Tigo Optimisers on a string with 2 orientations not optimising as hoped

[EastCoastDIYer]

My Tigo TS4-O optimisers on one of my strings is not behaving as I would expect and would like a second opinion on what Tigo support have left me with please.

On clear sunny days, my panels are massively underperforming and I can't find a good reason why. Tigo support have humoured me with many responses to a ticket I raised with them, but ultimately what they have said back to me doesn't add up, or I'm left feeling like I'm missing key part of the equation that explains this.

I had my solar installed last year 18/12/23 and live in the UK. My house is an L shape with a ridged roof on all of it, and I have a two string Solis Hybrid Inverter with String A with 10 south facing Jinko Tiger Neo 435w Mono panels, and on String B I have 3 panels on the south facing roof and 5 on the west facing roof. All panels are the same and have Tigo TS4-O monitored optimisers on all of them, connected to a CCA. Tigo tells me that they are all on the latest firmware. The Jinko Tigers produce approx 35 volts from very low light.

The optimisers on String A are behaving as expected. At the moment in the winter, there's a tree which casts a scattered shadow across the lower panels, and I can see the optimisers are doing their job to allow the unshaded panels to keep producing an expected amount of power. For the optimisers to start working, it seems that as soon as there's more than 0.5 amps being recorded by all the Tigos, the string comes alive as I presume the optimisers are starting to do their jobs and bypassing tunnelling any shaded panels. 0.5 amps for each panel happens fairly early on in relation to when the sun comes up.

String B is where I have the problem. It is split across the south facing roof with 3 panels B1, B2 & B3 (alongside the String A panels) and 5 panels on the west facing roof B4, B5, B6, B7 & B8. The 3 south facing panels only start producing meaningful power after 12:00. All 3 are all unshaded by about 11:00, so it's not shade related. Taking B1 as an example, it's neighbour A5 at 11:20 is producing 303 watts from 35v x 8.66amps. B1 is producing 30 watts from 39v x 0.77amps. Every other of the 8 string B panels is producing at least 0.71amps at 34v or higher. B1 continues to underperform compared to A5 until about 12:00 when over the next 30 minutes it's amps ramps up until it's matching A5. At 12:00 there's still one panel, B5, with 0.78 amps due to some shading and being west facing, but the rest of the west facing have more.

Tigo support have told me that the TS4-O needs a minimum of 16v and 0.5amps for them to start optimising, and what I see on String A agrees with this, but string B doesn't as they're making more than those numbers but not optimising/ bypass tunnelling.

Tigo support also told me "In your case, the shading occupies more than 60% of the string, and B1/2/3 have to match the performance of the whole string to make it more efficient." The shading they are referring to is because the 5 West facing panels are facing away from the sun before approx. 12:00. I don't understand the part about "B1/2/3 have to match the performance of the whole string to make it more efficient" but that could be ignorance on my part. But what I do know is that these optimisers are often marketed as being a solution to having panels across more than 1 orientation on the same string. Certainly my installer thought that was the case. But now Tigo are saying that if more than 60% of panels are shaded, even if they have enough amps to enable the optimisers, then those in the sun can't work at their full potential. So can you only have them across more than one orientation if it's effectively a 50:50 split of panels?

Does this sound right, am I missing something or are they giving me the brush-off please?

Here's the wattage per optimiser on 16/01/24 @ 12:15



And current

Thank you, good people!

 

[BentleyJ]

Hope one of the forum members has some insight into how the Tigo algorithm actually works. @RCinFLA perhaps?

This case may be an example of how microinverters would outperform optimizers.

 

[400bird]

Tigo optimizers are limited to a 25% correction/difference between panels. I'm not sure how they calculate that, but there is at least 25% difference between B1,2, or 3 and B6

This case may be an example of how microinverters would outperform optimizers.

I'm not a Solar Edge fanboy, but Solar Edge optimizers don't do this. I think this issue is special to Tigo optimizers.

 

[Hedges]

I'm thinking you can put all 13 panels into one MPPT input, the other 5 panels into the other.

-----

Don't expect any power from a shaded panel. Whether or not it produces any will depend on how shadows fall on its three diode-bypassed sections.

Compare panels that both have unshaded exposure to the sun, just are different orientations.

To the first order, I think it is the orthogonal area presented to sun that determines watts and amps, but I haven't validated that. If you determine angle and use trig, you could calculate area. Or stand a ruler orthogonal to the sun at one corner of panel and place your finger on the ruler so shadow points to another corner, length or width.

"Orthogonal" may be difficult to identify, but pointed straight at sun makes shadow a spot, and from that determine orthogonal.

