Although a small source of primary energy, at only a fifth of the biomass contribution, hydropower is the largest renewable source of electricity. It has been in use for many years and is now considered a conventional form of power generation.
Although there are hydroelectric projects under construction in about 80 countries, most of the remaining hydro potential in the world may be found in developing countries, particularly in South and Central Asia, Latin America and Africa. Individual countries outside of these regions with remaining hydropower are Canada, Turkey and Russia
Hydropower represents 15.9% of the world’s electricity generating capacity. The theoretical potential worldwide is 2,800 GW, about three times the 978 GW which had been exploited by the end of 2009. However, the actual amount of electricity which will ever be generated by hydropower will be much lower than the theoretical potential because of environmental concerns and economic constraints.
44% of the world’s hydropower was generated in just four countries in 2009 – in the United States, Canada, Brazil and China. Asia accounted for 29%, an improving share on account of China’s expansion of hydro, followed by North America with 21% and Latin America with 21% and other regions accounting for 29%.
In Western Europe and the United States the scope for additional hydro capacity is limited. Eastern Europe is expected to maintain its reliance on fossil fuels and nuclear.
Hydro-electric power plants can generally be divided into three technology types.
‘High head’ power plants are the most common and generally employ a dam to store water at an increased elevation. Water can be stored during rainy periods and released during dry periods, providing a consistent and reliable production of electricity. Some of these plants have enormous heads as high as 1,000 meters. Most large hydro-electric facilities are of the high head variety.
‘Low head’ hydro-electric plants are power plants which generally use heads of only a few meters or less. Power plants of this type may use a low dam or weir to channel water, or no dam and simply use the ‘run-of-the-river’.
‘Pumped Storage’ facilities use excess electrical system capacity, generally available at night, to pump water from one reservoir to another reservoir at a higher elevation. During periods of peak electrical demand, water from the higher reservoir is released to generate electricity. Pumped storage sites are not net producers of electricity, it actually takes more electricity to pump the water up than is recovered when it is released but they are able to store electricity for use at a later time when peak demands are occurring. Storage is even more valuable if intermittent sources of electricity such as solar or wind is hooked into a system, which is then termed ‘hybrid’.