AEP has pioneered the use of NaS batteries in the United States. Following testing at its Dolan Technology Center near Columbus, OH, the utility became the first U.S. electric company to deploy NaS batteries in 2002 when it installed and operated a 100kW/500kVA demonstration unit in Gahanna, OH. In 2006, AEP installed a 1.2-MW stationary NaS battery near Charleston, WV. And in 2008, the utility installed three, 2-MW NaS batteries: one in Churubusco, IN.; one in Milton, WV; and one in Bluffton, OH. The 7.2 MW in NaS deployments are part of AEP’s electricity storage strategy that will also include transportable stationary batteries and distributed small scale energy storage systems.

AEP deployed all of its NaS installations as a means to provide load leveling and alleviate transformer loading during summer peaks, defer capital upgrades, and offer emergency backup power to several hundred customers during electrical system outages. Ultimately, the NaS units offer AEP a degree of flexibility in determining the optimal approach for handling reliability problems. The units buy the utility time to decide whether to redesign a substation, build generation, or keep the storage units in place permanently. (All of the NaS systems are capable of being relocated for an estimated $85,000 to $115,000 if and when the company’s needs for storage change.)

AEP’s 2-MW units were deployed in 2008, and are capable of providing islanding (backup power) for over seven hours when loss of utility power from the substation occurs. These newer installations can also perform load-triggered load leveling which, for example, allows the batteries to discharge just enough energy to hold a constrained substation transformer constant. As a result, a greater amount of energy can be reserved for islanding and battery life can be extended due to less frequent discharging.

AEP uses an in-house SCADA system and developed custom software to control all of its batteries based on the loading transformer. The software essentially creates a feedback loop where the load of the transformer is compared to a desired maximum, and the battery output is then adjusted to achieve that maximum.

Source: "Energy Storage and Project Demos" Electric Power Energy Research (EPRI)

Sodium-sulfur Battery