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PostPosted: Thu Oct 23, 2014 11:26 pm 
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Joined: Mon Apr 16, 2012 7:29 pm
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The calculation of electrical shading losses (shadings "according to module strings") is based on the hypothesis that when a little part of a string of modules is shaded, the whole string is supposed not to produce anymore electricity (for beam component). Up to version 6.26, the criteria during the simulation was that as soon as the "Linear" shading factor is not null, the electrical effect is accounted (ON/OFF) for the whole string.

However with the shading factor table, this created an artefact: if you have a little shading at sun's height = 20°, the "linear shading factor" (which is an interpolation between 20° and 30°) is not null up to 30°, so that the electrical shading is activated for the whole interval.
When comparing with the analytical calculation "Unlimited sheds", this gave overestimations of the electrical effect of about 2-3% for one module in landscape (less for 2, 3, 4 strings in the width of the shed).

Therefore since V 6.27, the electrical effect is only activated when the "Linear shading" calculation exceeds a threshold. This threshold was established by comparing the results with the "Unlimited sheds", which is supposed to be much more reliable as it is an analytical calculation. This threshold depends on the number of strings in the width of the shed. It also takes into account the fact that when the first bottom row of cells is partially shaded the electrical loss of the string is partial.

However this new strategy may have unexpected effects: for example if you have HV lines over your plant, the "Linear shading" factore may be insufficient (below the threshold), so that the "Thin objects" electrical calculation is not activated. In the present time we don't have an automatic solution for addressing this problem.

NB: You can modify or suppress the threshold (for example in the latter case) in the hidden parameters, topic "Miscellaneous: meteo, simulation", item "Threshold shading factor from table for module activation" if you are using the table calculation, or "Threshold shading factor from calculation for module activation" if you are using the calculation within the simulation ("Slow" option).


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