No. Your house remains connected to the grid and you draw electricity from the grid when you need it. With net-metering in Massachusetts, the utility (NSTAR) essentially acts as a “virtual battery” for your system. That is, whenever your solar panels don’t produce enough electricity to meet your electrical demand, you can get the rest from the grid. When you produce more electricity than you consume, your meter will spin backwards and reduce your bill or create a credit on your bill that essentially stores your “overproduction” for future use, just as a battery would.
You can install a battery backup system to help you ride through power failures. This is an added cost that should be discussed with the installers.