ABSTRACT
The term hydro-power is usually restricted to the generation of shaft power from falling water. The power is then used for direct mechanical purposes or, more frequently, for generating electricity. Other sources of water power are waves and tides (Chapters 12 and 13). Hydro-power is by far the most established and widely used renew-
able resource for electricity generation and commercial investment. The early generation of electricity from about 1880 often derived from hydroturbines, and the capacity of total worldwide installations has grown at about 5% per year since. Hydro-power now accounts for about 20% of world’s electric generation. Output depends on rainfall and the terrain. Table 8.1 reviews the importance of hydroelectric generation for various countries and regions, while Figure 8.1 indicates the global increase. In about one-third of the world countries, hydro-power produces more than half the total electricity. In general the best sites are developed first on a national scale, so the rate of exploitation of total generating capacity tends to diminish with time. By the 1940s, most of the best sites in industrialised countries had already been exploited – hence the large ‘fraction harnessed’ percentages shown in Table 8.1. Almost all the increase in Figure 8.1 is in developing countries, notably India, China and Brazil, as reflected in the ‘under construction’ column in Table 8.1. However, global estimates can be misleading for local hydro-power plan-
ning, since small-scale (1MW to ∼10kW) applications are often neglected, despite the sites for such installations being the most numerous. This may be because the large surveys have not recognised the benefits perceived by the site owners, such as self-sufficiency or long-term capital assets. Thus the potential for hydro generation from run-of-river schemes (i.e. with only very small dams) is often underestimated. Social and environmental factors are also important, and these too cannot be judged by global surveys but only by evaluating local conditions. Coupled with the direct construction costs, these factors account for the ‘economic potential’ for the global study
of hydro-power in Table 8.1, being only about half the ‘technical potential’ assessed by summing (8.1) across the region. Hydro installations and plants are long-lasting with routine maintenance,
e.g. turbines for about fifty years and longer with minor refurbishment, dams and waterways for perhaps hundred years. Long turbine life is due to the continuous, steady operation without high temperature or other stress. Consequently established plant often produces electricity at low cost (<4 Eurocent/kWh) with consequent economic benefit. Hydro turbines have a rapid response for power generation and so the
power may be used to supply both base load and peak demand requirements on a grid supply. Power generation efficiencies may be as high as 90%. Turbines are of two types:
1 Reaction turbines, where the turbine is totally embedded in the fluid and powered from the pressure drop across the device.
