Perhaps smaller generators, such as gas fuel cells like the "Bloom Box" will find their way into substations, to supplement what is already available in the neighborhood. That could take over for the solar/wind/etc. when it's not sunny or windy.
I'm not saying that centralized power plants should or will go away soon, but there are smaller-scale technologies that people will want to cash in on. There will always be a need for base-load generating, and I'm sure there are plenty of smart people who can figure out demand models for traditional generating stations and contingencies for when the weather doesn't pan out. It's not a change that is going to happen overnight. These small-scale things are probably not going to do serious damage to big power any time soon. It may be that, as time goes on and better technologies become available, the supplemental power is used to phase out dirtier tech like coal.
Ironically, the solar highway project I posted about a while ago had its first day of grid-tied generation when all of the panels were covered in snow. They even produce some power (around 500W) at night, although nowhere near the designed capacity of 104kW.
