subject: How Green Is Hydroelectricity? [print this page] Hydroelectricity has a fairly clean image but there are several factors that make it less than desirable as a mainstream energy source. These factors are both environmental and aesthetic.
There is much talk about the environmental impacts of hydroelectric power, as they rely on damming of rivers and permanent flooding of the low lying land behind the dam. While this is not desirable, it is merely an alteration to the environment. If the dam remained flooded this would not pose long term ecological threats to us from this modification.
The real problem with Hydroelectricity installations is the amount of methane gas they produce. This gas comes from plants that rot in the absence of oxygen. The process of methane formation is very similar to that which produced oil and the other fossil fuels.
The following describes a section of land that is submerged by the construction of a hydroelectric facility.
First the land is submerged and the vegetation with it. The vegetation drowns and begins to rot. Since there is very little available oxygen, the plant material breaks down to form, among other things, methane that is absorbed by the water.
Nothing unusual has occurred so far. This is exactly what would happen with any permanent flooding. But this is a power station and in most cases also an urban water supply. Because of this, the water levels will rise and fall greatly throughout the year, generally dropping to low levels in hot and dry seasons. During these times lower sides and possibly the bottom of the dam become exposed.
This exposed land is ideal for growing plants and so it blooms with new life. As most dams are shallow, the amount of land exposed at the edges as the water drops can be very large. The shallower the dam, the more land is exposed annually.
Eventually the rains come and the dam refills, filling the new plants with water. Then it is the turn of these plants to rot anaerobically, releasing even more methane into the water.
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 approximately 21 times more effective than Carbon Dioxide as a greenhouse agent. This makes hydroelectric energy anywhere up to three times more polluting per megawatt of electricity generated than the equivalent coal or oil fired power station. This figure is dependent on the climate the dam is located in and the geography of the region. The effect is significant nonetheless, with the Intergovernmental Panel on Climate Change (IPCC) now taking hydroelectric energy methane production into account when inventorying national greenhouse gas emissions.
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.
