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

[Kirpal Khalsa]

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> 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* <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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