Overlapping landscape panels

Every so often there's an install where you can get one more row of panels on the roof if you're willing to overlap them a little so you get a bit of shading in the winter.

If you're installing the panels landscape, you'll only lose one row and it's partner's output, 1/3rd of the panel, and only for a couple of weeks when you're likely to suffer snow anyway.

But the other day an experienced installer said this was a bad idea. He claimed this would seriously load the bypass diode, and cause it to heat up.

This is the first I've heard of this. Comments?

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Overlapping landscape panels

    i can't say for sure about the "overlap" as any shading isn't good and i certainly hope you aren't saying to literally place pvs partially on top of each other, but the built in diodes are rated to take the current of the pvs with no problem no matter what the source of the shading is. if they didn't then why have them in there?
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Overlapping landscape panels

    If you are only talking an overlap of an inch or two, and there are several inches of air space between (front of one panel to the back of the panel overlapping it) so sun can get in at higher angles, maybe. It would take a lot of number crunching to see if the summer gain is worth the winter loss. Getting a foot between the panels might make the problem a non-issue.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    Re: Overlapping landscape panels

    Shade is bad. You will loose power. It also depends on if the shade covers a small amount of a series string or a parallel string. one way may reduce a small amount of power, the other way may shutdown all the cells in a couple of strings (in a single panel), and then if the diodes bypass, you could loose 2/3 of the panel output. For just a small patch of shade in the wrong spot!
    If the shade is wrong for a panel, even microinverters can't solve that problem.
    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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  • Maury MarkowitzMaury Markowitz Registered Users Posts: 9
    Re: Overlapping landscape panels

    I realize I left out one important note: this is for spaced rows on a flat roof.

    Here in Toronto the sun gets down to 26 degrees over the horizon. Panels are "perfect" at 30 degrees. So if you do the math, to get no shading at all in the winter you have to space them out about a panel's width apart.

    So there's cases where if you space them less, say 1.8 times, you get shading in the dead of winter -- when there's no sun anyway. But in the summer there's no shading at all, and you might get a whole extra row of panels on the roof.

    Some of the panel companies even suggest doing this.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Overlapping landscape panels

    That's the situation I was trying to describe - lots of room between so higher-angle sun gets in with no shading. Again, it would take some number crunching to be sure the loss of the shaded panels around December 21 justifies the extra panels the rest of the year. And as someone else mentioned, the configuration of the panels would be critical - you would have to be sure you didn't mix strings on the shaded row of panels.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • PhotowhitPhotowhit Solar Expert Posts: 5,806 ✭✭✭✭✭
    Re: Overlapping landscape panels

    OK so I'll be the dummy here, I don't under stand how panels reguardless of spacing between them, given that they are the same thickness/ in the same plane can be shaded by another in the same plane, reguardless of how far apart they are...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Overlapping landscape panels

    I'll try an old-fashioned ASCII demonstration...

    ........1*
    ...........2*
    \........\
    ..\........\

    Sun coming from the 1st asterisk, high in the sky spring-summer-fall, is OK. Coming from the 2nd asterisk would be a problem in winter. Not any different than any other flat-roof mount or ground mount, but I think the OP is asking about having the panels fairly close. So in a standard configuration the demo above might represent a view from 20 feet away, in this case its a close-up of maybe 2 feet away.

    Clear as mud?

    Edit: sorry, had to replace spaces with periods to keep the spacing right.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Overlapping landscape panels
    techntrek wrote: »
    i'll try an old-fashioned ascii demonstration...


    Edit: Sorry, had to replace spaces with periods to keep the spacing right.

    Hint: use the code wrapper.
             1*
                2*
    \        \
      \        \
    
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: Overlapping landscape panels

    Assuming the panels are configured as two or three strings of parallel cells, with the strings running along the long axis (never seen otherwise), you'd have to look at the historical production for the period in question to determine if you really =are= losing production to snow cover, then compare the snow cover losses to the partial shading losses -- keeping in mind that you'll lose a whatever percentage of that bottom row of cells is shaded.

    For example, if you have panels with 4" cells in 2 parallel strings and you are shading 1", you'll lose 25% of the string and 12.5% of the panel. It would be a win, under this scenario, if you have fewer than 8 strings. Current lose is fairly linear in the percent shading of the most shaded cell per string.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Overlapping landscape panels

    Ah, I hadn't noticed that option before, or the html tag option either.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Maury MarkowitzMaury Markowitz Registered Users Posts: 9
    Re: Overlapping landscape panels
    techntrek wrote: »
    That's the situation I was trying to describe - lots of room between so higher-angle sun gets in with no shading. Again, it would take some number crunching to be sure the loss of the shaded panels around December 21 justifies the extra panels the rest of the year. And as someone else mentioned, the configuration of the panels would be critical - you would have to be sure you didn't mix strings on the shaded row of panels.

    Sure, but that's true of any install. Mixing rows is always bad, IMHO.

    My question is whether or not this will have a negative impact on panel life. Not opinions, has anyone out there *actually done this*?
  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    Re: Overlapping landscape panels
    Sure, but that's true of any install. Mixing rows is always bad, IMHO.

    My question is whether or not this will have a negative impact on panel life. Not opinions, has anyone out there *actually done this*?

    I've never seen any indication that a partially shaded panel will fail early. You may use the diodes more, but it's a simple PN junction, but if sized properly, shoudl have zero effect.
    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 ,

  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Overlapping landscape panels

    There is a little effect from the diodes... There is between 0.2 and 1.0+ voltage drop.

    Pump 10 amps through a 1.0 volt drop and you have 10 watts of power dissipation (assuming all the current when through one diode)...

    For a solar panel made of glass and plastics--there is certainly a possibility of adding 1-10 watt point source already nice and hot from sunlight of causing problems. Glass and plastics have very low thermal transfer characteristics and diodes will fail quite nicely if they get too hot.

    I have not taken a panel apart to see how "they" do the diodes--but, all things considered, I would prefer to not use they bypass diodes as a major current path (i.e., 1/3rd shaded panel) if I could avoid it.

    Personally, I always wondered why this was not more of a problem (overheating diodes in solar panels because of poor cooling).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Overlapping landscape panels

    The "correct" bypass diodes types are rated for 200C junction temps.

    www.diodes.com/datasheets/sbr/SBR10U45SD1.pdf
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