Electricity can be generated through the conversion of the kinetic energy that resides in tidal currents in a similar way to a wind turbine. The ubiquitous nature of tidal energy, and the predictability and reliability of tidal currents, gives tidal-stream energy distinct advantages compared to other renewable energy technologies. Individual tidal energy devices have been installed and proven, with commercial arrays planned throughout the world. Yet, the true global resource and ocean conditions are broadly unknown, affecting optimal global device design. Present methods are unsuitable as the industry matures beyond the fast, shallow, well-mixed, and wave sheltered "demonstration" sites - influencing investor confidence. Transformative understanding of this sustainable natural resource for the coming century is therefore needed to bring a step change towards a sustainable, high-tech and globally exportable, UK renewable energy industry.
CHALLENGE 1: How much tidal energy is there in the world and how is it distributed?
OBJECTIVE 1: Resolve the true tidal-stream energy resource using unique datasets, consistent modelling framework, and state-of-the-art modelling techniques.
Global tidal resource assessments are based on coarse, data constrained, models that are not validated for the few tidal energy sites resolved, as developed for other applications (e.g. global energy budgets); therefore, the global tidal energy resource is only broadly known. Fine-scale bathymetric constrictions (e.g. coral reef passes), biological communities (e.g. flow diverted around kelp beds) and ocean currents, can all accelerate currents between constrictions; meaning many sites initially dismissed as commercially unviable may actually be suitable. A consistent modelling framework (e.g. resolution and physics), and comparison of modelling techniques, will be developed to reduce bias and determine the potential global resource.
CHALLENGE 2: How do conditions vary globally and will this change in the coming century?
OBJECTIVE 2: Realistic oceanographic conditions at potential tidal-stream energy sites for the coming century will be determined
For sustainable device design, realistic oceanographic conditions must be characterised for the lifetime of deployments, and cascaded through high-fidelity device-scale models (e.g. CFD); yet oceanographic conditions, and the impact of climate change, at tidal energy sites is largely unknown. Previously unviable tidal energy regions may become economically viable in the future (as near-resonant tidal systems and their associated currents are sensitive to sea-level rise), and, due to wave-tide interaction processes, oceanographic conditions at tidal energy sites may change. Dynamically coupled wave-tide ocean-scale models will be developed to inform the developing industry (e.g. optimal and resilient design), with new techniques that can simulate the interaction between the resource and devices.
CHALLENGE 3: Are current methods of suitable as the industry develops?
OBJECTIVE 3: Improved methods of device behaviour in resource and environmental assessment models
The industry is evolving beyond fast, shallow, well-mixed and wave sheltered sites, to areas of the world with complex oceanographic conditions (e.g. ocean currents and swell wave dominated climates). New approaches are needed to understand the interactions between devices, resource and environment. Device-scale interaction studies assume well-mixed (i.e. homogenous) channelized flows, with tidal turbine loading from waves assessed assuming waves travel in-line with tidal currents (waves following or opposing current), which is not the case beyond an extremely limited number of tidal straits (e.g. Pentland Firth). Furthermore, device interaction with the flow must also be resolved within resource assessment, beyond simplified momentum sink terms. Device behaviour and interactions will improved at both ocean and device scales.
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