If you’ve never seen a hydroelectric dam before, then you have no idea of the size of these structures. They span for kilometers and have heights that can reach over 200 meters. They hold back trillions of litres of water in their reservoirs and cost hundreds of millions of dollars to make. So how exactly is hydroelectric energy produced and how much is produced by one of these structures?
Hydroelectric Dams
The dams are built along a simple principle. Gravity. The dam wall is built to hold back and collect a large amount of water as a reservoir and then to release it through chutes, called penstocks, at the base of the dam. Along those chutes there are collections of turbines which are rotated as water pours past them. This simple process is the basis of almost all hydroelectric power. The process has been used for thousands of years, first for milling grain by rivers then on to industrial power plants.
Naturally such power has it’s advantages and disadvantages. For advantages we see that it produces no waste product, so it’s a green technology in that sense. It’s powerful and by closing certain chutes you can control the amount of power produced easily. For all intensive purposes it’s renewable as our water supply is constant on the planet. They are also a great way of controlling rivers which are prone to seasonal flooding and the Garrison Dam is a good example of this as it’s saved over a billion dollars in potential flooding since it’s creation. One of the most advantageous aspects of hydroelectric dams is that they last for decades and the power that they produce is the cheapest on the planet.
The are also disadvantages of hydroelectric dams. One of the largest is the creation of the reservoir and the flooding it produces. These reservoirs often displace hundreds to over a million residents such as during the construction of the three gorges dam in China. Now in the United States, many of these reservoirs were later converted to outdoor recreational areas and tourism destination with great success, but in many other countries these lakes are left on their own with no added benefit. Another issue is the build up of silt in the reservoir which can put serious limits on the dams control of the water level and may even cause flooding over the reservoir with time. The final and largest fear for people down river from the dam, is the fear of a dam failure. The amount of water that would instantaneously cascade into the hundreds of communities downstream would be devastating. In 1975 the Banqiao dam failed, which led the the deaths of over 200 000 people and 11 million evacuees.
How Much Electricity can be Produced by a Hydroelectric Dam?
Well currently 20% of the world runs off hydroelectric power and there is a total energy supply over 755 Gwe. Norway produces close to 99% of all it’s power from hydroelectrical power stations which is some 27.5 GW. The amount of electricity that’s produced depends on the size of the dam and the flow of the water. You can have tiny dams set up on streams to produce enough power for a single house or monsters such as the Xiluodu Dam in China, which will be created in 2015 with a capacity of over 12 600 MW. In the United States the largest dams are in the hundreds of GW. So it varies greatly.
