Lots of excellent comments above.

I have a couple of PV-solar/battery/inverter setups, one for my bare-bones office upstairs and one for a cabin on my property.

Some random observations:

- I find 45-60W of generation and a 60Ahr battery the minimum practical configuration for daily use. You can get by on a lot less for lighting only (esp. LEDs!) but if you want to power tiny fans or laptops, don't go small.

- You can scrounge efficient 12VDC mini-fans from the power supplies of old desktop PCs. Wire two in series and connect to a battery; they move just enough air to be useful.

- It's much cheaper, per watt, to buy discrete components these days (inverters and deep-cycle batteries) than to get all-in-one units like Xantrex (though I have had good luck with their products).

- Gel-cell batteries can be stored/used inside safely, because they don't normally vent. But be cautious in freezing climates: you can't charge a gel-cell when it's frozen.

- It's cheaper to spend money on super-efficient appliances than to add extra generation capacity (for photovoltaic setups anyway).

- Wal-Mart in Canada has just started stocking inexpensive LED bulbs, both 120VAC and 12VDC. I bought a number of them, and based on a couple weeks' use, I'm quite impressed. My office/computer desk now consumes 2W for lighting, and if I need to I can power these off-grid indefinitely. The brand is "Lights of America" (no affiliation). [EDIT: prices in CAD: 8.50 for 1 and 1.5 watt bulbs, 10.00 for 2 watt, 14.50 for 3.5 watt, 30.00 for 3 x 2 watt linkable pucks and 5 watt singles.]

- If you have a photovoltaic/battery setup, you're flying blind without a multimeter (and taking chances without a charge controller). I do like benjammin's idea of a headlight in series as a field expedient charge indicator; though I don't think it would work with PV panels.

Good luck!
Doug