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Tigo Optimisers - How much shade can they handle?

UV-PWRD

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Jan 13, 2021
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I have 2 arrays, 9 panels each, all same brand/model of 250w panel. Panels in each array are all oriented the same and are laid out similarly, 5 panels on the bottom row, 4 panels on the top row a little over a panels height further up the roof.

All with Tigo TS4-R-O optimisers on them. No cloud connect etc though so I do not have panel level monitoring.

My understanding was optimisers will allow as much power from unshaded panels as possible when some of the others are shaded?

In one array, I noticed power dropped off sharply today and asked my wife at home to take a look at the panels and send me a photo. 5 panels in full shade, leaving 4 exposed to almost full sun, yet that particular array was only producing under 200w, when it appeared 4 of the panels had plenty of sun.

I appear to be seeing increased production from the system on both arrays in general (for winter as I have shading issues during winter specifically when the sun is lower), but I was under the impression that I could effectively have say 8 of 9 panels shaded and still see decent output from the 1 remaining panel (extreme example)

Is there a limit to how many panels you can have shaded when all are fitted with optimisers or is this indicating I have a bad optimiser/other issue?
 
I spoke to Tigo, who were great, they are sending me the controller to do some monitoring with to see what's up as I have good voltage but very low current during that specific event, both panel array voltage shows I am not missing any panels.

It could just be a quirk of the MPP 7248 not liking what it's seeing from the array.
 
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I understand there is some limit to current boost (your original question). Fully shaded, we expect it to bypass by diode or "ideal diode".)

But what are the PV panels specs and what are your SCC (MPP 7248?) specs?
With only 4 panels producing, the Vmp may be too low for it.
 
38v Voc per panel, at the peak today I was seeing 320v for that string so I'm not missing any panels. The 7248 has a minimum of 80v and an MPPT range of 90-450.

So I'd think I was hitting 80-90v on the 4 unshaded panels.
 
38 Voc. What about Vmp? (which drops a bit with heat, from spec measured at 25 degrees C.)
Scaling from other panels I've got, I come up with 30.5 Vmp

30.5 x 4 = 122Vmp for 4 in series. If Tigo has diode not FET for bypass, let's assume 1V per panel is lost, so 117Vmp remaining.
Well above 90V at 25 degrees C, enough for any heating effect that might reduce Vmp.

So that doesn't seem to be the problem.
 
For some reason I thought Vmp was 35 but I need to check.

I dont think I've lost a panel or am sitting below voltage thresholds as I had something like 260-270v, but only 0.7a at the time.

It's also only 15deg here currently.
 
Is that on-grid or off? If battery based, SoC can be another reason power output is reduced. But both arrays would likely respond similarly.

I'm too lazy to track down and read the MPP 7248 manual. Any chance it requires similar input voltage on its multiple inputs?
 
I did some testing over the weekend as I had 2 good days of sun.

Turns out it's the inverter + battery but not as I assumed.

As above, I assumed maybe it was SoC related and in a way it was, but I also discovered a quirk of the inverter.

As the battery was getting closer to full (high 80% range at this point) and only pulling around 25a of charge given the bulk charge voltage setting, the inverter again ramped down PV2, this just happens to coincide with the shade situation I was describing, 5 panels in full shade, 4 not.

I tested adding load to the system, hot water in this case, and found that PV2 would then throttle up (to about 4 panels worth of output) and PV1 would actually throttle down to distribute the load evenly across them both. This only happens if I could exceed PV1s possible total output, if I dropped my loads, be that battery charging or something else, below the threshold of PV1s output, the inverter would throttle back PV2 again and load up PV1 and just pull power from that 1 array.

So while we all might think the inverter would/should share the loads evenly always it appears to favour PV1 in my case to support loads up until PV1 can no longer do so, then it brings PV2 online and throttles down PV1 a little. When the battery is much emptier it draws from both as you'd expect.

If this was a grid connect system you'd never see that as there'd always been max draw but in an off grid/battery system loads do drop away to nothing at times.
 
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