A U.S.-backed effort in Florida to explore the energy-producing potential of ocean currents has reeled in a private player – the Swedish startup Minesto, which uses a winged, turbine-tipped device that gathers energy by darting around underwater, kite-like, in a figure-eight pattern.
Is there any real hope for it? There might be – but it could take a while.
Ocean current energy isn’t as far along as tidal stream or wave energy, which themselves remain at least a few years from significant commercialization. Nonetheless, currents – slow-moving but broad and constant – offer an enticing energy resource, and Minesto appears to be as far along as anyone else in putting them to work.
Last November, in waters off Portaferry, Northern Ireland, the company staked its claim as the first “marine power plant designed for low velocity currents” to produce electricity at sea.
That was with a one-quarter scale model of the system called “Deep Green,” which continues to undergo testing in Strangford Lough. But that’s not a current environment – the water comes in, the water goes out. For currents, Minesto is heading to Florida and the Southeast National Marine Renewable Energy Center (SNMREC), run by Florida Atlantic University (FAU) with nearly $6 million in support so far from the U.S. Department of Energy.
It was just a month ago that the U.S. Bureau of Ocean Energy Management approved a five-year lease for FAU to develop an ocean-current test site about 13 miles off the Broward County coast.
“SNMREC is preparing unique testing facilities located in the Florida Current, where Minesto has assessed the ocean current resource to be favourable for Deep Green,” Anders Jansson, CEO of Minesto, said in a statement. “SNMREC are experienced in resource modelling, marine measurements, environmental assessments and regulatory framework, helping Minesto to accelerate potential development in the U.S.”
In an email interview, Minesto business developer Karin Agestam said Deep Green’s basic design doesn’t figure to change if the plan to scale up the device in Florida comes to fruition. (For its initial full-scale installation, Minesto is eyeing a device with a wing span of 12 meters and a rated capacity of 500 kilowatts.) “The unique challenge for ocean currents is that the water depths increase, which requires a different mooring setup,” she said.
The Florida test site is in waters 280 meters deep. Currents run stronger near the surface, however, so developers want their devices to be as high up as possible without conflicting with shipping and other users – 30-50 meters below the surface seems to be the sweet spot.
Even there, the water moves at just 5 or 6 mph, far slower than the air speeds that turn wind turbines. But water has the advantage of being constant and hundreds of times denser than air, and Minesto says lift forces acting on Deep Green’s wing zip the tethered device, which carries an onboard generator, along at up to ten times the speed of the water.
Of course, water also has its downsides – it’s complicated, dangerous and expensive to work in, it can degrade machinery, and hazards as yet unknown might lurk, to devices and perhaps to the environment. In addition, while the SNMREC site could provide a good next step for Minesto and the ocean current industry (such as it is), it’s not the be-all and end-all, not yet at least.
For commercialization of arrays of devices, should Minesto make it that far, grid-connected testing will be a necessity. Wave and tidal stream developers have the busy European Marine Energy Centre in Orkney, Scotland, for such testing, and the United States is planning to develop a similar center for wave devices off Oregon’s coast in the next several years. SNMREC, when it begins operating in the coming year, won’t be grid-connected, although there’s talk that someday that could change.
“One option can be to test the technology on several markets in parallel and then not all installations have to be grid connected,” Agestam said.
