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Wave power project nears prototype stage

January 24, 2003, 09:00 CET

Norsk Hydro Technology Ventures' capital investment in the Pelamis wave power generation concept - developed by Scots start-up company Ocean Power Delivery - successfully passed key tests last week, paving the way for a prototype off the Orkney Islands this summer.

"We're in a very exciting phase of the project... the moment of truth," says Ocean Power Delivery (OPD) co-founder Dr. Richard Yemm. "We've already learned an enormous amount with this rig," he adds in reference to the full-scale joint test-rig currently being tested in a waterfront warehouse in Edinburgh.

Power in motion

The Pelamis Wave Energy Converter is a semi-submerged, articulated structure composed of four cylindrical steel sections linked by hinged joints. It is 120 meters long and has a 3.5 meter diameter. Moored at its nose, the Pelamis points into the dominant wave direction. Waves travel down the length of the machine, causing each section to articulate about the hinged joints between sections.

"The up, down, side-to-side motion pumps high-pressure fluid to hydraulic motors through smoothing accumulators," explains OPD business development director Max Carcas. "The hydraulic motors drive electrical generators to produce power, which is fed down umbilical cables to a single subsea cable to shore, where it is tied into the land-based power grid.

The point of the full-scale joint test-rig is to fully test the complete electro-hydraulic power take off system on land first, rather than the first time being in the sea off Orkney.  This ties in very much with OPD’s philosophy, which is to model, test and validate each element of the technology before progressing to the next stage.  It also builds on successful testing of a one seventh scale full-systems prototype tested in the sea off Edinburgh last year."

Show time

Before the Pelamis prototype is installed off Orkney this summer, the full-scale joint test rig will have been run in an accelerated lifetime test for three months. “The aim of this is to ensure that if there are any major show stoppers, that they are identified well in advance of deployment,” says Carcas. "We can always deal with minor problems but not the show stoppers.”

A crucial aspect to testing is "survivability," he adds. In addition to subjecting equipment to demanding specifications tests, the steel structure has also been going through rigourous design verification. Pelamis is designed to harvest maximum energy from small waves and limit power absorbtion in large waves. It escapes heavy pounding and potential hydrodynamic damage from storm waves by slicing into swells like a surfboard.

44-24OPD plans call for eventually placing 40 Pelamis units each in offshore wave power farms (covering approximately one square kilometer) capable of generating a total 25 MW of electricity - sufficient energy for more than 20,000 homes.  The prototype unit will generate 0.75 MW.

A gas turbine producing the same amount of energy as one fullsize Pelamis unit would consume 600 tonnes of fuel and emit 2,000 tonnes of CO2 into the atmosphere per year.

Pelamis performs best at sea depths between 50-100 meters, where ocean swell energy is optimally harnessed at practical offshore distances. The units will be towed to shore for maintenance work.

If all goes well, OPD's first wave power farm could be in place by 2004/2005, Carcas indicates.

Power potential

"One-quarter of the UK's electricity can potentially be met by wave power," claims Carcas. "There's enough wave energy off Britain's coastline to provide three times its consumption (some 350 TWh in 2002). We estimate some five to eight percent of that can be economically realized."

The UK Energy Ministry is expected to publish a White Paper early this year that will hopefully provide strong backing for renewable energy development.

"I am a strong supporter of wave energy and am determined to ensure that the UK remains the world leader as the technology takes off," UK Energy Minister Brian Wilson said recently.

The World Energy Council  predicts wave power can eventually supply 15 percent of current global energy demand.

"Considering the inclusion of technology, commercial support and government signals, it’s become clear we're doing something worthwhile... something that should be done,” muses Yemm. “ There's a huge resource out there that can power Europe's energy needs. We're not using it - and it should be tapped."

See also:

Norsk Hydro Technology Ventures invests in wave energy
Ocean Power Delivery