You really cannot comment on final cost until after the development and implementation of the system. Initial cost are always high.
I can say with a high degree of confidence that within the next many years, solar cells are not going to be a cheaper way of shingling a roof than asphalt shingles (without subsidies of one and/or tax penalties on the other). It's ridiculous that he'd even suggest that. If that were the case, I'd just use the solar cells to shingle my roof, without worrying about plugging them into anything. If they're just as waterproof as asphalt shingles, and cheaper to buy and install, I don't even need the solar power household infrastructure, since they're just a superior roofing product, right?