Electricity systems must always be able to supply energy needed during periods of “peak” demand, which is higher in the summer and winter than in the spring and fall. To be absolutely sure there will be enough electricity for those periods, systems need to have enough generation resources to meet these expected peaks in demand plus a capacity reserve margin of at least 15 percent.

By 2010, without the addition of new generating capacity, the Pepco zone may not be able to meet its reserve requirements.

The Role of PJM

The PJM Interconnection — the regional transmission organization (RTO) serving the Washington, D.C., area — coordinates the movement of wholesale electricity in all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and the District of Columbia. PJM dispatches approximately 164,634 megawatts of generating capacity over 56,070 miles of transmission lines to roughly 51 million homes and businesses.

Using sophisticated modeling, PJM evaluates energy demand and then schedules generation resources, which includes includes external imports (power generated outside PJM's geographic boundaries) and exports to optimize the production of electricity throughout the PJM transmission grid. PJM schedules generation under a set of economic and reliability driven requirements. These requirements include not only the production of energy but the deliverability of that energy to the customer load.

Powering Central D.C.

The U.S. Department of Energy and the District of Columbia Public Service Commission have determined that Potomac River Generating Station is critical to maintaining a reliable power supply for the central business district of Washington, D.C.

There are only three ways to get energy into Central D.C.: Potomac River Generating Station, and two 230,000-volt transmission lines that deliver electricity from other generating sources in the regional electric grid operated by PJM. Those 230-kilovolt (kV) lines are key. If either or both of those 230-kV lines are out of service, there will not be enough electricity going into Central D.C. to sufficiently power much of the city, including the Blue Plains Sewage Treatment Plant.

While there are two generating stations located within the District of Columbia (Benning Road and Buzzard Point), these facilities do not have the ability to serve Central D.C. load under all operating conditions of the transmission system.