[RE-wrenches] Adding Battery to Grid Tie

[Zeke Yewdall]

There's two main ways to do it.  Either keep it as is and AC couple it into
the new battery system, or commandeer the DC from the PV array and feed
into a new battery system.

While AC coupling is common for a lot of the options -- Franklin, Tesla,
many others, and just about all of the AIOs, I don't like it much if I can
avoid it. Usually less control options if you get into limited or zero sell
back situations instead of net metering, compared to a DC coupled solution,
and difficulty with black start.  If you already have embedded
microinverters on the roof, it's probably the best option though.   I think
the SolArk can choose either AC coupled PV array or generator input, but
not both.  Midnite can do both, and not sure about EG4.

Most of the AIO's can take a 600 volt string inverter array into their DC
inputs, and just get rid of the old string inverter.  Just make sure the
old array doesn't have existing ground faults -- many old inverters were
pretty blind to ground faults on the negative leg especially, and the AIO's
running a floating array will not be happy with multiple faults in old
arrays.

There are also a bunch of battery capable string inverters from Fronius,
SMA out now... typically pretty poor surge and imbalance performance from
them, so if you are doing backup for well pumps or septic pumps, it's
something to consider.

Zeke

-- 
Zeke Yewdall
PV Engineer
NABCEP #031508-89
zeke at darkforestsolar.com
303-523-3592
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