Hydro-Power

I

Introduction

Hydro-Power, power produced by the fall of water from a higher to a lower level, and extracted by means of waterwheels or hydraulic turbines. Hydro-power is a natural resource, available wherever a sufficient volume of steady water flow exists. The development of large-scale hydro-power today requires extensive construction, including storage lakes, dams, bypass canals, and the installation of large turbines and electric generating equipment. Because the development of hydroelectric power requires a large capital investment, it is often uneconomical for a region where coal or oil is cheap, even though the cost of fuel for a steam-powered generating plant is higher than the cost of running a hydroelectric plant. There are, however, many small hydro-power schemes producing less than 10 megawatts, and micro-hydro-power schemes that often do not require a dam or reservoir. Increasing environmental concerns are focusing attention on renewable energy sources.

II

History

The use of water-power dates from ancient Greece and Rome, where waterwheels were used for the milling of corn. The availability of cheap slave and animal labour, however, restricted its widespread application until about the 12th century. During the Middle Ages, large wooden waterwheels were developed with a maximum power output of about 50 hp. Modern large-scale water-power owes its development to the British civil engineer John Smeaton, who first built large waterwheels out of cast iron.

Water-power played an important part in the Industrial Revolution. It gave impetus to the growth of the textile, leather, and machine-shop industries in the early 19th century. Although the steam engine had already been developed, coal was scarce and wood unsatisfactory as a fuel. Water-power helped to develop early industrial cities in Europe and the United States until the opening of the canals provided cheap coal by the middle of the 19th century.

Dams and canals were necessary for the installation of successive waterwheels when the drop was greater than 5 m (16 ft). Large storage-dam construction, however, was not feasible, and low water flows during summer and autumn, coupled with icing during the winter, led to the replacement of nearly all waterwheels by steam when coal became readily available.

III

Development of Hydroelectric Power

The earliest hydroelectric plant was constructed in 1880 in Cragside, Northumberland. The rebirth of water-power came with the development of the electric generator, further improvement of the hydraulic turbine, and the growing demand for electricity by the turn of the 20th century (see Electric Motors and Generators). By 1920 hydroelectric plants accounted for 40 per cent of the electric power produced in the United States.

The basic principle of operation of most major installations has remained the same during the 20th century. Plants depend on a large water-storage reservoir upstream of a dam where water flow can be controlled and a nearly constant water level can be assured. Water flows through conduits, called penstocks, which are controlled by valves or turbine gates to adjust the flow rate in line with the power demand. The water then enters the turbines and leaves them through the so-called tailrace. The power generators are mounted directly above the turbines on vertical shafts. The design of turbines depends on the available head of water, with so-called Francis turbines used for high heads and propeller-turbines used for low heads.

In contrast to storage-type plants, which depend on the impounding of large amounts of water, a few examples exist where both the water drop and the steady flow rate are high enough to permit so-called run-of-the-river installations; one such is the joint US-Canadian Niagara Falls power project.

In the early 1990s, the United States was second to Canada in total production of hydroelectric power. Canada gets about 62 per cent of its electricity from hydroelectric sources. Worldwide, hydroelectric power represents approximately a quarter of the total energy generated and is growing in importance; in many countries, it is the dominant source of electric power. The leaders are Norway (99 per cent), Democratic Republic of the Congo (97 per cent), and Brazil (96 per cent). The Itaipu plant on the Paraná River, between Brazil and Paraguay, officially dedicated in 1982, has the greatest capacity (12,600 megawatts when placed in full operation) in the world. The world’s largest scheme, the Three Gorges Dam, is under construction at Sandouping in China on the Yangzi river, and will have an installed capacity of 18,200 megawatts. These may be compared to the Grand Coulee Dam, which provides about 6,500 megawatts. Hydroelectric plants in Scotland provide only 2 per cent of power generation in Britain. The world capacity of small-scale hydroelectric installations is 27,800 megawatts, and that for large-scale installations is 605,800 megawatts.

Hydro-power currently accounts for approximately 85 per cent of renewable energy in the European Union, which has set a target of 8 per cent of electricity to be generated by renewable sources by 2010. This will require hydro-power to make by far the largest contribution, with the European Renewable Energy Study envisaging the European Union increasing hydro-power output from 165 to 185 billion kWh per year.

Small-scale hydroelectric plants, with capacities between 1 kilowatt and 1 megawatt, have been developed in some countries. In many of China's districts, for example, such dams are the main source of electric power. Other developing nations are also making use of such projects, which can make good use of available labour.