Does shade on one panel degrade all panels

System
System Posts: 2,511 admin
in General Solar Power Topics #1
Just starting out and have been told that if, for instance, there were 20 panels on the roof all tied together and if some shade was on one panel that it would cut all the panels output. Is this true or would it just cut output on the one panel that was shaded?
Thanks.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Does shade on one panel degrade all panels

    it's the panel that was shaded that gets dropped from production.
    in series the pvs have bypass diodes that allow the power to pass through.
    in parallel it just doesn't get added, but a minute amount of power can be dissipated in the shaded pv from the other pvs producing unless blocking diodes are employed.
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  • Gazz
    Gazz Solar Expert Posts: 38 ✭
    #3
    Re: Does shade on one panel degrade all panels
    niel wrote: »
    it's the panel that was shaded that gets dropped from production.
    in series the pvs have bypass diodes that allow the power to pass through.
    in parallel it just doesn't get added, but a minute amount of power can be dissipated in the shaded pv from the other pvs producing unless blocking diodes are employed.

    The problem I get is that I get a massive power drop with some shading I have, but what I have found is that if I reset my inverter the power comes back up. I am having the panels moved to reduce the shading, but cannot understand why the inverter does not manage the shading better.
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #4
    Re: Does shade on one panel degrade all panels

    Sounds like MPPT algorithm issue. What brand and model?
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  • Gazz
    Gazz Solar Expert Posts: 38 ✭
    #5
    Re: Does shade on one panel degrade all panels
    AntronX wrote: »
    Sounds like MPPT algorithm issue. What brand and model?

    SMA 3000 the supplier swapped it for a SMA 2500 and it did the same.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #6
    Re: Does shade on one panel degrade all panels

    What is the combined output voltage vs the voltage of the load being supplied?
    Still sounds like an MPPT problem though, like for some reason it's refusing to sweep until you reset.
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  • Gazz
    Gazz Solar Expert Posts: 38 ✭
    #7
    Re: Does shade on one panel degrade all panels
    waynefromnscanada wrote: »
    What is the combined output voltage vs the voltage of the load being supplied?
    Still sounds like an MPPT problem though, like for some reason it's refusing to sweep until you reset.

    Totally agree the MPPT is not doing what I though it should do, the only voltage I am aware of is what the Inverter is reading which is normally around 420V. The trouble is in the UK solar PV is quite new and it is not easy getting support from the manufacturers as they are in Germany.

    Could you explain what I should be checking for.
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  • LucMan
    LucMan Solar Expert Posts: 223 ✭✭✭
    #8
    Re: Does shade on one panel degrade all panels

    Check the MPPT voltage range specs for your inverter.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Does shade on one panel degrade all panels

    For each type of GT inverter, there is an acceptable range of voltage/current from the solar panels... Something like 200 to 600 VDC is a typical range.

    If the voltage from the solar panels is near the edges of the range (near 200 volts or over 400 volts as an example), some GT inverters have limits and may not correctly change MPPT operating points (they adjust the current taken from the panels to maintain Vmp-array for best Power=Voltage*Current output)...

    Your system, depending on the brand/model of solar panels (vmp/imp ratings), may be wired into two series strings of 10 panels x 2 parallel strings.

    For example, if two panels in one string are covered, you now have an "unbalanced" amount of Vmp from the two strings... Once may be at 300 vdc, and the other Vmp may be at 240 volts. At this point the inverter will probably be confused... It could stabilize at 300 VDC, 240 VDC, or somewhere in between.

    The "optimum" operating point for such a string with a single input inverter is always a less than ideal solution... Any of the three power peaks above is not optimum as one or the other (or both) strings are not at Vmp for their specific conditions. And the MPPT input is not usually designed to find the optimum operating point when there are mixed Vmp strings. I would not be surprised if a 10+10 string with 2 panels shaded on one string where operating only at 50% rated capacity even though the there is 90% power available because of the multiple Vmp peaks and unbalanced nature of the operating points.

    The true solution would be two central inverters finding the Vmp-array optimum point for each string--or using micro inverters to optimize Vmp-panel for each separate solar panel.

    By the way, are we talking to two different posters (C5AI and Gazz) or the same person with two logins?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Gazz
    Gazz Solar Expert Posts: 38 ✭
    #10
    Re: Does shade on one panel degrade all panels
    BB. wrote: »
    For each type of GT inverter, there is an acceptable range of voltage/current from the solar panels... Something like 200 to 600 VDC is a typical range.

    If the voltage from the solar panels is near the edges of the range (near 200 volts or over 400 volts as an example), some GT inverters have limits and may not correctly change MPPT operating points (they adjust the current taken from the panels to maintain Vmp-array for best Power=Voltage*Current output)...

    Your system, depending on the brand/model of solar panels (vmp/imp ratings), may be wired into two series strings of 10 panels x 2 parallel strings.

