The Magazine for Underwater Professionals

Apr/May 2018

RENEWABLES

Measuring an underwater hurricane

Sensors help unlock Canada's enormous tidal energy potential in the Bay of Fundy

Cape Sharp Tidal gets ready to deploy a two-megawatt turbine at the FORCE site in Minas Passage, Bay of Fundy. Photo: Len Wagg

Home to the highest tides in the world, the Bay of Fundy stretches 270 kilometres along the US and Canadian coastlines, pushing roughly 160 billion tonnes of water in a single tide – more than all the freshwater rivers and streams in the world combined.


Often referred to as the “Everest of Tidal Power”, Fundy’s tidal flow speeds up as it pinches through a narrow section called the Minas Passage, resulting in water speeds that can exceed 20 kilometres per hour.


It’s a lot of water, moving very fast. With the emergence of a new clean technology called “in-stream” tidal – which acts much like a windmill under the water – the energy potential in the Minas Passage is staggering: roughly 7000 megawatts, enough to power two million homes.


“Seven thousand megawatts is the headline,” says Tony Wright, general manager of the Fundy Ocean Research Center for Energy (FORCE). “But to get a real understanding of what can be safely harnessed requires more research, and more data.”

 

POWER
Acquiring this information is not easy. As Wright puts it: “The Minas Passage pinches 14 billion tonnes of water through a five-kilometre gap, exceeding speeds of 10 knots at peak flow. Tough conditions for a diver or an ROV. Its raw power is intimidating. And the high turbulence and low light make it hard to measure the hydrodynamics and biological features.


“At the same time, getting this data is absolutely critical to proving whether this technology can be part of our future energy mix.”


The deployment of the first grid-connected device at the FORCE site – a 16-metre diameter OpenHydro turbine – made tidal energy a real possibility. It also raised concerns, as the effects of large-scale development on marine life are not yet well understood. While international research over the last 10 years indicates that fish and marine mammals generally avoid in-stream turbines, the findings must be tested in the uniquely challenging conditions of the Minas Passage.


“We’ve built three subsea instrumentation platforms to help us fill in some of the knowledge gaps,” says Wright. “We call them ‘FAST’ platforms – short for Fundy Advanced Sensor Technology.”
Equipped with arrays of environmental sensors to monitor both the physical and biological characteristics of the FORCE test area, the FAST platforms can work autonomously, or be cabled to shore for real-time data viewing and collection.


“They give us an ability to drop a sensor kit in a specific high flow area, and either recover the platform in a month or so and download the data, or connect a cable to shore and run in real-time,” says Andrew Lowery, technical director for FORCE. “Most importantly, the platforms are robust: they’re designed to survive the punishing force of the tide without flipping over or tumbling away – as some of our first instruments did.”

 

WATCH
Dr Kira Krumhansl, a marine biologist working as FORCE’s director of environmental programmes, says: “We’re currently outfitting one of our cabled platforms – known as FAST-2 – with instruments to watch how marine life directly interacts with tidal devices. These cabled platforms are critical to support monitoring efforts that require large data output and relatively high power to operate.”


Working with Open Seas Instrumentation, Nova Scotia Community College, Acadia University, Dynamic Systems Analysis, Ocean Moor Technical Services, and Cape Shape Tidal, FORCE is installing a sonar imaging camera on a dynamic mount, which would enable researchers to direct the sonar at specific targets. The goal is to position the sonar so that the turbine is in the field of view – allowing for direct observations of marine animal interactions with an operating turbine.


Krumhansl says: “For the last two years, we’ve been monitoring fish using downward-looking hydroacoustic sonar – using a boat to run transects over the turbine test area to measure any changes in fish distribution. Using a bottom-mounted sonar – positioned on FAST-2, with the turbine in the field of view – allows us to gain a more continuous and detailed picture of what is happening right at the turbine face.”

 

WHITEWASH
Says Lowery: “The Minas Passage is so turbulent you can’t just use a camera. We get asked that a lot: ‘Why not just use video?’ If you put a camera at our site during peak flood tide, it’s like turning on your high beams in a snowstorm. It’s just a whitewash; you don’t see anything. That’s why FAST is so important – to see what’s going on down there.”


