Hydroelectricity

Hydroelectricity as can be seen in table 1 in the introduction is the 2^nd biggest source of electrical power generation globally and yet it somehow gets overlooked as a renewable resource. This is owing to the fact that a number of the current hydroelectric power plants have caused long lasting environmental damage in the form of damaging or destroying habitats and also displacing indigenous peoples from their homes

Current status

Table 3. Hydropower: capability at end 2005³(TWh/yr)

As can be seen in table 3 there is a worldwide capacity for hydroelectric power generation of 16,494 TWh. This is close to the total electricity production in 2006. There is a clear difference between the gross theoretical capability and the technically exploitable capability. The latter represents the amount of power that can be extracted using todays technology and the former represents the total energy that could be used in an ideal system. Obviously a situation where every joule of energy can be extracted from a system but it is worth noting that as technology progress there is extra potential power to be exploited.

Environmental impact

There are two main types of hydroelectric power plant. A run-of river and a reservoir. A run of river is placed directly on a river and allows the flow of the river to turn its turbines for power generation. A reservoir type power plant dams a river to build a reservoir which can then build up a pool of water which it can allow to flow through the turbines as it is needed to generate power. There are environmental concerns associated with both

With the construction of a dam an area of land will have to be submerged. This has lead to the displacement of millions of people⁴ from their homes. While a dam does not pose the risk of exploding the way a nuclear or thermal plant does there have been catastrophes in the past that have lead to many deaths where dams have burst.

Another problem associated with dam construction is that it changes the sedimentation regime of a river. This can lead to the destruction of ecosystems.

Recently it has been suggested that the large resevoirs can cause flooded vegetable matter which, ordinarily decays to produce CO₂ to instead ecay producing methane (CH₄). While these amounts would be far less than a traditional thermal power station methane is around 11 times more damaging to the atmosphere than CO₂. This varies from dam to dam and depending on what type of vegetation id submerged.

If the site is chosen carefully this risk can be minimized and greenhouse gas emission should be a fraction of a traditional coal fired station.

Cost

The cost per KW of a hydroelectric dam is largely in the upfront cost of construction, especially where a large reservoir has to be built. Table 4 lists the cost per kw of some power plants form around the globe

Table 4. Typical hydro power project costs⁵

One benefit of hydroelectricity is that where as a coal or oil fired plant may run for 30 years a hydroelectric power plant, with some updating can run for 100 years which in the long run will greatly reduce the costs.

Inherent disadvantage

One of the key problems facing all renewable energy is the consistency of the supply and hydroelectric power is no different. Weather patterns change, rainfall can decrease and rivers can run dry. Even with a reservoir if there is a drought then the generators will not be able to run at full capacity and in extreme cases not at all. Careful planning and good historical records can help minmise this impact but for the purposes of baseloaded electricity for the grid it is a danger that needs to be assessed.