by Cassandra Burgess
In order to make tidal energy converters economic enough to compete in the energy market, it is essential to build them as efficiently as possible, but also important to design them to avoid environmental impacts on the habitats in which they are installed. These impacts can be more difficult to predict when planning an array of tidal energy converters than a single turbine. Roberts, Nelson, Jones, and James worked to solve these two problems by creating a modeling framework that optimizes the placement of tidal energy converters in Cobscook Bay, Maine. The model uses restrictions on water height and velocity based on the region so it can be applied to other regional sites as well. It also allows researchers to input environmental restrictions on the decrease in velocity due to the turbines, and on changes in the bed shear stress at the site. These constraints represent points at which the turbines might change fish behavior by causing fish to congregate in the turbine wakes, and at which erosion of the ocean floor becomes serious. Using these restraints the researchers found that the non-environmentally constrained system had an output 19% higher than the originally planned placement, and the environmentally constrained system had an output of 16% higher.
For the purposes of this modeling process the environmental constraints were set arbitrarily. In future models, research would be necessary prior to the planning of the tidal energy converters to determine what levels of change the ecosystems could reasonably withstand. Once this is determined, the model can optimize the placement of tidal energy converters while minimizing the environmental impact. This model differs from previous models because it is on a much finer scale. While previous models have been able to accurately predict the impacts of tidal energy converters on a broad scale, this model looks at the fluid dynamics near the turbines themselves. This improvement allows for analysis of the environmental impacts near the turbines, as well as for better information on the turbulence and velocity changes created, both of which affect the power output of nearby turbines. Because this model was able to optimize both energy output and environmental impact, two areas most concerning when constructing a tidal energy array, the researchers recommend that it be used in the planning for future array sites.
Roberts, Jesse, Nelson, Kurt, Jones, Craig, James, Scott, 2014. A Framework for Optimizing the Placement of Current Energy Converters. 2nd Marine Energy Technology Symposium, April 15-18, 2014. [GSSS: Optimization Tidal Roberts]