When different orientations are in series, the optimizer has to boost current and reduce voltage to match other panels. It can only do that within a limited ratio. Optimizer will not boost voltage and reduce current.

If total string voltage would be too low, can't go below minimum MPPT voltage.

Best if all on a single string are of same orientation. You have 13 panels on side with "A", 5 panels on other side.

Links to data sheets?

I was checking whether we could have two parallel strings into one input, but the panels I'm finding are 11 to 13 A Imp, and inverter is 16A so only one string per input works.

You have 13 panels on the "A" side, 5 panels on the "B" side. The specs I'm reading looks like you could put 13s into one MPPT without exceeding Voc, and 5s into the other while remaining above minimum MPPT voltage. Maybe there is a watts per MPPT input limit, but I don't see it.

Let's consider the actual data sheets for your equipment, and if it still looks good, discuss with your installer having all panels on a single roof face being in one sting.

 

[Oldphile]

What is the operating voltage range of the MPTT?

 

[SeaGal]

Welcome. I'm also in East Anglia and have a Solis, but no experience of optimisers.

I'll read all the detail when I have more time, but a quick thought is whether you are getting enough voltage into the Solis MPPT input for it to be working efficiently if you only have effectively 3 or 5 panels working at one time?

 

[Hedges]

The one I found is 90V to 520V, 600V max. But I don't know if the right model.

https://www.solisinverters.com/dataFile/436c0fe404a64887b473a73297e7a370

 

[SeaGal]

But I don't know if the right model.

It's more likely the EH1P S5 model as the S6 is not yet approved for UK grid connection. But the figures sound the same as mine but with a 120V start up value.

 

[Hedges]

Evaluate my idea to put 13s on one MPPT, see if that meets specs.

 

[SeaGal]

Evaluate my idea to put 13s on one MPPT, see if that meets specs.

So Voc = 39.36V x 13 panels = 512V x temp coeff of -0.25%, would be max of +10% for min of -15C here; = 563V. So pretty high, but sure, do-able.

This year and last we got to -5C here (but only for 2 - 3 weeks), have seen -11C about every 10 years for a week or so, but normally lows will only be 0 or -1 overnight.

 

[SeaGal]

Have now read all the detail, and would agree with @Hedges - try all 13 S facing in one string and the west facing on separate string.

 

[EastCoastDIYer]

Wow, thanks everyone for quick and thoughtful responses!

I was thinking about moving B1, B2 and B3 over to String A. My installer thought it wasn't possible, can't remember their reasoning, but having researched it more and followed these instructions I've calculated that I should be able to have 13 panels on String A without overvolting in cold, and string B has just enough voltage in the hot to not shut off the string.

The inverter, a Solis S5-EH1P6K-L, has VStart of 120, VRated of 330 and VMax of 600. Calced up, the min modules is 4.7, so my 5 is good and max modules is 13.8, so 13 would be fine. In current weather conditions, with 13 panels, String A would make 455 volts, but VRated is 330. Any idea how much of an impact to efficiency this would make in reality?

Getting an understanding of why the Tigo's aren't working is partly out of principle and so that I can avoid this mistake in the future. If I can fix the issue somehow without re-stringing, then brilliant.

I'll try to respond to each person's comments in individual posts.

 

[SeaGal]

In current weather conditions, with 13 panels, String A would make 455 volts, but VRated is 330.

see my calcs in post #10

 

[EastCoastDIYer]

Tigo optimizers are limited to a 25% correction/difference between panels. I'm not sure how they calculate that, but there is at least 25% difference between B1,2, or 3 and B6

I'm not a Solar Edge fanboy, but Solar Edge optimizers don't do this. I think this issue is special to Tigo optimizers.

There's enough evidence and opinion out there saying "Optimisers are not miracle workers" which is the vibe I was getting from Tigo support, but later in the day I get numbers like this which seems to contradict that on my installation:

12:20:


12:30:

It's like it reaches some sort of threshold where the optimisers suddenly kick in.

Here's the corresponding amps for 12:20:


And 12:30:

Obviously at 12:30 the minimum amps is 1.6 whereas at 12:20 it's 0.76, but both are over the 0.5 that Tigo Support said was minimum amps.

 

[Quattrohead]

I recently read somewhere about a 25% maximum deviation but I do not remember if it was Tigo or Enphase.
So yes optimizers and micro inverters can perform very well in various situations but they are not miracle workers.

