Hydroelectric Power for a bright future
Hydroelectric power can provide most of present and future needs, but it will take time and investment to build dams, plants, and distribution lines so fossil fuel power is needed until that day. Africa has abundant rivers that could supply most or all of their electrical needs for the foreseeable future through dams, waterfalls, and pumped storage.
“Hydropower produces more than three-quarters of the world’s renewable energy output each year. And its carbon emissions—over the entire lifecycle of construction, operation and decommissioning—are often far lower than those from all other renewable sources, including wind and solar. Across Africa, hydropower is responsible for 84 per cent of all non-fossil fuel energy use. But in a continent rich in lakes and rivers, the opportunities for expanding hydropower are huge.”
78 percent = Proportion of global renewable energy generation from hydropower in 2012
7.5 percent = Proportion of African energy use from non-fossil fuels in 2013
84 percent = Proportion of African non-fossil fuel energy use from hydropower in 2013[1]
Africa is estimated to have 4 million gigawatts-hours per year (GWh/yr) or 4 billion megawatts-hours per year (MWh/yr) total hydroelectric generating capacity, or about 12 percent of the world’s hydropower potential, with a technically feasible output of about 1,800 terawatts-hours per year (TWh/yr) or 1.8 trillion MWh/yr. [2] Yet Africa produces only about 3 percent of the global hydropower and exploits less than 10 percent of its technical potential.[3]
Some notable systems have been built in Africa and some are under construction or planned. The largest in Africa is the Aswan, capacity 2,100 MW, followed by the Cohora Bassa in Mozambique at 2,075 MW capacity. The soon-to-be-completed Grand Ethiopian Renaissance Dam (GERD) on the upper Nile will have a capacity of 6,000 MW. It will triple the electrical output of the country and be capable of selling power to surrounding countries and/or multinational grids.
An example of a waterfall being used for power is Victoria Falls, Zambezi River, on the border between Zambia and Zimbabwe, which has three power plants with a total capacity of 108 MW. A proposed hydroelectric dam below the falls on the Zambezi River at Batoka Gorge will have a capacity of 1,600 MW.
For comparison, India has become the 7th largest producer of hydroelectric power in the world. India’s installed utility-scale hydroelectric capacity is 44,594 MW, from major power plants plus many smaller plants. Its potential is over 155,000 MW from large and small plants and 94,000 MW pumped storage potential, with 4800 MW installed to date. Its many waterfalls are used as well as hydroelectric dams and pumped storage reservoirs. The hydro-electric power plants at Darjeeling and Shivanasamudram were established in 1898 and 1902, respectively. They were among the first in Asia. India has been a dominant player in global hydroelectric power development. India also builds hydroelectric plants in other countries and may be a resource for countries in Africa and similar energy poor regions.
Hydroelectric Power Details
Hydroelectric plants are classified as Large if their capacity is over 500 MW, Medium if over 10 MW, and Small: Mini (10 MW), Micro (100 kW), or Pico (5 kW). Many more Small facilities are and can be built with much lower capital investment up front. Smaller hydroelectric facilities can be scaled to more closely meet local needs in isolated areas, and several of these can be connected to a distribution grid to provide electricity to a wider area.
Hydroelectric power plants use the force of falling water to turn turbines attached to generators, so that heating water for steam and subsequent cooling is not needed. Hydroelectric dams also provide flood control and create reservoirs to provide a reliable source of clean water, irrigation water, aquaculture, fishing and manufacturing industries, and much needed water transportation. Reservoirs resupply the water table by lateral seepage.
Pumped storage in conjunction with hydroelectric dams can help to reliably supply needs in seasons when water flow is reduced or demand peaks. The way it works is that water is pumped up to fill a mountaintop reservoir when demand is below capacity, and the stored water is used when demand is high. The efficiency of many of these systems is above 70 percent.
A good example in my personal experience is Raccoon Mountain Pumped-Storage Reservoir near Chattanooga, Tennessee. It is located above Nickajack Lake Reservoir on the Tennessee River. Water is pumped from the reservoir at the base of the mountain up to the mountain top reservoir during low demand periods and released to generate additional power for the TVA system of hydroelectric dams in peak demand periods. At present there are more than three dozen pumped storage facilities in nineteen countries with 1,000 MW capacity or greater and many more with lower output capacities.
Racoon Mountain Pumped Storage hydroelectric generation[4]
Waterfalls can provide power without the need to build a dam. Part of the natural gravity-fed flow is channeled through turbine generators to supply power. One long-standing example is at Niagara Falls, straddling the US and Canadian border. This area has had a succession of hydroelectric power plants in both countries as both demand and capacities have increased. Hydroelectric power generation in this area has remained uninterrupted since local service began in 1882 in the US and 1892 in Canada. The famous Adams Power Plant, built by Westinghouse with Tesla designed turbines, opened in 1895 to supply power to New York counties nearby. Currently operating plants include a pumped storage facility, Lewiston Pump-Generation Plant, in conjunction with the Robert Moses Power Station in the US.
Smaller hydroelectric facilities can use run-of-the-river systems. In this system, no dam is needed if there is a gradient. Some of the water is diverted from the river using a sloping or vertical channel through turbines to generate electricity and then is returned to the river downstream. As a rule, the higher the drop, the greater generating capacity, but Micro and Pico plants can run on as little as a one-meter drop to supply local power or to connect to a larger network.
Even in relatively arid areas, hydroelectric power can provide most of the electrical power in rainy seasons and can be backed up with fossil fuel thermal power plants to fill in any gaps during dry seasons. As an added bonus, in dry seasons the reservoirs behind hydroelectric dams can provide needed water for agriculture and homes, especially if power generation is switched to backup power to conserve water in the reservoir. The combination of hydropower and thermal power generation can provide reliable power throughout the year.
[1] Source: International Energy Agency/BP.
[2] Abbreviations: GWh/year = Gigawatt-hours/year or billion watt-hours/year; MWh/year = Megawatt-hours/year or million watt-hours/year; TWh/year = Terawatt-hours/year or trillion watt-hours/year. Tera- is 1000x Giga-, which is 1000x Mega-.
[3] Appleyard, David, “Africa’s Hydropower Future,” Hydroworld.com, January 1, 2014, http://www.hydroworld.com/articles/print/volume-22/issue-1/regional-profile/africa-s-hydropower-future.html.
[4] Tennessee Valley Authority