In the electric power grid generation and consumption must be always the same. For sure the load change continuously in time, therefore an equal generation change must always correspond to the load change. But if generation is run at 100 % of rated nominal power, as soon load increases, for example, there would not be any generation increase because we are at the limit, following a blackout. Therefore, surely generation is always run with a margin of available power.

My question is: how far can the generation (total generation in an interconnected system) be from its nominal rated power? Are there some rules to avoid critical/dangerous conditions about this? When can we say that we are in high load/low load condition?

  • \$\begingroup\$ I read somewhere that they try to maintain a margin of failure of a few generators. So if a few generators were to break down right now, there would still be enough generators online to handle the load. Don't quote me on that. \$\endgroup\$
    – user253751
    Apr 1, 2022 at 10:35

1 Answer 1


In the USA, the term for the "margin of available power" defined in the question seems to be called "reserve capacity." The target reserve capacity for the various regional systems in the US seems to be about 14 to 16 percent. It appears that the target is evaluated and revised from time to time, perhaps seasonally.


North American Electric Reliability Corporation

US Energy Information Agency

  • \$\begingroup\$ The amount of reserve capacity turns out to be a big political issue, especially when there are outages like the one that hit Texas last winter. In practice, the reserve is maintained by individual generators as operating reserve. \$\endgroup\$
    – LShaver
    Apr 1, 2022 at 14:14
  • \$\begingroup\$ @charles Cowie ohhh great! Thak you! Do you have also information regarding Europe scenario and If there are definitions of high/low load condition? \$\endgroup\$ Apr 1, 2022 at 15:20
  • \$\begingroup\$ @Samuele Beneto Di Giola: I have never looked for information about systems other than North America. \$\endgroup\$
    – user80875
    Apr 1, 2022 at 21:28
  • \$\begingroup\$ @LShaver: I believe the issue was mostly and may still be that Texas mostly maintains independence from other US system operators and doesn't have much capability to import from other systems. Their reason for maintaining independence is political. If they engage in interstate energy commerce, the federal government could regulate their natural gas prices and they don't want to risk that. \$\endgroup\$
    – user80875
    Apr 1, 2022 at 21:57

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