How Green Is Hydroelectricity?

Hydroelectric energy has several drawbacks that make it a less than ideal option compared to the clean power potential of solar energy. The factors are both aesthetic and environmental.

The most visible environmental aspect of Hydroelectricity is its impact on the environment, as it requires the damming of rivers. This causes the flooding of low lying land behind the dam and while this is often not desirable, the reality is that it is just an alteration to the environment. If the dam was to remain filled with water all the time, this would have no environmental effect outside the dam area.

What does cause problems, however, is the significant amount of methane generated by hydroelectric energy installations. Methane is produced when organic matter breaks down anaerobically (without oxygen). This is similar to the processes that resulted in the formation of coal, oil and natural gas.

The following gives you an idea of what happens to the land behind the dam after the Hydro facility has been built.

The valley behind the dam fills with water and all the plants drown and start t rot. Since they are under water they are not exposed to much oxygen gas, so they decay anaerobically. This produces a variety of products including significant amounts of methane. This methane is absorbed into the water.

So far all is normal, just the same as any other permanent flooding. But since this is a power station and in most cases also an urban water supply, the levels tend to fluctuate annually. The water levels drop in dry times. This exposes sections of land at the bottom of the dam.

As soon as these areas are exposed they blossom with new plant life. This happens at the edge of the water in the dam as the water level drops. Since most Hydroelectric dams are quite shallow, a great deal of land is exposed annually in this way.

After a time the rains return and the dam fills up again. The new vegetation is then also covered with water and so rots anaerobically and so more methane enters the water of the dam.

This continues on an annual basis, resulting in a steady supply of methane in the dam water from newly added plant matter. Methane is generally insoluble in water so when the water passes through the turbines of the power station it is released into the atmosphere.

Methane is a dangerous greenhouse gas. It is approximately 21 times more effective at trapping heat in the atmosphere than Carbon Dioxide. This means that electricity from a Hydroelectric plant can be up to three times more polluting per energy unit than the same energy from a coal or oil fired plant. This figure depends on the climate and geography the Hydro plant is located in, as these factors determining the amount of vegetation added to the dam each year. The Intergovernmental Panel on Climate Change (IPCC) has recognized this issue and now includes methane from Hydroelectricity in national emissions totals.

While Hydroelectricity is a renewable energy source it is not as environmentally friendly as it looks. If there is discussion about whether to build a new Hydro plant, methane emissions have to be considered. Far cleaner are the options of solar and wind power that once built have no emissions whatsoever. - 39468