Shares of GT Solar plunge 15.5 percent on downgrade

LOS ANGELES (Reuters) - Shares of GT Solar International Inc (SOLR.O) tumbled 15.5 percent on Tuesday after the company's quarterly results led a Piper Jaffray analyst to downgrade the stock.

Piper Jaffray analyst Jesse Pichel cut GT to "underweight" from "neutral," citing major concerns about its backlog for polysilicon equipment.

"We speculate that many (polysilicon) start-ups in China could shut down, and it will be difficult for SOLR to get new bookings or realize its contracted backlog," Pichel said in a note to clients on Tuesday.

Pichel said the company's historically largest customer, LDK Solar Co Ltd (LDK.N), is on a "financial precipice" and is "unlikely to remain a customer."

GT shares fell 86 cents, or 15.5 percent, to $4.68 in afternoon Nasdaq trading.

Merrimack, New Hampshire-based GT said on Monday its quarterly profit fell by two-thirds, but it maintained its previous outlook for the fiscal year.

Raymond James analyst Pavel Molchanov said the results were in line with preliminary results released last week.

"Perhaps there were expectations that orders would pick up more than they did," Molchanov said.

The solar industry is hoping for its brightest quarter so far this year, after the credit crisis and falling prices hampered new projects and profits for many companies.

(Reporting by Laura Isensee; editing by John Wallace)