Low Density Tidal Energy Arrays Minimize Impact

by Cassandra Burgess

The configuration of a tidal energy array partially determines the level of environmental impact. In determining the optimal configuration for a particular area, it is important to consider not only power output, but also environmental impacts. Fallon, et al. discuss the impacts of a tidal energy array located in Ireland in their 2014 paper. They use a two dimensional model and average speeds over the depth of the channel. This simplifies the modeling process, but it also overestimates some of the impacts. They then analyze grid spacing for turbines, with turbines spaced 0.5, 2, and 5 times their diameters apart. The model indicated that the 5 diameter spacing had the least environmental impact. It decreased velocities by 19.9% less than the 0.5 diameter spacing outside the grid, and increased flood velocities by 27.3% less. The 5 diameter spacing also changed the tidal range of heights by only 1% while the 0.5 diameter changed them by 6.4%. Because the 5 diameter spacing has significantly less impact on the hydrodynamic environment around the turbines, the authors conclude that it is desirable to use low density arrays when possible. Continue reading

Marine Energy Device Mooring and Foundation Designs

by Cassandra Burgess

The deployment of marine renewable energy (MRE) devices requires new approaches to offshore mooring and foundations. Mooring and foundations are essential components of MRE device structures, enabling a device to remain in one spot while responding to the movement of tides or waves. Foundations and moorings often account for up to 10% of the total cost of building and maintaining an MRE device; designing a foundation of mooring that can be built at minimal cost requires analyzing the site characteristics, the direction and magnitude of forces on the device, and responses of different technologies to these forces, and the ease of installing and decommissioning the device. These steps present a novel challenge for MRE devices, because such devices have different requirements than traditional offshore technologies. One of the main challenges in applying traditional technologies to this problem is that MRE devices often need to be able to move. This is because the response of the device itself to tides and waves, which is necessary for energy production, is generally linked to the response of the foundation or mooring system. Thus these systems are required to endure loads both horizontally and vertically and to move with the device in some cases. This differs from more common offshore technologies, such as drilling platforms, where movement is not desired. Because of this novel challenge, Karimirad, Koushan, Weller, Hardwick, and Johanning suggest in their 2014 paper that new guidelines need to be developed to aid in the design of MRE device structures. Continue reading

Clean Current Utilizes Marine Tidal Turbines to Produce Renewable Energy

by Mariah Valerie Barber

Clean Current Power Systems Incorporated is a private company based in British Columbia that focuses on hydrokinetic power generation. Specializing in marine energy engineering, Clean Current was the first company to use a tidal turbine or marine turbine energy. Clean Current’s tidal turbine utilizes the same basic framework used by the standard river in-stream turbine, only the company has incorporated bi-directional technology that allows the turbine to change directions automatically depending on the movement and direction of the tides. Clean Current’s tidal turbines are predicted to last up to 25 years and are able to be placed in marine areas from 7 to 25 meters in depth. Continue reading

Accuracy of Models for Wind and Tidal Turbines

by Cassandra Burgess

Computation Fluid Dynamic models are used to investigate the influence of rotating wind and tidal energy generator turbines on the surrounding environments. Johnson et al. (2014), compared current analytical and numerical models and experimental findings to a new computational fluid dynamic (CFD) model, and found that the CFD model agreed well with a simple conservation of momentum model, but did not closely match the experimental and numerical findings on reactions to the spinning turbines. This result was especially pronounced far from the turbine. The numerical and experimental findings predict much more turbulence downstream from a turbine, and larger changes in velocity. Continue reading