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Which gain can I expect from Backtrackintg strategy ?
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Author:  André Mermoud [ Mon May 21, 2012 11:14 am ]
Post subject:  Which gain can I expect from Backtrackintg strategy ?

In tracking arrays mutual shadings may be very important, as the gains are mainly waited when the sun is low on the horizon.
The backtracking strategy tries to suppress the mutual shadings by reorienting the modules.

But it is an illusion to think that you should obtain a much better yield with Backtracking. When the trackers perform a normal tracking (most perpendicular to sun as possible, with mutual shadings), or perform a Backtracking (deviating from the optimal orientation) they intercept about the same "Light tube" ! In one case you have shading losses, in the other one losses for mis-orientation (cos angle). It is not clear which configuration receives more irradiance: without backtracking, the shadings usually don't affect the full "length" of the modules (=> more "active" area), with backtracking you have additional IAM losses.

The only decisive advantage of the backtracking – if any – is to avoid the electrical effect of shadings (i.e. when a part of a string is shaded, the full production of the string is affected).

As an example, here is a comparison between "normal tracking" (with shades) and backtracking, for a N/S axis horizontal trackers array in Santiago (Chile). The phi angles limit is +/- 45°.
Attachment:
File comment: Backtracking and Normal tracking comparison
Backtracking_Compar.PNG
Backtracking_Compar.PNG [ 29.93 KiB | Viewed 6991 times ]

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