September 6, 2018 Energy Written by Greentumble Editorial Team
Hydroelectricity pros and cons
Hydropower, the creation of mechanical energy

through the transfer of kinetic energy created by the flow of water, is currently the only large-scale renewable alternative to traditional electricity sources, such as fossil fuels [1]. As economic development spreads throughout the world, so does the demand for electricity, causing global electricity production to double in just the last two decades.

Worldwide, 66 countries already generate at least half of their power from hydroelectricity, but only one third of the economically feasible potential of hydroelectric power has been realized [2].

Widespread poverty has inhibited the access to electricity in much of the developing world, additionally restricting the availability of elementary services like light and running water.  The creation and expansion of sustainable, cost-effective, and renewable energy sources is key, as development cannot be enabled without energy [2].

In the last twenty years, calls for more renewable energy have been hampered by the fact that fossil fuels were initially displaced by primarily nuclear power.

Despite its lack of greenhouse gas emissions, public concerns over its safety has limited its expansion while hydropower, along with other renewable sources, continue to represent only a tiny fraction of the global production of power [2].


What is hydroelectric energy?

Hydroelectricity, provided through a number of hydropower technologies, all rely on the ability to produce electricity through the force of moving water.  The water can come from many sources, from natural flows of the tide or waves, rivers, or man-made conduit projects like impounded reservoirs, dams, or irrigation canals [3].

Hydroelectricity operates in much the same mechanism as wind power does with moving air.  To tap the kinetic power of the flowing water, turbines are installed within the water and, as the water passes through the turbine, it causes the blades to turn, spinning a generator and creating electricity [4].

Hydropower turbine

Hydropower turbine

Energy produced by the kinetic energy of water can be measured simply, through calculations of the streamflow and the available drop, called the “head,” through which the streamflow can convert that hydraulic energy to electricity [4].

Currently, hydropower accounts for 7 percent of the United States’s electricity generation in 2013; approximately 52 percent of the total renewable energy generated in that year [3].

In Brazil hydroelectricity dominates the market, providing closer to 80 percent of installed capacity [5].

Worldwide, hydroelectricity was responsible for 16 percent of global power production in 2008, but speculators predict that it has the capacity to produce five times that [6].

History of hydropower

The use of water to generate electricity is, in fact, thousands of years old. We have evidence that the Greeks used water wheels in their process of grinding wheat into flour, and that was over 2,000 years ago. 

In the 1700s, a French engineer, Bernard Forest de Bélidor, started what could be considered modern hydraulic theory when he wrote his book, Architecture Hydraulique.

In the late 1800s, hydroelectricity uses really blossomed, from the creation of arc lighting, to industrial flour processing, to circulation across the national power grid. Many people have a good mental image of the Hoover Dam, which was built in 1931 and still produces four billion kilowatt hours each year per 10 acres of floor space [7].

Hoover dam

Hoover dam

Hydroelectricity is so reliable that many of the hydropower plants built 50 to 100 years ago are still operational [6].

From 1990 to 2008, global hydropower generation increased by 50 percent, and the top ten countries alone represented two-thirds of the entire world’s hydropower generation [6].

Advantages of hydropower


#1 Totally renewable

Water is the ultimate renewable resource — it moves constantly through a global cycle as it evaporates from oceans and lakes, forms clouds, returning to the Earth in the form of precipitation, rain or snow, then returning to the oceans and lakes to restart the cycle.

The cycle is driven by only the sun, and the cycle itself is constantly recharging without intervention [8].

The “fuel” used by hydroelectricity — water — is also not used up or reduced.

#2 Super reliable

Typically, hydropower is considered to be extremely reliable, with high efficiency, easy adjustability, and very low operating and maintenance costs.

Its adjustability is key: it has an immense storage capacity and fast response characteristics, which means that, when there is a large fluctuation in demand for electricity, it is able to accommodate quickly and easily, a flexibility that sets it apart from many other sources of renewable energy [6].

Hydropower plant

Hydropower plant

And, unlike other sources of energy, it does not contribute to issues of air quality, greenhouse gases, or acid rain [4].

#3 Cooperation with conservation

In other developing countries, hydroelectric production is cultivated in tandem with ecosystem and biodiversity conservation in watersheds, helping to create cooperation through a beneficial relationship between forest conservation and economic development for local communities near hydroelectric installations [9].

