The Bay of Fundy in Canada offers a unique environment for testing tidal energy technologies. Scientists with the Fundy Ocean Research Centre for Energy are pioneering methods to gather more accurate data on the bay's tremendous currents before deploying new tidal energy turbines.
By Matthew Lumley
Located off the northern coast of Maine and between the Canadian provinces of Nova Scotia and New Brunswick, the Bay of Fundy is an ocean bay 270 km (170 miles) long that hosts the world's highest tides. In fact, the Bay of Fundy pushes about 160 billion tonnes of water every tide - more than all the freshwater rivers and streams in the world combined.
Often referred to as the "Everest of Tidal Power" by technology developers, the Bay of Fundy provides very strong, uniform and predictable currents. The regions where these currents occur are very wide and long, differing from other regions of strong water flow that occur in narrow restricted passages. Because of the strong currents, the seabed has been eroded to bedrock, providing a solid and stable foundation for the placement of tidal energy devices.
In 2009, the Fundy Ocean Research Centre for Energy (FORCE) was established to study the potential for tidal turbines to operate within the Bay of Fundy environment. FORCE receives funding support from the government of Canada, the province of Nova Scotia, Encana Corporation and participating tidal turbine developers.
FORCE's test site is in the Minas Passage area of the Bay of Fundy near Black Rock. Minas Passage, only 5 km wide and bordered by basalt cliffs, is the entrance to Minas Basin, the region of the world's highest tides. At mid-tide, the current in Minas Passage is about 4 km3 per hour. With the incoming tide, about 14 billion tonnes of seawater flows through Minas Passage into Minas Basin.
Features of the site include water depths up to 45 meters at low tide, a sediment-free bedrock sea floor, straight flowing currents and water speeds up to 5 meters per second on ebb and flood tides, generating power comparable to a hurricane force wind. For tidal turbine developers looking for a potent resource, faster is better. As water speed doubles, its potential power output increases eight times.
|OpenHydro and Nova Scotia Power deployed North America's first 1 MW in-stream tidal turbine in the Minas Passage on Nov. 12, 2009.|
Four technologies have been selected for demonstration at FORCE: OpenHydro, Marine Current Turbines, Alstom and Atlantis Resource Corporation.
FORCE has built $30 million of electrical infrastructure - including subsea cabling (designed and built in Italy by Prysmian), an onshore substation (designed by Strum Engineering and built by Rafes Construction), and transmission line (installed by Nova Scotia Power Inc.) - to connect this powerful, renewable resource to the North American power grid. In 2012, FORCE connected and energized both the substation and transmission line. Later this year, FORCE will install the first of four subsea power cables to the ocean test site.
Untapped potential in the Minas Passage
John Woods, Vice President of Energy Development for Minas Basin Pulp and Power - the company that first developed the FORCE site and is partnered with Marine Current Turbines to deploy a device - says: "We are installing a turbine in one of the fastest flowing tidal races in the world, 40 meters below the surface of the ocean. Some people like outer space, but we think the most exciting frontier in science is right here in the ocean: its potential to change our energy future can't be underestimated."
Woods believes the key to harnessing Fundy's enormous power is in the data. "Our technology, designed by Marine Current Turbines, has performed well in the United Kingdom. To translate that success to the Fundy environment, we need to know everything about this tide - its speed, its direction, and how it changes, moment by moment."
Acquiring this information is not easy.
As FORCE Executive Director Doug Keefe puts it: "We have a huge volume of water at our site, moving very fast: 14 billion tonnes of water pinching through the a relatively narrow 5 kilometer gap called the Minas Passage. You can't put a diver in it. No one has successfully operated a remotely operated vehicle in it. Its raw power is intimidating. And yet it has so much potential we absolutely need to understand it and how to work in it safely."
FORCE's need for a clearer picture of its tidal resource has led to work with a number of nautical scientists, among them Simon Melrose from Oceans Ltd., an oceanographic services company based in Newfoundland and Nova Scotia.
One of Melrose's key tools for site characterization is an acoustic Doppler current profiler (ADCP), which measures current velocities by sending acoustic pings through the water and tracking the movement of air bubbles, fine silt and other particles in the water column.
Typically, scientists and others avoid high-flow sites like the Minas Passage because they are challenging to work in and hard on equipment due to the punishing water forces. Additionally, it is difficult to obtain accurate readings at an extremely loud, turbulent site when using delicate acoustic sensing instruments like an ADCP.
"We have done a couple of things to get better data. First of all, we now secure our instruments to the sea floor with a 1,000-pound mounting system. That cuts down on all the random noise, and keeps them stable - we learned that the hard way by losing one or two," Melrose says.
|The harsh marine environment requires unique technologies built with hardy materials that can withstand the tidal current, coarse sand, and ocean debris.|
"We also began taking continuous samples of data, using a steady burst of pings rather than more traditional intermittent samples. By sending a continuous stream of pings, we can capture not only basic velocities, but all the variations in velocity at different depths for different turbine designs."
