[RE-wrenches] AC Coupled with Generator

[Mac Lewis]

Hi Ray,

With that size grid-tied system, you would want to use a battery based
inverter(s) near the (6.7/0.8) 8000W range.

The frequency shift of the Sunny Islands will work with kicking out the
enphase inverters but you wouldn't get the same output ramping that it
would offer if it was a Sunny Boy grid-tied inverter.  The Sunny Island can
effectively solve your generator backfeeding because there is a reverse
current sensor that will disconnect the AC input at whatever level you
want, 50 mA is default I think.  You may need to give the Sunny Island
generator start control for this however.

You can read about it here on page 137.

http://files.sma.de/dl/15216/SI4548-6048-US-BE-en-21W.pdf

You'll need to give the Sunny Island a digital signal that tell it whether
its connected to a generator or a grid as outlined in the manual.

 This is where the Radian is nice because it has two AC Input terminals.

Sounds like an interesting project.

Good Luck.




On Mon, Aug 17, 2015 at 8:36 PM, Jerry Shafer <jerrysgarage01 at gmail.com>
wrote:

> I cant see this working well without some battery based inverter
> Jerry
> On Aug 17, 2015 10:10 AM, "Ray Walters" <ray at solarray.com> wrote:
>
>> HI Esteemed Wrenches:
>>
>> I am consulting on a system I have never seen, that consists of a 6.7Kw
>> Enphase roof mounted system, and 2 backup generators.  Each generator has
>> an automatic 200 amp transfer switch to back up its own 200 amp panel.
>> Both 200 amp panels are fed by a 400 amp service from the grid.
>> The Enphase PV backfeeds a subpanel in another building which then is fed
>> by a 2 pole 60 amp breaker in one of the 200 amp panels.
>> Currently they are having issues with the generators kicking out because
>> of the Enphase inverters.  That part I understand: you can't backfeed a
>> generator, or its voltage regulation freaks out.
>>
>> Now we get to the fun part: they want to create a third critical load
>> subpanel with loads selected from both 200 amp panels to be powered by
>> batteries and an inverter.
>> I am considering the Sunny Island since it makes the most sense with its
>> ability to signal the Enphase inverters to shut off when the batteries are
>> full.  I also see this as a partial solution to the generator issue, since
>> normally the Enphase will be connected to the output side of the Sunny
>> Island.  However, when the generator is used to charge, we will be back to
>> directly coupling the generator output to the Enphase.
>>
>> Here are some possible solutions I'm considering:
>> 1) Use a separate charger for the generator so that it will only feed DC
>> to the batteries, and not be AC coupled.
>> 2) convert the PV back to DC with charge controllers, but that would
>> involve ditching and adding another conduit run between buildings.
>> 3)  Put the Enphase PV on a relay that would disconnect the PV when
>> charging with the generator.
>> 4) Something I haven't thought of that one of you clever folks can
>> suggest......
>>
>> As always, thanks in advance for all you responses,
>>
>> --
>> R.Ray Walters
>> CTO, Solarray, Inc
>> Nabcep Certified PV Installer,
>> Licensed Master Electrician
>> Solar Design Engineer
>> 303 505-8760
>>
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-- 



Mac Lewis

*"Yo solo sé que no sé nada." -Sócrates*
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