Series string shading summed up in 4 pictures

[fafrd]

I just let the shading happen unless it was midday. [b[I don't think it's worth it to buy optimizers if 99% of the day it is not shaded[/b]

The situations where optimizers pay for themselves through increased output are few and far between.

In the case of the vertically-oriented shading you pictured, optimizers would not change much of anything.

I believe they boost current at the expense of voltage, so even when current was near zero because MPPT minimum forced panel voltage close to Voc, they won’t change anything.

And if I have it backwards and they boost voltage at the expense of current, you would need an optimizer on every panel in the string to get a slightly earlier startup in the morning (marginal / inconsequential increase on a % basis of full-day production).

If incremental cost beyond RSD is close to $0, why not? But when incremental cost beyond RSD approaches ~half the cost of an additional panel, hard to justify…

 

[Lt.Dan]

This is from my Tigo Monitoring app. Lifetime metrics show 1.66MWh that would have been lost without the Optimizers. 1.66MWh is no small number. My system has only been up for 11months. I also only have 1 panel that is consistently shaded by an eve on my roof.

 

[Will Prowse]

This is from my Tigo Monitoring app. Lifetime metrics show 1.66MWh that would have been lost without the Optimizers. 1.66MWh is no small number. My system has only been up for 11months. I also only have 1 panel that is consistently shaded by an eve on my roof.

View attachment 165872

Can you post a picture of that shading. Holy cow.

 

[Lt.Dan]

Can you post a picture of that shading. Holy cow.

Its a lot of work to get up there lol. This is the layout of my roof from the Tigo app. You can see D11 (which isn't its exact location, but the eve directly below it is the one that casts a shadow. It doesn't get full sun until roughly 2pm.

 

[Will Prowse]

Its a lot of work to get up there lol. This is the layout of my roof from the Tigo app. You can see D11 (which isn't its exact location, but the eve directly below it is the one that casts a shadow. It doesn't get full sun until roughly 2pm.

Gosh that is so cool. And yeah that's a challenging spot at certain times of day. Perfect for optimizers for sure

 

[wattmatters]

Lifetime metrics show 1.66MWh that would have been lost without the Optimizers.

I'd want to know how that is being estimated.

 

[Lt.Dan]

I'd want to know how that is being estimated.

That I don't know. Tigo doesn't explain anything very well. And I'm not very good at navigating their website.

 

[Lt.Dan]

Gosh that is so cool. And yeah that's a challenging spot at certain times of day. Perfect for optimizers for sure

A pic from the ground

 

[wattmatters]

I just let the shading happen unless it was midday. I don't think it's worth it to buy optimizers if 99% of the day it is not shaded

Yup. Usually makes the most sense.

I have more seasonal shading impacts. Chimney and trees. But with two strings in parallel into each my two MPPTs, it's not worth adding optimisers to all 40 panels. No chances in Hades of recovering enough energy to pay for that.

Based on the shade modelling I did with Pylon Observer, I lose about 850 kWh/year to shade.



I'd be lucky to recover 1/3rd of that with optimisers which would cost about A$4k to install (they have to go on all 40 panels due to parallel strings) for an increased energy yield of less than A$50/year. This is with a Fronius Symo 10 kW 3-phase grid-tied inverter.

 

[Lt.Dan]

I should add that I didn't choose the Tigo optimizers because of they're claimed increase of PV, but because I was required to have Rapid-Shutdown on all 44 of my panels. The Tigos were only $5-10 more each unit, and now I have per-panel monitoring

 

[wattmatters]

That I don't know. Tigo doesn't explain anything very well.

I am not surprised. I suspect the estimate is somewhat generous.

 

[wattmatters]

I was required to have Rapid-Shutdown

Yes, this is a uniquely US requirement AFAIK. Partly why Enphase is bigger over there.
We have different isolation requirements here.

 

[farmhand]

I'm currently having temperature problems with that combiner box. Diodes showing 220⁰F with IR thermometer. Heat sink is inside the box. When hard charging, makes the box hot inside and ends up tripping the breaker. 155⁰F on the breaker. Been opening the cover mid morning to absorption.
Thinking about bypassing them.

The 6 string I got off amazon has fine screened side vents. Maybe put a __vdc micro fan in it to cool while it's generating?

 

[fafrd]

That I don't know. Tigo doesn't explain anything very well. And I'm not very good at navigating their website.

My suspicion is that Tigo takes 100% credit whenever a bypass diode activates that would have activated anyway without any Tigo optimizers present…

 

[Lt.Dan]

My suspicion is that Tigo takes 100% credit whenever a bypass diode activates that would have activated anyway without any Tigo optimizers present…

I have some sh*t old panels though. God knows if the bypass diodes even work lol.

 

[fafrd]

I have some sh*t old panels though. God knows if the bypass diodes even work lol.

If the bypass diodes are dead, an optimizer isn’t going to do anything to revive them…

 

[Solar254]

 

[fafrd]

Pretty sure that before a panel can heat up like that from shading (‘going resistive’) the bypass diodes need to have fried.

Or alternatively, the MPPT needs to be so stupid it never drops string voltage enough to activate bypass diodes.

Overuse of bypass diodes during high-production hours leads to frying them and once they are fried, overheating the shaded cells is inevitable.

The suggestion that Tigo optimizers can protect shaded panels from this sort of damage suggests that they can somehow protect the bypass diodes from getting fried but I believe that could only be possible if they include internal circuitry to bypass an entire panel without making use of the panels 3 bypass diodes.

I’ve never seen any description to that effect but am interested if anyone knows more.

 

[cs1234]

Do ground mounted panels with plenty of clearance under them generally get this hot and fail from shade issues? Or is this because all the heat on these components is trapped against a roof?

 

[Hedges]

On the roof does run hotter.
Shade on a ground-mount panel with others in full sun would also be prone to same damage, but lower ambient temperature helps.
I am inadvertently performing a long-term study of this, as a moderate size bush has become a big tree, but I'm not logging good data.
I plan to disassemble the ULA mount and rotate 90 degrees, use for morning sun.

Overuse of bypass diodes during high-production hours leads to frying them and once they are fried, overheating the shaded cells is inevitable.

Meaning design with diodes was not well engineered, at least for severe shading. Maybe designed for commercial systems, not random placement near dormer windows etc. on residential.

The suggestion that Tigo optimizers can protect shaded panels from this sort of damage suggests that they can somehow protect the bypass diodes from getting fried but I believe that could only be possible if they include internal circuitry to bypass an entire panel without making use of the panels 3 bypass diodes.

True. Which runs counter to harvesting the most power. I think each optimizer should draw down panel voltage to activate bypass diode for a shaded section, including for some half-cut panels.