Shaving load peaks from the substation

Brad Roberts, S&C Electric Co.

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As load growth on U.S. transmission and distribution grids continues to shrink reserve margins nationwide, utilities are looking for new ways to meet demand peaks. Until recently, the most elegant (no moving parts) option at utility-scale levels—adding a sizable storage battery to a substation—remained just out of reach because available batteries weren't able to meet the hours of discharge on a daily basis.

Welcome to the future of bulk electricity storage (see box). Earlier this year, American Electric Power (AEP) installed a 1.2-MW sodium sulfur (NaS) battery and accompanying inverter (Figure 1) at the Charleston Substation of its subsidiary, Appalachian Power. The Charleston Substation was chosen to host the installation for several reasons related to economics, service reliability, and local load growth.

Hook up with the Electricity Storage Association

The ability to store large quantities of electricity for retrieval on demand has long been considered the Holy Grail of power transmission and distribution. For the past 15 years, the Electricity Storage Association (ESA) has been the primary springboard for developing and testing new technologies capable of making utility-scale electricity storage a reality.

All of the companies and government agencies that participated in the AEP NaS battery project are ESA members. The organization's 70-plus member equipment suppliers, consultants, and government agencies meet at least once a year to provide a forum for discussing existing and planned electricity storage projects.

For more information about the ESA, visit www.electricitystorage.org.

1. Small package, big punch. The 1.2-MW Distributed Energy Storage System installed at the Charleston Substation of AEP's subsidiary, Appalachian Power. Courtesy: American Electric Power

The main function of the system is to supply up to 7.2 MWh of electrical energy on demand for peak-shaving purposes. However, it also has a business purpose. According to AEP, the system will enable deferment of equipment upgrades to the Charleston substation for six or seven years, at which time the battery can be relocated to another substation and play similar roles there. The battery's manufacturer—NGK Insulators Ltd. of Japan—expects the battery to last for 15 years, assuming that it will be charged and discharged 4,000 to 5,000 times up to 90% of its full capacity.

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