The oceans offer a large, but as yet almost untapped, source of renewable energy that could make an important contribution to the future energy mix. Large amounts of energy are in principle available from tides, ocean currents, waves, and thermal and saline gradients in (or at the edge of) the oceans. Estimates of how much can be practically and economically extracted vary widely, but detailed studies suggest that the UK, which has around half of Europe’s potential, could be provided with some 10% of its current electricity needs by tidal barrages (half from the Severn), 10% by tidal streams, and 10% by waves (allowing for shipping lanes).
Designing robust structures to extract this energy efficiently in harsh offshore environments poses some formidable engineering challenges. At this early stage of development device architectures have not yet converged. Many different device configurations are presently being developed and tested. Innovation is required in device design and for scale up to commercial levels. Further investment and political support for the industry will also require a good understanding of the energy and commercial potentials of proposed solutions and their ecological impacts.
Research in Oxford
The UK is at the forefront of marine energy research. Oxford engineers work on the design of marine turbines, wave energy convertors, and off-shore platforms for wind turbines and drilling. They also model flows in tidal basins in order to assess their potential as energy sources. Oxford zoologists study the ecological impact of marine energy systems (including off shore oil drilling – see fossil fuels, where work by engineers on undersea pipelines is also described). Integrating large amounts of electricity from variable and intermittent sources, such as tides and waves, will put demands on electricity networks and would benefit from large scale energy storage.
Simulated flow through a 3-bladed tidal turbine with interaction of the helical blade tip vortices with the turbine’s support column
Oxford engineers are working on all scales of the tidal energy generation problem; device design, tidal farm design and planning, and large (basin) scale hydrodynamics and resource estimation.
The performance of different device designs and configurations are investigated, modelled and examined in detail, including the impact of waves and turbulence. Device-device interactions, both constructive and destructive, are studied to optimise tidal farm performance, whilst analytical and numerical techniques are being employed to understand how much tidal power can be extracted from a variety of coastal basins and what effect power extraction will have on the natural hydrodynamics within these basins. This work has led to new energy extraction limits for tidal fences, replacing the Betz limit (see case study).
Artists impression of the Transverse Horizontal Axis Water Turbine, exhibiting its hydroelastically efficient truss blade structure
Oxford engineers have developed an innovative, second generation transverse horizontal axis water turbine. Testing has successfully demonstrated the potential to deliver significant power through the turbine’s ability to block the flow. The turbine, and associated generators, transmission equipment and energy take-off systems, are being developed by a spin-out company (Kepler Energy).
For more information go to Tidal Energy Research Group.
Research is focused on understanding the dynamics and statistics of ocean waves, as well as their interaction with wave energy devices. Mathematical approaches are being developed to improve wind and wave forecasting accuracy. This work is required to assess the resource and its potential integration into the energy system, and informs modelling of the interaction of waves with off-shore structures. Linear and non-linear wave modelling are being used to assess the performance and inter-device interactions of floating wave energy convertors.
For more information see Ocean & Coastal Engineering.
Oxford engineers, who have worked on the design of off-shore platforms and drilling rigs, are developing robust designs to support off-shore structures, including wind turbines, which have to withstand extreme conditions. This research includes understanding extreme wave loading on submerged and surface piercing structures and load minimization through streamlining support structures. It further explores problems related to the design of foundations and their behaviour under monotonic and cyclic loading. Instrumentation has been deployed to monitor the behaviour of installed foundations, and novel ideas (such as screw piles or drilled and grouted anchors) are being developed.
Oxford zoologists have expertise in the assessment of human impacts on marine ecosystems, both coastal and offshore. This includes sea-going multidisciplinary research using a variety of sampling technologies from trawls and corers to Remotely Operated Vehicles and acoustics. Oxford are also world leaders in the mapping and assessment of biodiversity and ecosystem services using a variety of GIS and satellite technologies applicable to both terrestrial and marine ecosystems.