The Energy Information Agency (EIA) provides information about how each U.S. state and the District of Columbia produces its power.
Power in Maryland is mainly produced by nuclear, natural gas and coal facilities. These day, more and more renewable energy is coming onto the grid, soon making a significant power production from renewable sources.
Virginia is primarily coal and nuclear powered. The renewable energy is primarily from hydroelectric facilities.
Washington D.C. doesn’t have “classic” conventional power plants and imports all its power from Maryland’s Pepco, but all its own energy production comes from renewables, mainly distributed solar power.