[RE-wrenches] Any thoughts on this approach to adding battery backup to an existing grid tie system will be appreciated.

[Ray]

I didn't watch the whole thing, but it looked like a standard AC couple 
set up with an Outback Radian.  My understanding is that Outback no 
longer supports AC Coupling, BTW.  I would never use that for an off 
grid system or  for longer outages.  In a very brief explanation,  it 
essentially bypasses any charge controlling to the batteries, and puts 
full Array power into the batteries until a relay (or phase shifting) 
disconnects the array.  No three stage charging, no taper charging, no 
float, no temp compensation.  Its like trying to fill a 5 gal bucket 
with a fire house, or drive a car with a throttle that's either off or 
at full throttle, no in between.  The other issue is that if the 
batteries get low and the inverter shuts off, the system will not 
recharge, and after a couple of weeks the batteries will be sulfated 
beyond recovery.

My guess is that manus that advocated this approach got into trouble 
from end users that fried expensive battery banks during longer 
outages.  I would consider it the equivalent of cheap backup generators: 
a great backup system for folks that don't need it.   There are probably 
thousands of those out there with happy customers and installers, 
because its never actually been used for more than a few hours, and the 
batteries are properly charged from the grid 99.8% of the time.

Ray Walters
Remote Solar
303 505-8760

On 9/12/18 6:11 PM, Ken Schaal wrote:
> https://www.youtube.com/watch?v=eyhkIfS5Z-Q
>
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