Flaw Hits Hundreds of EU Offshore Wind Turbines

April 27, 2010 | 4 Comments

Hundreds of European offshore wind turbines have a design fault allowing them to slide on their bases and finding a solution could take months and cost millions of pounds, European turbine makers and wind farm operators said.

The problem involves towers using grouting, a mixture of cement, sand and gravel, to attach the turbines to their base, they said, reported Reuters. In some cases the main superstructure of wind towers has moved several centimetres on its base after being installed.

It is an industry-wide problem related to a general design and not one particular tower model, industry executives said. It is not expected to delay new projects nor hit electricity production.

"We expect to have settled on a solution in the next four to six months. For the wind farms under construction, including London Array, we have made some design changes in relation to this issue," a spokesman for Denmark's Dong Energy said. "It will not delay the London Array project as foundation work has not started yet."

Dong owns half of the one gigawatt London Array offshore wind project in southeast England where construction is expected to start in 2011. Germany's E.ON owns 30 percent and Abu Dhabi green investment firm Masdar owns 20 percent.

Dong has problems at the UK Dogger Bank and Gunfleet Sands wind farms, as well as the Danish Horns Rev 2 facility. The company estimates it could cost up to £13 million [US $20 million] to restructure all 164 turbines.

Swedish turbine maker Vattenfall is also investigating three of its offshore wind farms, but declined to comment on how long the inspection would take or how much the solution might potentially cost.

"The investigations of Horns Rev 1, Kentish Flats and Thanet is still ongoing but we can confirm that we have found settlements between the foundation pile and transition piece on most of the foundations examined so far but no visible cracks," a spokeswoman said.

Vattenfall's 100 turbine UK Thanet wind farm is in the process of being built, with 46 turbines yet to be put up, but the investigation is not expected to delay construction or reduce power output from any of the three farms, she added. The company said the two UK and one Danish wind farms comprises 146 turbines and the inspection is expected to take 3 to 4 weeks.

Britain's Robin Rigg wind farm also used grouting to install the wind turbines, but inspections by operator E.ON UK have yet to reveal any problems. "We've checked out Robin Rigg, and don't think there's a problem there," a spokesman said.

The problem is also not expected to impact power generation in any of the affected turbines, and may not even require action, according to British green energy association Renewable UK.

"Basically, it doesn't affect the production of electricity. Our members are looking at what, if any, remedial action needs to be taken," a spokesman said.

In an attempt to shift from fossil fuels to renewable energy, Britain aims to install 32 GW of offshore wind capacity by 2020 at a cost of a £100 billion.

This article was reprinted with permission from Power-Gen Worldwide as part of the PennWell Corporation Renewable Energy World Network and may not be reproduced without express written permission from the publisher.

4 Comments

Roger Dyer
May 6, 2010

When I look at the majority of the construction industry I am continually amazed that one can earn a living from a little knowledge. One has to try hard to really appreciate how the designers can make such a fundamental mistake, when any experienced concrete engineer would have spotted it in a design check? Answer; they never asked anybody with practical experience as it conformed to the DNV standards. I seem to remember the Norwegians losing a major concrete platform from the same oversight.
This 'new failure mode' seems to appear in more and more and more major failures. I did some work with Prof. John Strutt (Cranfield) and Prof. Tim Davies (Warwick and Bradford Uni.) On this for BP (oops! have they just had a big failure). Major concern is that this sort of failure puts it in the BIG $/£ area (eg Ford putting the wrong tyres on one of their SUV models).
My own particular interest is that my March 1969 Thesis was STEEL-ENCASED CONCRETE COLUMNS. I feel I could have spotted their oversight if they had asked me or read my references. Only problem is that much of the historical research is not on the internet. I see this as more and more of a ongoing problem with younger engineers. Their attitude is that if it does not come up on a Google search it cannot be important. How can we get through to the younger audience in engineering training?
Actually it isn't hard to teach. It's the mind set that's the problem. You have to be interested to do so. What I struggle with is how can younger people training as engineers not want to know?

Just about sums up what its all about doesn't it?

J Pelou
May 2, 2010

lorsque j'explique que sur terre, meme sous mer, tout "flotte" et que ce qui est geant est encore plus vulnerable que le reste, du simple fait de l'application des lois physiques de mouvement appliquées a un pylone !!
une eolienne poser sur un tripod solution utilisée sur les permieres eolienne Rogallo en france, vers 1960-70, formant une pyramide reposant sur le sol ou fond sur une surface induisant faible poussée unitaire serait preferable mais la solution considerée comme moins "elegante" que ces poteaux geants induisants des vibrations & couples de basculement gigantesques

Jerry Cheesman
April 27, 2010

Perhaps the shift of several centimeters, is related to a shifting of the allignment of the entire bolt cage, but that is unlikely. I believe it is related to the clearance between the bolt cage members and the openings of the superstructure where the bolt cage fits into the tower piece. Surely, they torqued and rechecked the torque on all the bolt cage bolts. While I have not worked offshore, I have done some work on land and usually, there are three leveling bolts which the first tower piece sits down on. Then the piece is checked for plumb at the top. An adjustment of the leveling bolts may occur to correct plumb to the individual tower piece, then The three bolts are tightened first. Next, the bottom nuts at the top of the rest of the bolt cage are run up to the bottom of the tower piece, then all the rest of the top nuts and washers are tightened in the proper sequence with an impact, and the epoxy grout is put in, and strength tests conducted before the final torque, of the top of the bolt cage. Perhaps the urgency of the situation, during installation, may lead to a shortened cure time relating the the dryness of the grout mix process. This may also be complicated by the ambient temperature at the time of installation. For instance, I noted several offshore projects were initiated in the middle of the winter. Perhaps there will be more comments from workers who are more familiar with the techniques and conditions offshore which may better explain this issue.

Tomasz Rubanowicz
April 27, 2010

I do not want to give my speech pejorative overtones, but this issue "eksptenloatacyjny" happens in every industry, so it is not so terrible. Terrible is that this error will cost electricity consumers billions of euros. It is a pity also that the designers did not anticipate a problem at the "card".