Environmental Issues and Future Markets

While most of the major sites are already exploited, there remains significant potential for growth of hydropower. Many existing sites are still capable of being expanded. DoE's Hydropower Program has identified nearly 6,000 sites that could produce as much as 30,000 MW of additional hydropower capacity. Moreover, hydropower is only generated at a very small percentage of the nation's dams. Of a reported 75,000 to 80,000 dams in the United States, only 3% are used for hydroelectric generation. The National Hydropower Association reports that in the 1980s, 91% of the 765 federally licensed hydro projects did not require a new dam and that more than 20,000 MW of new capacity could be installed in the United States without the construction of a new dam.

Given the climate of rising energy prices and air emission regulations, there is a strong market growth potential for hydropower in large, medium, and even very small applications. However, there remains long-standing environmental and land-use issues that must continuously be resolved.

The majority of concerns regarding hydropower focus on the environment. While there are many advantages of hydropower dams, such as provision for irrigation, recreation, and flood control, when wild rivers are dammed up, ecosystems both up and down the river change. Downstream, water flow rates decline and water levels change, affecting habitats for many animals. Every case is different, but with such a drastic change in the environment, it is likely that some species or environmental element will be impacted. The most obvious impact of hydropower dams is the upstream flooding of vast land areas, much of which may have been previously forested or used for agriculture. This can also eliminate land from native peoples and destroy rare ecosystems. An extremely large project could flood thousands, and even tens of thousands, of square miles of land. Even if the opposition can be overcome or an equitable settlement reached, there often remains significant cost associated with relocation and compensation to affected individuals.

Fish that populate these areas often get stuck in the penstock, which leads them to almost certain death in the turbines. Screens, as shown in Figure 14-13, can greatly limit this and modern turbines can be designed to allow fish passage to further reduce death rate. Damming a river can alter the amount and quality of water in the

Fig. 14-13 Large Fish Screen at Hydropower Plant. Source: Bureau of Reclamation

river downstream of the dam. It can also prevent fish from migrating upstream to spawn. Setting minimum downstream flow requirements and employing fish ladders can mitigate these impacts. However, screens and fish ladders add significantly to capital costs, negatively impacting project cost-effectiveness.

Silt can slowly fill up a reservoir, decreasing the amount of water that can be stored. This also can deprive the river downstream of silt, which fertilizes the river's flood plain during high water periods. Bacteria present in decaying vegetation can also change mercury, present in rocks underlying a reservoir, into a form that is water-soluble. This mercury can accumulate in the bodies of fish and pose a health hazard to those who depend on these fish for food. Dams are also susceptible to growth of other forms of hazardous bacteria. Continual efforts are being made to reduce these potential negative impacts, with a strong focus on reducing fish mortality rates and maintaining downstream dissolved oxygen at proper levels.

Still, in certain limited cases, facilities located on or near rivers can effectively apply hydropower systems for mechanical drive or electricity production services. Today, standardized micro-turbine systems are available for applications ranging from a few MW down to a few kW. These can be applied in run-of-the-river type systems that use the power in river water as it passes through the plant without causing significant change in river flow. Hence, given unique access to a flowing river, hydraulic turbines merit consideration as a prime mover system of choice for a commercial, industrial, or institutional facility. In consider ation of potentially negative environmental impact, new hydropower facilities can be designed with the power plants placed underground, and selective withdrawal systems can be used to control the water temperature released from the dam.

Larger projects will continue to find many challenges in overcoming environmental and land-use issues. However, they also will continue to enjoy the benefit of economies of scale and federal agency support. Small projects will be aided by the availability of standardized designs for micro-turbine applications and the ability to work through various siting issues more quickly than with larger projects. The development and permitting process can be extremely laborious and costly and, therefore, risky. However, there have been so many successful ventures of all capacity ranges that market confidence is solid.

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