To tackle this issue, a group of researchers used aerial drones and boat-based surveys to map the intricate tidal flows surrounding the world's most powerful tidal turbine - Orbital Marine Power's O2 - located in the Orkney Islands, Scotland. The O2, unlike traditional tidal stream turbines, floats on the sea's surface and is anchored to the seabed via mooring lines. With a length of over 70 meters, the O2 connects to the grid at the European Marine Energy Centre (EMEC) and is capable of powering approximately 2,000 UK homes annually.
The study focused on how tidal flows exceeding 8 knots could influence the turbine's performance and its downstream wake, which could affect the placement of future turbines and impact marine ecosystems. The research offered new insights into the optimal positioning of tidal turbines and stressed the need for site-specific assessments to close the gap between real-world data and simulation models.
Additionally, the study built upon previous research showing that turbine wakes can create favorable foraging areas for nearby seabirds, though densely packed turbine arrays could limit the movement of certain marine species. During their surveys, researchers even observed orcas passing the O2 turbine, highlighting the importance of studying interactions with marine habitats.
The study, published in 'Nature Communications', involved scientists from the Marine Biological Association (MBA), the University of Plymouth, and the University of the Highlands and Islands (UHI) Shetland.
Dr. Lilian Lieber, Research Fellow at the MBA and the University of Plymouth and lead author of the study, explained, "Conducting oceanographic surveys in one of the world's most powerful tidal streams, where currents can exceed 8 knots, is both exhilarating and challenging. Yet collecting data in these turbulent environments is crucial for addressing some of the complexities the tidal energy industry faces today. The optimal placement of these turbines in narrow channels fringed by islands is a complex endeavour, but our novel methods provided robust insights into these turbulent flows and wake signatures."
Tidal energy is considered one of the more reliable renewable energy sources due to the predictability of tides. Tidal turbines, similar to underwater windmills, convert the kinetic energy of moving water into electricity. Since water is over 800 times denser than air, these turbines can generate more energy than wind turbines of the same size.
Previous research suggests that tidal stream energy could eventually supply up to 11% of the UK's annual electricity needs. However, the sector still faces challenges, including the high costs of scaling up the technology, grid capacity issues, and ensuring turbines remain functional in turbulent waters.
Shaun Fraser, Senior Scientist and Fisheries Lead at UHI Shetland, said, "This study showcases the benefits of combining scientific expertise and deploying new technologies so that significant progress can be made in understanding dynamic tidal environments. With further development of marine renewable energy infrastructure in the Highlands and Islands region likely in the near future, this work is more relevant than ever to local industries and communities."
The study aimed to contribute to overcoming these obstacles by advancing the field measurement techniques necessary for the sustainable development and long-term reliability of tidal technologies.
Research Report:Sheared turbulent flows and wake dynamics of an idled floating tidal turbine
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