Hydroelectric Power: Pros and Cons Explained

Hydroelectric power has been around for hundreds of years, albeit in different guises. From water wheels and wooden shafts to the amazing technology we have today, utilizing impoundment, diversion, and pumped storage hydropower.

Currently, it is the most widely used of all renewable energy, globally.

What is Hydroelectric Power?

hydropower diagram

Hydroelectric power, HEP, is a form of renewable energy – energy from a source that isn't depleted when it is used, such as wind, solar, and water.

Hydroelectricity captures the power of water in motion, such as that flowing over a waterfall, and converts it into electricity.

It is not a new concept; the Ancient Greeks and Chinese built huge waterwheels hundreds of years ago and installed them into rapidly flowing rivers. They realized that usable energy was created as the water cascaded from a high level down to a lower one.

How is Energy Harvested from Moving Water?

Hydroelectric power is created in a power plant. One of the largest examples is the Hoover Dam.

Instead of relying on kinetic energy alone – the energy a particle has by reason of its motion – the plant relies upon the force of the water to drive a turbine. The turbine powers a generator which then converts the harnessed energy into electricity.

The electricity produced powers the plant and the excess is transported to other areas.

How a Dam Works to Produce Electricity

A dam is a man-made barrier that restricts or stops the flow of water to create a reservoir. Hydropower is used in conjunction with dams to generate electricity.

Initially, a large dam is constructed across a lake at a very high elevation to form a reservoir.

A generator is situated at a lower elevation, and the controlled downhill flow of water powers a turbine, and in turn, the generator. The generator converts all of the energy into electricity.

When more electricity is required, the water flow can be manually increased to meet demand. Similarly, when demand decreases, the water flow can be reduced. This method is exceptionally efficient and prevents the overproduction of power.

In an ideal climate, there is always enough rainfall to replenish the stock of water in the reservoir. When summer has been particularly dry, there is always a bank of excess electricity to power a pump and carry the water back uphill.


Electricity generated from water is the most widely used renewable energy source in the world. The global hydroelectric installed capacity exceeds 1,295GW.

This is more than 18% of the world's total installed power generation capacity and more than 54% of the global renewable power generation capacity.

Hydroelectric use in the USA doesn't follow these trends. There are more than 2,000 power plants that account for 6.4% of its total electrical production output. However, in 2019, for the first time in over a decade, wind power surpassed hydropower in output capacity.

Hydroelectricity still accounts for 25% of all renewable energy used in America.

The Pros of Hydroelectric Power

Using water power to generate electricity has many advantages:

It is a Renewable Energy

There is an inexhaustible supply of water. Fossil fuels such as coal, oil, and natural gas, even uranium, will eventually run out.

Water is constantly being replenished by rainfall.

It is Clean

It doesn't burn like fossil fuels and therefore, creates no emissions. Hydropower releases zero pollutants such as soot or sulfur dioxide.

Water power produces no carbon dioxide, the greenhouse gas. CO2 from power generation is considered to be a major player in climate change.

It is Safer

Nuclear power is obviously dangerous, the by-products of which cause major disposal problems. Hydroelectric power poses no such problems.

It is Cheap

Operating expenses are negligible, water is in constant free supply, in comparison with fuels that have to be extracted from the ground.

It is Cyclical

The heat from the sun, evaporates water from the ground that has fallen as rain. Water vapor condenses in the atmosphere until the droplets of water are heavy enough to fall.

The cycle is constant, ensuring reservoir levels are topped up naturally.

It is Flexible

Controlling the output of electricity is simple by adjusting the flow of water.

When power consumption is low, the flow is reduced. This conserves reservoir levels for the peak period of high consumption or drought.

It is Reliable

Hydroelectricity supplies a constant energy source with few fluctuations.

The Cons of Hydroelectric Power

hydropower disadvantages

Using hydropower to generate electricity also has many disadvantages:

It Has Environmental Consequences

Water power might seem like an environmentally friendly energy. This isn't necessarily true, as significant electricity production requires a large-scale dam, and power station to be built on rivers and lakes. This often results in flooding to the adjacent land.

Property and land that is waterlogged comes at a high cost to the the land owners, both emotionally and financially.

Distress to Wildlife

When the natural flow of water is interrupted, the effect on ecosystems, wildlife, and habitats can be enormous.

Slowing the movement of water naturally raises the temperature. Sadly, this is detrimental to fish, resulting in the death of many.

Dams also obstruct the migration patterns of some fish.

Disruption to Nature

The most appropriate places to build dams and power stations are in areas of outstanding beauty. Huge amounts of construction work are undertaken, not just in erecting the dam, but also in the installation of a substation and pylons to transport the electricity.

There also needs to be a busy road network in place.

All of this construction work often results in the loss of value of surrounding land and properties.

It Might Not Be as Emission-Free as Once Thought

As vegetation decays, it releases carbon dioxide. Flooding and water-logging rapidly increases the rate at which rotting occurs, possibly resulting in the harmful gas entering the atmosphere near/to HEP sites.

Expensive Construction

The building of any type of power plant is expensive, including a hydroelectric plant.

This is somewhat offset by zero fuel expenses, less employees, and low maintenance costs.


Hydroelectricity generation and energy prices are directly linked to water availability. Prolonged droughts could have potentially catastrophic effects on production capacity.

Final Thoughts

All energy, renewable and non-renewable, has its positive points and drawbacks, hydroelectric power pros and cons are no exception.

Although proposed sites are hard to come by due to lack of available reservoirs, and the exorbitant initial costs, water power is still growing in popularity year upon year.

This is likely due to the fact that it pairs well with other renewable energies, it is clean, and is capable of meeting peak demand.

Dillon Clayton
Dillon is an Energy enthusiast. The goal of his posts on Energy Follower are to help inform people of the energy options around them based on impartial research.

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