[RE-wrenches] Convert Grid Tie SW4048 to Backup System; Add New Inverter, AC Coupled

[Richard L Ratico]

Hi Wrenches,

This is a repost. No replies the first time, so I'm trying one last time.

I may be "adopting" an eleven year old, Y2K, grid tie with battery back-up
system. It consists of 12 - Astro-Power 120 modules, installed in 2000, 12 -
Evergreen  EC-110 modules installed in 2004, only one MX60, which controls BOTH
sub-arrays, one SW4048 in SELL mode through a dedicated load sub-panel.
Existing, seven year old battery is shot (8-Trojan L-16). Initial bank of
unknown batteries was replaced after only four years.

Recent long, nearby, utility outages have the client requesting a proposal to
include a new back-up generator and to restore the system selling to the grid.
Client may decide go straight grid tie to eliminate the batteries. They have
found the maintenance to be a hassle.

My thoughts so far: 

1)To take advantage of most of the existing hardware, I wonder if it makes sense
to try to improve the system efficiency by relegating the SW to a manual back-up
mode only, where, say, by means of a timer controlling grid availability through
AC1, it would only charge a smaller battery bank once a week. The battery bank
would be small,
a single string of either, sealed gel units or T-105s with the new Trojan
watering system. 
2) Provide new grid-tie inverter/s (appropriate string type or Enphase 190s) to
handle the net metering. 
3) Provide a way to AC couple the new inverter/s to the SW in the event of an
outage.
4) Provide a new Honda 3000 inverter type generator connected to AC2 in the SW.
5)Provide a way to lockout the grid tie inverter/s when the generator is
operating.

Any thoughts or suggestions would be greatly appreciated.

Thanks in advance, 

Dick Ratico
Solarwind Electric
Bradford, VT