Will shading keep me from getting ANY solar power in the winter?

[robby]

Uhhh, sorry, but that’s an overstatement (at least when half-cut panels are considered).

Let’s say a leaf blocks 2 adjacent cells under control of seperate bypass diodes by ~75%. With conventional panels, both shaded segments get bypassed reducing the shaded panels output by 66%.

With conventional panels in a very long series string, that’s a minor output drop and not much different than what you’d get with Microinverters.

But with a short string of 4S or 3S, it’s a drop of 17% to 22%. Microinverters are not going to do any better with conventional panels, but hard to call that level of production loss ‘minimal’.

Use half-cut panels in that same 4 or 3 panel array and a Microinverter will limit production loss to 12.5% (4S) to 17% (3S), so about 3/4 of the loss associated with either panel type in a series string.

Of course if you use half-cut panels in a long series string, they won’t make much difference in this shading scenario (since limiting the entire string to half-current is far worse than just dropping voltage of a single panel from full Vmp to 1/3Vmp.

But for modest-voltage strings composed of a relatively small number of half-cut panels in series, Microinverters absolutely provide superior output to string inverters.

I will let the video speak for itself and not derail the OPs thread.

 

[fafrd]

I will let the video speak for itself and not derail the OPs thread.

Well first, since shading is the precise topic of this thread, I don’t anything about our exchange is the least bit OT.

And second, I went ahead and watched the relevant part of the first video and unless I’m missing something, it agrees 100% with my earlier analysis (for long series strings of conventional panels).

Blindly using analysis and results from ~600V strings to extrapolate what you can expect with shorter string lengths of 2-4S would be foolish.

String inverters fed by long series strings can perform as well as microinverters (and even a bit better since conversion efficiency at high voltage is easily a bit higher than conversion efficiency at lower voltage of Vmp that Microinverters are limited to).

String inverters fed by short (2-4S) strings of half-cut panels will perform worse than Microinverters fed by half-cut panels under almost any shading scenario.

Of course, how much worse is a question of the precise shading situation involved, but I provided a single-leaf shading scenario where a Micro-inverter-based system will deliver 5 to 6% more output.

If you want a more extreme example, consider a string inverter fed by 16 half-cut panels where half the panels are partially blocked by shade across their lower half.

The string inverter can either operate at full Vmp and half Imp or at half Imp and full Vmp, only delivering about 50% of unshaded output in either case.

Hook those same 16 panels half-cut panels up to Microinverters and output will be full Vmp x Imp for the 8 unshaded panels and full Vmp x half Imp for the 8 partially-shaded panels, meaning 75% of unshaded output.

So in that specific shading situation, Microinverters can deliver 50% more power output than string inverters with a long series string.

Half-cut panels have completely changed the math regarding output levels in the presence of shading (at least for certain shading situations which are not uncommon). That was the primary motivation for their introduction.

Referring to old videos and results based on conventional panels which neglect to compare against similar results from half cut panels (often because they did not exist yet) is slightly off point (at least for the OP’s questions).

 

[bgflyguy]

Dc micro inverters ?

https://www.amazon.com/gp/aw/d/B08LBWKTNF/ref=ox_sc_act_image_2?smid=A2VHGGOHXF24LJ&psc=1

 

[Sprucebeach]

Uhhh, sorry, but that’s an overstatement (at least when half-cut panels are considered).

Let’s say a leaf blocks 2 adjacent cells under control of seperate bypass diodes by ~75%. With conventional panels, both shaded segments get bypassed reducing the shaded panels output by 66%.

With conventional panels in a very long series string, that’s a minor output drop and not much different than what you’d get with Microinverters.

But with a short string of 4S or 3S, it’s a drop of 17% to 22%. Microinverters are not going to do any better with conventional panels, but hard to call that level of production loss ‘minimal’.

Use half-cut panels in that same 4 or 3 panel array and a Microinverter will limit production loss to 12.5% (4S) to 17% (3S), so about 3/4 of the loss associated with either panel type in a series string.

Of course if you use half-cut panels in a long series string, they won’t make much difference in this shading scenario (since limiting the entire string to half-current is far worse than just dropping voltage of a single panel from full Vmp to 1/3Vmp.

But for modest-voltage strings composed of a relatively small number of half-cut panels in series, Microinverters absolutely provide superior output to string inverters.

I’ve got a very similar situation. I elected to go for a 1S parallel array of half-cut panels to maximize my output in the presence of partial shading.

Half-cut panels are essentially 2 half-panels in parallel, so you’ll get half-output from several panels at noon on your Oct 22 pic.

By connecting all panels in parallel, you’ll get the maximum current that each half-panel can contribute without any shaded panel blocking or starving any other panel (and without needing to purchase any optimizers).

