Hydroelectricity is the electricity produced by harnessing the gravitational force of flowing water. It is one of the three major sources of electricity, the other two being fossil fuels and nuclear fuels. Hydroelectricity is categorized as a renewable energy resource. It is one of the cheapest and oldest methods of producing power, making it a competitive source of renewable energy.
Hydroelectricity technologies are broadly classified into four categories – conventional (dams), pumped-storage, run-of-the-river and offshore marine (tidal). Once a hydroelectric power plant is built, it does not produce any direct waste and has a substantially lower output level of greenhouse gas emissions compared to fossil fuel-powered energy plants. At present, hydroelectric power accounts for one sixth of the world's electricity production.
According to the International Hydropower Association’s 2017 Hydropower Status Report, an estimated 31.5 GW of hydropower capacity was put into operation, including pumped storage, bringing the world’s cumulative installed capacity to 1,246 GW in 2016. China alone accounted for almost one-third of global hydropower capacity and added around 11.74 GW of new capacity in 2016, taking its cumulative installed capacity to 331 GW. The top countries in terms of hydropower capacity are China, the US, Brazil, Canada, India, Japan and the Russian Federation, which together accounted for more than 60% of installed capacity at the end of 2016.
Image: Grand Coulee Dam. Photo courtesy of U.S. Bureau of Reclamation/Wikipedia.
The major advantages and disadvantages of the hydroelectric energy are given below.
Advantages of hydroelectricity
Renewable: Hydroelectric energy is considered as renewable because it uses the earth’s water to generate electricity. Due to the natural water cycle, water is recycled back to the earth and will never run out of supply. The amount of hydroelectricity produced can vary as a result of draught and lower water levels but this is seasonal.
Clean and safe: Unlike fossil fuels, biomass and nuclear power, hydroelectric power is a clean and green alternative source of energy. Since hydroelectric dams do not use fuel, they do not release any greenhouse gases or toxins into the environment. As a result, hydroelectric power features prominently in the clean energy plans of many countries.
Flexible: Hydropower is a flexible source of electricity as hydro plants can be scaled up and down quickly to meet the changing energy demands. Furthermore, compared to gas turbines or steam plants the start-up time taken by hydro turbines is very less. Hydropower units also serve as backup for non-hydro generators.
Cost competitive energy source: Despite of exorbitant upfront building costs, hydroelectric power is a cost-competitive source of energy. Hydropower plants require low cost of maintenance and operation. Since they have few parts, the plants need minimal replacements. In addition, the dams will be designed for long-term use. Hence, they are capable of producing hydroelectric power up to an average lifetime of 50 – 100 years.
Image: The Three Gorges Dam on the Yangtze River, China. Photo courtesy of Source file: Le Grand Portage, Derivative work: Rehman/Wikipedia.
Contributes to the economic growth of remote areas: Hydroelectric power plants attract construction of infrastructure, industry and commerce. This will in turn increase access to education, healthcare and overall quality of like of residents in the remote areas.
Suitable for industrial applications: While majority of the hydroelectric plants supply to public electricity networks, some will be constructed to serve specific industrial enterprises. Dedicated hydroelectric plants are often built to supply large amounts of electricity for aluminum electrolytic plants.
Other uses: Reservoirs created by hydroelectric projects often become tourist attractions in their own right. The lake that forms behind the dam can be used for recreational purposes such as water sports and leisure activities such as fishing and boating. The lake’s water can also be used for irrigation and aquaculture purposes. Large hydroelectric power plants can control floods as they have the capacity to store vast quantities of water.
Disadvantages of hydroelectricity
High upfront capital costs
Hydroelectric power plants and dams can be incredibly expensive to construct, regardless of the type of building, due to logistical challenges. Moreover, the projects take long periods of time to finish. They will have to operate for a long time too to recover the money invested for the construction.
As dams hold back large volumes of water, a sub-standard construction, natural disasters or sabotage, and the extreme influx of water can be catastrophic to downriver settlements and infrastructure. These failures not only affect the supply of power but also affect the flora, fauna and other forms of life.
Reservoirs and hydropower plants are often considered as environment friendly. However, it appears that hydroelectric dams contribute more to global warming than previously estimated. Researchers found that plant material in flooded areas begin to rot and decompose in an anaerobic environment. This will result in the release of substantial amounts of carbon dioxide and methane, which leads to increase in pollution levels.
Image: Hydropower plants release of substantial amounts of carbon dioxide and methane. Photo courtesy of a454/FreeDigitalPhotos.net
May lead to droughts
One of the main flipsides of setting up hydroelectric power plants is the occurrence of local droughts. The overall cost of energy is calculated depending on the availability of water. A drought could potentially affect this, causing people not to acquire the power they need.
Ecosystem damage and loss of wetlands/lands
Big reservoirs associated with traditional hydroelectric power plants cause submersion of extensive areas upstream of the dams, sometimes destroying lowland and riverine valley forests, marshland and grasslands. Hydroelectric power plants can also spell doom to surrounding aquatic ecosystems both upstream and downstream of the plant site. Since turbine gates are often opened intermittently, interruptions of natural water flow can have a great impact the river ecosystem and the environment. The fish in the river can be affected by the draining of the water from the dam as well as the fish that is in the dam. Animals such as birds, cranes and other aquatic birds, and some plant species thrive in marshy habitats. However, because of the hydroelectric power plant construction these habitats will be destroyed.
Relocation due to risk of floods
Local populations living downstream can become vulnerable to flooding due to the possible strong water currents that might be released from the dams. As a result, people are forced to relocate to facilitate the construction of the dams needed to generate hydroelectricity. The World Commission on Dams estimated in 2000 that dams had physically displaced 40-80 million people worldwide.