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 £80M 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 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 of 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,” he commented.

In 2016, Research Council funding allowed Baker and his team to look at developing these machines in collaboration with a number of wave energy device developers. In the lab, five small-scale electrical generators were built and taken to the wave tank at the University of Edinburgh where they were connected to a couple of buoys to demonstrate that, on a small scale, heaving motion could be converted into electricity. The team also developed the power converter, and put this all together. It meant that not only could they generate electricity from waves in the sea, but they could also control it. They could decide, in a particular wave, exactly how the buoy should oscillate in order to maximise the amount of power extracted.

“That project finished in 2019 and demonstrated that this was all technically feasible at small scale,” Baker explained. “The project that we’re doing now, which started in 2021, is  proving out that our technology can be scaled up, can be integrated into a wave energy device and can be installed at sea in the real marine environment.

“The university has a research vessel and has offshore research in other areas like biofouling and offshore communications, etc. Joining together a few different research areas, we realised we’ve got everything we need to take this technology forward and get it ready for the commercial world.

“We are doing it at small scale, primarily because we are doing it with a limited budget.  It makes sense to prove it at small scale in an academic environment, and then allow industry to manufacture on a bigger scale. That’s exactly the approach that wind power took, it started off small and onshore, and then it grew and is now moving very quickly,” Baker said.

Protecting the device

A major part of the project is how the system will be protected from biofouling once it is in the water. There are different parts of the device, such as the main body. For this, protection will be similar to the protection used on ship hulls. However, what the project is concerned with is the actual electrical generator. The ideal solution here is something you can install, and leave alone for two decades. You don’t want to install something that will wear out or fail. The project is looking at the idea of not having any seals.

“Normally, what you do with wave energy machines is if you put them in the marine environment, you seal them to protect them from the seawater. The problem you have however is that eventually those seals fail, or they need replacing,” explained Baker. “The alternative is not to have any seals at all – we’re just going to flood the electrical machine with seawater. Now that is good for me as an electrical engineer, because it cools the generator down, but then it introduces the problem of biofouling. The research we are undertaking is looking at how we stop biofouling slime build-up in the electrical generator itself. We’ve got a single moving component, no seals, no gearboxes. We’ve just got one thing moving so it’s actually potentially a very reliable solution to this power take off problem.”

Going forward

The project team are currently in the practical testing phase and modelling the performance of the generator, with plans to begin mechanical design and construction by the end of the year. The goal is to have the device installed and operational by early next year, with monitoring equipment in place to ensure that everything is functioning as intended.

However, there are significant challenges in designing a robust system that can efficiently generate power in both low-energy and high-energy situations while surviving harsh marine environments, Baker explained. He said the team are currently at the simulation stage and lab testing phase, with research staff modelling the device to ensure that it will oscillate as expected and be capable of extracting power while also surviving extreme conditions, testing small models in a wave tank, and investigating biofouling solutions in a slime farm.

One major concern is the risk associated with deploying novel technology in a harsh environment with a modest budget. There is always the possibility of unforeseen complications, such as weather-related issues or the need for over-engineering to ensure that the system is rock solid. Nonetheless, the team remain committed to demonstrating the general principles of the technology, which will be open access and available for adoption by everyone.

The team is a collaboration between electrical engineers, naval architects and a communications and system engineer with expertise in the ‘internet of things’ and offshore communications. There is growing interest in developing internet-enabled technology for offshore applications, such as monitoring fish movements or offshore communication, which will require a reliable source of electricity. The team believes that the offshore oil and gas industry, which currently relies on fossil fuels, could be a potential medium-term market for the technology, as the wave energy generators could provide a reliable source of electricity to oil rigs.

The project is innovative research with significant risk, but it appears the team are confident in their ability to bring together novel technologies to generate electrical power from wave energy.