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.
"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?" 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. Mick Abraham, Proprietor www.abrahamsolar.com Voice: 970-731-4675 ---------- Original Message ----------- From: "Allan Sindelar" <[EMAIL PROTECTED]> To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org> Sent: Wed, 10 Dec 2008 13:16:26 -0700 Subject: [RE-wrenches] Module Voltage Question for Off-Grid Designers > Wrenches, > Here's an issue I haven't seen directly addressed, and I would like to know > what the rest of you are doing. > 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. > 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). > 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. > 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. > 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. > 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? > Thanks, as usual. > Allan > Allan Sindelar > allan_(at)_positiveenergysolar.com > NABCEP certified solar PV installer > Positive Energy, Inc. > 3225A Richards Lane > Santa Fe NM 87507 > 505 424-1112 ------- End of Original Message -------
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