Which is your favourite hydroelectric power project?
Hydroelectric Power
The heat of the sun evaporates water from the Earth's surface, sea and land, and some of the rain that later falls from the clouds runs into lakes and rivers, and eventually back into the sea. This is only one route that water takes, but it does mean that the sun's energy is continually giving us water flowing down rivers. Mankind has been harnessing this energy for a long time, for example diverting water along irrigation channels, and using water mills to grind corn.
In more recent years we have used the power of water to create electricity - hydroelectric power, or hydropower for short. Usually, but by no means always, this involves the construction of dams with turbines in. As the water falls, it turns the turbines which drive the generators. The amount of energy produced is directly proportional to the volume and the difference in height between the top and the bottom of the dam (the head). The earliest hydroelectricity was produced at Appleton, Wisconsin, USA in 1882. The largest is the Itaipu dam in Brazil/Paraguay. Canada produces the most.
Turbines can also be placed in strongly flowing water without a dam blocking the river, and they can also be placed in places where there is a strong tide (tidal power), for example in the Bay of Fundy, which is surrounded by Nova Scotia, New Brunswick and Maine.
One of the advantages of hydroelectric power is its reliability. Barring a major drought or accident or someone upstream taking all the water, then it will never run out. Where dams are used, the storage of water behind them can be used to even out the flow.
Another advantage is that hydroelectric power can be switched on and off in reaction to demand, very quickly, unlike many conventional power plants where stopping and starting incurs costs, and in some cases can take a very long time.
Where the geography is suitable, water can be pumped to a higher level using spare off-peak electricity and then released to generate hydroelectric power when it is needed. This enables the storage until it is needed of excess off peak power from plants which are best not stopped, making them more efficient. One example is the Ffestiniog Pumped-Storage Scheme in north Wales. The water is pumped up to Llyn Stylan, and then released to power the turbines and fill a lower reservoir on demand, at 60 seconds notice. The scheme was constructed inside a mountain. This is a useful and efficient way of managing electrical capacity.
Most hydroelectric schemes are built and operated to produce electricity for public consumption, but a few are built privately for particular projects, such as an aluminium processor.
The amount of hydroelectricity produced by a country varies enormously as a proportion of total electricity produced because of the variations in suitable geography and amount of water. Canada and Norway, for example, produce a great deal of hydroelectricity, and Iceland and Austria produce a fair amount. But while some countries produce nearly all their water this way, others use little or none: the world average is about 20%. Developed countries have mostly used all their best sites, so most construction is now in undeveloped and developing countries. Environmental considerations have slowed progress in places.
Hydroelectric plants tend to be immune to the prices and availability of fossil fuels and labour, and tend to be comparatively long-lived. They emit little in the way of carbon dioxide and methane, and do not produce any sulphur dioxide, nitrogen oxides, dust, or other combustion products. However, reservoirs do cover large areas of land which once grew vegetation and probably trees too, which had to be burnt or left to rot, and vegetation along the edge tends to drown whenever water levels rise. This tends to produce pollution such as methane and to take carbon sinks out of use. There is debate about the extent of this, which in any case varies from dam to dam.
Damming rivers can have negative effects, as the water might also be required for irrigation or for salmon runs at times which do not fit in with the electricity demands. The water may also be required for people if there is a drought, so there can be conflict. There are increasing concerns about environmental affects such as the plight of salmon populations in spite of fish ladders. Turbines can harm the fish swimming up to spawn and the smolts coming down. Water coming out of turbines can be colder than suits the aquatic population, but other sections of the waterway can be too warm for the fish. The reservoirs can be useful for recreation, however. People will need to be re-housed if they live in an area that will be inundated by the reservoir. Religious and archaeological sites may also be lost. People may also be at risk from breached dams if they live downriver, and may lose their livelihood if they depended on the river for fishing or irrigation. Another concern is the effect on river beds and mouths, as they are either scoured out, or increased sediment accumulates because of the altered flow, and oxygen levels can be affected too.
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