Twice a day, 115 billion tons of saltwater churn in and out of the Bay of Fundy, a funnel-shaped pocket of the Atlantic Ocean wedged between the Canadian provinces of New Brunswick and Nova Scotia. Swelling steadily through the 174-mile journey to the narrow head of the bay at Minas Basin, tidewaters can surge to 53 feet—the highest in the world (Figure 1). More spectacular is the force harbored within these unique waters as a result of a natural anomaly: The sloshing effect created by tidal resonance—a coincidence in the time taken by a large wave to travel the length of the bay and back and the time between the high and low tides—can amplify these tides with enough energy to supply most of Ontario’s electricity needs.
1. World’s highest tides. During a springtime high tide (top), waters at the head of Minas Basin in the southeastern corner of the Bay of Fundy may surge to heights of 53 feet. At low tide in autumn, much of the bay becomes exposed, appearing like a wide channel of braided rivers (bottom). Depth is indicated by dark blue for deep water and purple for shallower water. Source: NASA
Despite the sheer power potential of this region—and others worldwide, such as the Bristol Channel in the UK, an inlet that shares similar geographic characteristics—only one commercial-scale power project has been implemented in the Bay of Fundy: the 18-MW Annapolis Royal Generating Station in Nova Scotia. That plant is the sole operating commercial tidal energy generating station in North America, and one of only three in the world. It shares its barrage technology with the 1966 Rance River plant in France, a larger installation with peak power capacity of 240 MW and annual production of 600 GWh, and Kislaya Guba, a 400-kW project in northwestern Russia. Even the Annapolis station did not begin operation until 1984—and only after several other efforts to construct tidal power plants in the region had failed.
The idea to harvest tidal energy from the Bay of Fundy extends as far back as 1925, when Maine voters approved $100 million to support hydraulic engineer Dexter Cooper’s proposed construction of a power plant to reap power from the tides racing through Passamaquoddy Bay on the Maine coast. Around the same time an official feasibility study was begun for construction of an 800-MW tidal power scheme on the Severn estuary in the Bristol Channel. But while the Severn study concluded that the project was technically feasible, it was thought of as economically unsound.
President Franklin D. Roosevelt thought the Passamaquoddy project would make vital contributions to the nation’s burgeoning power needs and granted it $10 million of federal funding in 1935. Nevertheless, this project, like many others in the long history of marine energy, never materialized.
But now, that’s all about to change.
The marine energy renaissance
Increasing concerns about the environmental, economic, and strategic costs of relying on fossil fuels, coupled with the widespread success of wind and solar power, are giving new life to hopes of capturing energy from the oceans. Oceanic bodies—which collectively cover a little more than 70% of the planet’s surface—may be a potentially significant, currently untapped reservoir of energy.
Decades of research and development have yielded several innovative ways of using oceans to fuel power generation. They include wave energy, ocean current energy, salinity gradient energy, and ocean thermal energy. Recently, with determined governments and companies in tow, several ocean power prototypes have been tested and pilot plants commissioned.
In 2006, for example, following a 22-year-long power-project lull in the Bay of Fundy, the Electric Power Research Institute (EPRI) of Palo Alto undertook a continent-wide study and identified four potential sites for commercial-scale power generation. EPRI’s list included three passages around Deer Island in Passamaquoddy Bay and Nova Scotia’s Minas Passage.
The study’s results immediately prompted Nova Scotia and New Brunswick to begin the site-evaluation process, and three companies secured permits to test their technologies in the Bay of Fundy. Last year, Nova Scotia Power announced that, following the successful installation in the Minas Basin of a tidal demonstration project by OpenHydro, the manufacturer of an open-center stand-alone turbine, the Canadian utility plans to develop large-scale tidal farms in the region.
In addition to being renewable, some types of marine energy, particularly those that derive generation from waves, or from tidal and ocean currents, are predictable (which gives them an edge over wind and solar power). Tides, determined by lunar gravitational pull, can be forecast years in advance, and currents can be mapped by satellite. Doing so could help guard against blackouts.
Offshore or submerged zero-emission turbines would also offer an added aesthetic benefit not enjoyed by offshore wind turbines: invisibility.
Among marine power’s disadvantages are a host of environmental uncertainties and a long list of technical hurdles, from operation to installation. Yet, as the ensuing stream of research and development yields significant results, it can be said with some certainty that the fledgling sector of marine power is about to grow up and take off.
The remainder of this article is a survey of the different concepts currently in use or under development for the extraction and conversion of marine energy to electricity.
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