Non fossil fuel energy will require more smaller production sites to replace an equal amount of energy.  This means lots of capital investment.  To replace a large percentage of oil/NG/coal it will have to be a mix of alternative energies spread all over the country, rather than a relatively few refining sites.  Lots of small integrated wind, solar, hydro coordinated into the grid with some going to transportation.  This will require a huge building boom.  In a climate of cheap oil there is not going to be enough return on investment (compared to other uses of the money) for capital to flow to those projects in any meaningful way.  They will be proof of concept, or additional, rather than replacement of fossil fuels.

Without some incentive I don't see the market shifting away from fossil, even after peak oil.  There will still be more ROI bringing small oil fields online.  This will be true even as supply continues to drop.  No one has been able to beat the energy density of fossil fuels with any alternative source.