Shares in Vestas Wind Systems A/S (VWS.KO) plummeted Monday after the world's largest manufacturer of wind turbines revised its profit guidance for 2011 and said it wouldn't complete some projects on time due to problems commissioning a new generator factory in Germany .

The Denmark-based company said the delay in deliveries will hamper full-year sales as well as its earnings margin; it now expects full-year sales to come in at EUR6.4 billion, from previously expected EUR7 billion, and the margin on earnings before interest and taxation, or EBIT, to arrive at 4% in the full year, down from a previous target of 7%.

At 949 GMT Monday, Vestas' shares traded down 18.3%, at DKK91, after having opened down as much as 24% an hour earlier.

The warning marks the latest unexpected twist for Vestas, whose shares have often moved in large swings in either direction following earnings reports or unplanned news. Company shares jumped 25% the day of its most recent earnings report in August.

Vestas said the revision was needed because a new generator factory in
Travemunde , Germany , hasn't been progressing as planned. "In order not to compromise on safety and quality in an already very busy fourth quarter, Vestas has chosen to postpone the handing over of a number of projects, primarily in Europe ," the company said.

The 3 percentage points EBIT margin cut corresponds to a full-year EBIT some EUR234 million lower than previously guided, according to two analysts. The company expects EUR35 million in fines and other costs connected to the postponed deliveries.

The company also pre-released preliminary third-quarter numbers which show revenue dipped to EUR1.34 billion, from EUR1.92 billion last year and a loss after tax of EUR60 million for the third quarter from a profit of EUR187 million.

Jyske Bank analyst Janne Vincent Kjaer characterized the news as a "major disappointment," noting that the "EBIT margin has been really hard hit."

Credit Suisse said the disclosure revives questions about Vestas' execution.

"Given Vestas' overcapacity since 2008, investor and analyst concerns on Vestas have centred more upon the top-line - on pricing, order flow and sales - for the past three years. Now execution issues have once again come to the fore, we believe perception of risk on Vestas stock moves up," said Credit Suisse.

The negatives were mitigated somewhat by news that Vestas was maintaining its target of a full-year order intake of between 7,000 and 8,000 megawatt of installed electricity production capacity, analysts said.

Kjaer said Vestas has a promising projects pipeline for 2012 and sees no reason to adjust her results estimates for next year.

Vestas Chief Executive Ditlev Engel said the delayed projects would be completed in 2012 and that the earnings on the individual profits are "still satisfactory." The decision to postpone deliveries was made with great regret, but "safety and quality has top priority and a decision to speed up the projects in question would have been irresponsible," Engel said.