Triton is a highly efficient multi-mode point absorber that consists of a catenary moored surface float connected to an optimally-shaped, vertically asymmetric heave plate by three taut, flexible tethers. Unlike most conventional WECs, Triton’s surface float is excited by ocean waves in multiple modes – heave, pitch, surge and roll – allowing for increased energy capture across a wide range of ocean conditions enabling a substantially lower levelized cost of electricity.

Triton’s projected performance is based on extensive numerical modeling validated by tank testing at 1:50 scale. Testing of a 1:20 scale model is planned for Q3 2016.

Triton’s drivetrain uses a variable linear hydraulic gearbox to amplify and transfer loads from the tethers to the generators. The gearbox is a high reliability hydrostatic system similar to that used in hydraulic presses. It delivers the benefits of a conventional rotary gearbox without complex moving parts. Specifically, it also allows for optimum matching of the wave-generated forces to the generator input forces, so that the generators operate at maximum efficiency while allowing the appropriate system compliance for coupling with the input wave.

Every WEC has an optimal force/displacement profile for maximum mechanical energy capture and efficiency in each wave condition. Triton’s linear gearbox design allows the load amplification factor to be adjusted to optimal levels during operation based on the wave state, enabling generator displacements to be maintained at an optimum level that is largely independent of the surface float’s displacement, maximizing power transfer over a wider range of sea states than other WECs.

The linear gearbox thus makes a significant contribution to the wide power bandwidth, increased reliability, and reduced cost. It also enables various non-continuous control strategies such as latching and declutching without imposing excess loadings on the generator or marine system, which may enable the use of advanced active control algorithms to boost power in lower sea states. Optimization of the linear drivetrain, including the linear gearbox, is being funded by Wave Energy Scotland.

Triton will be towed to deployment sites with the surface float and heave plates hard-mated to each other. After mooring the surface float, the system is de-latched so that the heave plate can be lowered to the target depth using on-board winches, as shown in the figure below. The winches are employed in reverse for heave plate recovery.

These self-deployment and self-recovery functions remove the need for specialized vessels or heavy lift equipment, as regular vessels are sufficient to tow the system and supply hydraulic power for winch operations. The use of a transport configuration also allows towing and installation in higher sea states, increasing the duration of acceptable weather windows and thus reducing vessel standby costs.

SURVIVABILITY
Triton’s tuning approach (aligning device response with the dominant incident wave conditions to maximize energy capture under smaller waves) can also be used to perform load shedding in larger waves. Adjusting drivetrain parameters and dynamic ballasting of the surface float can both be used to alter the mass properties and reduce the devices’ response to the incident wave.

With funding from the Department of Energy, Oscilla Power is investigating use of the hard-mated configuration for survival situations. This will enable a reduction in the required over-design for extreme conditions, and thus a reduction in capital cost.

RELIABILITY
Low reliability and availability, driven largely by drivetrain complexity, has historically been one of the principal drivers of high maintenance cost and low annual energy production faced by wave energy converters. Generator technologies optimized for low cost in a fixed foundation, non-salt water context are unlikely to be the low cost solution for wave energy conversion.

Enabled by its gearbox’s flexibility, Triton will use low-displacement solutions, such as the magnetostrictive generators developed by Oscilla Power for use in wave energy conversion, to deliver high efficiency energy conversion with unparalleled reliability.

Triton’s initial deployments are anticipated to use proven, high-power density linear generators. These will have significantly lower mass and volume than direct drive generators due to the speed increase enabled by the linear drivetrain.