Controlling an energy storage system includes accessing monitored sensor data and component data, if the DC bus voltage is less than the renewable energy power module (REPM) output voltage then selecting battery modules in combination with a power-network inverter to source power to the bus, else if greater than the REPM voltage then selecting battery modules in combination with the inverter to sink power from the bus, instructing respective control processors of the selected battery modules and a control processor of the inverter to either source/sink power respectively to/from the DC bus, accessing updated DC bus voltage and updated REPM output voltage, and if the DC bus voltage and the REPM output voltage are about equal, then periodically accessing sensor data and component data, else reselecting and reinstructing the battery modules in combination with the inverter. A system for implementing the method and a non-transitory computer-readable medium are also disclosed.