Shadow on PV panels.

JESSICAJESSICA ✭✭Solar Expert Posts: 289 ✭✭
Hi:

Due to the movement of the sun, from October until March the lightning rod, which protrudes about 8 feet above the ceiling, cast a very thin but long shadow on some of my panels (Kyoceras 130). Could this shadow harm the cells in any way? Does the shadow significantly reduces power output? [Note: The shadow exists only from about 1:00 PM until sunset.]

Comments

  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    Re: Shadow on PV panels.

    It will not harm your panels--but can dramatically reduce your afternoon output (very roughly 10%-50%, depending on how defuse the shadow is, how your panels are wired, what kind of solar controller you have, what the loads are, etc.).

    Try holding up a similar shape/size in front of the panels at noon (or earlier) and see how much the power output is affected (if this is a grid tied system--shadow effect should show up immediately on the Watt/Power Output Meter)... If this is a off-grid system charging a battery bank--you may only be able to measure the effect when the charge controller is in "bulk" charge mode--maximum power from the panels--once the charger changes to absorb or float mode; you will not be able to see the difference as the charge controller is already taking less than maximum current/power from the panels).

    -Bill

    PS: "Can" is the operative word here... A quick test will tell you how much (if any measurable amount) your array's output would be affected.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 ✭✭✭✭✭ Solar Expert Posts: 8,416 ✭✭✭✭✭
    Re: Shadow on PV panels.

    Your installer should have brought that to your attention, before the install started.
    Shadow will reduce the power of an entire string, not just one panel. It can become qute significant, and in the winter, when the sun is lower, days shorter, you will notice the loss even more.
    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

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

  • JESSICAJESSICA ✭✭ Solar Expert Posts: 289 ✭✭
    Re: Shadow on PV panels.

    Thanks.

    BB:

    My controller is an Outback mx60; there are six panels, in two 36 volts strings; loads are small: a fridge, tv, and some fans. I use the system only during day hours, and go back to the grid during the night.

    Mike:

    The installer was me. There was (is) no way to avoid the problem. Given the location and orientation of the panels, either the rod cast a shadow in winter or in summer. (Obviously, I could have placed the rod farther away from the panels, but then its effectiveness could have been diminished.) Nevertheless, since here in Puerto Rico there are scarce lightning episodes from November until March, I am planning to remove the rod and then install it again in April or May, when rainy season starts. (I installed the rod inside a schedule 80, ¾ pvc tube, and it is relatively easy to remove it.)
  • mike95490mike95490 ✭✭✭✭✭ Solar Expert Posts: 8,416 ✭✭✭✭✭
    Re: Shadow on PV panels.

    > I installed the rod inside a schedule 80, ¾ pvc tube,
    > and it is relatively easy to remove it.

    You do have a heavy 4g or larger ground wire from the rod (via a direct path) to a 6'ground rod in the dirt, right ?
    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 ,

  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Shadow on PV panels.

    jessica,
    putting the rod into sched 80 is putting insulation around it making it nearly useless. i wish i could picture your arrangement to advise further on the rod placement, but i know the sched 80 is large enough to impede your system from outputting properly. i would think if it has to be where it is that going to a small copper rod or pipe like 1/4in with no sched 80 around it would be far better for both functions although it will still take away from the pvs to some degree.
  • JESSICAJESSICA ✭✭ Solar Expert Posts: 289 ✭✭
    Re: Shadow on PV panels.

    Niel:

    About 8 feet of the rod protrudes above the pvc tube, where lightning would strike it. In the bottom, 2 feet of the rod are exposed, and then attached to # 2 wire (cable) which goes to the ground via another copper rod. The pvc tube where the rod is inserted (imagine a mechanic pencil) is itself attached to the wall, and its purpose is to insulate the rod form the wall and serve as a frame for the rod.
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Shadow on PV panels.

    can you describe the arrangement on the home as to the placement of both the pvs and the lightning rod and why the rod can't be moved? tell me is the rod's #2 ground wire being used as a ground vehicle for the pv system also and if not what are the proximities to each other? pictures would help here if you can, but i'd understand if you can't.
  • mike95490mike95490 ✭✭✭✭✭ Solar Expert Posts: 8,416 ✭✭✭✭✭
    Re: Shadow on PV panels.

    Quick fix, (if it is configured this way) is at the Upper PVC tube attachment to the eaves or house wall, is lengthened, so the rod leans away from the house several feet, it will only be a few degrees off vertical, and won't affect house protection. But it will move the shadow off the roof/PV's.
    But you HAVE to have a good, low impedance, path from the tip of the rod, to the lower part of your ground rod. A slight bit of angle will not affect that at all.

    A strike on the rod will likely fry all your household electronics, but the house will be protected from fire, which is the original idea of Ben Franklin's Lighting Rod (save the house, the heck with the eletronics !)
    The rod should not be tied at all to the electrical panels ground. Should have it's own ground rod.

