Nobody has answered the flywheel question yet (I’m sorry if somebody did and I missed it), but I would also like more information about this. It seems like a flywheel combined with an electric motor powered off solar would be very efficient, no?
The big question would be what are your power needs? What do you plan on running?
If you only intend to use a power shaver in the morning and a small light at night, your first idea with UPS’ just might work. A 50" plazma display and a couple tanning beds - you might want to scale up.
A friend of mine bought some property in the middle of nowhere, fully off the grid, to use as a weekend retreat. He built a small cabin and heated it with a small wood stove. For power (mostly lighting) he went to a marine store and wired the cabin like a boat - all 12v. He’d take a small generator up friday night and charge a handful of deep cycle batteries. They’d last the weekend.
In fact, most of the things on his property were based on marine technology. He’d catch run-off from his roof into large 55+ gallon drums. One drum connected to a handpump marine head in the outhouse. The output went to a deep sewage drain field he created. I don’t think it would handle a the Brady Bunch full time, but for a handful of people every other month (and him alone on most weekends) it worked nicely.
His homemade galvanized horse trough hot tub ran on propane. 
I guess the other question for the OP is how long are you intending to be off the grid? If it is a year or two then I can see smaller investments - more jerry-rigged solutions. If this is a long term thing, then I think you’d be looking at larger solutions.
Assume a permanent situation with three people and normal household needs. I know normal can mean a lot of things, in our case regular appliances plus a few bigscreen tv’s, computers, etc. I’m willing to shell out the big bucks at the beginning to do it right. That’s why I’m interested in a flywheel system. It sounds like it is (or will be) the storage system of the future.