Technology

The hydrokinetic device (turbine) is a floating structure with a single horizontal-axis rotor that converts the kinetic energy of tidal streams into electricity at an efficiency of 40%. Applying tidal fence theory, the turbine's tidal energy conversion efficiency could exceed 80%.

Through the use of an angled deflector, waves flow over the structure (overtopping) into an elevated reservoir to capture the potential energy of the waves. The same rotor is then used to convert the kinetic energy of the tidal stream and potential energy of the waves into electricity. This approach significantly increases the accessible energy density for the selected turbine location and delivers transformational project economics.

The turbine is a semi-submersible floating structure that minimises wave-impact forces and risks to fish and marine mammals. Its low-profile design, similar to a yacht sail, extends approximately 10 metres above sea level.

Our floating design approach has many advantages. It facilitates routine maintenance and defouling activities by eliminating the need for specialist lifting equipment or complex engineering designs to recover the turbine from the seabed. It also negates the need for expensive, voltage-limiting subsea inductive couplings.

All routine maintenance and repair activities, including anchor cable replacement, can be completed on site with the use of a service vessel incorporating a 10-tonne crane. For steel turbines, dry-dock visits will be required every 10 years for hull inspections, whereas concrete turbines can remain at sea indefinitely.

The prototype has a rating of 1.0 MW; however, larger structures are considered quite feasible as the technology for the construction of large floating structures is well understood in the oil and gas industries, as well as in the civil-engineering industry.

Hydropower good-practice guidelines - UK Environment Agency, December 2012.