    For example, if two panels in one string are covered, you now have an "unbalanced" amount of Vmp from the two strings... Once may be at 300 vdc, and the other Vmp may be at 240 volts. At this point the inverter will probably be confused... It could stabilize at 300 VDC, 240 VDC, or somewhere in between.

    The "optimum" operating point for such a string with a single input inverter is always a less than ideal solution... Any of the three power peaks above is not optimum as one or the other (or both) strings are not at Vmp for their specific conditions. And the MPPT input is not usually designed to find the optimum operating point when there are mixed Vmp strings. I would not be surprised if a 10+10 string with 2 panels shaded on one string where operating only at 50% rated capacity even though the there is 90% power available because of the multiple Vmp peaks and unbalanced nature of the operating points.

    The true solution would be two central inverters finding the Vmp-array optimum point for each string--or using micro inverters to optimize Vmp-panel for each separate solar panel.

    By the way, are we talking to two different posters (C5AI and Gazz) or the same person with two logins?

    -Bill

    Sorry if I have confused you, I am Gazz and am a different poster to C5AI.

    I have 12 Sanyo HIT 240 and a Sunny Boy SMA3000 in a single string. I think I understand your explanation. But even early this morning it was cloudy and generating only 200w I reset the system and it came back up with 400w. Why does it not track better? The system is sized correctly I think, I'm even using a smaller SMA2500 inverter at the moment to see is that makes a difference.
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  • jcgee88
    jcgee88 Solar Expert Posts: 154 ✭✭
    #11
    Re: Does shade on one panel degrade all panels
    Gazz wrote: »
    Sorry if I have confused you, I am Gazz and am a different poster to C5AI.

    I have 12 Sanyo HIT 240 and a Sunny Boy SMA3000 in a single string. I think I understand your explanation. But even early this morning it was cloudy and generating only 200w I reset the system and it came back up with 400w. Why does it not track better? The system is sized correctly I think, I'm even using a smaller SMA2500 inverter at the moment to see is that makes a difference.

    First, kudos to Gazz for successfully hijacking this thread!

    I'll now add my $.02 to further hijack it. ;-)

    While there have been many posts that debate the relative
    merits/liabiltities of micro-inverters vs string inverters, Gazz's
    situation does highlight a subtle but distinct advantage of micro-
    inverter architecture. In Gazz's case, he can only see his
    entire array as a black box, and hence his only recourse is to
    "push the button" to reset his string inverter. In other words,
    he has no tools at his disposal to diagnose root cause of
    his harvest loss during and shortly after shading incidents.

    Micro-inverters give you easy (=web browser) visibility to
    individual panels. He'd have the ability to see the pattern*
    of the shading on the array, the shading's immediate
    effects on production, and how individual panels recover
    from that shading.

    *e.g., what time the shading starts/finishes, which panels
    got shaded, what percent of peak power is being lost per
    panel, etc.

    To determine root cause for a really tough problem, the
    time honored technique is to isolate and test individual
    components. Sometimes, this is the only way to figure
    out what's going on. Micro-inverters may not be perfect
    for everyone, but this is an area where they truly shine.

    John
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #12
    Re: Does shade on one panel degrade all panels

    Hmmm... If you have 12 panels in series and assume your min/max temperature is 0C/45C (Xantrex sizing tool) -- Then Voc-cold to Vmp-hot is 555.9 to 354.06 volt range.

    For a (US version) SMA 3000, the Vmp tracking range is:
    Peak Power Tracking Voltage:
    180 – 400 V @ 208 V
    200 – 400 V @ 240 V
    So--On a cold morning, I am guessing that you are above the MPPT tracking range.

    The solution would appear to be to cut the string into 2 strings x 6 in series or add more panels for 2x7 or 2x8 panels in series/parallel. (check the Euro-version of the SMA 3000; 2x6 or 2x7 panels may not work well on warm days--I have to go right now).

    You might want to contact SMA for details. Just my guess...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Gazz
    Gazz Solar Expert Posts: 38 ✭
    #13
    Re: Does shade on one panel degrade all panels
    BB. wrote: »
    Hmmm... If you have 12 panels in series and assume your min/max temperature is 0C/45C (Xantrex sizing tool) -- Then Voc-cold to Vmp-hot is 555.9 to 354.06 volt range.

    For a (US version) SMA 3000, the Vmp tracking range is:
    So--On a cold morning, I am guessing that you are above the MPPT tracking range.

    The solution would appear to be to cut the string into 2 strings x 6 in series or add more panels for 2x7 or 2x8 panels in series/parallel. (check the Euro-version of the SMA 3000; 2x6 or 2x7 panels may not work well on warm days--I have to go right now).

    You might want to contact SMA for details. Just my guess...

    -Bill

    Thanks I'll have a closer look.
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