#4 Economically efficient

Though the costs of setting up hydroelectricity can vary from site to site and depend primarily on the size of the project, large-scale installations (>300 MW) typically require $2 million USD per megawatt (MW) and $2 million to $4 million USD per megawatt for projects smaller than 300 MW.

Oftentimes it is more cost effective to refurbish existing plants, as many of them could have their capacity raised by 5 to 20 percent.  These refurbishment projects are oftentimes also easier and faster, as they do not require additional environmental assessments or social surveys, making them additionally cost effective [6].

The average cost of electricity from a hydroelectric station that is larger than 10 MW is 3 to 5 U.S. cents per kilowatt-hour [10]

In general, the largest hydroelectric plants are also the most cost effective, helping hydropower costs to run at about one third of the costs of fossil fuel (coal or oil) or even nuclear power [11].

#5 Potential for expansion

Hydroelectric energy has huge potential — in the United States alone, it could add 60,000 MW of capacity by 2025 if properly expanded and included in energy policy. 

That figure only represents 15 percent of the estimated totals of untapped hydropower resources in the US, indicating that further expansion could yield even larger potential [3].

#6 Recreational opportunities

In many areas, the constructed hydroelectric plant reservoirs can provide recreational opportunities such as swimming, boating, and fishing.

Dammed river in the Alpine landscape offers a place to recreation

Dammed river in the Alpine landscape offers a place to recreation


#7 The future of energy

Engineers are also constantly looking to advance and expand the scope of its application, as well as develop better technologies that can increase both the efficiency and cost effectiveness of hydroelectricity. 

The improvement of these technologies can also open up new venues for hydroelectric exploitation, including smaller rivers and shallower reservoirs [6].

Disadvantages of hydropower


#1 River damming

To construct most hydroelectric facilities, a river must be dammed.

A dam is required in order to harness the gravitational force of falling water that is needed to generate electricity. The damming of rivers can cause many negative impacts to the local riparian (river) ecology and communities as the area upstream from the dam is flooded to create a reservoir.

#2 Water is in demand

Hydropower, though it sounds obvious, requires water, and, though it does not deplete that water, it still competes with other uses.

Water, as the fundamental resource for countless plants and animals, in addition to agriculture, sanitation, industry, and development, has many avenues it must sustain, sometimes simultaneously. And, unfortunately, it is unevenly distributed across the globe, and present in quantities that are insufficient for the need for it in many parts of the world. 

By 2025, it is estimated that at least 50 countries, representing 3 billion people worldwide, will be affected by water stress and/or scarcity [2].

As a result, many hydropower projects are perceived as a “burden” on this already overtaxed resource. And, despite their potentially damaging impacts on the planet, fossil fuels are not thought of as a similarly life-sustaining resource [2].

#3 Poor environmental consideration

Hydropower also raises specific environmental impact issues, particularly regarding its transformation of land use and river flow patterns [2]. Hydroelectric projects have broad impacts on both the flora and fauna of the regions in which they are implemented, and hydropower development needs to take all of those aspects into consideration before it is cemented.

Hydroelectric power project alters natural habitat in Peru

Hydroelectric power project alters natural habitat in Peru

Because hydroelectric power plants and dams utilize the flow of water, this also alters the natural flow of rivers. Algal blooms can occur in reservoirs due a lack of dissolved oxygen levels that result in more stagnant water conditions. To address this issue, reservoir water can be aerated, and it is important to maintain a minimum flow of downstream water to preserve riparian habitats.

Financers, such as the World Bank, have had to scale back and reassess their commitment to hydropower to take into account the reflection of all of those sectors in which large-scale development projects such as these have a cost [6].

#4 Ecological impacts

Wildlife habitat can undergo flooding when hydroelectric plants are built, and can have dramatic impacts on a local ecosystem and the animals and plants that live there. Wildlife migrations may be dramatically altered, and there may be a loss of suitable habitat as well as a loss of important species.

In many cases, fish may no longer be able to swim upstream when a dam has been constructed along their migration route to their spawning grounds, and fish may be injured or killed by hydroelectric power turbines.

To aid fish passage, fish ladders or elevators have been added to many hydroelectric dams as well as the implementation of screens, racks and lights to reduce fish injuries and fatalities. It is also important to maintain a minimum spill flow beyond the turbines to assist with fish passage.

#5 Community resettlement problems

Involuntary population displacement is a very significant challenge within hydropower projects, and, as the technology expands, considerations made for resettlement must be modernized as well [2].

