A system includes an uninterruptible power supply (UPS) configured to selectively provide power to a critical load from a grid and an energy storage device, and a grid edge controller configured to communicate with a controller of the UPS and to cause the UPS to operate the energy storage as a distributed energy resource (DER) for the grid while preserving autonomous operation of the UPS to serve the critical load. The grid edge controller may be configured, for example, to maintain a critical reserve in the energy storage device that enables the UPS to maintain the critical load, while allowing the energy storage device to also be used for demand management, frequency regulation and other grid-oriented tasks. The grid edge controller may be configured to control the UPS, for example, via an application programming interface (API) of the controller of the UPS.