ENERGY BASICS: hydropower

Hydropower in the United States produced about 260 billion kilowatt-hours of electricity in 2021 — about 6.3 percent of the nation’s total.

That level of generation has remained stable since the 1970s. Hydropower accounted for a much larger share of the nation’s power generation back then — about 16.4 percent in 1970. The decline is a result of the growth of other renewables, such as wind and solar, which were all but non-existent in 1970.

In fact, wind surpassed hydropower as the largest source of renewable energy in 2019. 

All hydropower installations depend on moving water spinning turbine blades to generate electricity.

Diversion facilities divert water from a moving stream or river to run through turbine blades.

Impoundment facilities, the most common hydropower generators, trap water behind a dam and release the water as needed to generate power.

Pumped storage facilities pump water during periods of low demand for electricity from a lower to an upper reservoir. When power demands warrant, that water is released back into the lower reservoir through a turbine to generate electricity.

All but two states — Delaware and Mississippi — have hydropower facilities.

Unsurprisingly, the level of hydropower-generated electricity varies substantially from state to state. Washington state uses hydropower for about 66 percent of its electricity needs. The state is the largest hydropower producer, providing between one-fifth and one-third of the nation’s water-driven electricity — 27 percent in 2020. Most of the state’s hydropower plants are located on the Columbia River. 

Hydropower traditionally has been seen as environmentally benign, although all energy-generation technologies involve some kind of environmental impacts.

Construction of hydropower facilities, such as large dams, typically require large quantities of steel and concrete — likely produced with carbon-generating technologies — although calculations of these one-time emissions are spread across the life-span of the facility.

Large hydropower facilities typically create large reservoirs, which have significant impact on local ecosystems.

More recently, studies have found significant carbon emissions from such reservoirs, with levels differently significantly depending on local factors.

The need to move away from power-generation that produces greenhouse gas emissions has sparked some discussion of using more dams for power generation. According to the U.S. Department of Energy, less than 3 percent of multi-purpose dams in the United States are used to generate electricity. A 2016 DOE study, the Hydropower Vision Report, said the country could increase its hydropower capacity from 101 gigawatts to nearly 150 GW by 2050.

On the other hand, climate change is having an impact on current hydropower capability and may degrade it further. The Energy Information Administration reported on June 1, 2022, that generation from California’s hydropower facilities as a result of drought conditions may over the summer be down by 48 percent from projections under non-drought conditions.