Jul 16 2018

Blyth Offshore Demonstrator Array 2: A Case Study

Overview:

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Pictured: Proposed arrays for Blyth Offshore Demonstrator Arrays 2 (operational), 3 &4 (proposed). (Credit: EDF Energy)

While the original, 2 turbine, 4 MW offshore wind installation off the coast of Blyth, UK has been scheduled for incomplete decommissioning as of January, 2017 (4C Offshore, 2018) due to mechanical and cable failures, the Blyth Offshore Demonstrator Project – Array 2, a 41.5 MW installation is officially operational as of June, 2018 (4C Offshore, 2018). The Blyth Offshore Demonstrator is owned by EDF Energies Nouvelles, a subsidiary of EDF Group, and is being constructed by EDF Energy Renewables, a 50:50 joint venture between EDF Energies Nouvelles and the UK company, EDF Energy. The installation consists of 5 MHI Vestas V164 8.0 MW turbines. These incorporate a power mode uprating to 8.3MW – the largest currently available (EDF, 2017). The installation is located 6.4 kilometers off the Blyth, UK shore. The water depth at the installation site is 29-42 meters. The cost of the project was about 145 million pounds or 192 million USD, approximately 36% of which was spent in the UK. The 5 turbine system produces enough energy for 34,000 homes and save approximately 58,000 tons of carbon dioxide emissions each year. The project incorporates a host of innovations in the foundation process and the use of a 66 kV cable, the details of which will be discussed later.

History and Recent Developments:

Following approval and lease acquisition from The Crown Estate by EDF Energy Renewables in 2015, permitting, consent acquisition, site investigation, procurement, and seabed preparation, all five turbine foundations were fully installed as of August 18th, 2017 (4C Offshore, 2018). Following turbine and cable installation over the course of September through November the installation was producing power as of November 20th, 2017 (4C Offshore, 2018). A minor issue with a section of the cable array prompted the replacement of that section of cable on December 7th, 2017. The installation was fully commissioned on January 9th, 2018 and the Blyth wind farm was inaugurated by EDF Energy Renewables at the opening ceremony on June 22nd, 2018. The Blyth Offshore Demonstrator Project – Array 2 is expected to be decommissioned at the end of its 22-25-year design life in accordance with the terms of its Crown Estate lease (4C Offshore, 2018).

Innovative “Float and Submerge” Technique:

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(Credit: BAM Nuttall, 2017)

As aforementioned, this project was the first to utilize a new foundation installation technique. This process, a gravity based foundation (GBF) design method, involves floating the foundations into position at sea and submerging them onto the seabed to provide the support structures that act as the foundations for the installation of the turbine towers. (EDF, 2017) It is the first time this method has been used for offshore wind turbine installation, having previously been used for offshore oil and gas extraction. Current methods of offshore wind deployment consist of the monopile method, in which a monopile is sunk 30-60 feet into the seabed, the gravity foundation method which utilizes a large concrete or steel base, and the tripod method, in which the piles are driven, again, deep into the seabed (Whitlock, 2017). The float and submerge method has the advantage of enabling the gravity base foundations to be towed out to sea by tugboats, rather than utilizing more expensive heavy-lift crane vessels.  The design also reduces the need to use expensive marine equipment for the installation on the sea bed itself does not utilize a pile driving technique which has been proven a major source of auditory pollution in the nearshore and offshore marine environments (Peng et al., 2015).

Cable Innovation: From 33kV to 66 kV:

The project is also the first of its kind to utilize a new kind of export cable technology. From the Developers Brochure: “Blyth Offshore Demonstrator will be the first offshore wind project to use 66kV rated inter array and export cables to connect the turbines to the new onshore substation on part of the site of the former Blyth power station” (2017). In, “The Use of 66kV technology for Offshore Wind Demonstration sites”, Neumann et al. (2014) addressed the feasibility of developing a system implementing 66kV at the Blyth Offshore Demonstration site, citing several potential benefits. These include “the potential to reduce the amount of submarine cabling required, reduced losses in the connection at 66kV versus 33kV, and the potential to eliminate offshore substations in some cases.”

