Energy storage technology could become an important tool for reliable electricity transmission under proposed rule changes ISO New England has submitted for approval to the Federal Energy Regulatory Commission (FERC).
Storage can take a variety of forms, with two prominent examples being emerging battery technology and pumped hydro. These types of resources already participate in New England's wholesale electricity markets by buying and selling capacity, energy, or ancillary services.
The proposed change would create a new, separate class of storage resources that would not participate in the markets, meaning they would have minimal effect on wholesale electricity prices. Instead, these resources would be purpose-built as transmission equipment and known as "storage as a transmission-only asset" (SATOA).
While SATOAs would be owned and maintained by transmission companies, ISO New England system operators would control their use. They would be used under rare system conditions to prevent localized overloading after at least two unplanned equipment outages on the transmission system.
To illustrate when a SATOA would be used, imagine a town served by three transmission lines. The town uses 100 megawatts (MW) of electricity and each transmission line is designed to supply 75 MW. If one transmission line were to be knocked out by a storm, the other two lines would continue to supply all the electricity the town needs with no problem. If the storm took down two lines, the remaining third line would be overloaded and a power outage would be imminent. But if there were a SATOA in the area, ISO system operators could activate it to provide power and relieve the strain on the transmission line.
SATOAs also could be deployed as a last resort to help prevent or mitigate controlled outages in the unlikely event that demand for electricity were to exceed the regionally available supply, or to assist with system recovery after an outage.
Construction of SATOAs by transmission companies would depend upon selection in the open regional system planning process administered by ISO New England, similar to the way reliability-based system upgrades are handled today.
The ISO has asked FERC to approve the rule change request by March 29 to allow implementation by a target date of July 1, 2024.