Energy Secretary Steven Chu fiercely defended a $535 million government-backed loan guarantee to failed solar panel manufacturer Solyndra today, and denied GOP lawmakers' charges that the California firm won the financing because of its political connections.

"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 told the House Energy and Commerce Committee panel investigating Solyndra. "I want to be clear: over the course of Solyndra's loan guarantee, I did not make any decision based on political considerations."

Chu is the highest ranking Obama administration official to appear before the panel since it opened its investigation of the California firm, which filed for bankruptcy on Aug. 31 and ceased operations soon after.

Solyndra has been held up as the poster child of President Obama's clean-energy policy, and GOP lawmakers have suggested that the California firm was awarded the loan guarantee because of the company's ties to Obama. George Kaiser, whose charitable foundation was a big investor in Solyndra, was a major contributor to Obama's 2008 presidential campaign. GOP presidential hopefuls have made Solyndra an issue on the campaign trail and will almost certainly continue to hammer Obama on the loan guarantee program as the campaign season heats up.

In the opening minutes of Thursday's hearing, GOP lawmakers made clear that Chu will face tough questioning about why the Department of Energy approved the loan guarantee to Solyndra when several administration officials had expressed concern about the company's long-term viability.

"At every opportunity, Solyndra and DOE officials, including Secretary Chu, publicly assured the American people that Solyndra was on track and would eventually thrive, right up until the time that Solyndra declared bankruptcy," said Rep. Fred Upton, R-Mich., chairman of the House Energy committee. "They continued telling this story even when clearly should have known it was not the case."

Chu noted that loan guarantee program has received broad support from lawmakers—including 500 letters to DOE from members of Congress endorsing projects in their backyards. At least 30 GOP lawmakers wrote Chu seeking loan guarantees or other DOE financing for clean energy projects, according to documents obtained by USA TODAY.

Among those who wrote to Chu was Upton, who pushed for a loan guarantee for the Michigan clean energy firm United Solar Ovonic. But as the Detroit Free-Press reports, United Solar, which did not receive the loan guarantee but received more than $170 million in government investment and congressional earmarks, and its parent company are now under financial duress.

Rep. Cliff Stearns, R-Fla., who heads the panel investigating Solyndra, was even more blunt in his criticism.

"While our investigation continues, it is readily apparent that senior officials in the administration put politics before the stewardship of taxpayer dollars," Stearns said.

Rep. Henry Waxman, D-Calif., noted that Bush administration appointee Steve Isakowitz, who served as DOE's chief financial officer until July, told the panel in an interview that he never received any pressure from Chu or any other administration officials on Solyndra.

"It is time for House Republicans to stop dancing on Solyndra's grave and start getting serious about energy policy," Waxman said.