Accommodating High Levels of Variable Generation - NERC

Transmission Planning & Resource Adequacy
other weather-dependent energy sources, such as hydro, as their mutual weather dependence
could result in correlated decline or increase in output across multiple resource groups for certain
weather patterns. For example, if seasonal weather patterns are shown to result in both dry (lowhydro)
and low-wind conditions (low-wind), planning scenarios should consider simultaneous
low production levels from the affected resources. Similarly, if wet seasonal conditions are
shown to occur with high wind conditions, seasonal planning scenarios should consider
simultaneous high wind and hydro production.
3.3. Transmission Planning
Transmission planning processes to integrate large amounts of variable generation rely on a
number of factors, including:
• Whether government renewable policies or mandates exist;
• Level of variable generation mandated and available variable generation in remote
locations;
• Time horizon across which capital investments in variable generation are to be made; and
• Geographic footprint across which the investments occur.
At low variable generation penetration levels, traditional approaches towards sequential
expansion of the transmission network and managing wind variability in Balancing areas may be
satisfactory. However, at higher penetration levels, a regional and multi-objective perspective
for transmission planning identifying concentrated variable generation zones, such as those being
developed in ERCOT’s Competitive Renewable Energy Zone (CREZ) process, California’s
Renewable Energy Transmission Initiative (RETI) and the Midwest Independent System
Operator’s Joint Coordinated System Planning Study, 59 may be necessary.
Within a balancing area, as the level of variable generation increases, the variability when
coupled with extreme events may not be manageable with the existing conventional generation
resources within the balancing area alone. Furthermore, base load generation might have to be
heavily cycled for the local generation to follow the sum of load and variable generation
variations, posing reliability concerns as well as economic consequences. If there is sufficient
bulk power transmission, this situation can be managed by obtaining ancillary services and
flexible resources from a larger generation base, such as through participation in wider-area
balancing management or balancing area consolidation (see Chapter 4). Transmission planning
and operations techniques, including economic inter-area planning methods, should be used for
59 www.jcspstudy.org
Accommodating High Levels of Variable Generation 42