[Greenbuilding] Electrical line shading of solar PV modules

elitalking elitalking at rockbridge.net
Wed Apr 13 22:52:15 CDT 2011


Thanks so much, Gary, for your study of power line shading over photovoltaic.  

http://www.builditsolar.com/Experimental/PVShading/PVShading.htm

It seems from your study that the thin shadows do not have a significant impact.  Also, it seems you are right that distance softens the shadow as shown on Nick Pyner's picture.

http://homepages.ihug.com.au/~npyner/wireshad.JPG

I will see if other feedback supports your main theory.  I am still a novice. Based on Gary's study, it seems the site looking thru the power line is the better location.  

However, I went back to proposed site and considered locating the collectors under the power line so there are no shadows from power line.  I am not sure if this would be allowed in easement of power line.  I also checked sun exposure 15' from centerline on South side of power line to get out of easement.  These changes bring me closer to the solid objects shading the collectors in the mornings of November, December, and January.  The recommendation I read is to if possible have full sun between 9am - 3pm (6 hours).  Sunrise in October, January, and February is delayed until 10:15am or 10:30am.  The location south of power line gets shadowed 1:30pm in December.  Therefore, during the low production part of the year, more power production is lost.  However, by February until October, the collectors are in full sunshine.  Late fall and early December have low daily insolation.  Since the months that the collector is full sun have higher insolation, perhaps on an annual basis, that shading would not be a significant reduction. Does any have a sense of what percentage of reduction might be?

I do not know if any recall our discussion of intermittent heating of high mass building about a year ago.  However, this installation is being considered to produce the power to run electric heat element in an un-insulated solid masonry Quaker meeting house. I have always considered insulation and tightness to be more cost affective than production.  However, I am reconsidering that in this case.  If photovoltaic's can be continually producing power all year including the peak late spring early summer months, we can lower the conventional electricity that has to be produced to serve the grid.  Therefore, when we consume it inefficiently intermittently in the winter months, we can achieve net zero in electric consumption.   The combination of continual steady production with intermittent seasonal high consumption seems to balance out.     

Of course the conflict to being efficient is servicing a building for only 4 or 5 hours of use a week.  

Eli 

  ----- Original Message ----- 
  From: Gary BIs 
  To: Green Building 
  Sent: Tuesday, April 12, 2011 1:49 PM
  Subject: Re: [Greenbuilding] Electrical line shading of solar PV modules


  Hi Eli, Keith, ...
  Finally got some descent sun and a little time to do the further testing on the effect of power line shadows on PV array output.

  The new results are here:
  http://www.builditsolar.com/Experimental/PVShading/PVShading.htm

  It looks to me like for real world wire shadows from wires 20+ ft away that the effect might be small to none.

  Would appreciate any comments on this, or things that might be wrong in the test.

  Gary


  On 12:59 PM, gdreysa wrote: 
    Hi Eli,
    I'd agree with Keith that some caution is in order here.

    This is a picture of my Enphase PV array with some modest shading:
    http://www.builditsolar.com/Projects/PV/EnphasePV/Shading.htm

    You can see from the real time output plot that even the panel with just a line across it is very much effected.
    The shadow is wider than a power line would cast, and maybe the effect would diminish as the shadow gets narrower, but I'd be careful.

    If I think about it later today and the weather cooperates, I'll set up narrower shadow and let you know how that comes out.

    The micro inverters are good in that a shadow across one module only effects the output of that one module and not the whole string, but a wire shadow that goes across several modules could still have a serious effect.

    Gary


    On 12:59 PM, Keith Winston wrote: 
      I'm not quite sure what you mean by "smaller than the sun's disc"... larger power lines can cast distinct shadows. If those align with an axis of the modules, then they may shade an entire row of cells in a module, overcoming the ability of the bypass diodes to "bypass" the shaded cells (most modules are, I believe, still bypassed on a cell-by-cell basis, and are wired in series along one of their axis). So I'll stand by my earlier comment that a power line could very well create significant shading. But I agree with the microinverter suggestion.

      Keith



      On Mon, Apr 4, 2011 at 11:22 AM, Gordon Howell -- Howell Mayhew Engineering <ghowell at hme.ca> wrote:

        Thanks for your question Eli:

        It doesn't appear that the electrical lines would be a significant issue.  They are likely smaller than the sun's disc.

        If you use Enphase module-inverters (one inverter for each PV module) then any shaded module wouldn't affect the PV array's performance, because each PV string is a PV module.

        To clarify:  the industry term that is an internationally-recognised standard for PV modules is "module", not collector, not panel.  See attached file for pictoral description.









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