Effect Of Utility Pole Wire Shading?

I'm in the final stages of planning a 5.1KW system: presently two strings of 12 each, Kyocera 210 watt panels.

I am now wondering if the whole project is questionable due to shading from power lines near the panels.

The panels will be mounted on a patio roof with a 4 degree tilt angle south (going to a higher angle is not cost effective given the added cost of mounts and our low energy costs during winter months.) There will be eight panels east to west, three north to south, portrait style.

Summer is the most important power generating season and the power lines will shade the panels: to the west they will shade three panels between sunrise and about 10:00 AM - a 3" wide sort of medium dark shadow across three panels at a time portrait style moving across all the eight panels. On the east, starting around 2:00 in the afternoon three much more diffused shadows, very light, about 4" wide will start across in like fashion. By about 5:00 or so the shadows will pass.

The plan to minimize the effects is to configure the strings one east and one west so the shadows affect only one string at a time, more or less. An alternative is to go to three strings with, of course, a bit lower voltage dropout point. I figure at least one string will be partially shaded for about 1/2 the daily output period. If this drops the panel output significantly, it might make the installation marginal.

Is there any way to predict the reduction in power during over the periods when the power line shadows pass over the panels?

Is this a deal breaker? Any suggestions?

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Effect Of Utility Pole Wire Shading?

    If I'm reading your message right, you're saying none of the panels will have any shadow on them from 10:00 AM to 2:00 PM? This is "peak sun time" and if they're clear then that's when most of your power will be made anyway. If this is the case, try to get them aimed South for mid-day.

    I'm also a bit confused as to how panels on the West get shaded in the morning and those on the East in the afternoon. It's often difficult to visualize these things. You're quite right, though; shadows that afflict an entire string are bad. If it hits just one panel at a time, that's not so hard to put up with. But power lines being horizontal, there's no way to avoid this is there?

    Panel angle, btw, is a function of your Latitude. Raising the angle to what's right for your location and shifting the panels around a bit may allow you to avoid the shadow for most of the day. I checked the (vertical - trees) shadows on my roof for a year to get optimum location. :roll: Still not perfect, but it's the best they can be.
  • x_logo
    x_logo Registered Users Posts: 12
    Re: Effect Of Utility Pole Wire Shading?

    Sorry I wasn't clear.

    I got power lines on the east that land at the service entrance. The main lines are on the south, running east and west (far enough not to have much effect) and yet another set of lines on the west, running north and south, much closer.

    So the lines on the west shade in the AM and the lines on the east shade in the PM. Its a 1960's track home and its on a corner so I got lines everywhere but north, naturally.

    Our power company here in AZ is Salt River Project. They charge more during summer and less in winter. Also we have gas heating so winter production at normal tilts would be in excess of usage. In April the power company steals any leftover credits so any excess winter production is wasted. Calculating the electrical production multiplied by the seasonal rates at different tilts gives an optimum angle of about 14 degrees. Note that using a heat pump instead of gas would change the calculations. And if the winter rates rise compared to summer rates the optimum tilt will change as well.

    The output difference between 14 degs and the "flat" 3 deg patio slope is only about $20.00 per year at current rates. The DIY flat mounts for 24 panels are less than $600 total (not counting the time to drill holes) and store bought panels are **much** more, not readily available that can manage three panel tall portrait tilt, and are not stamped by an Arizona PE for wind rating.. Therefore the cost of tilting the panels would never be recovered by increased output. Strange but true.

    Hard to figure the shading effects but I am inclined to agree that the reduction in output will occur when output is declining with the lower sun position and might not have too big an overall affect. Still trying three strings instead of two might help.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Effect Of Utility Pole Wire Shading?

    Okay, I think I have a better understanding of our situation now.

    You're lucky you're down there and not up here: at 52 Lat I'm on the roof twice a year adjusting panel angle! It won't make that much difference where you are. As you've already figured out, with your rate schedule and the cost of tilting mounts it isn't worth it.

    If your panels will be mostly clear in the middle of the day that's the best you can hope for. You don't really get a lot of power early/late in the day anyway.

    Arizona, eh? Be sure and check out our host NAWS!
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Effect Of Utility Pole Wire Shading?

    smaller sized strings may help, but this is not good as power lines will cast enough of a shadow to disrupt output. you will have to see the place where the pvs will be and take note of the shading that occurs. you may want or need somebody to visit your proposed site for an evaluation and advice.
  • x_logo
    x_logo Registered Users Posts: 12
    Re: Effect Of Utility Pole Wire Shading?

    Yes, I had a sales rep from a solar installation firm look at the site. The shading problem was briefly noted and was not mentioned further as a major problem. But now, after reading further, am a bit concerned.

    Here is what I figured -- feel free to correct or comment:

    The Kyocera KD210GXLP I plan to use has 54 cells and I read somewhere it has three bypass diodes: one for each 18 cells. Don't know the physical configuration of the cells so it is impossible to predict what group of 18 cells will be affected by the power line shadows. With so many cells there is a high probability than all three diode groups will be affected. The shadows, a bit diagonal, will affect several cells both rows and columns at the same time. Worst case then would be each of the three diode groups of cells would be working in bypass mode dropping the output effectively to zero.

    At least three panels will be affected as the shadow works its way across the array. When the shadows transition between panels there might be some overlap affecting more than three panels but the time period might be small -- say 15 minutes. Worst case then, four panels would be at zero output.

