Exploring Hydroelectric Power In Terms Of Sustainability
Introduction
Hydroelectricity is the generation and distribution of electricity obtained from the kinetic energy of falling water or any other hydraulic source. In general, hydroelectricity is produced by water falling on a turbine which rotates a shaft that turns an electric generator.
According to Strezov, V. (2013) 17% of global electricity production was generated by hydroelectric plants in 2012. This is due to its energy source, flowing water, which is a clean, renewable and free source of energy when harvested.
Hydroelectricity is seen as a completely clean source of electricity; however, this is not entirely true as it does have some greenhouse gas emissions in its construction and operation. Large hydroelectric dams require a lot of cement for concrete to construct them. Cement production releases a lot of CO2. Hydroelectric dams also produce methane as organic matter at the bottom of the water decays in an absence of oxygen.
Considering hydroelectricity as a means of production of electricity is important in today’s world and in the future as we slowly phase out fossil fuels. We are looking for a carbon neutral solution for renewable energy. Hydroelectricity is one of the most reliable, affordable and sustainable energy sources in the world.
Hydroelectricity Requirements and Restrictions
In order to find a suitable site for a hydroelectric plant you must take many factors into consideration. Nield, D. (2019) claims that scientists have identified 530,000 sites worldwide suitable for pumped-hydro energy storage, capable of storing more than enough energy to power the entire planet. These identified sites would rely on the use of solar and wind energy to pump water into reservoirs when demand is low, and these renewables are in abundance.
One determining factor of the placement of a hydroelectric plant is its size. Larger plants produce more electricity but use considerably more concrete in their construction whereas small plants produce less electricity but require less concrete and have less methane emissions.
The environment surrounding the plant must also be considered as the natural biodiversity may be affected by the addition of a dam or reservoir. This may displace animals and insects and destroy life in the area. Large hydroelectric dams often displace many people from their homes and land and relocate them elsewhere. This can be very problematic as seen in Sarawak, Malaysia. Ahsan, R. (2016) discusses how the Bakun Dam displaced over 10,000 indigenous people from their 70,000 hectares of land and relocated them with only 4000 hectares of land.
Plant Operation And Generator Function
A hydroelectric plants operation starts with its dam or reservoir. This raised water level is used to create controlled falling/flowing water. The water in a dam or reservoir is potential energy. This falling water falls onto a water turbine causing the blades of the turbine to rotate. This process is similar to a wind turbine except the energy is provided by the falling water and not by wind energy. The turbine converts the waters kinetic energy to mechanical energy. The type of turbine used depends on the type and size of the hydroelectric plant. Larger plants with more flowing water require a different design to accommodate this volume of water.
A shaft connects the turbine to a generator. The generator converts the mechanical energy into electrical energy. The rotor of the generator is covered in magnets of opposite poles beside each other. As the shaft turns the rotor of the generator, it creates a temporary magnetic field within the windings of copper wire surrounding it. The number of windings in the generator is grouped in threes. This creates three-phase power as the rotor turns between the windings. The copper windings are charged by this magnetic field and electricity is transferred through a wire connected to these windings. This generated electricity is then transferred to the grid via transmission lines and subsequently to homes and businesses.
Hydroelectric Plant Efficiency
There are two main factors that determine the quantity of electricity produced by a hydroelectric plant. The distance the water falls and the amount of water falling. The energy falling water has is directly proportional to the distance it falls. The higher the water falls from the more energy can be harnessed from it. The greater the volume of water falling onto the turbine the more energy can be produced. The amount of falling water is also directly proportional to the energy that can be harnessed from it.
Hydroelectric power generation can be the most efficient way to generate electricity as the energy is converted directly from kinetic energy to electric energy with no inefficient intermediate conversion or losses. As shown above, large scale generation is more efficient than on a smaller scale, this is due to the water turbine type used. The type of turbine used is dependant on the rate of water flow and the pressure of the flowing water.
Another small factor to consider when it comes to a hydroelectric plant’s efficiency is the evaporation of water in the reservoirs, this stored energy is lost as water evaporates, however, this is insignificant as water evaporating has little impact on the power generation of the plant.
Pumped-hydro energy storage could be used to decrease losses from other sources of renewable energy such as wind and solar as their excess, otherwise lost energy is used to pump water into reservoirs to be used later in the production of hydroelectricity.
Effects Of Weather And Seasons
Varying Weather Parameters
According to a study examining the effect of weather parameters on hydroelectric power generation in Kainji Dam Niger State, Nigeria, “All the parameters exhibit fluctuations at various levels while statistical analysis, revealed that there is increased electricity generation during the dry season than the rainy season. However, the amount of power generated in August, September and October is high and are relatively comparable to the amount generated in the dry season months.
This means low power generation could be attributed to low or no rainfall in April to July within and outside the country and probably heavy rainfall mostly outside the country (upstream), causing dry season months to generate more power as the study reveals. ”
The paper went onto say “The research indicated that rainfall with 0. 83 correlation coefficients have strong relationships with the amount of power generated, while temperature and evaporation with 0. 21 and 0. 33 do not have significant relationship with the amount of power generated. ”, showing that rainfall does affect power generation where temperature and evaporation do not.
Flooding
Hydroelectric plants can prevent but also cause flooding. A build-up of sediment in reservoirs can reduce the reservoirs ability to control large inflows of water caused by unusually heavy rain in rainy seasons and consequently lead to unpredictable overflowing of the dam.
Hydroelectric plant dams can prevent flooding by retaining large volumes of water, this single body of water can be more easily monitored, and flooding can more easily be prevented.
Conclusions and Recommendations
In conclusion, hydroelectricity appears to be a promising source of sustainable, renewable energy for the future. The research suggests that pumped-hydro energy storage is the future of hydroelectricity generation as stored water acts as a huge source of stored potential energy as an alternative for using large and expensive batteries storing chemical energy.
There are also many potential sites for pumped-hydro energy storage that could, in theory, provide more than enough energy to meet the worlds energy demands. This method of energy storage eliminates the energy currently lost in wind and solar renewables.
In relation to the production of methane in the reservoirs, a potential solution could be to capture the methane gas (CH4) (which has a greenhouse factor of 30) from the reservoirs by some means, burn the methane in oxygen (O2) to produce more electricity, converting the methane into carbon dioxide (CO2) (greenhouse factor of 1) and water (H2O) then capture the CO2 emissions directly via carbon capture methods after burning and bury the carbon in the ground. This would make hydroelectricity plants carbon negative while in operation.
Bibliography
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