[RE-wrenches] 120 Vac and 12Vdc mixed distribution system

[Jason Szumlanski]

I have an off-grid client who is working on replacing old equipment at a
cabin. He has a lot of 12 volt distribution in the house for lighting,
fans, and a 12 volt refrigerator. He also has 120 volt AC loads that run
through a separate distribution panel where the only source is a 2000 Watt
Honda generator. There is no inverter present. The batteries are charged
through a Trace C40.

He currently has a few ancient solar panels and a struggling Bank of AGM
batteries. It's time for an upgrade. I can easily supply enough PV power
for what he needs. He currently has a 9 kilowatt hour battery capacity that
he was happy with when the batteries operated optimally. Nonetheless, I
would probably future-proof him with a 10 to 15 kilowatt hour LiPo to
double or triple his usable capacity.

For convenience, obviously it would be nice to have an inverter to
eliminate or reduce the generator requirement. But he seems committed to
keeping his 12 volt distribution because it would be costly to replace
fixtures. I think he would consider replacing the 12 volt refrigerator if
he has an inverter.

He definitely wants LiPo batteries.

I don't like the idea of 12 volt direct from a battery plus connecting an
inverter to that same battery. It is going to be hard to measure and
monitor things.

I am thinking about using a 48 volt battery with a single phase 120 volt
inverter, getting him to change to a 120 volt refrigerator, and using a DC
converter to give him somewhere in the range of 100 amps at 12 volts for
his existing DC lighting and fan loads. Is this a bad idea? Should I stick
with a 12 volt battery system? He does have a tiny 12 volt pressure pump
which might be an issue for the converter. I'm not sure. I am a bit worried
about the efficiency loss and capacity of DC converters and not sure how to
size it.

Jason Szumlanski
Florida Solar Design Group
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