Breakdown of energy capacity in the U.S. 2019, by time to full load

One third of U.S. energy capacity needs more than 12 hours in order to operate at full load. Steam turbines such as those used in gas-fired and coal power plants need the longest to become fully operational. By comparison, the majority of conventional and pumped storage hydro turbines needs less than ten minutes from cold shut down to full load. They account for eleven percent of the U.S. energy capacity. Loading time was not applicable for variable renewable sources such as wind and solar power as they depend on weather phenomena.