Tidal Power

The Scottish islands of Orkney are home to the European Marine Energy Centre, a research centre focused on the development of tidal (and wave) power.

Power Engineering International speaks to tidal power turbine technology equipment developers to find out more about the five ongoing projects at this hotbed on the seabed.
 
Tim Probert, Deputy Editor
The 20 000 people on the rugged islands of Orkney in Scotland’s extreme north are vastly outnumbered by sheep. But out to sea, beyond the wind-scoured landscape and dramatic cliffs, is the world’s leading tidal energy research center.
The European Marine Energy Center (EMEC) at the Fall of Warness, to the west of the island of Eday, offers five test berths at depths ranging from 25 meters to 50 meters in an area 2 km across and 4 km in length.



The site was chosen for its high velocity marine currents which reach almost 4 meters per second at spring tides. In each of the five test beds, 11 kV sub-sea cables extend to the center of the tidal stream. Developers are responsible for installing their devices, connecting to the designated cable and removing their devices when testing is complete.


WORLD’S FIRST TIDAL CURRENT TURBINE
In 2003, Norwegian tidal energy technology firm Hammerfest Strøm installed a 300 kW test turbine, the world’s first tidal current turbine, in Kvalsund, Norway, within the Arctic Circle near Hammerfest, Europe’s most northern city. Operating at a depth of 50 meters, the turbine – developed in conjunction with ABB, Rolls-Royce, Skelmer Skanska, SINTEF Energy Research, Sta-toil and Venturous – has been generating electricity for the grid since 2004, when it was permanently connected to the national grid, supplying 700 MWh per year.

The submerged structure weighs 120 tonnes and has gravity footings of 200 tonnes. The three-bladed turbine is made of fiberglass-reinforced plastic and measures 10 meters from hub to tip. By rotating the propeller blades around their own axis at slack water when the current turns the turbine is ready for the reversing current (pitch control), keeping the nacelle fixed.
Each propeller is coupled to a generator, from which the electricity generated is fed to shore via a sub-sea cable. The turbine was designed for a three-year test period, but was operated for approximately four years without maintenance, according to Hammerfest Strøm.

THE HS1000 UPGRADE
Hammerfest Strøm will be installing a 1 MW prototype, the HS1000, at the EMEC site this summer. The company, which was set up in 1997, plans to test two turbines a season to make sure that it has calculated the effects of the waves correctly.
After testing, the plan is to install ten HS1000 tidal turbines by 2013 in Argyll Sound, between the Inner Hebridean islands of Islay and Jura off Scotland’s west coast. Spanish utility Iberdrola’s subsidiary ScottishPower Renewable, a shareholder in Hammerfest Strøm, has already submitted a planning application to develop this array of HS1000 turbines.

An impressive list of companies is backing Hammerfest Strøm to succeed. In addition to ScottishPower Renewable, which holds an
11 per cent stake, Norway’s state-owned oil and gas giant Statoil holds a 22 per cent share.

The major shareholder, however, is Austrian hydropower solutions provider Andritz Hydro, which in August 2010 acquired a 33 per cent stake in Hammerfest Strøm, including its Scotland-based subsidiary Hammerfest Strøm UK.
Last August, the Norwegian firm awarded contracts to construct the first of its HS1000 tidal power turbines. Fife-based Burntisland Fabrications was awarded the £2 million ($3.1 million) contract to build the sub-structure for the 25-meter high HS1000 tidal turbine, which is to be deployed at the EMEC site, at its factory at Arnish in Stornoway on the Isle of Lewis.

The HS1000 is essentially an upscaled version of the same technology, says Stein Atle Andersen, managing director of Hammerfest Strøm. “With the experience of the 300 kW version, we have designed the HS1000, which is based on the same technologies. But there are, of course, improvements and upscaling,” he said.
Similar in basic design to competing tidal stream turbines, like Atlantis Resources’ AK1000 (see p.22), the HS1000 is essentially a wind turbine fastened to the seabed. While the Atlantis machine has two turbines, one for upstream and one for downstream, the HS1000 is a single rotor turbine which operates on a significantly variable pitch.

The diameter of the HS1000 turbine totals 23 metres. The HS1000 is a gravity-based turbine, which requires a great deal of ballast in addition to the nacelle and the sub-structure. The sub-structure of the nacelle for the HS1000 weighs about 300 tonnes, not including the ballast. The amount of ballast required depends on the tidal flow of the site, says Andersen.
The HS1000 is specifically designed for the EMEC test site in Orkney, which means it is designed for a current of more than 4 meters per second plus wave influence, i.e. the additional flow from the turbulence of waves.

COSTS AND SUBSIDIES
Producing electricity with the original 300 kW turbine in Norway is estimated to cost from $0.043 to $0.05 per kWh, three times that of typical hydropower generated in Norway. Under the current UK Renewable Obligation subsidy scheme, tidal power projects are eligible for three Renewable Obligation Certificates (ROCs) in Scotland and two in England, but the industry is pushing for this to be raised to five ROCs.
Andersen said: “There is an ongoing discussion, but the industry and tidal project developers would welcome a move in that direction. In the long term there will be a competition between marine energy technology like wave, tidal and offshore wind. I cannot see any reason why all three shouldn’t be at more or less the same cost level in the future.”

Other than Scotland, Andersen says Hammerfest Strøm is exploring Ireland, Australia, New Zealand and the Americas as target markets for the HS1000 tidal stream turbine.
Hammerfest Strøm is looking particularly closely at harnessing the tides of Canada’s Bay of Fundy, on the northeast end of the Gulf of Maine between the Canadian eastern provinces of New Brunswick and Nova Scotia. Last year, Hammerfest Strøm executives met officials from the Nova Scotia provincial government and the Fundy Ocean Research Center for Energy to look at the medium to long-term possibilities in the region.


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