A few years ago I looked into a solar system for my house, not to go off the grid, but only to reduce my overall energy costs. What I found out is that the system I put together would pay for itself in about 20 years. However, that does not take into consideration what power you might be able to sell back to the electric company, or any tax breaks you may have available to you. Also, from what I've read, the life expectancy of a solar system is about 20 years. In my case, my local power company does not participate in the buyback program.....and, my electric meter is an electronic unit that doesn't run backwards if you are producing more power than you're using.
Just like with hybrid cars and other "green" energy choices, I don't think they are economically feasible with the current technology.