Pelamis = sea snake = wave power (in Portugal)

Pelamis in productionPelamis in action

 

Source: BBC news

 

Suddenly a lonely spot on the Portuguese coast has become the centre of the wave power industry.

The beach at Agucadoura, just north of Porto, is where electricity from the world’s first wave farm is being cabled ashore. Five kilometres out to sea a Pelamis wave machine is gently riding the Atlantic swell, generating power for the Portuguese grid.

The wave farm has just been officially launched after a frustrating delay of more than a year. “We had an issue with the underwater connections”, explains engineering manager, Ross Henderson. He is sitting with me in the beachfront substation which takes in the power. “I can’t believe such a small thing cost the project a whole year.”

 

The practicalities

To understand the engineering problem, you have to appreciate how the wave machines work. Pelamis is an ancient word for sea snake. And it is true that the machines look like giant metal snakes floating in the water.

Each one has four long sections with three “power modules” hinged between them. There are large hydraulic rams sticking into the modules. As the long sections twist and turn in the waves they pull the rams in and out of the modules like pistons.

The huge force of the rams is harnessed to run generators in the power modules. But tethering the snakes to the seabed is a major challenge. The system has to be able to cope with the worst sea conditions.

 

Pelamis Wave Power developed an underwater plug, which floats 15 to 20 metres below the surface. The snakes can be attached in one movement without any help from divers. But when the system was installed off Portugal in slightly deeper water than engineers were used to, the plug wouldn’t float properly. The foam keeping it buoyant couldn’t stand the extra water pressure.

“We worked it out quickly, but it took a while to fix the problem,” laments Ross. “Our buoyancy foam was fine when we tried it out off Orkney but it couldn’t cope in Portugal.”

The Pelamis engineers designed new floats, changing the foam. Then they had to wait through a stormy winter before they could install them.

 

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