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Integrating Energy Storage into the Distribution System

Energy storage systems can reduce thermal strain on the grid during peak load periods and provide a reliable backup power supply during grid outages. These systems make the grid more resilient to damage caused by extreme weather, natural disasters, and cyberattacks. In addition, energy storage systems, when coupled with renewable energy sources, can help electric utilities meet peak demand requirements without the need for additional conventional generation from burning fossil fuels. Superstorm Sandy caused major damage to the infrastructure used to transport fuels including the natural gas used in gas-fired backup generators.

Large-Scale Energy Storage Systems

Large-scale energy storage systems allow electric utilities to better utilize renewable generation produced by commercial wind and solar plants. These systems, installed at collector substations, can provide megawatt-hours of energy storage and include controls that permit this power to be dispatched when it’s needed the most ¾ during periods of peak usage. Large-scale systems dramatically reduce greenhouse gases by deferring, or eliminating, the need for additional generation produced by traditional generating sources. These systems displace peak energy costs with off-peak costs.

There are greater demands for electricity at certain times of the day. The grid can add more generation, charge time of use, or provide technology that “shaves” the peak. This is commonly referred to as peak shaving. The peak-shaving capability of large-scale energy storage systems is especially valuable during heat waves when high electricity demand and with high temperatures can cause significant thermal strain to power grid equipment. Such thermal strain can shorten the life of power grid assets and lead to equipment failures that result in outages.

Large-scale energy storage systems can also supply an immediate source of backup power in the event a major storm, other natural disaster, or cyberattack results.

Large-scale energy storage systems can be combined with a fault location, isolation, and restoration (FLISR) system to achieve dynamic islanding upon the loss of power to the feeder from the serving substation. Service is restored to the maximum number of customers based on load information captured by the FLISR system before the loss of power, and the amount of energy available in the battery. The island is minimized as the battery is depleted and/or power is restored to the feeder.

Small-Scale Energy Storage Systems

Small-scale energy storage systems use pad-mounted energy storage units distributed along residential feeders at the edge of the power grid. These battery-based units permit the integration of the community’s intermittent renewable generation resources ¾ such as rooftop photovoltaic panels and wind turbines ¾ into the grid, where these increasingly popular resources can be dispatched when needed.

The battery-based energy storage units can be aggregated to collectively provide peak shaving, improve power quality, and/or improve local voltage control to reduce losses and thus improve distribution feeder efficiencies. This aggregation of energy storage units can eliminate the need for costly, time-consuming infrastructure build-outs. Distributed energy storage can be a means for peak shaving since it doesn’t require customer involvement. The mesh communication system used to link the energy storage units can help the utility quickly find the site of a problem on the distribution system without first dispatching a crew to locate it.

The energy storage units offer reliable, local backup power for consumers as well. The close proximity of the energy storage units to consumers helps ensure the availability of supplemental power in the event of an outage. A typical 25-kVA energy storage unit can offer supplemental power to several homes for up to three hours—more than sufficient for the duration of many outages. They can also be deployed at traffic signals and used for emergency lighting, emergency communications, and more.

A fleet of larger-capacity energy storage units ¾ typically rated 250 kVA ¾ distributed throughout the grid can support hundreds of homes, small businesses, and critical infrastructure during an outage. When combined with the community’s renewable generation resources, the resultant microgrid is capable of operating for many hours or even days. Groups of these larger-capacity energy storage units can be arranged as “virtual power plants” and suitably planned to be storm-ready in anticipation of an outage. With the deployment of virtual power plants, utility crews can concentrate on service restoration elsewhere on the system.

The distribution grid, transformed into microgrids, offers an additional benefit: increased resilience to potential cybersecurity attacks.

Example Results of a Large-Scale Energy Storage System

Electric service in Presidio, Texas, is supplied by a troublesome, difficult-to-access 69-kV line. Repairs to this line frequently take a long time. Because of its limited connection to the grid ¾ and its high summer and winter peak loads ¾ Presidio often experiences protracted power outages, especially from storm-related damage.

To improve power quality and reliability, the serving utility, AEP, procured a large-scale energy storage system which they applied in conjunction with a distributed-intelligence FLISR system to provide dynamic islanding for the entire town. The energy storage system has substantially improved power quality and decreased the number of outages experienced by utility customers in the Presidio area.

Small-scale community energy storage projects have been deployed in the United States, the United Kingdom, New Zealand, and elsewhere.

Roadmap Recommendations

Implementation of an energy storage system typically involves several steps, including:

  • performance of analytical studies to determine the energy storage solution which will maximize reliability and availability of the grid
  • appropriate planning and procurement services to ensure timely project completion
  • a communication site survey to ensure acceptable signal strength between radios installed in the energy storage units

