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PostPosted: Mon May 21, 2012 11:14 am 
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Joined: Mon Apr 16, 2012 7:29 pm
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When you compute shadings with the option "according to module strings", the full rectangle-string is considered electrically inactive as soon as hit by a shade. Nevertheless, some part of the string energy is recovered by the by-pass diodes; this parameter describes which fraction of the string production is really lost.

In version 5:
The version 5 calculation cannot give a reliable value for this "Fraction for electrical effect" parameter. This is dependent on the shades distribution on the field and the electrical array configuration. For a shed arrangement (where the shades are very "regular" and several sub-modules are shaded), it is near to 100%, because as soon as 1/3 of its sub-modules are shaded, a string doesn't participate to the electrical production anymore. When with more "distributed" shades like Chimneys, far buildings, it could probably be of the order of 60 to 80%, depending on the "regularity" of the shade (a diagonal-like shade has a lower impact as it concerns modules better distributed in the array).

In version 6
The realistic calculation of the electrical effect of shadings implies the exact positioning of each module on the geometrical plane, using the "Module Layout" tool, the identification of each electrical string in the array.
Coupled to the shading calculation, the "Module layout" tool evaluates the real I/V curve of the PV array (on one MPPT input), and provides a realistic evaluation of the loss due to the electrical mismatch.
Now comparing the Electrical loss calculated by this "Module layout" option, and the "Electrical loss" evaluated by the approximated shading mode "according to module strings", you will be able to establish the "Fraction for electrical effect" to be applied in order to match the Module Layout calculation.
As an example, if you get 4% electrical loss from the option "according to module strings", and 3% with the Module Layout, the fraction for electrical loss will be 75%.


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