Description
Mocean Energy concluded the Mocean Wave Energy Converter (WEC): Blue Horizon project to complete the detailed design, build, and testing of a sea-going prototype Mocean WEC, funded by Wave Energy Scotland (WES) through its Novel WEC Programme.
The primary purpose of testing has been to gather performance data and learnings from deployment of the device in order to inform further development of Mocean’s wave energy converter designs. In addition to the power performance of the WEC, the test programme assessed the behaviour and practicalities of the mooring system and the electrical connection.
The Mocean WEC is a hinged raft that differs radically in shape from the classic symmetric twin-pontoon configuration. During the course of the project, Mocean constructed and operated a prototype 10kW WEC, named “Blue X”, with dimensions 19.3m (L) x 4.6m (W) × 7.6m (H). A notable characteristic of the prototype is that is designed to operate without connection to an umbilical. This design requirement was put in place to facilitate the testing at the performance test site. The rotation of the aft hull with respect to the forward hull drives a gearbox and then a generator. Power from the generator is then conditioned and used onboard the WEC to power local system. Power beyond that needed to power on-board systems is stored in 30 kWh of batteries. Once the batteries are fully charged, excess power is dissipated through an onboard dump resistor.
The mooring system was made of two identical mooring lines, each line consisting of an anchor clump weight then heavy ground chain, lighter riser chain followed by a 3t subsea buoy and connected to each other with further light chain and polyester line. This system allowed 360-degree yaw of the device around the swivel allowing it to self-orientate and maximising energy capture.
Location
The device was installed at EMEC Scapa Flow Non Grid-Connected Wave Test Site, to the south of Kirkwall, Orkney Island, United Kingdom.
Licensing Information
The European Marine Energy Centre (EMEC) has been accredited with the UK Accreditation Service (ISO 17025) since 2005. EMEC has been granted the consents required to install an agreed ‘envelope’ of device types at these sites.
For each developer wishing to install at EMEC’s test sites the consenting process requires the developer to produce the following documentation to accompany their Marine Licence applications, alongside the relevant site-wide environmental report and navigational risk assessment:
- Project Information Summary
- Project-specific Environmental Monitoring Programme (PEMP)
- Project-specific Navigational Risk Assessment (NRA)
- Third-party Verification/Certificate (TPV/TPC)
- Decommissioning Programme (DP)
Blue X had an installed capacity of less than 1MW and was not connected to the grid, therefore no Section 36 consent was required or Environmental Impact Assessment. In addition, EMEC test site deployments require no terrestrial planning applications. No Licence to Disturb European Protected Species or Basking Shark was required for this project, therefore only a Marine Licence was necessary.
|
Licence |
Competent Authority |
Reference |
Date Issued |
Expiry date |
|
Marine Licence (Marine Scotland Act) |
Marine Scotland |
MS-00009295 |
29/04/2021 |
30/08/2021 |
|
Marine Licence extension |
Marine Scotland |
MS-00009422 |
18/08/2021 |
30/12/202 |
Project Progress
The detailed design stage started in the January of 2019, and fabrication was completed in the spring of 2021 in Fife. The project had seen an approximate delay of 6 months due to Covid-19. Fabrication of Blue X was postponed which had a knock off effect on succeeding planned tasks and brought further delays due to replanning and resubmission of licences with revised timelines.
In detail, Blue X was constructed at Cowdenbeath and transported by road to Rosyth for final assembly and commissioning in April 2021. At Mocean’s Rosyth site, Mocean carried out the first lifts of the complete WEC. The wet commissioning and trim adjustment in the water by the addition of ballast was completed by May, before Blue X was transported by road and ferry to Kirkwall in Orkney. As built WEC mass and mass distribution was very close to design, resulting in minimal ad hoc ballast.
The WEC was transported as a whole unit on a low-loader trailer from Rosyth to Orkney via the Aberdeen freight ferry as part of the detailed route planning, which took into account dimension limits and road suitability.
It was then launched from Hatston Pier and towed to EMEC’s Scapa Flow scale test site to begin its test phase in mid-June. Blue X was installed at the test site over the course of two days; the first day was the mooring installation, and the second day was the tow and WEC hook up.
Following the installation at Scapa Flow, Blue X operated successfully for the 5-month testing period on site at Scapa Flow before recovery to the quayside in November 2021 after 154 days at sea. The WEC was briefly recovered to Copland’s Dock (Stromness, Orkney) for an electrical upgrade halfway through the 5-month testing program where operations as lifting, detachment and reattachment of WEC from moorings, and maintenance were further demonstrated and improved.
Key Environmental Issues
The seabed throughout the Scapa Flow test site is composed of flat muddy sand, with the identified biotope (loose lying mats of Phyllophora crispa on infralittoral muddy sediment) not listed on the UK Biodiversity Action Plan or the Scottish Biodiversity List.
