Marine Energy

Ocean Kinetics and Green Marine partnering to decommission OpenHydro tidal turbine

Ocean Kinetics and Green Marine partnering to decommission OpenHydro tidal turbine

Scottish firms Ocean Kinetics and Green Marine (UK) have formed a joint venture partnership to decommission OpenHydro’s tidal energy platform in the Orkney Islands, Scotland.

Work is advancing to remove the steel superstructure installed in 2006 at the European Marine Energy Centre’s (EMEC) Fall of Warness test site, which OpenHydro used to streamline its tidal turbine technology development.

As Hydro Review reported in 2018, OpenHydro’s technology, called the Open-Centre Turbine, comprises four key components: a horizontal-axis rotor, a direct-drive permanent magnet generator, a hydrodynamic duct, and a subsea gravity base foundation. The commercial-scale turbine is 16 m in diameter and is rated at 2 MW. It weighs about 300 tonnes and is predominantly a steel assembly.

The OpenHydro test rig consisted of two steel piles drilled and grouted into the seabed, with a steel superstructure attached to provide a working area. The turbine component was fixed to the piles using two steel collars, which allowed the unit to be raised and lowered into the tide using two 15 tonne hydraulic winches.

The decommissioning work scope involves the entire removal of the steel superstructure, diamond wire cutting of the piles, and cable disconnection and termination. For this project, Ocean Kinetics is providing divers, riggers, welders and remotely operated vehicle (ROV) services. Green Marine is providing offshore management, the Green Isle vessel, moorings and operational cable experience. Both firms are sharing responsibilities for operational engineering, cutting and heavy lift operations.

Green Marine Operations Manager Terry Norquay said the entire topside infrastructure has been removed, with work imminently progressing to the pile removal and cable termination.

Work is being undertaken during Neap tides with water speeds approaching 6 knots (3 metres per second). Engineering teams are aiming to capitalize on slack tide windows, when the water changes direction and flows at a much slower speed (0.5 metres per second), allowing operation in calmer conditions.

To complete the final elements of the decommissioning project, the Green Isle will be spread moored, in a four-point mooring configuration in order to remain stationary in the tide and allow divers to safely enter the water.

Under the Marine Licence which allowed OpenHydro to operate, the seabed must be returned to its original condition, which means cutting each pile foundation flush to the seabed. To achieve this result, diamond wire cutting machines will be turned upside-down to create an optimal finish.

OpenHydro was the first developer to use the tidal test site at the Fall of Warness off the island of Eday when its test rig and 250 kW turbine were installed in 2006. The device was the first tidal turbine to be grid-connected in Scotland and the first to generate electricity to the national grid in the UK, according to a release.

Ocean Kinetics was established in 1992 to provide marine engineering solutions to clients in Shetland. Green Marine (UK) Ltd was founded in 2012 in the Orkney Islands and operates throughout Europe.