid based on supplying subsidy-free power for an average of €4.40/MWh ($4.90/MWh) in Germany, and the UK is poised to follow suit.

While such a reduction in cost has been welcomed, it has given pause for thought for wave and tidal energy developers because what once seemed a bridgeable gap in cost of energy now seems further away than ever.

The situation is even more troubling for wave energy. “A rethink is required on wave energy technology if it is to be an affordable source of renewable electricity,” said a report by the UK’s Energy Technologies Institute (ETI) earlier this year. Despite having shown an ability to work technically, wave energy is up to 10 times more expensive than other renewable technologies. Tidal technologies, the ETI says, have more chance of success, but will require government support.

Offshore wind has reduced a lot of its costs by scaling up, to up to 8MW currently, with 10MW predicted for the 2020s, up to 15MW from 2030, and even 20MW beyond that. Yet, tidal energy turbine size has not grown much since Marine Current Turbines (MCT) put its twin, 1.2MW turbine SeaGen S installation in the water, back in 2008, says tidal energy veteran an MCT co-founder Peter Fraenkel. Indeed, Atlantis Resources’ MeyGen tidal stream project – billed as the first tidal array, with four machines – is using 1.5MW turbines.

There are others, meanwhile, who argue against scaling up. Simply scaling up a single turbine, as has been done in offshore wind, would not be feasible in depth limited tidal stream sites, they say. There are also companies with completely new ideas, such as Minesto and its subsea kite concept. However, there is still the concern that without some sign of government support (subsidies and funding), and the opportunity to scale up, the industry will be stuck where it is for some time – if not just disappear altogether, Fraenkel warned the All Energy conference in Glasgow, early May.

Tim Cornelius, CEO of Atlantis Resources, told the event that the question is how to get to £100/MWhr. Atlantis Resources is behind the MeyGen project in Scotland’s Pentland Firth – a gravity-based, seafloor-installed four turbine array – with plans to build out to 396MW.

Scotrenewables SR2000. Photo from Scotrenewables.

Going big

Atlantis Resources AR1500 turbine.Image from Atlantis Resources.

Brendan Corr, CFO at OpenHydro, which is delivering 2MW “open hole,” seafloor fixed turbine devices in France and Canada, thinks scaling up is the way to go. However, the environment has to be right. “We have 100 engineers and I think they can do [design] bigger,” he says. “That will happen. But, you have to start somewhere and have line of sight on build up and, at the moment, we don’t have that in the UK,” he told All Energy.

OpenHydro uses a bi-directional permanent magnet motor ring generator on a gravity-based foundation. Its first device was connected at the European Marine Energy Centre (EMEC) in 2008 and has been operating there since, with various generation models, up to today’s 16m-diameter device. Over that time, a 16% improvement in turbine efficiency has been achieved, said Sue Barr, external affairs manager for OpenHydro, at All Energy. The firm says it has 3.7GW of projects in the pipeline, including two, two-turbine demonstration arrays in France and Canada and a project for one turbine offshore Goto, Japan. Barr says the firm is hoping it can deliver commercial turbines by 2020.

David Collier, project manager on Atlantis’ MeyGen project, points out that energy density is higher in tidal stream, with devices a quarter of the size of wind needed to produce the same power. Bigger devices also help to hold gravity based devices on the seafloor, he adds.

Andrew Scott, CEO at Scotrenewables, whose 2x1MW turbine SR2000 sits on the surface with the rotors hanging submerged beneath, says increasing the swept area, i.e. that covered by turbine blades, is the way to go. Indeed, the firm, whose device is being tested at EMEC, is looking to increase its machine’s rotor diameter from 16m to 20m, with composite blades, he told All Energy. But, it’s not the only cost driver, he says. “There are different constraints on tidal. We are constrained by the seabed. That will lead to a desire to build bigger machines, balanced against the constraints at sites and water depths.”

OpenHydro’s device mid-deployment. Photo from OpenHydro.

Strength in numbers

“Unless we start to scale tidal turbines up, we will go bust because it will have no commercial future,” Fraenkel says. “System costs are too high by a factor of three and output too low. By whittling down costs, at best you get 10-20%. You can’t just halve costs unless you have a stupid design in the first place. But, you can scale up rotors, 400-500%. This is what the wind industry has been doing.”

Fraenkel has proposed SuperTideGen, a floating structure with two connected structures, each with two blades, totaling 4MW at 2.4m/sec or 6MW at 3m/sec. Being near the surface yields 20% more energy than submerged systems, he says, and the rotors could be raised out of the water for maintenance. It would also be a “cheap and simple to install or reposition.”

Dutch turbine maker Tocardo sees a future for smaller turbines, mounted on a single structure, which it’s calling the Universal Foundation System (UFS). Tocardo’s 100-250kw turbines direct drive turbines have so far just been used as part of sluice gates, but it is now working on the InToTidal project with EMEC, Leask Marine, and French test house Ifremer. This hopes to put five Tocardo turbines on a UFS totaling 1.4MW by 2017-2018. One of the firm’s T2 turbines was deployed at the Fall of Warness site, offshore EMEC, this March.

