By Paul Halpern
Harnessing the Sea: The Fundy Tidal Power ProjectEngineering
The mighty tides of the Bay of Fundy could provide a dependable and renewable source of power. While environmental studies weigh up the potential impacts, Nova Scotia is putting three in-stream genera...
The mighty tides of the Bay of Fundy could provide a dependable and renewable source of power. While environmental studies weigh up the potential impacts, Nova Scotia is putting three in-stream generating technologies to the test.
For decades, possibly centuries, there’s been interest in what use could be made of tidal energy in the Bay of Fundy,” says Lesley Griffiths.
Located at the northern end of the Gulf of Maine between the west coast of Nova Scotia and the east coast of New Brunswick, the funnel-shaped Fundy has the highest tides in North America. During its 12.4-hour tidal period, some 115 billion tonnes of water traverse the length of the bay twice — equivalent to the combined flow of every river on earth.
Harnessing that energy for power generation has long been the subject of study and research. Now, steadily rising oil prices, the need to reduce greenhouse gas emissions from fossil fuels, and the burgeoning demand for renewable energy have made exploitation of the Fundy tidal resource an attractive option. But bringing Fundy tidal power into reality requires careful study, testing, and implementation.
Griffiths, a principal of Griffiths Muecke, an environ-mental and community planning firm of Halifax, is the process lead for the Fundy Tidal Energy strategic environmental assessment (SEA), a report that was released this May 1. The assessment was completed by the Offshore Energy Environmental Research Association (OEER), a nonprofit consortium comprising four universities and funded by Nova Scotia Energy.
Earlier, in January of this year, the Fundy Tidal Generation Demonstration project was announced by Nova Scotia Premier Rodney MacDonald. The demonstration will test three different in-stream generation technologies. It is funded by the technology providers, the province’s Ecotrust for Clean Air and Climate Change, and EnCana Corporation of Calgary.
In-stream generation involves placing small-footprint turbines directly into the tidal flow, anchored to the seabed well below the surface. The three project developers are Nova Scotia Power with an OpenHydro turbine; Minas Basin Pulp and Power with an Underwater Electric Kite (UEK) HydroKinetic turbine; and Clean Current of Vancouver with a proprietary Mark III turbine. They hope to have machinery in the water by 2010. Minas Basin Pulp and Power will also build and manage the project’s on-shore facility, the Fundy Institute for Tidal Energy. In April, Minas Basin proposed a similar pilot project using the UEK for the New Brunswick side of the Fundy.
How the turbines work
All three turbines stress simplicity of design, which is critical in underwater installations. Each uses a single moving part: a central horizontal-axis turbine with no driveshaft or gearbox, housed within a permanent magnet generator. The OpenHydro and Clean Current turbines are anchored to the seabed, while the buoyant UEK, suspended from the seabed, can rise or descend with the tide. OpenHydro and UEK both use a single turbine rotor. Clean Current’s bidirectional rotor includes augmentor ducts to accelerate tidal flow to the turbine.
The OpenHydro and Clean Current turbines include large central holes that allow fish and marine mammals safe passage past the rotor blades. The UEK uses vanes on the front of the turbine assembly for the same purpose; the proprietors say that small marine life can pass safely through its ducted rotor.
A major engineering challenge is how well any of these designs will perform in what Griffiths calls the “very tough” Fundy environment. Especially in the upper bay, the Fundy waters carry a high load of suspended sediments, Griffiths says, “so any machinery in the water is going to be sort of sandblasted.” Similarly, the powerful Fundy currents will give the systems an unprecedented torture test. An earlier Clean Current installation at Race Rocks Ecological Preserve in B. C. showed unexpectedly rapid wear on the turbine’s bearings, and the turbine blades on a UEK installation in Manhattan’s East River collapsed under a stronger-than-expected current.
Installing and maintaining the generators presents another challenge. The slack tide period in the Fundy when work can proceed safely is very short — perhaps as little as an hour a day. Additionally, the danger to divers is extreme in the Fundy tidal environment, so developers will need to avoid using divers as much as possible.
To add to the engineering challenge, Griffiths says, “Another possible question is ice. There have been questions about whether submerged ice that has picked up sediment and breaks free from the shore may be rolling around down there.”
What effect on the ecosystem?
The SEA Report released in May addresses the major environmental concerns and data gaps identified in an earlier background report prepared by Jacques Whitford consulting engineers of Dartmouth, N. S., in association with the Huntsman Marine Science Centre of St. Andrews, N. B. and consulting engineers Devine Tarbell and Associates of Portland, Oregon, W. F. Baird and Associates of Ottawa, and Jim Calvesbert Consulting of Dartmouth, N. S.
Griffiths says that the emerging major environmental question for the SEA is the unknown cumulative effect of removing significant amounts of tidal energy from the Fundy ecosystem.
An underwater turbine in the water will remove tidal energy from the Fundy system and turn it into electricity. While this is not a major concern for the initial demonstration project, at commercial production scales, the amount of energy taken from the Fundy could slow the tidal currents significantly.
The Fundy is a remarkably rich and complex ecosystem that supports a wide variety of life, ranging from microscopic diatoms to endangered Right Whales, as well as varied and economically important fisheries, aquaculture, commercial shipping, ecotourism, recreation, and other human activities. The life, including human life, that the Fundy ecosystem supports has adapted over centuries to the existing tidal patterns. The big unanswered question is at what point would tidal power generation start to impact that ecosystem, and how might those impacts affect life in the Fundy at every scale?
In addition to environmental impacts, the project raises socioeconomic issues. “If tidal energy is pursued on a commercial scale,” Griffiths asks, “how should it proceed such that it provides the greatest benefits to small communities in the Fundy?”
If it sounds like the current answer to these questions is “We don’t know,” that’s correct. Because the Fundy is so varied and so complex, and the data gaps so significant, the SEA sets as one of its major sustainability principles that, “application of marine renewable energy developments should go ahead only when a proponent can demonstrate that there will be no significant adverse effects on the fundamental hydrodynamic processes of the Bay of Fundy tidal regime… or on biological processes and resources.” The report also says that “development should take place incrementally, supported by an effective and transparent research and monitoring program, installations should be removable, and clear thresholds should be established to indicate when removal would be required.”
That said, the SEA concludes that “there is no evidence that precludes moving to the next stage of TISEC [Tidal In Stream Energy Conversion] development — one or more carefully designed, located and managed demonstration projects,” as long as they are guided by an articulate set of sustainability principles and ongoing research, including assessments of any sites selected for turbine installation.
Still, Griffiths says, “We’re getting to the point where we can’t answer some of these questions until someone puts something in the water, so I think that may be the next stage.”
Paul Halpern is a freelance writer based in Halifax, N. S.