Panel shading question

Gazz
Gazz Solar Expert Posts: 38
I am very new to this, have had a 2.9KW Sanyo (12x240 HIT) system for 2 weeks. I have some shadowing towards the end of the day (could not be helped) is there any way of telling what effect this is having on output. I have sunny boy SB3000 the only reading on the display is output and Volts. My thoughts were that so long as the voltage does not drop then the system is not being to adversely effected.

Meaning if in ideal conditions I am reading 440V if it does not move much from that with shadow I am only loosing the area of the one panel and it is not dragging down the entire string.

If it drops to 300V then something is going wrong.

Thanks for any help, although there is not much I can do.

Gary

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Panel shading question

    Hmm... hard to say.

    Do you know how your system array is wired? One long series string of panels, two series strings in parallel?

    Normally, I would expect to see voltage to drop rather than current if this was long string of panels (10 panels in series, block one, then input voltage drops by 1/10th).

    If you have two parallel strings and block one panel, you might see the string voltage stay high--but the one string blocked looses current output, not voltage so much. This would be normal as the MPPT tracking ends up tracking the string in "full sun" and the other string is "lost". Sort of like paralleling a 10 "D" Cell flashlight battery string with a 9 cell string... The 10 cell string will do most of the work.

    The other issue is how much shading are we talking about... Power output curves Pmp, Vmp, Imp are fairly flat within 10% of the peak (5% on either side)... And being "off" by 10% is not a huge effect. If you are looking at 30-40%+ shading difference between strings--that is another matter.

    You can use the PV Watts website to estimate your "average" power output from your system. It has an output "Output Hourly Performance Data" button... You can compare an "ideal system" in average weather and see what the predicted output vs your actual output is (you may have to look around +/- today's date as these are actual output based on the "average" weather for that date (i.e., a single "real" day's output that is typical for a 20 year period).

    Generally, most of your power is generated in the "middle third" of the day--so at the edges, when you have shading, the losses are not that high as a percentage of daily output.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: Panel shading question

    Thanks BB, I have 12 panels in one string. the shading I am talking about is one portrate panel shaded across the panel covering about 50%.

    Also I have read that panel output goes down in high temperatures, what is considered high? I am in the UK so it unlikly to go above 80F.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Panel shading question
    Gazz wrote: »
    Also I have read that panel output goes down in high temperatures, what is considered high? I am in the UK so it unlikly to go above 80F.

    Toasting in the sun, that dark panel will get up to 120F easily, depending on how much airspace is below it and the roof, if there is a breeze, or whatever.
    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
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Panel shading question

    You are welcome... Ideally the MPPT controller would drop the string voltage to account for the drop in voltage... However, depending on brand/model, it may take 5+ minutes to "notice" the shading during the next Pmp/Vmp/Imp measurement cycle.

    However, your system is still operating "close enough" to optimum that your losses from optimal are only in the few percent range--not enough to worry about.

    Temperature rise on a panel baking in hot sun can be as much as 35C (63F) over ambient. Wind, air space for ventilation >5" or so (mounted above roof), etc. all help reduce panel temperature. If you have an IR thermometer, you could measure your rise.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Panel shading question

    Sunnyboy shows much more than volts and amps, just knock on the display to see other details
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: Panel shading question
    Sunnyboy shows much more than volts and amps, just knock on the display to see other details

    Yes but is't it just Volts and instant Watts and today and total KWH, is there any thing else it can tell me.
    Thanks
  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    Re: Panel shading question

    For about $140, you can purchase a communications interface board for your SB inverter, that will give you plenty of details. I purchased the 232PB-NR interface board for my SB 7000 inverter. Plugged in the piggy back card, made a connection to a laptop via the serial RS232 interface, and everything worked just fine.

    Hope this helps.

    Best regards,

    Bill
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: Panel shading question
    a0128958 wrote: »
    For about $140, you can purchase a communications interface board for your SB inverter, that will give you plenty of details. I purchased the 232PB-NR interface board for my SB 7000 inverter. Plugged in the piggy back card, made a connection to a laptop via the serial RS232 interface, and everything worked just fine.

    Hope this helps.

    Best regards,

    Bill

    I have the sunny beam with a wireless card in the sunny boy, is there anything I can do with that?

    Gary
  • jcgee88
    jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Panel shading question
    Gazz wrote: »
    I am very new to this, have had a 2.9KW Sanyo (12x240 HIT) system for 2 weeks. I have some shadowing towards the end of the day (could not be helped)...

    What hours are you counting as "end of day?"

    If you are talking about, say, from 6:30 pm and on,
    when the harvestable energy is low, and you can't
    do anything about the shading anyways, it's probably
    best just to not worry about it.
    Gazz wrote: »
    is there any way of telling what effect this is having on output. I have sunny boy SB3000 the only reading on the display is output and Volts.

    My micro-inverter implementation gives me a
    web browser interface to my array's performance.
    This web interface displays the instantaneous watts
    per panel and thus it's a snap for me to see the
    effect of shading on a per panel basis. For
    example, I have one panel in early morning that gets
    about 10% shaded by a flue cap, and I can see that
    that panel's output is cut by 2/3rds (peak of 100
    watts reduction) compared to its neighbor.

    I understand that your type of central inverter
    will sync to the lowest output panel, thus if the
    shading occurs early enough and long enough to
    be significant, you could have more loss than you
    thought. If the shading is restricted to a panel
    or two and the total loss is material, you could
    consider splitting off those two panels with their
    own micro-inverter.

    I would advise that you monitor your instantaneous
    watts every few minutes around the time the
    shading occurs, and see how steep the dropoff
    is.
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: Panel shading question
    jcgee88 wrote: »
    What hours are you counting as "end of day?"


    I would advise that you monitor your instantaneous
    watts every few minutes around the time the
    shading occurs, and see how steep the dropoff
    is.

    I think what I have to do is what you suggest, monitor it closely around the shading time and see if there is a big drop off.

    The problem is ever since the installation a few weeks ago we have a no clear days, just my look.

    Thanks