While intra-array 66 kV cable systems were not approved at the time this paper was written, their analysis of these benefits of the 66kV system is supported by other studies from organizations such as the Carbon Trust’s Offshore Wind Accelerator (OWA) which also showed that in addition to the benefits discussed by Neumann et al., 66kV systems “increase the power density through the cables and hence result in more cost effective cable systems” and that transmitting power back to shore at this higher voltage is also “a more efficient and cost effective option”. (Ferguson et al., 2012).

Video: 66kV cable being simultaneously laid and buried. (Credit: Boskalis Subsea cables & Flexibles, 2018)

Environmental Impact Assessment and Monitoring:

As with any offshore wind installation, rigorous environmental impact assessments were conducted before and during commission of the project. According to the EDF Energy, “The Environmental Impact Assessment (EIA) carried out by the former project owner NAREC included extensive site studies on marine ecology, birdlife, landscapes and seascape, commercial fishing and other environmental matters” (2017). According to Natural Power, a consulting firm hired by EDF Energy to conduct environmental impact surveys, “Natural Power has undertaken benthic and fish monitoring to update baseline knowledge of the environment before construction.” The firm also notes in the 2017 case study of the project, that “since consent was awarded, a Marine Conservation Zone has been designated (in part) for benthic habitats and this area includes the near shore section of the export cable route.”

Furthermore, in 2015, EDF Energy Renewables commissioned Newcastle University to “install C-pod devices at the site to monitor the vocalizations of some marine mammal groups” (EDF, 2017). These devices informed developers of what mammals are doing in the area and also provided information on the relative occurrence and distribution of porpoises and dolphins for monitoring. The devices remained at the site until 2018 (EDF, 2017). While sufficient, some recent studies suggest further monitoring could be useful in the determination of chronic environmental impacts on marine mammal populations specifically (Mann and Teilmann, 2013).

Investment:

The project is a 50:50 joint venture funded by both EDF Energies Nouvelles and EDF Energy (4C Offshore, 2018). The developers pledged approximately 36 percent of the construction cost were to be spent in the UK and a Blyth Offshore Demonstrator Community Fund was established to support local groups and charitable activities in the area. The project also played a role in testing and proving new and emerging offshore installation methods and technologies, encouraging investment in the sector (EDF, 2017).

Bibliography:

  1. Ferguson, et al. “Benefits in moving the inter-array voltage from 33 kV to 66 kV AC for large offshore wind farms” EWEA 2012
  2. P. Neumann, M. J. Mulroy and C. Ebden, “The use of 66kV technology for offshore wind demonstration sites,” 3rd Renewable Power Generation Conference (RPG 2014), Naples, 2014, pp. 1-6.
  3. EDF Energy Renewables. (2017). Blyth Offshore Demonstrator Wind Farm [Brochure]. London.
  4. Events on Blyth Offshore Demonstrator Project – Array 2. (n.d.). Retrieved July 16, 2018, from https://www.4coffshore.com/windfarms/project-dates-for-blyth-offshore-demonstrator-project—array-2-uk70.html
  5. Mann, J.; Teilmann, J. (2013). Environmental Impact of Wind Energy. Environmental Research Letters, 8, 1-4
  6. Natural, P. (2017). Natural Power – Blyth Offshore Demonstrator Project Case Study(Rep.). Natural Power.
  7. Peng, C., Zhao, X., & Liu, G. (2015). Noise in the Sea and Its Impacts on Marine Organisms. International Journal of Environmental Research and Public Health, 12(10), 12304–12323.
  8. Whitlock, R. (2017, July 13). Wind – New ?Float and Submerge? method utilised on UK offshore wind farm. Retrieved from https://www.renewableenergymagazine.com/wind/new-a-float-and-submergea–method-20170713/

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