This is an excellent example of an on grid home that encompasses a battery bank. This gives the home owner the best of all worlds. When the grid goes down this system provides power to major appliances, powering these thru what we term a critical load subpanel. These electrical loads typically include the water pump, furnace, communications and lighting. In normal day to day operation the system powers the home and sends any extra power backwards thru your meter, giving a credit toward your power bill. Having a system that provides both on grid feedback and battery backup for grid down times does necessitate additional equipment and cost over a more standard grid tie system.