It would have been one of the largest offshore wind farms in the world. On paper, the Celtic Array spread across 2,200 square kilometres of the Irish Sea southeast of the Isle of Man, with somewhere between 146 and 440 turbines and a possible nameplate capacity of 5.4 gigawatts - enough to power perhaps four million homes. The maps were drawn. The consultations ran. And then, in July 2014, the developers walked away. The reason was not politics or environmental opposition. It was the seabed itself.
Britain's Round 3 offshore wind programme, announced in 2008, was the most ambitious push for offshore generation any country had ever attempted. The Crown Estate - owner of the seabed out to twelve nautical miles - identified zones with up to 33 gigawatts of total potential and ran a competitive tender to allocate them to developers. In January 2010 the British gas company Centrica won the Irish Sea zone: a 2,200-square-kilometre patch of water southeast of the Isle of Man, west of Cumbria, north of Anglesey, with an estimated potential of 4.2 gigawatts. In March 2012 Centrica took the Danish offshore specialists DONG Energy on as a joint-venture partner, paying 40 million pounds for half of the Irish Sea subsidiary.
The site was too large for one continuous wind farm and too crisscrossed by shipping. The Liverpool-to-Belfast lane ran straight through it. Tanker traffic feeding the Mersey ports crossed it from south to north. Liverpool-to-Dublin ships skirted its southern edge. The developers carved out three development zones with shipping lanes between them: a 359-square-kilometre northeast zone with 1-2 gigawatts of potential, a 255-square-kilometre southwest zone with 0.5-0.8 gigawatts, and a 617-square-kilometre southeast zone with 1.4-2.6 gigawatts. The southeast zone went first, submitted in 2012 to the Infrastructure Planning Commission as the Rhiannon Wind Farm - named for the Welsh mythological queen, with the cables coming ashore at four landfall sites on North Anglesey.
Two years of stage-one and stage-two public consultation followed. By March 2014 the project had been refined to between 146 and 440 turbines of 4-15 megawatts each, with up to eight HVAC offshore substations and a 400-kilovolt onshore substation at Rhosgoch on Anglesey feeding into the Wylfa-to-Pentir line. The water on site was 36 to roughly 70 metres deep, with a tidal range of up to 8.5 metres. Then, in July 2014, Centrica and DONG terminated the project. The problem turned out to be the seabed. Survey work had revealed wildly differing ground conditions - sand in some areas, hard rock in others - which would have required different turbine foundation designs for different parts of the same wind farm, driving costs above what the developers could justify against an uncertain electricity price.
The Celtic Array's cancellation in 2014 was a blow to the British offshore wind industry, which had become used to projects only getting larger and cheaper. It was a useful corrective: not every patch of sea is buildable, and the Irish Sea's complicated glacial geology - the same legacy of grinding ice sheets that gave the basin its sandbanks and freshwater-lake history - was harder than the early surveys had suggested. The lessons did not end the industry. Other Round 3 sites went ahead, and the Walney Extension off Cumbria became, briefly, the largest offshore wind farm on Earth. But the patch of Irish Sea southeast of the Isle of Man is still empty, the wind blowing across water no one is harvesting, the legend of Rhiannon undisturbed.
The Celtic Array zone was centred near 53.77°N, 4.41°W in the Irish Sea, southeast of the Isle of Man and roughly 19 km from Anglesey, 34 km from the Isle of Man, 60 km from Cumbria. From a cruising altitude of 10,000-30,000 ft on the busy Dublin-Liverpool, Dublin-Manchester, or Belfast-Liverpool corridors, the water below is empty - no turbines, no infrastructure. Nearby aerodromes: Isle of Man Ronaldsway (EGNS) 25 nm north, Anglesey/Valley (EGOV) 30 nm south, Liverpool (EGGP) 60 nm east, Dublin (EIDW) 55 nm west. The Walney Extension wind farm sits 70 nm east-northeast off the Cumbrian coast; Arklow Bank Wind Park sits 65 nm south off County Wicklow. Wind here is strong and variable; the same characteristic that made it attractive for turbines makes it taxing for general aviation.