Look at any schematic for current home power systems, and you will see, somewhere, an inverter. An inverter is a magic doo-dad that changes the 12v DC (direct current) that's stored in your batteries, into AC (alternating current, 110v if you're in Japan or North America and 220v almost anywhere else) that normal people use in their household appliances.
Me, I'm such a very, very special person and though I have a small inverter (above), I almost never, ever use it.
The reason for this is that every single piece of electricity powered equipment I have runs on direct current anyway. Converting the DC from the batteries into AC in an inverter which then feeds into a gadget that is going to convert it all into DC again is wasteful and makes no sense.
That inverter uses quite a bit of electricity on it's own, so much that it heats up and needs an electricity-hogging fan to cool it down. And it's noisy.
My modem, my wireless router, my charger for flashlight batteries, the iPod charger, the phone charger, they all run on 12v DC. And for the computer I have an adapter that converts the 12v DC into 18v DC.
The only things I don't power directly through the DC system are the chargers for my Ni-Mh battery packs for my headlight and for my camera batteries. So if I don't charge these at work, I need my little inverter. I'm sure these chargers can be hacked to work on DC, but I don't want to mess around with battery chargers.
Never, ever, ever tell people who work in shops that you need something for your "solar power system". Tell them you need a charger/adapter "for your car". Cars use 12v, and most of the assorted hardware you need to set up a home power system can be found in the aisles devoted to electrical components for cars.
Some lamps actually run on 12v too, especially those with LEDs or halogen bulbs, and have small components inside that revert the "normal" AC into 12v DC. I've messed around with some of those so they work on my system.
To be sure, converting it all into AC would make some sense if I had lots of power and a large house, say, and had electrical stuff all over the place. The wires need to be pretty thick if you're going to transport 12v over large distances. Much, much thicker than if you go for "normal" AC. And goodness, the cost of wires add up fast.
So here's another case of small being beautiful. Or at least easy.