Hydropower is the leading renewable energy source used by electric utilities to produce power. It is a very reliable energy source and is used in all regions of the country. In 2014, hydroelectric generating facilities produced approximately 48 percent of the energy generated in the U.S. from renewable sources, and six percent of total electricity generation.

There are two primary issues affecting hydropower. The first is the availability of water. During periods of drought, hydropower cannot produce as much electricity as during periods of average or above average rainfall.

The second major issue is the lack of sites to develop high-capacity hydroelectric plants. The remaining undeveloped sites that can be used for hydroelectric power are only capable of generating a few megawatt-hours on average.

Top Hydropower Producing States, 2014

Smith Mountian
Source: U.S. Energy Information Administration, Electric Power Monthly, Table 1.13.B (February 2015)

Types of hydropower plants

Hydropower plants are generally subdivided into three types: impoundment, run-of-river and pumped storage. The type of plant is determined by how the water is gathered and funneled to the turbine through a penstock or canal.

Impoundment: Most common in the U.S. These plants use a large dam to hold back water in a reservoir and then route it through a penstock to the turbine to generate electricity. Impoundment plants are generally larger than the other types of hydroelectric plants and offer the added benefit of being able to control the amount of water that flows through the penstock, enabling responsiveness to electricity needs. The dam also controls water levels to provide flood control, irrigation and/or recreation.

Run-of-river: Utilizes the flow of water within the natural range of the river and require little to no impoundment. Diversion plants are a subset of run-of-river plants that divert the flowing water through a canal into the turbine. While these plants lack the control provided by impoundment plants, they have a much smaller impact on the water flow.

Pumped storage: Uses an upper and lower reservoir and provides the means to transfer water between the two. Water is released from the upper reservoir, through the turbine and into the lower reservoir when electricity is needed. When demand is low, the plant uses electricity from the grid to pump the water back up to the upper reservoir. In general, these plants are net users of electricity but act as an energy storage device, delivering a valuable source of peak power.

AEP’s Smith Mountain Hydro Project on the Roanoke River southeast of Roanoke, Virginia, was the nation's first major development that combined run-of-the-river hydro with pumped storage generation. Water held in the lower reservoir (Leesville) is pumped back into the upper reservoir (Smith Mountain) during off-peak hours, for use in generating electricity during times of peak demand. The Smith Mountain and Leesville facilities have a combined generation capacity of more than 600 MW.

Smith Mountian
AEP’s Smith Mountain

Hydropower at AEP

AEP operates 17 hydroelectric and pumped storage projects in five states. These projects produce approximately 850 MW of generation. In 2014, Appalachian Power Company (APCo) received new licenses from the Federal Energy Regulatory Commission (FERC) for its London, Marmet and Winfield hydroelectric facilities located on the Kanawha River in West Virginia. The new licenses extend the operations of these facilities by APCo through January 31, 2064. These facilities have a total capacity of 43.6 MW.