However, it seems that even higher winds struck the Cemmaes wind farm of 24 Wind Energy Group MS-3 machines in mid Wales, destroying two sets of blades and bringing down one entire rotor. Two of the damaged wind turbines were sited at the northern perimeter of the wind farm and one in the middle of the site. "The loads on the structure were simply so great that blades ended up breaking and were found some distance from the machines," says David Lindley of National Wind Power (NWP), the project's developer. He surmises that the three machines were each struck by particularly severe and very local gusts during the storm. Assessing the exact wind strengths at Cemmaes on December 8 is difficult, says Lindley. The turbines shut down in the afternoon at their cut-out wind speed of 25 m/s. Later that evening a power line came down leaving the wind farm and much of the surrounding area without power for 22 hours, putting the wind monitoring equipment out of action. The designed survival wind speed of the MS-3 is 60 m/s and extrapolation of available data in the region suggests winds reached speeds of around that strength during the storm, says Lindley. "Who knows, maybe they were more," he adds. If the winds were in excess of 60 m/s the question of insurance might arise. "That's down to us to determine with our insurers," says Lindley.
Wind data gathered earlier in the day at Cemmaes has been compared with that recorded at the Ecogen development of Mitsubishi machines to the south. "When they were getting 23 m/s we were getting 35 m/s," says Lindley. "We were seeing gusts of the order of 10-14 m/s higher." He points out that hurricane-type storms are known to cause havoc along a selective track. A testimony to the extreme winds at Cemmaes on December 8 is the uprooting of a glass fibre transformer housing. It was torn off its concrete pad at ground level and blown some considerable distance. "No human could stand," says Lindley of the night in question. "A sheep would have been blown off the ridge," adds NWP's Peter Musgrove.
Criticism of the siting of wind turbines on an exposed ridge like that at Cemmaes is refuted by both Lindley and Musgrove. They point out that Scotland is much windier than Wales and that many companies are intending to develop wind farms there. Lindley stresses that out of 71 MS-3 turbines operated by NWP, just three, facing extreme conditions, were damaged in the storm. Nonetheless, all MS-3 machines were taken out of operation in the week following the storm, pending inspection and a thorough investigation of the failed rotors. They were expected back on line again before Christmas.
No damage was recorded at other UK wind farms, but Ecogen says winds were the strongest anyone in the area of its Llandinam project in mid Wales could remember. They reached their peak at midnight on December 8, with speeds of 40 m/s. Afterwards, some of the 103 Mitsubishi turbines could not be re-started remotely from the control room in Newtown and had to be started on site. The story was the same at the Taff Ely wind farm of Nordtank machines, also in Wales, says Nordtank's UK agent Børge Sørensen.