Solar power companies such as Solyndra fail when "the bottom of the market falls out," Chu testified before a subcommittee of the House Energy and Commerce Committee Thursday.
He told the panel new plants to manufacture solar panels opened in China and elsewhere while the market for the panels softened because of economic troubles in Europe, The New York Times reported.
Republicans on the committee maintain incompetence and political influence were the problems.
Rep. Clifford Stearns, R-Fla., chairman of the subcommittee, said, "It is readily apparent that senior officials in the administration put politics before the stewardship of taxpayer dollars."
Chu, a physicist and Nobel laureate, answered questions for more than 5 hours.
He accepted responsibility for his decisions to OK the loan guarantee in 2009 and then restructure the loan in February, but rejected Republican allegations that energy officials did not subject Solyndra to enough scrutiny and approved the loan for political reasons, The Hill said.
"As the secretary of energy, the final decisions on Solyndra were mine and I made them with the best interest of the taxpayer in mind," Chu said. "I want to be clear: Over the course of Solyndra's loan guarantee, I did not make any decision based on political considerations."
Chu refused to apologize for his role in the matter despite being asked to do so by Energy and Commerce Committee Chairman Fred Upton, R-Mich., The Hill said.
"Who has to apologize for the half a billion dollars in taxpayer money that's out the door?" Upton asked.
"Well, it is extremely unfortunate what has happened with Solyndra," Chu said. "Was there incompetence? Was there any influence of a political nature? I would have to say no."
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