Why bother with the DC converters if you only have 2 strings?
Get a wide-range, dual-channel inverter (Power One 5000) and plug in
the modules
however you like. The bypass diodes in the modules will bypass the
shaded module
sections as appropriate for the conditions, and rest of the modules
(not shaded) will
contribute power used by the wide-input MPPT at the optimal string
voltage.
The input channels are separately controlled, so they both operate at
their optimal
MPPT voltage at all times.
The input voltage range is extremely wide, 90 to 550 Vdc (Mppt), with
a startup
voltage of 200 Vdc and a maximum Voc of 600 Vdc. That's extremely
flexible gets
you very close to harvesting 100% of the available module output.
Cost, performance, and reliability seem far better with a PV/inverter
combination
than what you get if you add DC converters to each module.
/wk
Date: Wed, 28 Oct 2009 16:29:56 -0700
From: Matt Lafferty <[email protected]>
To: "RE Wrenches" <[email protected]>
Subject: [RE-wrenches] Shade Mitigating DC Device Application
Message-ID: <f3827d62f9fa4f1e983c525a44f44...@gilligone>
Content-Type: text/plain; charset="us-ascii"
Esteemed Wrenches,
Your collective wisdom & conjecture is sought in resolving the
following
riddle:
There once was a home in the hills.
With morning sun the roof is filled.
Blasted mountain rising in the west,
Makes a shady mess at very best.
"Onward! Fear not!", sayeth the man.
"Twenty-four modules. Not one less!"
"Black box of magic for every one."
"And string inverter plus Island of Sun!"
With fifty-one hundred watts of DC.
Two series strings of four times three.
Black boxes of magic, but not by that name.
At quarter the price are they really the same?
'Tis not the matter, least not today.
To you the group... What do you say?
For greatest performance over time to yield...
2 balanced strings of shade and of sun,
Or put worst shade all onto one?
Snake-oil merchants say not to worry.
Magical boxes change dark to light in a hurry.
What say ye, from out in the field?
Balance the strings, or not?
<End>
Some factors to consider.... The site is shade-challenged, primarily
in the
afternoon. There will be two strings of 12 modules each feeding a
single
inverter. Enphase is off the table for now. Homeowner specifically
wants to
do back-of-module DC shade mitigation. The array layout is such that
configuring the strings so there is a dominant sunny one and
dominant shady
one is possible. It is also possible and almost as easy to configure
the
strings so they are more balanced with each other. Assuming that
each module
is equipped with a black box, will it make any difference which
configuration gets used?
I have my theory on the subject and am interested in yours. Thanks in
advance for any and all feedback.
Pray for Sun!
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Message: 3
Date: Wed, 28 Oct 2009 18:21:14 -0600
From: Mick Abraham <[email protected]>
To: [email protected], RE-wrenches
<[email protected]>
Subject: Re: [RE-wrenches] Shade Mitigating DC Device Application
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
This jester must ask, with a hint of glee...
is this off the grid, or is there u-til-i-tee?
Mick Abraham, Proprietor
www.abrahamsolar.com
Voice: 970-731-4675
On Wed, Oct 28, 2009 at 5:29 PM, Matt Lafferty
<[email protected]> wrote:
Esteemed Wrenches,
Your collective wisdom & conjecture is sought in resolving the
following
riddle:
There once was a home in the hills.
With morning sun the roof is filled.
Blasted mountain rising in the west,
Makes a shady mess at very best.
**
*"Onward! Fear not!*",* *sayeth the man.
*"Twenty-four modules. Not one less!"*
*"Black box of magic for every one."*
*"And string inverter plus Island of Sun!"*
With fifty-one hundred watts of DC.
Two series strings of four times three.
Black boxes of magic, but not by that name.
At quarter the price are they really the same?
'Tis not the matter, least not today.
To you the group... What do you say?
For greatest performance over time to yield...
2 balanced strings of shade and of sun,
Or put worst shade all onto one?
Snake-oil merchants say not to worry.
Magical boxes change dark to light in a hurry.
What say ye, from out in the field?
Balance the strings, or not?
<End>
Some factors to consider.... The site is shade-challenged,
primarily in the
afternoon. There will be two strings of 12 modules each feeding a
single
inverter. Enphase is off the table for now. Homeowner specifically
wants
to do back-of-module DC shade mitigation. The array layout is such
that
configuring the strings so there is a dominant sunny one and
dominant shady
one is possible. It is also possible and almost as easy to
configure the
strings so they are more balanced with each other. Assuming that
each module
is equipped with a black box, will it make any difference which
configuration gets used?
I have my theory on the subject and am interested in yours. Thanks in
advance for any and all feedback.
Pray for Sun!
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