Accommodating High Levels of Variable Generation - NERC

Transmission Planning & Resource Adequacy
Demand response can operate in every time frame of interest, from seasons to seconds,
supporting variable generation integration. Demand response has already been shown in some
balancing areas to be a flexible tool for operators to use with wind generation 71 and is a potential
source of flexibility equal to supply-side options (i.e. to counter variable generation down
ramps). Different demands have different response capabilities, and different costs to respond.
More work is required to identify demand response opportunities and to develop commercial
arrangements to obtain a significant aggregate response.
Energy storage technologies also have the potential to assist the large-scale integration of
variable generation. 72 The ability of storage to transform energy into capacity has many
advantages depending on the technical capabilities and economics of the technology. Pumped
hydro comprises the vast majority of energy storage used today, though there are numerous
storage technologies in various stages of development and commercialization that can provide
effective system flexibility. Technologies, like battery energy storage (BESS), flywheel energy
storage (FESS), and Compressed Air Energy Storage (CAES), are rapidly becoming commercial.
73 The present economic drivers for energy storage with fast discharge are stronger and growing
faster than those with longer term discharge characteristics.
However, the cost of storage devices compared to other methods of flexibility currently has
limited their applicability to specific and limited situations. The benefits of energy storage are
most broadly realized and valuable when operated as a system resource for the benefit of the
entire system, and not in a dedicated mode for any individual resource such as variable
generation plants. 74 As a system resource, energy storage may be linked to power system
network controls and responsive to system operators to provide ancillary services such as
regulation, demand following (ramping), capacity, etc. As a network resource, it is available to
balance variability of any combination of resources and demands.
Nevertheless, the recent Department of Energy 20% by 2030 report 75 indicates that serving 20%
of annual energy with wind resources in the United States would not require storage resources,
assuming sufficient transmission exists. 76
71 J. Dumas, “ERCOT February 26, 2008 EECP Event,” Presented at UWIG Spring Workshop, Fort Worth, TX,
April 2008.
72 KEMA, “White Paper - Benefits of Fast Response Storage Devices for Regulation,” November, 2008
73 Greenblatt, J.B., Succar, S., Denkenberger, D.C., Williams, R.H., Socolow, R.H., “Baseload wind energy:
modeling the competition between gas turbines and compressed air energy storage for supplemental generation,”
Energy Policy, Volume 35, pp. 1474 – 1492, 2007.
74 Sullivan, P., Short, W and Blair, N. “Modeling the Benefits of Storage Technologies to Wind Power,” American
Wind Energy Association Wind Power Conference, Houston, Texas, June, 2008.
75 See http://www.20percentwind.org/ for more details
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