Tidal and Wave Power Full of Promise in Scotland

by Erin Larsen

In the northeast-most corner of Scotland sits the future site of the world’s largest array of tidal turbines, undersea windmills turned by the waters. As the race to develop alternatives to fossil fuels continues to accelerate, ocean energy is a clean-tech holy grail. Now, with Scotland’s estimated $1.5 billion MeyGen turbine project under way, the promise of tidal energy has never been closer.

Once all the undersea cables are laid, substations are built, and 269 turbines are put in place, MeyGen will have a production capacity of 400 megawatts of power – enough to power 175,000 homes. The project is being overseen by Atlantis Resources. Continue reading

Optimizing Tidal Energy Converters

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]

https://vtechworks.lib.vt.edu/bitstream/handle/10919/49219/99-Roberts.pdf?sequence=1

 

Fish Behavior near Tidal Energy Turbines

by Cassandra Burgess

Any man-made structure in a marine environment has the potential to impact the organisms living there. Previous research has shown that fish actively avoid trawlers and boats, and that abandoned oil platforms often become a place for fish to congregate. It has yet to be determined how fish will react to the presence of tidal energy generators. This may be an important design consideration. Vietnam and Zydlewski (2014) conducted research on fish behavior at a turbine in Cobscook Bay, Maine. This bay is known for high biodiversity, and provided the chance to study a range of fish species. The study found that over 50 percent of the fish they monitored in the area interacted with the turbine in some way, and that 34.8 percent were observed to enter or exit the turbine during the 22 hours study. They also found large fish (greater than 10 cm in length) were more likely to avoid the turbine at night than small fish. At night small fish had only a 0.002 probability of avoiding the turbine, while large fish had a probability of 0.109 of doing so. Continue reading

Impacts of Tidal Energy Converter Configurations

by Cassandra Burgess

As tidal energy develops throughout the world several different designs for Tidal Energy Converters (TECs) have been developed. The main classifications are reciprocating and rotating devices, of which rotating are the most common. Within this category the TECs can be either floating and anchored to the bottom or fixed to the bottom by a rigid structure. Each of these designs has different impacts on the environment it is placed in. Sanchez et al. (2014) tested these impacts in Northwest Spain in Ria de Ortigueria by using a three-dimensional model to examine the impacts of two plants, one floating and the other bottom-fixed. The researchers found that both plants had little effect on water more than 4 kilometers away, but large impacts near the plants. The plants also exhibited very different patterns in changes in flow near the plants. Thus the authors argue that because TECs clearly have an impact on the flow of water around them, further investigation will be necessary to find the impacts of this change in flow on ecosystems. Continue reading