The power of moving water has been used as an energy source since time immemorial. It’s not hard to see why: when you stand by the sea and watch the waves pounding onto the shore, or gaze at a waterfall plunging down hundreds of feet, or just walk beside a swollen river and see it sweep debris along in its path, the sheer power of water is impressive and even a little frightening.
Different Ways to Harness Water Power
Hydro-electric power plants, which use the gravitational potential energy of falling water to produce electricity, are used in many parts of the world. Tidal power stations are a far less common method of generating electricity, using the rise and fall of tidal waters.
Less common still is the production of electricity from offshore wave power; this is still an experimental technology. Other ways of using water power are being researched. Alongside the large-scale installations that harness the power of massive quantities of water, there is also a place for small-scale water-powered installations, such as waterwheels, that can supply energy to meet cottage industry or domestic needs.
Hydroelectric plants use the flow of river water. Turbines are installed in a position where they will be rotated by the water as it rushes past; the turbines are linked to a generator, and thus electricity can be produced constantly, as long as the water keeps flowing at speed.
In order for a hydroelectric power station to work efficiently, strong water pressure is necessary. This can be produced by building a dam, which will cause water pressure to build up. Turbines can then be installed in tunnels in the dam, through which the water escapes; the rate of flow through these tunnels can be controlled, and has the potential to be very fast indeed due to huge pressure from the weight of water behind the dam. Constructing such a dam is a major engineering project; it is very expensive and causes a great deal of disruption to the environment.
Hydroelectric stations can also be sited alongside naturally fast-flowing rivers. This avoids the need for a dam, but it is not possible to control the rate of flow.
Hydroelectric power stations are effective, and around one-fifth of the world’s electricity is generated in this way. No waste or emissions are produced. The disadvantage is that the installation of the plant causes some disruption to the environment as a habitat for marine life, and for the people who live in the vicinity.
Waves are a constant source of kinetic energy; the challenge is to find an effective way of harnessing this energy to generate electricity. Depending on weather conditions, wave movement can vary from extremely energetic to almost still. This poses various technical and engineering problems, as any installation will have to be flexible enough to cope with widely differing levels of power input, and will also have to be robust enough to withstand violent storms.
Portugal was the first country to create a commercial wave farm, in 2006. There is also a wave farm off the Scottish island of Islay. Various alternative methods of converting wave power into electricity have been devised but not yet fully tested. However, another prerequisite of this type of offshore installation is that it can co-exist with other marine-based industries, such as fishing and tourism.
Where the right conditions exist, the tidal flow of the waters in estuaries can be harnessed by building a barrage, across the river mouth. Twice a day, for a total period of around ten hours, the ebb and flow of the tide produces sufficient water pressure through the barrage to operate turbines. France has one such scheme is in operation at Saint Malo, on the River Rance, and it works very effectively; similar schemes in Russia, Canada and China, have also proved successful. However, the number of sites that meet all the criteria for this type of scheme are limited, and their impact on the environment has to be considered. Potential sites have been identified in the UK but not exploited.
For and Against
In theory, water is a fully renewable, completely free source of energy. In practice, whilst small-scale applications of water power are environmentally-friendly and cost-effective, large-scale applications require considerable investment because of the major civil engineering works involved; and earthworks of this magnitude cannot help but leave their mark on the environment.
Indeed, some such installations are so impressive in their own right that they have become tourist attractions. But for now, the energy contained in many of the world’s rivers and oceans must remain untapped unless, or until, we can find new ways of harnessing the power of the waves and tides that will have less impact on the environment.