The Energy Information Agency (EIA) has provided data that shows 25% of America’s power plants can start up (going from being shut down to fully operating) within one hour.

This is based on data collected in EIA’s annual survey of electric generators.

Some power plants, especially those powered by coal and nuclear fuel, require more than half a day to reach full operations.

The time it takes a power plant to reach full operations can affect the reliability and operations of the electric grid.

The EIA post continued to inform that generator startup time differs across electricity-generating technologies because of the differences in the complexity of electricity generating processes, especially when starting again after all processes have been stopped (cold shut down).

EIA stated that most hydroelectric turbines, which use flowing water to spin a turbine, can go from cold start to full operations in less than 10 minutes. Combustion turbines, which use a combusted fuel-air mixture to spin a turbine, are also relatively fast to start up.

Steam turbines often require more time. A fuel heats up water to form steam, and that steam needs to reach certain temperature, pressure, and moisture content thresholds before it can be directed to a turbine that can spin the electricity generator.

The EIA reported that nuclear power plants use steam turbines, but these plants have additional time-intensive processes that involve managing their nuclear fuel. Almost all nuclear power plants require more than 12 hours to reach full operations.

The EIA says power plants that require more than 12 hours to start up are increasingly rare and only 4% of the generating capacity that came online from 2010 to 2019 requires more than half a day to reach full load.