First Solar ( FSLR) says it has produced 1 gigawatt of its advanced solar modules for the first time since beginning commercial production in 2002.

Shares of First Solar, however, were down 2.5%, or $3.17, to $121.63 in recent trading Friday.

The company took six years to produce its first 500 megawatts and eight months to produce its second. First Solar has announced it will have the capacity to produce more than 1 gigawatt per year by year-end -- the equivalent of an average-sized nuclear power plant, the compan says.

"This volume allows us to rapidly reduce manufacturing costs, thereby furthering our mission of making solar power an affordable alternative to conventional energy sources," said Bruce Sohn, First Solar president. "We appreciate the many contributions our associates have made in reaching this 1GW milestone and are grateful for all their hard work."

OptiSolar, an independent maker of photovoltaic panels based in Heyward, Calif., that First Solar made a deal with, will lay off most of its employees, according to a report Thursday in the Sacramento Business Journal. Earlier this month, First Solar had announced it would buy OptiSolar's project development portfolio for about $400 million in stock.