U.S. Renewable Power Generation (GWH)
Source: U.S. Energy Information Administration

The issue
Water is the leading renewable energy source used by electric utilities to produce power. The Hydro Research Association reports that water produces almost 20% of the world’s electricity. In 2009, hydroelectric generating facilities produced approximately 65.5% of the energy generated in the U.S. from renewable sources, according to the U.S. Energy Information Administration (EIA). Also in 2009, the EIA reported that hydroelectric facilities, excluding pumped storage facilities, account for 7.6% of the total U.S. summer capacity and 61.9% of renewable summer capacity.

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 plants are the 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 plants utilize 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 plants make use of an upper and lower reservoir and provide 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.

U.S. Renewable Power Capacity
Source: U.S. Energy Information Administration

Key issues
There are two primary issues affecting hydropower. The first is the availability of water. During periods of drought, hydropower can not 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.

Hydropower at AEP
The AEP generating fleet includes 870 megawatts of hydroelectric capacity. The majority of this capacity is comprised of the 586-MW Smith Mountain Pumped Storage Facility, owned by Appalachian Power Company. The remaining 284 megawatts of hydroelectric capacity is split among plants owned by Appalachian, Ohio Power Company and Indiana Michigan Power Company.

Hydropower (PDF)

• U.S. DOE Energy Efficiency & Renewable Energy - Water Power
• U.S. DOE Idaho National Laboratory - Hydropower
• The Hydro Research Foundation
• The National Hydropower Association