By Becky Childs
Supporting marine renewable energy (MRE) research with live data from buoy networks The nearshore and offshore regions running from the shallow coastal shelf to the intertidal zone are dramatic, tempestuous and extremely complex environments that offer the potential to reliably provide vast amounts of renewable energy to most coastal countries in one form or another. In order to be able to harness this capability safely and efficiently it is critical that we continue to expand our knowledge and understanding of the hydrodynamics of these environments.Read more
The nearshore and offshore regions running from the shallow coastal shelf to the intertidal zone are dramatic, tempestuous and extremely complex environments that offer the potential to reliably provide vast amounts of renewable energy to most coastal countries in one form or another. In order to be able to harness this capability safely and efficiently it is critical that we continue to expand our knowledge and understanding of the hydrodynamics of these environments.
The ocean offers huge possibilities for generating electricity from waves and tides, and the UK is very well placed to exploit this form of electricity generation. Marine renewable energy is of particular interest in Wales, where the unique coastline offers significant capacity to generate MRE as there are areas with high tidal ranges that are ideal for tidal lagoons in addition to fast tidal currents for tidal stream energy and regions exposed to substantial wave action, required for wave energy devices.
The SEACAMS2 project is a collaboration between Bangor University and Swansea University that supports research and innovation in applications of marine renewable energy, climate change resilience and resource efficiency, and is part funded by the European Regional Development Fund. Data, products and services resulting from SEACAMS2 collaborative research in the Marine Centre Wales, home to the Centre for Applied Marine Sciences (CAMS), will be available to marine industries, government and scientific users and the general public via the Integrated Marine Data and Information System (iMarDis) data service which offers a single point of access.
Figure 1 -- Acoustic transceiver and CTD package in buoy moonpool (photo: Martin Austin, 2018).
Their data assist our understanding of how we can generate electricity from the waves and tides and how we can quantify that resource, help predict how this resource may vary in the future as a result of climate change, identify regions that are ideal for each energy type, and minimise the impact on the environment of this process of energy generation including the effects of any turbulence on devices and the surrounding ecosystem.
Ocean Scientific International Ltd (OSIL) worked with Bangor University to provide a network of three telemetered data buoys for the collection and measurement of oceanographic, meteorological and water quality data parameters around the coast of North Wales for the SEACAMS2 project.
The buoys were required to provide a data link from existing packages of seabed-mounted instrumentation located directly below the platforms to an instantly accessible web portal, from where the data can be integrated into existing CAMS IT infrastructure and disseminated to the public via iMarDis. Deployed for an initial period of two years, the buoy network will remain in-situ for at least a further year as a result of a no-cost extension to SEACAMS2 and could potentially remain deployed indefinitely if funding allows for a future extension.
Figure 2 -- Seabed instrument package consisting of multiple acoustic instruments sampling hydro- and sediment dynamics from the benthic boundary layer to the sea surface (photo: Graham Worley, 2018).
Establishing the link
The benthic instrument packages are deployed in energetic and shallow nearshore coastal locations that are potential sites for energy extraction. Each is furnished with a range of Nortek equipment including an AWAC directional wave and current profiler, an Aquadopp HR profiler to sample the benthic boundary layer for sediment transport and turbulence studies and a Signature 1000 AD2CP current profiler providing high-resolution current and turbulence data.
These coastal observatories measure: wave-driven currents; wave spectra; integrated wave parameters (period, frequency, amplitude, wavelength, and speed); tidal currents; turbulence; water surface elevation and sediment dynamics. These readings allow the hydrodynamic profiles of the deployment locations to be studied in great detail to assess their feasibility for MRE developments and their optimal siting. Some of the instruments are self-logging, and are retrieved at regular intervals to recover data, but others are real time instruments sampling in bursts and provide NMEA data strings of wave parameters, in addition to three-dimensional current speed at multiple elevations above the seabed, every 30 minutes.
The data buoys interrogate the real-time seabed instruments using an acoustic modem to avoid introducing unnecessary cabling that could be damaged in the dynamic deployment conditions, and data from the sensors are received into the data logger that is integrated into the electronics system of each buoy. The buoys have also been provisioned for the mounting of an anemometer and a CTD, and additionally report data from these instruments in conjunction with transmitting ancillary data from the on-board power system and sensors.
The data are relayed via a dual telemetry system, comprising a GPRS modem, which can be used if there is sufficient network coverage at the installation locations, and an Iridium modem which is used in place of the GPRS modem if coverage is poor and transmits the data as Short Burst Data (SBD) messages. Cellular coverage could not be guaranteed in the deployment locations, so the synergistic telemetry solution from buoy to shore provides a highly reliable, low latency solution, which can accommodate the integration of various instruments with NEMA, RS232, RS485 and SDI12 outputs (amongst other industry standard protocols).
Figure 3 -- Buoy deployment in Colwyn Bay from RV Prince Madog (photo: Martin Austin, 2018).
Maintaining the connection
The robust and stable 1.9 m data buoys were selected for their high reserve buoyancy and their ability to endure harsh conditions and exposed coastal locations, but they require regular management checks like any other deployed equipment to ensure that the systems functionality is not impaired. Easy access to the buoy power system and electronics for maintenance was provided by a secure service door in the top section, and the moon pool, which is formed by the central steel structure of the buoy and provides a protected area for the installation of surface instruments, can also be accessed through the top frame. The waterproof electronics housings and all cables were equipped with wet mateable subsea connectors to simplify in-field servicing.
To ensure that the buoys are self-sufficient with respect to power during long winter months OSIL developed a tailored power system comprising an array of high-power solar panels, a solar regulator and a battery bank fitted to each buoy top section.
The mooring systems were designed for the specified locations to accommodate a wide variation in mooring requirements, including mean water depths ranging from 10 to 50 m and tidal current speeds of 3.5+ knots There is an emphasis on damping the effects of waves on the buoy and providing shock absorption in extreme weather conditions as these harsh Irish Sea locations see 6 m tides and a maximum wave height of 7 m with two sites exposed to the prevailing south-westerly winds, and one to northerly winds.