[RE-wrenches] Off-Grid to Grid-Connected -essential loads

[Phil Undercuffler]

Benn,

If the client prefers the independence and thought of remaining
primarily offgrid, has sufficient PV and battery for his loads, but
wants to use the grid as his "generator" then HBX can really be a
great solution.  I'll take exception to William's comments -- with the
FX you can set grid charging separately from HBX, no double conversion
required.  If the batteries get low because of bad weather or bad
in-laws, HBX simply transfers the loads over to the grid.  You can
program the system to recharge with either grid or renewables.  With
that PV array and battery ratio, it shouldn't take long to refill the
batteries purely from solar.

Grid-tie can also be a good solution as every electron the system can
generate goes to good use, either powering loads or spinning the meter
backwards.  In addition, the batteries don't cycle so should last
longer.  However, your client's 9kW of array is more than two GVFX
inverters can process.  In addition, talk with your inspector and
utility first.  They might require the entire system be brought up to
modern code standards before allowing interconnection.  Depending upon
how old the downstream wiring and components are, that might be easy,
might be hard.  In either case, if you have an X240 for OB Stacking it
will need to come out.

Anytime you have a battery based system and grid, you will need an
upstream panel and a downstream panel, even if you keep the entire
house on the PV system.  You already have the downstream covered, but
Dan's right about needing a service rated upstream panel, and you will
likely need to move the Neutral-ground bond to this panel as most
inspectors will require the bond to be at the first point of
disconnect and point of highest potential fault current.  Make sure
you float all the neutrals in the existing AC Flexware as part of the
retrofit.  If you go with the grid-tie, the upstream panel will need
to be larger than 100A to comply with 705, Dan was a little off on
that.  With a battery based inverter, you only need to calculate based
on the grid interactive component, but still a 100A loadcenter isn't
enough to allow more than ~4.8kW in selling.

Best wishes with the project, whichever direction you take.

Phil