Accommodating High Levels of Variable Generation - NERC

Power System Operations
participating in wider-area arrangements such as ACE sharing (such as WECC’s ACE Diversity
Interchange 93 ) or wide area energy management systems.
In many locations, balancing energy transactions are scheduled on an hourly basis. With the
advent of variable generation, more frequent and shorter scheduling intervals for energy
transactions may assist in the large-scale integration of variable generation. For example, as
noted above, balancing areas that schedule energy transactions on an hourly basis must have
sufficient regulation resources to maintain the schedule for the hour. If the scheduling intervals
are reduced for example to 10 minutes, economically dispatchable generators in an adjacent
balancing area can provide necessary ramping capability through an interconnection. 94
In summary, with adequate bulk power transmission, variable generation plants aggregated
across larger balancing areas or participation in wider-area balancing management may
significantly reduce variability (both of variable generation and demand), increase predictability
and therefore reduce the need for additional flexible resources. With adequate available
transmission capacity, larger balancing areas and more frequent scheduling within and between
areas provide more sources of flexibility. Therefore, the task force recommends:
NERC Action: The impact of securing ancillary services through larger balancing areas
or participation in wider-area balancing management on bulk power system reliability
must be investigated. The NERC Operating Committee should review and study the
consequences of larger balancing areas or participation in wider-area balancing
management like provisions of ancillary services from other jurisdictions, ACE sharing,
and/or shorter scheduling intervals within and between balancing areas to effectively
manage variability of generation resources over a larger footprint. In addition, existing
and proposed BAL Standards should be reviewed to determine their sufficiency.
Industry Action: State, provincial and federal government agencies and policymakers
should be informed of the issues and opportunities associated with transmission and
larger balancing areas which can increase access to ancillary service requirements and the
desirability of more frequent scheduling intervals, including sub-hourly scheduling or
regional dispatch optimization.
93 See http://www.wecc.biz/index.php?module=pnForum&func=viewtopic&topic=909
94 Reduced scheduling intervals would also produce a system response more closely aligned with real-time events
and provide closer to real-time market data for providers of demand response services
Accommodating High Levels of Variable Generation 61