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RE: Solar Panel damage



Hi Bob, 

It occurs to me too that if you have access to the internals of the panel, you ought to be able to put a diode in parallel with each cell, that will prevent excessive reverse voltage on any single cell in a series array, preventing the heat build-up and lost power output from that panel.  With some of the intelligent, switching supply based, charge controllers out there, loss of a single cell wouldn't cause the panel total power output to fall as much, either.

73, Bob, KD7NM

>-----Original Message-----
>From: Bob Bruninga [mailto:bruninga@usna.edu]
>Sent: Wednesday, October 22, 2003 5:43 AM
>To: amsat-bb@AMSAT.Org
>Cc: TAPR APRS SIG
>Subject: [amsat-bb] Solar Panel damage
>
>
>I learned something new today about Reversed solar cell damage:
>
>I think everyone who works with solar panels is aware of the 
>shadow effect
>which means that a shadow across one cell reduces the power out of the
>entire panel as if the whole panel was in shadow (the current 
>out of the
>entire series string is no better than the worst illuminated cell).
>
>But what I never realized before is that the shadowed cell 
>then is driven
>in reverse, and reverse bias heats the cell and at voltages 
>over 5 volts
>can do permanent damage to the cells.  This is usually not a 
>problem in 12
>volt systems where the difference between the open circuit 
>voltage and the
>battery charge voltage is only a few volts (say 18 and 14).  But in 28
>volt systems, where the open circuit voltage is say 36 to 40 and the
>battery is 28, then the shadowed cell will see 8 to 12 volts reverse
>voltage, and that is enough to permanently damage the cell.
>
>Fortunately, it takes a while to do it, and since satellites 
>in orbit and
>the moving sun for terrestrial cells nominally keeps the shadow moving,
>this is not that big a problem.  But a drop of bird byproduct that
>permanently blocks a cell for long period of time will kill 
>the cell and
>the panel...
>
>I knew about the shadow effect, but never realized the potential for
>permanent damage.
>
>Just FYI
>Bob, WB4APR
>
>
>----
>Sent via amsat-bb@amsat.org. Opinions expressed are those of 
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>

----
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