That's not a good idea. Solar panels wear out, and you probably won't know how worn out they are until you buy them and install them. Which is a little bit too late for most refunds. Your best bet if you're dead set on being foolish, is probably some place like craigslist.
IF used panels are available, they are probably worn out and NOT putting out the power they were designed for. (They DO wear out!) I do NOT know of any place they are sold.
