[RE-wrenches] Shade Mitigating DC Device Application (Matt Lafferty)

Wed Oct 28 23:58:13 PDT 2009

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 <gilligan06 at gmail.com>
> To: "RE Wrenches" <re-wrenches at lists.re-wrenches.org>
> Subject: [RE-wrenches] Shade Mitigating DC Device Application
> Message-ID: <F3827D62F9FA4F1E983C525A44F44CE8 at 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 <mick at abrahamsolar.com>
> To: gilligan06 at gmail.com, RE-wrenches
> 	<re-wrenches at lists.re-wrenches.org>
> Subject: Re: [RE-wrenches] Shade Mitigating DC Device Application
> Message-ID:
> 	<3dff9f8c0910281721r3a729f1er48806fe6aa5a1cba at mail.gmail.com>
> 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  
> <gilligan06 at gmail.com> 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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>>
>> List Address: RE-wrenches at lists.re-wrenches.org
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>>
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