Is it possible (or is it a good idea) to distribute 12V DC over cabling that's been prepared for 220V AC. I'm worried that the voltage drop will be much to high with 12V DC. I'm asking cause the house already has 220V cabling with sockets and light switches, and using 12V DC would either require me to re-cable or use the existing infrastructure. I just don't know if it's possible.I still will need the arduino to switch the power source from the generator to the batteries, the all-in-one solutions that do that are too expensive. I found some products that do just that, but they are ATMel based switches that cost a lot, i can easily do that with Arduino i think.
You WILL have to re-wire for 12V.