The aim of the SHY project (“Seawater Hydraulic PTO using dynamic passive controller for wave energy converters”) is to develop and validate four distinct products of an innovative power take-off system that individually and together are expected to have a significant impact on the viability of wave energy as a renewable energy source.
The SHY project will develop a composite linear pump and controller valve that use seawater as the working fluid, and enable the use of a dynamic passive controller to maximise power capture.
A dynamic passive controller involves the dynamic control of active energy i.e. only damping forces. This has been shown to provide a significant increase in power capture relative to optimum linear damping - without the requirement to provide additional reactive energy.
The performance of this control strategy and associated technologies is proven by applying it to the Wavepiston wave energy converter (WEC); however, it is expected to be equally suitable for a wide range of converters that utilise a hydraulic PTO. A numerical model of the system has been constructed and used to develop a control strategy designed to minimise the levelized cost of energy, rather than maximise power capture, which is a common, but sub-optimal, objective for many control strategies. The control strategy is first calibrated using a test programme at DTU and subsequently validated using the Wavepiston offshore test bench at PLOCAN.
Two generations of the linear pump and controller valve are fabricated, designed for mass production with consideration of its full lifecycle impacts (although the actual prototypes may use low-volume techniques to limit project costs). The second generation prototypes will be based on learning from experiences and the performance of the first generation.
A condition controller designed to increase the remaining useful life and thus reduce the LCOE is also investigated. This includes identifying condition signatures that indicate a deterioration in one or more components and then using this signature to estimate the remaining useful life followed by identification of modifications to the control strategy to extend the remaining useful life.
The modular nature of Wavepiston WEC, whereby each energy collector includes a power take-off unit, makes it ideally suited for the project. Wavepiston consists of multiple energy collectors coupled on a string, with each complete string corresponding to a Wavepiston WEC. Multiple WECs constitute a Wavepiston wave energy farm. Each energy collector has a sail that is moved back and forth by the surge motion of passing waves. This horizontal movement drives hydraulic pumps generating pressurised seawater, which is piped through the string to an onshore conversion station. There, the high-pressure seawater is used to generate electricity via a hydropower turbine and/or desalinated water via a standard reverse osmosis system.
Through technology validation in the relevant environment, SHY will target TRL5 by the end of the project.
