- Dr. Brian Polagye, Mechanical Engineering
- Andy Stewart, Applied Physics Laboratory
The upcoming deployments of tidal and wave energy devices introduce both new needs and new opportunities for environmental research. While autonomous instrumentation packages are suitable for pre-installation surveys, this is not a viable approach for studies that require making observations within 1-2 characteristic length scales of an operating device or when observations have high power or data bandwidths. However, the power export cables from operating marine renewable energy devices create opportunities for cabled monitoring. In preparation for the first deployment of tidal turbines in Puget Sound, we are working with Snohomish County Public Utility District and OpenHydro, Ltd. to develop an Adaptable Monitoring Package (AMP). The AMP is also critical infrastructure for the Pacific Marine Energy Center (PMEC) where it will be used to monitor environmental changes around wave energy converters.
Figure - Preliminary AMP Layout with Instrumentation
This system will mount to a wave or tidal energy converter where it will have power and fiber connections back to shore, allowing for real-time monitoring and control. In order to perform maintenance on the instrumentation and to reconfigure the package for new experiments, the AMP is designed for recovery from and redeployment to a mount point on the converter (e.g., a socket). While marine renewable energy converters may remain in the water for several years between maintenance overhauls, the instruments on the AMP will likely require servicing every three to six months. We are developing a specialized deployment tool skid that will mate to a small inspection class ROV to fly the AMP down to its turbine mount. This system will enable recovery and redeployment of the AMP independently of the marine renewable energy converter being monitored.
The layout of the AMP is based on the specifications of the instrumentation payload, as well as the need to deploy the system in areas with strong currents and wave action. By encasing the instruments in a streamlined body, a smaller and less expensive ROV may be used for deployment operations. The primary instrumentation housed within the first-generation AMP will include:
- Stereo-Optical Camera System with Strobe Lighting for marine animal monitoring and localization with the potential for species identification.
- BlueView Acoustical Camera for marine animal detection.
- iCListen Hydrophone Array for converter sound characterization and marine mammal localization.
- Acoustic Doppler Current Profiler (ADCP) for measurements of current velocity in a tidal turbine wake.
- Acoustic Doppler Velocimeter (ADV) for measurements of turbulence.
- CTDO measurement of conductivity, temperature, depth, and dissolved oxygen.
- Chelonia C-POD measurements of cetacean echolocation (primarily porpoise and dolphin).
- Vemco fish tag receivers
All forms of power generation, including renewables, have environmental impacts and it is important to fully understand impacts for rationale cost-benefit analysis. Because tidal hydrokinetic energy is a new form of marine renewable energy, our understanding of potential environmental impacts is evolving. Environmental effects are the broad range of potentially measurable interactions between tidal energy devices and the marine environment. These may occur during device installation, operation, maintenance, decomissioning, or an accident. Boehlert and Gill (Oceanography 2010) talks about these interactions in terms of stressors from the devices (e.g., noise) and receptors in the marine environment (e.g., marine mammals). These stressors may be categorized as follows (Polagye et al. 2010):
- Presence of device: static effects - stressors caused by the presence of the device and foundation, including new structures in the water column and disturbances during installation and/or removal.
- Presence of device: dynamic effects - stressors caused by the operation of the device, including blade strike, entrainment, impingement, and the device wake.
- Chemical effects - stressors due to contaminants from lubricants, paints, or coatings.
- Acoustic effects - stressors from noise due to device operation and/or installation.
- Electromagnetic effects - stressors from electromagnetic fields associated with the generator and power electronics on a device and/or power cable.
- Energy removal - stressors, primarily on the far-field environment, which are a consequence of energy removal from tidal systems.
- Cumulative effects - stressors arising from a combination of other stressors and/or multiple sites developed in the same geographically connected body of water.
Because each stressor and receptor has multiple elements (e.g., injury, behavioral change for a fish) there are literally thousands of potentially measurable interactions. And it is infeasible to attempt to monitor all of these during pilot projects. Prioritization based on the best possible information and expert opinion has been recommended as one path forward (Polagye et al. 2010). Using this prioriziation, monitoring (both before and after turbines are installed) is targeted at potential environmental impacts, those environmental effects which rise to the level deleterious ecological significance. If environmental impacts are identified, then these should be mitigated against.
