My motivation for delving into solar power was also to have backup during a grid failure. I suffered through a multi-day outage after an ice storm and decided not to go there again!
While looking at options and possibilities, I chose not to mess with grid-tie because I didn't want to mess with inspections and the utility company. Also, at the time, they required a "small monthly fee" to be allowed to backfeed and that would have completely obliterated any savings benefit of grid-tie. Not to mention they didn't PAY me for the production, they simply deducted kWh per kWh down to zero - couldn't eliminate the bill!
My system has 2kW in panels on the roof, a full Outback setup (FM80 CC, VFX3648 inverter, FNDC battery monitor, Mate interface), 48V 220AH battery bank (8 Trojan T105 golf cart batteries), a breaker subpanel for my backed-up circuits, and all the associated wiring and hardware. Total cost (excluding labor which was all my own) is less than $10k, closer to $8k IIRC, although spread over several years start to finish.
I had originally had the idea to simply make a completely isolated "backup system" that might run a few things full-time but otherwise I'd move plugs from the regular "grid" outlets to my "backup" outlets I would install in strategic locations around the house. I never got around to putting in those outlets - ran two "temporary" lines (one running down the hallway to the back of the house!) and two years later...!
This year I finally got off my duff and finished up. The breaker panel is mounted beside the grid panel, I disconnected the "critical loads" from grid and attached them to the sub panel. Now I can run most of the house from inverter, and in an outage the switchover is completely seamless - the lights don't even flicker!
In my experience batteries don't really like being floated long-term, it's best to use them - also, if you don't use them you won't know if they're getting weak until it's too late! So my system switches off-grid daily. I switch to inverter at 5AM, which draws the batteries down to 85-90% SOC just to give the charge controller a *little* something to do. By noon to 1PM the system is floating and at sundown I switch the loads back to grid. Can't go 24x7, as the battery bank isn't large enough - would discharge too deeply each overnight. During an actual outage I'd shut down some stuff that is normally left running, which would extend runtime considerably.
Certain loads I figure I'll only (or primarily) run on the generator during an outage. I *can* run the furnace on the inverter, but at 800-900W full-tilt the battery bank isn't going to sustain that very long. I figure I'd only do that in a pinch - say, the house is 40 degrees and the ice storm is still raging!
If it's daylight with good sun, not so much of a problem, I could run straight off the panels.
On south and west-facing panels, I wouldn't worry too much about it. If you go with a battery based system you are likely going to have several strings anyway to keep the voltages down where the charge controller is happy. I have four parallel strings of panels - and only one faces south. They are all paralleled together and feed one MPPT charge controller. It works just fine, power production is what I expected to see. The only "problem" with west-facing panels is lower production in winter, but then again they produce *more* in summer (at least at my latitude).
