A string inverter PCS for use with a photovoltaic array and configured to supply power to one or more back-up loads , the string inverter PCS comprising: at least one string-level DC input channel for receiving DC power from a photovoltaic array, wherein the at least one input channel performs maximum power point tracking; at least one input-output channel for connecting the string inverter to a battery pack ; a DC to DC buck-boost circuit coupled between the at least one string-level DC input channel and the at least one input-output channel for preventing more than a predetermined amount of DC voltage from reaching the battery pack; a DC to AC inverter circuit having an output terminal; a revenue grade power meter configured to measure an AC output of the DC to AC inverter provided on the output terminal; an anti-islanding relay coupled to the revenue grade power meter , and a protected load relay coupled to the anti-islanding relay, and a switch , coupled to the protected load relay, and configured to control, together with the anti-islanding relay and the protected load relay, a flow of power between the DC to AC inverter , the AC grid and the one or more back-up loads based at least in part of the position of the switch, the switch being a three-position switch, wherein in a first position, AC power output from the DC to AC inverter is permitted to flow from the DC to AC inverter via the protected load relay to the AC grid and the one or more back-up loads; in a second position, power is permitted to flow from the AC grid to the one or more back-up loads bypassing the DC to AC inverter with inverter output disabled; and in a third position, the AC grid and the one or more back-up loads are electrically disconnected from the DC to AC inverter . at least one string-level DC input channel for receiving DC power from a photovoltaic array, wherein the at least one input channel performs maximum power point tracking; at least one input-output channel for connecting the string inverter to a battery pack ; a DC to DC buck-boost circuit coupled between the at least one string-level DC input channel and the at least one input-output channel for preventing more than a predetermined amount of DC voltage from reaching the battery pack; a DC to AC inverter circuit having an output terminal; a revenue grade power meter configured to measure an AC output of the DC to AC inverter provided on the output terminal; an anti-islanding relay coupled to the revenue grade power meter , and a protected load relay coupled to the anti-islanding relay, and a switch , coupled to the protected load relay, and configured to control, together with the anti-islanding relay and the protected load relay, a flow of power between the DC to AC inverter , the AC grid and the one or more back-up loads based at least in part of the position of the switch, the switch being a three-position switch, wherein in a first position, AC power output from the DC to AC inverter is permitted to flow from the DC to AC inverter via the protected load relay to the AC grid and the one or more back-up loads; in a second position, power is permitted to flow from the AC grid to the one or more back-up loads bypassing the DC to AC inverter with inverter output disabled; and in a third position, the AC grid and the one or more back-up loads are electrically disconnected from the DC to AC inverter . <EOS>