Battery vs no Battery grid tie systems - efficiency [RE-wrenches]

[Warren Lauzon]

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Well, from the comments so far, it appears that for battery backup grid tie 
systems, the Outback is really the only way to go at this point if you have 
a large battery system. I am surprised at how little they reduce 
efficiency - but most people can probably live with the 5-10% loss if they 
are set on backup power, whereas the SW types we always tried to talk people 
out of, because they were so inneficient for grid tie.


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----- Original Message ----- 
From: "Doug Pratt" <dmpratt at sbcglobal.net>
To: <RE-wrenches at topica.com>
Sent: Monday, April 18, 2005 9:34 PM
Subject: RE: Battery vs no Battery grid tie systems - efficiency 
[RE-wrenches]


If you tell customers that a battery-based system is going to cost them
about 5% (watts into the grid), that's fairly honest. That's also assuming
you're running an FX or a Sunny Island with sealed batteries and carefully
adjusted charging settings.

The old SW units can easily eat 30% or more of your PV power. The default
factory battery charger settings are *very* aggressive, and will waste a
huge amount of power as heat. You must set them down to a gentle float
voltage, about 2.25v per cell is usually comfortable. (And then add the SW
Memory Kit from Right Hand Engineering for about $100 so the #*&% thing
won't forget all the setting every time someone does battery maintenance!)

Cheers,
Doug Pratt

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