National Security Resiliency and Sustainability Act of 2020 This bill, for FY2021 and any subsequent fiscal year, directs the Department of Defense (DOD) to improve its energy efficiency, including by reducing energy intensity in DOD buildings by 2.5% annually through the end of FY2027. It also adds requirements relating to clean energy including that electric energy and thermal energy in DOD buildings are comprised of clean energy. DOD must develop, implement, and annually update an integrated Strategic Sustainability Performance Plan for each of FY2021-FY2040.