Operating reserve

Electric power transmission Electric power distribution Power factor
An idealized representation of the four kinds of reserve power and the time intervals after an unexpected failure that they are in use.[1]

In electricity networks, the operating reserve is the generating capacity available to the system operator within a short interval of time to meet demand in case a generator goes down or there is another disruption to the supply. Most power systems are designed so that, under normal conditions, the operating reserve is always at least the capacity of the largest supplier plus a fraction of the peak load.[2]

The operating reserve is made up of the spinning reserve as well as the non-spinning or supplemental reserve:

Generators that intend to provide either spinning and non-spinning reserve should be able to reach their promised capacity within roughly ten minutes. Most power system guidelines require a significant fraction of their operating reserve to come from spinning reserve.[3] This is because the spinning reserve is slightly more reliable (it doesn't suffer from start-up issues) and can respond immediately whereas with non-spinning reserve generators there is a delay as the generator starts-up offline.[5]

In addition, there are two other kinds of reserve power that are often discussed in combination with the operating reserve: the frequency-response reserve and the replacement reserve.

Centrally controlled air conditioners and thermostats that are used in large residential areas can be used as a fast and considerable operating reserve. Advantages of this technology are under studies. [7]

Operating reserve is a crucial concept for ensuring that the day-ahead planning of generators' schedule can withstand the uncertainty due to unforeseen variations in the load profile or equipment (generators, transformers, transmission links) faults.

The California Independent System Operator has an operating reserve at 6% of the metered load. Included in that is a spinning reserve at 3% of the metered load.[8]


  1. ^ B. J. Kirby, Spinning Reserve From Responsive Loads, Oak Ridge National Laboratory, March 2003.
  2. ^ Jianxue Wang; Xifan Wang and Yang Wu, Operating Reserve Model in the Power Market, IEEE Transactions on Power Systems, Vol. 20, No. 1, February 2005.
  3. ^ a b c Spinning Reserve and Non-Spinning Reserve, California ISO, January 2006.
  4. ^ WSCC Operating Reserve White Paper[permanent dead link], Western Systems Coordinating Council, July 1998.
  5. ^ The Value of Reliability in Power Systems, MIT Energy Laboratory, June 1999.
  6. ^ a b Eric Hirst, Price-Responsive Demand as Reliability Resources, April 2002.
  7. ^ N. A. Sinitsyn. S. Kundu, S. Backhaus (2013). "Safe Protocols for Generating Power Pulses with Heterogeneous Populations of Thermostatically Controlled Loads". Energy Conversion and Management. 67: 297–308. arXiv:1211.0248. doi:10.1016/j.enconman.2012.11.021.
  8. ^ "Spinning Reserve and Non-Spinning Reserve" (PDF). caiso.com. 2006-02-03. Archived (PDF) from the original on 2006-02-03. Retrieved 2020-08-28.