How does Shadow Scan Work?

Author: Craig

2021-10-28 11:22

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 find the first maximum power point.

 

Fig 1. MPP Tracking Under Uniform Condition

 

So what happened when there is shadowing 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 only one maximum power point. (Fig 2) However, the tracker will still stop at the first maximum power point it meets, which could cause power loss from the solar system.

Fig 2. MPP Tracking Under Shaded Condition

 

That is why shadow scanning function or optimizer is adopted in solar system.

 

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

 

How Does Shadow Scan Work?

Shadow scanning function, an optional and periodical operation, is available on all GoodWe residential and commercial inverters. The operation principle is as following:

* FIRST STEP: Ready for scanning (Fig 4)

When the function is activated, MPP tracker will track back to the original voltage point to get ready for scanning the whole voltage range.

Speed: 15V/500ms

Start Point: Present Working Voltage

Back-track Point: PV String Open-Circuit Voltage or Max MPPT Range, or PV power ＜50W

 

Fig 4. Ready for Scanning

 

* SECOND STEP: Scan Whole Voltage Range (Fig 5)

By scanning the whole voltage range to find out the real highest power point.

Speed: 4V/500ms

Start Point: Ready Point - PV String Open-Circuit Voltage or High MPPT Range, or PV power ＜50W

Back-track Point: Low MPPT Range

Fig 5. Scan Whole Voltage Range

 

* THIRD STEP: Track Back to The MPP Voltage (Fig 6)

As the tracker find out the real maximum power point, it will track back to the point to make sure the inverter works at the max power of PV strings.

Speed: 15V/500ms

Start Point: Low MPPT Range

Back-track Point: MPP Voltage / Maximum Power Point

Fig 6.  Track Back to The MPP Voltage

 

NOTE: During scanning, the scanned MPPT will not stay on the maximum power point. The real power will change following the scanning process. 

 

SCANNING INTERVALS

The GoodWe solar inverters differ in shadow scan interval. We defined shadow scan interval time as the overall scan time of the specific inverter. The overall scan time is equivalent to the number of MPPTs times the scan interval between MPPTs as following.

 

Note:

1. All MPPTS on one inverter are scanned one by one, Multi MPPTs will not be scanned at the same time.

2. Shadow scan function is turned off as default setting on each inverter. If it needs to be activated, please do the commission on the display or through SolarGo APP (Fig 7)

(Please refer to the attachment for more information.)

     

     Updated on April 27, 2022

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