fixed and tracking panels on same combiner box

lotek
lotek Solar Expert Posts: 65 ✭✭✭✭
in Solar Beginners Corner #1
If I connect 3 strings of 4 panels from my fixed panel roof and 1 string of 4 panels that track, (all panels being the same make and size) what will be the result? Will I loose the extra power gathered by the tracking panels, in early and late hrs, when I combine them with the less effective fixed panels?
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #2
    Re: fixed and tracking panels on same combiner box

    You will need a blocking diode on the fixed array. This will stop the power from the tracker bleeding into the fixed early and late in the day.
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #3
    Re: fixed and tracking panels on same combiner box
    n3qik wrote: »
    You will need a blocking diode on the fixed array. This will stop the power from the tracker bleeding into the fixed early and late in the day.

    Which, unless I'm mistaken, each and every panel already has, so there wouldn't be any need for another one.

    To the OP; The only effect is that it will look like one large array that has 3/4 of the array in shade during early/late hours.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: fixed and tracking panels on same combiner box

    not all pvs come with a blocking diode, but they do come with bypass diodes. different purposes.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #5
    Re: fixed and tracking panels on same combiner box

    Bypass diodes ( shading protection ) are standard, blocking ( reverse voltage protection ) is almost never part of a panel, except maybe those 5 watt deals for automotive battery toppers

    You will want separate charge controllers as the VMP will be substantially different between the tracker and fixed arrays, tying them together will pretty much kill any advantage of the tracker performance wise with a single controller.
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  • lotek
    lotek Solar Expert Posts: 65 ✭✭✭✭
    #6
    Re: fixed and tracking panels on same combiner box

    Solar Guppy. in a past post you stated " With even the smallest amount of day light, panels will put out a VOC of near the vmp value," It was my understanding, at that time, that once voltage was reached, it was just a matter of watts produced in lower vs higher light conditions.

    Using my unsubstantial logic I deduced that the combined wattage of the array would at least be transmitted to the controller at the lowest VOC or average VOC
    evergreen 210 is 18,7 vmp @ 25 degrees and 17vmp @ 44.8 degrees.
    In the morn and eve temps would be closer to 45 degrees, so voltage from 4 panels should range around 74 volts.
    Where has my math gone awry?
    How much power would I loose by combining panels with “near vmp value” and average vmp??

    3 strings of 4 panels @ lower voltage + 1 string of 4 panels @ higher voltage
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #7
    Re: fixed and tracking panels on same combiner box

    VMP has many factors, temperature is the largest one and roof vs and open framed tracker could easily be 20-30C different.

    Irradiance also effects VMP, the more direct the light, the higher the VMP value is.

    So a cool string pointed dead on to the Sun connected in Parallel with stings on a hot roof could be substantially different VMPs .. if you combine then and run to a single Mppt charger, it will find the best power for the combined arrays, but that's not the same as having two Mppt controllers each tracking the string separately and maximizing the harvest

    As a guess, maybe a 5-10% hit in harvest combining vs separate controllers for this configuration, depends on the heat and just how far apart the two true VMP points are.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #8
    Re: fixed and tracking panels on same combiner box
    Solar Guppy wrote: »
    As a guess, maybe a 5-10% hit in harvest combining vs separate controllers for this configuration, depends on the heat and just how far apart the two true VMP points are.

    But more than just one string ? When do charge controllers go on sale?
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #9
    Re: fixed and tracking panels on same combiner box
    Solar Guppy wrote: »
    Bypass diodes ( shading protection ) are standard, blocking ( reverse voltage protection ) is almost never part of a panel, except maybe those 5 watt deals for automotive battery toppers

    I wasn't aware of the difference. I've read up on it and now understand what you mean.

    Apologies n3qik, my bad.


    RIF!
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,023 ✭✭✭✭
    #10
    Re: fixed and tracking panels on same combiner box

    I have 8 panels on ground mounts and 4 on a tracker. The clearances and hence ventilation are the same for each array. See any problems this way? Might I have to adjust the sweep intervals to make my MX60 work properly? Never noticed any problems before.

    Ralph
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #11
    Re: fixed and tracking panels on same combiner box
    Ralph Day wrote: »
    I have 8 panels on ground mounts and 4 on a tracker. The clearances and hence ventilation are the same for each array. See any problems this way? Might I have to adjust the sweep intervals to make my MX60 work properly? Never noticed any problems before.

    Ralph

    What do you consider a "problem" ?, is it ideal for maximum harvest, no, will it function? absolutely.

    The best test I could suggest is pick a time with clear conditions, run as normal take a reading, then run the tracker alone for just enough time to get a reading then the other strings, then all three again. Compare and see if there is a repeatable difference between all three and 1 + 2
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,023 ✭✭✭✭
    #12
    Re: fixed and tracking panels on same combiner box

    Thanks SG, I may try that when i've another set of hands and eyes present.

    Right now it's solar noon...12 panels all pointing the same way, no differences. In 4 hours 4 panels will be more insolated than the other 8, because they've tracked. Won't the MX60 sweep and mppt setup based on the voltage coming in? Are we saying that the 4 tracking panels are really only performing as the 8 racked ones are...they limit to the lesser voltage? Sorry if this sounds dense.

    I get an earlier morning startup and a longer float stage while tracking is enabled than if I disable the tracking and just point them south.

    Ralph
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #13
    Re: fixed and tracking panels on same combiner box
    dwh wrote: »
    I wasn't aware of the difference. I've read up on it and now understand what you mean.

    Apologies n3qik, my bad.


    RIF!

    No problem, we are all here to lean from each other.
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