Skip Navigation LinksDEP > Citizens > Saving Energy > Renewables > Hydroelectric

Hydroelectric Power

According to the PA Public Utility Commission's 2015 Annual Report on Alternative Energy Portfolio Standards Act of 2004, there are approximately 175.8 MWs of low-impact hydroelectric, 677.8 MWs of conventional non-low impact hydro and 1,540 pumped storage hydro capacity in Pennsylvania. The U.S. Department of Energy reports that hydroelectric power is the largest source of renewable electricity in the United States, producing about 6.3% of the nation's total electricity throughout the last decade.

Hydropower is a clean energy resource, can generate power quickly for emergency back-up, provide flood control, irrigation and water supply.

How Does Hydroelectric Power Work?

Hydroelectric power is the transformation of the kinetic energy of water, a function of mass and velocity of water flow. Hydroelectric power is created when the kinetic energy of flowing water is channeled by a dam into a turbine that spins a generator to convert the energy into electricity.

Types of Hydroelectric Power


These hydroelectric stations are those with small or no reservoir capacity so that only the water coming from upstream is available for generation at that moment and any oversupply must pass unused. A constant supply of water from a lake or existing reservoir upstream is a significant advantage in choosing sites for run-of-the-river. For more information visit the U.S. Energy Information Administration.

Low-Impact Hydro

These systems need to meet stringent environmental criteria such as river flow, water quality, fish passage and protection, threatened and endangered species, and public access/recreation.

Note: Both low impact hydro and run-of the river projects must adequately protect or mitigate their impact on the environment and society. For more information visit the Low Impact Hydropower Institute.

Conventional (dams) – Impoundment Hydropower

Most hydroelectric power comes from a dam that runs water into a turbine and generator. The power extracted from the water depends on the volume and on the difference in height between the source and the water's outflow. For more information visit the U.S. Energy Information Administration.

Pumped Storage

This method produces electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand, the excess generation capacity is used to pump water into the higher reservoir. When the demand becomes greater, water is released back into the lower reservoir through a turbine.