Today’s electric system is almost unrecognizable from the electric system a decade ago. Generation from natural gas and renewables has accelerated to replace the rapid and unprecedented retirement of coal-fired generators. Wind, solar, and geothermal electric generating capacity in the United States has now eclipsed capacities from hydroelectric and nuclear resources combined. Carbon dioxide (CO2) emissions have reached their lowest levels since 1987. Meanwhile, both total generation and electric sales have held relatively steady for 10 years.