Abstract
As a result of ongoing climate change, the pressure for the development of new sources of renewable energy has increased. It is extremely likely that climate change is caused by anthropogenic activities. Thus even if dramatic gains are made in energy efficiency; the addition of novel renewable energy sources is critical to reducing fossil fuel emissions. Even current goals for a reduction in the growth of greenhouse gas emissions mean that all possible low-carbon or non-carbon emitting energy sources be considered. In the marine environment, energy in tidal currents, waves, and thermal structure may be extracted to produce electricity. These energy sources are a critical element in the overall renewable portfolio since, unlike wind and solar energy, both marine thermal and tidal energy are reliable additions to the overall electrical grid. In the case of tidal energy, the contribution of periodic but reliable sources of renewable energy becomes increasingly critical as wind and solar penetration in the grid increase. In a high renewable energy penetration grid, a resource like tidal energy does not provide the same base load capacity as, for example, a nuclear power plant. However, tidal energy can have the effect of reducing the size of either storage or peaking capacity that is required for grid stability by providing power for recovery of dispatchable loads. However, as an immature technology, significant questions remain regarding basic questions like the scale of the potential resource, the impact on sediment transport, the effects on fish populations and communities, and the ability to design a system which is acceptable by the people in the associated communities.
The objectives of the funded project were to examine tidal power development in Maine from all perspectives: engineering, resource assessment, biological effects, and social dimensions. Resource and environmental research focused on data collection for the Cobscook Bay/Western Passage, possibly the most viable commercial tidal energy site in the US, tidal power sites along with initial evaluation of the suitability of the approach for at least two other tidal development sites in Maine. Concomitantly, alternative energy research is used as a basis of education for a number of graduate and undergraduate students at the University of Maine and Maine Maritime Academy. The Maine Tidal Power Initiative has developed resource and environmental assessment protocols in conjunction with the deployment of a specific marine hydrokinetic device. The protocols are transferrable throughout Maine and the US to evaluate tidal energy resources and better understand the potential impact of this development on the environment. Again, site-specific social science and environmental research focused on the Cobscook Bay/Western Passage area near Eastport Maine. The protocols and methods developed at these sites have also been used to perform initial scoping reviews of locations in Castine Harbor and Wiscasset, Maine that represent a more modest and more typical small scale energy resource.
Specific barrier issues which have been addressed for the industry are technologies and protocols for measuring and modeling tidal flows, responses of fishes to those flows, and people interacting in these environments. Measuring tidal flows is critical to the key economic driver for this industry, the size of the potential resource. The second barrier issue is the need for methods for measuring the impact of marine hydrokinetic (MHK) devices on fish. Acoustic methods have been used with ground truth validation from trawls. The protocols developed in this project have already had a significant impact on the approach that has been taken at other sites. Finally the assessment of the human community response to these technologies and impact on community cohesion and participation is perhaps the largest single barrier to the acceptance of the projects. This work also has the potential to be replicated at other sites, although in both the case of the environmental effects and the social response to these projects, details of the species impacted and the economic and social environment are the ultimate determinants of impact and acceptance.
The technology focus for most of this work has been the cross-flow turbine developed by Ocean Renewable Power Company. Testing in the University of Maine tow tank has allowed a large design space to be explored for the optimization of the commercial turbine design. The design code developed for the project was validated using this data set. Both the design code and the data will be placed in a public repository. The most important outcome of the turbine design portion of the work is some general design parameters that can be used to assist in the site assessment and for benchmarking of proprietary designs. The design as well as the data is available for resource assessment and design comparisons. The appeal of this turbine design is that the potential exists for a low solidity turbine with lower tip speed ratios, which will have good performance. The low solidity and tip speed ratio is likely to reduce the risk of fish impacts and thus reduce environmental impact and community resistance to these technologies.
The need for low carbon energy sources is undeniable. Resistance to large-scale renewable energy development also continues to increase. The overall approach to this project, where the design of the system considers environmental impacts and social acceptance from the initial engineering design stages and continues with an adaptive management scheme, is the only option for addressing energy needs at the scale required.