Lower-than-expected Solar PV output; might split orientation be cause - could optimisers fix this?

brendandonlon

Hi all - thanks to the regular contributors for a really useful forum… apologies in advance if this isn't the best place to post this query.

I'm looking at the outputs from a new PV system since 7th September. It's 18 panels totalling 6.75kw; 5 each on the East / West main roof, and 8 on a North-South flat-roof extension.

Thanks to the tools like https://pvwatts.nrel.gov/pvwatts.php and others, I was expecting approx 400w for the first 30 days, but only managed approx 300w.

I'm presuming that the split orientation is the reason - and as the entire system is feeding into one inverter without any separation between strings, might it be worth my while to look at adding optimisers?

Or is a 300w output within the range of what to expect for this kind of system last month in Ireland, given weather variability?

simpsimp

From my limited understanding, in a two string inverter with split orientation, each string should be dedicated to an orientation.

Are you sure that the installer didn't split the array by orientation, 5 / 8 into each string? That would be standard.

idc

How many MPPT/Strings do you have ? At a guess 2 -- one for the 8 north-South roof and the other string is the two sets of 5 panels?

The two sets of 5 how are they wired together? are all 10 panels in series or are they wired as 2 parallel strings of 5 panels in series ?

brendandonlon

I can't see any info about strings in the Solis Cloud App - would this info be on the panel of the inverter itself?

idc

Don't have a solis so can't help there, my own inverter app/website only reports total PV generation, but menus on the inverter itself show real time generation for each string

con747

https://www.boards.ie/discussion/comment/119797860#Comment_119797860

When you open the Solis cloud app click on your plant name and on the next screen click on device, then click on your inverter number, after that you should see PV1 and PV2 down the screen a bit which are your strings AFAIK.

You can also check the inverter and battery and other stuff on that screen.

DC999

Congrats on solar 1st off! There's stuff you can check, but first off call the installer tell them you don't get the output you expect. And ask them to explain how it's setup. Then would be expected to give you a handover. Ask have they put optimisers on any panels or how they 3 roof directions are setup.

You’ve 3 directions (E, W and flat roof which is N&S) but most invertors only take 2 inputs (called strings). So that can reduce output.

Likely N&S is on it’s own I’d guess – but just a guess.

And if E&W are then on the 2nd, that will cause issues unless there are setup a certain way or have optimisers. As in when West is in the shade but East is in the sun, both only produce the shaded level. I’ve an E/W split but they are on a string each so they operate independently.  

Take a pic of the inverter itself. Can be easier to take a pic with the flash on to then room in if it’s hard to see. You’ll see cables going in from the panels. Are there 2 of those going into the inputs marked string1 and string 2?

Also any shade will hammer output unless those panels in shade have optimisers. Winter is bad for low sun so I see shade now that wasn’t there earlier in the year. So learn what the roof is doing on a clear day. Take pics and check when the sun it hitting each and check the app and see what the output is doing. Then you'll know in the future if something isn't right.  

I don’t have a Solis but from my browser I can drill down in parts of the invertor app I have. I can see the strings, optimisers if they are there….It's just reporting so I can't change anything by mistake - which is good. As others say, see can you get that from the inverter menu itself either. But lean on the installer to give you a 15min overview.

Also output is muck at this time of year. So check Daily pv production - Page 105 — boards.ie - Now Ye're Talkin' to see the sort of numbers people are getting as a comparison. But you still want yours to produce the most it can of course. 

On my flat roof I get moss and leaves from the main roof. Then don't clear with rain (like the main roof does) so I give them a sweep every so often.

JHet

https://www.boards.ie/discussion/2058269155/lower-than-expected-solar-pv-output-might-split-orientation-be-cause-could-optimisers-fix-this

Did you input your data into PV GIS?

Would need to know where you're located, and the slope of the east/west roof, but using the following assumptions here's what I got for you. It does seem low.

Location: Picked a random location in Dublin

East/West Roof Slope: 35 / 35 degrees

East/West Roof Azimuth: -90/90

Flat Roof Slope: 0

Flat Azimuth: 0

I modified a sheet I maintain to add a third string. Here is the PV GIS with the above assumptions:

brendandonlon

Many thanks for all the super-helpful replies - thanks to @con747 I can confirm I found the PV1 / 2 details - much appreciated. I'll need to wait for daylight to confirm my assumption, but I'm pretty certain one is East facing, and the other is West facing. From some online research, it seems like the Solis Inverter manages these two strings automatically, apparently.

And yes, the insights of this thread and my subsequent Googling confirm that the reason for my (slightly) under-par set-up is that the installer is trying to squeeze three strings out of a two string inverter, and that the flat roof is shaded for a portion of the morning by the house itself.

I was working via a one-stop-shop provider, so there was a bit of confusion / dilution between me saying "give me as much PV as you can fit!" and the installer trying to explain (via an intermediary at the one-stop-shop) that the flat roof panels wouldn't produce as much as their potential, and to manage my expectations accordingly. (They've installed them as little "tents" so they face East-West on the North-south flat roof - see above pic.)

I've no issues with the installers - they were very helpful. I suspect in the longer term, it may be worth trying to upgrade to an inverter that can handle 3 strings, and then prop up the flat roof panels so they face due south, rather than east-west. The only 3 string inverter I could find on a single phase was https://en.goodwe.com/ms-series-single-phase-residential-solar-inverter - anybody have any experience with this model?

But for now, I'm still happy with the current setup. From looking at the daily PV data on this forum, there's a huge variety in PV output depending on orientation and complexity of strings, so I'm pretty happy with what I'm getting on a first-time install with little or no research beforehand!

Thanks again for all the help…

silver_sky

Sounds like the little array on the flat roof may work best on it's own inverter. Maybe a small 3kW one or such.

brendandonlon

Yes, that's another option - not sure how I could then manage the power output from two inverters in terms of battery / load / grid?

brendandonlon

One final post on this - now that I know where to look, I can even get a graph from the browser-interface of the inverter for the two strings… here's today so far. Definitely one string each for East and West, with a jump in output on the East string once the shadow from the house clears the panels on the extension roof behind the house. Thanks again to all for help and advice.

DC999

Brill, glad it's making sense for you. Now your next problem is not checking the stats every 5 mins :) I've a Huawei and the graph + stats only updates every 5 mins. But it's close enough. Not sure what's the delay on a Solis.

con747

https://www.boards.ie/discussion/comment/119799001#Comment_119799001

@Jonathan Maybe a guide to use the apps could be added to one of the stickies so new installers can access the sections not obvious on the apps.

Jonathan

https://www.boards.ie/discussion/comment/119805353#Comment_119805353

Sure. Send on some screenshots. I only have the Solis Cloud app myself.

con747

https://www.boards.ie/discussion/comment/119805500#Comment_119805500

Same here, I'm not the best with tech more mechanical so if anyone else can do up something to help new installers like the one above navigate through the non obvious sections of the various apps we all have? It took me a couple of weeks to stumble on the different sections in the Solis Cloud app!