Hydraulic Turbines
Introduction
To put this chapter into perspective, some idea of the scale of hydropower development in the world might be useful before delving into the intricacies of hydraulic turbines. A very detailed and authoritative account of virtually every aspect of hydropower is given by Raabe (1985), and this brief introduction serves merely to illustrate a few aspects of a very extensive subject.
Hydropower is the longest established source for the generation of electric power, which, starting in 1880 as a small DC generating plant in Wisconsin, United States, developed into an industrial size plant following the demonstration of the economic transmission of high-voltage AC at the Frankfurt Exhibition in 1891. Hydropower was expected to have a worldwide yearly growth rate of about 5% (i.e., doubling in size every 15 years), but this rate has now proved to be too optimistic. In 1980, the worldwide installed generating capacity was 460 GW according to the United Nations, but in 2007 the figure was just exceeding 700 GW. This works out at roughly 1.6% annual yearly growth. The smaller growth rate must, primarily, be due to the high costs involved in the civil engineering work, the cost of the power and related electrical plant, and to some extent the human cost due to massive population displacements with necessary new building.
According to the Environmental Resources Group Ltd., in 2007 hydropower constituted about 21% of the world’s electrical generating capacity. The theoretical potential of hydropower is believed to be 2800 GW. The main areas with potential for growth are China, Latin America, and Africa.
Table 9.1 is an extract of data quoted by Raabe (1985) of the distribution of harnessed and harnessable potential of some of the countries with the biggest usable potential of hydropower. From this list, it is seen that the People’s Republic of China (PRC), the country with the largest harnessable potential in the world had, in 1974, harnessed only 4.22% of this. However, the Three Gorges Dam project on the Yangtze River is now the biggest hydropower plant in the world. It contains 32 Francis turbines, each capable of generating 700 MW, the total generating capacity being 22,500 MW.
Tidal power
This relatively new and very promising technology, in which tidal stream generators are used to generate power, is still under active development. Very large amounts of energy can be obtained by this means and, unlike wind power and solar power, it is available at known times each day. The most efficient type of generator is still to be determined. The world’s first commercial tidal stream generator, SeaGen, was installed in 2008 at Strang ford Lough, Northern Ireland. The prototype version comprises two 600 kW axial-flow turbines, 16 m in diameter. Further details on this tidal turbine are given toward the end of this chapter.
Wave power
Several energy conversion systems have now been developed for obtaining electrical power from sea waves. One notable example is the Wells turbine, which uses an oscillating water column generated by the waves to drive this special type of axial-flow turbine. Several of these turbines have been installed (in Scotland and India) and details of their rather special fluid mechanical design are given in this chapter.
Features of hydropower plants
The initial cost of hydropower plants may be much higher than those of thermal power plants. However, the present value of total costs (which includes those of fuel) is, in general, lower in hydropower plants. Raabe (1985) listed the various advantages and disadvantages of hydropower plants and a brief summary of these is given in Table 9.2.
