Two identcal SmartSolar MPPT 250/100 but one produce very much lesser

Q&A and troubleshooting
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1

Hello *,

I was running a SmartSolar MPPT 150/70-Tr VE.Can with 1,86kWp (south oriented) since 2018.

In June I got 12 Solarpanles Longhi 455Wp.

Last month I installed the two new SmartSolar MPPT 250/100-Tr VE.Can where I use Strings of 4 in series where the first one has 3640Wp and the second 1820Wp (I will get 4 more modules) and all are installed side by side west oriented to get in the Winter more sun.

However, my Energy readings are strange, because the second one produce lesser then 33% of the first one, while it should produce 50%.

Cabling as ABSOLUT identical (25mm2, same lenght of cables, all three VE.Can are shown in ColorControl GX).

Example:

      Solar_1  Solar_2 Solar_3
DAY   150/70   250/100 250/100
      1860Wp   3640Wp  1820Wp
01       480      880     320
02       890     1160     510
03       340      610     210
04      2240     2670    1230
05       420      750     250
06       850     1500     640
07       160      230      50
08       630     1160     450
09       190      330      60
10       350      620     210
11       430      780     370
12       520      870     330
13       400      730     250
14       640     1020     430

Note: Solar_3 has the same config as Solar_2 by sharing the config file.

How is this possible?

Solar_3 broken?

Thanks for your help

2

Could be normal. Half the panels doesn’t necessarily mean you get half the output.

Efficency varies depending on load, so you even can see that the 150/70 is more efficent than a “underloaded” 250/100.

To make sure there is no technical issue, you could swap the panels between 2 and 3 and see if mppt2s efficency will also drop bellow the 150.

3

Tonight I will try to change the cabling in the Fusebox and will see

4

Yes that would be the easiest to start getting an idea.

If then the other mppt shows this effect, it could either be due to efficency-reasons, OR one of the panels in the only-4-panel-string could have a ditch as well.

To figure that out, you then could disconnect 4 of the 2x4-String and compare both mppts by running a 1x4 each. (Considering all the 8 panels in the 2x4 as “healthy base” to compare with)

5

Oops, forgotten to reply…

I have swaped the sets and it is the same result.

It seems, the reason is NOT the overpowering of Solar_2 (3640Wp) vers Solar_3 (1820Wp) but that the SmartSolar is working better under full load.

I have tested all three MPPTs with only 4 modules (the 150/70 wad running with 2x2 while the 250/100 had 1x4) and the 150/70 outperformanted the 250/100

6

Makes sense, the 150 has less bucking to do to get down to 48V nominal, versus the 250s and 450s.

When I compared my 150/35, 250/100 and 450/100 (different panels but same point in time), results seemed to match Victrons stated efficiency specs (150>250>450). Losses on the 450 were about double the 250.

7

I have the impression, that the promised efficiency is only under full load, hence you NEED to overpower the MPPT by at least 10%

1860Wp on a 150/70 is sub optimal, but smaller CAN versions do not exist. Unfortunately I bought it around 3 month before the 250/70 came out. However, I think on change the 150 to a 250, since 6 modules have only 228Voc and the 250V just fit.