Solar PV - Effects of Shading

shoehorn

I've seen conflicting information on the impact of shading on PV generation.

1. That shading on part of just one panel will reduce the output of the whole string
2. That shading on part of just one panel will only reduce the output of that panel, while the unshaded panels will be fine.

Which is the case? Or something else?

Also, if panels are split between different roof slopes, I believe that's 2 strings - is there any problem that one is in shade while the other is not? Do they each require their own inverter to avoid the shaded string dragging down the output?

slave1

1. is correct unless you have an optimiser installed (around mid €40 each) on any impacted panel
2. Correct if you have an optimiser installed

Other Q, install optimisers to eliminate this issue

shoehorn

https://www.boards.ie/discussion/comment/119444628#Comment_119444628

Thanks.

So a fully shaded string brings down the whole plant (both strings?)

Say if ESE string is fully shaded and SSW string is in full sun, the SSW string (with no optimisers) will be as poor as the shaded ESE string?

I had thought shading problems would be confined within a string.

My panels were recently installed like this, with no optimisers, and I've seen decent generation, even with one string in full shade.

pale rider

Not at all.

My understanding was shade on one panel will reduce power generation but not on the string

Both arrays can produce different power depending on Sunshine hitting those panels.

i have two arrays, no optimizers, System works very well.

unkel

No. You thought right, strings are independent. Slave1 didn't say otherwise.

Optimizers are only any good if you have one or a few panels in the string that get shading while the rest of the string is not. They are not the most reliable / long living and they add considerably to the pay back time of your system, so if you can avoid using them, you should.

shoehorn

OK I misunderstood the reply. That's great to hear. Thanks.

slave1

I agree/disagree with Unkel as it depends.....I need optimisers on my house roof due to Winter shading from neighbourhood trees but I didn't use them because Winter generation is low anyhow and secondly, I'm not getting up on a roof should an optimiser "fail", I simply leave panels frozen over in depths of Winter.

I put in a second array and used Optimisers as I have easy access to them and they attract shade in Summer due to a neighbours back garden tree.

So yes and no, it depends, if you have Winter shading I'd question it, especially with poor access to rear of panel, if you have shading throughout the year then I'd seriously consider them. In the overall cost of a PV system they add little is the other consideration...

unkel

Very much agree with that. It would be lunacy to have 10 panels with 10 optimizers on your high roof as you can expect one to fail every year, and you would be up on your ladder each time. That's why I'm no fan of micro inverters up on the high roof either. Same problem.

For the easier accessible ones - I'm not convinced their outlay would ever be regained unless it's an edge case. Like one or two panels in an array shading for a significant part of the day. These things add a lot to the cost of the system. Depends also on how much PV you have and how much you would like to have. If your lower roof space is very limited, then yes, could make sense.

bullit_dodger

Do they fail often though? I don't have any on my main installation, and with me using micro-inverters effectively I've panel isolation anyway on my shed, so I don't (and won't) ever need them......but I am curious though as to the MTBF on them. Anyone know?

Is any brand more problematic than others? The reason why I'm asking is that it would be good to get real life experience so that we can pass that knowledge onto others. Like "stay away from x" etc.

unkel

A reasonable guess of MTBF of any piece of Chinese electronic equipment is 5-10 years. So if you have 10 of them installed, you can expect at least one will fail on average per year

If that happened to my string inverter, I'd have it replaced myself, no need for any ladders or any electricians, in 30 minutes. With a micro inverter or optimizer on your high roof, not so easy. Even to figure out which one is faulty.

slave1

I'd have no idea how to figure out a failed optimiser, a future me problem I won't worry about today

graememk

https://www.boards.ie/discussion/comment/119449675#Comment_119449675

It should bring the whole string down. Possibly no voltage at all on the string... although it depends on how it fails.

DC999

I've optimisers on a flat roof that gets shaded in morning and evening now. And low sun will deffo have way more shading with neighbours trees. Without them they would drag down the other panels on the main roof above it the same direction. Roof wise I don't have a choice but to use the flat roof. Or lose 5 panels on a small roof.

Mine have a 25 year warranty with Huawei. If they had a really bad MTBF they wouldn't have that warranty lifespan I reckon. Not cheap relative to other optimisers AFAIK though. That's 2.5 times more warranty than the 10 years on my Huawei inverter! So can't imagine they are gonna break my heart. I will report somewhere on this forum if they do fail.

Installer said they have seen 20% better performance on 2 unshaded strings facing same way at same height with compared them. So they added optimisers on one and had 20% more output than the other. Didn't seem like a hard sell as they don't even price them as he said people won't pay the cost. Too early for me to know if they are getting that sort of output improvement.

But at rare time I have seen one optimiser / panel at 15w while the other panels have been around 100w. Could even be a bird sitting on one. Or shade.... Granted it's not often so overall won't affect output hugely. But on a small roof that's maxed out space wise and with no ground space for more panels, every % gain to me helps. If I had more space I could add another panel or two and wouldn't even matter

slave1

I've seen the 20% figure quoted before too

unkel

A panel costs about €120, an optimizer about €40. That's 33% more. If a panel with an optimizer produces 20% more, you are losing out and your payback system increases. In other words, the optimizer makes it worse. As I said before, that's fine if you have very limited space for panels. But don't think you're onto a winner here.

