Accommodating High Levels of Variable Generation - NERC

Introduction
Mindful of NERC’s mission, this report does not address market, regulatory or policy issues and
is neutral to the market environment in which the variable generation interconnects. Further,
NERC does not advocate a particular resource mix, weigh cost allocation approaches or
recommend specific technology solutions to address identified reliability concerns.
Within this context, the following guiding principles were used by the IVGTF in the preparation
of this report:
• Bulk power system reliability must be maintained, regardless of the generation mix;
• All generation must contribute to system reliability within its physical capabilities; and
• Industry standards and criteria must be fair, transparent and performance-based.
1.1 Key Aspects of Bulk Power System Planning and Operations Must Change
Appreciating how today’s bulk power system is planned and operated can be helpful in
understanding potential changes required to integrate large quantities of variable generation. The
supply of electricity has traditionally come from nuclear, large-scale hydro and fossil-fueled
internal-combustion resources. Industry experience with these generating technologies is based
on many years of accumulated knowledge, expertise and experience. Fundamentally,
conventional generation resources have relatively predictable operating performance, their
characteristics are well understood, and these resources are fully integrated into the long-term
and short-term planning and operations of the electric power system in a highly reliable manner.
Planning entities develop long- and short- term plans for transmission reinforcements required to
reliably interconnect generators, serve demand, and ensure the resulting system meets NERC and
regional reliability standards. NERC’s Regional Entities and Planning Coordinators assess the
reliability of the bulk power system by forecasting the long-term supply and demand as well as
assess generation and transmission system adequacy. Key issues and trends that could affect
reliability are also studied. With this approach, sensitivities and bulk power system weakness are
identified and addressed in a proactive manner.
Reliable power system operation requires ongoing balancing of supply and demand in
accordance with established operating criteria such as maintaining system voltages and
frequency within acceptable limits. System Operators provide for the minute-to-minute reliable
operation of the power system by continuously matching the supply of electricity with the
demand while also ensuring the availability of sufficient supply capacity in future hours.
Operators are fully trained and certified and have long standing business practices, procedures,
control software and hardware to manage the reliability of the bulk power system.
There are two major attributes of variable generation that notably impact the bulk power system
planning and operations:
Accommodating High Levels of Variable Generation 3