Energetic tidal currents occur when a tidal exchange is funneled through relatively narrow, shallow channels. The resource shares many characteristics with atmospheric winds, but with a crucial difference – tidal currents are predictable over time scales ranging from minutes to decades. The predictability of a renewable resource is the primary attractor to tidal energy development. The engineering mechanics and cost of harnessing tidal currents have seen significant research activity, but environmental and societal implications of large-scale tidal resource utilization were largely unexplored at the start of this project. Over a five-year period, the Sustainability of Tidal Energy project team at the University of Washington expanded basic knowledge in both areas.

Two commercial developments provided real-time opportunities and challenges during this project. A utility-led tidal energy demonstration project in Puget Sound, Washington obtained its final permits for operations before being abandoned due to escalating costs caused by technical challenges and socio-environmental pressures. The second development, a community-scale river energy project led by a native village in Alaska enjoyed strong local support. In a parallel development, the first commercial, grid-connected tidal energy project entered operation in Scotland, demonstrating that the end goal of large-scale tidal energy utilization is possible. This evolving backdrop of commercial development provided the research team with unique opportunities for national and international collaborations with developers, government regulators, and other researchers. As one example, graduate student participation in research symposia organized by the International Network on Offshore Renewable Energy strengthened international linkages and collaborations.

Environmental research efforts advanced methods to monitor of marine ecosystems at tidal energy sites. Research results included evaluating representative ranges of point instrument measurements, identifying extreme events that trigger increased monitoring or initiate operational modification, and objectively determining whether operating tidal turbines change the biological environment. Members of the research team also made the first measurements of acoustic particle velocity around a river current turbine using a drifting hydrophone array. Acoustic particle velocity is more likely to influence fish behavior than acoustic pressure, but is more difficult to measure. Finally, using numerical models, graduate student researchers studied flow fields around turbine arrays in realistic settings and how tidal energy extraction affects water flows in tidal channels. These results, reported in conference proceedings and peer-reviewed publications, advance the global dialogue on environmental effects of large-scale tidal energy utilization.

Societal research products from two Master’s theses included examining contrasts between technology adoption within the United States and between Europe and the United States. Researchers also conducted a survey on attitudes and knowledge of tidal energy in Washington State. Published outcomes revealed that the public is willing to support additional tidal energy research and development and has a preference for combined public-private efforts. The survey also showed that while Washington State residents were generally supportive of tidal energy, their subject knowledge was limited. This result motivated a series of Puget Sound public seminars that presented research results and highlighted tidal energy’s future role in the region. Additionally, these results, reported in conference proceedings and peer-reviewed publications, advance the nascent study of human dimensions of marine renewable energy.

Tidal energy is most economically viable in locations where topography concentrates tidal currents. This physical concentration also heightens the potential for environmental and societal conflicts. As a culmination activity, several scenarios for large-scale tidal energy development were investigated at an expert workshop. Scenario choices were guided by issues identified through the project’s environmental and societal research, and analogous external tidal energy developments. Workshop participants concluded that arrays of tidal turbines can be compatible with social and environmental priorities, particularly if array designs include holistic considerations beyond the scope of traditional engineering and economic analyses. As costs of marine energy continue to decline, tidal energy will provide substantial, sustainable, and predictable electricity to the world.

Last Modified: 12/11/2017
Modified by: Brian Polagye