Federal officials and energy experts offered their most blunt assessment to date regarding the ongoing vulnerability of the U.S. power grid, telling a Senate committee that solar-generated attacks alone cost $10 billion a year. In testimony before the Senate Homeland Security and Governmental Operations Committee, the officials noted that the attacks are growing and pose a substantial, long-term risk to a vulnerable power grid. They warned that a catastrophic failure would cut off electricity to millions of Americans, probably for months at a time, causing untold damage and social chaos, adding that the grid is an easy target for solar,...