Nova Innovation’s managing director Simon Forrest says starting small will help development, making it easier and cheaper to fix issues, with less risk. The firm installed its third 100kw M100 turbine in its three-turbine Shetland Tidal Array in the Bluemull Sound this year and is producing power to the grid.

To float or not

Nova Innovations M10. Photo from Nova Innovation.

Views also remain divergent on how tidal turbines should be deployed – on the seafloor or from floating structures. MeyGen’s turbines are gravity based and set to be re-designed for the Phase II of the project. OpenHydro’s devices are also seafloor fixed. But Scotrenewables, described as the first commercial utility scale device and most powerful in the world, and Sustainable Marine Energy (SME) have floating devices from which turbines hang, as favored by Fraenkel.

“I think floating has a number of benefits going for it,” says Scotrenewables’ Scott, including ease of installation and operation using £300/day ($387/day) multicat vessels, or even ribs, and having the turbines closer to the higher flowrates. “Floating means a vast majority of components are above the surface for access and maintenance,” Scott says. Outages relating to an AR1500 turbine on the MeyGen project meant it has had to be retrieved from the water, which would be costlier than sending a rib to a moored structure. Scotrenewables’ SR2000 was installed in October 2016 and recently produced 18MWh of power over a continuous period. Scott says the SR2000 has a 40% capacity factor, which favors well compared with offshore wind.

Magallanes Renovables, based in northwest Spain and founded in 2007, has been testing a scale version of its 45m-long, 25m-deep, floating tidal energy platform, mounted with two 18m-diameter rotor turbines, in Spain and at EMEC. A full-scale device, moored from lines on its bow and stern, for sites with more than 100m water depth, is due at EMEC this year. Magallenes, which has support from ABB and Orkney firm Leask Marine, says 90% of the device’s equipment will be able to be fixed inside the structure’s space.

Schottel Hydro, also has a floating concept, based on a single point moored structure – using oil and gas technology – holding multiple turbines. “The small turbines we have are very light weight and easy to handle, easy to exchange in an hour or two,” says Niels Alexander Lange, managing director at All Energy.

The big benefit of smaller units is seen as the ability to use smaller vessels. However, Dave Rigg, head of operations at Atlantis Resources, told All Energy: “In the future, when you get more deployments, the seabed will get very busy and you wouldn’t want to use moorings in that space.” He also says that, while using smaller vessels might seem attractive, “using DP vessels in that environment offers more certainty than any other asset you might want to use in that environment.”

Maturity

Maturity is also an issue. OpenHydro’s Corr told All Energy that he believes tidal is at the same point offshore wind was in the 1980s. Following the learning curve of offshore wind can get tidal to the same point, he says, and faster.

“We can learn from their mistakes, how they reduced the levelized cost of energy, and that’s a huge benefit,” Atlantis Resouces’ Collier says. “The turbines are only a proportion of the cost – less than half. The rest of the cost has to come down proportionately and I think we have done this. We are in a position shortly to identify a direct path to reduce the cost of energy to compete directly with offshore wind.

“The turbines we currently have are fat and I think we can take a lot of fat out, reduce the cost, reduce the size, find a way to combine the power offshore, in strings, like in offshore wind, and we need to find a way of increasing the system voltage. We are also looking at going to fixed speed rotor, rather than variable speed, which also has advantages. When you put that together, you have a different type of farm and different costs. It’s a process and I think we’re going to get there.”

Projects have been underway at EMEC, to reduce costs. An Orkney vessels trials project, with 20 companies working together, looked to more 60 different vessel operations more efficient, enabling local, smaller vessels to be used, saving 70-80% cost compared to using DP vessels, EMEC’s Eileen Linklater told All Energy.

Further projects are ongoing around sub-systems, integrated monitoring, component analysis, subsea cable life cycle studies, and others. FORESEA, an EU project, has also made an arrangement with EMEC to offer free access to test berths.

Converter station inspection

A drone’s eye view of Helwin Alpha. Photo from Cyberhawk.

Cyberhawk discusses a recent offshore wind inspection operation using drone technology.

Drone inspection and survey firm Cyberhawk Innovations has made a move into offshore wind converter stations.

The firm, which whas already used its drones to inspect offshore wind turbines and met masts, was picked by Siemens to perform close visual inspections of three converter stations – Borwin B, Helwin A and Sylwin A – offshore Germany, belonging to transmission system operator TenneT.

A two-man team did the inspections in seven days during December 2016. Alternative methods for the inspection would have included using rope access or elevated platforms.

The use of its asset management software, iHawk, allowed Siemens to access high definition images of the entire converter station structure, and quickly see the defects identified. This quality of the data, and speed in which it was provided, helped quick and effective asset management decisions to be made.

Thanks to Cyberhawk’s inspection team working closely and effectively with a third-party maintenance team in a single mobilization, the project proved to be extremely time and cost efficient for Siemens.