Physical and cyber vulnerabilities to the power grid are the Achilles heel of the nation’s security apparatus, energy security experts said Wednesday during the Independent Power Producers of New York’s spring conference. According to the panel of experts, more pressing than physical attacks on key energy assets are cyber attacks. “This is going to be a huge threat,” said Public Policy associate Aimee P. Ghosh. “It’s not if something is going to happen, it’s when something is going to happen.”