New system to harness energy from marine currents

TidalStream is developing a low cost buoyancy-controlled platform that can provide up to 10 MW from a single installation, float-out deployment, and onboard maintenance access.

The plant, called Triton, consists in 6-metre diameter turbines (2 to 6) mounted on twin floating vertical booms tethered to a gravity base on the seabed.

The TidalStream ‘Triton’:

* is designed to survive the incredible power of the sea in all conditions
* is simple to install, maintain and remove in fast tidal races
* provides easy access in a wide range of conditions for routine maintenance and unscheduled repairs with minimal downtime
* can be equipped with up to 10 MW of turbine capacity from a range of turbine suppliers
* provides a highly cost-effective and efficient turbine deployment system.

Ocean tidal streams are one of the key sources of clean’ energy still to be fully commercialised. For the UK alone they could provide up to 16% of the nation’s total electricity requirement and are an essential part of helping to meet carbon emission reduction targets.

However, up until now, the problem has been the lack of a cost effective and practical tidal turbine deployment and maintenance system that can meet this challenge.

The ‘Triton’ Semi-Submersible Turbine (SST) concept is designed for deep water, such as the 60m deep Pentland Firth – too deep to mount turbines on towers to the seabed economically and too rough for surface floaters to survive.

Instead, the turbines are mounted on semi-submersible spar buoys tethered to the seabed gravity anchorages by a swing-arm

A key feature is that the turbines use technology and components developed from the wind energy, that already exist and that have been developed over the last 20 years. It is only the support structure that is truly new and innovative.

For routine maintenance, access can be gained from an ordinary service vessel to the control room at the top of one of the spars. While for emergency or extraordinary maintenance or repair, the buoys can be brought to the surface until they are floating, so that the turbines are no longer submerged underwater.

"In traditional turbines, even simple tasks such as replacing a circuit board or checking a sensor would require the removal of the turbine. Furthermore, site visits take place several times a year,” said John Armstrong, founder of TidalStream. This is why simple maintenance can determine the success of a marine technology, and Triton designers focused on this aspect.

The capacity of the device ranges between 2 and 10 MW (depending on the amount of turbines and marine current velocity) and – according to TidalStream developers – it is designed for sites that are up to 60 metres deep, where water is too deep to mount turbines on towers and too rough for surface floaters to survive.