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:[email protected]>[email protected]> wrote:
I cant see this working well without some battery based inverter
Jerry
On Aug 17, 2015 10:10 AM, "Ray Walters"
<<mailto:[email protected]>[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
<tel:303%20505-8760>303 505-8760
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