U.S.-based First Solar Inc, the world's No. 2 maker of solar cells, will ramp up production at its German plants, scheduled to close later this year, to meet an unexpected surge in demand, a spokesman said on Tuesday.

Shares of First Solar jumped as much as 14.8 percent on the news, and were the biggest gainer among solar companies on the Nasdaq.

"We expect that we can run both plants at almost full capacity until October and slowly reduce production after that before we close them by the end of the year," the spokesman said.

First Solar said in April it would shut down its production site in Frankfurt (Oder), Germany, in the fourth quarter, as it moves its focus away from Europe, where governments have been changing subsidy policies that had boosted demand for the company's panels.