A little more musing here...and I'm looking for others' opinions on
this theoretical piece.
If you have two unmatched strings, won't the string with the larger
Imp define the MPP of the inverter?
If so, I would expect that the weaker string would be forced to
operate at the Imp of the stronger string.
If the stronger string operates at a higher Vmp, it will pull the
weaker string's operating voltage above its own MPP, which could
pull the current down substantially as voltage moved from Vmp toward
Voc.
Conversely, if the stronger string operates at a lower Vmp, it will
pull the weaker string's operating voltage back toward its own MPP,
which would maintain approximately the same current at a slightly
lower voltage. This would reduce output slightly, but not nearly as
much as in the other direction.
Does this make sense? And does real-world experience bear this out?
On 1/15/2011 11:50 AM, William Miller wrote:
Friends:
I have a client with a Xantrex GT2.8 inverter. Feeding it are 8
Solar World SW175 modules. This is half the modules that this
inverter can handle. The client wants to realize the full
potential
of this inverter. Adding 8 additional SW175 modules would be
ideal,
but they are no longer manufactured.
I need to find a group of modules to match the 175s. I am
contemplating 9 SW240s. The specifications for this match up are
below. I imagine the IV curves are similar for these two modules
as
they are the same chemistry and the same manufacturer.
8-SW175 9-SW240
Voc 403 382
Vmp 283 275
Imp 4.95 7.87
Pcsi 1252 1715
Ptotal 2.967
Might this match be close enough? I know this over-powers the
inverter slightly. I imagine that the Xantrex will self
regulate
this very rare over wattage condition.
Comments?
William Miller
Please note new e-mail address and domain:
William Miller
Miller Solar
Voice :805-438-5600
email: [email protected]
http://millersolar.com
License No. C-10-773985
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