If you look to the sky for a source of renewable energy you’ll find it pretty quickly. The Sun is hard to miss. The invisible stuff that spins wind farms into motion — the wind — is just as tangible. The molten insides of Earth are an almost eternal source of energy.
To turn these elemental forces into electricity suitable for mass consumption means laying down vast areas of solar panels, studding landscapes with giant propellers or relocating cities to where the crust is thin.
Another solution, perhaps more suitable to a country where most of the population lives near the coast, is to harness the power of the sea. If the CSIRO is right, the waves between Geraldton, in Western Australia, and the southern tip of Tasmania generate the equivalent of 1,300TWh a year, or five times the country’s total energy requirements.
Tap into that and all our problems are solved. Even better, most of the ugly technology would be underwater. Out of sight, out of mind.
One scenario presented in the CSIRO’s 2012 report Ocean Renewable Energy found generators with 30% wave energy extraction could provide more than 50TWh of electricity by 2050, about a ninth of national requirements.
But don’t get too excited just yet, because the future of wave energy will be determined by cost and politics. At the moment, the chief concern is economics of extraction.
In their June report Ocean Energies, Moving Toward Competitiveness, analysts at EY estimated more than 100 wave power pilot projects have been launched globally over the past few years, with installed capacity about 4MW. Of that, 1MW is in the UK, about 0.76MW in Canada and 0.4-0.5MW in South Korea, China and Portugal.
The challenge for wave power projects anywhere in the world is to drive down the levelised cost of energy, which EY says remains higher than any other marine energy technologies, including tidal energy. Australian firms and researchers are at the vanguard of R&D but large international engineering firms and utilities are watching keenly. When a time comes that a wave energy converter stands out as commercially feasible, multinationals can be relied on to drive costs down as they take it mainstream.
TRIAL AND ERROR
Harnessing the power of waves is not as simple as designing a doodad that turns wave energy into electricity, testing it and distributing duplicate devices offshore. Depending on their placement relative to each other, the output from a farm of wave energy converters could be measured in a very wide range. Get it wrong, and the experiment will be a very, very expensive failure, even if the technology works.
Something as simple as a turbine relies on dependable, monotonous force. The reciprocating up-and-down motion of a piston is transformed into rotary motion via moving parts. If bobbing buoys were substituted for pistons, wave energy converters would require the equivalent of cranks and crankshafts. The devices being tested in Australia mostly use the principle of resonance, where they are “designed to have a natural frequency”, says Richard Manasseh, associate professor and acting director of the Centre for Ocean Engineering, Science and Technology, at Melbourne’s Swinburne University of Technology.
In the mind of a mathematician the device is analogous to a pendulum or mass bobbing up and down on a spring, each described by known differential equations. Such systems have a natural frequency, like the vibrations of a bell. “If you imagine the sea is dead calm, if the machine is a natural resonator and you give it a tap it will execute whatever motion it’s designed to execute with a particular number of beats per minute,” Dr Manasseh says.
Things really get going when waves of the same frequency combine with the natural frequency of the device, causing resonance. When a device is resonating its motion becomes very large. “The device will be moving more than the water around it,” Dr Manasseh says.
Enormous buoys bobbing at greater amplitude than the waves passing over them will send out their own waves, which will bounce off nearby devices arranged in an array. Groups of generators will therefore operate as one system. Depending on their relative position to each other — up or down — an array of devices will have different natural frequencies. “If you tune your individual machine so that it resonates at the frequency of the waves in that particular location, when you put another one next to it it won’t necessarily behave as you expect.”
Maths can’t explain everything below the surface of the sea, says Dr Manasseh, and loss of energy to dissipation is very difficult to scale up from laboratory or computer simulations. Instead, researchers must carry out experiments on full-scale machines.
“We know there’s going to be a difference in frequency when you put the machines together; what we don’t know is how much energy they really would absorb.”
A SHORE THING
Swells are created by the wind, so wave power is effectively wind power. The “roaring forties” that hit Australia’s shoreline from the southwest are responsible for generating and pushing waves that may be travelling almost as quickly as the wind by the time they reach us. Swells off our southern coast may be between 100m and 200m crest-to-crest — and big swells carry big energy.
Not many people live along Australia’s southern coast, of course, but wave energy is being looked at in north-western Europe, battered by swells from the North Atlantic, and the north-west United States.
Swinburne is also interested in whether arrays of wave generators may reduce coastal erosion, negating the need for breakwaters that can impact marine life and shoreline ecosystems.
If wave technology works it may be used to offset the use of diesel at small island-based communities.
WHERE THE WAVES ARE
CSIRO Oceans and Atmosphere senior research scientist Mark Hemer is studying “the energy in the resource” – or rather the latent potential of ocean wave patterns around Australia. “It’s about providing a competitive data set where developers can go in and choose sites on the basis of the amount of energy,” he says.
