 In April 2010, engineers reported a fundamental flaw in the design of offshore wind turbine foundation structures. The problem affects wind farms across Europe, requiring further investigation into the potential effects on all offshore turbines that have monopile foundations of this design.
Danish company Dong Energy (who had learned of the problem from Shell) confirmed that grout designed to act as an adhesive between the pile foundation and the transition section of the turbine tower base was failing, and had caused some turbines to slip by up to 25mm. The majority of the 336 UK turbines were built to this same specification and so could potentially develop this fault. Although no safety issues have been identified, as supporting brackets used during construction and left in place have stopped the turbine towers from slipping further, more detailed analysis of the problem is required.
Strainstall Monitoring were approached by three power generation companies and subsequently contracted to carry out testing on a number of wind turbines at four of the twelve wind farm sites around the UK coast. Strain gauges, displacement sensors and accelerometers have been installed between the monopile transition piece and the main tower to measure displacement and strain, and on the main tower to monitor bending, torque and axial load. A forth company has also appointed Strainstall to fit similar monitoring equipment to wind turbine foundation structures of a different design during their construction.
The strain gauge installation programme started in July, and it is hoped that it will be completed by January 2011. A two year monitoring programme will follow, and it is hoped that the results will show that the wind turbines are structurally sound and so can be left as they are, but with a permanent monitoring and alert system to notify operators should conditions change. The alternative solution would be to insert wedges under the brackets or weld new ones, which would cost millions of pounds.
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