Harnessing the power of waves

wave energy
wave energy

By Paul Grad, engineering writer

There has been increasing activity in Australia in the development of wave energy technologies and systems, stimulated by the government-mandated target of 20 per cent of Australia’s domestic energy to be produced from renewable sources by 2020, and the pricing of carbon dioxide emissions.

According to a recent CSIRO report on ocean renewable energy, tidal and ocean current technologies will not contribute to Australian electricity generation, but wave energy technologies have the potential to contribute significantly. Under a few scenarios examined by the report, wave energy could contribute more than 10 per cent of Australia’s total electricity generation by 2050.

Australia has one of the best wave energy resources in the world. The CSIRO report says the total wave energy crossing between Geraldton in Western Australia and southern Tasmania amounts to five-times Australia’s total energy needs.

Of the many Australian companies developing ocean renewable energy technologies, the most advanced are the CETO submerged buoy system from Carnegie Wave Energy Limited, of North Fremantle, Western Australia, and the oscillating water column system from Oceanlinx, of Sydney.

The CETO system operates out of sight, anchored to the ocean floor. An array of fully submerged buoys is tethered to seabed pump units. The buoys move in harmony with the motion of the passing waves, driving the pumps, which turn pressurises water that is delivered ashore via a pipeline.

Late last month, Carnegie released the design of its next generation CETO five unit to be used in the Perth Wave Energy Project – the company’s major commercial scale in-ocean testing site at Garden Island, Western Australia. In CETO 5 the diameter of the buoyant actuator, which has the most influence on power output, has been increased to 11m from the 7m diameter of CETO 3. Rated capacity is now 240kW, about three times that of CETO 3. As with previous units, all critical performance parameters will be validated through the use of specialised measurement and communications equipment.

The other most advanced technology, Oceanlinx’ oscillating water column consists of a piston and a cylinder. As waves rise within the column, it drives a column of air ahead of it through a turbine. The company has developed two variants of the oscillating water column concept: greenWAVE, for shallow water application, and blueWAVE and ogWAVE for deep-water application.

Oceanlinx’ chief executive officer Ali Baghaei presented a paper titled The World’s First 1MW Wave Energy Converter during the International Conference on Ocean Energy (ICOE) held in Dublin, on October 17-19. Ali’s talk referred to the company’s project at Port Macdonnell, South Australia, scheduled for completion by the end of 2013.

A wave energy device called BioWAVE – in which the converter is attached to the seabed and can be fully submerged – is offered by BioPower Systems of Sydney. An array of buoyant floats, or ‘blades’, interacts with the rising and falling sea surface and the subsurface back-and-forth water movement. The pivoting structure moves in tune with the waves, and the motion is converted to electricity by and onboard module, called O-Drive. The power is taken onshore by cables with an AC-DC-AC conversion system.

A 250kW demonstration project is under development to supply power into Hydro Tasmania’s distribution system on the local islands and into the Victorian power grid. The project is expected to be in place late next year. There are further plans to develop a 1MW plant, followed by multi-unit wave energy farms, planned by 2015.

BioPower Systems recently announced a strategic alliance with Shanghai Electric, a Chinese wind turbine maker, to develop wave energy technology to commercial scale. BioPower’s partners or investors include Lend Lease, Bosch and Siemens of Germany, and Keppel Prince Engineering, of Portland, Victoria.

A full-size wave farm of 5MW with proposed delivery next year is planned by AquaGen Technologies, of Melbourne. Its SurgeDrive technology transfers the wave motion, via tension transfer components, to generation equipment located out of the water.

The largest ocean renewable energy project in Australia is a wave farm now under construction off the coast of Portland, Victoria by Ocean Power Technologies Australasia Limited. The plant will be built in three phases and will have a total capacity of 19MW. The project could be scaled up to 100MW.

Overseas, some of the most advanced projects are the Pelamis system, from Pelamis Wave Power Ltd, of Edinburgh, Scotland; the Wave Dragon, of Wave Dragon ApS, of Copenhagen, Denmark; the Seabased linear generator from Seabased AB, of Uppsala, Sweden; and the Limpet, from Voith Hydro Wavegen Limited, of Inverness, Scotland.

Pelamis is a 750kW device, which has undergone extensive testing off the Orkneys and Portuguese coasts. The Pelamis machine is made up of five tube sections linked by universal joints, which allow flexing in two directions. It floats semi-submerged and faces into the direction of the waves. The bending movement of the sections is converted into electricity via hydraulic power take-off systems inside each joint of the tubes. Power is transmitted to shore by means of standard subsea cables.

The Wave Dragon can be supplied in the power ratings of 4MW, 7MW, and 11MW. It operates as an overtopping, tapered channel, terminator type wave energy conversion device. It has an automatically adjustable float height, operated via a pressurised air system, allowing the device to tune itself to the predominant wave height.

The Seabed, at Lysekil, Sweden, is being tested in units of 10kW, 20kW and 50kW. Commissioning has started of a wave farm with 10 wave energy conversion devices from 20kW to 50kW. The Seabed is a single body point absorber comprising a floating buoy tethered to a linear permanent magnet generator set on the sea floor. The tether connects the buoy to a neodymium-iron-boron permanent magnet actuator. The converter is held in place by a concrete foundation.

The Limpet uses the oscillating water column method of operation. The water column is set at an angle to the vertical. Its rated power is 500kW. It was operated for several years on the Island of Islay, off the west coat of Scotland. Voith Hydro Wavegen, owner of the Limpet technology, said the unit on Islay was the world’s first commercial-scale wave energy device generating wave energy for the grid.