Fresh blow for wind farms as possible flaw is scrutinised

The problem that has emerged is over the turbines' "monopile" foundations. The issue is centred on the grouting in the transition piece linking the turbine to its foundation, and the towers that are affected have shifted several centimetres under the impact of harsh offshore conditions.

The fault is not associated with a particular turbine model or manufacturer. Rather, it is an error in the generic design schematics signed off by the DNV, the Norwegian accreditation body, so the problem could show up in any turbine with a monopile foundation structure.

The industry is keen to play down the significance of the problem, stressing that the fault can be fixed and that there are no safety or performance implications. Even if every one of Britain's 336 offshore turbines were affected, the total cost of fixing the glitches would be "just" £50m, a fraction of the total cost of the installations, according to Charles Anglin, a director at RenewableUK, an industry group. But until all the checks have been completed, it is not possible to reliably estimate the impact.

"The problem is it will take a while to quantify the scale of the issue, "Mr Anglin said. "It is a concern and the industry is acting on it, but this is not something which is going to put anyone at risk or reduce output," he added.

The grout troubles first showed up last October at a wind farm at Egmond aan Zee in the Netherlands owned by Shell and Vattenfall.

Since then a task force of the big players in the offshore wind industry – including Centrica, E.ON and Dong Energy – has been working on the most effective solution to correct the monopile issue.

"Everybody in the industry has this problem so all of us are interested in solving it," a spokesman for Dong Energy said. "This shows this is a young industry and there are experiences to learn from."

Dong Energy has discovered the fault on three of its wind farms: at Dogger Bank off the coast of Liverpool, at the newly-commissioned Gunfleet Sands, and at the massive Horns Rev 2 facility off Denmark. A total of 164 turbines are affected, the company reports.

With the help of the industry task force, Dong expects to decide which of three possible technical solutions to pursue within another four to six months. At this stage, the company does not expect the cost to come in above the Kr100m (£12m) threshold above which it must make a public statement.

E.ON, another significant investor in wind farms, says its Scroby Sands facility's 30 turbines are not affected because they use an older "flange" technique rather than grout.

But, the 60 turbines of the Robin Rigg farm and another two at Blyth are now being checked, although the inspections were delayed by the recent spate of harsh weather.