Wave Energy Scotland PTO development programme

16 May 2017
Quoceant's lab for the WES PTO project

Quoceant's lab for the WES PTO project

Wave Energy Scotland has announced that it has selected three wave energy technologies to move forward with stage 3 of its Power Take Off (PTO) development programme. So, which projects are set to share a slice of the £7.5 million investment? And what technological development will the funding enable?

QUANTOR HYBRID TECHNOLOGYOne of the schemes to benefit from the cash injection is the Quantor hybrid hydraulic PTO - Stage 3 project, a joint enterprise between two Edinburgh-based companies, hydraulics company Artemis Intelligent Power, which acts as the project lead, and marine energy and technology consultancy Quoceant.

The project team will use the award, a little shy of £2.5 million, to ramp up development of a novel Quantor PTO device based on a 'quantised chamber-switching' concept that employs Digital Displacement (DD) technology to smooth out the load steps and provide continuously variable control.

The project will take the technology to full integrated testing on a state-of-the-art laboratory test rig,  designed and built as part of the project, and used to simulate the action of a range of wave energy converters responding to different sea conditions.  This phase will also allow the team to directly test all the device elements and better quantify the performance of the system in terms of control responsiveness and efficiency.

"We are also planning to demonstrate the performance of the system in driving a heave compensation winch, where we believe major benefits may be available through reduced primary power requirements, reduced size and cost, and reduced energy losses," says Ross Henderson, Project Lead at Quoceant, which has already built up extensive expertise in wave energy technology following its previous work on the development of the Pelamis Wave energy converter.

In Henderson's view, a key advantage of the technology is its ability to maintain high efficiency while transmitted power 'varies from peak to zero to reverse over the wave cycle.'  In simple terms, this means that losses are kept relatively low because the bulk of the power transmitted does not need to pass through rotating machines to vary the load, instead 'passing directly between multiple actuators and the energy storage.'

"This also allows the overall power rating to be very high relative to the average, a similar regime to heave compensation where almost all the power is reactive but a widely varying power must be transmitted under tight load and motion control," he says.

"Quoceant and Artemis are developing this technology to be scalable and adaptable to suit a range of wave energy converters.  We also believe it to hold promise for a number of wider applications, which come up against similar challenging control and motion applications such as those experienced in the offshore oil and gas sectors," he adds.

DIRECT DRIVE
Elsewhere, the University of Edinburgh-led C-GEN Direct Drive project consortium, which also includes Forth Ports, DNV GL, and Bernard Hunter Crane, will receive some £2,499,556 to advance work on the third stage of their initiative, which will entail the development of a cutting edge drive linear generator for wave energy devices.

As part of the work, the team has agreed to construct a 150kW demonstrator drive - before testing it at sea to assess its capacity to operate effectively in a suitable environment and under required loads.  The plan is that this demonstrator device will be built using modular principles, so that some or all of it can eventually be integrated into a complete wave device in an anticipated WES Stage 4 project.

RECIPROCATING GENERATOR
The third scheme to be awarded a slice of the WES funds is led by the Italian manufacturing and engineering group Umbra Cuscinetti, which, along with a range of partners, including the University of Edinburgh, Bureau Veritas, and Seapower, has been awarded a total of £2,469,450 to embark on the next stage of its Electro-Mechanical Reciprocating Generator (EMERGE) project.

The main thrust of this initiative will focus on the continued development of the company's innovative Electro-Mechanical Generator (EMG) technology, a novel direct-drive system capable of converting the linear, reciprocating motion of waves into electricity via the integration of a re-circulating ballscrew and a permanent magnet generator.

Early on in the project, the EMG technology will be submerged in synthetic salt water and exposed to bench testing with a Hardware-In-the-Loop (HWIL) configuration.  Following this, it will be integrated with a point-pivoted wave energy converter before embarking on sea trials at the European Marine Energy Centre (EMEC) in the Orkney Islands.

According to Luca Castellini, Energy R&D and Business Development Manager at UMBRA Cuscinetti, the EMG is 'very attractive' for wave energy applications, particularly when compared to existing state-of-the-art PTOs, which he says are 'mainly represented by hydraulic or pneumatic systems and linear electrical generators.'

"It presents considerable technological advantages compared to both and aims at replacing them in most of the existing wave energy applications," he says.

"The EMG can be integrated straightforwardly into a range of WEC concepts that require direct conversion of linear motion into electricity, namely point absorbers and submerged pressure-differential concepts.  Furthermore, it can also fit on WEC architectures in which a predominant rotational motion occurs - [including on] attenuators and oscillating wave surge converters - if this is transformed into a linear motion through a lever mechanism," he adds.

Castellini also reveals that, in order to 'maximize the market potential and embrace the widest range of WEC developers,' UMBRA is currently developing three different families of ballscrew generators, based on identical working principles but conceived for different work environments.

"The execution of sea trials in conjunction with WECs is considered of primary importance by UMBRA, as the dynamic response of the prime mover provides invaluable information for future PTO development and commercialisation.”

By Andrew Williams

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