HOW ELECTRICITY IS PRODUCED AT SMITH MOUNTAIN

Operation of the project makes maximum use of one of our natural resources - water  - through a process called pumped storage. Water stored in Smith Mountain Lake first drops through the turbine generators in the Smith Mountain Dam power-house to produce electricity. Instead of allowing all of the spent water to run away downstream, much is caught and held by Leesville Dam, the lower dam in the project, to be pumped back into Smith Mountain Lake later for re-use. A portion of the water goes through turbine-generators at Leesville, generating additional electricity.

SMITH MOUNTAIN PROJECT OPERATION 

Smith Mountain is a pumped storage project that utilizes an upper reservoir (Smith Mountain Lake) and a lower reservoir (Leesville Lake.)  The water that is stored in Smith Mountain Lake first passes through turbine-generators in the powerhouse to produce electricity and is then discharged into Leesville Lake.  Most of this water is retained in the Leesville Lake and is pumped back into the Smith Mountain Lake for re-use.  A portion of the water goes through the  turbine-generators at the Leesville powerhouse to generate additional electricity and to meet the minimum discharge requirements of the project's Federal Energy Regulatory Commission (FERC) license. 

The Smith Mountain development utilizes a two-foot power pool.  This means that when Smith Mountain generates power by passing water through the turbines, the Smith Mountain lake level can fluctuate up to two feet before the Leesville Lake becomes full.  In other words, a two-foot decrease in Smith Mountain results in Leesville Lake increasing thirteen (13) feet or from a minimum elevation of 600 feet to maximum elevation of 613 feet.   Once Leesville is full, power cannot be produced at Smith Mountain until some portion of the water is pumped back to Smith Mountain Lake. 

There is no set schedule for operating the project.  Generation generally takes place when the demand for electricity is high and water from the lower reservoir is pumped back into the upper reservoir when the demand for power is low.  The operation of the project can change on an hourly basis depending on system demand.      

The normal full pond elevation at Smith Mountain is 795 feet but the normal operating range under full pond conditions is considered to be between 793 feet and 795 feet because of the two-foot power pool.  Normal operating range for Leesville is between 600 feet and 613 feet.  Under low in-flow conditions, the pond elavation at Smith Mountain can fall below 793 feet.

 ADJUSTED ELEVATION 

Lake level information can be found on AEP’s website AEP.com under Environmental / Renewables and Energy Efficiency or by calling the automated system at 540-985-2767.  The Smith Mountain forebay level is the actual (current) level of the Smith Mountain Lake as measured at the dam.  The Smith Mountain adjusted elevation is the elevation Smith Mountain Lake would be if the water that is held in Leesville for reuse (between elevations 600 and 613) is pumped back into Smith Mountain. Under this scenario, when the adjusted elevation and the actual elevation are the same, the project is at its maximum power producing potential.   

The adjusted elevation is important to know because it places the current level of Smith Mountain Lake in relation to the two foot potential fluctuation.  If the lake level and the adjusted lake level are the same, then the lake may drop two feet during the day.  On the other hand, if there is a difference of two feet between the lake level and the adjusted lake level, then the lake level will not drop further because the lake is at the bottom of the two-foot power pool.  The Smith Mountain Project is normally considered full when the adjusted elevation is 795 feet.  The adjusted elevation may be more than 795 feet during periods of high inflow and less than 795 feet during periods of low inflow.