A 1S array means higher currents, so you’ll need to invest in heavier-gauge home run wires if you are going for a DC-coupled array.

The other way to achieve the same output as a parallel 1S array is to go with a Microinverter-based array (still using half-cut panels) - this will allow each panel to contribute it’s maximum output current before converting it to AC power.

I was getting 8kWh from my 1.14kW 1S3P array this summer and am still getting ~1/3 of that amount today (December 1).

Interestingly, on overcast days I can actually get as much output as I get on clear days. The clouds reduce overall output levels but the diffused light eliminates the shading so I get about as much output as I’d get without any shading (in the presence of overcast / clouding).

But half cut panels are the only hope you have of salvaging much of any output with that extreme degree of shading.

What about the other roof orientations? Any better as far as shading?

I guess this is a reply to several of your posts, fafrd. I'm finally getting back to deciding what to do. Although I posted on this DIY forum there are too many things I don't have a good grasp of, and in the end I will be working with an installer. But I still want to try to understand the best way forward myself.

It was encouraging to read that your situation was similar to mine and you were getting 1/3 power in December. I could live with that in the winter or even 1/5 power. At least I'd have *some* power in winter grid-out situations.

I could put about 17 half-cut panels in landscape under the ridge vent. I could ultimately put two more shorter rows of panels on the porch roof but there would be a declining ROI from that with the lower row. Even in summer, sunset is earlier for those panels and sunrise is later the lower on the roof I go. I'm thinking about a Sol-Ark 12K with its two MPPT's so that in the summer I could sell some power back to the grid if I end up with maybe 30 panels.

But Initially, because the porch roof support needs some repair, I'd just put 17 panels under the ridge vent. I'm trying to understand what you described doing in your Dec. 3 post (and the second option you mentioned of using microinverters) and figure out how it applies to me but I'm having trouble. Can you take pity on my ignorance and describe how I might wire my 17 panels across that upper roof in those two ways?

 

[fafrd]

I guess this is a reply to several of your posts, fafrd. I'm finally getting back to deciding what to do. Although I posted on this DIY forum there are too many things I don't have a good grasp of, and in the end I will be working with an installer. But I still want to try to understand the best way forward myself.

It was encouraging to read that your situation was similar to mine and you were getting 1/3 power in December. I could live with that in the winter or even 1/5 power. At least I'd have *some* power in winter grid-out situations.

I could put about 17 half-cut panels in landscape under the ridge vent. I could ultimately put two more shorter rows of panels on the porch roof but there would be a declining ROI from that with the lower row. Even in summer, sunset is earlier for those panels and sunrise is later the lower on the roof I go. I'm thinking about a Sol-Ark 12K with its two MPPT's so that in the summer I could sell some power back to the grid if I end up with maybe 30 panels.

But Initially, because the porch roof support needs some repair, I'd just put 17 panels under the ridge vent. I'm trying to understand what you described doing in your Dec. 3 post (and the second option you mentioned of using microinverters) and figure out how it applies to me but I'm having trouble. Can you take pity on my ignorance and describe how I might wire my 17 panels across that upper roof in those two ways?

Microinverters are pricier but close to ideal for dealing with shading. Microinverters essentially translate to each individual panel having its own MPPT controller, so you’ll be getting the maximum output possible from any partially-shaded array. The ‘cost’ of Microinverters (in addition to $$$) is that they output AC power.

If you have the freedom to export, AC energy is not a problem and even if you don’t, a Solark hybrid should have the ability to ‘throttle’ Microinverter output to match demand (make sure you get new Microinverters supporting ‘frequency shift’).

I believe the ‘second way’ you are referring to is the approach I used of a DC-coupled 1S string. That would be tough but not impossible for 17 panels depending on your battery voltage.

If you have a 48V battery, you cannot go 1S and need at least two panels in series (2S) to achieve a high-enough voltage.

In that case, unless you have pairs of panels that suffer similar/identical shade patterning, you may well be better off aiming for the longest strings your MPPT will support.

Ants by the he way, if your shading is horizontal in nature, half-cut panels in landscape orientation will gain you nothing over standard full-cut panels.

Horizontal shading with half-cut panels in portrait orientation (or vertical shading with half-cut panels in landscape orientation) is where half-cut panels truly shine…

In terms of how all of this works, a simplistic model where any half-panel without shading puts out 50% current and any half-panel with any shading at all outs out 0% current is the easiest way to think about it.

Whatever panels that are in series will be limited to the current output of the weakest panel (unless thee is sufficient voltage headroom to bypass a shaded panel).

If you can afford Microinverters, it’s probably what I’d suggest for your situation.

 

[Sprucebeach]

Thank you so much! You've really taken pains to explain things in a way that I can understand. I have a better framework now for thinking about this. Thanks again.