The Scapa Flow test site is not located within any designated conservation areas, however, the site is located within a wider expanse of Orkney coastline and inshore habitats which represent, in some areas, Special Areas of Conservation (SACs) and Special Protection Areas (SPAs). The nearest protected sites are:
- Keelylang Hill and Swartabeck Burn site of special scientific interest (SSSI), 7.6 km north-northwest: moorlands which are important for density and diversity of the bird community including birds of prey and moorland breeding birds.
- Orkney Mainland Moors SPA, 7.6 km north-northwest: a site that supports populations of European importance of the Annex I species hen harrier, red-throated diver, and short-eared owl.
- Waulkmill SSSI, 7.6 km northwest: site which encompasses a wide range of nature conservation interests including a sandflat and well-vegetated shingle spit.
Key environmental areas that are requested by EMEC to be addressed in each developers environmental plans and the mitigations that were in place as part of the PEMP are presented below:
|
Impact |
Mitigation |
|
Displacement due to noise (during installation, maintenance, operation and decommissioning of device)(particularly vessel noise) |
The Scottish Marine Wildlife Watching Code (SMWWC) was adhered to. EMEC monitored noise using static and drifting passive acoustic recorders as part of the SeaWave project. |
|
Displacement due to physical presence of device |
Aggregation study was undertaken by Universities of Exeter and Plymouth. |
|
Physical harm caused by collision |
The Scottish Marine Wildlife Watching Code (SMWWC) was adhered to. |
|
Physical harm caused by entanglement in device moorings |
Mooring lines were kept onsite for as short a period as possible. |
|
Physical harm caused by noise |
The Scottish Marine Wildlife Watching Code (SMWWC) was adhered to. EMEC monitored noise using static and drifting passive acoustic recorders as part of the SeaWave project. |
|
Introduction of non-native species (via vessel or equipment) |
Local vessel and equipment was used, reducing the potential for introduction of NNS. Compliance with good practice measures. |
Papers, Reports, Research Studies
Scapa Flow Scale Site Environmental Description 2019
An acoustic survey was undertaken by EMEC in order to characterise the acoustic output of the Blue-X wave device deployed at the European Marine Energy Centre Ltd (EMEC) Scapa Flow scale wave test site. The acoustic characterisation was funded by the SEA Wave (Strategic Environmental Assessment of Wave Energy technologies) project.
As part of the same programme, an ROV and AI, baited and midwater cameras were deployed by the Universities of Exeter and Plymouth, to study to what extent the device acts as an aggregation site for fish. The official report is pending, with some initial results being shared with Mocean. Of particular interest were the aggregations of small fish (mostly juvenile cod and poor cod) around the chain and clump weights, showing how these structures can act as aggregators by providing cover, even after a relatively short time on the seabed (these shoals were not present in ‘control’ transects away from the device). Further, analysis of the baited camera videos shows significantly greater abundance of juvenile cod near the device compared to controls ~ 500m away.
Baseline Assessment: Mocean Wave Energy Converter: Blue Horizon
| Receptor | Study Description | Design and Methods | Results | Status |
|---|---|---|---|---|
| Birds | Bird characterization survey | Boat-based bird surveys conducted in Scapa Flow between June and August 2008. Supplemented with literature review. | Guillemots, black guillemots and fulmars were the species most often recorded, with greylag geese and European storm petrels in the dominant group of species on some survey occasions. Scapa Flow held the highest populations of redbreasted merganser, red-necked grebe, Slavonian grebe and European shag of all areas of search in Scotland according to Lawson et al. (2015). | Completed |
| Invertebrates, Physical Environment | Initial site selection: determining biota and sediment particle size. | Grab sampling. | Moderately low energy site. “Sheltered Muddy Gravels” and “Subtidal Mixed Sediments”. The infaunal community was composed largely of deposit feeding species (mainly polychaetes and bivalve molluscs), with only a few crustaceans present. Two common species were Lumbrineris gracilis and Thyasira flexuosa which made up approximately 10 - 20% of individuals at all stations. Aquatera conducted surveys to the west of St Mary’s on the eastern side of Scapa Flow, and reported results that are mostly consistent with the surveys conducted by Moore (2009). The observed habitat resembled the biotope “Loose-lying mats of Phyllophora crispa on infralittoral muddy sediment” (SS.SMp.KSwSS.Pcri), which is not currently list as an Annex I habitat (on the UK Biodiversity Action Plan or on the Scottish Biodiversity List) and no benthic species of conservation importance were identified at the test site during surveying. | Completed |
| Physical Environment | Initial site selection: Bathymetry commissioned by EMEC to Netsurvey Ltd. | Geophysical bathymetry survey. | Water depths ranged from 15 to 30m across the site approximately 1 m deeper than charted depths. | Completed |