There isn’t much point dropping expensive technology into parts of the sea where the waves are temperamental. Any surfer would tell you the same thing.
A report in 2012 looked at tides, ocean currents and temperature, with data collected at buoys around Australia and using satellite measurements. The conclusion back then was “waves is where most of our energy is,” Dr Hemer says.
The country’s peak science body is working with ARENA on an Australian wave energy atlas which Hemer says links in with its Australian Renewable Energy Mapping Infrastructure project. A beta version of the wave energy atlas is finished but a formal release is expected in October, he says. Part of the project involved working with Carnegie Wave Energy and looking at the modulation of the wave field around its devices in Western Australia.
October will be a busy month for the ocean energy crowd, with researchers, service providers and policy-makers expected to congregate in Melbourne for the inaugural Australian Ocean Renewable Energy Symposium, scheduled for October 18 to 20. Australia has one of the leading projects in the world but the industry hasn’t collected into a coordinated sector. Until that happens it may be hard to build a profile.
“There are advantages to [wave energy] but disadvantages as well,” says Dr Hemer. “It’s expensive putting things in the water and to maintain them. That’s the challenge they have to overcome.”
Carnegie’s “CETO 5” system of three submerged buoys off Garden Island in Western Australia has been pulled out of the water to be eventually replaced by CETO 6, the next iteration of the technology which is expected to be four times as powerful, from 240kW to 1000kW the company says. The previous deployment was slightly inside a reef but the next generation will be farther out, where the waves are bigger. One of the limitations of CETO 5 was having to pump water onshore, an obvious point of loss. Instead of pumping pressurised water on shore to drive a turbine the new device will generate power inside its buoyant actuator.
Carnegie’s project was the only grid-connected wave array in the world that survived according to plan, partly funded by ARENA in its quest to help push technology forward. At the start of June the CETO 5 iteration of the Carnegie project had clocked up 14,000 continuous hours of power to naval base HMAS Stirling.
The CETO 6 device will be 18m in diameter (7m wider than CETO 5) and placed about 9km offshore where the wave energy is about three times greater than at the previous location.
To last, wave energy devices must be tough enough. And that makes them expensive. In January Bombora received funding from ARENA to complete a levelised cost of energy study for its mWave system, under trial near Perth. The mWave is powered not by endless swaying motions but by concussion from above. As waves pass over the device, air-filled membranes are pushed and shoved so that air is forced through a turbine before being recirculated. The converter is mounted on piles, 10 metres below the surface.
A mid-sized test version is working away at Melville Water in the Swan River, Western Australia, where there aren’t many waves at all. The conditions are still good enough for testing. “It’s producing energy,” says Bombora communications consultant Jane Stacey. Going on those results, a full-scale device should turn out 1.5MW and a farm of 40 converters produce 60MW, she says. It may be expensive today, but Bombora expects cost of energy from mWave to be equivalent to wind and solar by 2025. Until that day, the other benefits of ocean power are enticing enough to keep them motivated.
Systems sunk beneath the waves are obviously easier on the eye than fields of solar panels or crops of giant white propellers. The trade-off is that about 20% of a wave’s energy is lost between the surface and 10m down, according to Bombora’s estimates.
Bombora is working on a plant in Peniche, Portugal, with a farm of 40 units turning out a hoped-for 60MW.
“We’re moving forward to full scale,” says Bombora CEO Sam Leighton, of the 75m devices planned for Portugal. “One of our key design briefs has been to make this effectively in harmony with the environment. People can still enjoy the environment, and we can harvest the energy.”
Also in the water, and Australian-designed, is BioPower Systems’ project off Port Fairy, Victoria. The company is expecting 250kW from its bioWAVE wave energy converter, a 26m-tall pivoting structure fastened to the seafloor. When storms blow in, the device folds flat to the seabed until conditions return to normal. Like so many great ideas, the design was inspired by nature — undersea plants.
The tides are also an eternal source of ocean energy, but the CSIRO found the parts of Australia with the biggest tidal range are in far-flung places such as King Sound in north-west Western Australia and Banks Strait, Tasmania. Matching energy generation with requirements is another challenge for tidal, where changes in the rush of water to or from the shore will not always be conveniently matched to when folk onshore want to switch their lights on. But if a change in tides is a certainty, at least waves are more predictable than the wind. The CSIRO found a wave forecast for 36 hours is “nearly as accurate” as a wind forecast for 12 hours.
Waves can’t be turned off (unless the wind stops) and potential energy in our churning oceans looks as limitless as the power of the sun. Around the world the race is on to find a way to turn that elemental force into cheap energy. Devices have come and gone, destroyed by storms or over-hopeful hypotheses. The ones that made it have been utilised to power military needs, data requirements and remote locations, where there may be very few alternatives for generating electricity. “Everyone wants to crack this one,” says Bombora’s Stacey.
By Jeremy Chunn