Jul 08 2015

London Array Wind Farm

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Introduction

The London Array wind farm off the coast of the United Kingdom is the largest offshore wind turbine array in the world, consisting of 175 wind turbines producing 630 MW of power. Inaugurated on July 4, 2013, the London Array recently celebrated its second-year anniversary holding that title, and looked to the future to expand and cross the 1 GW line (1000 MW), though opposition has brought setbacks and halted any plans for growth. Safety for local birds, the red-throated diver in particular, has introduced debate over the environmental impact of the turbines and brought all planning to a standstill.

Aerial View of London Array. Courtesy of Incisive Media.

Aerial View of London Array. Courtesy of Incisive Media.

Initial Development and Construction

In 2002, a research paper was published by The Crown Estate documenting a future strategy for expanding offshore wind energy in the United Kingdom (UK). The paper, Future Offshore: A Strategic Framework for the Offshore Wind Industry, presented the need for sustainable renewable energy, possible locations for wind farm development, developmental lease agreements, financial allocations, and legal frameworks for development past territorial waters (UK DTI 2002). Extensive research was completed for possible locations and it was decided that a distance of 20km offshore would provide the most cost effective utilization. A few years later, The Crown Estate awarded the 50-year lease to a group of renewable energy developers: E.ON UK Renewables, Shell Wind Energy, and CORE Limited, though Shell and CORE would later sell their shares in the project.

Thames Estuary & London Array. Courtesy of NASA.

Thames Estuary & London Array. Courtesy of NASA.

The location chosen was just over 20km off the coast of Kent, England in the outer Thames Estuary, cited for high wind speeds, suitable ground conditions, and the multiple surrounding ports, which would give greater access for construction (London Array). Construction of 175 wind turbines and 2 offshore substations began in March of 2011 and would take over 5 million man-hours to complete (London Array). These 177 monopiles, as well as the onshore substation at Cleve Hill, represent Phase One of the London Array Project. The monopoles measure 68m tall and can weigh up to 716 tons. On top of the monopoles, transition pieces are placed of varying lengths and weights, up to 28m long and 330 tons. The water depth of each turbine can vary based on tides from a few feet to 25m (London Array).

 

Proposed underwater cable layout

Proposed underwater cable layout, London Array Marine Environmental Monitoring Plan

 

All of the 175 wind turbines were supplied by Siemens Wind Power. They are the G4 Platform turbines—SWT 3.6-120, which stands for Siemens Wind Turbine, 3.6 MW, 120m diameter. The hub of the rotor stands at 87m above sea level and each turbine features three rotors of 58.5m in length (Siemens 2014). The total coverage area for a single turbine is 11,300 . The maximum output of each turbine is 3.6 MW, so the total for all 175 equals 630 MW, enough power for close to 500,000 homes (Whiting 2013). Since completion of this project, Siemens has introduced a larger 130m diameter turbine capable of delivering 4.0 MW of power (Siemens 2014).

Construction continued through 2012 and in October of that year, the Cleve Hill substation was commissioned, and the first power was generated. The final turbine was installed in December of 2012, with all 175 turbines confirmed operational April 2013. On July 4, 2013, Prime Minister David Cameron formally inaugurated the London Array Wind Farm. The cost of the project was €2.2 billion, around $2.86 billion USD at the time.

Cleve Hill Substation. Courtesy of London Array

Cleve Hill Substation. Courtesy of London Array

Operations

Each wind turbine can start generating electricity at a minimum wind speed of 4 m/s (8.9 mph) and will reach full power at 13 m/s (29 mph). If wind speeds surpass 25 m/s (55 mph), the turbines will automatically shut down for safety reasons. The turbines are designed to run 24 hours a day for 20 years, and are serviced by technicians regularly (London Array). The turbines are connected to each other and to one of the two offshore substations, which then travels to the Cleve Hill onshore substation, where it is transferred directly into the UK power grid.

At maximum capacity, the London Array Wind Farm can generate 630 MW of power, enough to power 490,000 homes in the UK. According to the project information guide, this reduces production by over one millions tons every year (London Array).

