Dong Energy, along with British testing and inspection services provider ESG, has completed the large-ever testing of wind turbine piles and found that that offshore wind projects can reduce their cost significantly with new design methods.

wind turbine piles

The companies have tested 28 piles on two different onshore sites in Cowden, England and in Dunkirk, France, a move to assist the development of new design methods for offshore wind farms.

The Pile Soil Analysis (PISA) project conducted around 28 tests to evaluate and validate a new design method developed by the PISA academic working group led by Oxford University and including Imperial College London and University College Dublin.

The tests were conducted by pulling the piles sideways into the soil until failure in order to investigate the static monotonic, as well as the response under cyclic lateral loading.

The piles of three different diameters supplied by Bladt and Dansteel were tested using fibre optic strain gauges installed by Marmota Industries.

The data collected during the tests will be analyzed over the next six months to confirm the new design methods.

Dong Energy lead Geotechnical engineer Alastair Muir Wood said: "We’re very pleased with the test results, which confirm that traditional design methods in these soils are very conservative.

"The results indicate that in these site conditions there may be opportunities for savings identified by reducing the quantity of steel in the foundation. In other words, there’s a savings potential, that will contribute to reducing the cost of electricity."

ESG project director Steve Turner said: "The PISA project has provided some of the most challenging testing we’ve ever undertaken. With the largest test, we were simultaneously monitoring more than 250 different precision instruments, whilst applying a load greater than the weight of 37 London double decker busses."

PISA project was undertaken by industry group led by DONG Energy along with EDF, RWE, Statoil, Statkraft, SSE, Scottish Power, Vattenfall, Alstom and Van Oord.

PISA R&D manager Jesper Skov Gretlund said: "If the thickness or length of the steel piles can be reduced by even a small fraction, the saving in cost is quite considerable since smaller construction vessels can be used and larger turbines constructed.

"The next challenge is to analyse all of the data collected in order to refine our methods and apply these findings to our foundation designs."

Image: The companies have tested 28 piles on two different onshore sites in Cowden, England and in Dunkirk, France. Photo: courtesy of Dong Energy.