Types of hydroelectric energy
The two main types of hydroelectric energy are small and large scale. The basic principles are the same, essentially, only the size of the turbines changes.
The Sir Adam Beck Generating Complex in Ontario. Photo courtesy of Ontario Power Generation
The most well known method is large scale hydro, which tends to involve damming a river, creating an artificial lake and allowing water to pass through the dam in a controlled way.
The most famous example of this kind of dam is probably the Hoover Dam, on the border between Nevada and Arizona, in the USA. In modern terms, it is actually a lightweight in terms of energy production from hydroelectricity.
The largest hydroelectric dam is the Three Gorges Dam in China, which generates 18.2 GW.
This is achieved with approximately 26 turbines, generating about 700MW each, though more are under construction to increase the electrical output.
Small scale hydroelectric power is really much less impressive, as it is far less obvious. Small scale hydro is used to power small communities who are lucky enough to have flowing water nearby - damming is not really necessary.
Environmental Concerns
Photo courtesy of Michael Stone
In terms of greenhouse gas emissions, the technology is wonderful, as all the energy comes from moving water and not from any form of combustion. As with most things, such gases are emitting in the construction phase, however.
The problems arise when you consider the impact on the local region directly. You suddenly get a large lake formed behind the dam that did not exist before, and the river on the other side of the dam reduces in volume.
This has a rather large impact on local wildlife and ecosystems. Unlike wind and solar technologies which tend to have only a minimal impact on their environment, large scale hydro can seriously affect its environment.
There are also only so many rivers that can be dammed, and we certainly don't want to dam every single river available due to the Environmental impacts. There is also a rather entertaining website which shows the impacts of a well run and a poorly run dam, which you might like to investigate.
How does hydroelectric energy work?
The kind people at Ontario Power Generation suggested to me a video which answers the question "what is hydroelectric energy", and here it is...
What is hydroelectric energy? - told by Ontario Power Generation
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