Grid-tie inverter :
A grid-tie inverter is a power inverter that converts direct current (DC) electricity into alternating current (AC) with an ability to synchronize to interface with a utility line. Its applications are converting DC sources such as solar panels or small wind turbines into AC for tying with the grid.
Off-Grid invertermeant to be used with solar, wind or hydro power systems for a home or business totally disconnected from the electric utility company. They can also be used for providing emergency backup power to homes that currently use the power from an electric company