A grid-interactive backup system is designed for commercial sites that want to reduce normal electricity costs while also maintaining selected loads during utility outages. During grid-connected operation, the battery may support peak shaving, solar self-consumption or tariff shifting. When the grid fails, the system isolates a protected section of the facility and uses the battery and available solar generation to maintain critical operations. I see this configuration as particularly relevant for factories, hotels, warehouses, clinics, schools, supermarkets and cold-storage facilities in markets where the grid exists but is unreliable. The most important design decision is not the battery cabinet size but the critical-load boundary. A factory with an 800kW total load may need to protect only 180kW of production controls, refrigeration, communications and safety equipment, while a hotel may maintain elevators, reception, lighting and essential guest services without backing up every air-conditioning unit. Backup operation also requires more than installing an ATS beside the battery. The PCS must be capable of grid-forming operation, the protected loads must be separated safely from the utility network, and the EMS must manage the transition between grid-connected and islanded operation while preserving sufficient battery reserve. Motor starting, transfer time and load sequence must also be considered because compressors, pumps, chillers and elevators may create much higher temporary demand than their normal running power. Before selecting this architecture, I need the peak load, average load, critical-load schedule, motor-starting information, required backup duration, switchboard arrangement, existing solar capacity, grid voltage and acceptable transfer time.