[RE-wrenches] Module Voltage Question for Off-Grid Designers

[Matt Tritt]

My favorite is the Sharp 175 for off-grid and solar pumping 
applications; a sturdy, well built and consistent module for most 
applications. You can even get them fairly often!

Matt T

Kirpal Khalsa wrote:

> Allen..Greetings....yes indeed it is an issue. we have been addressing 
> with multiple charge controllers per system. we don't fight the 
> current (not electrical).  In the future the way i see it- the 
> electronics will be more flexible and be able to handle the larger 
> variety of string voltages.  For example the long long long awaited 
> apollo solar t100 which will allow voltages to exceed the 150V limit 
> we have had for a long time.  They have apparently even lined up some 
> breakers which will work with these greater voltages.  3 modules in a 
> series will no longer be a maximum.  I understand midnite solar also 
> has a charge controller which will allow the 150V max to go by the way 
> side.  We are trying to be flexible as modules become less standard 
> and hope that the electronics will allow us to address thesee 
> challanges as time goes by.
>
> One thing that we would love to see is more large wattage modules with 
> j boxes rather than pre-wired MC cables.  In many of our off grid 
> systems the array is located in readily accesible locations and 
> crafting a fence or sticking the array over 8 feet of the ground is a 
> big hassle/extra expense.  This has proven to be a bigger concern for 
> us rahter than the voltage variety.  If you know of any 72 cell or for 
> that matter 60 cell modules  which allow flex conduit between j boxes 
> we would love some info.......
>
>
> -- 
> Sunny Regards,
> Kirpal Khalsa
> NABCEP Certified Solar PV Installer
> Renewable Energy Systems LLC
>
>
> On Wed, Dec 10, 2008 at 12:16 PM, Allan Sindelar 
> <allan at positiveenergysolar.com <mailto:allan at positiveenergysolar.com>> 
> wrote:
>
>     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_
>     <mailto:allan at positiveenergysolar.com>
>     NABCEP certified solar PV installer
>     Positive Energy, Inc.
>     3225A Richards Lane
>     Santa Fe NM 87507
>     505 424-1112
>
>
>
>
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