Green machine: Wave power line jacks into the grid.

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Green machine: Wave power line jacks into the grid

* 16:00 24 August 2010 by Paul Marks
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Green machine is our weekly column on the latest advances in environmental technologies.

Surfers, bodyboarders and dolphin-spotters at the English seaside resort of St Ives were mostly unaware of a techno drama being played out about a kilometre beyond the breakers this month. Since 1 August, engineers on the cable ship Nordica have been trying to begin deployment of Wave Hub, an undersea extension cord that could make harnessing wave energy more viable. The first part of the roll-out hasn't gone at all smoothly, however.

So just what is Wave Hub? Essentially, it's a four-way socket that will be installed 50 metres down on the seabed 16 kilometres from shore, where the Atlantic swell is deemed perfect for serious energy captureMovie Camera, and connected via a giant 50-megawatt-capacity cable to an electricity substation in Hayle, on St Ives bay.

It will allow different designs of wave-powered generatorsMovie Camera to be compared. Giving each generator its own connection to land would be inefficient: Wave Hub will allow up to four wave-energy conversion machines to be stationed and plugged into the hub simultaneously, providing an easy way to compare how good each machine is at injecting power into the national grid on a commercial scale.

"What electric utility companies really need is such a test-bed – a place where they can test wave-energy technologies in a realistic setting and see if the economics make sense. That's what Wave Hub offers," says Max Carcas of Pelamis Wave Power, based in Edinburgh, UK.
Yellow submarine

Right now, the best UK test bed is the near-shore European Marine Energy Centre in the Orkney Islands off northern Scotland. There, 12 cables connect to wave and tidal power test sites.

"But you can't make an industry with just one machine feeding each cable," says Neil Kermode, managing director of EMEC. "To farm wave energy on a mass scale you need to aggregate the power at sea from an array of machines and convey it to the shore on one high-voltage cable. That's what Wave Hub will offer and we are working closely with them."

Wave Hub itself comprises transformers that convert the wave-generated power into a grid-usable voltage, all in a submersible yellow housing. But the process of connecting it has proved more troublesome than the project's backers – which include a regional government agency and the European Union – had anticipated.

The power cable is being spooled off a giant drum on board the Nordica, anchored 1.8 kilometres from shore. To minimise the risk of damage to the cable, it has to be floated ashore and gently winched up the beach – which took several attempts, as parts of the cable kept sinking at inopportune moments.
Sinking feeling

The contractor CTC Marine of Aberdeen, UK, had initially used 50-metre-long sausage-shaped flotation bags to float the cable because they allow for faster spooling of the cable. Unfortunately, failure of one of these long bags increases the likelihood of the heavy cable (which weighs 56 kilograms per metre) sinking – which is what happened.

What's more, the cable landing point at Hayle beach is only very gently sloping, so CTC needed a high spring tide to float the cable to the beach – but the flotation failures meant the team missed a number of high tides

After replacing the long floats with a series of smaller buoys CTC succeeded in floating the cable on the high tide at 5 am yesterday. The next step is to connect it to the grid and then send the Nordica out to sea to deploy the rest of the cable. Finally, Wave Hub itself will be placed in 50 metres of water 16 kilometres from land.

Once Wave Hub is installed, though, the South West Regional Development Agency, the public body leading the project, wants to know why the chosen flotation tech caused a three–week delay. "We will be wanting a coherent and detailed explanation," programme chief Guy Lavender told New Scientist. Tweet