The SMA Sunny Boy, Fronius and Xantrex GT-3 inverters are string inverters. The name “string” comes from the way the PV modules are wired together, in series to achieve a higher voltage. These inverters are designed to run at voltages up to 600 VDC. String wiring is faster to install, more efficient and allows the use of smaller gauge wire. DC voltage this high can be very dangerous and life-threatening, so string inverters should be installed and serviced by qualified electricians.
Module optimizers, such as those from Tigo and SolarEdge, mount behind each module like a micro inverter and provide individual module MPPT tracking and monitoring but have a DC output that is connected to a string inverter. these devices simplify system design and increase safety at a cost slightly below that of a micro-inverter.A grid-tie PV system uses the utility company, in effect, as its storage battery. When the sun is shining, your electricity comes from the PV array, via the inverter. If the PV array is generating more power than you are using, the excess is sold to the power utility company through your electric meter, by making the meter run backward. When you need more power than the PV array can supply, the utility makes up the difference. This type of system makes the most sense in most cases where you have utility power, because there are no batteries to maintain or replace. Unfortunately, if the utility power goes down, this type of inverter will go off, too, regardless of whether or not the sun is shining.