Grid Tied with Batteries [RE-wrenches]

[Christopher Freitas --- OutBack Power]

Not sure of what happened to Travis' message - it was caught by my spam 
filter and none of the text showed up on the Topica site.  Here is his 
original posting:

Travis Creswell wrote:
 
> Hello Wrenches,

> I'm curious of the advantages of the Outback over the SW set up.  I 
> can see some clear advantages like not keeping the batteries float 
> charged with the grid.

> What about total system efficiency?  Outback publishes over 90% 
> efficiency but what is the total system efficiency?  Did I hear 
> something about a side by side comparison with batteryless system?

> As always, thanks in advance.

> Travis Creswell
> Ozark Energy Services
> Joplin, MO

A quick summary of the improvements available in the OutBack Grid-tie 
units:

1. Does not charge the battery 24 hours a day - it only runs the charger 
after an outage or if a DC load pulls down the battery voltage.  We 
allow the PV to do the battery charging.  

2. Sells the power from the PV array while holding the battery just 
above the rest voltage of the battery.  This reduces the amount of power 
lost to the batteries while selling.  With four Concorde AGM batteries 
(100AH @ 48VDC) I measured about 25 watts lost in them while selling - 
compared to about 50 watts twentyfour hours a day with a SW grid-tie 
system.

3. Includes MPPT (via the MX60 controller) wit it co-ordinated by the 
HUB through inverter-to-controller communication.  

4. Better efficiency by using only one inverter when the PV array is 
producing less than 500 watts or so.  

5. No GTI interface required with the OutBack - less parts / smaller 
footprint on the wall / quicker to install.  

6. OutBack's remote display uses CAT5 cable - can be 1000 feet away.   
SW is a 25 conductor printer cable with max distance of 50 feet.

7. Zero AC power drawn at night with the OutBack - versus - 50 to 100 
watts all night long with the SW series.  

I did testing side-by-side with a SMA Sunny Boy system in Northern 
California with two 2400 watt Kyocera PV arrays on the same roof.  The 
results were about 5% less in spring/summer/fall and about 10% less in 
the winter months.  Overall I would say it will probably 7% since more 
power is produced in the summer months.  Your results may vary due to 
temperatures and the impact of shading is different on the two systems.  


As far as efficiency - this is a complex issue and involves a lot of 
system specific questions.  Based on the side-by-side testing,  I would 
say around 7% less KWH produced (which is what matters in the end - 
right?).  

Christopher Freitas
OutBack Power Systems, Inc.
cfreitas @ outbackpower.com  
www.outbackpower.com
Arlington WA USA
Tel 360 435 6030  


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