Well Stormy, my book learnin is a bit old, but when I went to school, the inverters had the electrical components inside that allowed just that type of action. They can do this to power key loads such as emergency medical devices and things like a freezer, and not send anything back to the grid. This would work for solar or a generator. You would either need to pre wire circuits in the main panel, have the power go to a separate panel, or just have an extension cord or two that then could power the devices that need the constant power. The next step up from that would be a non grid tied system where you keep it all...all of the time. The main problem with all of this is even if you have a "transfer power switch", you need to make sure you are not back feeding or "islanding" power back into the grid. This could kill a utility worker who is working on a power line he thinks is dead.