Local citizens, particularly those in communities adjacent to and impacted by the construction of a hydroelectric project, have historically not always been consulted, nor have thorough environmental impact reports been conducted, causing the advancement of hydroelectricity expansion to stagger and often stop as better strategies and protocols are properly developed.

The world’s largest hydroelectric facility, China’s Three Gorges Dam, displaced more than 1.4 million people at the time it was constructed [6].

#6 Abuse of vulnerable populations

Similar to other major public infrastructure projects like highways and power stations, communities surrounding potential hydropower project locales must be handled competently and fairly and with maximum consideration for their needs.

Flooded valley to support hydroelectricity project

Flooded valley to support hydroelectricity project

In the past, projects such as these have resulted in vulnerable populations being dispersed, as well as the loss of livelihoods for people living adjacent to ideal zones for hydroelectric development. 

Hydroelectric facilities have often disrupted the water flow to communities that were downstream from the plant and reduced their access to water from the river. This has led to conflicts among those who share these water resources.

With proper management, these projects can generate benefits for the communities that can offset the adverse impacts, such as collective irrigation or the raising of community standards, with the goal being the fostering of regional social and economic benefits [2].

#7 Vulnerability to climate change

Hydropower, to engage the appropriate kinetic energy of flowing water, requires the appropriate drop, or “head,” making higher altitude venues more effective hydroelectric resource locales. High mountain water resources are, however, particularly subject to climate change, potentially threatening the sustainability and security of the hydropower systems of some countries. 

Given that the life cycle of these hydrological regimes relies on accumulation in the form of snow and ice, and subsequent melting processes, an overall increase in global temperatures could yield obvious impacts, and “trickle down” issues for stakeholders who rely on those dams and reservoirs for irrigation and flood prevention [12].

How does hydroelectricity affect the environment?

Review of the the impacts of hydroelectricity projects on the environment is crucial, given that some of the world’s most biodiverse river basins, including the Mekong, the Amazon, and the Congo, are currently experiencing unprecedented increases in hydropower construction proposals.  

Historically, hydropower construction proposals have tended to overestimate the economic benefits of these projects and underestimate the potentially far-reaching impacts on biodiversity [13].

Many of these key high conservation value sites had, thus far, not been subject to hydroelectric development because of the lack of infrastructure and limited demand for energy in the regions.  Particularly in tropical river fisheries, the construction of large dams can impede fish migrations and prevent many species from completing their life cycles.

Turbulent water released by the hydropower plant

Turbulent water released from the hydropower plant

Physical alterations of riverine watersheds can also cause an ecological regime shift, as well as alter nutrient dynamics, delay seasonal flood pulses, and reduce functional productivity.  These river systems support the livelihoods of millions of people, so their ecosystem health and regulation is key not only for environmental concerns.

Carbon balance

It was asserted in the early 1990s that the implementation of man-made freshwater hydroelectricity projects, such as dams and reservoirs, had created an increase of carbon and methane emissions.  In the ensuing years, efforts have been made to reduce these increased emissions and help to balance the carbon output of hydroelectric projects through the measurement of “gross emissions” from specific reservoirs.

Management plans have also been drawn up, particularly in hydroelectricity-dependent countries like Brazil [6], to address these potential issues and monitor and analyze the impact of these reservoirs and dams.

Conclusion: Pros outweigh the cons

In countries with ample water, hydropower should be utilized to its maximum potential, especially when taking into consideration all of the appropriate environmental assessments and prioritizing community needs and engagement. 

If financiers ensure that the refurbishment of existing plants is prioritized, and that all new projects are responsibly established, there is no reason that hydroelectricity cannot be maximized for the benefit of millions more households a year.

Hydropower has a longstanding history of reliability and efficiency. And, without the drawbacks of fossil fuels or even other “clean” energy like nuclear power, it could be a clear frontrunner of the energy sector.

Any previous issues that hydropower caused in the past with negative environmental impacts or ramifications for local communities can be easily mitigated with proper planning. The only potential setback would be the onset of climate change, which could change the global distribution of water and its availability.  If hydropower is allowed to replace climate change-exacerbating sources such as fossil fuels, these problems can also be minimized.

Hydropower is clean, flexible, reliable, and completely renewable in a way that few other sources of electricity compare. It Is low-cost and has the potential to bring electricity worldwide and help global development and welfare improvement.