While we make the transition, people will still have to be getting most of their electricity from coal, natural gas, and nuclear. You can't turn that stuff off one day and the next day turn on renewables. To pretend otherwise is ridiculous. So the real question is how much extra will we need to pay to make the transition.
As for your friend, what does he do for electricity during the night and cloudy days? My guess is that he still is hooked up to the public utility. It's possible that your friend might even become a net electricity provider, but that's only part of the problem because he still can't provide for his needs at night or during storms. For our society as a whole to go to renewables, we have to crack the storage and variability problems. To get to 80% renewables, nobody has any idea of how to do that, or at what cost.
Right now, our current infrastructure can handle about 20% renewables without major concerns about storage or the variability. See, for example, page 447 of
http://www.nerc.com/files/2011%20LTRA_Final.pdf . Beyond that we face major hurdles that could significantly affect our grid's ability to provide us reliable power. What's interesting is that California and Colorado have renewable mandates which require them to get above 30% renewables by 2020 or so. These are state laws with numbers pulled out of hat; we shall soon see if they reflect reality.
If you don't look at the whole system, you're missing the problem.
