In places such as Scandinavia, hydroelectric power provides the vast majority of renewable energy and generates most of the electricity. In developed countries, rivers that are suitable for generating hydroelectric power typically already have one or several dams or are located in conservation areas that prohibit dams, and so the majority of new hydroelectric projects are in developing countries.
Hydroelectric power derives from transfers of kinetic energy when a volume of water flows down from a high elevation source, such as a reservoir, through a generator turbine and out to the streambed below.
Hydroelectric power. Water flows down a pipe called a penstock, through a water turbine, and, finally, downstream. The turbine drives an electrical generator. The energy extracted depends on water volume of the reservoir and the height differential.
Compared to other renewable energy sources, hydroelectric is highly predictable and flexible and can readily meet daily peak loads. Operating and maintenance costs of hydroelectric facilities, after construction, are lower than costs for any other energy source. Reservoirs also serve for flood control, irrigation, and urban water supplies. Hybrid systems are envisioned that would use wind, solar, or tide/wave power to pump water behind dams and then release the water to generate electricity when it is needed.
On the negative side, construction costs of large hydroelectric projects are enormous, and such projects often displace communities that have developed along rivers and disrupt river ecosystems. For example, the Aswan Dam on the Nile River in Egypt, completed in 1976 at an estimated cost of $4.4 billion (in year 2000 $U.S.), required relocation of 90,000 people and of archaeological sites such as the temple at Abu Simbel. The dam retains silt that the river previously deposited down river in yearly floods. This silt made the Nile Valley fertile for agriculture and fishing. Adjustments to these changes have proved difficult.
Number of existing and planned large dams in major watersheds as of 1994. A large dam meets at least one of the following criteria: height greater than 150 m, water volume greater than 15 × 106 m3, reservoir storage capacity of at least 25 km3, or generating capacity greater than 1000 megawatts. (After Revenga et al. 1998.)
The Three Gorges Dam on the Yangtze River in China, when it becomes fully operational in 2011, will be the world’s largest hydroelectric facility. Construction costs will total more than $23 billion (in year 2000 $U.S.), but sale of the electricity that it generates should recover these costs in about a decade. Unfortunately, the rising waters behind the dam will displace more than 1.5 million people and submerge some 1300 archaeological and cultural sites. Sedimentation of silt behind the dam eventually will interfere with its operation, and lack of silt deposited below the dam will lead to erosion and sinking of land far downriver, in the delta region. The dam has slowed the flow of the Yangtze, and this reduces the ability of the river and its tributaries to flush out polluted areas. Altered fish migrations and other changes to the river ecosystem are likely to drive endangered species such as the Siberian Crane and Baiji Yangtze river dolphin to extinction.
Experiences with giant hydroelectric projects such as the Aswan and Three Gorges dams have led many governmental and nongovernmental agencies to favor smaller projects. What smaller dams sacrifice in efficiency, they compensate for in being more affordable and causing fewer societal and environmental disruptions. The amounts of electricity generated can often integrate directly into existing distribution systems. A smaller dam also presents less of a security risk: Breach of the dam from natural causes or human actions will be less catastrophic.
This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.
©2010 Sinauer Associates and UC Regents