The plant in Pocatello, Idaho, ran some of its reactors to refine polysilicon, the business ingredient in most solar panels.
"This is an historic day for Hoku," said Hoku President Scott Paul. "I am extremely proud of our team's accomplishment."
The primary purpose of the testing, which ran for five days, was to confirm system integrity and validate operating procedures, Paul said.
Hoku plans commercial production runs later this year.
The plant has been under construction for years. Construction at one point was held up by interruption of funding during the credit crisis. Hoku was eventually bailed out by a solar panel company from China that had intended to be a major customer.