I highly doubt an optimizer will give you 20% more production from that panel over the year. Anyone any vids where someone demonstrates something of this order? Optimizers are good if one or a few panels have shading quite a lot, which would bring the whole string down without one

bullit_dodger

I've actually got a good example of shading. Although for me since I use micro-inverters for my DIY jobbie.... the use or non-use of optimizers question is sort of a moot point - although in general I'm in the "it depends" on the shading if using optimizers is right for you.

Since it drags down the whole string, using optimizers can have some benefits. If your looking at a panel in isolation, it's hard to see the ROI, but if you have say a chimney or a tree which casts an annoying shade on 1-2 panels for a few months of the year.....and then you have 10 other panels in the string are dragged down as a result - I guess there's a case to be made for them.

Any way for those who don't know how damaging the effect of shading is.....here's two (identical 400w) panels I have.....

Production of the panels at that time today at 11:45am

That tiny little bit of shading on the bottom right of the right panel, basically killed 40% of the panel output. Crazy right?!.....

unkel

I have a test panel on a micro inverter plugged into a socket via a wattmeter. Interesting to do experiments like this and indeed if I place my hand in a corner of the panel, covering maybe 2-3% of the panel in shade, output could drop by 30-40% easily

DC999

Jaysus, had no idea that little shade would have such an impact. Our flat roof gets some moss landing on it from the gutters when birds are in them. And just general dust and stuff lands on it. And can't clear with gravity or rain (if did rain).

Before I read this I was on the flat roof earlier today with a mop and bucket cleaning the flat roof. Made sure my other half didn’t spot me either. Reckon the neighbours think I've finally lost it :)

bullit_dodger

https://www.boards.ie/discussion/comment/119456389#Comment_119456389

LOL - that's funny.

One word of caution though, be careful cleaning the panels with water on a hot day. It might be 25C outside, but the panels (being black) could easily be 60-70C. You come along and throw cold water on the panel and you could cause cracking in the glass. It's unlikely to be fair, but if you can avoid it and clean the panel early morning/later on in the day, you'll reduce your risk.

DC999

Oops. Good call. 1st time doing it and it would have been warm alright. Lesson learned.

Might even do it in the dead of night so no one sees me :)

bullit_dodger

The Phantom solar scrubber!

slave1

Previous reading I did says an A4 sized dark shade on a typical panel will effectively wipe that panels output to "nothing" (and all other panels unoptimised on that string)

slave1

https://www.boards.ie/discussion/comment/119456160#Comment_119456160

I don't know what impresses me more when I look at your "DIY jobbie", your "DIY Jobbie" or how you got away with those two panels from 'other half

bullit_dodger

LOL!

Well they can go flush against the wall in a few minutes when I want to use the decking area - like so.

So it doesn't completely ruin the area. I did consider using actuators like Chamionc has on his, but I couldn't figure out a decent mounting system. Maybe someday i'll come back to it. It'd be a good "party piece" :-)

One thing it taught me was that there's often areas around your house that you wouldn't have considered mounting panels. If you have a spare south facing wall....that's actually not a bad place for a few panels, even if they are flush with the wall like I've done above. Sure, you'll get limited production in summer when the sun is overhead as the "slant angle" is poor, but from Aug->Apr a south facing wall mounted panel is a decent enough proposition. It actually does better than north facing panels!

unkel

I like the look of that, lovely dark blue hue coming from it. Gives the place a contemporary look. And indeed vertical south facing panels are quite productive, well worth your while.

@slave1 - "I don't know what impresses me more when I look at your "DIY jobbie", your "DIY Jobbie" or how you got away with those two panels from 'other half"

I can't believe that's coming from you. You have bloody panels everywhere including lots of ground mound all over your place 😂

slave1

https://www.boards.ie/discussion/comment/119457562#Comment_119457562

..true, but do you think that was an easy sell? Got there in the end though 🤐

championc

If you have East and West panels on the same string, you can avoid optimizers by paralleling them in pairs - one East with one West

bullit_dodger

https://www.boards.ie/discussion/comment/119470891#Comment_119470891

Don't even have to be east/west, any aspects really. (As long as all the panels on each string are facing the same)

championc

https://www.boards.ie/discussion/comment/119470910#Comment_119470910

Read my post again. I was talking about someone with a SINGLE string setup / inverter

slave1

https://www.boards.ie/discussion/comment/119470891#Comment_119470891

Doesn’t impact me but never thought of that

bullit_dodger

https://www.boards.ie/discussion/comment/119470945#Comment_119470945

True mate - I got that, but I was commenting/clarifying more for the benefit of anyone out there who maybe suffering with shading/optimiser use. If they read your post in isolation, they may think.

"Pity I have a SE/SW roof......so I can't use that solution"

I was just clarifying that the orientation of the panels on your roof doesn't matter. E/W, N/S, N/W....etc all the same as long as you install like for like panels and the same number of them.

championc

https://cleversolarpower.com/shading-solar-panels/