[Greenbuilding] Electrical line shading of solar PV modules

[Gordon Howell -- Howell Mayhew Engineering]

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