It was an ironic encouraging sign: Ocean Renewable Power Company wasn’t hoping to have to take its tidal power device out of Cobscook Bay twice for repairs in its first six months of deployment – but that the company was able to pull off the retrievals with relative ease suggests that mounting the device on the seafloor might not be an impediment to smooth operation and maintenance.
This is one of the main questions about bottom-mounted devices; will it be too difficult and expensive to keep them functioning? The assumption that it will be underlies the design of the Evopod from the Scottish company Oceanflow Energy.
Demonstrated a few years ago at a one-tenth scale, Oceanflow is aiming to have a one-quarter scale version of its device deployed this year in Sanda Sound in southwestern Scotland. In announcing earlier this month a seven-year site lease with the Crown Estate, the company said a sub-50-kilowatt device “will be grid connected and could be a forerunner to other community energy scale tidal power projects around the coastline of Scotland.”
The Evopod concept uses three-bladed turbines that look a lot like those used in other tidal power concepts, such as the Alstom device being tested at the European Marine Energy Centre and the Verdant Power device that has been tested in New York City’s East River and last year was licensed for deployment.
But both of those devices, like ORPC’s Maine device – which uses turbines that look more like egg beaters operating horizontally – are bracketed to the seafloor. Evopod says floating is a better way to go:
A key obstacle to the economic potential of tidal stream turbines is the high cost of intervention to recover bottom mounted devices in the event of component failure. Oceanflow recognises that component failure is inevitable in a multi-device farm installation and that intervention must be simple, cheap and fast. Floating solutions overcome the disadvantages of bottom mounted devices in that they are more accessible for first line maintenance and, with the Evopod disconnectable mooring and power export solution, easily recoverable to sheltered water for servicing or repair activities.
Oceanflow says the Evopod is “tethered to the seabed using a catenary spread mooring system with simple pin-pile or gravity anchors,” and adds that “units for deployment at coastal sites exposed to harsh wave climates employ a swivel mooring connection that allows the free floating device to maintain optimum heading into the direction of flow.”
Scotland, of course, is aggressively pursuing a wide range of renewable sources, and it’s reasonable to call the country the world leader in marine energy. Oceanflow won support in 2010 and then in August last year received a £750,000 grant through the WATERS (Wave & Tidal Energy: Research, Development & Demonstration Support) program that aims to build marine power into a £4 billion industry in Scotland by 2020.