Solar Micro Inverters are very small inverters designed to handle the output of a single solar pv panel. This avoids the issues usually associated with string inverters, as micro inverters serve to isolate each solar panel from each other.
This means that any factors that affect a panels performance would have no effect on the other panels in the string. For example, if one panel were to become shaded, only the panel(s) being shaded would be affected - the rest of the system would not be affected.
The main disadvantages of micro inverters is time and cost. With a string inverter, an installer would install the panels, wire them, and then run the wire to the central inverter. With micro inverters, each module must be installed, and then the micro inventers must be installed and wired to each individual module. Then the micro inverters must be wired to a trunk cable, and then run to the junction box.