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FYI series panels and shading


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Series vs. Parallel is a common topic of discussion which often ends up with the caveat "If one panel in series string goes, the whole thing goes."  That may be true for *some* installations, but here is how mine behave.  

Pictured below is the shading on 2 of 6 series-connected various brands of 125w-135w panels:
shadedpanels.jpg

And this is what the controller says:
controller.jpg


So, 57.2 x 5.6 = 320w (IN)


This is normal (full sun) about 20 minutes later:
controllerfullsun.jpg

Input =84.8 x 6.6= 560w.
Output is 53.4 x 10.3= 550w.  Not bad efficiency for 560w IN.

Output shaded = 53 x 6 = 318
Output not shaded = 53.4 x 10.3 =550

(550 -318)/550= 42% loss, with 2 panels in partial shade.

Looks like those two shaded ones (Kyocera) have diodes.  Thank heaven for that!

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I had the same results, have 3 in series, some loss but not near as bad as some predicted when partial shading. Are you running a 48 volt battery bank?

Foretravel 40ft tag 500hp Cummins ISM  1455 watts on the roof, 600 a/h's lithium in the basement.

 

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13 minutes ago, hemsteadc said:

Yes I am.  Relion 48v 100ah pack.

Very nice. Looks like Outback charge controller, does it charge batteries directly?

Foretravel 40ft tag 500hp Cummins ISM  1455 watts on the roof, 600 a/h's lithium in the basement.

 

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14 minutes ago, hemsteadc said:

Not sure what you mean by directly. 

Do the batteries have a built in BMS [battery management], or does the charge controller control the charge and voltage to the batteries.

Foretravel 40ft tag 500hp Cummins ISM  1455 watts on the roof, 600 a/h's lithium in the basement.

 

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Yes, it has BMS, and the controller is hooked to the battery just like any 'normal' battery.  I set the charge voltage for the specified 58.5 bulk and 55.2 float.

I have 2- 48v 15a shore chargers specially modified to produce only the above two voltages. 

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 Hemstead, wow good info thanks for the data and details. Sounds like your system, configured as is, works great Congratulations !!!! 

 As an engineer this topic is like so many technical concerns I dealt with over the years, THERE ARE TRADE OFFS. In series voltage increases so current down to the controller decreases which can (BUT subject to conductor size) lessen voltage drop concerns. In correct parallel voltage is equivalent but current down to the controller increases. Although there are many variables and subject to the methods, configurations and equipment used, parallel wiring can, in some situations, be advantageous if some of the panels are shaded . I would prefer all panels be of the same design, type, rating, voltage and even age when using multiple units, although, sure all sorts of engineering correct combinations still work fine, no problem...

 Soooooooooooooo different configurations and different roof real estate and the systems and methods used can dictate whether series or parallel or a combination is best on a particular RV.

 Study your roof real estate and potential shading and research your equipment and then make an informed decision of what's best for YOUR RV which may or may not be the same as another persons.   For my RV roof given panel locations and AC and roof vents and other factors I chose parallel wiring (3 now soon to be four panels 1 KW) but that doesn't mean it's best for some other RV.    

Yall take care, best wishes n God Bless

John T

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A fellow on the 'other board' pointed out my voltage is low, so I went up there and checked 'em. Not a fun job.

Here are some voltage readings starting with the 1st panel in the string to the last:

Kyocera 17
Kyocera 17
BP   15
BP 15
off brand 17
Old Kyocera roughly 2!  Yes, 2. 

Now, I couldn't lower the panels all the way down and still keep the voltmeter probes on the connection, so these measurements are close but not 100% accurate.  The Outback controller says about 90 volts.  So we have (3x 17) + (2 x 15) = 81v, so the Old Kyocera (OK) must be around 9 volts.  Incoming amperage is 6.6, so the OK is still able to pass amps, or I'd be dead in the water.

It's a little difficult to tell if the BPs were more like 14 or 15.. if 14 that would put the OK at around 11v.

Anyway, things are a bit sick.  If I do any replacement it will be the OK panel.  I might be able to live with the under-performing BPs.
 

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