Each of Rocky Mountain Institute’s four scenarios for the future U.S. electricity system (detailed here) will have a very different electricity generation mix. Increasing efficiency in each case reduces the overall energy consumption, though this is partially offset by the increased adoption of electric vehicles.
Maintain represents “business-as-usual,” with little smart grid deployment, bulk energy storage, or demand response capability. Most U.S. electricity demand is met with increased generation from natural gas and coal-fired power plants. The 2050 system requires 1,470 GW of nameplate capacity—45% fueled by natural gas and 22% by coal. The gas-fired plants are used more for peaking than the coal, reversing their contributions to annual electricity generation (27% gas and 43% coal).
The Migrate case transitions to a grid relying heavily on nuclear power (18% of capacity, 36% of generation) and gasified coal (IGCC) equipped with carbon capture and sequestration (17% of capacity, 30% of generation). Carbon dioxide emissions are significantly reduced, but the system also faces many cost, financial, and technology risks.
In Renew, increased energy efficiency flattens demand growth, and 81% of U.S. electricity comes from utility-scale renewables.
Finally, the Transform case is a radical shift in grid design and operation. Mostly distributed renewables supply 90% of grid electricity, with all remaining generation coming from natural gas combined-cycle plants.