Hydropower in the United States

Hydropower made up 2.7% of the energy (and 23% of renewable energy) used in the United States in 2018 and 6.7% of electricity generated in the United States in 2019.

What is hydropower and how is it used?

• Hydropower is generated by the force of moving water, and there are several types of hydropower facilities. Often, flowing water turns blades in turbines, which spin generators to produce energy.

• Other systems can generate energy from ocean currents, tides, and waves, although these technologies are less common and not always included in the category of hydropower.

• Hydropower technology to generate electricity originated in the late 1800s, (although water wheels were used to perform work long before that). Hydropower infrastructure such as dams and turbines produced over 40% of U.S. electricity during the early 20th century. With the growth of other technologies, it now represents a much smaller fraction of U.S. energy, but sites like the Hoover Dam and Niagara Falls continue to generate hydropower.

What are the advantages and disadvantages of hydropower?

• The cost of hydropower varies, but compared to other energy options, it is a relatively low-cost source.

• Many hydropower facilities can also store energy by pumping water upwards so it can be released to turn turbines and generate electricity when needed.

• The energy output of many hydropower facilities can be quickly ramped up or scaled down to increase the reliability and flexibility of energy systems. This is an upside — allowing less consistent forms of renewable energy to be added to the grid. However, hydropower generation faces regulatory and operational constraints that limit this flexibility.

• The average age of U.S. hydropower dams is now around 60 years, and aging infrastructure carries increased risk of failure and harm to surrounding areas.

• Hydropower facilities like dams and turbines often interfere with ecosystems. For example, the migrations of water animals can be disrupted, and the biochemical balance of marine environments can be altered.

• Decomposition of organic matter in reservoirs produces greenhouse gases, primarily methane, whose quantities are not yet precisely calculated.

• Reservoirs are estimated to produce about 1.5% of global human-caused emissions of carbon dioxide, methane, and nitrous oxide. However, greenhouse gas emissions  per unit of energy generated vary greatly at different facilities based on such variables as local ecology and generation technology; some emit at rates as low as clean-energy sources like wind, while others emit at rates several times higher.