    Mike
    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 ,

  • JESSICAJESSICA ✭✭ Solar Expert Posts: 289 ✭✭
    Re: Shadow on PV panels.
    niel wrote: »
    can you describe the arrangement on the home as to the placement of both the pvs and the lightning rod and why the rod can't be moved? tell me is the rod's #2 ground wire being used as a ground vehicle for the pv system also and if not what are the proximities to each other? pictures would help here if you can, but i'd understand if you can't.

    Niel:

    The rod CAN be moved, but if I do so it will cast the unwelcome shadow during summer time. (Obviously, I can just move the rod twice a year to avoid that problem...).
    Anyway here are some answers: Two rows of 3 panels each, one row below the other, facing south. The rod is a 5/8, 20 feet long, steel, that goes through the eaves (don’t know if this is the right word) and, as said, protrudes about 8 feet above the ceiling. It is inserted in the ¾ pvc tube, and it is fastened to the side of the house (concrete wall, reinforced concrete roof). It is placed about 2 feet below the pvs, to the south, and about 6 feet away from them, to the west (Hence the problem: As the sun goes down, but only from fall to spring, the unsolicited shadow is cast on the pvs.)
    If you can wait, I can borrow a digital camera, take some pictures and send them (At least, I can TRY.), if this explanation is not enough.
    Nevertheless, what I was really worried about was the possibility of some damage to the pvs.

    One more thing: Yes , the # 2 wire is also the grounding vehicle for the pvs.

    Thank you all for your help.
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Shadow on PV panels.

    yes, i think some pics are in order because there are usually 4 sides to a house and sometimes more and i'm having some difficulty trying to know why all of the other sides are detrimental to the pv's view to the southerly sun for a lightning rod. also, when you get the pics on here try to say what the direction it is that we and the camera would be looking at so we get the idea of the relation to the sun's radiation. examples: looking north 0 or 360 degrees, east 90 degrees, south 180 degrees, and west 270 degrees. your pvs face or 'look' south so i'm assuming them to be at 180 degrees and this is the degrees of a circle so we can relate to it as a direction.
    mike,
    although one might think having the pv and lightning rod ground leads seperate would be good or helpful, i don't see much of a difference there because a direct hit will wipe everything out anyway and just an emp event is picked up by both wires anyway making their seperation irrelevant. imo piggybacking with a split bolt connection to this single existing ground wire does not hurt anything unless it has a direct path into the home as in wiles' determination mandating the ground lead go into the home. but then seperating won't stop it from entering the home because the other lead will be energized and send it in the home anyway. what is your reasoning for the seperation?
  • mike95490mike95490 ✭✭✭✭✭ Solar Expert Posts: 8,416 ✭✭✭✭✭
    Re: Shadow on PV panels.
    niel wrote: »
    mike,
    although one might think having the pv and lightning rod ground leads seperate would be good or helpful, i don't see much of a difference there because a direct hit will wipe everything out anyway and just an emp event is picked up by both wires anyway making their seperation irrelevant. imo piggybacking with a split bolt connection to this single existing ground wire does not hurt anything unless it has a direct path into the home as in wiles' determination mandating the ground lead go into the home. but then seperating won't stop it from entering the home because the other lead will be energized and send it in the home anyway. what is your reasoning for the seperation?

    The household ground (split phase neutral) is basically only a safety ground. It was never intended or designed to handle a lighting bolt. (here in So Cal, no lighting, code uses a clamp on a cold water pipe or a rebar/ufer ground) Feeding a lighting strike into a electrical panel ground, will absolutely guarantee the contents of the house will be zapped, and maybe cause a fire. I believe all the NEC code & Wiles' wiring is only for safety of a shorted wire, not lighting protection. (but I haven't read the entire thing, I just know how the physics of it will work)

    When lighting strikes, all bets are off, and I think you just plan on a large homeowners claim, and buy new gear. The Franklin Rod is to prevent a house fire, by directing the strike path away from the house, and into the ground. Feed that to your electrical panel, and I think you can imagine what WILL happen.
    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 ,

  • mike95490mike95490 ✭✭✭✭✭ Solar Expert Posts: 8,416 ✭✭✭✭✭
    Re: Shadow on PV panels.
    mike90045 wrote: »
    The rod should not be tied at all to the electrical panels ground. Should have it's own ground rod.
    right near the base of the lighting rod. When you have a jillion amps of electricity flowing, it does not like to bend. any bend in the wire shows as impedance. While lighting is DC, it is pulsed, with several strikes in a second or 2, all in the same channel. When you curve or bend the wire, to lighting, it looks like you have wound an inductor, and you force it away from your ground rod. Then the fun begins.

    some description here:
    http://en.wikipedia.org/wiki/Lightning_rod#Lightning_protection_of_mast_radiators

    The external links section has several good articles to read.
    http://en.wikipedia.org/wiki/Lightning_rod#External_links
    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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