NNMREC (UW and OSU), Pacific Northwest National Laboratory, NOAA Marine Fisheries, and Washington Sea Grant organized a workshop in March 2010 to develop a better understanding of the environmental effects of tidal energy and its potential environmental impacts. Further information may be found on the workshop website.
Industry Challenge: A critical unknown for large-scale operation of in-stream turbines are estuary-scale environmental effects. Estuaries are ecologically sensitive areas facing a host of human pressures and in-stream turbines must be deployed in a manner that does not exacerbate existing problems or cause new ones. Energy extraction through tidal power generation may change the energetic characteristics of an estuary and impact flushing and water quality. Substantial energy extraction from an estuary may result in reduction of the tidal range, which may affect the extent and the character of sensitive near shore habitat areas such as tidal flats. Finally, altered flow patterns around the device themselves may affect migration patterns of marine creatures as well as patterns of sedimentation and the benthic habitat These unknowns are of utmost concerns to regulators, as well as the citizens of the community contemplating tidal power generation who need to evaluate trade-offs between substituting for non-renewables and preserving the regional environment.
Approach: The University of Washington has performed leading edge work on estuary-scale environmental effects from in-stream extraction (Polagye et al. 2008). The Center proposes to further leverage its oceanographic expertise to address broad environmental concerns, such as estuarine circulation, basic biological productivity, and dissolved oxygen (Edwards et al. 2007). The Center will work with scientists and regulators to establish at which point in the scale of implementation the estuarine-scale impact becomes relevant, and to relate this to ecosystem-level concerns such as biological productivity and dissolved oxygen levels in water. These will help inform regulatory decisions on appropriate types of monitoring and studies and allocation of scarce resources.
Outcomes and Impacts:
- Research: Improved understanding of estuarine dynamics and implications for turbine operation.
- Industry: Critical points for turbine impact on estuaries to determine reasonable deployment size.
- Regulatory: Guidance on appropriate environmental monitoring at various phases of array build-out.
Characterization of the interactions between marine animals and tidal turbines requires the ability to identify marine animals and quantify their position relative to the turbine. We have developed a custom camera system to provide optical and acoustical imagery of the near-field environment of a tidal turbine, that addresses the site-specific conditions at tidal energy sites (e.g., depth, turbidity, ambient light levels, and current velocities). This system incorporates two optical cameras for stereo imaging, four strobe lights for artificial illumination, an acoustical camera for target detection, and the necessary power and media conversion electronics for a cabled connection to shore. Stereo-imagery allows for quantifying of both the size of targets and their position in 3D space. Both the readily interpretable nature of these optical images and the quantification possible with stereo imaging will play a crucial role in the identification of the various marine animals that may be ear a tidal turbine.
Figure - Prototype Stereo-Optical Camera System
Optical camera calibrations and evaluations of target tracking abilities were conducted in a salt-water pool in the Oceanography Department at the university.
An initial evaluation of the camera system was performed in August 2012 at the Admiralty Inlet site by deploying the system from the RV Jack Robertson on a 5-meter tall test frame. The results of these tests are described in a conference paper presented at the MTS/IEEE Oceans 2012 conference. This deployment allowed us to evaluate the system performance at a proposed turbine site and determine an appropriate mounting position for the cameras relative to the operating turbine.
Figure - Camera Test Frame on the deck of the RV Jack Robertson
In order to evaluate the endurance of the system (e.g., ability to resist biofouling) and determine an appropriate maintenance interval, the camera test frame has been deployed off of a dock near Edmunds, WA for the spring and summer of 2013. During this test the system is cabled to shore and imagery is collected at regular intervals to evaluate the system performance over time.
Best of Endurance Test Imagery: Picasa Web Album
- Brian Polagye, Mechanical Engineering
- Jim Thomson, Applied Physics Laboratory
- Peter Dahl, Applied Physics Laboratory
The installation, operation, maintenance, or removal of a device from the marine environment will create anthropogenic noise. Because marine mammals and some fish are senstive to loud noise, it is important to quantify the noise generated by operating devices and be able to make pre-installation predictions of the area ensonified by device operation.
These efforts are closely tied to site and device characterization activities.
Figure - Estimated M-weighted received sound pressure levels for mid frequency cetaceans (dB re 1uPa) in the vicinity two hydrokinetic turbines operating at rated power in northern Admiralty Inlet, Puget Sound, WA. Black line denotes the 120 dB re 1uPa isobel (NMFS harassment threshold). White lines denote 1000 m contours from the project center point.