Help with question about wire derating

[fafrd]

Lot of very interesting discussion and links in here so far - but I havent seen (or I missed it) any mention of using optimizers like Tigo's. It would remove any shading and voltage variability issues. And it's rapid shutdown capable and easy to implement. Each Tigo TS4-O optimizer runs about $50 US and will work with any inverter or MPPT controller.
Also, it gives you panel-level monitoring so if you ever lose a diode or a panel goes dead you'll know about it immediately.

Half-cell panels are essentially a mini 1S2P array, so I suppose an optimizer apply Vmp to both half-panels and if one half-panel is delivering next to nothing due to shading, the optimizer could take 1/2 Isc @ Vmp and convert it to Isc @ 1/2 Vmp for output into a series string.

Still not convinced it’s worth the premium, but the right 1kW product combined with RSD for 2 450W panels in series might be worth looking into...

 

[Hedges]

I don't particularly know him, have occasionally made a posting he appreciated.

Leaking Electrolyte from Bigbattery Powerblock

Depends on presence of children, pets, clueless significant other. It is probably reasonably safe especially after you've inspected and monitored it. And implemented any suggestions like orienting for vents up and placing in "secondary containment" (rubbermaid pan). Obviously a lot better than...

diysolarforum.com

But you could describe the issue, pose a question for him.
You've noted a particular model SCC with wide spread from top of MPPT to max voltage.
If you look over specs of the SCC he has reported on, you might identify one he already has that is good for testing the issue. Although, every brand's algorithm differs.

You should probably address a message directly to him succinctly describing the question (which appears relevant to off-grid and mobile systems he works with.)
I've noticed that messages addressing me with the '@' sign don't get flagged for me, so saying @Will Prowse probably won't get his attention.

 

[Maast]

FYI, the Tigo TS4-A-O will do up to 500W but for reliability I wouldnt take it past 425W so if you're looking at 450W panels (?!!) these wouldnt work for you.
I'll bow out of your conversation now... sorry to intrude.

 

[fafrd]

FYI, the Tigo TS4-A-O will do up to 500W but for reliability I wouldnt take it past 425W so if you're looking at 450W panels (?!!) these wouldnt work for you.
I'll bow out of your conversation now... sorry to intrude.

You’re not intruding at all - your contributions are appreciated.

If you have any experience with Tigo optimizers and/or shaded arrays, I’d like to hear more. It’s a bit OT from the original thread title, but since all of the issues related to pushing wire capacity to the limit were motivated by the desire for a 1SxP array to better-deal with shading, it’s relevant.

I’m not wedded to 450W panels, but they are coming. I’m doing a first small build with 3 380W panels awaiting a second-stage build 2-3 years from now based on 10 larger panels (Trina 450W panels are my placeholder for now).

As the higher-power panels mature, I expect optimizers, SCCs and inverters to evolve to better-support them (along with more cost-effective RSD solutions).

I’m just trying to figure out what roof-to-cellar home-run wires to install so that wires I install in 2021 will still be usable in 2023...

I’d ideally like a 1kW Tigo-duo optimizer that would allow me to turn two 450W panels into an optimized 2S string which could then be connected 2P.

 

[fafrd]

FYI, the Tigo TS4-A-O will do up to 500W but for reliability I wouldnt take it past 425W so if you're looking at 450W panels (?!!) these wouldnt work for you.
I'll bow out of your conversation now... sorry to intrude.

Also, my existing 4kW grid-tied array never exceeds 3kW, so in my location and on my roof, it’s pretty safe to assume a 450W panel will never exceed 340W...

The aspect of Tigo’s optimizers I’m struggling to understand is how they determine output voltage with an MPPT charge controller as the master.

MPPT controller puts out a voltage, Tigo optimizers adjust all currents to that voltage , MPPT tries a higher voltage, optimizers reduce current to match that higher voltage (power is the same), etc...

Does an MPPT always choose the lowest voltage for a given power level and do Tigo optimizers only decrease current for higher output voltage and never increase current for lower output voltage?

