That way I think about off grid solar is that you are purchasing the power all at once in advance. That part might cost more today that what you can get on the grid but eventually it will pay off especially if the grid power prices go up. Another consideration is the sovereignty. When the grid power goes down it's very likely I'll still have power from my solar power system. Not to mention once you interact with a solar power system you start to value the electricity much more and will likely be more efficient in the way you use it. 

I use copper wire. I don't know about aluminum one way or another.