Energy Storage- Shaving load peaks from the substation

Welcome to the future of bulk electricity storage. 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.

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.

In addition to using the battery system to shave demand peaks, AEP envisions employing it to accumulate and store for subsequent dispatch electrical energy generated by intermittent generating units such as wind turbines and solar cells. The name given to the system—the Distributed Energy Storage System (DESS)—implies that it will have many applications on the utility's T&D grids. "Our goal is to deploy plenty of distributed energy storage capacity on our grids over the next decade," said AEP Program Manager Ali Nourai. "We intend to have a very resilient system that can absorb customer-operated distributed generation capacity as it connects to our grid."

AEP and several other U.S. utilities are currently field-testing a variety of distributed energy storage systems. Although the Charleston battery project (which cost about $2,000/kW) was slightly more expensive than upgrading the substation's components to handle higher loads, the system is expected to deliver many intangible benefits, including invaluable and unique operating experience.

The project was partially funded by a grant from the U.S. Department of Energy's Sandia National Laboratories. Sandia will closely monitor the system's performance during the first year of service and produce detailed reports that will help other potential users of energy storage better understand the costs and benefits of using bulk storage to prop up a grid being stressed by peak demand.

AEP chose the NaS battery system for its very high power density and its operating experience in Japan. Over the past decade, NGK and the battery's co-developer, Tokyo Electric Power Co., have deployed in their home country NaS batteries totaling 150 MW of capacity.

source: powermag.com