A December 2018 report by the North American Electric Reliability Corporation (NERC) indicates that acceleration of coal and nuclear plant retirements could result in black outs. NERC is an international nonprofit agency that examines and promotes grid reliability among utility systems in the United States and Canada. The agency released its Generation Retirement Scenario—a 44-page report—that found an aggressive rate of coal-fired and nuclear plant retirements could put the electric grid reliability at risk. Grid reliability is the ability of the system to deliver electricity as it is demanded. If electric utilities are not able to meet demand at any given time, a blackout could result. The retiring coal and nuclear power plants generate electricity 24/7, but wind and solar units that are replacing them produce power only intermittently—only when the wind blows and the sun shines—and natural gas units replacing them may not have sufficient infrastructure to ensure availability of the needed fuel.