The project will supply 8.7MW of frequency regulation support for the PJM Interconnection electricity grid and will capture, store and reuse energy derived from Septa subway trains using regenerative braking.

The equipment will be installed between seven sub-stations across Philadelphia and expand the existing 1.8MW of storage Saft has provided in two earlier installations.

Energy company Constellation will fund, own and operate the project, which uses Saft's Synerion 24P modules in rack-based installation.