The National Academies: What You Need To Know About Energy

The National Academies

What You Need To Know About Energy

Hydroelectric

Until recently, hydropower provided the largest contribution to our renewable energy supply, and its significance to renewable energy sources is still great. In 2008, hydropower accounted for about 2.5% of our total energy production. All of the energy generated through hydropower goes toward electricity generation, and in 2008, 6% of our electricity came from this source.

All of the energy generated through hydropower goes toward electricity generation, and in 2008, 6% of our electricity came from this source.

In just the past few years, as a result of increased investments in biofuels, biomass sources (which include wood and wood byproducts, municipal waste, methane from landfills, and fuel from agricultural crops) have come to account for more of our total renewable energy supply than hydropower sources. With energy from biomass products expected to increase more than 55% by 2030, this trend is likely to continue. Hydroelectric energy depends on the availability of suitable waterways, many of which have already been developed. In the United States, most of the hydropower capacity is located in the west, with Oregon, Washington, and California representing the three top-producing states.

There are several benefits that make hydropower appealing. Flowing water is an inexpensive domestic source of energy, and unlike fossil fuels, it does not emit heat-trapping greenhouse gases that contribute to climate change. Unlike other renewable energy sources, such as wind and solar, this energy source is not intermittent. But as with any source of energy, it also has its drawbacks. Principal among them is the concern that damming rivers and streams can be disruptive to local ecosystems both upstream and downstream of a hydroelectric plant, altering the habitats of plants, fish, and animals. For example, salmon must swim upstream to spawning grounds in order to reproduce, but dams from hydroelectric plants block their path. In some cases, efforts have been made to build “fish ladders” that allow salmon to leap up a series of small steps past hydroelectric plants. Other negative ecosystem effects remain more difficult to address. For this reason, it is unlikely that conventional hydropower resources can be significantly expanded in the future.

Future hydropower technologies may include devices which can harness energy from waves, tides, ocean currents, and marine thermal gradients. The current contribution of such technologies to our energy supply system, however, is extremely small. Nevertheless, the promise of expanding our hydropower resource to include these additional renewable, non-intermittent, and emissions-free sources of energy remains very appealing.

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Energy Hands-on

What do you know about energy?

True or False: Lighting accounts for 18% of all electricity used in the United States.

  • Correct!

    Lighting accounts for 18% of the electricity used in the United States. A 12% decrease in overall electricity use in buildings could be realized if incandescent bulbs were replaced with CFL or LED bulbs.

  • Sorry, that’s incorrect.

    Lighting accounts for 18% of the electricity used in the United States. A 12% decrease in overall electricity use in buildings could be realized if incandescent bulbs were replaced with CFL or LED bulbs.

Energy Defined

British Thermal Unit

A unit of measure for the energy content of fuels. One Btu is the amount of energy needed to raise a pound of water by one degree Fahrenheit.

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