WASHINGTON, March 3 (Reuters) - U.S. Energy Secretary Jennifer Granholm said on Wednesday she is ready to use $40 billion in her department’s loan program office that went unused in the last four years to boost the transition to clean energy. “I am ready to rev those engines back up so that we can spur the next generation of innovation and deployment,” Granholm said during the virtually-held CERAWeek conference. She did not offer details on how the loans would be offered. Granholm said Jigar Shah, an expert in clean energy finance, will head the department’s loan programs office. The loans office was founded with stimulus funding in 2009 during the Obama administration. It has loaned money and been paid back by successful businesses, including Tesla Inc , but has been slammed by some Republicans for support of Solyndra, a failed solar company.