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Call me "old school", but the only modules I keep in stock are 36 cell. I would consider 72 cell modules for stock but otherwise I "just say no" to all of the screwball cell counts that are out there. It's not that I refuse to sell anything else...but if I go goofy on the cell count I just order those modules as I need them.<font size="2">
<br />
<br />"Why go goofy?", I ask myself. My occasional "string inverter" sale can often be accommodated with 36 cell modules...ditto for pumps...and of course a 36 cell module fits right in to battery charging setups regardless of whether the solar array is wired "classic" or at elevated voltage. Cost per watt for my preferred 36's is about the same as everything else, so again I ask: "Why go goofy?"
<br />
<br />The main thing that causes me now to consider 72 cell modules for stock is the Enphase M175 inverter. My preferred 36 cell modules are a little too big on amperage to work well in pairs with the Enphase 175. If anyone has a surplus batch or used batch of "Enphase appropriate" modules with 72 cell count, contact me off list for a possible cash sale.
<br />
<br />Mick Abraham, Proprietor
<br />
<a target="_blank" href="http://www.abrahamsolar.com/">www.abrahamsolar.com</a>
<br />
Voice: 970-731-4675
<br />
<br /><b>---------- Original Message
-----------</b>
<br />
From: "Allan Sindelar" <allan@positiveenergysolar.com>
<br />
To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org>
<br />
Sent: Wed, 10 Dec 2008 13:16:26 -0700
<br />
Subject: [RE-wrenches] Module Voltage Question for Off-Grid Designers
<br />
<br />> <font face="Times New
Roman">Wrenches,</font>
<br />> <font face="Times New Roman">Here's an issue I haven't seen directly
addressed, and I would like to know what the rest of you are
doing.</font>
<br />> <font face="Times New Roman">It's getting harder to get 24V nominal
modules. Because the bulk of industry growth is high-voltage grid-tied
applications, modules no longer have to be a standard voltage. Just pick the
number of modules to best fit the chosen inverter's string voltage
range.</font>
<br />> <font face="Times New Roman">But for off-grid, the odd cell counts and
resulting "nontraditional" DC input voltages challenge the traditional
rules of off-grid design. I may be fighting a losing battle here, as the
industry changes so rapidly and fundamentally. I have been trying to stay with
72-cell modules for offgrid, as this most readily combines with existing systems
with 36-cell modules (12V) and 72-cell modules (24V).
</font>
<br />> <font face="Times New Roman">For example, I will use the new Canadian
Solar 170-200W modules. They are 60-cell modules, with a Vmppt of around 28
volts - too low to charge 24V batteries with a standard charge controller. We
can use them in any new systems with an MX60 or similar voltage-converting MPPT
controller. Two or three in series would charge a 24V battery; 3 in series would
charge 48V. Four in series would violate Code, as low-temp voltage would easily
exceed 150V.
</font>
<br />> <font face="Times New Roman">Unless 60-cell modules remain a standard
in the future, any future array additions would have to be on their own charge
controller, in order to match a different I-V curve and MPP voltages into the
same battery bank. Is this prohibitive? No, it just runs counter to the
longstanding standards of off-grid design that allow modules to be added in the
future: these modules will not add well to existing systems, and will not easily
allow additional dissimilar modules to be added later.
</font>
<br />> <font face="Times New Roman">I had this same objection to using Day4
modules, although they were better at 16Vnom. Three made up a standard 48V
array, so strings could be combined with two-module strings of similar 24Vnom
modules.</font>
<br />> <font face="Times New Roman">Who else is trying to stay with 24V
modules? Anyone still using 12V modules in off-grid (residential-scale, not
little apps) designs? Who has a crystal ball and knows what modules will be like
in 20 years, or even two years? Wat are the rest of you
doing?</font>
<br />> <font face="Times New Roman">Thanks, as
usual.</font>
<br />> <font face="Times New
Roman">Allan</font>
<br />> <font face="g">Allan
Sindelar</font>
<br />> <a href="mailto:allan@positiveenergysolar.com"><u><font face="g" color="#0000ff" size="2">allan_(at)_positiveenergysolar.com</font></u></a>
<br />> <font face="g" size="2">NABCEP certified solar PV
installer</font>
<br />> <font face="g" size="2">Positive Energy,
Inc.</font>
<br />> <font face="g" size="2">3225A Richards
Lane</font>
<br />> <font face="g" size="2">Santa Fe NM
87507</font>
<br />> <font face="g" size="2">505
424-1112</font>
<br /><b>------- End of Original Message
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