[RE-wrenches] Inter-row shading, additional information

[Bill Brooks]

William, 

 

In a series string, the one-cell shading in the long dimension will reduce
the voltage of the string by 1/3 of one module. This is often a small amount
of voltage since 12 or 13 modules are in string. In lower voltage systems,
the loss will be much more pronounced. No shading is good and shading on a
portion of a single module in a string will not effect performance
substantially. The problem comes with interrow shading where each module
looses 1/3. Now the overall loss is much more than 1/3 of the string because
the other strings will dominate the inverter voltage (assuming you have
multiple strings-that is why you have multiple rows). If only one row is
shaded, then the output of that string will be reduced to operating at the
shade light level. If all strings except the first row are shaded, then a
sophisticated inverter will try to powertrack the array at 2/3 voltage-and
therefore 2/3 power. This only works if the inverter can operate at 2/3
voltage. If not, then the whole array will likely work off of the first row
output and ALL the subsequent rows will produce power at whatever light
level the shade delivers.

 

Bill.

 

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of William
Miller
Sent: Friday, April 23, 2010 11:26 PM
To: RE-wrenches
Subject: [RE-wrenches] Inter-row shading, additional information

 

Friends:

I was incorrect on one point in my previous post on the subject.  The
SolarWorld SW230 is comprised of one series string of cells.  It acts
somewhat like there are three strings because of the bypass diodes. If you
shade one cell of one group, the bypass diodes kick in and allow the module
to continue to produce power but at a reduced level.

Our test showed that if the short edge is shaded for more than half of a
cell width on the narrow edge, the total output caved.  The same shading on
the long edge reduced output minimally.

William Miller






Please note new e-mail address and domain:

William Miller 
Miller Solar
Voice :805-438-5600
email: william at millersolar.com
http://millersolar.com <http://millersolar.com/> 
License No. C-10-773985

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