[RE-wrenches] AC Coupled with Generator

Fri Aug 21 05:27:15 PDT 2015

I'm considering an AC coupled system with Enphase 
that would shed inverters a group at a time, 
ending up with one still charging until the set point is reached.

At 12:56 AM 8/21/2015, you wrote:
>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
>303 505-8760On 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>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 
>><<mailto:jerrysgarage01 at gmail.com>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" 
>><<mailto:ray at solarray.com>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
>><tel:303%20505-8760>303 505-8760
>>
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>>
>>--
>>
>>
>>
>>Mac Lewis
>>
>>"Yo solo sé que no sé nada." -Sócrates
>>
>>
>>
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