[RE-wrenches] AC coupled, grid-tied Sunny Island - contactor & bypass

[August Goers]

Hi Kelly -

Sounds like a fun project. We've got a few 10+ kW grid tied Sunny Island
projects and although they are not with Enphase inverters I thought I'd
pass on how we've been wiring them up with good results.

We tie the solar inverters into the critical loads panel and then put a
transfer switch (either auto or manual depending on the client's choice)
between the main and critical loads panel. The Sunny Island(s) output
circuit (AC1) is also tied into the critical loads panel and the AC2
connection is tied into the main. During normal on-grid operation the PV
is tied directly to the main through the critical loads panel and transfer
switch so there are no losses through the Sunny Island. The Sunny Island
at that point is simply keeping the batteries charged though the AC2
connection and monitoring the grid. When the grid goes down the transfer
switch disconnects the critical loads panel from the main and the Sunny
Island kicks in. The PV inverters shut off immediately during the switch
but then kick into waiting mode once receiving the signal from the Sunny
Island. The PV stays on during the grid outage until the batteries are
fully charged then the voltage increases until the PV turns off, goes back
into waiting mode and the whole process repeats - this is assuming that
we're getting more PV than load. I've tested both scenarios and if the
load is larger than the PV then the inverters will stay on indefinitely.


What was your reasoning for tying the PV into the main and using a relay
to switch to the critical loads panel during a power outage?

Best,

August


August Goers

Luminalt Energy Corporation
1320 Potrero Avenue
San Francisco, CA 94110
m: 415.559.1525
o: 415.641.4000
august at luminalt.com

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kelly
Keilwitz, Whidbey Sun & Wind
Sent: Thursday, January 13, 2011 7:33 PM
To: RE Wrenches listserve
Subject: [RE-wrenches] AC coupled, grid-tied Sunny Island - contactor &
bypass

Wrenches,
We are including 2 Sunny Island inverters into a previously battery-
less grid tied design utilizing 20 kW of PV on Enphase micro inverters
and 2 SMA Windy Boy 6000 inverters (10 kW XZERES 442 turbine). Our
customer wishes to run his fuel generator as little as possible when
the grid goes down. Nothing is in the power room yet, the house is
under construction. Only the wind turbine is installed.

With a pass-through limit of 56A, the two Sunny Islands cannot conduct
the combined RE production to the grid. There is not enough critical
load demand to justify two more SI's, nor is there space for them. Our
plan is to connect the micro-inverters (84A, peak) directly to the
main service (grid) in normal mode, switching to the critical load
panel (SI AC output) when the grid goes down. The Windy Boys (56A)
would remain connected to the critical load panel.

I'm hoping that the frequency shifting control of the Windy Boys from
the SI's will allow the PV micro inverters to connect and stay
connected to the SI's while there is demand on the critical loads and
the batteries are charging. When there is more PV output than load
demand we expect that the SI frequency will rise to the point where
the micros will go out of spec and disconnect, maybe in a nicely
staggered pattern.

Questions:

1. Has anyone experience with this much grid-direct RE capacity and/or
micro-inverters AC coupled to Sunny Islands? I'm a little scared by a
previous post from Darryl wherein he found that the RE capacity from
the GD inverters should be 1/2 that of the battery-based inverters in
an AC coupled system. Please let me know if you are certain that this
is not going to work!

2. Any experience with specifying a contactor/relay to switch the PV
output? The contactor will be controlled by one of the SI relays.
Switching from the main panel (grid) to the critical load panel will
be during a grid outage, so doesn't need to be load-rated, but
switching back after the grid comes back up could be load-break. Our
current solution is to use two 80A contactors from Schneider
(#LC1D80G7) with an intertie kit.

3. Any suggestions for an inverter bypass (service disconnect) for the
two SI's? We're considering either a monster 2P2T 200A switch (100 A
would do), or using a gen-transfer type panel for the critical loads.

Comments and informed opinions quite welcome.

Thanks,
-Kelly

Kelly Keilwitz, P.E.
Principal
Whidbey Sun & Wind
Renewable Energy Systems
kelly at whidbeysunwind.com
PH & FAX: 360.678.7131
NABCEP Certified PV Installer
WA Electrical Administrator







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