| Marine Mammals | Baseline acoustic characterization (2019) | Seabed-mounted hydrophone deployments. | Background noise levels were in line with that which could be expected for this type of shallow water site. Contributions over and above these conditions were then identified, with the major contribution being the natural sounds from wind/waves and precipitation. The major anthropogenic source was shipping noise from distant static and mobile sources. Local shipping traffic also contributed to the sound field, although this was only present for around 7% of the time. Other sounds identified included a thunderstorm, aircraft and various biological sources. | Completed |
| Fish | Baseline description of fish in Scapa Flow region. | As with much of UK waters, fish studies of high spatial resolution are currently poorly represented for this part of Orkney. Despite this, it is possible to make general statements based on the location of the site, known seabed conditions, and from existing resources e.g. the Orkney Biodiversity Records Centre. | Fish species that are commonly found in Scapa Flow are typical of north Scottish waters and include pollack (Pollachius pollachius), saithe (Pollachius virens), ling (Molva molva), ballan wrasse (Labrus bergylta) and cuckoo wrasse (Labrus mixtus). Less abundant species include poor cod (Trisopterus minutes), goldsinny (Ctenolabrus rupestris), conger eel (Conger conger) and cod (Gadus morhua), which is widely distributed around Orkney in the summer months. Mackerel (Scomber scombrus) present during their migratory passage past Orkney, may also be found in the more energetic waters of Hoxa sound in the south of Scapa Flow. Other species that may be seasonally present include juvenile and non-spawning adult monkfish (Lophius piscatorius) and gurnard (Triglidae spp.). | Completed |
Post-Installation Monitoring: Mocean Wave Energy Converter: Blue Horizon
| Stressor | Receptor | Study Description | Design and Methods | Results | Status |
|---|---|---|---|---|---|
| Noise | Fish, Marine Mammals | An analysis of underwater acoustic data collected in order to characterise the acoustic output of the Blue-X wave device deployed | Two bottom-mounted acoustic frames were deployed 220 meters from the Blue-X device (Location 1: 2°57.03’W 58°53.54’N and Location 2: 2°56.60’W 58°53.44’N). Locations were selected taking into consideration other sea users and the device’s area of excursion. Each frame was fitted with a SoundTrap ST300HF recorder (5671 and 5135, deployed at location 1 and 2 respectively). | The acoustic survey undertaken showed that the SPL values reported fall below the generic threshold for behavioural disturbance of 120 dB re 1μPa SPL for continuous noise. | Completed |
| Habitat Change | Invertebrates, Physical Environment, Sediment Transport | Post-recovery survey of seabed. | A drop camera survey was taken after the removal of Mocean device to identify the "as left" state of the deployment site; the asset that has been identified and were recovered during survey. This was achieved using a Spyball drop camera. | As the deployment was of a single floating WEC attached to the seabed by means of two anchor points, there was no significant disturbance to the site during the decommissioning and removal of the device and associated infrastructure. Thus, a specific site restoration programme was not necessary. Specifically, the removal of the components constituting the device mooring system only had minimal influence in a quite limited zone and did not impact on areas to be conserved. | Completed |
| Displacement | Fish | Collect seabed biodiversity, fish biomass and marine soundscape data using baited and unbaited underwater cameras, an active acoustic echo sounder. | -Baited Remote Underwater Video deployed to seabed and left in position. Buoy at surface. -Remote Operated Vehicle navigated from static vessel. -Suspended near-surface cameras (PELAGICAM) deployed to hang midwater, with weights on seabed and buoys at surface. -Unbaited AI-driven camera system (with sound recorder) deployed to seabed and left in position. Buoy at surface. | Deployed cameras showed aggregations of small fish (mostly juvenile cod and poor cod) around the chain and clump weights, showing how Blue X can act as aggregator by providing cover, even after a relatively short time on the seabed (these shoals were not present in ‘control’ transects away from the device). Further, analysis of the baited camera videos shows significantly greater abundance of juvenile cod near the device compared to controls ~ 500m away. | Completed (waiting for final issue of report) |
| Changes in Flow, Habitat Change | Fish, Invertebrates | Biofouling and non-native species monitoring. | Growth sample was collected from the underside of the device from OIC Marine Environmental Unit. | No further work was deemed necessary as no non-native species were found. | Completed |
| Collision | Marine Mammals | Observation of marine mammals (Cetaceans, Seals, Basking Sharks). | Observations during scheduled site visits and installed WEC cameras. | There is no evidence of marine mammal strike with the system components during deployment and retrieval or with Blue X during operation. | Completed |