Environmental Impact

As with any new development but especially with the planning of renewable energy, countless environmental impact studies were completed prior to any construction. Maintaining a healthy and safe environment for marine and land organisms is of the highest importance when developing renewable energy, and the impact on habitats, migration behaviors, feeding locations, breeding grounds, and ecosystem health had to be considered and any consequences had to be mitigated. Some consequences are positive, such as the removal of emissions that would otherwise be introduced from other energy sources. But some consequences are very harmful, like possible migration impedance by the rotor blades, or breeding ground relocation from onshore substation construction. According to one study, construction of the Cleve Hill substation was to take place only between the dates of April to September to minimize infringement of the breeding season of the Marsh Harrier, a sensitive bird species of the area (Proudler 2007). Construction of drainage ditches and trenches for the power cables was closely monitored and completed in a similar pattern to that mentioned above to mitigate infringement of the breeding season of Bearded Tits and Water Voles (Proudler Annexes 2007). Nest boxes were built for the Bearded Tits, and a follow-up study documented that 42% of the constructed nest boxes were utilized regularly by the birds (Wilson 2005). Rare plant species were documented and monitored; the seeds from Whilst Least Lettuce (Latuca saligna) and other rare or scarce species were harvested in the event that construction wiped out the species (Proudler Annexes 2007). Many other species of fish, amphibians, birds, and mammals were closely studied and minimization of ecological impact was attained.

London Array Today

Current stake holders of the wind farm include DONG Energy with a 25% stake, E.ON UK with a 30% stake, Masdar with a 20% stake, and as of January 2014, La Caisse de dépôt et placement du Québec holds a 25% stake (bought from DONG).

Phase 2 expansion of the wind farm was set to add an additional 370 MW, bring the total power generation to 1 GW (1,000 MW), though government constraints brought the expansion down to a 240 MW addition, and in February of 2014, the Phase Two expansion plan was cancelled due to environmental concerns. A government assessment of the impact on the migratory patterns of the Red-Throated Diver would require monitoring through 2017, and even then would not guarantee a go-ahead for expansion. The lease for Phase Two development has been voided at this time and no plans to further expand the London Array wind farm are expected in the future. Regardless of future growth, the London Array remains a modern marvel as the largest wind turbine array in the world, and sets a benchmark for continued development of renewable energy sources.

 

Sunset view of London Array turbines. Courtesy of London Array.

Sunset view of London Array turbines. Courtesy of London Array.

 

Resources

  1. Henson, K. Pre-construction Marine Environmental Monitoring Plan: London Array Offshore Wind Farm. February 2010. London Array Ltd. Accessed 6 July 2015. Available at: http://www.londonarray.com/downloads/surveys/LAL-EMP-Preconstruction.pdf
  2. London Array: The World’s Largest Offshore Wind Farm. London Array Limited. Accessed 6 July 2015. Available at: http://www.londonarray.com/wp-content/uploads/London-Array-Brochure.pdf
  3. Proudler, T and Henson, K. Annexes to the ecological mitigation and management plan. London Array Offshore Wind Farm Project and Associated Grid Connection Works. 2007. Accessed 6 July 2015.Available at: http://www.londonarray.com/downloads/surveys/o071025%20EMMP%20Schedules.pdf
  4. Proudler, T and Henson, K. Ecological Mitigation and Management Plan: London Array Offshore Wind Farm Project and Associated Grid Connection Works. October 2007. London Array Limited. Accessed 6 July 2015. Available at: http://www.londonarray.com/downloads/surveys/o071025%20EMMP%20Main%20Body.pdf
  5. Siemens: Siemens G4 Platform – 3.6 MW and 4.0 MW geared wind turbines. Siemens AG Energy Sector. 2014. Accessed 5 July 2015. Available at: http://www.energy.siemens.com/hq/pool/hq/power-generation/renewables/wind-power/platform%20brochures/G4%20Offshore%20brochure_English_Apr2014_WEB.pdf
  6. UK Department of Trade and Industry. Future Offshore: A Strategic Framework for the Offshore Wind Industry. Report by UK Department of Trade and Industry (DTI). 2002. Accessed 6 July 2015. Available at: http://tethys.pnnl.gov/sites/default/files/publications/A_Strategic_Framework_for_the_Offshore_Wind_Industry.pdf
  7. Whiting, J. London Array is Inaugurated as the World’s Largest Turbine Array. 12 July 2013. Tethys. Accessed 6 July 2015. Available at: http://tethys.pnnl.gov/blog/london-array-inaugurated-worlds-largest-turbine-array
  8. Wilson, J. Nest box provision to provide additional nesting sites for bearded tits Parurus biarmicus at Leighton Moss RSPB Reserve, Lancashire, England. Conservation Evidence. 2005. 30-32. Accessed 6 July 2015.Available at: http://www.londonarray.com/downloads/surveys/o071025%20EMMP%20Schedules.pdf

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