The following article is part 2 of a multi-part series.
B. Transmission and Distribution System Support
The increased utilization of energy storage systems for transmission and distribution support will lead to improved reliability and efficiency in the delivery of electricity. Transmission and distribution systems have dynamic characteristics (i.e., capacity and load) at each location within the system. The versatility and range in operational performance of energy storage systems allows for its deployment throughout the transmission and distribution system. Specifically, energy storage can provide: 1) transmission and distribution stability; 2) transmission congestion relief; 3) transmission or distribution equipment upgrade deferral; and 4) provide onsite substation power. Electric utilities may also utilize distributed energy storage systems to provide distribution system support services.
1. Transmission/Distribution Stability:
Energy storage systems connected to transmission and distribution systems improve stability and performance by counteracting voltage dips and other similar events that disrupt the flow of electricity over transmission lines.  Improved transmission line reliability increases load carrying capacity, which in turn improves efficiency by reducing congestion relief and the need for further investment in transmission expansion.
2. Transmission Congestion Relief:
Transmission congestion decreases system efficiency and increases electric prices through congestion charges or locational marginal pricing. It occurs when peak load requires more electricity than the transmission systems can provide. Furthermore, congestion drives the increased need and associated costs of transmission system expansion. Energy storage systems that are deployed downstream from the transmission congestion point can alleviate congestion and thus, mitigate upwards pressure on electric prices and defer and/or eliminate the need for further transmission expansion.
3. Transmission/Distribution Upgrade Deferral:
Incremental increases in capacity provided by energy storage systems defer the need for utility investment in transmission and distribution system upgrades. Specifically, utilities can deploy stationary or transportable energy storage systems to defer upgrades in equipment and improve power restoration times. Stationary distribution deferral allows a two to four year delay of new equipment and lines where load growth is low and capital expenditures are high. Transportable distribution deferral allows utilities to place transportable storage systems in areas of need to improve power restoration times and outage mitigation. Energy storage systems also extend the life of existing transmission and distribution equipment by reducing the load demand on the equipment. By extending the life of existing transmission and distribution equipment, energy storage technologies improve asset utilization, reduce utility investment risk on large equipment, free capital and reduce overall transmission and distribution costs to ratepayers.
4. Distributed Energy Storage:
Distributed energy storage is an emerging transmission and distribution support application. The application involves electric utilities controlling and aggregating small scale energy storage systems located on the utility side of the meter to provide large scale distribution support. Utilities remotely manage the charge and discharge of each storage system to support grid peak loads and backup power.
C. Ancillary Services
Ancillary services are necessary to maintain the reliable transmission of electricity. Storage systems that provide ancillary service mitigate system disturbances in voltage, momentary fluctuations in load, frequency, energy imbalance and unexpected generation outage. Each disturbance provides a constant threat to the reliable delivery of electricity throughout the bulk electric system.
The operational characteristics of some energy storage systems make them an ideal resource for ancillary service. Storage systems performing ancillary service applications provide faster response times to automated control signals over traditional generation resources. Faster response times can result in a reduction of resources needed to perform adequate service. This, in turn, improves efficiency across all energy markets by freeing traditional generation resources to perform more operationally efficient services such as capacity service.
 Energy storage systems installed onsite at substations provide an efficient means to power switching components, communication and control equipment while not being energized by the grid.
 Energy storage systems can also provide other transmission stability applications such as damping, sub-synchronous resonance damping and under-frequency load shedding reduction. Ibid. .
 Electricity Energy Storage Technology Options: A White Paper Primer on Applications, Costs and Benefits, Prepared by Electric Power Research Institute, Rastler. D (Principal Investigator), December 2010.
 Ibid. .
 Ibid. .
 Ibid. .
 Ibid. .
 Regulation service corrects momentary fluctuations in load in a control area by supplying extra generating capacity.
 Frequency Response maintains the primary frequency (60Hz).
 Energy imbalance service supplies an hourly imbalance between transmission energy supply and load being served in a control area. This service corrects any imbalance over an hour between scheduled delivery of energy and the actual load that the energy serves.
 Contingency reserve service provides power during unexpected generation outages. Reserve service requires two different response times. Spinning reserve must respond instantaneously to unplanned outages. Non-spinning or supplemental reserves typically have 10 minutes or longer to respond. Discharge time varies upon load dynamics and market rules.
 Makarov, Y.V., Ma, J., Lu, S., & Nguyen, T.B. Assessing the value of Regulation Resources Based on Their Time Response Characteristics. Pacific Northwest National Laboratory, PNNL 17632, June 2008.
Written by Robert Clifford. Robert is a Boston-based attorney who represents clients before the Federal Energy Regulatory Commission and state public utility commissions.