Generating Power From Tidal Lagoons

Source: By BETH GARDINER, New York Times • Posted: Thursday, October 30, 2014

An artist’s rendition of the proposed offshore visitor center for the Swansea Bay tidal lagoon project in Wales. CreditJuice Architects

But the company pushing a new project on the coast of Wales thinks its twist — a 21st-century update of traditional dam-based hydropower — will be much easier to bring to fruition. If it wins government permission to go forward, Tidal Lagoon Power Limited says the approach, known as tidal lagoon generation, could provide as much as 10 percent of Britain’s power from six of its projects within a decade.

That is an optimistic assessment. Still, those hoping the seas will become a big contributor to the world’s future energy needs will be watching to see what happens in Swansea Bay, Wales.

Even if the project succeeds, tidal lagoon power is unlikely to become more than a niche source of energy. Because it requires an unusually large difference between the levels of high and low tides, known as the tidal range, it is likely to be workable in only a few places, like Cook Inlet in Alaska and parts of South Korea.

“You have to find just the right site,” Mr. Arent said. Still, tidal lagoon could be a useful contributor, he said, because, unlike the wind and sun, tides are predictable. “This is one aspect of a broadening view of ‘How do we think about the use of energy from our water resources?”’

Tidal Lagoon Power’s plan, estimated to cost 1 billion pounds, or $1.6 billion, to build an 11.5-square-kilometer, or 4.4-square-mile, lagoon along Britain’s west coast emerged after proposals for a much larger project, stretching across the mouth of the nearby Severn river, foundered last year after decades of wrangling.

Critics said that £25 billion proposal made little economic sense and would have damaged the estuary’s rich ecosystem. The area has been a focus of attention in renewable energy circles because its tidal range is among the biggest in the world.

The lagoon project would be far smaller than the old estuary-spanning idea, but proponents hope it would be the first of six that eventually contribute a significant chunk of Britain’s power. The country is pushing to meet its goal, made binding in 2009 by the European Union, of getting 15 percent of its electricity from renewable sources by 2020.

The idea behind tidal lagoon generation is straightforward. Engineers would build a large holding pool along the shore, contained by a U-shaped seawall. When the tide rises, water levels become higher outside the pool than in. Sluice gates open to let water enter, turning turbines as it flows. When the tide recedes, the levels are higher inside than outside, and the water, when released, turns the turbines in the other direction.

In principle, it is not so different from projects like the 48-year-old barrage, or dam-like structure, which harnesses flows at the mouth of the Rance river in Brittany, France, or the newer Sihwa Lake station in South Korea. Because they often block estuaries, though, such plants raise worries about damage to local environments.

The lagoon approach seeks to minimize such impact. Swansea Bay, if approved, would be the first tidal lagoon to be built.

Worldwide, plants in the broader category of tidal range now have about 500 megawatts of energy-generating capacity, and that could rise to 800 megawatts by 2020, including lagoon proposals, said Angus McCrone, chief editor at the market research firm Bloomberg New Energy Finance. That is tiny compared, for example, to global solar panel capacity, which grew by 100 megawatts every day in 2013, according to International Energy Agency estimates.

More barrage-type projects are under consideration in South Korea and elsewhere, and a few other lagoons, in the early stages of planning, have been proposed in addition to Swansea Bay. Halcyon Tidal Power, for example, hopes to build its own lagoon near the Swansea site and is proposing another in Nova Scotia’s Scots Bay.

Because the technologies involved are familiar, analysts say the lagoon idea seems more ready for commercial-scale application than tidal stream generation, in which turbines are driven by fast-flowing currents, an underwater version of a wind farm. Tidal stream has yet to come into wide use, as engineers seek a design and the materials best suited to withstand the powerful forces of the sea.

The biggest concern for the Swansea Bay project, energy experts say, is its high cost, and the fear of budget overruns, in part because of the need for a 10-kilometer, or 6.2-mile, seawall.

Like nuclear power and other renewables, tidal lagoon would require a government-guaranteed rate for its power. A report that Tidal Lagoon Power commissioned from the consulting firm Poyry in Finland estimated that the Swansea lagoon would require a price of £168 per megawatt hour, just above the guarantee provided to offshore wind farms, considered a very expensive form of energy.

The five projects the company hopes to build subsequently, elsewhere in Britain, would be much larger, bringing the cost down to £92 per megawatt hour, Poyry estimates. That is the same price as that guaranteed to the planned Hinkley Point C nuclear plant in England, which drew concern about costs when it was announced.

Ali Lloyd, one of the authors of the Poyry report, said price might not be an insurmountable barrier.

In order to meet their challenging renewables target, the British authorities are prepared to offer high initial subsidies to technologies whose costs look likely to fall in the longer term, Mr. Lloyd said. “The same logic will have to apply for tidal lagoons,” he said.

He believes there is a better way to design the lagoon, using turbines like those being developed for tidal stream projects, and placing them in series, rather than in parallel, an idea he referred to as “tidal gardens.” That would allow the turbines to run more efficiently, and with a lower differential in tides, meaning the expensive walls required could be smaller, and the number of potential sites much larger, he said.

The planning authorities are now evaluating the company’s proposal. The British secretary for energy and climate change, Edward Davey, who has the final say, is expected to announce a decision in the spring.

Mr. McCrone, the market research editor, said investors appeared interested. He believes the lagoon has about a one-in-three chance of being built, better odds than he had given to the big Severn barrage proposals.

Mr. Field, of Tidal Lagoon Power, called that estimate conservative. The company hopes to begin construction next year and generate electricity by 2018. Mr. Field said the plant would run for 120 years, while subsidies would last 35, meaning that in the long term, its electricity would be considered cheap.

Mr. Lloyd said tidal lagoons could ultimately be a small but meaningful contributor to the global energy mix.

“If you are serious about decarbonizing your electricity supply, frankly you need all the technologies available, whether that’s wind, solar, nuclear,” or anything else, he said. “There’s a role for all of them.”