It is true that "anti-islanding" is necessary to keep linemen safe from electrocution. There are different types of systems available. An example, the Xantrex XW6048 inverter/charger system can be programmed as a stand alone grid tied PV system, it can be formatted to be a battery backed grid tied system, if the power fails the DC from the panels still charges a battery pack, or it can be programmed as an off grid system. IF you KNOW the DC voltage of a particular system, one can find an actual stand alone inverter that would be used on an off grid application to supply power to specific devices, like refrigerators, furnace blower motors, ceiling fans. One such system was diagrammed in Home Power Magazine a year or so ago. The stand alone system was driven through a disconnect switch to insure the grid tied system could not send power back into the grid, "back feed". Then the smaller system produced enough power on battery to fool the grid tied system into producing power while the sun was out.