The $2.9 billion London Array—the world’s biggest offshore wind farm—opened this July in the Outer Thames Estuary about 12 miles off the coasts of Kent and Essex. The 175-turbine installation is arranged in a vast 95-square-mile area in rows and columns aligned to the prevailing south-westerly wind, all rising out of relatively shallow waters of about 82 feet deep (Figure 5).

Though the 630-MW wind farm has been fully operational since April, it was officially opened by UK Prime Minister David Cameron in early July. Owned by Denmark’s Dong Energy (50%), Germany’s E.ON (30%), and Masdar (20%) of Abu Dhabi, the project is larger in both size and nameplate capacity than the 500-MW Greater Gabbard project that was completed last year off the East Anglian coast.

Siemens supplied and installed the 175 wind turbines at the London Array. Each features a rotor diameter of 120 meters and a rating of 3.6 MW. The project is connected by 279 miles of offshore cabling and one onshore and two offshore substations, also supplied by Siemens. These were built at a cost of about $709 million, according to a recent cost assessment from UK power and gas market regulator Ofgem.

The two-phase project was initiated in 2001 when a series of government environmental studies in the outer Thames Estuary confirmed the area is a suitable wind farm site. Planning consent for a 1-GW offshore wind farm was granted in 2006, and permission was granted for the onshore works in 2007. In 2008, however, the project stalled as Shell WindEnergy pulled out of the consortium. Despite engineering and weather delays, the first turbine was installed in January 2012, first power was achieved in October that year, and the final turbine was installed in December 2012.

The London Array, the latest of about 20 offshore farms completed in the UK, brings the nation’s total offshore wind capacity to 3.6 GW. The UK government has, however, tempered ambitions for a more massive offshore wind expansion, lowering ambitions from 18 GW by 2020, as set in 2011, to 11.5 GW by 2020, the latest projections from the Department of Energy and Climate Change show.

Government reforms of the electricity market drafted in late June could see subsidies for wind farms increase by about 10% starting next year to allay worries of wind turbine operators and manufacturers who have frozen investment in the UK’s offshore sector on fears that subsidies would be cut to unsustainable levels. For offshore installations, the draft subsidy level, or “strike price” is£155 ($237.96)/MWh from 2014, dropping to£135 ($207.25)/MWh in 2018; for onshore wind farms, the level is£100 ($153.52)/MWh, falling to£95 ($145.84)/MWh in 2018. And in August, the government unveiled a strategy to improve the UK’s offshore wind supply chain, including an investment of£66 million ($101 million) over five years to help bring new products to market. The government also said it will require developers of offshore wind farms above a certain size to produce a supply chain plan before they can apply for long-term contracts.

The UK has committed to European targets, which means it must source 15% of its power from renewables by 2020. But recent data from the Office for National Statistics shows that only 4.1% of the UK’s total energy consumption came from renewables and waste sources in 2011. In that year, meanwhile, fossil fuel imports rose to their highest level ever recorded.

Beyond the London Array, several mammoth offshore wind farms are in the pipeline. In late July, Swedish firm Vattenfall confirmed it would build the 228-MW Pen y Cymoedd wind farm in south Wales starting early next year. That 76-turbine wind farm could be completed within two years and have a 25-year lifespan. Meanwhile, earlier in July, the UK government approved RWE Innogy’s plans to build the 1.2-GW Triton Knoll offshore wind farm in England, a facility that could be far larger than the London Array.