Accommodating High Levels of Variable Generation - NERC

Transmission Planning & Resource Adequacy
generation are added to a system with a given correlation between the existing and added wind
capacity, the incremental contributions to reliability decrease. Once the LOLP in a given hour is
sufficiently small, the addition of more capacity in that hour has a relatively small contribution to
reliability.
Figure 3.3: Alternative peak periods are used to assess wind capacity value in the U.S. 56
In high variable generation penetration scenarios, a larger portion of the total supply resource
portfolio, in comparison to today’s power systems, will be increasingly comprised of energylimited
resources – meaning that their availability at times of peak electricity demand is limited.
Energy output from variable resources is not as consistent as output from thermal power plants
and cannot be dispatched when the fuel (wind, solar, etc.) is not available. This fact somewhat
complicates, but does not fundamentally change existing, capacity-driven resource adequacy
planning processes in that the process must still be driven by a reliability-based metric such as
LOLE, LOLP, or EUE. Consistent methods are required to represent capacity values of variable
generation suitable for NERC reliability assessments. Therefore, the recommended NERC action
is:
56 Note PNM does not have an official method for calculating Capacity Value.
Accommodating High Levels of Variable Generation 40