"Current" affairs: Harnessing renewable energy of the Bay of Fundy's tides

With the ebb of the tides in the Bay of Fundy, the receding water exposes islands and sets boats down on the ocean floor, up to 16 metres below where they started. This vertical change in water depth—up to twice the height of a two-storey house—is unmatched elsewhere in the world. But what may be even more impressive, and what draws engineers and scientists interested in renewable energy to the bay, is its powerful currents.

Every day, the tides move 640 billion tons of water through the Bay of Fundy—more than 16 times the volume of all the Earth's rivers combined. The currents responsible for moving all that water are some of the strongest and most dangerous in the world, reaching speeds of up to 18 km/h. These powerful currents create a sloshing effect in the bay, piling up water and then draining it, and contain immense energy potential. The challenge, however, lies in harnessing it.

A team, with members from the Ocean program at the NRC's Ocean Coastal and River Engineering Research Centre and from Dalhousie University, is helping better understand the forces that a type of turbine, called an in-stream tidal turbine, has to withstand. The Dalhousie members are supported financially by the Ocean Frontier Institute through the Ocean Graduate Excellence Network (OGEN).

A complicating factor for tidal turbines in the bay is turbulence. The water flow in the bay is not smooth like the water flowing over the top of a waterfall. It's more like the bottom of the falls, roiling and swirling. This turbulence causes turbine blades to experience rapidly changing twisting and bending stresses, altering in just seconds. As a result, the Bay of Fundy has been known to tear blades from turbines.

"We wanted to address the lack of research on stresses on turbines, information that could support future tidal turbine designs. At the NRC, we have a program dedicated to marine energy. We're trying to innovate and are here to help the public and help the industry grow," says Julien Cousineau, Research Engineer at the NRC.

Dominic Groulx, who is a professor with the Department of Mechanical Engineering at Dalhousie University, and his research team developed a computer model for turbine performance using data collected on the currents in the Bay of Fundy by Dalhousie oceanographers. "The model helps to predict how turbines will perform in real-world scenarios, an essential step in designing for durability," says Groulx. This model uses the turbulent flow of the bay and the changing pressures across the turbine.

The project team plans to build a scale model of a turbine and use the NRC's wave basin facilities to generate waves and currents that will allow researchers to compare the computer model with lab results. "This step is vital for validating the theoretical work of the computer model and ensuring that the turbines will perform as expected under actual operating conditions, says Groulx."

Tidal energy is particularly interesting because it offers a consistency not found among other renewable sources. "The tides are as predictable as clockwork. We know exactly 500 years from now when high tide will occur at any given place on Earth," Groulx emphasizes. Unlike wind and solar energy, which are variable and difficult to forecast far into the future, the predictability of tides makes tidal energy valuable for our renewable energy mix. In addition, the potential exists for tidal energy production in many locations around Canada.

"In this project, it's no longer just me and a PhD student in my lab. It's me and a PhD student in my lab and a group of people from the NRC who really know what they're doing. This partnership helps create a bigger, broader research team with different views on things. We're going to ask different questions; we're going to look at the results differently. A bigger and diverse team, as we now know, also helps increase what we'll get out of any project by allowing us to see things in slightly different ways."

Quick facts

1. Tidal energy is a renewable energy source. It's also one of the most consistent renewable energy sources because the tides flow back and forth twice a day in a predictable pattern, unlike wind energy, which varies with wind speed.
2. Canada has the longest coastline in the world and offers many locations with the potential for tidal power generation. In particular, Canada is home to the Bay of Fundy, which has the highest tides in the world and very high tidal energy potential.
3. Every day, the tides move 640 billion tons of water through the Bay of Fundy, more than 16 times the volume of all of the Earth's rivers combined.
4. In-stream tidal turbines, which look a lot like wind turbines, have to withstand forces under the water at least 1,000 times those experienced by wind turbines. Researchers at the NRC and Dalhousie University are collaborating to study the forces that the Bay of Fundy's tides exert on turbines in order to provide the information needed by turbine designers.
5. Computer models of the turbines will be paired with physical scale models and tested in the NRC's wave basin facilities to ensure the computer model accurately represents a real turbine.