[Greenbuilding] Electrical line shading of solar PV modules

[elitalking]

I should have taken a picture of power lines from the proposed location.  I need to get better information about distance and angle.  However, I am estimating that the power line is about 25' from proposed collectors at 45 degree angle.  The lines are above winter angles. If 45 degrees is correct, this put it in direct sun patch in March and September.  This is just a typical neighborhood power line.  3 lines are thin, likely no insulation.  2 lines are thicker with insulation.  These may be communication cables like telephones.  

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Kieth Winston wrote:
Well, it also depends on specifics of the install: how close the wires are to each other, if their shadows line up along the axis of the modules, etc. At the very least it's likely to be a good candidate for a microinverter install, to minimize shading effects.


Howell Mayhew wrote:
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.

My comments:
The lines run east and west, therefore, they are likely to cast a shadow over the whole array when it does not miss them all.  I am near positive that the lines are significantly smaller than the sun ball.  Likely if I was looking straight at the sun through these wires, I would not see the wires.  We are considering microinverters.  However, if we used a single inverter, does an equal shadow on all panels make a difference?  I took my readings from a single point.  However, the array will have length.  The only shading from other objects between 9am - 3pm will be in December when this location will not see sun until 10:15am.  During this process of rising, it may fully expose some modules before others.  Therefore, microinverters would help.  

I like microinverters because they allow the system to expand and contract.  Therefore, you can undersize or oversize the actual load you are trying to satisfy and take them away or add to them as required to match the actual production with the actual consumption.  However, there may be an economy to installing a single inverter to match the whole array. 

Thanks for comments 
Eli 

----- Original Message ----- 
From: "Gordon Howell -- Howell Mayhew Engineering" <ghowell at hme.ca>
To: "Keith Winston" <keith at earthsunenergy.com>; "Green Building" <greenbuilding at lists.bioenergylists.org>
Sent: Monday, April 04, 2011 3:57 PM
Subject: [Greenbuilding] Electrical line shading of solar PV modules


> Thanks Keith:
> 
> It depends significantly if the height of the electrical line's 
> shadow on a cell is larger than the diameter of the sun's disc (as 
> viewed from the cell) or not.  If the shadow is smaller then portions 
> of the beam radiation will not be shaded and so it won't eliminate 
> the photon shower on the cell and thus the current generated.  It 
> thus is a "soft shadow" (not fully shaded) and not a "hard 
> shadow".  It will still effect the cell and perhaps the module and 
> string, but not nearly as much as a fully-shaded cell.  I don't know 
> if I've ever seen a shadow from an electrical line to be larger than 
> the sun's disc.
> 
> +Gordon
> 
> 
> 
>>Date: Mon, 4 Apr 2011 11:43:05 -0400
>>From: Keith Winston <keith at earthsunenergy.com>
>>To: Green Building <greenbuilding at lists.bioenergylists.org>
>>Subject: Re: [Greenbuilding] Electrical line shading of solar PV modules
>>
>>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
> 
> 
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