[RE-wrenches] AC Coupled with Generator

Thu Aug 20 21:56:57 PDT 2015

Hi Folks;

I've done more research on the whole AC coupled issue, and one flaw I 
found with both the Sunny Island and the Radian is that they can't 
really do a full 3 stage charge for the batteries in off grid mode.
They detect that the batteries are full and disconnect the AC coupled GT 
inverters, but this is about as subtle as the very early charge 
controllers, and amounts to 1 stage charging.  This is fine for 
temporary outages, and when the grid comes back, the batteries get a 
good 3 stage charge.  But these folks are really wanting a design that 
could be taken off grid permanently.   Also as you my recall, the GT PV 
system is Enphase, so we can't use the more sophisticated controls that 
SMA offers for the Sunny boys.
I hate to say it, but I might be back to a diversion load with PWM 
controller.  Not elegant, but we could get 3 stage charging.
Every time I look at AC coupled setups, I just want to start over with 
charge controllers.

R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 8/17/2015 9:39 PM, Mac Lewis wrote:
> 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 <mailto: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
>     <mailto: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 <tel:303%20505-8760>
>
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> -- 
>
>
>
> Mac Lewis
>
> *
>
> "Yo solo sé que no sé nada." -Sócrates
>
> *
>
>
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