The main source of U.S. electricity is still coal though U.S. government wants to see more electricity coming from renewable energy sources such as wind and solar.
According to latest study by the National Renewable Energy Laboratory (NREL) renewable energy sources can account to 80% of total U.S. electricity generation by 2050. This doesn't necessarily require huge improvements in technology as NREL believes that the technology needed for this transition to renewables is already available today.
This report mentions that the current electric system needs to show more flexibility in terms of adequate storage solutions as well as providing more transmission lines.
U.S. has abundance of different renewable energy resources (solar, wind, geothermal, hydro) at its disposal which should result in highly diversified energy portfolio and improve nation's energy independence and energy security.
More renewable electricity would also reduce the amount of greenhouse gas emissions leading to major benefits in global fight against climate change because U.S. is second largest greenhouse gas emitter, behind China.
This report has concluded that there are no long-term constraints to renewable electricity technology manufacturing capacity, materials supply, or labor availability. The study also agrees that renewable energy industry needs to lower the costs and improve the efficiency of renewable energy technologies in order to make them more cost-competitive with fossil fuels.