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| Fig. 1: Water flows through a penstock which pushes a turbine to produce mechanical energy. Source: Environment Canada. |
During the 1980s and 1990s, civil and environmental rights activists combated investment in large dam projects, pointing out that Africa's history of large hydroelectric dams has been one of overlooked social costs to local communities, forced migrations of millions, destroyed watersheds and ecosystems, and false promises to rural communities that have been forced off their lands without compensation. [1] Despite these very real concerns, The New Partnership for Africa's Development (NEPAD), an organization that purports to prioritize African people, has joined the G8 and the World Bank in revitalizing large-scale hydroelectric dam development in Africa. Seeking funding for at least 13 dam projects, NEPAD and other private investors such as the African Development Bank, power companies, and Chinese hydroelectric companies have increased hydropower construction 53% since 2004. [2]
Botswana Power Corporation is in the final stages of planning for the construction of the Grand Inga Dam, the fourth hydroelectric dam that will be constructed on the Inga Rapids of the Congo River, which lies in the latter portion of the Livingstone Falls, a series of 32 rapids and cataracts along the Congo River that span approximately 220 miles (354 km). The total drop of the falls is about 850 feet (260 m), despite only minor rapids over an 87-mile (140-kilometre) stretch to Isangila. [3] The currently standing Inga 1 and 2 dams, constructed, owned and operated by the state owned power utility Société Nationale d'Electricité (SNEL) in 1972 with a generating capacity of 351 MW and 1982 with a 1424 MW capacity respectively, generate almost half of the Congo's 100,000 MW hydropower potential. Delayed due to the tumultuous political climate throughout African, the Grand Inga dam will require around $80 billion US dollars of investment to produce a maximum potential of 39,500 MW of electricity, over twice the capacity of the infamous Three Gorges Dam in China and enough to supply electric to all of the 500 million Africans living off the electrical grid. [4] The river maintains a steady flow of 42,000 m3/s on average since large swaths of the river basin lie above and below the equator, and consequently some part of the river is experiencing a rainy season at all times. [5] Though this fact makes the river a particularly desirable place to construct a hydro-scheme; to say that the river will produce 39,500 MW of electricity is misleasding since the entire river would have to be diverted to realize this potential; given that people who rely on the river will most like prevent its entire diversion, the river will probably produce significantly less than 39,000 MW of electricity. [5]
Nevertheless, current plans suggest that the Grand Inga dam will be built with 52 power generators of 750 MW capacity each, producing a total of 39,000 MW or 1.30 × 1018 joules/year, exactly where the Congo's rapid drops about 100 meters, or 315 feet, over a 9-mile long bend in the river that creates the largest waterfall in the world, spanning from Kinshasa, the capitol of the Democratic Republic of the Congo to the Atlantic Ocean. [6] Westcor, an entity formed in 2004 through an agreement signed by the utility companies of five African countries, is currently finalizing product design for Inga 3, which will generate around 3,500 MW through HV lines connected to Zambia, Zimbabwe, the Republics of the Congo and of South Africa.
Generating hydroelectric power requires one natural resource: a large river with a significant elevation change. Water at high elevations can be stored behind a dam in a reservoir in multiple tanks as potential energy, and when the electricity is needed, the water is released into a penstock (large pipe). This penstock then moves the water through a hydraulic turbine (see above image), which converts the moving water into mechanical energy. A propeller then pushes the water through a shaft, which is attached to an electric generator and converts the mechanical energy into electrical energy, or electricity, as seen in the figure to the right. Generators use crucial electromagnetic laws - Faradays laws to be exact - in employing electromagnet that circulate direct current through wire loops that wind around field poles (stacks of magnetic steel laminations) that are placed along the perimeter of the rotor. Because it is connected to the turbine shaft, the rotor makes the electromagnetic field pole move past the conductors, which causes voltage to develop at the generator output terminals, creating a flow of electricity.
Hydropower plants work the same way that coal plants do, but instead of using steam to turn a, hydropower plants manipulate river flow. When demand for electricity is not high, hydroelectricity can be stored in pumped storage - a mechanism that makes hydroelectric plants more efficient when supplying peak power demand than fossil fuel or nuclear plants. The pumped storage keeps water in a reserve until demand returns, when it pumps water that has already moved through the turbines back out. The reservoir is essentially a battery that can activate and adjust quickly to market demands.
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| Table 1: Technical specifications of the Inga dams. |
© Ayana Wilson. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] D. A. McDonald, Electric Capitalism: Recolonising Africa on the Power Grid (Earthscan, 2008), p. 148.
[2] S. J. Wachter, " Giant Dam Projects Aim to Transform African Power Supplies," New York Times, 19 June 2007.
[3] "Livingstone Falls," Encyclopedia Britannica.
[4] World Development Report 2008: Agriculture and Development (World Bank Publications, 2007).
[5] T. Hathaway, "Grand Inga, Grand Illusions?" World Rivers Review 20, 6 (2005).
[6] World Energy Council, How to Make the Grand Inga Hydropower Project Happen for Africa," March 2007.