Mismatch module losses? [RE-wrenches]

Allan Sindelar allan at positiveenergysolar.com
Wed Oct 31 16:16:29 PDT 2007


Alex/Dave,
Sky's answer is correct. If you series modules of different amperages, the
voltages will add, but the currents will approximate that of the smallest
module. So coming in at 24V is your only option.

Any better solution will cost $$$, both to approximately double each of the
three strings to raise voltage and to use a controller such as the MX60 or
the SB3048 to step down a 48V array. Neither is cheaper than big wire,
unless the customer also needs more array. And if the cabin is for
summer-only use, keep the C40.

Allan at PosE

----- Original Message ----- 
From: "Sky Sims" <sky at ecologicalsystems.biz>
>
> 3 different module types nice. No one will recommend doing this, but if
> I wanted to maximize the performance my guess would be to series string
> the 2 80watt modules and series string the 2 120watt panels then put the
> 175watt module in its own series string. Then I would parallel all 3
> strings together. My experience when playing around with this type of
> scenario is that the voltages will hit some sort of parity that allows
> all the strings to contribute to the overall wattage and the amps will
> simply add together. After you hook it all up prudence would require
> that you verify with an amp probe under load whether or not all the
> panels are actually feeding power to the charge controller.
> Disconnecting strings and doing voltage and amperage checks and
> reconnecting strings will give you a definitive answer as to whether or
> not the power is being clipped to any significant degree.
>
> Sky Sims
> Ecological Systems
> www.ecologicalsystems.biz
> 220 County Road 522
> Manalapan, NJ 07726
> ph)732-462-3858  fax)732-462-3962
>
> -----Original Message-----
> From: Alex Cozine [mailto:acdc.cozine at gmail.com]
> Sent: Wednesday, October 31, 2007 11:45 AM
> To: RE-wrenches at topica.com
> Subject: Mismatch module losses? [RE-wrenches]
>
>
>
>     Is there really that much difference?  I have a Solar Service
> upgrade
> for a off grid cabin near Mt. Rainier.  They need to move their
> trace2524
> inverter, c40 charge controller 125vdc input, and bank of 8 batteries in
> 24
> volt conf.
> The array consists of --2- 80watt 21.8Voc 4.85 Isc shells-- and --2- 120
> watt 21.5Voc 7.45 Isc kyoceras--.  Plus they bought one new module
> --175watt
> 44.4Voc 5.3 Isc sunworld--.  This is all on a hill 160 feet away.
>
> What is the most efficient way to wire up these modules for this 24 volt
> system?
> We put one 80watt module in series with one 120watt module and to the
> combiner box.
> Then the other 80watt in series with the other 120 to the combiner
> Then the 175 to the combiner.
> Paralleled all 160' down to the power shed into the c40.
>
> Is there a big loss putting an 80 watt module in series with a 120 watt
> module?
> I was thinking the amperages would average out.  Is that true?  or does
> the
> 120 watt module act like a 80 in that conf.?
> Does anyone have an explanation for why I could've chosen to put the
> 80's in
> series and the 120's in series?
>
>
> Thanks,
>
>
> Alex and Dave Cozine
> Brothers Electric & Solar
> Tacoma Washington
> brotherselectricsolar.com
>


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