Do you think that PVWatts data I'm using is off, or are you suggesting that if I built half the system that my array wouldn't meet all the needs? With the 30KW system we've got planned, we're showing 30KWh a day (national average usage) in December with the weather. We've sized the array for the worst case scenario of winter sunlight. Using the full array, and if our data is correct, I think our structure will easily work on much less than the national average usage of electricity (and I think Wk's usage is much higher than the national average) because we're going to build our home with energy efficiency in mind (R value of 60) and the climate in Seattle is temperate so it won't be difficult to get away without air conditioning and minimal heating. Of course that number is just an average so there will be days with less or perhaps no energy production from the array. Maybe even weeks. In that case, we're thinking about using a propane generator to make up for what the battery bank can't supply. But our energy needs should be pretty modest.
The grid seems like more trouble than its worth and I share Wk's view that in the future it will be less worth it.
But of course I could be on a fool's errand. I'm far from technically savvy.
I don't know your particular situation (panel facing, shade, etc..), or anything else that might be specific to your situation rather than national average. However, I do have a 10 kw system and am located in the Portland area. The challenge with solar and going off-grid in the Pacific Northwest is the big swing between the peaks in the summer, and the troughs in the winter. To go off-grid, you need to handle those troughs.
Using single days, we had a couple of days last summer that cleared 70 kwh for the day. On the worst days in the winter though, we won't get 5 kwh (this year, Dec 1 - 18, we produced 3-6 kwh a day, or about 90 kwh over 18 days: how would that work out at your house, with your consumption, even with 3x the panels?).
At a monthly scale, our best month last year was June at 1626 kwh. Our worst was December for 180 and January for 250. If you triple those numbers, then December is 540 for you, and January would be 750 kwh. At the very least, be sure you have heat that doesn't need electricity to generate or distribute it
I expect that being further north, your swings will be slightly stronger than ours (bigger summers, lower winters). But you're not that much further north.
Or more simply, to go off-grid and be reliant on your own power production, the averages are only a starting point. You need to be able to handle your individual days, and the stretch of cloudy days you get at your location. Also - summer time and A/C won't be a problem. Your problem with a 30 kw system is you'll be wasting power over the summer. Crank up the AC - turn your house into a refrigerator - you'll have the power for that
One idea for getting started - get some kind of a system installed and run it for a couple of years - see what the power production is like in December and January, and see if you can get through it comfortably. All you need is one winter with no sun for a month, and things are going to be dicey.