With a non-optimized pair of panels in parallel with a pair of panels optimized, I understand how it will work (MPPT will choose Vmp of the non-optimized pair and the Tigo Optimimizer will assure that the optimized pair of panels will follow).

But if both 2S sub-strings are optimized, how does the MPPT settle on the best voltage with the optimizers following it all the way?

 

[fafrd]

Also, my existing 4kW grid-tied array never exceeds 3kW, so in my location and on my roof, it’s pretty safe to assume a 450W panel will never exceed 340W...

The aspect of Tigo’s optimizers I’m struggling to understand is how they determine output voltage with an MPPT charge controller as the master.

MPPT controller puts out a voltage, Tigo optimizers adjust all currents to that voltage , MPPT tries a higher voltage, optimizers reduce current to match that higher voltage (power is the same), etc...

Does an MPPT always choose the lowest voltage for a given power level and do Tigo optimizers only decrease current for higher output voltage and never increase current for lower output voltage?

With a non-optimized pair of panels in parallel with a pair of panels optimized, I understand how it will work (MPPT will choose Vmp of the non-optimized pair and the Tigo Optimimizer will assure that the optimized pair of panels will follow).

But if both 2S sub-strings are optimized, how does the MPPT settle on the best voltage with the optimizers following it all the way?

Found this on Tigo’s website:

‘For a great explanation on the science of Tigo’s MPPT please see the article and whitepaper called “Impedance Matching”. The Tigo technology effectively sets the string current using the best module(s) as a reference. The inverter sees a relatively steady current and adjusts the global load on the system to find MPP at a system level.”

So that just changes the question to “how do Tigo optimizers ‘know’ which module is ‘best’???”

if there is some loss of power when a voltage is being increased, I understand how it can work because the ‘best’ module will have slightly higher power at Vmp_panel than it will at (Vmp_panel + deltaV).

What is the efficiency of these Tigo optimizers when they ‘impedance match’ (convert fraction x Isc @ Vmp to Isc @ Vmp x fraction)?

Especially if there are 2 2S strings with optimizers in parallel, I’m not fully understanding.

 

[fafrd]

RTFW

Apparently some panels have instructions that say partial shading during full sun is improper use. So would violate warranty terms.
Other brands are fine.
The diode would (almost always) be spec'd to carry that much current, question is whether the module design provide adequate heatsinking.

I don't have info on which ones have this problem.

I’ve been thinking more about this bypass diode thing.

My grid-coupled array is Microinverter-based and has much less shading than the roof face I’m putting this new array on, but it does have some shading.

So my microinverters must occasionally be activating one or two bypass diodes to maximize output when some shade arises.

And you also mentioned how surprised you were with the small loss of output you saw with some shade, do you are obviously having some bypass diodes occasionally activated as well.

I’m just not settled yet on how much effort I should go to to minimize/eliminate the possibility of bypass diodes being exercised as my shade moves across the roof in the morning.

It is true that this new array will have shading at near-maximum illuminance levels, while my existing array only gets shade late in the afternoon as illuminance levels have started to fade...

 

[fafrd]

FYI, the Tigo TS4-A-O will do up to 500W but for reliability I wouldnt take it past 425W so if you're looking at 450W panels (?!!) these wouldnt work for you.
I'll bow out of your conversation now... sorry to intrude.

I just read on Tigo’s website that their optimizer opens up ‘designing with different string lengths’ and if I understand correctly, this means 1 panel with an optimizer can be connected in parallel with a 2S string to form a 2S1.5P string with maximum current of 1.5Isc.

Or alternatively, 2 panels with optimizers in Series could be combined in parallel with a 3S string to make a 3S1-2/3P array.

So I appreciate your suggestion to consider Tigo Optimizers and am mulling over the possibility of handling my 10 panels by making a 3S1-2/3P array, a 2S1-1/2 array, and a 1S2P array.

The basic optimizer is rated for 500W but my 450W panel will be below that limit and in practice will pretty much never be exceeding 340W...