EIA: “About 25% of U.S. power plants can start up within an hour”

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Guess “Did you know?” by David Middleton

In a world where mostly unreliable power plant (solar & wind) construction is on the rise, backup power generation becomes more important every day. Unreliable generation capacity in the US has doubled since 2013 and now comprises 12% of our generating capacity. Backup power needs to be able to spin up quickly, ideally within minutes, certainly in less than 1 hour.

NOVEMBER 19, 2020
About 25% of U.S. power plants can start up within an hour
About 25% of U.S. power plants can start up—going from being shut down to fully operating—within one hour, 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.
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). A generator’s startup time is different from a generator’s ramp rate, which reflects how quickly that generator can modify its power output once it’s operating.
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.
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. Power plants that require more than 12 hours to start up are increasingly rare. Only 4% of the generating capacity that came online from 2010 to 2019 requires more than half a day to reach full load.
Natural gas combined-cycle systems, which involve both a steam turbine and a combustion turbine, account for more capacity than any other generating technology in the United States. Most of those systems can reach full operations in between 1 hour to 12 hours, although some can start up within an hour.
The percentage of the generator fleet that does not respond to this question in EIA’s survey has doubled—from 6% in 2013, when EIA first collected this data, to 12% in 2019—as a result of the number of utility-scale solar and wind power plants added in recent years. This question is not relevant for these types of plants.
Principal contributor: Owen Comstock
EIA

63% of US generating capacity requires more than 1 hour to go from cold start to full load.

Source: U.S. Energy Information Administration, Annual Electric Generator Inventory

Hydroelectric turbines are the fastest fastest from cold start to full load.

Source: U.S. Energy Information Administration, Annual Electric Generator Inventory
Note: Only technology/fuel combinations with at least 10 gigawatts of operating capacity are shown.

The concept is not applicable to wild and solar. In the example below a wind turbine starts generating electricity when the wind speed exceeds 8 miles per hour (mph), reaches full output at 31 mph and blows up (/Sarc) at 55 mph. To quote Sammy Hagar, “I can’t drive fifty-five!”

The Power Curve: Note specific wind speeds vary by types of turbines. (Figure Credit: Sarah Harman, DOE)

On sunny days, solar PV takes about 4 hours to go from cold start to full output, works for about 4 hours and then ramps down for about 4 hours.

Solar PV keeps “banker’s hours”. (DOE)

Unless the weather’s bad.

Solar doesn’t show up for work on cloudy days. (DOE)

Fortunately for those of us who like to have electricity at night, on cloudy days and on days with too little or too much wind, natural gas combined cycle is the generating source that’s mostly replacing coal.