International Marine Energy Journal

Effects of small marine energy deployments on oceanographic systems

2023-03-14T18:13:16+00:00

The placement and operation of marine energy deployments in the ocean have the potential to change flow patterns, decrease wave heights, and/or remove energy from the oceanographic system. Changes in oceanographic systems resulting from harvesting marine energy, particularly tidal and wave energy, may be of concern. These changes include alterations in nearfield and farfield physical processes, as well as potential secondary environmental effects such as changes in sediment transport patterns, biological processes, or coastal erosion. Knowledge of changes in oceanographic systems associated with marine energy is primarily available from numerical modeling studies, informed by some laboratory tests and very few field measurements. A literature review was conducted using the Tethys knowledge base and other online sources, building on conclusions from the Ocean Energy Systems-Environmental State of the Science report. Potential changes in oceanographic systems that may be caused by marine energy differ between tidal and wave devices because of different extraction mechanisms and siting locations. Numerical models show that tidal extraction on the order of hundreds of megawatts or with significant channel blockage is required to create changes in oceanographic processes that exceed natural variability. Effects from wave energy extraction in arrays are localized and dependent on array spacing and proximity to the shore. Available evidence supports the conclusion that the risk of significant environmental effects from such changes could be retired (i.e., less investigation required for every project) for small deployments—those representative of the state of the industry in 2021. Determining changes in oceanographic systems to be low risk for small deployments can thereby streamline environmental consenting by reducing monitoring needs at this early stage in the industry.

Engaging the Regulatory Community to Aid Environmental Consenting/Permitting Processes for Marine Renewable Energy

2022-07-26T14:52:15+01:00

Regulators involved in consenting/permitting marine renewable energy (MRE) have faced multiple challenges due to relatively new, unfamiliar technologies and uncertainty surrounding potential environmental impacts. This has resulted in slow progress for the MRE industry, including long consenting timeframes and extensive and expensive monitoring requirements, which increase financial risk for investors. OES-Environmental has surveyed regulators internationally to understand their key knowledge gaps and perspectives to support the development of the MRE industry. From the results of these surveys a data transferability process and a risk retirement pathway have been developed to assess consenting and monitoring requirements in proportion to risk. A tool for discovering existing data sets by using an online matrix has been developed, along with training materials, regulatory guidance documents, and a strategic outreach plan to engage regulators and advisers. his engagement and the application of these products should lead to a better understanding of the environmental effects of marine energy, and more efficient consenting processes.

Environmental and Social Acceptance module: reducing global and local environmental impacts for Ocean Energy Projects

2022-04-04T23:37:49+01:00

Designing reliable ocean energy devices with reduced costs is crucial for the sector’s development. This development of renewable energies should also be implemented in a sustainable manner and not cause additional environmental stress and related damage. In order for the ocean energy sector to consider environmental impacts at the earliest stage of concept creation, the Environmental and Social Acceptance (ESA) module was developed and included in an integrative suite of design and assessment tools (namely DTOceanPlus) to support technology innovation processes. Several complementary features were developed in the ESA module which provides insight into impacts at different levels. At local scale, environmental impacts are assessed in relation to the different design choices using thirteen functions (i.e. Footprint of the array, Collision risk with devices, Collision risk with operating vessels, Energy modification, Reef effect, Reserve effect, Resting place, Chemical pollution, Turbidity, Temperature modification, Electrical fields, Magnetic fields and Underwater noise) that cover various potential pressures induced by the ocean energy array. Moreover, surveys and mitigation measures are provided regarding endangered species potentially present. At global scale, a life cycle assessment is conducted to evaluate the carbon footprint of a project in terms of its contribution to global warming and the cumulative energy demand. Two reference models were used to exemplify the use and relevancy of the different features. Overall the ESA module provides insight and support to the ocean energy sector to achieve sustainable development of marine renewable energies.

Dynamic Characterization, Flow Modeling, and Hierarchical Control of an Energy-Harvesting Underwater Kite in Realistic Ocean Conditions

2022-03-07T17:08:33+00:00

This paper presents a hierarchical control framework for a
kite-based marine hydrokinetic (MHK) system, along with a detailed characterization of the dynamic and energetic performance of the system under realistic flow conditions. The underwater kite, which is designed to be deployed off of an offshore floating platform, features a closed-loop controller that executes power-augmenting, cyclic cross-current flight. The robustness of the kite's undersea flight control algorithm is demonstrated in a realistic four-dimensional flow model (which captures both low-and high-frequency spatiotemporal variations in the current) that accounts for turbulence and wave effects, which is coupled with a detailed dynamic model that captures the six-degree-of-freedom kite and floating platform dynamics, in addition to the tether dynamics. Using data obtained by the Coastal Data Information Program (CDIP) 192 Oregon Inlet buoy [1], wave data from the Wave Information Studies Hindcast model [2], and a spectral turbulence model developed at Florida Atlantic University, we demonstrate the robustness of the kite's control system and the sensitivity of both average net power output and peak-to-average power to wave parameters. In common wave conditions, the average and net power output are shown to be highly robust to the peak period and significant wave height. In extreme wave conditions, the peak-to-average power ratio is shown to be highly positively correlated with an effective wave energy density metric, which characterizes the wave energy density presented to the kite system based on a weighted distribution along depth of the kite.

A Linear hydrodynamic model of rotating lift-based wave energy converters

2023-04-06T08:01:01+01:00

A linear potential flow model of a rotating lift-based wave energy converter is developed by assuming that the lift is generated by a pair of equal and opposite circulations and that the amplitude of motion is small. The linearisation of the hydrodynamics means that the forces can decomposed and expressions for the wave excitation force and radiation damping force are derived independently and shown to be related to each other through the Haskind Relations. The expressions for the forces are used to show that there is an optimum phase and product of circulation and radius of rotation to maximise the wave power extracted, which is equivalent to the optimum phase and amplitude of motion from ‘conventional’ wave energy converter theory. It is also shown that at this optimum condition 100% of the incident wave energy can be extracted. It is shown that the forces are directly proportional to the velocities due to the motion of the vortices, the water particle velocities due to the incident wave, and the water particle velocities induced by the vortices. The effect of the vortex-induced water particle velocities is considered and the importance of including these velocities on the passive generation of circulation, e.g. by hydrofoils, is highlighted. The impact of a sub-optimum product of circulation and radius of rotation is also investigated and shown that the power capture is not highly sensitive to the optimal conditions in the same way as ‘conventional’ wave energy converters