Wave after wave

 By Nicholas Newman

Hydraulic rams, elastomeric hose pumps, hydraulic motors and turbines, air turbines, fixed oscillating water columns and wave energy farms. Nicholas Newman, from Scotland to Australia, describes a few innovative ideas to produce energy from ocean waves, either already commercialized or just projects. Through also here the future of renewable energy?

Ocean waves generate some 80,000TWh of energy per year, equal to five times current world demand and yet, remain largely unexploited. Innovative ideas under investigation today include hydraulic rams, elastomeric hose pumps, hydraulic motors and turbines, air turbines, fixed oscillating water columns and wave energy farms. Some devices being tested generate electricity on the spot and transmit it via undersea cables to shore, others pass the mechanical energy of the wave to land, before turning it into electrical energy.

Orkney-based Aquamarine Power‘s Oyster wave power technology aims to capture the power of nearshore wave energy. In essence, a wave-powered pump pushes water under high pressure to drive an onshore hydro-electric turbine. The Oyster power device is a buoyant hinged flap, which is attached to the seabed at depths of between 10 and 15 m (32 to 49 ft) around 0.5 km (0.3 miles) from the shore. In the future, subsea pipelines could connect multiple Oyster devices to a single onshore plant. This device, which has a maximum generating capacity of 800 kW, has evolved from being a laboratory concept model in 2003 to being tested as a working second generation commercially-ready device off the West Coast of Scotland since 2012. A third-generation device is due to be installed at the test site soon.

Aquamarine Power - Oyster wave farm animation

Since 2011, Australian wave energy developer Carnegie Wave Energy Limited has been working on its CETO system which operates underwater where it is safer from large storms and invisible from shore. The fully submerged buoys can drive seabed pump units to deliver high-pressure fluid onshore via a subsea pipe to standard hydroelectric turbines, generating zero-emission electricity. The high-pressure water can also be used to supply a reverse osmosis desalination plant, replacing or reducing reliance on greenhouse gas-emitting electrically driven pumps usually required for such plants. Carnegie is now on its sixth-generation model, the CETO 6. In 2017, a 3-unit array with a 3MW total capacity will supply power to the Australian island naval base of HMAS Stirling at a cost of $25m.

3D Animation for Carnegie Wave Energy

Another idea being explored is that of the underwater kite by Swedish company Minesto. Each turbine is suspended beneath a rigid kite tethered to the seabed. Weighing 7 metic tons (7.7 short tons) and operating at least 15 m (49 ft) below the water surface, each kite carries a turbine below it. The kite is designed so that it moves in a figure of eight when positioned in flowing water. Up until now, Minesto has been testing the kite turbine system in Strangford Loch in Northern Ireland. The commercial roll out will see 20 turbines being anchored off Anglesey, Wales at a cost of $39 million. When fully operational this marine power plant should generate enough electricity to power 8,000 homes.

about the author
Nicholas Newman
Freelance energy journalist and copywriter who regularly writes for AFRELEC, Economist, Energy World, EER, Petroleum Review, PGJ, E&P, Oil Review Africa, Oil Review Middle East. Shale Gas Guide.