Adding battery backup to existing grid-tie PV system [RE-wrenches]

[Jeff Irish]

Why did you chose to do this rather than use a Sunny Island?  We're pretty
happy with the Sunny Island performance and it can talk to the SB inverters
as a central controller.  Just curious.

Jeff
HVCE

> -----Original Message-----
> From: William Korthof [mailto:wkorthof at earthlink.net]
> Sent: Friday, May 19, 2006 2:59 AM
> To: RE-wrenches at topica.com
> Subject: Adding battery backup to existing grid-tie PV system [RE-
> wrenches]
> 
> 
> We have a customer from a several years back who bought a larger system
> (~7kW AC system) which used 3 SMA 2500 and 1 SMA 1800 inverters... they
> always wanted battery backup, but given their high end, low maintenance
> lifestyle, I wasnot eager to throw a pile of batteries, miles of heavy
> 48 volt wiring, and dual SW inverters at this application. But when they
> called a couple months ago discussing their extended and unseemly LADWP
> power outage frequency, and apparent willingness to let go of the
> whirlpool, sauna, wine chiller, outdoor light show, and multi-level HVAC
> refrigeration system (at least during power outages), I took note.
> 
> Rather than dig in and rewire the PV array (or alternately), install a
> backup power system that didn't use the PV system... we came up with an
> interesting compromise:
> install (1) new Outback GVFX inverter with (4) 8D deep cycle batteries,
> this inverter is directly grid-tied, like the existing SMA inverters.
> On the (backed-up) load side of the inverter, we conneced the frige, a
> few lights, computers, and a couple other important items. In addition,
> we reconnected the (1) SMA 1800 inverter onto the load side of the
> outback. When the outback is online (whether grid-tied or standalone)
> the SMA inverter feeds in power to offset emergency loads (and even
> charge the batteries if the power draw is lower than solar output).
> 
> This approach requires redundant inverter capacity (extra cost), but
> allows the PV array to be wired at high voltage, enabling a larger array
> and longer electrical feeder distances if needed.
> 
> I'm thinking that this is a reasonable compromise solution (cost, labor,
> performance...) for us to use as a retrofit/upgrade on older systems, as
> well as a decent way for us to furnish battery backup power with systems
> that wouldn't otherwise be compatible (Sunpower).
> 
> I'm sure others have already done this... were you satisfied with the
> results? Any issues of note?
> 
> 
> /wk
> 
> 
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