[RE-wrenches] Off-grid Sunny Island to backup

[bob at midnitesolar.com]

A Sunny Island (SI) will export excess energy to the grid when the 
battery voltage is driven above its target voltage (IE absorb or float)

so in the case of using a Classic or any other charge controller, the 
charge controller needs to be set to a higher voltage than the SI.

Typically I recommend setting the SI charge voltages about 1v lower than 
your Charge controller.

The issue with using the Midnite MNSICOMM is the SI tells the classic 
what to charge to so it never  pushes the battery

voltage above the setpoint, therefore it never sells.

boB



On 2/18/2019 7:54 AM, Mac Lewis wrote:
> Hi Brad,
>
> I have heard that the selling from the Midnite charge controllers 
> doesn't work real well.  There is a MNSI comm box so it may be the 
> best way (certainly the cheapest).  Does anyone have experience with 
> this scenario, good or bad?
>
> Thanks for your input as always
>
> On Mon, Feb 18, 2019 at 8:27 AM Bradley Bassett <bbassett2 at gmail.com 
> <mailto:bbassett2 at gmail.com>> wrote:
>
>     I think you can leave it DC coupled and enable grid tie in the
>     Sunny Island inverters. It might not be quite as efficient but a
>     lot more cost effective. If you don't already have it Midnite
>     makes a comm box that makes the Classic look like an SMA device.
>     That might be helpful to coordinate MPPT and grid tie.
>
>     Brad
>
>     On Mon, Feb 18, 2019 at 5:19 AM Mac Lewis <maclewis1 at gmail.com
>     <mailto:maclewis1 at gmail.com>> wrote:
>
>         Hello Wrenches,,
>
>         We have been asked to take an SMA Sunny Island System that is
>         off-grid, and convert it to a backup system (Quad stack). 
>         Currently, this is a DC coupled system using Midnite charge
>         controllers.  We would like to add SMA grid-tied inverters to
>         backfeed excess power.  I have located this document:
>         https://files.sma.de/dl/7910/SB-OffGrid-TI-US-en-19.pdf
>
>         According to this document, there really isn't Sunny Boy
>         inverters available that can function as a backup for a system
>         like this.  Is this true?
>         Do you know of any distributors that may have stock of the  SB
>         XXXXTLUS-12 line of inverters that would work for this.
>
>         Thanks for your assistance
>
>         -- 
>
>
>
>         Mac Lewis
>
>         *
>
>         "Yo solo sé que no sé nada." -Sócrates
>
>         *
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> -- 
>
>
>
> Mac Lewis
>
> *
>
> "Yo solo sé que no sé nada." -Sócrates
>
> *
>
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