The data coming back is staggering. The speeds at various water depths are up to a meter per second faster than originally believed. It was known that peak surface water speeds at the site were fast. But new ADCP measurements indicate that at 10 meters above the seafloor, an average anchoring height for a 1-MW commercial turbine, speeds reach up to 4 meters per second. This speed translates into much higher power potential than original estimates.
Dr. Richard Karsten. a mathematics professor at Acadia University in Wolfville, Nova Scotia, has been hard at work quantifying that potential. While initial estimates only pegged Minas Passage at about 160 MW of potential, Karsten says, "We now understand the true potential is more than 40 times that amount - roughly 7,000 MW. And our models show we can extract about 2,500 MW without changing the tidal range significantly."
This amount of capacity is roughly equivalent to that of two medium-sized nuclear power plants, or nearly the combined size of the proposed Gull Island and Muskrat Falls project on Canada's Lower Churchill River - the largest undeveloped hydroelectric resource in North America.
The Minas Passage offers a clear energy opportunity. Taken as a whole, the Bay of Fundy actually offers an estimated 50,000 MW of potential energy - a significant figure, given Canada's total installed hydro generating capacity is about 90,000 MW, one of the highest in the world.
Woods with Minas Energy says, "When you consider those kind of numbers, the potential gets interesting: a business case for developers, a clean energy source for Nova Scotia and our neighbors, and the basis of an industry. And all within close proximity to an existing power grid, which makes a big difference to project economics."
Realizing that potential, suggests Oceans Ltd.'s Melrose, will all come down to the data. "We are compiling a massive amount of data that turbine engineers can use to understand loads, electrical engineers can use to calculate power output, and hydrodynamic engineers can use to assess blade design to maximize both safety and performance."
This new approach to measurement has already been invaluable to FORCE. Plans for laying the subsea cables that will connect turbines to the electrical grid have been improved, including better predictions around operating windows and more clarity around the impact of the water currents on the cable as it is deployed.
FORCE Executive Director Keefe says the project rests on one simple maxim: Good decisions are based on good information. "In 2008, we knew very little about Fundy's power. Now, thanks to some solid research, we are starting to get a much clearer picture - both of the challenges, such as working in narrow operating timeframes, and the enormous opportunity this kind of power represents."
Acquiring that data is still difficult. Significant challenges remain as impediments to both deployment and retrieval of ADCP units in the high-flow environment of the Minas Passage. Those challenges include mooring, seabed stability, station keeping, and accommodating tidal heights. One ADCP unit was snagged by a person while fishing and was lost. Another was located but could not be recovered, probably because it was buried in a gravel wave.
|The Minas Passage is home to the highest tides in the world and could hold a potential gold mine of tidal energy.|
Building an infrastructure for the future
These rigorous conditions have also challenged the ability of sensing equipment to measure flow in the Minas Passage, and required instruments to collect data outside their design purpose, such as using ADCP to measure turbulence. This challenge has presented an opportunity for new innovation in marine sensing. With support from the government of Canada, North American energy producer Encana and private partners, FORCE is building a recoverable research platform designed to operate in the underwater hurricane. This platform will be connected to the FORCE observation facility by a 3-kilometer submarine data cable.
With planned deployment trials this summer, FORCE is finalizing preliminary design of a platform that will allow:
- Continuous, synchronized data collection (including currents, turbulence and other environmental data);
- More accurate visualization of marine life behavior and movement;
- Real-time instrument adjustments;
- Future development of a new standard of high-flow turbine monitoring world-wide, essentially the prototype for a "black box" for all tidal turbines.
The project is expanding FORCE's family of researchers and industry partners, stretching from Nova Scotia's marine service and supply chain across to British Columbia's Ocean Networks Canada and OceanWorks (who together have built the Neptune and Venus ocean observatories), collectively propelled by growing interest in site characterization and monitoring techniques.
FORCE will continue with design, system integration and trials through 2013, anticipating the delivery and deployment of a fully instrumented monitoring platform in the Minas Passage in 2014. That platform is expected to be at least eight to ten tonnes to remain stable on the seabed; that weight will require a well-designed recovery mechanism. FORCE is working on a number of deployment concepts.
Keefe adds: "Standing at the window of our visitor center, the potential is obvious to anyone. As the tide moves in and out, the island just offshore forms a bow wave just like a ship steaming through the water. The water moves fast here. And there's 14 billion tonnes of it."
Once complete, FORCE and its partners will have access to fine-grain, real-time data, the key to unlocking the enormous commercial potential of the Bay of Fundy.
Matt Lumley is director of communications at the Fundy Ocean Research Center for Energy (FORCE) in its Halifax, Nova Scotia office.