Accommodating High Levels of Variable Generation - NERC

Transmission Planning & Resource Adequacy
known. For example, selection of a specific dispatch level for these generators, as is
required under deterministic planning methods, may not identify important scenarios
impacting reliability which should be studied and for which actions should be taken.
NERC’s Transmission Planning (TPL) Standards are the foundation for transmission planning in
North America. These standards are deterministic in nature and are based on the prespecification
of critical conditions. However, with the incorporation of variable generation
resources, planning process will need to be augmented as the number of scenarios for which
sensitivity analysis must be performed to “bracket” the range of probable outcomes, which can
dramatically increase. 62
Probabilistic or risk-based approaches are becoming more popular worldwide for system
planning. Some probabilistic planning criteria, tools and techniques have been developed over
the past several decades; however, they will require critical review for completeness and
applicability before they can become an industry-accepted approach to consistently measure bulk
power system reliability.
There is a marked benefit in pursuing probabilistic methods for both long-term and operational
planning of the power system in order to more systematically and adequately quantify the risks
associated with various planning options due to the high variability and probabilistic nature of
many of the elements of the modern power system (variable generation, market forces, etc.).
Much research is likely to be needed to fully develop and employ such methods. As a first step,
a present CIGRE effort 63 is identifying the gaps between deterministic and probabilistic methods,
assessing the benefits that can be reaped from probabilistic methods, considering the practical
challenges with attempting to apply probabilistic methods to planning, and identifying the
research and tools development that may be needed to move towards probabilistic methods.
The necessary detailed datasets to study all types of variable generation are not yet available. To
ensure the validity of variable generation integration study results, high-quality, and highresolution
(sub-hourly if possible) output data is required. Currently, historical data of variable
generation performance is very limited and difficult to obtain. As substantial amounts of
variable generation are expected to be added to the bulk power system during the next ten years,
industry must begin obtaining the data as required to design robust bulk power systems. To this
point in time, extensive modeling has been used to generate simulated data either directly or
indirectly from historical weather data. The use of indirect data is far from ideal and, as real data
becomes available, the validity of the original results should be reviewed.
62 FERC order 693, paragraphs 1694 to 1719 http://www.ferc.gov/whats-new/comm-meet/2007/031507/E-13.pdf
63 CIGRE Working Group C4.601, Power System Security Assessment.
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