 

[2TrevorJ]

I was stuck with trying to fit all my panels on my limited roof space so I chose to mix orientations thinking the same thing as you (that the Tigo's will make up for quite a bit of it of it (and the South facing panels might even help "light off" the East & West panels)). Just chasing high string voltage with the config. Then this dude showed up:

H5-H9 are in with the 4 East facing panels and I9 & L9 are in with the Westerly array. Bad juju. Not bad enough to reconfigure but you can see that daily production for the compromised panels are pretty far down compared to the pure South string (K) right next to the affected panels.

I'm not mad at Tigo...I think they are helping but my config is not.

Usually better off keeping all panels in a string on the same orientation/plane (optimizers or not) - even if you have to go parallel and sacrifice voltage.

 

[EastCoastDIYer]

Evaluate my idea to put 13s on one MPPT, see if that meets specs.

Good idea. I have done so, see #12. I'd actually worked this out before posting, but thought there most be a good reason why my installer didn't do this to start with. The more I look into it, the less reason I can see not to....

EDIT: There is a slight caveat to adding B1 B2 and B3 to String A - the west facing roof shades the South facing roof in the mornings. Having String A further from the west facing roof's ridge might mean String A optimisers start working earlier in the day. I need to review the shading that it generates to see which gets me more kWh - "A" string with 13 panels which starts optimising later or "A" string with 10 panels optimising earlier, but B1, B2 and B3 not optimising until midday.

Here's this week at 09:35. There's a chimney on the west facing roof too which you can see the shadow for:

But I might be letting Perfection be the enemy of Good here...

 

[EastCoastDIYer]

So Voc = 39.36V x 13 panels = 512V x temp coeff of -0.25%, would be max of +10% for min of -15C here; = 563V. So pretty high, but sure, do-able.

This year and last we got to -5C here (but only for 2 - 3 weeks), have seen -11C about every 10 years for a week or so, but normally lows will only be 0 or -1 overnight.

We have to use record low temps for this calc is my understanding as we only need it to go low enough once to overvolt and melt the inverter. -14c is the Record low for Ipswich (where I am) in the last 30 years. In reality though, -5c or -14c makes no difference to having 13 panels installed. Using -5c I could get 14 panels on String A in theory. But I don't have 14 panels south facing As an aside, it was -6c last night at my house. Chilly! BTW, it's not ice on panels B1 B2 and B3 which is the problem at the times I'm looking at. At 08:30 they're all frozen, but south facing all thawed by 09:30 - UPDATE: Ignore me - I didn't read your calcs properly and see that you used -15c. Good stuff!

 

[Hedges]

Any idea how much of an impact to efficiency this would make in reality?

Best possible implementation. Only negative impact is if MPPT is lower efficiency at higher voltage or higher wattage (which means more self-heating.)
Makes optimizers irrelevant. (except for half-cut panels with partial shadows.)

but thought there most be a good reason why my installer didn't do this to start with. The more I look into it, the less reason I can see not to....

Can't see the forest for the trees?
Have to move fast to make enough money to survive?
People who can, do. But aren't the sharpest tools in the shed?

Those of us who are armchair warriors, some with decades EE or contracting experience, have the luxury of leaning back and making a game of outsmarting the hardware and the "professionals." We could see the answers before pioneering OEMs like SMA had figured it out.

Most people go by what they're taught, don't understand or ponder to the depths some of us do.

Individual strings with bypass diodes work very well for conventional panels, if MPPT has a good algorithm.

Here's a thing, though: Although data sheet doesn't say "half cut", from the rectangular cells and quantity, that is what the panel I see is.
A ridiculous design in my opinion. Shadow on part of panel leaves it at full voltage, but half current. A dumb MPPT will just think, "oh, gee, current dropped in half and voltage went up a few percent." A smarter MPPT will do a sweep and reduce voltage until full current of other panels pushes through bypass diode.

If an optimizer could double current, then it would let you get 5/6 of panel output when one half-cell shaded. Otherwise, you either get 2/3 of output, or if MPPT is dumb you get 1/2 of entire string.

www.jinkosolar.com/uploads/JKM425-445N-54HL4R-(V)-F1.3-EN.pdf

 

[EastCoastDIYer]

Hedges, that all makes sense. I did ponder the ROI for optimisers on this and wasn't sure if the way the shading fell on the panels would trigger a bypass diode or not, but ultimately, I went with optimisers as they came with monitoring which would allow me to spot issues such as dead panels/dirty panels. So far, what they've managed to spot is their own shortcomings! But I still feel better about knowing what each panel is doing. There wasn't really any cost saving in getting panel monitoring without optimisation. So the TS4-A-O it is.