Accommodating High Levels of Variable Generation - NERC

Introduction
American Climate Change Initiatives. 5 The Canadian government has set an overall goal of a
20% reduction in greenhouse gas emissions by 2020 using a 2006 baseline, with specific energy
policies and greenhouse gas emission and renewable energy targets under development by each
province.
Most of these North American targets are expected to be met by wind and solar 6 resources. In
fact, based on the powerful economic and policy drivers mentioned above, wind resources are
expected to constitute a significant portion of all new generation being added to the bulk power
system in many parts of North America. 7
This proposed level of commitment to renewables offers many benefits, as well as certain
challenges, to the reliability of the bulk power system in North America. Unlike conventional
resources, output of wind, solar, ocean and some hydro 8 generation resources varies according to
the availability of a primary fuel that cannot be stored. Therefore, the key differences between
variable generation and conventional power plants are that variable generation exhibits greater
variability and uncertainty in its output on all time scales. Some amount of variability and
uncertainty already exists on the bulk power system with regard to the demand for electricity in
particular, and, to a lesser extent, to generation. To accommodate higher penetration of variable
generation, changes will be required to traditional methods used by system planners and
operators in order to maintain the reliability of the bulk power system on an ongoing basis.
Making these significant changes will be challenging for the industry, however they will be
needed to continue maintaining bulk power system reliability while integrating large amounts of
variable generation.
The North American Electric Reliability Corporation’s (NERC) mission is to ensure the bulk
power system in North America is reliable. To achieve this objective, NERC develops and
enforces reliability standards; assesses adequacy annually via a 10-year forecast and winter and
summer forecasts; monitors the bulk power system; and educates, trains, and certifies industry
personnel. NERC is a self-regulatory organization, subject to oversight by the U.S. Federal
Energy Regulatory Commission and governmental authorities in Canada.
5 Renewable Portfolio Standards in the United States”, Lawrence Berkeley National Laboratory, April 2008.
6 During the time period this report was being prepared, solar development activity (as measured by interconnection
requests for large solar plants) has dramatically increased. In the California ISO generation interconnection
queue, interconnection requests for solar resources (all types) increased from 51 applications representing 17,600
MW in January 2008 to 91 applications representing nearly 30,000 MW (Source: California ISO website). In
Arizona, the number of (non-California ISO) interconnection applications for large solar increased from four
interconnection requests representing 920 MW in November 2007 to 33 requests representing 8,013 MW in
December 2008 (Source: SWAT Renewable Transmission Task Force Presentation, January 2009)
7 http://www.nerc.com/files/LTRA2008.pdf
8 Hydro, typically large scale using dams are not considered variable in this report.
Accommodating High Levels of Variable Generation 2