    So, overall, my guess is that the shading will occur during about 35-40% of the day's production time during summer, affecting about four panels out of the 24 -- about 16%. Doing the math it would suggest that the shadows would cut overall summer production by as much as 6%. This will be on top of the lousy temperature coefficient which cuts into summer output when it is needed the most.

    This is not encouraging when calculating the payback for the system.

    Any further comments or suggestions would be appreciated.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Effect Of Utility Pole Wire Shading?

    I would be very concerned too--but short of doing a test on a similar system (string some rope across the array to simulate shadows)--I don't know that anyone can estimate the problem better than you just did.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Effect Of Utility Pole Wire Shading?

    This rang a bell in my unreliable memory so I went looking and found this:

    peakbagger
    Registered Guest

    Join Date: Apr 2009
    Location: Northern NH
    Posts: 15
    Default Re: Shade effect on PV Modules
    Home Power had an article awhile back where they tested panel for shading by covering up various combinations of cells. The short answer was a horizontal stripe of shading across the width of the panel was real bad for production while vertical stripes had less (but still significant impact as the diodes did their thing.


    I know that won't reassure you as horizontal stripes are what you're up against. But if that is with respect to the panels mounted 'vertically' (i.e. long up and down) then perhaps your trick of turning them 'horizontal' will help somewhat.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Effect Of Utility Pole Wire Shading?

    It can be bad. here's a shot of my install:
    http://www.mike-burgess.org/images/ViewInstall.JPG

    The high tension lines are to the east of me, and the wires are about 1" thick (wild guess, maybe more). However in the AM, they shade my west facing panels, so that is still before my main power hours. But, I can track the drop in output as each wire's shadow crosses the array. Because of the distance, the shadow is not a dark, crisp one, but is a fat, 50% shade line, by the time it's at my array.

    Shadow is bad. Oil up the chainsaw
    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 ,

  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: Effect Of Utility Pole Wire Shading?

    Shadow is bad. Oil up the chainsaw

    Words of wisdom Mike. And here i am worried about a little shadowing in December!

    http://forum.solar-electric.com/showthread.php?t=5942

    Ralph
  • x_logo
    x_logo Registered Users Posts: 12
    Re: Effect Of Utility Pole Wire Shading?

    Thanks for the comments. Yes I would like to chainsaw down the power poles but I it would likely cause unhappiness with the utilities.

    There are actually five wires on the west side that will work their way across the panels: three one inch diameter or so high voltage and ground, one twisted pair about 2" in diameter for the street lights and the big fat cable company one. The big fat cable company line casts a distinct dark shadow.

    The others cast a diffused shadow since they present a small percentage of the sun's apparent diameter. I was sort of hoping that these shadows would not be enough to drop the cell output to the point where the panel's dies.

    However, looking that the current vs voltage curves at different irradiance levels it appears that small reductions in solar levels produce only slight changes in voltage as the current output drops. However this doesn't appear linear so a larger shaded area is likely to produce a much larger proportional loss in output - voltage drops, the cells reverse bias and the bypass diodes conduct. So at some point the shading causes the output to drop like a rock. Without physical testing this would be hard to predict.

    If the numbers I ran a couple posts down apply to all five wires then output would drop as much as 30% of daily output, making the project uneconomical.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Effect Of Utility Pole Wire Shading?

    Yep--that is the problem. Any shade across a PV array can mean big losses.

    If you can use solar thermal (hot water, heating)--it may be a more cost effective project for you... The drop in output for solar thermal is simply the percentage of panel(s) area in shade. You don't have the non-linear effects that solar PV has.

    And, if you save $50 a month in natural gas vs $50 a month in electricity (with a lower installation cost for solar thermal)--you will still be ahead of the game.

    -Bill

    PS: I do like grid tied solar electric--it is virtually maintenance free except for replacing an inverter every 10-15 years or so... Solar thermal (especially hot water) can be an ongoing plumbing project even if it has a better return on investment.

    So, when my choice came, I did choose GT Electric over Solar Thermal for my home.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • x_logo
    x_logo Registered Users Posts: 12
    Re: Effect Of Utility Pole Wire Shading?

    Yes, solar water heating is in the plan. If the PVs don't work out then I might get even more radical with even more insulation.

    PV panels are almost "maintenance free" ... except ....

    In addition to inverter replacement cost there is the added cost associated with a new roof.

    On a "flat" (3 deg slope) patio roof the choice in roofing materials is not too appealing. Here in Arizona the heat tends to shorten the lifespan of many roofing materials. Chances are that the roof will need replacement before the panels so the cost of removing all the panels, wiring, and mounts, putting down a new roof, and then putting everything back together has to be added in.

    Not cheap.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Effect Of Utility Pole Wire Shading?

    Yea--new 40-50 year roof (if possible in Arizona) is a cost. But for me--my panels cover most of my roof--so it should (fingers crossed) last a good long time.

    The solar panels also dramatically reduced my attic temperature too.

    A 3 degree panel is also approaching "too flat" for self cleaning during the rain... So you may have to add the occasional scrub with soap and broom (not fun on a 2nd story panel job from the ladder).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • creakndale
    creakndale Solar Expert Posts: 27 ✭✭
    Re: Effect Of Utility Pole Wire Shading?

    If you had any prior inkling of relocating, then this significant shading solar PV deficiency could provide the final push to take the panels, etc. and move to a more suitable location.

    creakndale