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My solar panels not outputing what they should

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Posted by Brian Litzinger on September 28, 2003, 12:05 am
Per my previous posting I've measured more.

A quick recap: 24 Kyocera KC-120-1 panels. 48 volt system.  panels
arranged in groups of 4.  SW4048 inverter.

I call the groups of 4 panels, A, B, C, D, E & F.

I disconnected all groups then connected one group at a time to test.

                      A   B   C   D   E   F
DC amps to load      6.5 6.5 4.5 3.0 1.5 0.0
DC amps to ground    6.5 6.5 6.5 6.5 6.5 6.5

I tested the groups A through F and then F through A just to make sure
nothing funny was happening with the load.

I've taken groups C, D, E & F apart and plan to test each 12v panel

Can anyone suggest anything in particular to look for or provide some
insight into the results I am finding?


Posted by William P.N. Smith on September 28, 2003, 12:57 am
brian@worldcontrol.com (Brian Litzinger) wrote:

When you say "DC amps to ground" do you mean shorting the panels and
measuring short circuit current?  What's the open circuit voltage?

William Smith    w<underscore>smith@compusmiths.com
ComputerSmiths Consulting, Inc.    www.compusmiths.com

Posted by Solar Guppy on September 28, 2003, 1:49 am
 What was your "load" in the load test ? and the voltage during the "load"

The likely explanation is that their are panels that the bypass diodes are
conducting (either due to defective cells or cells with debris covering it ,
something the size of a nickel with do this !) , lowering the open circuit
string voltage. The current will remain the same in the Short test (since a
single panel will supply the 6.5 amps) but in Voltage test  (no load) if one
or more of the panels (in the KC120 case , even half a panel) are not
generating power , the voltage will either be lower , changing the IV curve
for the string and possible below the charge/float voltage needed to draw
current from the string.

One test , which doesn't require you undo the internal string wiring is
unhook the string to be examined from the other 5 and then measure the
voltage across each panel (should be about 21 volts under  NO load , any
time that you have unrestricted sun , not just noon time) ... if a panel or
1/2 panel isn't producing you'll just see the voltage across the bypass
diodes (about 1 volt) and have found your problem. If you see 10 volts ,
then 1/2 the array isn't producing power

Keep in mind , very small debris will stop the flow of power in the panel
and the bypass diode then conducts , so it might be something as simple as
bird poop causing your problems

My systems (2) are configured like yours 24 KC-120's , 6 strings , each
string 4 panels ... but I haven't had any failures on the 48 panels

Let us know what you find

Posted by Bill Kaszeta / Photovoltaic Re on September 28, 2003, 2:07 am
 Check for shorted or reversed  bypass diodes.  Measure open circuit voltage.
Groups could be miswired.

On 27 Sep 2003 17:05:12 -0700, brian@worldcontrol.com (Brian Litzinger) wrote:

Bill Kaszeta
Photovoltaic Resources Int'l
Tempe  Arizona  USA

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