Wave & tidal power |


Electric dreams for wave power


Newcastle University and the University of Edinburgh are collaborating on a project to demonstrate the advantages of using electric power technologies in wave energy converters


NEWCASTLE UNIVERSITY’S Dr Nick Baker, in collaboration with Dr Serkan Turkman and Professor Jeff Neasham at Newcastle University, and Professor Markus Mueller at the University of Edinburgh, is leading a team of researchers to develop an all- electric, mechanically simple drivetrain technology to power wave energy converters (WECs) efficiently. The Marinisation and Upscaling of All-Electric Drive Train (MU-EDRIVE) research project, funded by the UK Research and Innovation (UKRI) Engineering and Physical Sciences Research Council (EPSRC), will see deployment of the new drivetrain system, a generator and a power converter on a buoy 3km off the Northumberland coast at Blyth. In spring 2024, this prototype WEC will provide operational data while testing corrosion and anti-fouling technologies which prevent sea organisms, such as algae, sticking to the device and potentially interfering with its operation.


Driving the Electric Revolution With £80 million funding from UK Research and


Innovation, the Driving the Electric Revolution (DER) challenge is supporting UK business by investing in Power Electronics, Machines and Drives (PEMD) electrification technologies and skills. PEMD underpins electrification and is applicable across multiple sectors including marine energy. The MU-EDRIVE project is supported by Driving the Electric Revolution Industrialisation Centres (DER-IC), a UK-wide network of Universities and Research and Technology Organisations (RTO) with the mission to support the growth of UK PEMD supply chain capability, capacity, and competitiveness by providing open access to world-class design, manufacturing, test and validation capability. The DER-IC network, in which both the University of Edinburgh and Newcastle University are partners, will provide access to world-class equipment and capability to streamline and scale-up the processes used to manufacture MU-EDRIVE technology.


History of the project Numerous wave energy devices have been proposed


over the preceding decades with limited technical and commercial success. Unlike wind, the technology is a long way from convergence and maturity but globally, grid connected examples do exist and the market is growing. Wave energy has been held back by the need for moorings and electrical cabling for offshore/ocean operation, but with floating wind turbines coming into use, these challenges are being addressed together. Power take off (PTO) now remains the major


technology blockage. The main technical challenges 38 | June 2024 | www.waterpowermagazine.com


for PTO relate to the discrepancy between the natural motion of ocean waves (slow speed and reciprocating) compared to the conventional motion of electrical generators (high speed, uni-directional, rotary). Wave energy devices, therefore, need either some form of mechanical linkage between the moving part and the electrical machine, or to abandon conventional electrical machines and use bespoke slow speed generators. Concerns over gearbox reliability and part load efficiency of hydraulics indicates the ideal long-term solution is a suite of large slow-speed generators which can be adapted for specific wave energy converters. The ideal PTO for a wave energy device must react


large forces (or torques) to generate large power at low velocity, with high reliability, availability and efficiency over a wide range of loads. This is a demanding specification. All these aspects contribute to the Lifetime Cost of Energy, which dictates the economic feasibility of devices. At present, no single PTO technology is able to meet this specification for wave energy. The main options for the PTO used in a wave device


are hydraulics, a mechanical gearbox and direct drive. Most developers have focused on using hydraulics as the PTO, whether it be high-pressure oil or water. In talks with our industrial partners, we learnt that the only reason for using hydraulics was due its availability off-the-shelf. Everyone expressed concerns about the limitations, however, including low efficiency at part load; ability to provide control over a wide range of frequencies; and displacement leading to potential end-stop problems. Although gearboxes are well established in some areas, they are not well suited to oscillating applications. Experience in offshore wind also tells us they can prove problematic in the marine environment, and many modern large wind turbines have direct drive power trains. A direct drive power take off does not have any mechanical interface, but instead the generator is designed to operate at low velocity and high force. Previous work in direct drive power take-off for wave energy at Newcastle University has proved the concept will work in the laboratory, but solutions have not been fully optimised, designed for reliability, or matched to the characteristics of a specific wave device.


“One of the challenges is the fact that waves go up and down very slowly, whereas most electrical generators are designed to rotate very quickly at several thousand revolutions per minute. I’ve spent quite a bit of my professional life looking at developing electrical machines specifically for that low speed,” Baker commented.


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