Why shadow scan is needed?
As we know, the MPPT or Maximum Power Point Tracking function in a converting system ensures the solar inverter work at its maximum power by tracking DC voltage and current. This works for all inverters under normal conditions (without shadowing).
When the inverter works, the MPP tracker starts working (Fig 1), scanning from the right side (Open-Circuit Voltage) to the left side (Minimum MPP tracking voltage) to track the first maximum power point.
Fig 1. MPP Tracking Under Uniform Condition
So what will happen when there is shadow on PV module strings? MIGHT NOT BE AT ITS MAX POWER! When there’s a shadow, the output power has multiple extreme power points instead of one maximum power point only. (Fig 2) However, the tracker will still stop at the first maximum power point it tracks, which will cause a power loss of the solar system.
Fig 2. MPP Tracking Under Shaded Condition
That is why the shadow scanning function or optimizer is adopted in solar systems.
What is shadow scan?
When the shadow scan function is activated, the MPP will scan the whole voltage range regularly to help locate the real maximum power point from multiple fake MPP points like in Fig 3.
Fig 3. Shadow Scan Result Under Shaded Condition