a general term for markets that facilitate the provision of specialty services and functions beyond generation and transmission. These services generally maintain grid stability (e.g. frequency control), ensure that supply meets demand (e.g. spinning reserves) and support grid security (operating reserves).
Pros
Provides access to energy revenues that can fund improvements or projects.
Cons
Can be hard to access the marketplace.
Real Talk
Ancillary services were traditionally provided by combustion generators, however, the integration of intermittent generation and the development of smart grid technologies have prompted a shift in the types equipment that can be used to provide ancillary services. Energy markets will be needed, but they need to be shaped around new primary sources of PV and wind.