The United States requires a tremendous amount of energy to fuel its economy and support millions of households. Our nation relies mainly on coal, oil and natural gas as fuel to produce our energy. However, renewable energy sources are increasingly recognized as a critical component in our country’s energy portfolio. Renewable energy sources have the added benefits of lower air emissions and play a role in reducing our nation’s dependence on foreign oil supplies. Renewable energy facilities—wind, solar and hydroelectric—are derived from replenishable resources that are available in many regions of the country.
With 80,000 megawatts of generating capacity, hydroelectric power, or hydropower, is by far the nation’s largest renewable energy source. Hydroelectric plants have been producing clean, renewable energy for more than 100 years. Hydropower is fueled by water, so it’s a clean, renewable fuel source, and doesn’t pollute the air like power plants that burn fossil fuels. More than 160 million tons of carbon emissions were avoided in the United States in 2004 when 268 million megawatt-hours of hydropower were generated.1
Today’s hydropower turbines are capable of converting more than 90 percent of available energy into electricity, which is more efficient than any other form of generation. The best fossil fuel power plant is only about 50 percent efficient. In addition, hydropower has the unique ability to change output quickly. Its unique voltage control, load-following and peaking capabilities are critical for electric grid stability. This ability also provides an efficient and cost-effective way to support the use of intermittent renewable sources of power such as wind and solar energy.
Conventional hydropower facilities utilize reservoirs, run-of-river or pumped storage as a water source. To create a reservoir, a dam is needed to store water for use to meet changing electricity demands. The impoundment can offer secondary benefits including recreation, flood control and water supply. Run-ofriver plants utilize the water available at any give time to generate electricity before returning it to the river. Pumped storage plants use reversible pumping/generating units to pump water up to an upper reservoir when demand for electricity is low and release water back to a lower reservoir through the reversible units to generate power during periods of high demand.
The disadvantages of conventional hydropower have been well-publicized and, to a great extent, have limited the development of new hydropower plants in the U.S. Fish populations can be impacted if fish cannot migrate upstream past dams to spawning grounds. Downstream fish passage through turbines or spillways can result in fish injury or mortality. Hydropower plants can cause low dissolved oxygen levels in the water, particularly at high head impoundments, a problem that is harmful to riparian (riverbank) habitats. New hydropower facilities impact the local environment and may compete with other uses for the land which are more highly valued than electricity generation. People, plants and animals may lose their natural habitats, and local cultures and historical sites may be impinged upon. Because of these negative impacts, many environmentalists have actively lobbied to keep hydropower from being recognized as a renewable energy resource like wind and solar energy. This has severely limited government funding for new research and development and cut tax credit incentives which would spur development of new projects and addition of incremental capacity at many existing hydro plants. Many simply see hydropower as an outdated mode of generation which no longer has a place in an “eco-friendly,” high-tech world.
In response to these challenges, researchers have been working to develop new technologies to capture energy from flowing water without the disadvantages of conventional hydropower. These include:
• Wave energy. Wave energy conversion devices capture mechanical power from the waves near shore and use it to directly or indirectly power a turbine and generator.
• Hydrokinetic energy. Underwater turbines placed within rivers or ocean currents to capture moving energy from the flow of water across or through blades to power a generator, similar to how a wind turbine captures the wind. These can be placed either on the piers of existing bridges or on pylons anchored to the river or ocean bed. Silently, slowly turning with the current, these installations would be all but invisible above water.
• Tidal energy. Water levels in tidal areas are captured during high tide and stored. During low tide, flow is released through turbine generator units back to the ocean to create electricity.
• Constructed waterways. Vast amounts of flowing water in man-made conduits such as irrigation canals, aqueducts and water supply or effluent streams, can be captured for power generation. Environmental concerns associated with natural rivers and streams are a non-issue.
• Fish-friendly turbines. New fish-friendly turbine designs are being developed and tested for conventional hydro plants to minimize fish mortality. In addition, new systems are being developed to direct fish away from turbine intakes and toward their natural surface-oriented migration route. These technologies can be applied either to new conventional hydro projects, or for retrofitting of existing hydro plants to lessen their environmental impact.
With increasing demand for clean energy, conventional and new hydropower technologies are poised for tremendous growth. Electric utilities and equipment manufacturers are increasingly turning to consultants to help them develop new sources of clean, renewable energy and provide technical assistance to bring new, low-impact energy technologies to market. Hydropower is still an important domestic source of renewable, reliable and affordable electricity. With new technologies becoming available, its environmental impact can be effectively managed or mitigated. Hydropower can and should play a prominent role alongside other renewable energy sources in securing our energy future and independence into the 21st century. IBI
1 Source: National Hydropower Association website and assumes a national average electricity emission factor of 0.6 metric tons of avoided CO2 emissions per megawatt hour at a non-emitting power generator.
