The June issue of Popular Science features an article on energy technologies that they say will cut our oil consumption in half and reduce our dependence on fossil fuels to produce electricity almost entirely by 2025.
They forecast that ultralight parts and plug-in hybrids could reduce fossil fuel consumption by 19% and that use of biofuels could reduce fossil fuel consumption by 30%.
Electricity needs could be reduced by the following technologies and conservation.
Home Electricity Conservation - 36%
Wind - 20%
Biopower - 17% (biomass gasification and methane generation)
Distributed Generation - 10%
Solar Power - 10% (PV and thermal solar power)
Geothermal Power - 5%
Ocean Power - 2% (wave power and tidal power)
While I don't think that I would have come up with the same numbers, the numbers give some idea of what mix of technologies could be used to reduce our dependence on fossil fuels. My two concerns are that, while that degree of conservation proposed is possible, electricity costs would have to be extremely high before sufficient motivation for this degree of conservation would be possible. After reducing consumption as much as forecast by conservation the percentage of electricity produced by wind, solar, and ocean power is higher than could easily be integrated into a grid, without massive energy storage or a much stronger grid, because of the intermittency of these generation methods. Economical energy storage on a large scale is unlikely by 2025. Geographical separation of these methods in an area as large as the U.S. reduces the effects of intermittency, but a much stronger grid is required to transport the energy from one area to another which would mean a very costly investment in the electrical infrastructure. The area between the great plains and the east coast is not especially suitable for these methods and the grid would have to be reinforced significantly in this area. Superconducting power transmission would be especially useful, but development of economical systems is progressing rather slowly, although some usage could be expected by 2025.
I would hope that plug-in vehicles would be in wider use by this time, but that is very dependent on the acceptance of the technology by manufacturers. Their forecast for use of biofuels, although possible someday, is very unlikely by 2025.
The articles (without statistics) can be viewed at http://www.popsci.com/popsci/energy/