Serial vs. Parallel - Shading

calbiker
calbiker Banned Posts: 50 ✭✭✭✭
in General Solar Power Topics #1
Has anyone tested serial and parallel array configurations in regards to shading? Is one configuration better? Does panel brand have an influence?

Setup: 2 - 3 panels, charge controller, 12V batteries

Thanks,
Cal
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Serial vs. Parallel - Shading

    From my experience it's "Yes. No. No." :p

    The amount of shading can have a significant effect; if it knocks out one whole panel that's worse than if it just blocks one segment of that panel. Thus you have the phenomenon of which way the panel is oriented having influence on how the cast of a tree or phone pole may affect output.

    On a 12 Volt system I wouldn't expect much difference either way. A higher Voltage array can suffer from shading knocking out one (or more) panels in series as it causes the Vmp to drop below effective levels. This is the basis of a lot of the "micro inverter vs. central inverter" debate.

    As with so many things solar, it's more complex than "this is the one and only answer".
    Hopefully you'll get more answers than just mine. :D
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: Serial vs. Parallel - Shading
    calbiker wrote: »
    Has anyone tested serial and parallel array configurations in regards to shading? Is one configuration better? Does panel brand have an influence?
    As I understand it, if you have panels in series shading anywhere in the string can limit the output of the entire series string. If you have panels (or strings of panels) in parallel, shading on one string will not affect the output of the other strings.

    As far as brand is concerned, I have read that amorphous panels as a bit less sensitive to shading and bullet holes.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • KJINTF
    KJINTF Registered Users Posts: 15 ✭
    #4
    Re: Serial vs. Parallel - Shading

    There is a thread going on at RV.net that is trying to uncover the very same thing
    Take a look at http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25983904.cfm

    Sure would like to see some more testing

    Ken
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  • N8GS
    N8GS Registered Users Posts: 1
    #5
    Re: Serial vs. Parallel - Shading

    I'm the guy doing the testing over on RV.net
    Here are the results of some of my recent tests.
    The perfomance of series proved to be superior to parallel. Note that when running in parallel the shaded cells completely killed the output of that panel while leaving the unshaded panel uneffected.
    Have fun figuring out why it worked out this way. Gotta be something to do with diodes.
    Gale



    120418Seriespanelshadetest.jpg

    120411-singlepanelshadetests.jpg

    120407-Parallelpanelshadetest.jpg
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #6
    Re: Serial vs. Parallel - Shading

    Very interesting, do you have the volts to battery data as well?

    My experience with shade and 4 parallel panels, differs slightly and it was not charted, was that a slight, almost imperceptible shadow(s) had significant impact on both pre, during the felling of a 'nude' Aspen tree, and after, when the tree was on the ground.???
    Wife was watching and reading PV / battery values from the MX60 screen. From what I could see a 1 inch branch about 20 feet away was the culprit.
     
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #7
    Re: Serial vs. Parallel - Shading

    The other thing, is shade is going to activate the bypass diodes, which are generally, not well heat sunk., and go bad long before they should
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • KJINTF
    KJINTF Registered Users Posts: 15 ✭
    #8
    Re: Serial vs. Parallel - Shading

    Mike

    This is the first I have heard of the diodes going bad because of excessive heat caused by shading
    Panels mounted on RV's will encounter shading conditions
    Do you have by data supporting early failures that you can share with us?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Serial vs. Parallel - Shading

    We have the occasional question of where to get replacement diodes here...

    And, from what I have seen, I have always been a bit concerned about diodes in panels. Hot environment, sealed box, no metal/heat sinks, glass/teldar poor thermal conductors... Electronics do not like heat and they do not like temperature cycling.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    #10
    Re: Serial vs. Parallel - Shading

    Probably those panels that integrate bypass diodes within the panel are more susceptible of failure.

    Here's my understanding of parallel vs. serial.

    If multiple bypass diodes are use per panel then series has a significant advantage. If 1/4 of the cells are bypassed due to shade, the other 3/4 of cells in panel are still useful to increase array voltage. The panel with useful 3/4 cells is useless in a parallel config. It can provide no energy.

    If one bypass diode is used per panel then parallel has slight advantage.

    If no bypass diodes are used in the array then parallel has a huge advantage.

    STMicroelectronics is doing some cool stuff. They got a MPPT controller that's mounted within the panel junctionbox. The effects of shade or mismatched voltage (in parallel array) is minimized. Each panel needs a controller!

    http://www.st.com/internet/com/SALES_AND_MARKETING_RESOURCES/MARKETING_PRESENTATIONS/PRODUCT_PRESENTATION/stforsolarenergy_marketing_pres.pdf

    See page 7 for SVP1020
    On page 6 they got a fet replacement for blocking diode. Interesting.

    Cal
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