[RE-wrenches] Back feeding battery inverter with grid-tieinverter

[Mark Dickson]

The Outbacks will definitely work.  We recently completed and Fronius AC
coupled system (ran DC on the home run) and back feeding the Outback quad
stack.  We ran short on relays, so we used a Morningstar Relay Driver which
was very simple to use and gave us 4 additional programmable relays.  When
the batteries fill up we have the first relay kick on an electric space
heater, a second one kicks on some ice melters and the third cuts the power
between the Fronius and the AC panel.  It tested out great and I am
returning to commission it this Thursday-so we shall see.

 

Our system is an off grid system though and I am not sure how it would work
with the grid without the GFX inverters.  We have the generator for back-up.

 

Mark Dickson

Oasis Montana Inc.

 <http://www.oasismontana.com/>  <http://www.oasismontana.com/>
www.oasismontana.com

 

www.grid-tie.com <http://www.grid-tie.com/> 

 

 <http://www.pvsolarpumps.com/>  <http://www.pvsolarpumps.com/>
www.PVsolarpumps.com 

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Steve
Johnson
Sent: Tuesday, January 20, 2009 2:47 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Back feeding battery inverter with
grid-tieinverter

 

(This has already been said a few times but I am testing my new email on the
list and might as well put in my 2 cents. the first one bounced back so I'm
checking registration again)  steve

 

Jeff,

 

Why not send DC back to the garage and set your Sunny boy there.

By sending 350VDC back you will have considerably less voltage drop to deal
with than 240 VAC.  There is no charge controller as it is AC coupled.

 

I know the old SW4024 takes AC both ways on the AC in.

 

I am doing a similar installation, AC coupled, but with outback VFX instead
of Xantrex.

The outback will not backfeed the grid as it is an off grid inverter.  It
has an internal transfer switch.  The Aux relay has to be connected to a
relay to disconnect the sunny boy ac circuit to prevent of overcharging the
batteries as there is no charge controller.  So yes the sb charges the
batteries and feeds the subpanel both.

 

When the grid fails the sunny boy disconnects.  After 5 minutes it will see
the ac from the outback battery backup and reconnect (thru the emergency
panel).  Outback has an ac coupling paper on their website.  I am not
familiar with the new xantrex's.

 

Steve

 

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jeff Yago
Sent: Sunday, January 18, 2009 11:31 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Back feeding battery inverter with
grid-tieinverter

 

I know this subject has come up before, but there have been several
different suggested ways to handle the problem and I was hoping for easiest.
We install lots of both on grid and off grid systems.  However, we have a
client that will require a ground mounted array much futher away from the
inverter and batteries in the garage than we normally would want to do since
the voltage drop for this long distance would be excessive at low voltage
even with large cables.  We have decided to locate a weather-proof sunnyboy
grid-tie inverter at the array, and supply 120/240 volts to the critical
loads sub-panel which is supplied by a Xanrex XW inverter and battery bank
in the garage. I realize there are several design issues here when the grid
is down,  since we want the grid-tie inverter to remain on but be blocked
from the grid by the Xantrex inverter.  

 

The question is, what is the best way to keep a load on the sunnyboy since
it will not be grid connected during an outage.  Also, is there a best way
to feed the output from the Sunnyboy to the Xantrex that does not just power
the sub-panel loads during an outage, but also will re-charge the battery
bank through the Xanrex?

 

If you back-feed the Xanrex from the sub-panel it is normally supplying with
output from the Sunnyboy, will the Xanrex see this input and think the grid
is up and be able to re-charge the battery bank?

 

Will we need any separate transfer switches or power relays?

 

Thanks,

 

Jeff Yago

 

 

 

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