Re: Using an Inverter/Battery system as whole-house backup solution
Welcome to the forum.
You're going to have to define what you mean by "whole house back-up". This is because the average household is equipped with a 240 VAC 200 Amp service these days. That's 48kW of power potential. Obviously one 6kW inverter can't produce that.
What Xantrex is talking about is the standard install for a grid-tie/back-up inverter: you select certain critical loads and connect them to a sub-panel which is fed from the main panel via the inverter. In the case of the XW, this allows it to back-feed the grid through the main while also being able to power those critical loads when the grid goes down.
For back-up purposes only (no grid-tie) any good off-grid inverter-charger will work. The wiring direction is the same:
Main Panel ---> Inverter ---> Critical Loads
During normal operation the inverter does nothing but keep its batteries charged from the utility power which is also 'passed through' to run the critical loads. When the grid goes down the inverter automatically switches over to power the loads.
So the first step is to determine the size of the loads you must keep running during an outage and how long you expect that outage to be. That will determine what size inverter to have (including whether you need 240 VAC or just 120 VAC) and how big the battery bank has to be. Pretty much the same as picking a generator in that respect, except that you can easily refuel a generator. Recharging the batteries (as from solar) is another issue. For instance you want to recharge from a small gen: that means either using the inverter-charger in 'charge' mode (meaning disconnect from the main panel via transfer switch so that other circuits aren't energized) and having a generator large enough to charge the batteries and provide power to the loads in use. Recharging from solar panels is another matter, and involves further expense and installation.
With me so far?
Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.
Ohm's Law: Amps = Volts / Ohms
Power Formula: Watts = Volts * Amps