MIXED PANEL ARRAY'S [RE-wrenches]

Mon Aug 14 22:40:43 EDT 2000

Hi Steve,

You are right, it  is permissible to parallel modules.  The limiting factor for
12 volt systems seems to be the wire size that will fit in the junction boxes.
No protection is required between modules in parallel.  In systems where modules
are in series, the code permits "supplementary overcurrent devices," which may
be required by the manufacturer or UL.

Here is the quote on module arrangement from the NEC, copied from the NEC on CD
Rom.

"690-4. Installation

(c) Module Connection Arrangement. The connections to a module or panel shall be
arranged so that removal of a module or panel from a photovoltaic source circuit
does not interrupt a grounded conductor to another photovoltaic source circuit.
Sets of modules interconnected as systems rated at 50 volts or less, with or
without blocking diodes, and having a single overcurrent device shall be
considered as a single-source circuit. Supplementary overcurrent devices used
for the exclusive protection of the photovoltaic modules are not considered as
overcurrent devices for the purpose of this section.

Series sets may be isolated from each other by fuses to prevent backed.  So far
as I can tell, there is no backed protection required for systems rated under 50
volts in which no modules are in series.

If Travis' installation is subject to code enforcement, I think the main issue
could be the Solar Boost 50.  Although my experience with the device is very
positive, I haven't heard that it has received approval yet.

Drake

"Steve Willey, Backwoods Solar" wrote:

> TC:
> Yes observed and discussed with RV power.  The solarboost 50 will use a bit
> of power especially in the voltage conversion mode and it stops converting
> voltage and stops boosting and just passes straight through at low power
> levels in the area of 3 amps plus or minus one.  This is not significant
> when not converting voltage, just loses the boost function, but in 24 to 12
> you actually get less power out to battery than in from array at low amp
> levels.  If you have a smaller array, like well under the capacity of the
> Boost 50, then it will spend more time below the conversion and boost
> threshold than a larger array.  at some point the boost unit is not going to
> be effective.  I fear that effect combined with the amorphous lower PPP will
> cause you to gain little from the extra cost of the boost.  However if
> future higher power array is expected, then only the amorphous part is to be
> considered.
>
> I thought the Siemens instruction sheet limit on not paralleling modules was
> discussed earlier on this group and decided the instructions were obsolete,
> per the factory, and it indeed was permissible to parallel two modules??? ??
>
> Steve Willey   www.backwoodssolar.com
> Backwoods Solar Electric Systems
>
> ----- Original Message -----
> From: Travis Creswell, Ozark Solar <ozsolar at ipa.net>
> To: <RE-wrenches at topica.com>
> Sent: Monday, August 14, 2000 1:31 PM
> Subject: Re: MIXED PANEL ARRAY'S [RE-wrenches]
>
> > Steve
> >
> > I'm not sure what you are saying.  Is this something you have seen as I
> > don't think it would matter how large the array other than the the Solar
> > Boost 50 itself would represent a larger draw on a smaller array.  The
> main
> > reason I am considering going to 24 volts is to leave as much room in the
> > future for expansion. They are talking about wanting to be able to charge
> to
> > Campground host's RV batteries as well.  Also, to meet code you can never
> > parallel modules so I have to pull wires for all 6 modules to the combiner
> > box.  I just as soon pull 3 runs instead of 6 runs.
> >
> > As I understand MPPT there is not much potential for boosting during warm
> > weather and as batteries get fully charged.  The colder the weather the
> > higher the panels voltage gets this the more potential for boost.  It
> makes
> > sense that the UniSolar amorphous products don't have much application for
> > MPPT as their MPP is pretty low to begin with.
> >
> > Thanks
> > Travis Creswell
>
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For info contact list moderator by email:
 michael.welch at homepower.com
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