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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. <br><br>
At 12:56 AM 8/21/2015, you wrote:<br>
<blockquote type=cite class=cite cite="">Hi Folks;<br>
<br>
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.<br>
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. <br>
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.
<br>
Every time I look at AC coupled setups, I just want to start over with
charge controllers. <br><br>
<pre>R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre><font face="Courier New, Courier"></font>On 8/17/2015
9:39 PM, Mac Lewis wrote:<br>
<blockquote type=cite class=cite cite="">Hi Ray, <br><br>
With that size grid-tied system, you would want to use a battery based
inverter(s) near the (6.7/0.8) 8000W range. <br><br>
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.<br><br>
You can read about it here on page 137.<br><br>
<a href="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</a><br><br>
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.
<br><br>
This is where the Radian is nice because it has two AC Input
terminals.<br><br>
Sounds like an interesting project.<br><br>
Good Luck.<br><br>
<br><br>
<br>
On Mon, Aug 17, 2015 at 8:36 PM, Jerry Shafer
<<a href="mailto:jerrysgarage01@gmail.com">jerrysgarage01@gmail.com</a>
> wrote:<br>
<dl><br>
<dd>I cant see this working well without some battery based
inverter<font color="#888888"><br>
<dd>Jerry<br>
</font>
<dd>On Aug 17, 2015 10:10 AM, "Ray Walters"
<<a href="mailto:ray@solarray.com">ray@solarray.com</a>>
wrote:<br>
<dl>
<dd>HI Esteemed Wrenches:<br><br>
<dd>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.<br>
<dd>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.<br>
<dd>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.<br><br>
<dd>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.<br>
<dd>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.<br>
<br>
<dd>Here are some possible solutions I'm considering:<br>
<dd>1) Use a separate charger for the generator so that it will only feed
DC to the batteries, and not be AC coupled.<br>
<dd>2) convert the PV back to DC with charge controllers, but that would
involve ditching and adding another conduit run between buildings.<br>
<dd>3) Put the Enphase PV on a relay that would disconnect the PV
when charging with the generator.<br>
<dd>4) Something I haven't thought of that one of you clever folks can
suggest......<br><br>
<dd>As always, thanks in advance for all you responses,<br><br>
<dd>-- <br>
<dd>R.Ray Walters<br>
<dd>CTO, Solarray, Inc<br>
<dd>Nabcep Certified PV Installer,<br>
<dd>Licensed Master Electrician<br>
<dd>Solar Design Engineer<br>
<dd><a href="tel:303%20505-8760">303 505-8760</a><br><br>
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-- <br><br>
<font color="#305A78"><br>
</font><br>
Mac Lewis<br><br>
<font face="Verdana">"Yo solo sé que no sé nada."
-Sócrates<br>
</b></font><br><br>
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