Obama administration officials on Wednesday defended a $528 million loan to a solar-panel company that went bankrupt this month, claiming the firm fell victim to global economic trends but that federal investment in alternative energy must continue.

The testimony came as Republican and Democratic lawmakers raised sharp questions about the decision that ultimately left taxpayers on the hook for millions, and as newly released emails show administration officials were raising doubts about the loan proposal to Solyndra months before it was finalized.

Federal agents have expanded their examination of the now-bankrupt California solar power company Solyndra, visiting the homes of the company's CEO and two of its executives, examining computer files and documents, iWatch News and ABC News have learned.

Agents visited the homes of CEO Brian Harrison and company founder Chris Gronet and a former executive, according to a source who agreed to speak only on the condition of anonymity because of the legal sensitivity of the situation.

Gronet, reached at his home Friday morning, did not dispute that his home was visited by federal agents a day earlier.

"I'm sorry," Gronet said, "you probably understand full well that I cannot comment." The third executive could not be immediately reached.

Not only does the now-bankrupt solar energy firm Solyndra have a cozy financial relationship with the Obama administration, company representatives also made numerous visits to the White House to meet with administration officials, The Daily Caller has learned.

According to White House visitor logs, between March 12, 2009, and April 14, 2011, Solyndra officials and investors made no fewer than 20 trips to the West Wing. In the week before the administration awarded Solyndra with the first-ever alternative energy loan guarantee on March 20, four separate visits were logged.

George Kaiser, who has in the past been labeled a major Solyndra investor as well as a Obama donor, made three visits to the White House on March 12, 2009, and one on March 13. Kaiser has denied any direct involvement in the Solyndra deal and through a statement from his foundation said he “did not participate in any discussions with the U.S. government regarding the loan.”

FBI agents executed search warrants Thursday morning at the headquarters of California solar firm Solyndra, which received a $535 million loan from the federal government before filing for bankruptcy last week, FoxNews.com confirms.

Agents executed the search warrants at the company's headquarters in Fremont as part of a joint operation by the Federal Bureau of Investigation, Department of Energy and the Office of Inspector General, FBI spokesman Peter Lee said.

Lee told FoxNews.com that "multiple search warrants" were executed but said he could not provide details on what prompted the investigation.

A solar energy company that intends to file bankruptcy received $535 million in backing from the federal government and has a cozy history with Democrats and the Obama administration, campaign finance records show.

Shareholders and executives of Solyndra, a green energy company producing solar panels, fundraised for and donated to the Obama administration to the tune of hundreds of thousands of dollars.

Tulsa billionaire George Kaiser, a key Obama backer who raised between $50,000 and $100,000 for the president’s election campaign, is one of Solyndra’s primary investors. Kaiser himself donated $53,500 to Obama’s 2008 election campaign, split between the DSCC and Obama For America. Kaiser also made several visits to the White House and appeared at some White House events next to Obama officials.

Campaign finance records show Kaiser and Solyndra executives and board members donated $87,050 total to Obama’s election campaign.

President Nicolas Sarkozy's government on Wednesday unveiled a first budget since taking office that shied away from attacking France's huge deficit despite warnings that the state was bankrupt. Prime Minister Francois Fillon caused a stir last week when