After years in the doldrums, the quest to harvest energy from the oceans is gathering speed.
Several kilometres off the coast near Perth in Western Australia, hidden beneath the waves and out of sight of watchful boaters, three giant buoys will soon begin producing electricity as they bob to the rhythm of the Indian Ocean. At 11 metres wide and 5 metres tall, the squat orange floats look a bit like giant pumpkins. As waves pass by, the tethered buoys will drive hydraulic pumps on the sea bottom, converting the motion of the ocean into 720 kilowatts of electricity to power a nearby naval base.
Carnegie Wave Energy of North Fremantle, Australia, plans to have the system — the latest attempt at harvesting power from the sea — up and running by June. The pilot project will generate a lot of press, but veterans of the marine-energy field will watch warily to see how it fares. This industry has taken a slow road: none of the myriad devices designed thus far has proved its worth in the highly competitive energy market, and few have survived prolonged exposure to the harsh conditions in the sea. Despite an overall investment of around US$735 million over the past decade by a dozen leading companies, marine power from tide and waves has yet to take off. In fact, it remains the most expensive form of power on Earth.
But the outlook has brightened for those hoping to tap this source of energy. In the past few years, several major industrial leaders have acquired start-up companies that harvest energy from tides, the easiest type of marine power to capture. In March, three projects were approved for Canada's Bay of Fundy, home to some of the largest tides on the globe. The wave-energy industry, which is targeting a much larger but more elusive resource, has had a few setbacks, including a decision to scale back plans for an array off the coast of Oregon last month. But there is little doubt that both types of marine energy will eventually grow. Last year, the London-based consultancy Bloomberg New Energy Finance projected that up to 22 tidal projects and 17 wave projects generating more than one megawatt of electricity — enough to power around 250 homes — could be installed by 2020.
In theory, oceans could power the entire globe without adding any pollution to the atmosphere. And they could provide a more dependable source of electricity than the wind or sun. They are also geographically convenient: roughly 44% of the global population lives within 150 kilometres of the coastline.
Some nations have been using large, dam-like structures to block off inlets and draw power from tidal flow for decades, but the latest approaches are designed to be less intrusive. Although the potential environmental impacts are still under investigation, many researchers say that the sea could turn out to be an even more benign source of power than wind.
Indeed, energy experts envisage a day when the sea will deliver a significant amount of reliable carbon-free power to islands and burgeoning coastal cities around the world. “It has proved harder than people had expected at the start, but it has also proved possible,” says Neil Kermode, managing director of the European Marine Energy Centre, the leading test facility for wave- and tidal-energy devices in the Orkney Islands, UK. “We have shown that you can make electricity from moving sea water, and that's a huge step forwards.”
Twice a day, some 350 million cubic metres of tidal water flows through a narrow strait into Strangford Lough — a small inlet southeast of Belfast, UK — and then back out to sea. With each trip, it passes a pair of 16-metre-long propellers attached to a central tower that is anchored to the floor of the channel. The force of the water, equivalent to a wind blowing at 555 kilometres per hour, spins the propellers at up to 15 revolutions per minute, generating 1.2 megawatts of electricity.
In addition to the traditional propeller, tidal-power companies have experimented with contraptions such as corkscrews, hydrofoils and underwater kites. The device used in Strangford Lough, however, is leading the way. Built by Marine Current Turbines in Bristol, UK, the design has generated more than 90% of the industry's power to date, according to the company.
The achievements attracted the interest of engineering giant Siemens in Munich, Germany, which took control of the company in 2012. Marine Current Turbines is now preparing to deploy its first array of five 2-megawatt machines — each costing roughly £9 million (US$15 million) — off the coast of Wales by 2016. As well as boosting the size of the machines, the company added a third blade to reduce vibrations and make the machines more durable, says chairman Kai Kölmel. But he cautions that progress is likely to be incremental. “I think some of the venture capitalists are disillusioned, but this is not a quick-buck industry,” he says. “The wind industry didn't start up rapidly either.”
Even with major companies such as Siemens entering the game, the biggest challenge remains attracting the money needed to do the engineering and build prototypes, says Christopher Sauer, chief executive of Ocean Renewable Power Company, based in Portland, Maine. Sauer's company has developed and deployed, albeit briefly, a unique device off the coast of Maine that looks a bit like the spinning blades of a combine harvester. The company is now working on a second-generation device that should be ready for deployment as early as 2015. “We're doing the best that we can with the money we have,” he says.
Waves of energy
The power of waves is vast, but developing machines that can reliably extract that energy and withstand the often-punishing environment represents a wholly different kind of challenge. Companies have explored designs ranging from swinging flaps to gyroscopic devices that convert the rocking of a ship into a circular motion to drive an onboard generator. Each has its advantages, but the idea behind Carnegie Wave Energy's bobbing buoys in Australia was to escape the rough battering of waves at the surface. The submersion has the added advantage of keeping the devices out of sight and avoiding the debates over aesthetics that have arisen with wind farms.
As the waves carry the buoys up and down, the sea-floor pumps circulate fluid through a closed loop that extends roughly 3 kilometres to an onshore generation facility (see 'Water works'). Operating like a bagpipe, the system accumulates pressure and then releases it gradually to generate a constant flow of electricity. Each of the three devices can generate up to 240 kilowatts of energy.
“This is obviously not a commercial project, but there's not a commercial wave-energy facility in the world at the moment,” says Carnegie's chief operating officer Greg Allen. Nonetheless, it represents progress, he says: each device generates three times more power than the version that was tested in the same waters in 2011. Allen says that the first commercial projects could come as early as 2018. To gain a toehold in the market, the company aims to compete with diesel-fired power generators on islands.
Written By: Jeff Tollefson
continue to source article at nature.com