Short-term grid operations require real-time balancing of generation and load, or electricity supply and demand. The grid also requires certain “ancillary services” to ensure stable and reliable operations. Some of these services are used on a daily basis, such as inertia and frequency regulation, while others are dispatched under specific circumstances such as unexpected generator outages. Some are procured through markets, and others through standards and regulation.
The graphic below from the U.S. Department of Energy shows which grid services are generally procured through markets, and the speed of response required.