Marine renewables and offshore wind

In this episode of The Life Scientific with host Jim Al-Khalili, Deborah Greaves, Professor of Ocean Engineering at the University of Plymouth, talks about the power of waves and how they can be harnessed to produce renewable energy. She works with physical wave tanks in the lab combined with computer modelling to test how well wave devices would respond to stormy seas.

You can hear the full episode on: https://www.bbc.co.uk/sounds/play/m001pf3d

Offshore wind turbines in Rampion Offshore Windfarm, England. Image Credit: Nicholas Doherty, Unsplash

Prof Greaves has spent her career working in the field of fluid dynamics, simulating what happens when ocean waves crash into structures, which can be both a destructive force and a means of generating renewable energy, and has been raising awareness of the potential of wave and tidal energy in the push towards decarbonisation of energy. As an island nation surrounded by shallow coasts, Britain is uniquely placed to harness this potential source of energy. Wave and tidal energy, in terms of energy concentration, are more powerful than either wind or solar, however so far this has been difficult to generate on a large scale, something Prof Greaves and other scientists in the field have been working to fix.

The technology Prof Greaves has worked on aims to harness the immense power of sea waves, particularly during storms, as a means of generating power. Waves are irregular and have a certain randomness, and implementing the technology in the water as opposed to on land comes with structural challenges, as it must be able to survive within a marine environment even when waves become massive. In the 70s, there was a boom in research into waves, which declined somewhat as scientific priorities changed, however was revived again in the late 00s in part due to investment from European and UK strategy. More recently, separate parts of the overall challenges have been addressed in turn, and it is hoped that this will help unleash the potential for wave and offshore technology.

Prof Greaves talks fondly of her youth growing up by the sea in Plymouth, after which she completed her Bachelors degree at the University of Bristol in 1988 and worked in a civil engineering firm building tunnels and bridges for the London Underground. She later undertook a PhD at Oxford University investigating exactly what happens when waves crash into solid structures.

London Underground. Image Credit: Unsplash. Before pursuing her career in fluid dynamics and marine engineering, Prof Greaves worked as a civil engineer including building tunnels for the London Underground.

Deborah grew up in a humanities and music focused family, and broke with tradition to pursue science. As a teenager she designed and built a hands free light using diodes and resistors for her father's basement. As a schoolgirl, she knocked on the door of a local construction site to request work experience while they worked on the interchange of the A38 interchange outside Plymouth, since she enjoyed maths/physics and working outside and was advised by a family friend to investigate civil engineering. She spent a week on the site with the engineers, translating the design on paper to what was visible on the ground. During the 80s, few women were involved in engineering, but Deborah was unfazed, having been inspired by a talk at a local university by a female engineer who talked about how simple safety measures in road engineering could make real impacts on peoples' lives. At the engineering firm where she worked following graduation, there were a handful of women as well as a 5-a-side football group, however since most of the women didn't play football, Deborah took it upon herself to start a basketball team so all the employees could play together, and it was here she sweetly met her future husband. During this time, she volunteered to join an Arctic expedition group on research projects, staying a few weeks to monitor the progression and impact of glacier melting, as well as encountering the odd polar bear.

In 1992, she decided to change directions somewhat, and started her PhD in Oxford University on waves and computational fluid dynamics using numerical modelling. Her work focused on simulating vortex shedding (eddy currents and whirlpools) that occurs behind cylinders in a fluid stream, using equations of motion. Her technique used an adaptive mesh to solve the equations at different points in the grid, aiming to adapt the grid to be finest in points of high activity such as vortex flows, while balancing that increasing mesh density improves accuracy but increases computational costs. She applied her findings to steep waves as well as vortex shedding.

Computational models of waves have provided an insight into the behaviour of sea waves. Image credit: Unsplash

Following her PhD, she landed a lectureship at UCL in naval architecture, teaching about hydrodynamics, wave structure interaction and ship and submarine design and manoeuvring. After her first child was born, she and her family chose to move away from London and she secured a prestigious Royal Society fellowship in Bath to research harnessing the power of ocean waves as a renewable energy source, something that had interested her for a long time, to develop and apply numerical techniques to apply to the challenges of wave energy machines. Throughout maternity leave and working part time, Deborah continued to work on this area of interest that has been her area of research ever since. By 2008, she secured a role on a team working on marine renewable energy in Plymouth, buying the house next to her mother, allowing her to pursue her passion as well as be near her family. By now she was working on physical wave experiments as well as computational simulations, building the Coastal, Ocean and Sediment Transport Laboratory (COAST lab), which included flumes and tanks, the largest of which was a small pool. Lab pools are a vital part of wave energy research and are used to test that devices will work when put in the sea. Paddles generate waves and currents to mimic the sea's conditions, with a wind generation system is currently under development. This small scale environment allows scientists to see how the devices respond under a variety of conditions they are likely to experience when out in the sea.

COAST lab in Plymouth, where paddles generate waves to test models of wave energy devices to be put in the sea. Image credit: University of Plymouth

Computational modelling has limitations in what can be run, due to some model simplifications that have to be made as well as computational cost, so this is where the physical models and lab tanks can be very useful. However, the lab tanks have their own drawbacks, as some large scale effects cannot be reproduced in the lab environment, however putting both computational and physical models together allows for a much clearer picture of wave energy research.

While most people know what a wind turbine looks like, wave power devices come in all shapes and forms, for instance an oscillating buoy or a long snake like device, or an oscillating water column with an air chamber trapped above the surface, compressing the air above it just like a piston. Other options include seawall structures, where waves crash against them and break into a reservoir container, draining through a turbine below.

An illustration showing some types of marine renewable devices. Image Credit: Alternative Energy Tutorials

 One of her team's current areas of research is in flexible energy devices, which are constructed from air filled, flexible, membrane type materials. These are cheaper and lighter than steel, and survive well in storms. While the lack of standardised design in wave energy devices can be a challenge, it also provides opportunities for new ideas in the field as well as the option to tailor the device to the user's specific needs, such as to provide power to oil and gas platforms, offshore fish farming, small islands and remote communities that until now have relied on diesel. Test sites such as the European Marine Energy Centre (EMEC) in the Orkney islands provide locations to test the wave devices in the sea, as well as in the lab, where designs can be tweaked and improved.

In addition to her research, Prof Greaves is the Director of the Supergen Offshore Renewable Energy Hub, funded by the EPSRC, where she brings together researchers in offshore renewable energy to work with industry and policymakers to target the research strategies needed to address industry challenges, as well as support fundamental research which could have game changing long term impacts.

While wind arms, wave farms and tidal stream farms are not always ideally suited to being in the same location, there are significant maintenance, infrastructure and operation costs to be made by sharing these spaces, as well as optimising use of the valuable seabed which also provides vital marine habitats for wildlife. Energy islands, either physical islands or large floating structure, have also been proposed as an idea to combine these things offshore, and research into this is underway.

Targets around renewable energy are ambitious, and offshore wind is a key part of the UK Government's strategy for decarbonising the electrical grid, with targets to build 50GW by 2030, almost quadrupling our current capacity in the next 6 years, which would bring increased energy security and resilience, with the focus being building floating offshore wind.

Overall, I was very inspired and hugely enjoyed listening to Prof Greaves sharing her scientific journey and research pursuits, and I learnt a lot about exciting new technology and how science theories can be harnessed and applied to bring about positive change in the real world.