Accommodating High Levels of Variable Generation - NERC

Power System Operations
4. Power System Operations
This chapter describes the key issues and considerations related to the operation of the bulk
power system with large-scale integration of variable generation, with a focus on the integration
of wind resources, where substantial industry experience has begun to accumulate. That said,
much of this valuable experience can also be applied to the reliable integration of other variable
generation resources
As discussed in Chapter 2, where it is uncontrolled, the output of variable generation is
dependant upon the availability and characteristics of its primary fuel. For example, a variable
generator may produce no energy at the time of system peak demand even if it is not in an outage
condition, or it may produce peak energy during an off-peak period, and may ramp up or down
in opposite direction to system needs for ramping (See Resource Adequacy Planning in Chapter
3). This Chapter first describes the major operational characteristics and potential challenges
associated with high levels of variable generation in a power system and then provides a
description of potential solutions to address these challenges. These aspects are discussed within
three related, but distinct time domains: forecasting, commitment and dispatch. The issues and
opportunities associated with larger balancing areas or participation in wider-area balancing
management, along with reduced scheduling intervals is also discussed.
4.1. Forecasting
As described in Chapter 2, variable generation resources have a certain amount of inherent
uncertainty. However, in many areas where wind power has not reached high penetration levels,
uncertainty associated with the wind power has normally been less than that of demand
uncertainty. Operating experience has shown that as the amount of wind power increases (i.e.,
greater than 5% of installed capacity) there is not a proportional increase in overall uncertainty.
Consequently, power system operators have been able to accommodate current levels of wind
plant integration and the associated uncertainty with little or no effort.
Forecasting the output of variable generation is critical to bulk power system reliability in order
to ensure that adequate resources are available for ancillary services and ramping requirements.
The field of wind plant output forecasting has made significant progress in the past 10 years.
The progress has been greatest in Europe, which has seen a much more rapid development of
wind power than North America. Some balancing areas in North America have already
implemented advanced forecasting systems, and others are in various stages of implementation
process including the information gathering and fact-finding stage.
Accommodating High Levels of Variable Generation 54