Hydroelectric

For decades, hydropower has been the principal renewable energy source in the United States. In 2015, hydropower made up about 6% of total U.S. electricity generation and 46% of generation from all renewables. The U.S. Energy Information Administration projects that conventional hydroelectric power generation will increase more than 20% during the next 25 years—from 246 billion kWh in 2015 to 296 billion kWh in 2040.

In 2014, electricity generated from other renewable sources exceeded hydropower output for the first time. During the next quarter-century, solar energy is expected to grow about 11.7% per year and wind generation by 3.7% per year. In 2013, new laws went into effect to promote greater efficiency in facilities and to modify regulations involving small hydroelectric plants.

In 2015, hydropower made up about 6% of total U.S. electricity generation and 46% of generation from all renewables.

Hydroelectric energy depends on the availability of suitable waterways and facilities on many of them have already been developed. In the United States, there are approximately 2,200 hydroelectric plants, with most of the capacity located in the West. Washington, Oregon, and California represent the three top-producing states.

There is, however, no apparent shortage of resources. A 2014 U.S. Department of Energy study found that, not counting sites on federally protected land, the United States has approximately 65 gigawatts of hydroelectric power potential on waterways that at present have no dams or diversion facilities. But the development cost of hydroelectric facilities is high compared to many other renewable or fossil-fuel sources. 

There are several benefits that make hydropower appealing. For example, unlike other renewable energy sources, such as wind and solar, hydropower is not intermittent. 

But as with any source of energy, it also has its drawbacks. Predominant 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. In addition, reservoir volume is vulnerable to droughts and potential effects of climate change.

Future hydropower technologies may include devices which can harness energy from waves, tides, ocean currents, and marine thermal gradients. However, attempts to tap wide swaths of ocean or coastal straits and embayments for harvesting energy will run into challenging social or economic barriers (e.g., entrenched uses such as fisheries and shipping lanes or environmentally sensitive areas) as well as technology, materials, and engineering issues (e.g., proximity to utility infrastructure, survivability).

The current contribution of such technologies to our energy supply system, however, is extremely small. Nevertheless, the promise of expanding our hydropower resources to include these additional renewable, non-intermittent, and emissions-free sources of energy remains very appealing.