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.

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.