The currents of coastal tidal waters provide a source of energy, exploitable by devices which function much like submerged wind turbines. Yet owing to high water density, the blades of these devices can be smaller and turn more slowly. Additionally, topographical features, such as inlets, can amplify the kinetic energy produced by the fast sea currents creating funnels and channels through which water is forced. Despite this potential, the industry has faced a number of challenges and so hasn''t yet achieved comparable progress to other renewables, such as wind and solar. Operating at sea means that equipment has to be durable and resistant to salt corrosion and there remain concerns for marine life safety.
The EU-funded FLOTEC project was set up to exploit the ocean’s energy supply potential by using floating tidal stream turbines, demonstrating how the technology could; reduce cost and risk, improve reliability, while also setting out a commercial framework for its introduction to the European grid.
Setting a new tidal industry benchmark
Key to FLOTEC’s operation is the SR2000 tidal turbine, reputed to be the largest and most powerful in the world. Designed for a twenty-year lifespan, it can be deployed in any water with depths of at least 25m and with its agile anchoring system is adaptable to most seabed types. The floating platform holds two horizontal axis turbines mounted just below the sea surface where tidal flow is at its strongest.
In April this year, the SR2000 reached peak power at 2 Megawatt (MW) rated capacity. The project team have since built on this achievement by generating over 18MWh (megawatt-hour) within a continuous 24 hour testing period. This performance puts it at the same level as that achieved by established offshore wind turbines.
Further optimising energy extraction
The FLOTEC (Floating Tidal Energy Commercialisation) project had improved on the SR2000 tidal turbine with the Mark 2 iteration by increasing the rotor diameter from 16m to 20m, which the project anticipates will increase energy capture by 50%. In its quest to reach flexible, base-load energy generation the project also harnesses innovations in automated steel fabrication, integrated energy storage, centralised Medium Voltage power conversion, mooring load dampers and composite blade manufacturing.
To help facilitate ease of access and maintenance, the platform hull contains most of the internal components of the turbines above the waterline. A key feature to aid maintenance, and reduce draught while being towed, was designing the turbine blades so that they are retractable under the hull. The test programme is being conducted at the European Marine Energy Centre (EMEC) in Orkney, Scotland where the patented technology has been connected to the Orkney grid for phased power export. The project is investigating not only power and hydrodynamic performance but also low cost maintenance as well as developing vessel management strategy.
Charting a course forwards
The SR2000 Marks 1 and 2 will be deployed alongside each other at EMEC, forming a 4MW floating tidal array demonstrating energy extraction in locally varying tidal resources. The project aims to reduce the Levelised Cost of Energy (LCOE) which calculates investment against output, across energy assets of floating tidal energy. The hope to bring LCOE down from the €250/MWh currently estimated, to €200/MWh.
To support the industry, last year the EU''s DG for the Environment announced a roadmap, alongside a proposal for a 320 million euro investment plan, towards meeting 10% of the EU''s energy needs through tidal and wave energy by 2050. The money is intended to help companies bridge the gap between demonstrations and entering the marketplace.
For more information, please see:CORDIS project page