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
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
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.
AEP’s Smith Mountain
AEP operates 17
hydroelectric and pumped
storage projects in five
states. These projects
850 MW of generation. In
2014, Appalachian Power
received new licenses
from the Federal Energy
(FERC) for its London,
Marmet and Winfield
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.