The UPS approach is novel, and intriguing.
When I think about what is inside a UPS, I realize that the net effect is that there
will still be an inverter (built into the UPS) and there will be
two batteries - one dedicated to 12VDC use, and one to feed the inverter for 120VAC stuff. The result is that while off of shore power, either one of the two batteries could run low, leading to the frustration of having juice... but just in the wrong box.
If you add a
solar panel, which
battery would it charge?
The
advantages of the UPS are that recharging (of
one battery...) is automatic and switchover between shore power and battery/inverter mode is seamless
, while to do this with a separate inverter and common
battery means an autotransfer switch, some wiring, and some form of automatic charger setup.