This reports what percentage of this module's input power is currently being drawn from the DC source versus the AC source, on a scale where 0% means fully AC-sourced and 100% means fully DC-sourced from battery, giving a live snapshot of how the module is currently splitting its power draw between the two feeds. It is a direct indicator of whether the site's AC mains has failed or degraded, since a healthy grid-connected module should sit near 0% under normal conditions, and any meaningful climb toward 100% shows that module has shifted load onto the battery source. Seeing this value jump from near 0% to 80% during a storm is a concrete sign of an AC mains sag or outage forcing the module to lean heavily on battery power.