Benefits and Challenges
Hydropower poses unique challenges in energy development because it combines great benefits with some difficult environmental obstacles.
Large-scale hydropower plants are an important component of the national grid because of their ability to respond in seconds to large and rapidly varying loads, which other base-load power plants cannot. The large dams and reservoirs that supply these plants with water can provide substantial nonpower benefits as well, including stabilizing water supply, flood control, improved navigation, and water-based recreation.
Many renewable energy technologies are intermittent in nature, meaning they are not continuously available, because they rely on energy sources like the wind or sun. Hydroelectric generating plants can "store" energy and then release water to generate electricity when it is needed. This ability to store energy is an asset that can be combined with other renewable technologies like wind energy to enable larger scale use of renewable energy.
Another advantage of hydropower is that it has essentially no atmospheric emissions, such as greenhouse gases, other than water evaporation.
But for all its benefits, hydropower is not free from adverse environmental effects. Since hydropower plants require water to be channeled away from its natural flow, their design disrupts the environment. The environmental costs of large-scale hydropower plants include fish injury and mortality from passage through turbines and changes in the quality and quantity of water released below dams and diversions.
Dams change the stream water quality by altering water temperatures and the level of dissolved gases, thereby interrupting the ecology of the natural river system and damaging vegetation, fish, and other wildlife. Land and wildlife habitat is inundated, people are often displaced from fertile valleys, fish habitat is destroyed, and natural passage of the fish is restricted. Migrating fish cannot get past dams unless fish ladders are installed. Dams also change the turbidity of rivers by holding back silt and other debris, including nutrients.
Small hydropower projects do not affect large areas of land. They may inundate a few acres but usually they simply divert a portion of the flow of a river or stream. This can be enough to supply power to a small rural community that cannot gain access to the national electrical grid, and the environmental impact is much less than with large-scale projects. Small hydropower projects can be planned and built in a relatively short time with fewer materials and for much lower cost than large projects.