WHAT’S A SOLAR INVERTER?
Solar Panels convert light energy into DC (Direct Current) form of electricity. Inverters convert this DC electricity to the AC (Alternating Current) form – this is the type of electricity we use in our homes through the AC outlets and that is provided by the electric utility. The conversion can take place at each solar panel (micro-inverters) or the conversion of all the panels can take place centrally (string inverters).
One type is not inherently “better” than the other – they are just different ways of accomplishing the same thing; but, since they are different, one may be a better choice than the other depending on the situation. One other device, the power optimizer, which is not an inverter, is commonly used in a string optimizer based system to provide a functionality that is inherent with micro-inverters.
Since an inverter converts energy frorm one form to another, there will be a loss of energy in the process and the efficiency rating provides this value. Today, the gap in the efficiencies of the micro vs string inverters are almost negligible.
For technical reasons, for some solar panels, only the string inverter can be used (today), e.g. panels with 72 or 96 cells since most micro-inverters today support only 60 cell panels.
From a cost perspective, micro-inverters and the string inverter plus power optimizer options are about the same.
Most micro-inverters connect to one solar panel (there are some that connect to more panels).The micro-inverter takes the DC output from the solar panel as its input and then outputs the AC form. The AC outputs of each micro-inverter are connected together, close to the panels, and a single set of AC wires are routed to the cut-off switch at ground level.
The DC outputs of all solar panels are connected to a common set of wires on the roof and then routed to the DC cut-off switch at ground level. From the DC cut-off switch, the DC is inputted into the central string inverter that then outputs AC. They are call “string” inverters because each string inverter is connected to a grouping of panels called a “string.”
Power optimizers take the DC from the solar panel and provides an “optimized” DC output that is then fed into a string inverters. Power optimizers were developed to address some of the short-comings of string inverters such as marginal performance of some panels affecting the whole system and per panel monitoring. Although power optimizers are cheaper than micro-inverters, one power optimizer is required for each panel, in addition to the string inverter, making the total system about the same.