Wright agrees: “Fundy is unlike any other marine area. It adds a lot of complexity. And the FAST platforms are designed to help us out – to make site characterisation easier.”


The FAST platforms have expanded Nova Scotia’s ocean technology supply chain, propelled by growing interest in site characterisation and monitoring tools.


Wright says: “Through FAST, a lot of suppliers have come into the industry, demonstrating how they work. Those companies have been able to take their experience with FORCE and translate it into work with turbine developers. The incentive is the ‘Fundy Standard’. If you can prove your kit works here, that’s a brand that will go a long way.”

  • A smaller FAST platform is lowered to the seafloor to gather fish data in the Minas Passage. Photo: Dr Haley Viehman

A report by Nova Scotia’s Offshore Energy Research Association (OERA) supports Wright’s claim. The Value Proposition for Tidal Energy Development suggests the tidal energy industry can contribute CA$1.7 billion (£976 million) to the province’s economy, and create up to 22,000 full-time jobs through 2050. Already, FORCE’s research and developments efforts have involved more than 300 companies.


And many of these benefits are not directly tied to turbines – they arise from the research and monitoring technologies needed to identify and validate new sites in the Bay of Fundy.


This includes a new breakthrough technology called the ‘Vectron’. FORCE, in partnership with Nortek Scientific and Dalhousie and Memorial Universities, has developed the world’s first stand-alone instrument – the Vectron – to remotely measure turbulence at mid-water column.

 

CALCULATE
A leap forward in site characterisation technology, the Vectron makes high-fidelity velocity measurements through turbine hub height, which will be used to calculate a range of turbulence metrics including spectra and length scale distribution – identified as key contributors to turbine performance and loading.


Mounted on FORCE’s larger ‘FAST-1’ platform, the Vectron works in concert with a large range of sensors chosen to provide a comprehensive characterisation of tidal sites.


“Right now, tidal devices are reinforced much more than necessary – to guard against huge uncertainties in turbulence measurements and hence in predictions of extreme loadings,” says Dr Joel Culina, a physical oceanographer working at FORCE. “That’s a problem: these reinforcements are themselves very costly and, further, the added weight requires costly marine assets for deployment. We need better data and analysis. That’s why we’ve developed the Vectron.”


Essentially, the Vectron is a scaled-up acoustic Doppler velocimeter (ADV). An ADV measures velocity at high resolution but only over a very limited range and at a short distance from the sensor. The Vectron measures through several metres range and at a distance on the order of 10 metres from the sensor, while achieving a noise level comparable to that of an ADV.


“The Vectron represents a significant achievement in acoustic Doppler sensing technology,” says Dr Alex Hay, who led early Vectron testing in Dalhousie University’s Aquatron Laboratory – the largest university-based aquatic research facility in Canada. “The unprecedented quality of the Vectron’s turbulence measurements will represent a major advance in our understanding of the variability of the flow – particularly extreme flow – in the Minas Passage. The present lack of knowledge of the magnitude and frequency of occurrence of these extremes has led to overdesign – and higher costs – for the industry.”

 

DRIVE
Data derived from the Vectron can help drive down many in-stream tidal project costs – including siting, design and operation – not only in the challenging conditions of the Bay of Fundy, but at high flow sites worldwide.


Navdeep Bains, Canada’s minister for innovation, science and economic development, says: “Innovation is critical to economic success. The research into remote turbulence measurement being done at FORCE contributes valuable information on the role that tidal energy can play in providing cost-effective, clean, renewable energy around the globe.”


“That’s the goal,” adds Wright. “It’s not just about Fundy. Ocean energy – including river current – is a compelling frontier for the entire planet. Understanding whether it can be a safe and affordable energy solution down the road will take a lot of science. And that’s what FAST is helping us do.”

  • FORCE's Dr Joel Culina and Dr Alex Hay of Dalhousie University stand watch as the Vectron begins its first shallow-water trial on the FAST-1 platform at Parrsboro in Nova Scotia. Photo: Darren Pittman

 

 

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