Hydropower: Pros and Cons
As we all know hydropower is a renewable energy source and thus releases no harmful emission to the environment. Once a hydropower plant has been installed, it generates electricity at a minimal operational and maintenance cost. As such, they offer an extremely low cost per 1 kWh. They have long lifespans of more than 50 years and do not require frequent maintenance.
Hydropower offers many other unique advantages than any other form of renewable energy does. Some of them are as below.
- Hydropower can be converted into electrical power at a very high conversion efficiency. Usually, the conversion efficiency exceeds 90% whereas the conversion efficiency of a typical wind turbine is lower than 60%.
- Reservoir hydropower plants help in irrigation and help control flooding. Further, the reservoirs improve the water quality and ensure the reliability of water supply in irrigation.
- The most important advantage of hydropower plants is their flexibility. Hydropower plants can be started (or shut down) within few minutes though conventional power plants take several hours to start or shut down. Especially, reservoir hydropower plants can even be used to generate electricity to fill the valleys or to clip the peaks out in power demand since reservoir hydropower plants can be operated as and when they are needed within a short period of time.
- Unlike most of the other energy sources, hydropower plants can be used as either base load power plants or peaking power plants or load following power plants thanks to their flexibility and short response time. This unique feature of hydropower makes it an essential part in supply-demand management (SDM), and power quality enhancement as all other types of technologies (superconducting magnetic energy storage, Flywheel technology, etc.) used for load balancing are expensive.
Hydropower offers many benefits as mentioned above, but every story has two sides, hydropower plants come with some negative environmental impacts in some cases.
- The initial investment needed to construct dams and turbines is extremely high, though operational and maintenance costs are minimal.
- Hydropower plants do not release harmful emissions to the environment. However, their associated reservoirs may release carbon dioxide and methane as plants and trees covered by water decompose without oxygen thus releasing greenhouse gases into the atmosphere.
- Hydropower relies on rain and therefore, it is inherently seasonal dependent. Therefore, hydropower plants require large reservoirs to ensure the power reliability. Large reservoirs consume a large piece of land and are expensive to be built.
- They may have negative impacts on the natural environment, ecology and inhabitants of animals. In particular, the changes in water pathways, flow rate and velocity of water may endanger some species living in water.
- Majority of economically viable hydropower resources are already being used to generate electricity. World’s cumulative hydropower capacity was 970 GW by 2011  while worldwide hydropower potential was merely 2.36 TW 
To conclude, hydropower comes with both pros and cons. But its advantages outweigh almost all of its own drawbacks. Especially, it represents not only a renewable source of energy but also one of the best and probably the most cost-effective tool in the supply-demand management and power quality enhancement. Therefore, increasing grid-connected hydroelectric capacity allows more and more renewable power to be grid-connected.
Simply, hydropower is a decisive factor in renewable energy industry not only as a renewable energy source but also as a tool which promotes other renewable energy sources.
 Pazheri, F. R., Othman, M. F., and Malik, N. H. (2014). A review on global renewable +electricity scenario. Renewable and Sustainable Energy Reviews, 31, 835-845.
 Kaygusuz, K. (2002). Sustainable development of hydropower and biomass energy in Turkey. Energy Conversion and Management, 43 (8), 1099-1120.