Black and Veatch have put out a report forecasting the U.S. energy mix in 2035 (specifically, electricity generation). Here's the chart they produce, if you believe their assumptions and modeling:
So, they think we'll increase renewable energy production rather substantially, but the big story is about our future energy use is the substitution of natural gas for coal. On the plus side, natural gas burns far cleaner than conventional coal; on the negative side, much of the new natural gas sources will be pumped out of the ground via the controversial method of fracking. When it comes to energy, there's no such thing as a free lunch, it seems.
Via Grist, where you can get more commentary on the report.