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
<[email protected] <mailto:[email protected]>> wrote:
I cant see this working well without some battery based inverter
Jerry
On Aug 17, 2015 10:10 AM, "Ray Walters" <[email protected]
<mailto:[email protected]>> 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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