Power grids across North America and Europe have been on high alert all week as two massive solar storms have battered Earth, threatening to disrupt electricity supplies to millions of homes and businesses. On Monday, PJM Interconnection, which coordinates power to 61 million people across 13 U.S. states and the District of Columbia, alerted generators and transmission companies as the first storm was upgraded from “strong” to “severe” by the U.S. government’s Space Weather Prediction Center (SWPC) in Boulder, Colorado. Controllers across the United States and Canada have been issuing similar warnings and preparing to stabilize their grids as unusually strong electromagnetic radiation emitted from the sun interacts with the Earth’s own magnetic field and induces freak currents across the electricity transmission network.