Progressive Shading and Single MPPT

[pfowen]

I have a small system build in progress for my garage with x4 410w panels. I have two limits, VOC (38v) too high for 4s on my Victron 150/35 and Isc (14v) so 2s2p. Will be a 48v system for peak watts.

As the sun sets each panel will be progressively shaded by the house. Out of technical curiosity will the first shaded pair (2s) adversely impact the still unshaded pair to the point I should use a second MPPT. As prolly less than 1 hour of >45° (azimuth to panel face) sun not exactly high impact but every day’s a school day.

 

[timselectric]

Out of technical curiosity will the first shaded pair (2s) adversely impact the still unshaded pair to the point I should use a second MPPT

No
The shaded string will still produce enough VOC. Even when not able to produce output.

 

[sunshine_eggo]

Parallel strings have mixed influence on each other when shading is involved depending on the effectiveness of the MPPT algorithm.

There will be an advantage with separate MPPT.

Here's why...

Scenario:

String 1 unshaded.
String 2 shaded to the point that one bypass diode would activate bypassing 1/3 of one of the panels.

String 1 and string 2 in parallel means they must both be at the same voltage.

Independently:
String 1 should give max unshaded current at Vmp.
String 2 should give max unsahded current but at 5/6 Vmp.

So that's 11/12's of max rated output

In parallel:
String 1 will typically force string 2 to operate at string 1's optimal voltage, so string 2 would only provide what little current would pass through the shaded portion of the panel. This could be a pretty small number.

A robust MPPT algorithm will figure out that there is potentially more power down at 5/6 of Vmp where both can operate at max current.

If you need to truly maximize your harvest, independent MPPT are the best choice. If you anticipate a surplus on most days even with shading, a single MPPT will suffice.

 

[pfowen]

Thanks curiosity satisfied.