What's the Difference between on Grid inverter and Off Grid inverter?

3Phase 5KW On-Grid Solar inverter

On Grid or called Grid Tied Grid connect solar inverter convert solar DC power to normal AC power, then supply loads at first and feed surplus(if any) the power to utility electricity Grid to get FiT or Net-metering from Grid companies or your government. CoHeart has been developing On-Gird solar PV inverters since 2011 and now we have 3rd generation 250W-20KW without fans at highest efficiency! Patented topology and structure design with robust Grid adaptability! Best choice special for bad Grid !Features:Transformerless with Three Level topologyMax.efficiency 98.2%.Dual MPPT with wide input voltage rangeCompact structure No-Fan Design !Flexibility:Rain/Dust proof Aluminum-alloy case (IP65)Easy installation and free maintenanceRS485/WiFi/GPRS (optional) monitoringSet all on larger LCD display!Reliability:Reliable protection for over/under voltage, anti-islanding,short circuit,overload, ISO detect, RCD detect, over-heating etc.5-years quality warranty ..